Patent ID: 12240229

DETAILED DESCRIPTION OF EMBODIMENTS

The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. Throughout the drawings, like-referenced characters are generally used to designate like elements.

Definitions

Within this application the following terms should be understood to have the following meaning:

a) the term “receding contact angle” or “RCA”, refers to a receding contact angle as measured using a Dataphysics OCA15 Pro Contact Angle measuring device, or a comparable Video-Based Optical Contact Angle Measuring System, using the Drop Shape Method. The analogous “advancing contact angle”, or “ACA”, refers to an advancing contact angle measured substantially in the same fashion.
b) the term “standard aging procedure” refers to an accelerated aging protocol performed on each tested release layer at 160° C., for 2 hours, in a standard convection oven.
c) the term “standard air curing” refers to a conventional curing process for curing the release layer, in which, during the curing of the release layer, the release layer surface (or “ink reception surface”) is exposed to air.
d) the term “bulk hydrophobicity” is characterized by a receding contact angle of a droplet of distilled water disposed on an inner surface of the release layer, the inner surface formed by exposing an area of the cured silicone material within the release layer.
e) the term “image transfer member” or “intermediate transfer member” or “transfer member” refers to the component of a printing system upon which the ink is initially applied by the printing heads, for instance by inkjet heads, and from which the jetted image is subsequently transferred to another substrate or substrates, typically, the final printing substrates.
f) the term “blanket” refers to a flexible transfer member that can be mounted within a printing device to form a belt-like structure on two or more rollers, at least one of which is able to rotate and move the blanket (e.g. by moving the belt thereof) to travel around the rollers.
g) the term “on the release surface” with respect to an object such as an ink image or ink residue, means supported by and/or over that release surface. The term “on the release surface” does not necessarily imply direct contact between the ink image or ink residue and the release surface.
h) the term “has a static surface tension sufficiently high so as to increase said static surface tension of the aqueous treatment formulation”, and the like, with regard to a particular surfactant within that formulation, is evaluated by adding an additional quantities or aliquots of that particular surfactant to the formulation, and comparing the attained static surface tension of the formulation with the static surface tension of the formulation prior to the addition of those aliquots.
i) the term “liquid hygroscopic agent” refers to a hygroscopic agent that is liquid at least one temperature within the range of 25° C.-90° C., and has, in a pure state and at 90° C., a vapor pressure of at most 0.05 ata, and more typically, at most 0.02 ata, at most 0.01 ata, or at most 0.003 ata. The term “liquid hygroscopic agent” is specifically meant to refer to materials like glycerol.
j) the terms “hydrophobicity” and “hydrophilicity” and the like, may be used in a relative sense, and not necessarily in an absolute sense.
k) the term ‘(treatment) formulation’ refers to either a solution or a dispersion.
l) an x degrees Celsius evaporation load is now defined, where x is a positive number. When a solution is y % solids wt/wt and z % liquid wt/wt at x degrees Celsius, the ‘x-degrees Celsius evaporation load’ of the solution is that ratio z/y. The units of ‘evaporation load’ are “weight solvent per weight total solute.’ For the present disclosure, evaporation load is always defined at atmospheric pressure. For the present disclosure, a default value of ‘x’ is 60 degrees C. —the term ‘evaporation load’ without a prefix specifying a temperature refers to a 60 degrees Celsius evaporation load at atmospheric pressure.
m) when a portion of an ITM is in motion at a speed of v meters/second, this means that the portion of the blanket ITM moves in a direction parallel to its local surface/plane at a speed of at least v meters/second—e.g. relative to an applicator which is stationary.
n) the term ‘Static surface tension’ refers to the static surface tension at 25° C. and atmospheric pressure.
o) the term ‘thickness’ of a wet layer is defined as follows. When a volume of material vol covers a surface area of a surface having an area SA with a wet layer—the thickness of the wet layer is assumed to be vol/SA.
p) the term ‘thickness’ of a dry film is defined as follows. When a volume of material vol that is x % liquid, by weight, wets or covers a surface area SA of a surface, and all the liquid is evaporated away to convert the wet layer into a dry film, a thickness of the dry film is assumed to be:
vol/ρwet layer(100−x)/( )SA·ρdry layer)where ρwet layeris the specific gravity of the wet layer and ρdry layeris the specific gravity of the dry layer.
q) the term ‘Continuous wet layer’ refers to a continuous wet layer that covers a convex region without any bare sub-regions within a perimeter of the convex region.
r) the term ‘continuous thin dried film’ refers to a continuous dried film that covers a convex region without any discontinuities within a perimeter of the convex region.
s) the term ‘cohesive film/tensile strength’ refers to a construct which stays together when peeled away from a surface to which it is adhered—i.e. when peeled away from the surface, the ‘cohesive film’ retains it structural integrity and is peeled as a skin, rather than breaking into little pieces.
t) the term ‘a force applied normally’ refers to a force having at least one component in the normal direction—and optionally the ‘normally applied’ force may have an additional component in other directions (e.g. along a surface to which the force is applied).
u) unless stated otherwise, physical properties of a liquid (e.g. treatment formulation) such as viscosity and surface tension, refer to the properties at 25° C.
v) unless stated otherwise, a ‘concentration’ refers to a wt/wt—i.e. a weight of a component of formulation per total weight of that formulation.
A Discussion ofFIG.2

FIG.2is a flow-chart of a method of indirect printing by an aqueous ink onto a silicone-based release later surface of an intermediate transfer member (ITM). In some embodiments, the method ofFIG.2(or any combination of steps thereof) may be performed using apparatus (or component(s) thereof) disclosed inFIGS.3A-3B,4A-4B,5-9,10A-10D and11A-11C. In particular and as will be discussed below, embodiments of the invention relate to methods and apparatus useful for producing a wet treatment layer of uniform sub-micron thickness over large areas of the ITM and/or at high print speeds.

In different embodiments,FIG.2may be performed to produce an ink image characterized by any combination of the following features: uniform and controlled dot gain, good and uniform print gloss, and good image quality due to high quality dots having consistent dot convexity and/or well-defined boundaries.

Steps S201-S205relate to the ingredients or components or consumables used in the printing process ofFIG.2, while steps S209-S225relate to the process itself.

Briefly, the steps ofFIG.2are as follows: in steps S201and S205, an ITM (i.e. comprising a silicone-based release layer surface) and an aqueous treatment formulation (e.g. a solution) are provided, each having specific properties that are discussed below. In step S209, the aqueous treatment formulation is applied to the release layer surface of the ITM to form thereon a wet treatment layer. In step S213, the wet treatment layer is subjected to a drying process to form therefrom a dried treatment film on the ITM. In step S217, droplets of aqueous ink are deposited onto this dried treatment film to form an ink image on the ITM surface. In step S221, this ink image is dried to leave an ink-image residue on the ITM surface, and in step S225this ink-image residue is transferred to the printing substrate.

Embodiments of the invention relate to methods, apparatus and kits for achieving the potentially-competing goals of dot gain, image gloss and dot quality, preferably in a production environment in which high print speed is paramount. According to some embodiments, the inventors have found that it is useful to perform the method ofFIG.2so that the dried treatment film formed in step S213is very thin (e.g. at most 150 nanometers or at most 120 nanometers or at most 100 nanometers or at most 80 nanometers or at most 70 nanometers or at most 60 nanometers or at most 50 nanometers, and optionally at least 20 nanometers, or at least 30 nanometers) and/or continuous over large areas and/or characterized by a very smooth upper surface and/or rich in quaternary ammonium salts (e.g. to promote dot gain) and/or having properties (i.e. properties of the film per se, or of the film relative to the ITM surface) that promote good transfer from the ITM to substrate.

For example, thicker treatment films may negatively impact gloss or a uniformity thereof, since after transfer the dried ink residue may reside beneath the treatment film and on the substrate surface. Therefore, it may be preferred to produce a treatment film that is very thin.

For example, discontinuities in the treatment film and/or treatment film of varying thickness may yield images of a non-uniform gloss on the substrate, or may produce an ink-image residue (in step S113) that loses its mechanical integrity upon transfer to substrate. Therefore, it may be preferred to produce a treatment film that is continuous over large areas—preferably, sufficiently cohesive to retain structural integrity when to the printing substrate and/or having thermorheological properties so the treatment film is tacky at transfer temperatures between 75 degrees and 150 degrees Celsius.

For example, the presence of quaternary ammonium salts in the dried treatment film may promote spreading of the ink drop, but not necessarily uniform drop spreading. However, the combination of (i) a high concentration of quaternary ammonium salts in the dried treatment film and (ii) a treatment film of uniform thickness having an upper surface that is very smooth may promote uniform ink drop spreading.

Embodiments of the invention relate to techniques for achieving these results simultaneously, even if they entail potentially-competing goals. For example, the need for the treatment film to be very thin makes it more challenging to form a treatment film that is continuous over a large area and/or sufficiently cohesive for good transfer to substrate and/or having a very smooth and uniform upper surface.

A Discussion of Step S201

Although the ITM provided in step S201has a silicone based release layer, the release surface thereof may be less hydrophobic or appreciably less hydrophobic than many conventional silicone-based release layers. This structural property can be measured and characterized in various ways.

For example, as illustrated in step S201ofFIG.2, the intermediate transfer member (ITM) comprises a silicone-based release layer surface that is sufficiently hydrophilic to satisfy at least one of the following properties: (i) a receding contact angle of a drop of distilled water deposited on the silicone-based release layer surface is at most 60°; and (ii) a 10-second dynamic contact angle (DCA) of a drop of distilled water deposited on the silicone-based release layer surface is at most 108°.

Any one of a number of techniques for reducing the hydrophobicity of the silicone based release layer may be employed.

In some embodiments, polar functional groups are introduced into and/or generated in the silicone-based release layer. In one example, functional groups may be added to the pre-polymeric batch (e.g. monomers in solution) —these functional groups may, upon curing, become integral part of the silicone polymer network. Alternatively or additionally, the silicone-based release layer is pre-treated (e.g. by a corona discharge, or by an electron beam), thereby increasing a surface energy thereof.

Alternatively, the silicone based release layer may be manufactured to have a reduced hydrophobicity, even when substantially devoid of functional groups. In one example, the silicone polymer backbone of the release layer may be structured so that the polar groups thereof (e.g., O—Si—O) are oriented in a direction that is generally normal to the local plane of the ITM surface and facing ‘upwards’ towards the release layer surface.

To date, the inventors believe that the technique of the previous paragraph may provide superior image-transfer (step S225).

A Discussion of Step S205ofFIG.2

One feature of the aqueous treatment formulation provided in step S205is that a static surface tension of the aqueous treatment formulation is within a range of 20 and 40 dynes/cm. For example, the aqueous treatment formulation comprises one or more surfactants.

Thus, the aqueous treatment formulation of step S205is less hydrophilic than many conventional treatment solutions, and significantly less hydrophilic than water.

In some embodiments, the combination of (i) a silicone based release layer having a reduced hydrophobicity (step S201) and (ii) an aqueous treatment formulation having a reduced hydrophilicity, reduces (but does not necessarily eliminate) surface-tension effects which promote beading of the conventional aqueous treatment solution.

In addition to the static surface tension within a range of 20 and 40 dynes/cm, the aqueous treatment formulation provided in step S205has the following properties:a. the aqueous treatment formulation comprises at least 3%, by weight, of a quaternary ammonium salt. This may be useful for ensuring that the dried treatment film (i.e. produced in step S217) is rich in quaternary ammonium salts, which may be useful for promoting good dot gain;b. the aqueous treatment formulation comprises at least 1% (e.g. at least 1.5% or at least 2% or at least 3%), by weight, of at least one water soluble polymer having a solubility in water of at least 5% at 25° C. This may be useful for promoting formation of a polymer film or matrix in the dried treatment film (produced in step S217) that is sufficiently cohesive for good transfer in step225.c. a 25° C. dynamic viscosity that is at least 10 cP. As discussed below, it is believed that elevated viscosity is useful for counteracting any surface-tension driven tendency towards beading.d. a 60° C. evaporation load of at most 8:1 (e.g. at most 7:1 or at most 6:1 or at most 5:1 or at most 4:1), by weight. Thus, the solution has a low specific heat capacity relative to conventional treatment formulations having higher evaporation load. Moreover, for a particular requisite residue thickness for the aqueous treatment solution, and for a given heat output delivered to the aqueous treatment solution, the viscosity of the aqueous treatment formulation will increase rapidly as a function of evaporation to achieve a high absolute viscosity that effectively counteracts the surface tension.

Physically, it is more difficult to induce flow of fluids having a higher viscosity than fluids having a lower viscosity—i.e. to induce flow of fluids having the higher viscosity, a greater driving force is required. The combination of at least moderate initial viscosity (i.e. a 25° C. dynamic viscosity that is at least 10 cP) and rapid viscosity increase after evaporation (e.g. due to the low evaporation load) on the ITM surface ensures that the aqueous treatment formulation reaches a relatively ‘high’ (e.g. at least 10,000 cP) viscosity in a relatively short period of time (e.g. at most 1 second or at most 0.5 seconds). Therefore, even if there is some thermodynamic tendency towards beading, actual beading, which could negatively impact the properties of the dried treatment film (i.e. formed in step S213) is inhibited or appreciably mitigated.

In some embodiments, the 25° C. dynamic viscosity of initial aqueous treatment formulation may be at least 12 cP or at least 14 cP—for example, within a range of 10 to 100 cP, 12 to 100 cP, 14 to 100 cP, 10 to 60 cP, or 12 to 40 cP.

To summarize: the combination (A) of the release layer that is sufficiently hydrophilic sufficiently hydrophilic to satisfy at least one of the following properties: (i) a receding contact angle of a drop of distilled water deposited on the silicone-based release layer surface is at most 60°; and (ii) a 10-second dynamic contact angle (DCA) of a drop of distilled water deposited on the silicone-based release layer surface is at most 108°; and (B) the static surface tension of the aqueous treatment formulation in the range of 20-40 dynes/cm is useful for minimizing a magnitude of a thermodynamic driving force that would cause beading. Furthermore, the aforementioned viscosity-related features are useful for countering this driving force.

This reduction of a magnitude of a thermodynamic force that drives beading, along with the counteracting of this tendency, ensures that any tendency to bead does not prevent the formulation, in step S209, of a wet layer of treatment formulation in step S209having a uniform thickness.

In embodiments of the invention, the aqueous treatment formulation comprises a carrier liquid containing water, said water making up at least 65% (e.g. at least 70% or at least 75%), by weight of the aqueous treatment formulation;

A Discussion of Step S209

In step S209, the aqueous treatment formulation is applied to the silicone-based release layer surface of the ITM to form thereon a wet treatment layer having a thickness of at most 0.8 μm (e.g. at most 0.7 μm, or at most 0.6 μm, or at most 0.5 μm).

The “thickness of a wet layer” is defined as follows—when a volume of material vol covers a surface area of a surface having an area SA with a wet layer, the thickness of the wet layer is assumed to be vol/SA.

Preferably, step S209is performed so that the wet treatment layer has a uniform thickness and is defect free, preferably over a large area such as over the entire area of the release layer. This may be particularly challenging when the wet treatment layer is of sub-micron thickness.

As noted above, it is useful for the aqueous treatment formulation to have at least ‘moderate viscosity’ (e.g. a 25° C. dynamic viscosity that is at least 10 cP) in order to counteract beading. Nevertheless, there may be challenges associated with obtaining a layer of uniform, sub-micron thickness of the aqueous treatment formulation at such viscosities.

In step S209, an aqueous treatment formulation is applied to the silicone-based release layer surface to form a wet treatment layer having a thickness of at most 0.8 μm.

Embodiments of the invention relate to apparatus and methods for applying this wet treatment layer so that the thickness is uniform, preferably over large areas of the ITM.

In some embodiments, after coating the ITM surface with an initial coating of aqueous treatment formulation, excess treatment formulation may be removed from the initial coating or obtain a wet treatment layer having a uniform thickness of at most 0.8 μm.

In some embodiments, this may be accomplished by urging a highly-rounded surface (e.g. of a doctor blade) towards the ITM or vice versa. For example, a radius of curvature of the highly-rounded surface may be at most 1.5 mm or at most 1.25 mm or at most 1 mm.

At high print speeds (e.g. where the surface velocity of the ITM is relatively large (e.g. at least 1 meter/second or at least 1.25 meters/second or at least 1.5 meters/second)), the removing of excess liquid to form the treatment layer having a sub-micron thickness may entail establishing a relatively large velocity gradient (i.e. shear) in the gap region (e.g. the velocity gradient is normal to the ITM surface) in the between the highly surface and the ITM—e.g. a velocity gradient of at least 106sec−1or at least 2×106sec−1.

As noted above, the 25° C. dynamic viscosity of treatment formulation may be at least 10 cP. Even if step S209is performed at a higher temperature, the dynamic viscosity at these higher temperatures may be at least 3 cP or at least 5 cP or at least 10 cP. Thus, in some embodiments of the invention, a relatively large force is required (e.g. force to urge the highly-rounded surface towards the ITM or vice versa) to achieve the requisite uniform sub-0.8 μm (preferably) uniform thickness.

In some embodiments, the rounded surface is urged to the ITM or vice versa, at a force density in the cross-print direction of at least 250 g/cm or at least 350 g/cm or at least 400 gm/cm and/or at most 1 kg/cm or at most 750 g/cm or at most 600 g/cm.

In some embodiments, the wet treatment layer is formed by applying a pressure between an applicator and the ITM, a magnitude of the pressure being at least 0.1 bar or at least 0.25 bar or at least 0.35 bar or at least 0.5 bar, and optionally at most 2 bar or at most 1.5 bar, or at most 1 bar.

A Discussion of Step S213

In step S213, the wet treatment layer is subjected to a drying process form a dried treatment film therefrom.

For example, during the drying process of the wet treatment layer, a dynamic viscosity thereof increases by at least a factor of 1000 within a period of time of at most 0.5 seconds or at most 0.25 seconds.

In some embodiments, a thickness of the dried treatment film (e.g. cohesive polymer treatment film) is at most 150 nanometers, or at most 120 nanometers, or at most 100 nanometers, or at most 80 nanometers, or at most 60 nanometers.

In some embodiments, the dried treatment film has a smooth upper surface. For example, the drying process of the wet treatment layer is sufficiently rapid such that the viscosity of the aqueous treatment formulation increases rapidly enough to inhibit surface-tension-driven beading such that the dried treatment film has a smooth upper surface.

In some embodiments, the smooth upper surface of the dried treatment film is characterized by an average roughness Raof at most 12 nanometers or at most 10 nanometers or at most 9 nanometers or at most 8 nanometers or at most 7 nanometers or at most 5 nanometers. The skilled artisan is directed toFIG.13and to the accompanying discussion.

In some embodiments, the dried treatment film is continuous over an entirety of a rectangle of the release surface of the ITM, wherein said rectangle has a width of at least 10 cm and a length of at least 10 meters.

In some embodiments, the treatment film is transparent.

One of the purposes of the dried treatment film is to protect the ITM surface from direct contact with droplets of aqueous ink deposited on the treatment film. However, droplets of aqueous inks could ‘erode through’ a thickness of the dried treatment film, especially when the dried treatment film is thin (e.g. at most 150 or at most 120 or at most 100 or at most 80 nanometers). Thus, in some embodiments, a water-soluble-polymer concentration, by weight, of water soluble polymer within the provided aqueous treatment formulation (e.g. in step S205ofFIG.2or in step S95ofFIG.12) is at most 10% or at most 8% or at most 6% or at most 5%.

A Discussion of Steps S217-S221

In step S217, droplets of aqueous ink are deposited (e.g. by ink-droplet deposition) onto the dried treatment film to form an ink image on the ITM surface. In step S221, this ink image is dried to leave an ink-image residue on the ITM surface.

For example, a presence of quaternary ammonium salts in the dried treatment film is useful for promoting dot spreading and/or dot gain (e.g. uniform dot spreading and/or dot gain) when the droplets are deposited or immediately thereafter—the skilled artisan is directed to the discussion below with reference toFIGS.13A-13E. As noted above, the formation (in step S213) of a dried treatment film of uniform thickness and/or free of defects and/or having a very smooth upper surface may facilitate uniform flow of aqueous ink on the film upper surface.

A Discussion of Step S225

In step SS25, the ink-image residue is transferred to substrate. For example, the ink-image residue may be transferred together with non-printed areas of the dried treatment film onto the printing substrate.

In embodiments, the dried treatment film is sufficiently cohesive such that during transfer of the ink-image residue, the dried treatment film completely separates from the ITM and transfers to the printing substrate with the dried ink image, both in printed and non-printed areas.

In some embodiments, a temperature of the ITM during transfer is in the range between 80° C. and 120° C. In some embodiments, the ITM temperature is at most 100° C. or at most 90° C. In some embodiments, the ITM temperature is at least 100° C. or at least 110° C. or at least 120° C.

In some embodiments, a presence of water-soluble polymers in the aqueous treatment solution provided in step S205helps to ensure (i.e. by forming a polymer film or matrix) that the dried treatment film formed in step S213is sufficiently cohesive during transfer.

In some embodiments, the substrate to which the ink image residue is glossy paper—e.g. glossy coated paper.

The transfer may be perfect (i.e. an entirety of the ink image residue and the dried treatment film is transferred to substrate). Alternatively, the transfer may be less than perfect—towards this end, a cleaning station may clean away material remaining on the ITM surface after the transfer step of S225.

A Discussion ofFIGS.3A-3B

FIG.3Ais a schematic diagram of a system for indirect printing according to some embodiments of the present invention. The system ofFIG.3Acomprises an intermediate transfer member (ITM)210comprising a flexible endless belt mounted over a plurality of guide rollers232,240,250,251,253,242. In other examples (NOT SHOWN), the ITM220is a drum or a belt wrapped around a drum.

In the example ofFIG.3A, the ITM210(i.e. belt thereof) moves in the clockwise direction. The direction of belt movement defines upstream and downstream directions. Rollers242,240are respectively positioned upstream and downstream of the image forming station212—thus, roller242may be referred to as a “upstream roller” while roller240may be referred to as a “downstream roller”.

The system ofFIG.3Afurther comprises:(a) an image forming station212(e.g. comprising print bars222A-222D, where each print bar comprises ink jet head(s)) configured to form ink images (NOT SHOWN) upon a surface of the ITM210(e.g. by droplet deposition upon a dried treatment film—e.g. see step S217ofFIG.2or step S109ofFIG.12);(b) a drying station214for drying the ink images (e.g. see step S221ofFIG.2or step S113ofFIG.12)(c) an impression station216where the ink images are transferred from the surface of the ITM210to sheet or web substrate (e.g. see step S225ofFIG.2or step S117ofFIG.12).

In the particular non-limiting example ofFIG.3A, impression station216comprises an impression cylinder220and a blanket cylinder218that carries a compressible blanket219. In some embodiments, a heater231may be provided shortly prior to the nip between the two cylinders218and220of the image transfer station to assist in rendering the ink film tacky, so as to facilitate transfer to the substrate (e.g. sheet substrate or web substrate). The substrate feed is illustrated schematically.(d) a cleaning station258(i.e. inFIG.3Aillustrated schematically as a block) where residual material (e.g. treated treatment film and/or ink images or portions thereof) is cleaned (cleaning step is NOT SHOWN inFIG.2) from the surface of the ITM210.(e) a treatment station260(i.e. inFIG.3Aillustrated schematically as a block) where forming a layer (e.g. of uniform thickness) of liquid treatment formulation (e.g. aqueous treatment formulation) on the ITM surface (e.g. see step S209ofFIG.2or step S101ofFIG.12).

The skilled artisan will appreciate that not every component illustrated inFIG.3Ais required.

FIG.3Billustrates a plurality of ‘locations’ LocA-LocJ. that are fixed in space—LocAis at roller242, LocBis at the ‘beginning’ of image station212, LocCis at the ‘end’ of image station212, and so on. Thus, ink images (e.g. in step S217ofFIG.2) are formed in the region between locations LocAand LocB, at image forming station212on the upper run of ITM210. The ink images are dried (e.g. see step S221ofFIG.2or step S105ofFIG.12) in the region between locations LocCand LocEto form ink-image residues—this may occur as the ink images move (e.g. due to clock-wise rotation of the ITM) through drying station214. The ink image residues are transferred from the ITM surface to substrate at the impression station216between locations LocEand LocF(e.g. see step S225ofFIG.2or step S117ofFIG.12). Material remaining on the surface of the ITM210after transfer of the ink image residues may be cleaned from the surface of the ITM210at cleaning station258between LocGand LocH. A wet treatment layer may be formed in step S209ofFIG.2(or step S101ofFIG.12) on the surface of the ITM210at treatment station260between locations LocIand LocJ(e.g. see step S209ofFIG.2or step S101ofFIG.12). This wet treatment layer subjected to a drying process (i.e. to convert the wet treatment layer into a dried treatment film) (e.g. see step S213ofFIG.2or step S105ofFIG.12) —this may occur between locations LocJand LocAon the right-hand side. After the dried treatment film is transported (e.g. by counterclockwise rotation of ITM210) to image forming station212, ink images may subsequently be formed by droplet deposition to the dried treatment film (e.g. see step S217ofFIG.2or step S109ofFIG.2).

As illustrated inFIGS.3A-3B, the portion of the ITM between locations LocAand LocDare an upper run of the ITM210(i.e of a belt thereof). This upper run (illustrated inFIG.3C) is between (i) an upstream guide roller242that is upstream to image forming station212and (ii) a downstream guide roller240that is downstream to image forming station. The upper run passes though the image forming station212.

A lower run of the ITM is between locations LocDand LocAof ITM210and is illustrated inFIG.3D. This lower run passes through impression station216, cleaning station258and treatment station260.

One example of a treatment station is shown inFIG.4A.

In the particular non-limiting embodiment ofFIG.4A, the ITM210is moved from right to left as viewed, as represented by an arrow2012, over a doctor blade that is generally designated2014and is suitably mounted within a tank2016. InFIG.4A, the doctor blade202014is of the doctor rod type and is formed of a rigid bar or holder2020that extends across the entire width of the ITM210. In its upper surface facing the underside of the ITM210, the bar2020is formed with a channel or groove24within which there is supported a rod2022made of fused quartz and having a smooth and regular cylindrical surface with a roughness of no more than a few microns, preferably less than 10 microns and in particular less than 0.5 microns.

Prior to passing over the doctor blade2014, the underside of the ITM210(or lower run) is coated with an excess of treatment formulation (e.g. solution)2030(e.g. provided in step S205ofFIG.2or step S95ofFIG.12). The manner in which the excess of treatment formulation (e.g. solution) is applied to the ITM210, specifically to its underside in the present illustration, is described below by reference toFIG.5, but is not of fundamental importance to the present invention. The ITM210may for example simply be immersed in a tank containing the liquid, passed over a fountain of the treatment formulation (e.g. solution), or, as shown inFIG.5, sprayed with an upwardly directed jet1128.

In an embodiment of the invention, a liquid-permeable cloth is placed above upwardly directed spray heads, so that the liquid seeps through the cloth and forms a layer on the side of the cloth facing the surface to be coated. In this case, the spray heads will act to urge the cloth towards the surface, but it will be prevented by the liquid seeping through it from contacting the surface, the liquid acting in the same manner as in a hydrodynamic bearing.

As shown in the drawing, as the ITM210approaches the doctor blade2014it has a coating2030of liquid that is significantly greater than the desired thickness of the thin film that is to be applied to the ITM210.

The function of the doctor blade2014is to remove excess liquid2030from the ITM210and ensure that the remaining liquid is spread evenly and uniformly over the entire surface of the ITM210. To achieve this, the ITM210is urged towards the doctor blade2014, for example by means of air pressure (NOT SHOWN). Alternatively, the force urging the ITM210towards the doctor blade2014may be a backing roller1141, such a sponge roller in some embodiments, pressing down on the upper or opposite side of the web, either by virtue of its own weight or by the action of springs. As a further alternative, the doctor blade2014may itself be urged towards the ITM210while the latter is maintained under tension.

The tip of the doctor blade2014, being constituted by a cylindrical smooth rod2022, has a uniform radius over the width of the ITM210and its smoothness ensures laminar flow of the liquid in the gap between it and the underside of the ITM210. The nature of the flow may be similar to that of the liquid lubricant in a hydrodynamic bearing and reduces the film of liquid2030that remains adhering to the underside of the ITM210(i.e. the surface of a ‘low run’ of the ITM) to a thickness dependent upon the force urging the ITM against the doctor blade2014and the radius of curvature of the rod2022. As both the radius and the force are constant over the width of the web, the resulting film is uniform and its thickness can be set by appropriate selection of the applied force and the rod diameter. The excess of liquid removed by the doctor blade2014creates a small pool2032immediately upstream of the rod2022before falling into the tank2016.

In an alternative embodiment of the invention, the surface of the ITM210to be coated with liquid may face upwards instead of downwards. In this case, instead of applying an excess of liquid to the ITM210(i.e. the surface of a ‘low run’ of the ITM), the liquid may be metered onto the surface to develop and maintain a similar small pool of liquid upstream of the line of contact between the wiper blade and the surface on the upper side of the web. Air knives may be provided in this case to prevent treatment formulation (e.g. solution) from the pool from spilling over the lateral edges of the ITM210.

In embodiments of the invention, pool2032provides a constant supply of treatment formulation (e.g. solution) across the entire width of the ITM210so that all areas of the ITM210are coated even if the liquid has been, for any reason, repelled (e.g due to ‘beading’) from parts of the surface of the web prior to reaching the doctor blade2014.

The tank2016into which the surplus treatment formulation (e.g. solution) falls may be the main reservoir tank from which liquid is drawn to coat the underside of the web with an excess of treatment formulation (e.g. solution) or it may be a separate tank that is drained into the main reservoir tank and/or emptied to suitable discard systems.

The rod2022is made of a hard material such as fused quartz in order to resist abrasion. There may be small particles of grit or dust in the liquid which could damage the rounded edge over which the liquid flows. It would be possible to use materials other than fused quartz but the material should preferably have a Brinell hardness in excess of 100 (e.g. in excess of 200, or in excess of 500, or even in excess of 1000). In embodiments of the invention, the material should be capable of being formed into a smooth rod of uniform diameter and a surface roughness of less than 10 micron, in particular of less than 0.5 micron.

The rod2022which may have a radius of 6 mm but possibly of only 0.5 mm is relatively fragile and may require a bar2020for support. To hold the rod2022accurately in position, the bar is formed with a groove24within which the rod2022rests. The rod may be retained in the groove24in any suitable manner. For example, it is possible to use an adhesive and to use the bar2020to press the rod2022against a flat surface, such as a glass sheet, until the adhesive sets. As a further alternative, the groove may be accurately machined to be slightly narrower than the rod diameter and heat shrinking may be used to hold the rod in position within the groove.

Sometimes when using such a doctor blade to apply certain formulations (e.g. solution), a deposit34of the solute builds up on the downstream side of the doctor blade2014. While not wishing to be bound by theory, it is believed that this may be caused by the fact that a stationary film of the formulation (e.g. solution) adheres to the downstream side of the doctor blade and as it dries leaves behind the solute. Regardless of the reason for the formation of such a deposit and its composition, if allowed to grow excessively, it will eventually interfere with the layer of treatment formulation (e.g. solution) applied to the ITM210.

Embodiments of the invention relate to apparatus and methods for changing the doctor blade2014when it becomes soiled.FIG.4Billustrate an example of how the doctor blade may be changed easily, and preferably without the need to interrupt the web coating process, or the printing system that requires a conditioning agent to be applied to its ITM.

InFIG.4B, twelve doctor blades1122are mounted uniformly in recesses around the circumference of a cylindrical rotatable turret1120. The axially extending doctor blades1122behave in the same way as the doctor rods1122inFIG.4Aand the turret1120serves the same purpose as the rod holder2020. Instead of using rods of circular cross section, the doctor blades1122are constructed as strips having smooth rounded and polished edges. Strips having rounded edges of uniform radius of curvature may be produced, for example, by flattening rods of circular cross section. The doctor blades1122may suitably be made of stainless steel but other hard materials resistant to abrasion may alternatively be used.

The manner in which the turret1120and the doctor blades122interact with the ITM110is shown inFIG.5which illustrates one example of a cleaning station258and treatment station260(e.g. for applying a wet layer of treatment formulation—e.g. as in step S209ofFIG.2or step S101ofFIG.2).

In the example ofFIG.5, two separate tanks1125,1127are shown. A quantity of treatment solution (e.g. having one or properties of step S205ofFIG.2or step S95ofFIG.12) is stored in tank1125. For example, this treatment solution may be jetted (i.e. by jetting apparatus774) to the surface of the ITM210. Also illustrated inFIG.5are brushes1126A and1126B for mechanically removing material from the surface of the ITM210to clean the ITM surface—e.g. pressure may be applied between backing rollers772A-772B respectively disposed opposite brushes1126A-1126B.

In some embodiments, material removed from the surface of the ITM comprises dried treatment film which may be, for example, resoluble in liquid treatment formulation (e.g. having one or properties of step S205ofFIG.2or step S95ofFIG.12) stored in tank1125—this may allow for recycle of treatment formulation.

Irrespective of any mechanical properties of the system, in embodiments of the invention, the aqueous treatment formulation provided in step S205ofFIG.2or in step S95ofFIG.12is full resoluble (e.g. after drying, it may fully dissolve in aqueous treatment formulation).

Treatment formulation1128may be jetted by jetting apparatus1128. In the example ofFIG.5, one of the doctor blades1122is active—this is labelled1122ACTIVE. A relatively thick layer of treatment formulation may be applied (e.g. by apparatus1128), and excess treatment formulation may be removed by the combination of doctor blade1122ACTIVEand a backing roller1141which is urged towards doctor blade1122ACTIVE.

Jetting apparatus1128is one example of a ‘coater’ for applying a coating of treatment formulation to the surface of ITM210. Another example of a coater is a pool2032when liquid content of the pool is retained on the ITM surface.

Collectively, doctor blade1122ACTIVE(or rounded tip thereof) and backing roller1141(or alternatively a device for providing air pressure towards rounded tip1123) collectively a coating thickness-regulation assembly—thus, inFIGS.10A and11Athe “final thickness’ of the treating formulation may be regulated by according to an amount of force urgent the tip1123towards the opposing portion of ITM210(e.g. towards backing roller1141) or vice versa.

In the example ofFIG.5, only one doctor blade122interacts with the ITM110at any given time but when a blade becomes soiled, the turret120is rotated to bring the next adjacent doctor blade into the operating position in which the blade is functional, i.e. sufficiently close to the surface to remove excess liquid and allow only a film of the desired thickness to adhere to the surface downstream of the apparatus.

Prior to returning to the operating position, at some later stage in the turret rotation cycle, the soiled blade1122passes through a cleaning device, for example a brush1130, which removes any deposit and cleans the blade before it becomes functional again.

The rotation of the turret1120may be instigated on demand by an operator or it may be performed at regular intervals.

The number of doctor blades on the turret1120need not be twelve but it is desirable for there to be a sufficient number that during a changeover, as shown inFIGS.8-9, there should be a time when two doctor blades1122are functional and interact with the ITM110at the same time. As a consequence, there is a substantially continuous replacement of the blades, so that no interruption in the film metering operation, and this in turn permits the doctor blade to be changed without interruption of the printing system.

FIGS.8-9are more detailed perspective and exploded sectional views, respectively, of the turret1120and the doctor blade cleaning brush1130. Both are mounted on axles rotatably supported in a metal frame1140immersed in the tank1127. The axles of the turret1120and the doctor blade cleaning brush1130are connected to respective drive motors1412and1144mounted outside the tank1127. As can be seen fromFIG.7, the turret1120is made of a hollow cylinder and its cylindrical surface may be perforated to reduce it weight and moment of inertia, while still providing adequate strength to support the doctor blades1122.

While the doctor blades1122supported by the turret1120have been shown as flat strips, it should be understood that they may alternatively be formed as circular rod as described by reference toFIG.4.

It has been found that the vigorous agitation of the solution of the conditioning agent can, for certain conditioning agents, result in the formation of a foam or froth. It is possible to destroy the foam using ultrasound and such an anti-foaming device may be incorporated in the tank1125.

As illustrated inFIG.10A, when doctor blade1122ACTIVEis urged towards backing roller1141, or vice versa, doctor blade may penetrate into a lower run of the ITM210. As shown inFIG.10A, ITM210(i.e. a lower run thereof) is disposed in between roller1141and doctor blade1122ACTIVE. Therefore, when roller1141is urged towards doctor blade1122ACTIVE, roller1141pushes on ITM210(i.e. a lower run thereof) and ITM210is urged towards doctor blade1122ACTIVE—the converse is true.

In the examples ofFIGS.10A-10B, a central axis1188of doctor blade1122ACTIVEis illustrated. InFIGS.10A-10B, a rounded tip of doctor blade1122ACTIVEis labelled as1123.

In the example ofFIG.10A, tip1123faces a surface (i.e. local normal) of the ITM210. In the example ofFIG.10Adoctor blade1122ACTIVEis oriented substantially normal to a local surface of the ITM210that faces rounded tip1123.

In the example ofFIG.10A, downward force may be applied (i.e. via the ITM) by roller1141towards rounded tip1123. Alternative, air pressure may be used to bias the ITM210towards the rounded tip1123. This results in the doctor blade122ACTIVEremoving all but a thin liquid film (e.g. less than typically less than 1 micrometer) having a thickness determined by the radius of curvature and the applied pressure.

Jetting device1128or a bath in which the ITM surface may be soaked or any other device for applying an initial coating may be considered a ‘coater’ for coating the ITM with liquid treatment formulation. Furthermore, the combination of (i) rounded surface1123(e.g. rounded tip) and a device for applying a counter force (e.g. roller1141) to urge rounded surface1112towards an opposing of the ITM210(or vice versa) form a thickness-regulation assembly for removing excess liquid so as to leave only the desired uniform thin layer of treatment formulation (e.g. of submicron thickness).

In embodiments of the invention, even though the rounded tip1123is out contact from an opposing ITM surface (e.g. to maintain a gap therebetween, the applicator may still indirectly apply pressure to the ITM via the treatment fluid.

In some embodiments, the rounded tip applies a pressure of at least 0.1 bar or at least 0.25 bar or at least 0.35 bar or at least 0.5 bar, and optionally at most 2 bar or at most 1.5 bar, or at most 1 bar.

This pressure may be localized in the print direction. For example, a ‘strip of pressure’ (e.g. the strip may be elongated in a cross print direction) (e.g. having a length of at least 10 cm or at least 30 cm or at least 50 cm) may be applied to the ITM by the applicator so that (i) a maximum pressure applied to the ITM within the strip is P_STRIP_MAX, a value of which is at least at least 0.1 bar or at least 0.25 bar or at least 0.35 bar or at least 0.5 bar, and optionally at most 2 bar or at most 1.5 bar, or at most 1 bar; (ii) at all locations within the strip, a local pressure applied to the ITM by the applicator is at least 0.5*P_STRIP_MAX and (iii) on all locations in a cross-print direction on opposite sides of the strip (upstream and downstream to the strip—displaced from the strip by at most 2 cm or at most 1 cm or at most 5 mm or most 3 mm or at most 2 mm or at most 1 mm or at most 0.5 mm), a maximum pressure is at most 0.2*P_STRIP_MAX or at most 0.1*P_STRIP_MAX.

As shown inFIG.11A, a presence of the rounded tip1123(e.g. doctor blade) (e.g. held stationary) may cause a shear field or velocity gradient—see, for example,FIG.11BandFIG.11C. At locations on the ITM surface, the velocity of treatment fluid may be non-zero (e.g substantially equal to a velocity of the ITM) due to a no-stick boundary condition with the ITM surface; at the applicator the velocity of treatment fluid may be zero.

In some embodiments, i. the forming of the thin wet treatment layer (e.g. in step S209ofFIG.2or in step S101ofFIG.12) comprises creating a velocity gradient (e.g. in the direction normal to the ITM surface) of the aqueous treatment solution in an Intense velocity Gradient IVG location x=xIVG_locationlocation that is (i) normally displaced from the release surface of the ITM (e.g. by at most 3 microns or at most 2 microns or at most 1 micron) and/or between an applicator and the release surface of the applicator; and ii. in the IVG location, a magnitude of the velocity gradient equals or exceeds a VG value that is at least 106sec−1or at least 2×106sec−1or at least 4×106sec−1or at least 5×106sec−1or at least 7.5×106sec−1or at least 107sec−1or at least 2×107sec−1or at least 4×107sec−1or at least 5×107sec−1or at least 7.5×107sec−1.

In some embodiments, the velocity gradient is localized along a print direction such that:i. at an upstream location that is upstream of the IVG location, a maximum velocity gradient is at most x % of a value of the velocity gradient at the IVG location;ii. at a downstream location that is downstream of the IVG location, a maximum velocity gradient is at most x % of a value of the velocity gradient at the IVG location;iii. a value of x is at most 50 or at most 30 or at most 20 or at most 10; and/oriv. the upstream and downstream locations are each displaced from the IVG location by at most by at most 2 cm or at most 1.5 cm or at most 1.25 cm or at most 1 cm or at most 9 mm or at most 8 mm or at most 7.5 mm or at most 7 mm or at most 6 mm or at most 5 mm.

In some embodiments, the rounded surface is urged to the ITM or vice versa, at a force density in the cross-print direction of at least 250 g/cm or at least 350 g/cm or at least 400 gm/cm and/or at most 1 kg/cm or at most 750 g/cm or at most 600 g/cm.

Discussion ofFIG.12

Embodiments of the present invention relate to a printing process described inFIG.12. In some non-limiting embodiments, apparatus, systems and devices described in ofFIGS.3-11may be employed to perform the method ofFIG.12. The order of steps inFIG.12is not intended as limiting—in particular, steps S91-S99may be performed in any order. In some embodiments, steps S101-S117are performed in the order indicated inFIG.12.

In some embodiments, step S91may be performed to provide any feature or combination of features of step S201ofFIG.2.

In some embodiments, step S95may be performed to provide any feature or combination of features of step S205ofFIG.2.

In some embodiments, step S101may be performed to provide any feature or combination of features of step S209ofFIG.2.

In some embodiments, step S105may be performed to provide any feature or combination of features of step S213ofFIG.2.

In some embodiments, step S109may be performed to provide any feature or combination of features of step S217ofFIG.2.

In some embodiments, step S113may be performed to provide any feature or combination of features of step S221ofFIG.2.

In some embodiments, step S117may be performed to provide any feature or combination of features of step S225ofFIG.2.

Steps S91-99relate to the ingredients or components or consumables used in the process ofFIG.12, while steps S101-S117relate to the process itself. Briefly, (i) in step S101a thin treatment layer of a wet treatment formulation is applied to an intermediate transfer member (ITM) (e.g. having a release layer with hydrophobic properties), (ii) in step S105this treatment layer is dried (e.g. rapidly dried) into a thin dried treatment film on a release surface of the ITM, (iii) in step S109droplets of an aqueous ink are deposited (e.g. by jetting) onto the thin dried treatment film, (iv) in step S113the ink image is dried to leave an ink image on the dried treatment film on the ITM and (v) in step S117the ink-image is transferred to printing substrate (e.g. together with the dried treatment film).

The details of the ingredients of steps S91-S99, as well as the process steps S101-S117are described below.

In embodiments of the inventions, steps S91-S117are performed as follows:(A) in step S91, an ITM is provided—e.g. at most moderately hydrophobic and/or having hydrophobic properties and/or having a release layer that is silicone based and/or only moderately hydrophobic and/or lacking functional groups;(B) in step S95, an aqueous treatment solution is provided (e.g. (i) having a low evaporation load and/or (ii) that is surfactant rich and/or (ii) that is only moderately hydrophilic and/or (iii) comprising a water soluble polymer and/or (iv) comprising quaternary ammonium salts and/or (v) having a viscosity that is low enough so that the solution may be spread into a uniform thin layer and/or (vi) comprising hygroscopic material and/or (vii) substantially devoid of organic solvents and/or (viii) having at most a low concentration of flocculants containing polyvalent cations;(C) in step S99an aqueous ink is provided;(D) in step S101an aqueous treatment formulation is applied to the release surface of the ITM (e.g. an in-motion ITM) to form thereon a thin wet treatment layer (e.g. thickness ≤0.8μ);(E) in step S105, the wet thin treatment layer is subjected to a drying process (e.g. rapid drying) on the ITM release surface to leave a thin dried treatment film (e.g. thickness ≤0.08μ) of the water-soluble polymer on the ITM release surface. For example, the thin dried treatment film may have one or both of the following properties: (i) for example, the treatment film is continuous and/or cohesive film; (ii) an upper surface of the dried treatment film is characterized by a very low roughness;(F) in step S109, droplets of aqueous ink are deposited (e.g. by ink-jetting) onto the thin dried treatment film to form an ink image thereon;(G) in step S119, the ink-image to leave an ink residue on the dried treatment film (e.g. to achieve good ink-dot spreading)(H) in step S119, the dried ink-image is transferred (e.g. at a relatively low temperature) (e.g. together with the dried treatment film) from the ITM surface to printing substrate (e.g. paper-based or plastic-based).

In some embodiments, the process ofFIG.12is performed so that when the aqueous treatment solution is applied to the ITM in step S101, there is little or no beading so that the resulting thin dried treatment film (i.e. obtained in step S105) is continuous and/or has a smooth (e.g. extremely smooth) upper surface. This smooth upper surface may be important for obtaining a substrate-residing ink image of high quality.

One feature associated with conventional processes where the ITM is pre-treated and the ink image is applied on top of the pre-treated ITM, is that after transfer to substrate, the dried treatment formulation (e.g. after drying) resides over the ink image, and may add to the ink image an undesired gloss. To overcome or minimize this potentially undesirable effect, the thin dried treatment film is obtained in step S105(for example, having a thickness of at most 400 nanometers or at most 200 nanometers or at most 100 nanometers or even less). Furthermore, in some embodiments, this thin dried treatment film (i.e. obtained in step S105) is continuous, which can be beneficial, as discussed below.

Though not a limitation, in some embodiments, the process ofFIG.12is performed so that the image-transfer of step S117is performed at a low temperature (e.g. to an uncoated substrate) —e.g. a temperature of at most 90° C., or at most 85° C., at most 80° C., or at most 75° C., at most ° C., or at most 65° C., at most 60° C. —for example, at about 60° C.

A Discussion of Step S91ofFIG.12

In different embodiments, the ITM (i.e. the ITM provided in step S91ofFIG.12or in step S201ofFIG.2) may provide one of more (i.e. any combination of) of the following features A1-A5:A1: In some embodiments, the release layer is formed of a silicone material (e.g. addition-cured) —this provides the ITM with hydrophobic properties useful in step S117;A2: Before use in the method ofFIG.12, the silicone-based release layer has been produced in a manner that reduces a hydrophobicity thereof. For example, instead of relying on the addition of functional, reactive groups to imbue the release layer with hydrophilicity, it is possible to cure the silicone release layer so that polar atoms in polar groups (e.g. the oxygen atom in a polar Si—O—Si moiety) are aligned or otherwise face outwardly with respect to the release layer surface. In this example, the oxygen atom of the “Si—O—Si” is not capable, under typical process conditions, of chemically bonding to the materials within the treatment solution, to the dried ink image and/or to the dried treatment film in step S117. However, in steps S101-S105, it is possible to benefit from the hydrophilicity of the outwardly-facing, polar “O”.A3: the release surface of the ITM may have moderately hydrophobic properties but is not overly hydrophobic. Thus, the release surface may have a surface energy (at 25° C.) of at least 23 dynes/cm, and more typically, at least 25 dynes/cm, at least 28 dynes/cm, at least 30 dynes/cm, at least 32 dynes/cm, at least 34 dynes/cm, or at least 36 dynes/cm, and/or at most 48 dynes/cm, at most 46 dynes/cm, at most 44 dynes/cm, at most 42 dynes/cm, at most 40 dynes/cm, at most 38 dynes/cm, or at most 37 dynes.A4: a receding contact angle of a droplet of distilled water on the ink reception or release layer surface is typically at least 30°, and more typically, 30° to 75°, 30° to 65°, 30° to 55°, or 35° to 55°;A5: the release layer of the ITM may be devoid or substantially devoid of functional groups bonded within the crosslinked polymer structure; the inventors believe that such functional groups may increase or promote an undesired adhesion.
A Discussion of Step S95ofFIG.12

In step S95, an aqueous treatment formulation is provided. This treatment formulation comprises at least 50% wt/wt or at least 55% wt/wt or at least 60% wt/wt or at least 65% wt/wt water carrier liquid).

In different embodiments, the aqueous treatment formulation (i.e. the aqueous treatment formulation in its initial state before the application of step S101ofFIG.12or the aqueous treatment formulation in its initial state before the application of step S205ofFIG.1) may provide one of more (i.e. any combination of) the of the following features:

B1. Low evaporation load—In some embodiments, the initial aqueous treatment formulation has a low evaporation load and is relatively rich in material that is solid at 60° C. (and at atmospheric pressure). As will be discussed below, in some embodiments, this may be useful so that during step S105, the viscosity rapidly increases in a very short period of time, thereby counteracting any tendency of the aqueous treatment formulation to bead on the release surface of the ITM, which has hydrophobic properties. For example, the 60° C. evaporation load may be at most 10:1, or at most 9:1, or at most 8:1, or at most 6:1, or at most 5:1, or at most 4:1. In some embodiments, this is useful for achieving a continuous dried treatment film lacking in bare patches.
B2. surfactant rich—in some embodiments, the initial aqueous treatment formulation comprises at least 2% wt/wt, or at least 2.5% w/t, at least 3% wt/wt, or at least 4% w/t, or at least 5% wt/wt, or at least 6% wt/wt, or at least 7% wt/wt, or at least 8% wt/wt, or at least 9% wt/wt, or at least 10% wt/wt of surfactant(s). For example, one or more of the surfactants present in the initial aqueous treatment formulation (e.g. at least 50% or at least 75% or at least 90% by weight of surfactants in the treatment formulation) may be a solid at 60° C., thus contributing to the low evaporative load. In some embodiments, the relatively high concentration of the surfactant in initial the aqueous treatment formulation may serve to make the aqueous treatment formulation less hydrophilic, thereby reducing a tendency of the aqueous treatment formulation to bead on the release surface of the ITM in step S101and/or S105. In some embodiments, because the surfactant is a wetting agent, the relatively high concentration of the surfactant may be useful for spreading aqueous ink-droplets (or counteracting any tendency of the ink droplet to contract) over the surface of the dried ink film during steps S109and/or S113, thereby increasing a coverage of the resulting ink dot which eventually resides on the substrate.
B3. a presence (e.g. at relatively high concentration) of quaternary ammonium salts—in some embodiments, the initial aqueous treatment formulation comprises at least 1.5% (e.g. at least 2%, at least 2.5%, at least 3%, at least 4%, at least 5%) wt./wt. quaternary ammonium salts. In some embodiments, a solubility of the quaternary ammonium salts in water is at least 5% at 25° C. In some embodiments, the ammonium quaternary ammonium salt, contains aliphatic substituents.
B4. Moderately hydrophilic initial aqueous treatment formulation—in some embodiments, the initial aqueous treatment formulation is only moderately hydrophilic—e.g. having a static surface tension at 25° C. of at most 32 dynes/cm (e.g. between 20 and 32 dynes/cm) or at most 30 dynes/cm (e.g. between 20 and 32 dynes/cm) or at most 28 dynes/cm (e.g. between 20 and 32 dynes/cm). Because the release surface of the ITM has moderately hydrophobic (or moderately hydrophilic) properties, it may not be useful to employ an initial aqueous treatment formulation having high hydrophilicity, which would cause beading of the aqueous treatment formulation on the surface of the ITM in steps S101and/or S105. This may be especially important for situations where the thickness of the wet treatment layer is thin, and it is desired to avoid bare patches so the resulting thin dried treatment film is continuous.
B5. Presence of a water-soluble polymer which forms a polymer matrix (e.g. upon drying in step S105ofFIG.21or upon drying in step S213ofFIG.2) —in some embodiments, the initial aqueous formulation comprises at least 1.5% (e.g. at least 2%, at least 2.5%, or at least 3%) by weight, of at least one water soluble, polymer, more particularly, a matrix forming polymer, having a solubility in water of at least 5% at 25° C. Such polymer(s) include but are not limited to polyvinyl alcohol (PVA), water-soluble cellulose, including derivatives thereof, such as hydroxypropyl methyl cellulose, PVP, polyethylene oxide, and acrylic. In some embodiments, the formation of the polymer matrix promotes forming of the film and/or imbues the dried treatment film with desired elasticity and/or cohesiveness or tensile strength, even when the dried treatment film is quite thin.
B6. Relatively low viscosity before application to the ITM in step S101ofFIG.12(or before application to the ITM in step S209ofFIG.2) —as will be discussed below, in step S101ofFIG.12(or in step S209ofFIG.2) the inventors have found it to be desirable to apply a thin but relatively uniform wet layer of aqueous treatment formulation. Towards this end, the 25° C. dynamic viscosity of the initial aqueous treatment formulation may be at most 100 cP or at most 80 cP or at most 40 cP or at most 30 cP. Alternatively or additionally, the 25° C. dynamic viscosity of the initial aqueous treatment formulation may be at least 8 cP or at least 10 cP or at least 12 cP or at least 14 cP—for example, within a range of 8 to 100 cP, 10 to 100 cP, 12 to 100 cP, 14 to 100 cP, 10 to 60 cP, or 12 to 40 cP.

In some embodiments, this feature might be particularly useful when applying the treatment formulation to the ITM as it moves at high speeds (e.g. past an applicator arrangement—for example, a stationary applicator arrangement).

B7. Devoid of organic solvents such as glycerol—in some embodiments, a presence of low vapor pressure organic solvents might retard the drying of the treatment formulation on the surface of the ITM in step S105and/or result in a treatment film lacking desired elasticity and/or cohesiveness or tensile strength desired for the transfer step S117. In some embodiments, the formulation is devoid of organic solvents, irrespective of their vapor pressure in the pure state, and/or comprises at most 3%, at most 2%, at most 1%, or at most 0.5%, or at most 0.25% or at most 0.1% by weight, organic solvents. In particular, in some embodiments, the formulation is devoid of organic solvents and/or comprises at most 3%, at most 2%, at most 1%, or at most 0.5%, or at most 0.25% or at most 0.1% by weight, glycerol. In some embodiments, the formulation is completely devoid of glycerol.
B8. Comprising water-absorbing materials—in some embodiments, the initial aqueous treatment formulation comprises a solid water-absorbing agent that is selected to absorb water from the ink when the water-absorbing agent is disposed within the solid, dried treatment film. For example, such solid water-absorbing agents may have a melting point (i.e., when a pure state) of at most 60° C. or at most 50° C. or at most 40° C. or at most 30° C. or at most 25° C. —for example, at least 1.5% or at least 2% or at least 2.5% or at least 3T wt./wt. Examples of such water-absorbing agents include but are not limited to sucrose, urea, sorbitol, and isomalt.
B9. A presence of multiples types of surfactant including at least one surfactant whose surface tension exceeds that of the formulation as a whole—in some embodiment, the initial aqueous treatment formulation comprises first and second surfactants where the first surfactant is more hydrophobic (and has a lower surface tension than) the second surfactant (e.g., quaternary ammonium salts). In one example, the first surfactant comprises a silicon polyether and/or the second surfactant is a quaternary ammonium salt. For example, an absolute value of a difference in respective surface tensions between the first and second surfactants may be at least 5 dynes/cm or at least 7.5 dynes/cm or least 10 dynes/cm. For example, (i) a surface tension of the first surfactant is less than a surface tension of the initial aqueous treatment formulation (e.g. by least 1 dyne/cm or at least 2 dynes/cm or at least 3 dynes/cm or at least 4 dynes/cm or at least 5 dynes/cm or at least 7 dynes/cm) and/or (ii) a surface tension of the second surfactant exceeds a surface tension of the initial aqueous treatment formulation (e.g. by least 1 dyne/cm or at least 2 dynes/cm or at least 3 dynes/cm or at least 4 dynes/cm or at least 5 dynes/cm or at least 7 dynes/cm).

In some embodiments, the primary purpose of the first surfactant is to lower the hydrophilicity of the initial aqueous treatment formulation (e.g. to value described above in ‘feature A4’) —e.g. so that the treatment formulation does not bead in steps S101and/or S105. Alternatively or additionally, the primary purpose of the second surfactant is to provide any features described above in B3.

In different embodiments, the initial aqueous treatment formulation comprises at least 2% wt./wt., or at least 2.5% wt./wt., at least 3% wt./wt., or at least 4% wt./wt., or at least 5% wt./wt. of the first surfactant and/or at least 2% wt./wt., or at least 2.5% wt./wt., or at least 3% wt./wt., or at least 4% wt./wt., or at least 5% wt./wt. of the second surfactant. For example, a ratio between a wt./wt. concentration of the first surfactant and a wt./wt. concentration of the second surfactant is at least 0.1 or at least 0.2 or at 0.25 or at least 0.33 or at least 0.5 or at least 0.75 and/or at most 10 or at most 4 or at most 3 at most 2 or at most 4/3.

B10. Having at most a low concentration of flocculants containing polyvalent cations (such as calcium chloride) —in some embodiments, it is believed that these compounds are not good for the image quality.

A Discussion of Step S99ofFIG.12

Potential Features of the Aqueous Ink:

Feature C1: In some embodiments (e.g. related to the method ofFIG.2or ofFIG.12), the ink provides one or more features of (any combination of features) disclosed in PCT/IB13/51755 or US2015/0025179, PCT/IB14/02395 or U.S. Ser. No. 14/917,461, all of which are hereby incorporated by reference.
A Discussion of Step S105ofFIG.12
Feature D1: The dried treatment layer formed in step S105is thin but not a monolayer (e.g. significantly thicker than monolayer) —e.g. having a thickness of at most 100 nanometers. In some embodiments, the dried treatment layer is extremely thin, having a thickness of at most 80 nanometers, or at most 75 nanometers, or at most 70 nanometers, or at most 65 nanometers, or at most 60 nanometers, or at most 55 nanometers, or at most 50 nanometers. Nevertheless, in different embodiments, even if the dried treatment film is extremely thin, it is thicker than monolayers or monolayer-type constructs. Thus, in different embodiments, a thickness of the dried treatment layer may be at least 20 nanometers or at least 30 nanometers or at least 40 nanometers or at least nanometers. In some embodiments, providing this much ‘bulk’ (i.e. minimum thickness features—e.g. together with other feature(s) described below) facilitates formation of a dried treatment film that is cohesive and/or elastic—this may be useful in step S117where it is desirable for the dried treatment film (i.e. at that stage bearing the dried ink image thereon) to maintain its structural integrity as it is transferred from the ITM to substrate.

In some embodiments, the dried treatment formulation may add an undesired gloss to the resulting ink image after transfer to substrate—thus, the ability to form a thin but cohesive dried treatment layer may be useful. The thin layer also facilitates evaporation and drying of the layer into a film.

Feature D2: The dried treatment film formed on the ITM in step S105is continuous and is devoid of ‘bare patches’ thereon, despite the thinness or extreme thinness. As will be discussed below, in some embodiments, in order to achieve this (i.e. especially for thin or very thin layers), both of the following may be required: (i) the initially-applied wet layer applied in step S101is continuous and devoid of bare-patches, even if the initially-applied wet layer is relatively thin, having a thickness of at most about 1μ (or at most 0.8μ or at most 0.6μ or at most 0.4μ and more typically, at most 0.3μ, at most 0.25μ, or at most 0.2μ, and/or at least 0.1μ) and (ii) the drying process of step S105occurs very quickly, where the viscosity of the drying treatment formulation increases very rapidly (e.g. by a factor of at least 100 or at least 1000 or at least 10,000 within at most 100 milliseconds, at most 50 milliseconds, within at most 40 milliseconds, within at most 30 milliseconds, within at most 25 milliseconds, within at most 20 milliseconds, within at most 15 milliseconds or within at most 10 milliseconds). Because the ITM release layer has hydrophobic properties and the treatment formulation is aqueous and more hydrophilic, when the aqueous treatment formulation is applied to the ITM release layer, the aqueous treatment formulation may undergo beading. However, if the viscosity increases rapidly after application of the wet treatment layer, the higher viscosity treatment formulation may better resist beading than a formulation of lower viscosity. In some embodiments and as discussed above in feature “B1”, the aqueous treatment formulation may be rich in solids and/or include a low evaporative load—this may facilitate a rapid increase in viscosity.

Another anti-beading feature (i.e. anti-beading of the treatment formulation in steps S101-S105) useful for obtaining a continuous dried treatment film may relate to the relative properties of (i) the release surface of the ITM which in some embodiments has hydrophobic properties but is not overly hydrophobic (see feature (see Feature “BA”); and (ii) the aqueous treatment formulation which in some embodiments has hydrophilic properties but is not overly hydrophilic (see feature “B4”). When the static surface tension between the aqueous treatment formulation and the release layer of the ITM may be relatively small, there is less of a driving force towards beading, and the viscosity of the aqueous treatment formation (e.g. as it rapidly increases) may be sufficient to prevent beading.

As will be discussed above, despite the only moderate hydrophobicity of the release layer of the ITM (see feature “A3”), the ITM release layer may have specific properties (see feature “A5”), that limits an adhesion between the ITM release layer and the dried treatment film—thus, even if the treatment surface is only moderately hydrophobic to avoid beading of treatment formulation thereon in steps S101and/or S105, it may be possible (e.g. thanks at least in part to feature “B2”) to avoid paying a ‘price’ for this benefit in step S117when it is desired later to minimize adhesion forces between the release layer of the ITM and the dried treatment film.

In some embodiments, this is useful for producing substrate-residing ink images having appropriate image integrity (see, for example,FIGS.15A-15D).

Feature D3: The dried treatment film formed on the ITM in step S105is characterized by an extremely low surface roughness—in some embodiments, the surface roughness may be characterized by a roughness average Ra(a commonly used one-dimensional roughness parameter) of at most 20 nanometers or at most 18 nanometers or at most 16 nanometers or at most nanometers or at most 14 nanometers or at most 12 nanometers or at most 10 nanometers or at most 9 nanometers or at most 8 nanometers or at most 7 nanometers or at most 6 nanometers. The dried treatment film formed on the ITM may have an Raof at least 3 nanometers or at least 5 nanometers.

In some embodiments, it may be possible to achieve such a low roughness average Raeven for thin or extremely thin dried treatment films formed in step S105—e. g. even when a ratio between the roughness average Raand the thickness of the dried treatment layer is at least 0.02 or at least 0.03 or at least 0.04 or at least 0.05 or at least 0.06 or at least 0.07 or at least 0.08 or at least or at least 0.1 or at least 0.11 or at least 0.12 or at least 0.13 or at least 0.14 or at least 0.15 or at least 0.16 or at least 0.17 or at least 0.18 or at least 0.19 or at least 0.2.

In some embodiments, the dried treatment film to which the aqueous ink droplets are deposited and a surface (e.g. upper surface of) of the dried treatment film are characterized by a dimensionless ratio between (i) an average roughness Raand (ii) a thickness of the dried treatment layer, wherein said dimensionless ratio is at most 0.5, at most 0.4, at most 0.3, at most 0.25, at most 0.2, at most 0.15, or at most 0.1, and optionally, at least 0.02 or at least 0.03 or at least 0.04 or at least 0.05 or at least 0.06 or at least 0.07 or at least 0.08.

Feature D4: In some embodiments, it is possible to obtain a continuous dry film covering an entirety of a rectangle of at least 10 cm by 1 meter, or an entirety of 1 m2, 3 m2, or 10 m2. The film may have a thickness or average thickness of at most 120 nm, at most 100 nm, at most 80 nm, at most 60 nm, at most 50 nm, or at most 40 nm, and typically, at least 20 nm, at least 25 nm, or at least 30 nm.
A Discussion of step S109-S117

In different embodiments, steps S109and/or S113and/or S117may be performed to provide one or more of the following process-related features:

Feature E1: In some embodiments, step S117is performed at a low transfer temperature (e.g. at most 90 or 80 or 75 or 70 or 65 or 60° C. —due to thermoplastic properties and/or tensile strength), even when the image is transferred to an uncoated substrate. In some embodiments, providing a low-temperature transfer step may be useful to reduce or avoid clogging of the ink-jet heads, and/or may also be useful for making the printing process, as a whole, more environmentally friendly. In some embodiments, both the dried treatment film and the dried ink image are tacky at the transfer temperature and are thus amenable to being peeled cleanly away from the release layer, even at a relatively low temperature. This property may be at least partially attributed to the chemistry of the initial aqueous treatment solution. In some embodiments, the chemistry and structure of the release layer (see, for example, feature ‘A5’) may also be useful for providing a low-temperature transfer process in step S117.
Feature E2: Spreading—the manner in which droplets are deposited onto the film (e.g. the wetting angle) and the physical and/or chemical properties of the treatment film [A2 and/or A3 and/or A8—also the nanoparticles in the ink may contribute] is such as that a radius of an ink-dot exceeds a radius of the precursor droplet immediately upon impact on the dried treatment film—e.g. each droplet increases in size beyond the size resulting from spreading of the droplet caused by the impact energy of the droplet. [Dmax=2·Rmax, or Dimpact−max=2·Rimpact−max].

FIGS.13A-13Eschematically describe a process whereby an ink droplet is deposited on an ITM (e.g. a release surface thereof). InFIG.13A, an ink droplet moves towards the ITM.FIGS.13B-13Cdescribe the ink droplet immediately after collision between (i) the droplet and (ii) the ITM (or the dried treatment film thereon). Kinetic energy of the droplet causes deformation of the droplet—this is illustrated inFIGS.13B-13C. In particular, kinetic energy of the droplet causes the droplet to expand outwards—FIG.13Cshows a maximum radius of the droplet upon impact—i.e. the maximum increase of the radius due to deformation caused by kinetic energy of the droplet. After the droplet reaches this maximum radius (“R upon impact” or “R max impact”, used interchangeably), e.g. within 10 milliseconds of impact, due to kinetic energy-driven droplet deformation, the droplet (or a successor dot thereof since each droplet eventually becomes an ink dot upon drying—first the dot resides on the ITM (e.g. via the dried treatment film) as shown inFIG.13D, and after transfer the ink droplet resides on substrate as shown inFIG.13E). The droplet or dot successor thereof may further expand due to physicochemical forces or chemical interactions. This is a spreading phenomenon that is schematically illustrated by comparingFIG.13C or13Dwith13B. Once again, it is noted that13A-13E are schematic and there is no requirement that the deformed droplet will have the specific shapes illustrated inFIGS.13A-13E.

FIGS.14A-14Bprovide an instrumentally plotted topographical profile of a dried treatment film, produced in accordance with embodiments of the present invention.

General Comment aboutFIGS.2and12—In some embodiments, step S201ofFIG.2may be performed to provide any feature or combination of features of step S91ofFIG.12. In some embodiments, step S205ofFIG.2may be performed to provide any feature or combination of features of step S95ofFIG.12. In some embodiments, step S209ofFIG.2may be performed to provide any feature or combination of features of step S101ofFIG.12. In some embodiments, step S213ofFIG.2may be performed to provide any feature or combination of features of step S105ofFIG.12. In some embodiments, step S217ofFIG.2may be performed to provide any feature or combination of features of step S109ofFIG.12. In some embodiments, step S221ofFIG.2may be performed to provide any feature or combination of features of step S113ofFIG.12. In some embodiments, step S225ofFIG.2may be performed to provide any feature or combination of features of step S117ofFIG.12.

FIGS.14A-14Bprovide an instrumentally plotted topographical profiles of dried, continuous treatment films, produced in accordance with some embodiments of the present invention. The topographical profiles, produced by a Zygo laser interferometer, display an average film thickness of approximately 40-50 nanometers (FIG.14A) and approximately 100 nanometers (FIG.14B), respectively. The film surface is exceptionally smooth, exhibiting an average roughness (Ra) of about 7 nanometers inFIG.14A, and somewhat less inFIG.14B. In other topographical profiles, an average film thickness of approximately 40 nanometers and an Raof about 5 nanometers have been observed.

Despite the thinness of the film (typically at most 120 nm, at most 100 nm, at most 80 nm, at most 70 nm, at most 60 nm, at most 50 nm, or at most 40 nm, and more typically, 30 to 100 nm, 40 to 100 nm, 40 to 80 nm, 40 to 70 nm, or 40 to 60 nm), the film is typically devoid of bare spots and defect-free, even over large areas of 20 cm2, 50 cm2, or 200 cm2and more.

Without wishing to be limited by theory, the inventors believe that the ultra-smooth surface of the dried treatment film enables the spreading of the ink dots to occur in an even and controlled manner, such that the formation of disadvantageous rivulets and the like is appreciably mitigated or averted. The resulting ink dot shape is fairly similar in quality to the superior shape (convexity, roundness, edge sharpness) attained in Landa Corporation's Application No. PCT/IB2013/000840, which is incorporated by reference, for all purposes, as if fully set forth herein. This is particularly surprising in view of the spreading mechanism utilized by the present disclosure, as compared with the surface-tension controlled drop pinning and contraction disclosed in that application.

FIGS.15A-15Dillustrate some examples of ink dots on paper substrates. In particular,FIG.15Aprovides a top view of a magnified image of a single ink dot adhering to a coated paper substrate (130 GSM), after having been ink-jetted onto an ITM, and transferred therefrom, according to embodiments of the present invention;FIG.15Bprovides a top view of a magnified image of a plurality of inkjet ink dots disposed within a field of view on a coated paper substrate (130 GSM), in accordance with embodiments of the present invention;FIG.15Cprovides a top view of a magnified image of a single ink dot adhering to an uncoated paper substrate, after having been ink-jetted onto an ITM, and transferred therefrom, according to embodiments of the present invention;FIG.15Dprovides a top view of a magnified image of a plurality of inkjet ink dots disposed within a field of view on an uncoated paper substrate, in accordance with embodiments of the present invention.

Dot and convexity measurements were performed according to the procedures disclosed by PCT/IB2013/000840. In addition, dot and convexity measurements were performed substantially as described hereinbelow:

Image Acquisition Method

The acquisition of the dot images was performed using an LEXT (Olympus) OLS3000 microscope. The images were taken with an X100 and X20 optical zoom. The color images were saved in uncompressed format (Tiff) having a resolution of 640×640 pixels.

In addition, in order to measure the dot thickness and diameter, a ZYGO microscope having a X100 lens was used.

About the Analysis

The basic parameters of interest (and their units) included in this work are:

Diameter-fit to a circle [Ddot][mic]Perimeter [P][mic]Measured area [A ][pix{circumflex over ( )}2]Minimal convex shape area [CSA][pix{circumflex over ( )}2]Optical uniformity [STD][8 bit tone value]Thickness [Hdot]mic]
From these parameters, the following were calculated:

Aspect ratio: Raspect = Ddot/Hdot[dimensionless]Dot Roundness: ER = P2/(4π · A)[dimensionless]DRdot: ER − 1[dimensionless]Convexity: CX = AA/CSA[dimensionless]Non-convexity: Dcdot = 1 − CX[dimensionless]
The analysis was done using the MATLAB image processing tool, utilizing, where possible, the above-referenced analysis procedure applied in WO2013/132418.

Blanket

The ITM may be manufactured in the inventive manner described byFIGS.17-22and in the description associated therewith. Such an ITM may be particularly suitable for the Nanographic Printing™ technologies of Landa Corporation.

With reference now toFIG.16,FIG.16schematically shows a section through a carrier10. In all the drawings, to distinguish it from the layers that form part of the finished article, the carrier10is shown as a solid black line. Carrier10has a carrier contact surface12.

In some embodiments, carrier contact surface12may be a well-polished flat surface having a roughness (Ra) of at most about 50 nm, at most 30 nm, at most 20 m, at most 15 nm, at most 12 nm, or more typically, at most 10 nm, at most 7 nm, or at most 5 nm. In some embodiments, carrier contact surface12may between 1 and 50 nm, between 3 and 25 nm, between 3 and 20 nm, or between 5 nm and 20 nm.

The hydrophilic properties of the carrier contact surface12are described hereinbelow.

In some embodiments, carrier10may be inflexible, being formed, for example, of a sheet of glass or thick sheet of metal.

In some embodiments, carrier10may advantageously be formed of a flexible foil, such as a flexible foil mainly consisting of, or including, aluminum, nickel, and/or chromium. In one embodiment, the foil is a sheet of aluminized PET (polyethylene terephthalate, a polyester), e.g., PET coated with fumed aluminum metal. The top coating of aluminum may be protected by a polymeric coating, the sheet typically having a thickness of between 0.05 mm and 1.00 mm so as to remain flexible but difficult to bend through a small radius, so as to avert wrinkling.

In some embodiments, carrier10may advantageously be formed of an antistatic polymeric film, for example, a polyester film such as PET. The anti-static properties of the antistatic film may be achieved by various means known to those of skill in the art, including the addition of various additives (such as an ammonium salt) to the polymeric composition.

In a step of the present ITM manufacturing method, the results of which are shown inFIG.17, a fluid first curable composition (illustrated as36inFIG.24B) is provided and a layer16is formed therefrom on carrier contact surface12, layer16constituting an incipient release layer having an outer ink-transfer surface14.

The fluid first curable composition of layer16may include an elastomer, typically made of a silicone polymer, for example, a polydimethylsiloxane, such as a vinyl-terminated polydimethylsiloxane.

In some embodiments, the fluid first curable material includes a vinyl-functional silicone polymer, e.g., a vinyl-silicone polymer including at least one lateral vinyl group in addition to the terminal vinyl groups, for example, a vinyl-functional polydimethyl siloxane.

In some exemplary embodiments, the fluid first curable material includes a vinyl-terminated polydimethylsiloxane, a vinyl-functional polydimethylsiloxane including at least one lateral vinyl group on the polysiloxane chain in addition to the terminal vinyl groups, a crosslinker, and an addition-cure catalyst, and optionally further includes a cure retardant.

As is known in the art, the curable adhesive composition may include any suitable amount of addition cure catalyst, typically at most 0.01% of the pre-polymer, on a per mole basis.

Exemplary formulations for the fluid first curable material are provided hereinbelow in the Examples.

Layer16of the fluid first curable composition is applied to carrier contact surface12, and is subsequently cured. Layer16may be spread to the desired thickness using, for example, a doctor blade (a knife on a roll), without allowing the doctor blade to contact the surface that will ultimately act as the ink-transfer surface14of the ITM, such that imperfections in the doctor blade will not affect the quality of the finished product. After curing, “release” layer16may have a thickness of between about 2 micrometers and about 200 micrometers. An apparatus in which such step and method can be implemented is schematically illustrated inFIGS.24A and24B.

For example, the above-detailed release layer formulation may be uniformly applied upon a PET carrier, leveled to a thickness of 5-200 micrometers (μ), and cured for approximately 2-10 minutes at 120-130° C. Surprisingly, the hydrophobicity of the ink transfer surface of the release layer so prepared, as assessed by its receding contact angle (RCA) with a 0.5-5 microliter (μl) droplet of distilled water, may be around 60°, whereas the other side of the same release layer (which served to approximate the hydrophobicity of a layer conventionally prepared with an air interface) may have an RCA that is significantly higher, typically around 90°. PET carriers used to produce ink-transfer surface14may typically display an RCA of around 40° or less. All contact angle measurements were performed with a Contact Angle analyzer—Krüss™ “Easy Drop” FM40Mk2 and/or a Dataphysics OCA15 Pro (Particle and Surface Sciences Pty. Ltd., Gosford, NSW, Australia).

In a subsequent step of the method, the results of which are shown inFIG.18, an additional layer18, referred to as a compliance layer, is applied to layer16, on the side opposite to ink-transfer surface14. Compliance layer18is an elastomeric layer that allows layer16and its outermost surface14to follow closely the surface contour of a substrate onto which an ink image is impressed. The attachment of compliance layer18to the side opposite to ink-transfer surface14may involve the application of an adhesive or bonding composition in addition to the material of compliance layer18. Generally, compliance layer18may typically have a thickness of between about 100 micrometers and about 300 micrometers or more.

While compliance layer18may have the same composition as that of release layer16, material and process economics may warrant the use of less expensive materials. Moreover, compliance layer18typically is selected to have mechanical properties (e.g., greater resistance to tension) that differ from release layer16. Such desired differences in properties may be achieved, by way of example, by utilizing a different composition with respect to release layer16, by varying the proportions between the ingredients used to prepare the formulation of release layer16, and/or by the addition of further ingredients to such formulation, and/or by the selection of different curing conditions. For instance, the addition of filler particles may favorably increase the mechanical strength of compliance layer18relative to release layer16.

In some embodiments, compliance layer18may include various rubbers. Preferably such rubbers are stable at temperatures of at least 100° C., and may include rubbers such as alkyl acrylate copolymer rubbers (ACM), methyl vinyl silicone rubber (VMQ), ethylene propylene diene monomer rubber (EPDM), fluoroelastomer polymers, nitrile butadiene rubber (NBR), ethylene acrylic elastomer (EAM), and hydrogenated nitrile butadiene rubber (HNBR).

As a non-limiting example, Silopren® LSR 2530 (Momentive Performance Materials Inc., Waterford NY), a two-component liquid silicone rubber, in which the two components are mixed at a 1:1 ratio, was applied to the cured release layer16previously described. The silicone rubber mixture was metered/leveled with a knife blade to obtain an incipient compliance layer18having a thickness of about 250 micrometers, which was then cured for approximately 5 minutes at 150-160° C.

In a subsequent step of the method, the results of which are shown inFIG.19, a reinforcement layer or support layer20is constructed on compliance layer18. Support layer20typically contains a fiber reinforcement, in the form of a web or a fabric, to provide support layer with sufficient structural integrity to withstand stretching when the ITM is held in tension in the printing system. Support layer20is formed by coating the fiber reinforcement with a resin that is subsequently cured and remains flexible after curing.

Alternatively, support layer20may be separately formed as a reinforcement layer, including such fibers embedded and/or impregnated within the independently cured resin. In this case, support layer20may be attached to compliance layer18via an adhesive layer, optionally eliminating the need to cure the support layer20in situ. Generally, support layer20, whether formed in situ on compliance layer18or separately, may have a thickness of between about 100 micrometers and about 500 micrometers, part of which is attributed to the thickness of the fibers or the fabric, which thickness generally varies between about 50 micrometers and about 300 micrometers. However, the support layer thickness is not limiting. For heavy-duty applications, by way of example, the support layer may have a thickness of more than 200 micrometers, more than 500 micrometers, or 1 mm or more.

For example, to the multi-layered ITM structure described herein, including a vinyl-functionalized release coating16and a two-component silicone rubber compliance layer18, was applied a support layer20including woven fabric of glass fibers. The glass fiber fabric, having a thickness of about 100 micrometers, was a plain weave fabric having 16 yarns/cm in perpendicular directions. The glass fiber fabric was embedded into a curable fluid including a liquid silicone rubber Silopren® LSR 2530 corresponding to the compliance layer. Overall, the resulting support layer20had a thickness of about 200 micrometers and was cured at 150° C. for approximately 2-5 minutes. Preferably, more dense weave fabrics (e.g., having 24×23 yarns/cm) may be used.

Following the in situ formation, or attachment, of support layer20, additional layers may be built up on the reverse side thereof, as required.FIG.20shows an optional felt blanket22secured (e.g., by a cured adhesive or resin) to the reverse side of support layer20, andFIG.21shows a high friction layer24coated onto the reverse side of blanket22. As will be appreciated by persons skilled in the art, various relatively soft rubbers may serve for the preparation of a layer having high friction properties, silicone elastomers being but an example of such rubbers. In the absence of an intervening layer such as blanket22, high friction layer24may be attached directly to support layer20.

As mentioned, all layers (e.g.,18,20,22,24, or any intervening adhesive or priming layer and the like) added to the release layer of the ITM jointly form the base of the structure, as shown with respect to base200inFIG.23C.

Before the ITM is used, it is necessary to remove carrier10to expose ink-transfer surface14of release layer16, as illustrated inFIG.22. Typically, the finished product can simply be peeled away from carrier10.

If the carrier10is a flexible foil, it may be preferred to leave it in place on the ITM until such time as the ITM is to be installed into a printing system. The foil will act to protect the ink-transfer surface14of the ITM during storage, transportation and installation. Additionally, carrier10can be replaced, following completion of the manufacturing process, by an alternative foil that is suitable as a protective film.

FIGS.24A to24Dschematically illustrate an apparatus90in which the ITM may be manufactured.FIG.24Aprovides a schematic overview of such an apparatus90having an unwinding roller40and a winding roller42moving a flexible loop conveyor100. Along the path followed by conveyor100can be positioned a dispensing station52, able to dispense curable fluid compositions suitable for the desired ITMs, a leveling station54, able to control the thickness of the curable layer as it moves downstream of the station, and a curing station56, able to at least partially cure the layer enabling it to serve as incipient layer for a subsequent step, if any. The dispensing station52, the leveling station54and the curing station56constitute a layer forming station50a. As illustrated by50b, apparatus90may optionally include more than one layer forming station. Furthermore, a forming station50may include additional sub-stations, illustrated by a dispensing roller58in station50a.

In some embodiments, the need for loop conveyor100is obviated: carrier10is directly tensioned between rollers40and42. Unprocessed carrier10is unwound from unwinding roller40, and after passing through stations50aand50b, is rewound onto winding roller42.

Though not illustrated in the figure, the apparatus may further include upstream of the dispensing station a “surface treatment” station facilitating the subsequent application of a curable composition, or its attachment to the carrier contact surface or incipient layer as the case may be. As mentioned in relation with the carrier, the optional surface treatment station (not shown) can be suitable for physical treatment (e.g., corona treatment, plasma treatment, ozonation, etc.).

FIG.24Bschematically illustrates how in a forming station50of apparatus90, a carrier placed on conveyor100can be coated. At dispensing station52, the curable composition36of release layer16is applied to carrier contact surface12. As carrier10is driven in the direction of the arrow, the curable composition36is leveled to a desired thickness at leveling station54, for instance, by using a doctor blade. As the leveled layer proceeds downstream, it enters curing station56, configured so as to at least partially cure curable composition36, enabling the formation of incipient layer16at the exit side of the curing station. Such exemplary steps have been described in connection withFIGS.16and17.

FIGS.24C and24Dschematically illustrate how additional layers (forming the base) can be applied. InFIG.24C, a curable composition38is dispensed at dispensing station52(which can be same or different than the station having served to coat the carrier with the release layer16, as illustrated inFIG.9B). Curable composition38is leveled to a desired thickness at leveling station54, then enters curing station56, and exits curing station56sufficiently cured to serve as incipient layer18for a subsequent step, and so on. Such an exemplary step has been described in connection withFIG.18. With reference now toFIG.24C,FIG.24Cschematically depicts a curable composition39being applied at dispensing station52. The backbone of a support layer (e.g., a fabric) can be delivered by dispensing roller58. The exemplary fabric can be submerged into the curable composition at a station60prior to their entry into curing station56. In such a manner, a support layer20can be formed at the exit side of the curing station.

FIGS.23A and23Bschematically illustrate how defects would appear in a section of an outer layer80(e.g., a release layer) prepared according to the above-described method of the art.FIG.23Aillustrates different phenomena relating to air bubbles, which may be entrapped in any curable composition if the curing occurs before such bubbles can be eliminated (e.g., by degassing). As can be seen in the figure, as tiny bubbles82migrate towards the air interface, the orientation of layer80during manufacturing over a body800, hence the direction of migration, being indicated by an arrow, they can merge into larger bubbles. The bubbles, independently of their size, may either remain entrapped within the bulk of the layer or on its surface, the upper part of the bubbles envelope forming protrusions84. When bubbles adjacent to the surface burst while the curing of the layer is advanced, craters86may remain, even if the segment of the envelope of the bubbles protruding from the surface has disappeared. These phenomena therefore typically provide a “gradient” of air bubbles, the upper sections being generally either populated by larger bubbles than the lower sections and/or having a higher density of bubbles per cross section area or per volume, lower and higher being relative to the orientation of the layer during its manufacturing. The impact of bubbles-derived defects on the surface is self-evident, the heterogeneity of the surface typically negatively affecting any subsequent interplay, for instance with an ink image. With time, such ITM being typically operated under tension and/or under pressure, craters may widen and merge to form more significant fissures. Thus, such phenomena may affect the structural integrity of the surface and any mechanical property such integrity would have conferred to the ITM.

FIG.23Bschematically illustrates different phenomena relating to solid contaminants, such as dust. Though in the present illustration, the dust is represented as being in addition to air bubbles, this need not be necessarily the case, each such surface or layer defect able to occur independently. As can be seen in the figure, solid contaminants may remain upon the surface. If the settling of contaminants occurs after the outer layer80is cured, then such contaminants92may even be removed by suitable cleaning of the outer surface. Still, such a phenomenon is undesirable, as it would require additional processing of such an ITM before being able to use it. If such contaminations occur while the layer is still uncured, then the contaminants can be either entrapped on the surface of layer80, (e.g., contaminant94, which appears to be “floating”), or can even be submerged within the release layer, (e.g., contaminant96). As can be readily understood, larger/heavier contaminants may sink more deeply than smaller ones.

Unlike methods known in the art, the method disclosed herein includes forming a layer of a fluid first curable material with one side of the layer contacting a carrier contact surface, the layer constituting an incipient release layer. The carrier contact surface functions to protect the incipient release layer, giving the ink transfer layer desired properties, while the carrier acts as a physically robust support structure onto which other layers are added to form the ITM, until the ITM is complete. As a result, many potential sources of defect are avoided. Moreover, the finish of the ink transfer surface is primarily, if not exclusively, determined by the carrier contact surface.

FIG.23Cschematically illustrates a section through an outer layer16(e.g., a release layer) prepared according to the present method. For comparison with previous drawings, the section is shown without a carrier and in the same orientation asFIGS.23A and23B, though the manufacturing is performed in inversed orientation as shown by the arrow. The base200, which, as shall be detailed hereinafter, is attached to the first outer layer16after the layer is at least partially cured, is therefore not equivalent to body800already serving as support during the manufacturing process. For the sole sake of illustration, layer16is represented as including an important number of bubbles82, but this need not be the case. However, if present, such bubbles would display a distinct pattern than those previously described. First, as the now uppermost ink transfer surface14of layer16was previously in contact with a carrier, no protrusions can be observed, the release layer being therefore devoid of phenomena such as previously illustrated by surface protruding bubbles84. Likewise, craters previously illustrated as cavities86are very unlikely, as they would imply using an incompatible curable layer and carrier. As according to the present method, the curable material due to form the outer layer is to suitably wet the carrier, it is believed that substantially no air bubbles can be entrapped between the carrier and the incipient layer formed thereon. Thus, if at all present, such bubbles would be disposed in the bulk of the layer. However, as the manufacturing is performed in inverted orientation as compared to conventional methods, the gradient of bubbles would, for the same reason, be inverted. Thus, and as depicted inFIG.23C, tiny bubbles would be closer to the outer surface than larger bubbles, which would be closer to the base.

The inventive release layer structures of the present invention, produced from addition-cure formulations, may contain substantially no functional groups, or an insubstantial amount (e.g., an insubstantial amount of OH groups), covalently attached within the polymer matrix. Such functional groups may include moieties such as C═O, S═O, and OH, by way of example.

Because these release layer structures contain, at most, an insubstantial amount of such functional groups, it would be expected that the release layers thereof would be highly hydrophobic. The inventors have surprisingly found, however, that the release layer surfaces produced by the present method may actually be somewhat hydrophilic, and appreciably more hydrophilic than corresponding release layers, i.e., release layers having the same composition, but manufactured using the conventional curing technique in which the release layer is exposed to air (“standard air curing”). Without wishing to be bound by theory, the inventors believe that the intimate contact between the carrier contact surface and the incipient release layer surface, the somewhat hydrophilic properties of the carrier contact surface are induced in the release layer surface.

As discussed hereinabove, ITM release layers having low surface energies may facilitate transfer of the dried ink image to the printing substrate. However, during the ink reception stage, the aqueous ink drops jetted onto such a low-energy, hydrophobic release layer tend to bead after the initial impact, thereby compromising image quality. Higher-energy, less hydrophobic release layers may mitigate this effect, but are detrimental to image transfer quality. The inventors have found that the release layer structures of the present invention typically have release surfaces of characteristically moderated hydrophobicity, as manifested by receding contact angles for distilled water of at most 80°, or at most 70°, typically, at most 60°, or at most 50°, and more typically, 30°-60°, 35°-60°, 30°-55°, 30°-50°, 30°-45°, or 35°-50°. Surprisingly, however, both the ink reception and the transfer of the dry, heated ink image may be of good quality. It must be emphasized that yet lower values of the receding contact angle (and the dynamic contact angle discussed hereinbelow) may be achieved by employing carrier surfaces having higher hydrophilicity (lower contact angles with respect to drops of distilled water), and/or by corona (or similar) treatment.

Without wishing to be bound by theory, the inventors believe that the above-described induced surface properties improve the interactions between polar groups (e.g., O—S—O) on the release layer surface and corresponding polar moieties (e.g., OH groups in the water) in the aqueous liquids (e.g., aqueous inkjet inks) deposited thereon, thereby contributing to the reception of the jetted ink drops. Subsequently, after drying the ink and heating of the ink film to transfer temperatures, these interactions are weakened, enabling complete transfer of the dry or substantially dry ink image. Thus, the performance of the inventive release layer structure—at both the ink reception stage and the ink film transfer stage—is appreciably better than would have been expected for a release layer having moderate hydrophobicity, but devoid of the special surface structure and properties induced by the carrier contact surface.

EXAMPLES

Reference is now made to the following examples, which together with the above descriptions, illustrate the invention in a non-limiting fashion.

List of Materials Used

CASIngredientSupplierNumberDescriptionDMS-V35 ResinGelest68083-19-2Vinyl terminated polydimethyl siloxaneViscosity5,000mPa · sMW~49,500Vinyl~0.018-0.05mmol/gVQM-146 ResinGelest68584-83-820-25% Vinyl resin in DMS V46Viscosity50,000-60,000mPa · sVinyl~0.18-0.23mmol/gInhibitor 600Evonik204-070-5Mix of divinylpolydimethylsiloxane andCure Retardant2-methylbut-3-yn-2-olViscosity900mPa · sVinyl0.11mmol/gSIP6831.2 CatalystGelest68478-92-2Platinum divinyltetramethyldisiloxanePlatinum2.1-2.4%Polymer RV 5000EvonikVinyl-functional polydimethyl siloxanes(XPRV 5000)Viscosity3000mPa · sResinVinyl0.4mmol/gCrosslinker 100EvonikPolydimethyl siloxanes including SiHCrosslinkergroups in the polymer chainHydride7.8mmol/gHMS-301Gelest68037-59-2Poly(dimethylsiloxane-co-methyl-Crosslinkerhydrosiloxane), trimethylsilyl terminatedHydride4.2mmol/gSilsurf A010-D-UPSiltech134180-76-0polyether siloxane copolymerAdditiveSilGrip SR 545Momentive56275-01-5Silicone-based resin containing “MQ”Functional MQ resingroupsViscosity11mPa · sAluminized PETHanita Ltd.NRAluminized polyester filmSkyroll SH 92SKC Inc.NRAnti-static polyester filmSkyroll SH 76SKC Inc.NRUntreated polyester film

The carriers used as substrates in the production of the release layer surface include (1) an anti-static polyester film (Examples 1-7); (2) an untreated polyester film i.e., not anti-static (Example 11); and (3) an aluminized polyester film (Example 10).

Example 1

The ITM release layer of Example 1 had the following composition (wt./wt.):

NamePartsDMS-V3570XPRV-500030VQM-14640Inhibitor 6005SIP6831.20.1Crosslinker12HMS-301
The release layer was prepared substantially as described in the present blanket preparation procedure, provided below.
Blanket Preparation Procedure (for Release Layers Cured Against a Carrier Surface)

All components of the release layer formulation were thoroughly mixed together. The desired thickness of the incipient release layer was coated on a PET sheet, using a rod/knife (other coating methods may also be used), followed by curing for 3 minutes at 150° C. Subsequently, Siloprene LSR 2530 was coated on top of the release layer, using a knife, to achieve a desired thickness. Curing was then performed at 150° C. for 3 minutes. An additional layer of Siloprene LSR 2530 was then coated on top of the previous (cured) silicone layer, and fiberglass fabric was incorporated into this wet, fresh layer such that wet silicone penetrated into the fabric structure. Curing was then performed at 150° C. for 3 minutes. A final layer of Siloprene LSR 2530 was then coated onto the fiberglass fabric and, once again, curing was performed at 150° C. for 3 minutes. The integral blanket structure was then cooled to room temperature and the PET was removed.

Example 2

The ITM release layer of Example 2 has the following composition:

Component NamePartsDMS-V3570XPRV-500030VQM-14640Inhibitor 6005SIP6831.20.1Crosslinker HMS-30112Silsurf A010-D-UP5
The blanket was prepared substantially as described in Example 1.

Example 3

The ITM release layer of Example 3 has the following composition:

Component NamePartsDMS-V3570XPRV-500030VQM-14640Inhibitor 6005SIP6831.20.1Crosslinker 1006.5Silsurf A010-D-UP5
The blanket was prepared substantially as described in Example 1.

Example 4

The ITM release layer of Example 4 has the following composition:

Component NamePartsDMS-V35100VQM-14640Inhibitor 6003SIP6831.20.1Crosslinker HMS-3015
The blanket was prepared substantially as described in Example 1.

Example 5

The ITM release layer of Example 5 was prepared from Silopren® LSR 2530 (Momentive Performance Materials Inc., Waterford, NY), a two-component liquid silicone rubber, in which the two components are mixed at a 1:1 ratio. The blanket was prepared substantially as described in Example 1.

Example 6

The ITM release layer of Example 6 has a composition that is substantially identical to that of Example 4, but includes SR545 (Momentive Performance Materials Inc., Waterford, NY), a commercially available silicone-based resin containing polar groups. The polar groups are of the “MQ” type, where “M” represents Me3SiO and “Q” represents SiO4. The full composition is provided below:

Component NamePartsDMS-V35100VQM-14640SR5455Inhibitor 6003SIP6831.20.1Crosslinker HMS-3015
The blanket was prepared substantially as described in Example 1.

Example 7

The ITM release layer of Example 7 has a composition that is substantially identical to that of Example 6, but includes polymer RV 5000, which includes vinyl-functional polydimethyl siloxanes having a high density of vinyl groups, as described hereinabove. The full composition is provided below:

Component NamePartsDMS-V3570RV 500030VQM-14640Inhibitor 6005SIP6831.20.1Crosslinker HMS-30112SR5455
The blanket was prepared substantially as described in Example 1.

Comparative Examples 1A-1F

ITM release layers were prepared as “corresponding release layers” or “reference release layers” to the compositions of Examples 1-6, such that the corresponding release layers (designated Comparative Examples 1A-F) had the identical compositions as Examples 1-6, respectively. However, during the curing of the release layer, the release layer surface (or “ink reception surface”) was exposed to air (“standard air curing”), according to a conventional preparation procedure, provided below.

Comparative Blanket Preparation Procedure (for Release Layers Exposed to Air During Curing)

A first layer of Siloprene LSR 2530 was coated on a PET sheet, using a rod/knife, followed by curing for 3 min at 150° C., to achieve the desired thickness. An additional layer of Siloprene LSR 2530 was then coated on top of the previous (cured) silicone layer, and fiberglass fabric was incorporated into this wet, fresh layer such that wet silicone penetrated into the fabric structure. Siloprene LSR 2530 was then coated on top of the fiberglass fabric, and curing ensued at 150° C. for 3 minutes. Prior to forming the incipient release layer, all components of the release layer formulation were thoroughly mixed together. The release layer was coated on top of cured Siloprene LSR 2530 to achieve the desired thickness, and was subsequently cured at 150° C. for 3 minutes, while the release layer surface was exposed to air.

Example 8

Contact angles of drops of distilled water on release layer surfaces were measured using a dedicated Dataphysics OCA15 Pro contact angle measuring device (Particle and Surface Sciences Pty. Ltd., Gosford, NSW, Australia). The procedure used for performing the Receding Contact Angle (RCA) and Advancing Contact Angle (ACA) measurements is a conventional technique elaborated by Dr. Roger P. Woodward (“Contact Angle Measurements Using the Drop Shape Method”, inter alia, www.firsttenangstroms.com/pdfdocs/CAPaper.pdf).

The results for Examples 1-6 are provided below, along with the results for the release layers produced according to Comparative Examples 1A-1F.

In virtually all cases, the release surfaces produced against the carrier surfaces exhibited lower Receding Contact Angles than the identical formulation, cured in air. More typically, the release surfaces produced against the carrier surfaces exhibited Receding Contact Angles that were lower by at least 5°, at least 7°, at least 10°, at least 12°, or at least 15°, or were lower within a range of 5°-30°, 7°-30°, 10°-30°, 5°-25°, 5°-22°, 7°-25°, or 10°-25°.

Example 9

The release surfaces produced in Examples 1-6 and the respective release surfaces produced in Comparative Examples 1A-1F were aged at 160° C. for 2 hours, to simulate the aging of the release layer under extended operating conditions. Receding Contact Angles were measured, and the results are provided below:

Release SurfaceRelease SurfaceVS. PETvs. AirRCARCAComparativeRCARCAReleasebeforeafterreleasebeforeafterformulationagingagingformulationagingagingExample 175°80°Comparative95°95°Example 1AExample 245°60°Comparative65°65°Example 1BExample 340°50°Comparative63°65°Example 1CExample 465°62°Comparative79°75°Example 1DExample 570°74°Comparative80°80°Example 1EExample 656°70°Comparative74°70°Example 1F

With regard to the comparative examples, it is evident that the receding contact angle is substantially maintained after performing the aging process. With regard to inventive Examples 1-6, however, it is evident that the receding contact angle increases, typically by 4°-15°, after performing the aging process. Without wishing to be bound by theory, the inventors believe that the increase in contact angle in the inventive release layer structures may be attributed to a loss in hydrophilic behavior (or increased hydrophobic behavior) due to some change in the position of the polar groups (e.g., Si—O—Si) at the release layer surface.

Example 10

A blanket including a release layer of the composition of Example 2 was prepared substantially as described in Example 1, but against an aluminized PET carrier surface.

Example 11

A release layer having the release layer composition of Example 2 was prepared substantially as described in Example 1, but against a commercially available PET carrier surface that was not subjected to an anti-static pre-treatment.

Example 12

The release layers produced in Examples 2, 10, and 11, in accordance with the present invention, were subjected to contact angle measurements, to determine both the advancing contact angle and the receding contact angle. The results are provided below:

Release formulationCarrier filmRCA vs. CarrierExample 10Aluminized PET62°Example 11PET without anti-static62°treatmentExample 2PET with anti-static45°treatment
Examples 10 and 11 exhibited receding contact angles that were about 30° less than the receding contact angle of the same composition cured with the release layer exposed to air. The release layer surface of Example 2, prepared against an anti-static PET carrier surface, displayed a receding contact angles that was about 50° less than the receding contact angle of the same composition prepared while exposed to air.

Example 13

The carrier surfaces utilized in Examples 2, 10, and 11 were subjected to contact angle measurements, to determine both the advancing contact angle and the receding contact angle. The results are provided below:

CA of carrierCarrier filmACARCAAluminized PET80°40°PET without antistatic70°40°treatmentPET with antistatic40°20°treatment
It may be seen from the receding contact angles obtained that the three carrier surfaces exhibit hydrophilic behavior, and that the PET subjected to anti-static treatment exhibits the greatest degree of hydrophilic behavior (20° RCA vs. 40° RCA).

Significantly, the hydrophilic behavior of the carrier surfaces has been at least partially induced in the respective release surfaces: the formulation cured while exposed to air has an RCA of 65°; the same formulation, prepared against an antistatic PET surface, has an RCA of 45°; the anti-static PET carrier used displays an RCA of 20°. Thus, the inventive release layer structure has a release surface whose hydrophilicity/hydrophobicity properties lie in between the properties of the same formulation, cured in air, and the carrier surface itself.

Example 14

Release layer surface energies were calculated for ink reception surfaces of the following Examples: Example 1A, cured under exposure to air; Example 1, cured against an anti-static PET surface; and Example 1, cured against an anti-static PET surface and then subjected to the standard aging procedure at 160° C., for 2 hours. The three Examples have the identical chemical formulation.

For each of these examples, the total surface energy was calculated using the classic “harmonic mean” method (also known as the Owens-Wendt Surface Energy Model, see, by way of example, KRUSS Technical Note TN306e). The results are provided below:

Total SurfaceRelease formulationEnergy J/m2Example 1A -- Air Cured20.9Example 1 -- Aged22.6Example 126.1

In Example 1A, cured under exposure to air, the release layer surface is extremely hydrophobic, and the total surface energy of the surface is low, 20.9 J/m2, as expected. This is fairly close to the literature value for surface energy, for polydimethylsiloxane (PDMS). Significantly, Example 1, which was cured against an anti-static PET surface, exhibited a total surface energy of about 26 J/m2, which is moderately less hydrophobic than the “air-cured” sample. After this formulation was subjected to the standard aging procedure, the total surface energy decreased from about 26 J/m2to under 23 J/m2. This result would appear to corroborate the RCA results obtained for the various aged and un-aged materials of this exemplary formulation.

Example 15

Release layer surface energies were calculated for ink reception surfaces of the following Examples: Example 2A, cured under exposure to air; Example 2, cured against an anti-static PET surface; and Example 2, cured against an anti-static PET surface and then subjected to the standard aging procedure at 160° C., for 2 hours. The three Examples have the identical chemical formulation.

As in Example 14, the total surface energy was calculated using the classic “harmonic mean” method. The results are provided below:

Total SurfaceRelease formulationEnergy (J/m2)Example 2A -- Air Cured34.6Example 2 -- Aged39.9Example 249.1

In Example 2A, cured under exposure to air, the release layer surface is less hydrophobic than the release layer of Example 1A, the total surface energy of the surface being about 35 J/m2. Example 2, cured against an anti-static PET surface, exhibited a total surface energy of about 49 J/m2, which is significantly less hydrophobic than the “air-cured” sample. After this formulation was subjected to the standard aging procedure, the total surface energy decreased from about 49 J/m2 to about 40 J/m2. This result would appear to corroborate the RCA results obtained for the various aged and un-aged materials of this exemplary formulation.

Example 16

The temperature on the blanket surface is maintained at 75° C. The image (typically a color gradient of 10-100%) is printed at a speed of 1.7 m/sec on the blanket, at a resolution of 1200 dpi. An uncoated paper (A4 Xerox Premium Copier Paper, 80 gsm) is set between the pressure roller and the blanket and the roller is pressed onto blanket, while the pressure is set to 3 bar. The roller moves on the paper, applying pressure on the contact line between blanket and paper and promoting the transfer process. In some cases, incomplete transfer may be observed, with an ink residue remaining on the blanket surface. In order to evaluate the extent of that ink residue, glossy paper (A4 Burgo glossy paper 130 gsm) is applied on the blanket similarly to the uncoated paper and the transfer process is again performed. Any ink that remained on blanket and was not transferred to the uncoated paper will be transferred to the glossy paper. Thus, the glossy paper may be evaluated for ink residue, according to the following scale (% of image surface area):A—no visible residueB—1-5% visible residueC—more than 5% visible residue
Results of the evaluation are provided below:

Release formulationTransfer gradeExample 4BExample 1BExample 2AExample 3AExample 6C

Example 17

Example 16 was repeated for the release surfaces of Examples 2 and 3, but at a printing speed of 3.4 msec on the blanket. Both release surfaces retained a transfer grade of A.

Example 18

The ITM release layer compositions of Examples 2 and 3 were cured against a PET substrate according to the procedure provided in Example 1. The ITM release layer compositions of Examples 2 and 3 were cured against air, according to the procedure provided in Comparative Examples 1B and 1C. The samples were then subjected to dynamic contact angle (DCA) measurements at 10 seconds and subsequently at 70 seconds, according to the following procedure:

The drop is placed onto a smooth PTFE film surface with as little drop falling as possible, so that kinetic energy does not spread the drop. A pendant drop is then formed. Subsequently, the specimen is raised until it touches the bottom of the drop. If the drop is large enough, the adhesion to the surface will pull it off the tip of the needle. The needle tip is positioned above the surface at such a height that the growing pendant drop will touch the surface and detach before it falls free due to its own weight.

The dynamic contact angle is then measured at 10 seconds and at 70 seconds. The results are provided below:

Dynamic contact angleCured against PETCured against AirExampleafter 10 secafter 70 secafter 10 secafter 70 secEx 2105°97°114°103°Ex 387°70°113°94°

It is observed that the initial measurement of the dynamic contact angle, at 10 seconds, provides a strong indication of the hydrophilicity of the release layer surface. The subsequent measurement at 70 seconds provides an indication of the extent to which any liquid (such as a polyether glycol functionalized polydimethyl siloxane) disposed within the release layer has been incorporated into the drop. Such incorporation may further reduce the measured DCA.

Thus, the samples cured against PET exhibit substantially lower (more hydrophilic) initial DCA measurements (105°, 87°) relative to the hydrophilic initial DCA measurements (114°, 113°) of the respective samples cured against air. In addition to displayed hydrophilicity, the samples cured against PET exhibited a drop in DCA of 8 to 17° between the first and second measurements.

FIGS.25A-25Cprovide images of various ink patterns printed onto a release layer of an ITM of the present invention, in which the release layer of Example 2 was cured against the PET carrier surface.FIGS.26A-26Care images of the same ink patterns printed onto a release layer of Example 2, but in which the release layer was cured against air. Comparing betweenFIGS.25A and26A, it is manifest that the release layer of the inventive ITM exhibits a higher optical density, and more accurately reflects the ink image pattern. A comparison betweenFIGS.25C and26Cyields the identical conclusion. Comparing now betweenFIGS.25B and26B, it is evident that each ink dot inFIG.25Bis appreciably larger than the respective ink dots inFIG.26B.

As used herein in the specification and in the claims section that follows, the term “receding contact angle” or “RCA”, refers to a receding contact angle as measured using a Dataphysics OCA15 Pro Contact Angle measuring device, or a comparable Video-Based Optical Contact Angle Measuring System, using the above-described Drop Shape Method, at ambient temperatures. The analogous “advancing contact angle”, or “ACA”, refers to an advancing contact angle measured substantially in the same fashion.

As used herein in the specification and in the claims section that follows, the term “dynamic contact angle” or “DCA”, refers to a dynamic contact angle as measured using a Dataphysics OCA15 Pro Contact Angle measuring device, or a comparable Video-Based Optical Contact Angle Measuring System, using the method elaborated by Dr. Roger P. Woodward in the above-referenced “Contact Angle Measurements Using the Drop Shape Method”, at ambient temperatures, and as elaborated hereinabove in Example 17.

As used herein in the specification and in the claims section that follows, the term “standard aging procedure” refers to an accelerated aging protocol performed on each tested release layer at 160° C., for 2 hours, in a standard convection oven.

As used herein in the specification and in the claims section that follows, the term “standard air curing” refers to a conventional curing process for curing the release layer, described with respect to Comparative Examples 1A-1F, in which, during the curing of the release layer, the release layer surface (or “ink reception surface”) is exposed to air.

As used herein in the specification and in the claims section that follows, the term “bulk hydrophobicity” is characterized by a receding contact angle of a droplet of distilled water disposed on an inner surface of the release layer, the inner surface formed by exposing an area of the cured silicone material within the release layer.

Examples C1-C12

Exemplary compositions of the inventive ITM aqueous treatment liquids are provided in the tables hereinbelow:

conc.componentsC15.00%PVA 4-880.30%Xiameter OFX-52113.00%Silsurf A010 D up0.50%Lupasol PN 505.00%Sugar6.00%Foamquat SAQ9080.20%water

conc.componentsC23.50%PVA 8-880.30%Xiameter OFX-52113.00%Silsurf A010 D up0.50%Lupasol P3.00%Sugar5.00%Foamqust SAQ9084.70%water

conc.componentsC36.00%PVA 4-880.30%Xiameter OFX-52113.00%Silsurf A010 D up0.50%Lupasol PN 505.00%Sugar5.40%Larostate 264 A79.80%water

conc.componentsC44.50%PVA 8-880.30%Tego 2401.00%Silsurf A010 D up0.50%Lupasol PN 503.00%Basionics LQ017.00%Foamquat SAQ9083.70%water

conc.componentsC53.20%PVA 8-880.30%Xlameter OFX-52111.00%Silsurf A010 D up0.50%Lupasol PN 506.00%cliqsmart 129-306.00%Arquad O-5083.00%water

conc.componentsC65.00%Methocel E30.30%Xiameter OFX-52111.00%Silsurf 4010 D up0.50%Lopasol PN 506.00%cliqsmart 129-306.00%Foamquat SAQ9081.20%water

conc.componentsC75.00%Methocel E30.30%Xiameter OFX-52111.00%Silsurf A010 D up0.50%Lupasol PN 505.00%Basionics LQ015.00%Foamquat SAQ9083.20%water

conc.componentsC85.00%Methocel E30.30%Xiameter OFX-52111.00%Silsurf A010 D up0.50%Lapasol PN 506.00%Urea6.00%Foamquat SAQ9081.20%water

conc.componentsC95.00%PVA 8-880.30%Xiameter OFX-52111.00%Silsurf A010 D up0.50%Lupasol PN 505.50%Urea5.50%Foamquat SAQ9082.20%water

conc.componentsC105.00%PVA 4-880.30%Xiameter OFX-52113.00%Silsurf A010 D up0.50%Lupassol PN 505.00%Sugar6.00%Foamquat SAQ9080.20%water

conc.componentsC113.50%PVA 8-880.30%Dynax 40001.00%Silsurf A010 D up0.50%Lupasol PN 503.00%Basionics LQ017.00%Foamquat SAQ9084.70%water

conc.componentsC125.00%PVA 4-880.30%SYK 3071.00%Silsurf A010 D up0.50%Lupasol PN 505.00%Sugar5.40%Foamquat SAQ9082.80%water

Examples C13-C22

Compositions of ITM aqueous treatment liquids, and various properties thereof, are provided in the table below, as Example Compositions C13-C22.

EX. C13EX. C14EX. C15EX. C16EX. C17EX. C18EX. C19EX. C20EX. C21EX. C22% solids (by wt.)PVA6-884444444444PVA8-88sugar55550010105Silsurf A010 D-UP334.38333333Lupasol P0.840.50.50.50.5BYK 213440.30.30.30.30.30.30.30.30.30.3glycerinLarostate 264A3353Foamquat SAQ 905.55.5total solids (%)15.312.312.320.212.813.310.317.317.812.81200 dpi × 600M dot size47.3342.4447.5848.4341.641.541.946.543.239.5dpi, 2D-asK dot size48.7544.346.6248.3543.44343.548.545.942preparedViscosity (cp)15.578.3410.231910.713.69.311.213.911.2Transfer (K, 3/150),Burgo/CondatWetting (M)verygrainygrainysurface tension2521.528.726.2(dyne/cm)texturefailed

With regard to Examples C1-C12, the viscosity of each sample, measured at room temperature, is provided below (all values in cP):C1=19.2C2=18.15C3=22.3C4=36.2C5=19.8C6=21.2C7=28.1C8=18.0C9=50.0C10=48.2C11=20.2C12=20.7

The surface tensions for these aqueous treatment formulations was more homogeneous for these 12 exemplary formulations, and was generally within the range of 26-29 mN/m or 26-28 mN/m, at room temperature.

Example C23

An additional aqueous treatment formulation is provided in Example C23. This formulation is devoid of surfactant, other than the quaternary ammonium salt (Larostate 264A), which is present at a relatively high percentage (8% by weight) so as to sufficiently reduce the surface tension of the aqueous treatment formulation. The surface tension and viscosity at room temperature are 32.3 mN/m and 17.8 cP, respectively.

conc.components4.00%PVA 6-888.00%Larostate 264A0.30%Lupasol P4.00%Sugar83.700%water

Preparation of Pigments

Pigments used in the examples described below are generally supplied with initial particle size of a few micrometers. Such pigments were ground to submicron range in presence of the dispersing agent, the two materials being fed to the milling device as an aqueous mixture. Unless stated otherwise, 30 g pigment were mixed with the weight amount of dispersant satisfying the weight ratio indicated in the following examples. Deionized water was added to a balance of 200 g. This liquid slurry was size-reduced in presence of 4500 g of chrome-steel beads (Glen Mills Inc., USA) having a diameter of 0.8 mm in an Attritor HDDM-01/HD-01 by Union Process for a duration of time and at an energy input sufficient to prepare millbase comprising pigment particles having a median diameter (as analyzed per volume of particles) of 100 nm or less (DV50≤100 nm). Typically, the attritor was operated at about 3000 rpm, for at least 48 hours, the milling duration also depending on the initial particle size.

Particle size and distribution thereof in the compositions so prepared was determined using DLS methodology (Malvern Zetasizer Nano ZS). Unless otherwise stated, an aliquot was removed from the compositions being considered, and if necessary diluted in double distilled water (DDW), so as to obtain samples having a solid concentration of about 1 wt. %. The liquid samples were briefly sonicated (about 7 sec in a Sonics Vibracell VCX 750 (750 watts) at 75% of max power) ahead of DLS measurement to ensure a proper dispersion of the pigment particles during assessment of particle size and distribution. Results were analyzed based on the volume of the particles.

Once the pigment-dispersant mixture reached desired particle size, 50 g water were added to the chamber of the milling device and the resulting diluted dispersion was extracted therefrom. The beads were separated by filtration of the diluted millbase through a suitable mesh. The pigment concentration at this stage was 12 wt. %.

To the pigment-dispersant-containing millbase was added sodium dodecanoate (SDD), and/or at least one additive from the following additives: potassium dodecanoate, sodium oleate, potassium oleate, sodium myristate, potassium myristate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, potassium and sodium octanoate. Water was added as needed to yield a composition having a pigment concentration of 10 wt. %.

Example I1—Ink Composition

In the present example, the preparation of an ink composition is described: Heliogen® Blue D7079 was milled with Disperbyk® 190 in a HDDM-01/HD-01 attritor as previously described, the materials were mixed in the following proportion:

Heliogen ® Blue D707930 gDisperbyk ® 190 (40%)30 gWater140 gTotal200 g
The milled concentrate, now having a DV50 of less than 100 nm, was further diluted with 50 g water and extracted from the milling device at 12 wt. % pigment concentration. The millbase concentrate was further processed as below described for the preparation of an ink composition In a first stage, 2.4 g of sodium dodecanoate were added to 200 g of the millbase concentrate to yield a millbase. The mixture was stirred to homogeneity (5′ magnetic stirrer at 50 rpm) and incubated at 60° C. for 1 day. The mixture was then left to cool down to ambient temperature. In a second stage, ink ingredients were added to the millbase as follows:

Millbase Concentrate (from stage 1)202.4 gJoncryl ® 538 (46.5%)154.8 gBYK ® 3495 gBYK ® 3332 gPropylene Glycol240 gWater595.8 gTotal1200 g
The mixture was stirred for 30 minutes at ambient temperature, resulting in an ink-jettable ink composition having a viscosity of less than 10 cP.

Examples I2 to I5—Ink Compositions

The ink of Example I1 was formulated, but with the addition of 5, 10, 12, and 15 g, respectively, of TWEEN 20.

Dot Gain

Dot gain refers to the increase in dot size over the initial, spherical drop diameter. The dot gain is determined by the ratio of the final dot diameter to the initial drop diameter. It is highly desirable to find a way to increase dot size without having to increase drop volume.

Utilizing the inventive technologies disclosed herein, the inventors attained dot gains of at least 1.5 or 1.6, and more typically, at least 1.7, at least 1.8, at least 1.9, or at least 2.0, or within a range of 1.5 to 2.2, 1.5 to 2.1, 1.7 to 2.1, or 1.8 to 2.1.

For example, using drops having a volume of 6.3 picoliters (D=22.9 micrometers), and using the aqueous treatment formulations of the present invention, the dried ink dots obtained were within a diameter range of 40 to 48 micrometers.

As used herein in the specification and in the claims section that follows, the terms “hydrophobicity” and “hydrophilicity” and the like, may be used in a relative sense, and not necessarily in an absolute sense.

As used herein in the specification and in the claims section that follows, the term “functional group” refers to a group or moiety attached to the polymer structure of the release layer, and having a higher polarity than the O—Si—O group of conventional addition-cured silicones. Various examples are provided herein. The inventors observe that pure addition cure polydimethyl siloxane polymer contains O—Si—O, SiO4, Si—CH3and C—C groups, and that most other functional groups will have a higher dipole, such that they may be considered “functional”. It will be appreciated by those of skill in the art that such functional groups, may have a tendency or strong tendency to react with components typically present in aqueous inks utilized in indirect inkjet printing, at process temperatures of up to 120° C.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. In case of conflict, the specification, including definitions, will take precedence.

In the description and claims of the present disclosure, each of the verbs, “comprise” “include” and “have”, and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of members, components, elements, steps or parts of the subject or subjects of the verb. These terms encompass the terms “consisting of” and “consisting essentially of”.

As used herein, the singular form “a”, “an” and “the” include plural references and mean “at least one” or “one or more” unless the context clearly dictates otherwise.

Positional or motional terms such as “upper”, “lower”, “right”, “left”, “bottom”, “below”, “lowered”, “low”, “top”, “above”, “elevated”, “high”, “vertical”, “horizontal”, “backward”, “forward”, “upstream” and “downstream”, as well as grammatical variations thereof, may be used herein for exemplary purposes only, to illustrate the relative positioning, placement or displacement of certain components, to indicate a first and a second component in present illustrations or to do both. Such terms do not necessarily indicate that, for example, a “bottom” component is below a “top” component, as such directions, components or both may be flipped, rotated, moved in space, placed in a diagonal orientation or position, placed horizontally or vertically, or similarly modified.

Unless otherwise stated, the use of the expression “and/or” between the last two members of a list of options for selection indicates that a selection of one or more of the listed options is appropriate and may be made.

As used herein in the specification and in the claims section that follows, the term “%” refers to percent by weight, unless specifically indicated otherwise.

Similarly, the term “ratio”, as used herein in the specification and in the claims section that follows, refers to a weight ratio, unless specifically indicated otherwise.

In the disclosure, unless otherwise stated, adjectives such as “substantially” and “about” that modify a condition or relationship characteristic of a feature or features of an embodiment of the present technology, are to be understood to mean that the condition or characteristic is defined to within tolerances that are acceptable for operation of the embodiment for an application for which it is intended.

While this disclosure has been described in terms of certain embodiments and generally associated methods, alterations and permutations of the embodiments and methods will be apparent to those skilled in the art. The present disclosure is to be understood as not limited by the specific embodiments described herein, but only by the scope of the appended claims.