# Patent

## Title
Inkjet recording element

## Abstract

An inkjet recording element is disclosed having a support and, on the support, (a) a porous base layer comprising particles of fumed silica and a hydrophilic binder and (b) a porous gloss layer above the base layer comprising particles of colloidal silica and a hydrophilic binder, wherein the particles of fumed and colloidal silica are anionic. Also disclosed is a method of printing on such an inkjet recording element. The inkjet recording element can potentially have, in some embodiments, the advantages of improved image quality (reduced coalescence) and higher dye ink optical densities.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is related to U.S. application Ser. No. 11/936,819 (Publication No. 2009/0123675), filed concurrently herewith, by Lori Shaw-Klein et al., and entitled, “INKJET RECORDING ELEMENT” and U.S. application Ser. No. 11/936,810 (Publication No. 2009/0123655), filed concurrently herewith, by Lori Shaw-Klein et al., and entitled, “PROCESS FOR MAKING INKJET RECORDING ELEMENT,” both hereby incorporated by reference in their entirety.
FIELD OF THE INVENTION
The invention relates to an inkjet recording element and a method of printing on the recording element. More specifically, the invention relates to a porous recording element comprising a lower base layer, comprising anionic fumed silica with limited binder content, and an upper gloss layer.
BACKGROUND OF THE INVENTION
In a typical inkjet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol, or mixtures thereof.
An inkjet recording element typically comprises a support having on at least one surface thereof at least one ink-receiving layer. There are generally two types of ink-receiving layers (IRL's). The first type of IRL comprises a non-porous coating of a polymer with a high capacity for swelling and absorbing ink by molecular diffusion. Cationic or anionic substances are typically added to the coating to serve as a dye fixing agent or mordant for the anionic or cationic dye, respectively. This coating is optically transparent and very smooth, leading to a high gloss “photo-grade” receiver. However, with this type of IRL, the ink is usually absorbed slowly into the IRL and the print is not instantaneously dry to the touch.
The second type of IRL comprises a porous coating of inorganic, polymeric, or organic-inorganic composite particles, a polymeric binder, and additives such as dye-fixing agents or mordants. These particles can vary in chemical composition, size, shape, and intra/inter-particle porosity. In this case, the printing liquid is substantially absorbed into the open pores of the IRL to obtain a print that is instantaneously dry to the touch.
Organic and/or inorganic particles in a porous layer form pores by the spacing between the particles. The binder is used to hold the particles together. However, to maintain a high pore volume, it is desirable that the amount of binder is limited. Too much binder would start to fill the pores between the particles or beads, which would reduce ink absorption. On the other hand, too little binder may reduce the integrity of the coating, thereby causing cracking.
As the quality and density of inkjet et printing increases, so does the amount of ink applied to the inkjet recording element (also referred to as the “receiver”). For this reason, it is important to provide sufficient void capacity in the medium to prevent puddling or coalescence and inter-color bleed. At the same time, print speeds are increasing in order to provide convenience to the user. Thus, not only is sufficient capacity required to accommodate the increased amount of ink, but in addition, the medium must be able to handle increasingly greater ink flux in terms of ink volume/unit area/unit time.
A porous ink jet recording element usually contains at least two layers: a lower layer, sometimes referred to as a base layer as the main sump for the liquids in the applied inkjet ink, and an upper layer, sometimes referred to as a gloss layer, often an image-receiving layer, coated in that order on a support. The layers may be sub-divided or additional layers may be coated between the support and the uppermost gloss layer. The layers may be coated on a resin coated or a non-resin coated support. The layers may be coated in one or more passes using known coating techniques such as roll coating, premetered coating (slot or extrusion coating, slide or cascade coating, or curtain coating) or air knife coating. When coating on a non-resin coated paper, in order to provide a smooth, glossy surface, special coating processes may be utilized, such as cast coating or film transfer coating. Calendering with pressure and optionally heat may also be used to increase gloss to some extent.
Recently, higher speed printing has been demanded of inkjet printers. A problem arises when multiple ink droplets are deposited in very close proximity in a short time. If the porosity of the receiver is not adequate, the drops will coalesce, severely degrading the image quality. The amount of binder in the coated layers is important in the performance of the ink-recording element. If too much binder is present, the porosity of the receiver is diminished resulting in coalescence, and if too little binder is present, unacceptable cracking is observed.
EP Patent Publication No. 1,464,511 to Bi et al. discloses a two-layer inkjet receiver on a resin-coated support. The bottom layer comprises a dispersion of fumed silica treated with aluminum chlorohydrate to transform the silica particles into a cationic form, as indicated by a zeta potential above +27 mv after treatment. The cationic silica particle dispersion was mixed with boric acid and poly(vinyl alcohol) to form a coating composition for the bottom layer. The coating composition for the top layer comprised a dispersion of cationic colloidal silica, glycerol, and a minor amount of coating aid. The top and bottom layers were cascade coated at the same time in one pass, that is, simultaneous coating is disclosed in context. The coating weight of the bottom layer was about 28 to 30 g/m2 and the top layer was 0.2 g/m2. However, there is a problem with this type of inkjet receiver in that image quality is reduced by coalescence when high ink levels are printed.
In the comparative example 4 of the above-mentioned EP Patent Publication No. 1,464,511 A2, a comparative inkjet recording element with a cationic fumed silica base layer and an anionic colloidal silica upper layer is made and tested.
US Patent Publication No. 2003/0224129 to Miyachi et al. discloses an inkjet recording element similar to the above-mentioned EP Patent Publication No. 1,464,511 in which a layer mainly containing cationic colloidal silica is over a base layer containing cationized anionic inorganic particles that can be fumed silica.
U.S. Pat. No. 7,015,270 to Scharfe et al. discloses an inkjet recording element comprising fumed silica and a cationic polymer in which the dispersion used to make the inkjet recording element has a positive zeta potential.
It is known to provide crosslinker, for a binder in an ink-receiving layer, by diffusion of the crosslinker into the layer. For example, Riou, et al., in U.S. Pat. No. 4,877,686, describe a recording sheet for inkjet printing and a process for its preparation. The coating composition comprises filler, such as an inorganic particle, and a polyhydroxylic polymeric binder, such as poly (vinyl alcohol). In the coating process, the PVA is gelled or coagulated by borax. The gelling agent may be deposited on the base material prior to the coating. Alternatively, the gelling agent can be incorporated in the coating composition, but must be temporarily deactivated. For example, boric acid may be used in the coating composition and activated by contact with a higher pH base layer. A drawback of this incorporated crosslinker process is that although the boric acid does not completely gel the PVA coating composition, viscosity increases may be expected, which may have a negative impact on coating quality throughout a coating event. The disclosure of Riou, et al., is mainly directed to providing more regular-shaped dots. High print density and gloss demanded of a photographic quality print are not addressed by Riou, et al.
Kuroyama, et al., in EP Patent Publication No. 493,100, disclose an inkjet recording paper comprising a substrate which is coated with boric acid or borate and an inkjet recording layer formed on the borax-coating and comprising synthetic silica and poly(vinyl alcohol). The silica may be wet-process silica, silica gel, or ultrafine silica obtained by a dry process. The exemplary silica materials are silica gels with high surface area, but with large secondary particle size of several microns or more. These materials do not provide a high gloss expected for a photo-quality print. Cationic polyelectrolytes may be added to improve water resistance, thus implying a composition compatible with cationic species.
Problem to be Solved by the Invention
It is an object of this invention to provide an inkjet receiver with improved color print density, reduced coalescence, and improved gloss while avoiding excessive cracking of the ink-receiving layer.
SUMMARY OF THE INVENTION
The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, an inkjet recording element has a support and the following ink-receiving layers:
(a) a porous base layer comprising particles of anionic fumed silica, and hydrophilic hydroxyl-containing polymer as the primary binder crosslinked with crosslinker comprising boron-containing compound, wherein the base layer has a dry weight of about 10 to 35 g/m2, wherein the weight percent of total binder to total solids in the base layer is greater than 5.0 percent and less than 15.0 percent; and
(b) an uppermost porous gloss layer above the base layer comprising particles of colloidal silica and a hydrophilic binder and having a dry weight of about 1.0 to 7.5 g/m2, wherein the median primary particle size of the particles of colloidal silica is about 10 to under 45 nm, wherein said particles of fumed and colloidal silica exhibit a zeta potential below negative 15 mv.
In other words, the fumed silica in the base layer and the colloidal silica in the gloss layer are both anionic particles. In a preferred embodiment, the colloidal silica in the gloss layer comprises hydrophilic polymeric binder and is crosslinked with a crosslinking compound. In another preferred embodiment, the colloidal silica gloss layer has a dry weight of at least 1.5 g/m2 and the median particle size of the colloidal silica in the uppermost layer is less than about 40 nm.
The present invention has the advantages of improved image quality (reduced coalescence) and higher dye ink optical densities in an inkjet recording element. An inventive process of making such an element has the advantages of ease of handling precursor dispersions and improved properties of the resulting inkjet recording element, including improved gloss and reduced cracking for the elements having higher porosity in one or more layers of the element. It is very unexpected that an anionic composition for the ink-receiving layers in the inkjet recording element tends to provide better dye density than a comparable cationic formulation, especially since cationic materials would be expected to mordant more readily the typically used anionic dyes than anionic compositions for the ink-receiving layers. Surprising also, anionic compositions comprising anionic fumed silica tend to require less binder than comparable cationic fumed silica, as shown in examples.
In describing the invention herein, the following definitions generally apply:
The term “porous layer” is used herein to define a layer that is characterized by absorbing applied ink substantially by means of capillary action rather than liquid diffusion. The porosity is based on pores formed by the spacing between particles, although porosity can be affected by the particle to binder ratio. The porosity of a layer may be predicted based on the critical pigment volume concentration (CPVC). An inkjet recording element having one or more porous layers, preferably substantially all layers, over the support can be referred to as a “porous inkjet recording element,” even if the support is not porous.
Particle sizes referred to herein, unless otherwise indicated, are number weighted median particle sizes. In particular, in the case of colloidal silica, the median particle size is a number weighted median measured by electron microscopy, using high-resolution TEM (transmission electron microscopy) images, as will be appreciated by the skilled artisan. Herein each particle diameter is the diameter of a circle that has the same area as the equivalent projection area of each particle. In the case of colloidal silica, as compared to fumed silica, the colloidal particles may be aggregated on average up to about twice the primary particle diameter, which does not unduly affect the measurement of primary particle size.
In the case of mixtures of two populations of particles, the median particle size of the mixture is merely the median particle size of the mixture. Typically, for equal weights of two median particle sizes in a mixture, the median particle size of the mixture is relatively closer to the median particle size of the component having the smaller median particle size.
It is difficult to measure the secondary size of fumed metal oxide particles because the methods commonly used treat the particles as spheres and the results are calculated accordingly. (The primary particle size of fumed silica in dispersion can be measured by TEM, as with colloidal silica.) Fumed silica particles are not spheres but consist of aggregates of primary particles. In the case of fumed silica, the median secondary particle size is as determined by light scattering measurements of diluted particles dispersed in water, as measured using laser diffraction or photon correlation spectroscopy (PCS) techniques employing NANOTRAC (Microtac Inc.), MALVERN, or CILAS instruments or essentially equivalent means. Unless otherwise indicated, particle sizes refer to secondary particle size. The median particle size of inorganic particles in various products sold by commercial manufacturers is usually provided in the product literature. However, for the purpose of making accurate comparisons among products, the particular measurement technique may need to be taken into consideration. Use of a single testing method eliminates potential variations among different testing methods.
As used herein, the terms “over,” “above,” “upper,” “under,” “below,” “lower,” and the like, with respect to layers in inkjet media, refer to the order of the layers over the support, but do not necessarily indicate that the layers are immediately adjacent or that there are no intermediate layers.
In regard to the present invention, the term “image-receiving layer” is intended to define a layer that is used as a pigment-trapping layer, dye-trapping layer, or dye-and-pigment-trapping layer, in which the printed image substantially resides throughout the layer. In the case of a dye-based ink, the image may optionally reside in more than one adjacent image-receiving layer.
In regard to the present invention, the term “gloss layer” is intended to define the uppermost coated layer in the inkjet recording element that provides additional gloss compared to the base layer alone. It is an image-receiving layer.
In regard to the present invention, the term “base layer” (sometimes also referred to as a “sump layer” or “ink-carrier-liquid receptive layer”) is used herein to mean a layer under at least one other ink-retaining layer that absorbs a substantial amount of ink-carrier liquid. In use, a substantial amount, preferably most, of the carrier fluid for the ink is received and remains in the base layer until dried. The base layer is not above an image-receiving layer and is not itself an image-containing layer (a pigment-trapping layer or dye-trapping layer), although relatively small amounts of the ink colorant, in the case of a dye, may leave the image-receiving layer and enter the base layer, mostly in an upper portion. Preferably, the base layer is the ink-retaining layer nearest the support, with the exception of subbing layers. The base layer is the thickest layer under the image-receiving layer or layers.
The term “subbing layer” refers to any layer between the base layer and the support having a dry weight of less than 5 g/m2, preferably less than 1 g/m2. The subbing layer may be porous or non-porous and may be used to improve adhesion or accomplish some other function such as providing a crosslinking agent for diffusion.
The term “ink-receptive layer” or “ink-retaining layer” includes any and all layers above the support that are receptive to an applied ink composition, that absorb or trap any part of the one or more ink compositions used to form the image in the inkjet recording element, including the ink-carrier fluid and/or the colorant, even if later removed by drying. An ink-receptive layer, therefore, can include an image-receiving layer, in which the image is formed by a dye and/or pigment, a base layer, a subbing layer, or any additional layers, for example between a base layer and a topmost layer of the inkjet recording element. Typically, all layers above the support are ink-receptive. The support on which ink-receptive layers are coated may also absorb ink-carrier fluid. Whereas an ink-receptive layer is coated onto a support, the support is a solid material over which all the ink-receptive layers are coated during manufacture of the inkjet recording element.


DETAILED DESCRIPTION OF THE INVENTION
As indicated above, the present invention relates to a porous inkjet recording element comprising, over the support, a porous base layer nearest the support, and a porous upper gloss layer. The porous base layer nearest the support and porous upper gloss layer may optionally be divided into sub-layers, preferably immediately adjacent sub-layers, in which case independently the sub-layers individually and collectively meet the claim limitations of the layer, except for the thickness limitations. The layers, described herein, are preferably coated as a single layer.
In one embodiment, the inkjet recording element consists of a single porous base layer and a single upper gloss layer over the support, with the possible exception of layers less than 1 micrometer thick such as subbing layers.
In a preferred embodiment, the 60-degree gloss of the unprinted inkjet recording element is at least 15 Gardner gloss units, preferably at least 20 Gardner gloss units.
In a preferred embodiment, the present invention is directed to an inkjet recording element comprising, in order:
(a) a porous base layer comprising particles of anionic fumed silica, and hydrophilic hydroxyl-containing polymer as the primary binder, wherein the base layer has a dry weight of about 10 to 35 g/m2, preferably 15 to 25 g/m2, wherein the hydrophilic hydroxyl-containing polymer is crosslinked with crosslinker comprising boron-containing compound, wherein the weight percent of total binder to total solids in the base layer is greater than 5.0 percent and less than 15.0 percent, preferably less than 12 percent, most preferably less than 10 percent; and
(b) a porous gloss layer above the base layer comprising particles of anionic colloidal silica and a hydrophilic binder and having a dry weight of about 1.0 to 7.5 g/m2, wherein the median particle size of the particles of anionic colloidal silica is about 10 to less than 45 nm, preferably less than 40 nm, advantageously in some embodiments less than 30 nm, more preferably less than 25 nm.
The particles of both the fumed and colloidal silica exhibit a zeta potential below negative 15 mv.
The zeta potential is a measure of the surface charge of the particles, which can be shifted, for example, by any substances that become attached to the surface of the particles. Zeta potential is understood to mean the potential on the shearing surface of a particle in dispersion. In dispersions in which the particles carry acid or basic groups on the surface, the charge can be changed by setting the pH value. An important value in connection with the zeta potential is the isoelectric point (IEP) of a particle, which can also be considered the point of zero charge. The IEP gives the pH value at which the zeta potential is zero. The IEP of silicon dioxide is less than pH 3.8. The greater the difference between the pH value and IEP, the more stable the dispersion. Particles of the same material will have the same surface charge sign and will thus repel each other. However, if the zeta potential is too small, the repelling force cannot compensate for the van der Waals attraction of the particles and this will lead to flocculation and in some cases sedimentation of the particles.
The zeta potential can be determined in accordance with any method known in the art and preferably, for example, by measuring the colloidal vibration current (CVI) of the dispersion or by determining its electrophoretic mobility. The zeta potentials of the present compositions were measured on a Malvern Instrument ZETASIZER NANO-ZS. Dispersions were diluted in water of matching pH and rolled to assure good dispersion.
The colloidal silica particles in the gloss layer may be further characterized by surface area BET surface measurement. The preferred surface area for the colloidal silica particles is above 50 m2/g. Relatively larger surface areas among different colloidal silica products tend to be associated with smaller diameter particles. As used herein, the BET surface area measurement relies on the nitrogen adsorption method of S. Brunauer, P. H. Emmet and I. Teller, J. Am. Chemical Society, vol. 60, page 309 (1938).
As mentioned above, the amount of binder in an ink-receiving layer is desirably limited, because when ink is applied to inkjet media, the (typically aqueous) liquid carrier tends to swell the binder and close the pores and may cause bleeding or other problems. Preferably, therefore, the base layer comprises a less than an maximum amount of binder in the base layer, to maintain the desired porosity, preferably above a minimum amount of binder sufficient to prevent or eliminate cracking and other undesirable properties.
Any suitable hydrophilic hydroxyl-containing polymer crosslinkable by a boron-containing compound may be used as the primary binder in the base layer (optionally in the gloss layer) of the inkjet recording element.
The crosslinkable hydrophilic hydroxyl-containing polymer employed in at least the base layer may be, for example, poly(vinyl alcohol), partially hydrolyzed poly(vinyl acetate/vinyl alcohol), or copolymers containing hydroxyethylmethacrylate, copolymers containing hydroxyethylacrylate, copolymers containing hydroxypropylmethacrylate, hydroxy cellulose ethers such as hydroxyethylcellulose, etc. In a preferred embodiment, the crosslinkable polymer containing hydroxyl groups is poly(vinyl alcohol), including partially hydrolyzed poly(vinyl acetate/vinyl alcohol) or modified or unmodified PVA, or a copolymer of PVA comprising primarily (more than 50 mole percent) monomeric repeat units containing a hydroxy group, more preferably at least 70 mole percent of such monomeric repeat units.
In general, particularly good results are obtained employing, as the primary binder, poly(vinyl alcohol), also referred herein as “PVA.” As indicated above, the term “poly(vinyl alcohol)” includes modified and unmodified poly(vinyl alcohol), for example, acetoacetylated, sulfonated, carboxylated PVA, and the like. Copolymers of PVA, for example with ethylene oxide, are also preferred as primary binder.
The poly(vinyl alcohol) preferably employed in the present invention includes common poly(vinyl alcohol), which is prepared by hydrolyzing polyvinyl acetate, and also modified poly(vinyl alcohol) such as poly(vinyl alcohol) having an anionic or non-cationic group.
In one embodiment, the average degree of polymerization of the poly(vinyl alcohol) prepared by hydrolyzing vinyl acetate is preferably at least 300, but is more preferably 1000 to 10,000, or a preferred viscosity of at least 30 cP, more preferably at least 40 cP in water at a concentration of 4 percent by weight at 20° C. The saponification ratio of the poly(vinyl alcohol) is preferably 70% to 100%, but is more preferably 75% to 95% t.
Lesser amounts of supplemental non-hydrophilic (hydrophobic) binders may also be included in various compositions. Preferred polymers are water-soluble, but latex polymer can also be included for various reasons. (As used herein, the term “primary” refers to greater than fifty percent by weight of all binder.)
In a preferred embodiment, the supplemental polymeric binder, if different from the primary binder, may be a compatible, preferably water-soluble hydrophilic polymer such as poly(vinyl pyrrolidone), gelatin, cellulose ethers, poly(oxazolines), poly(vinylacetamides), poly(acrylic acid), poly(acrylamide), poly(alkylene oxide), sulfonated or phosphated polyesters and polystyrenes, casein, zein, albumin, chitin, chitosan, dextran, pectin, collagen derivatives, collodian agar-agar, arrowroot, guar, carrageenan, tragacanth, xanthan, rhamsan, methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, poly(2-ethyl-2-oxazoline), poly(2-methyl-2-oxazoline), poly(alkylene oxide), poly(vinyl pyrrolidinone), poly(vinyl acetate), polyurethanes, vinyl acetate-ethylene copolymers, ethylene-vinyl chloride copolymers, vinyl acetate-vinyl chloride-ethylene terpolymers, acrylic, polymers, copolymers or derivatives thereof and the like, or combinations thereof.
Preferred hydrophobic materials can include, for example, poly(styrene-co-butadiene), polyurethane latex, polyester latex, poly(n-butyl acrylate), poly(n-butyl methacrylate), poly(2-ethylhexyl acrylate), copolymers of n-butylacrylate and ethylacrylate, copolymers of vinylacetate and n-butylacrylate, and the like. Mixtures of hydrophilic and latex binders may be useful, for example, mixtures of poly(vinyl alcohol) and poly(styrene-co-butadiene) latex.
With respect to the boron-containing crosslinker, most preferably, a boron-containing compound such as borate or borate derivative, is contained in a subbing layer and diffuses into base layer to crosslink the crosslinkable binder in at least the base layer.
A borate or borate derivative employed in the subbing layer of the ink jet recording element can be, for example, borax, sodium tetraborate, and the like, preferably not an acidic boron-containing compound such as boric acid.
In one embodiment, the crosslinking compound is a borate salt such as sodium tetraborate decahydrate (borax), sodium borate, and derivatives of boric acid, boric anhydride, and the like, employed in combination with, as binder in the base layer, a poly(vinyl alcohol), that is, “PVA.” This combination has been found to be especially advantageous. It is known that PVA and borax interact to form a high viscosity or gelled mixture in solution that forms a crosslinked coating on drying. According to one embodiment, the borax is pre-coated on a web and then an aqueous coating composition containing the PVA is applied. The water from the coating composition solubilizes the borax, thus allowing it to diffuse through the coating, quickly thickening the composition.
The boron-containing compound, for example, the borate or borate derivative, is preferably used in an amount in a subbing layer of up to about twenty percent of the weight of the binder in the base layer. It is believed that upon coating of the base layer over such a dried subbing layer, most of the borate or borate derivative in the subbing layer diffuses into the base layer to crosslink most of the binder in the base layer, since such diffusion is typically rapid.
In order to impart further mechanical durability to the base layer, one or more supplemental, non-boron-containing crosslinkers that act upon the binder discussed above may be added in small quantities to the coating composition for at least the base layer. Such an additive can further improve the cohesive strength of the layer. Crosslinkers such as carbodiimides, polyfunctional aziridines, aldehydes, isocyanates, epoxides, vinyl sulfones, pyridinium, pyridylium dication ether, methoxyalkyl melamines, triazines, dioxane derivatives, chrom alum, zirconium sulfate, and the like may be used. Thus, a non-boron-containing crosslinker can be used in combination with the boron-containing crosslinker.
As indicated above, the base layer has a dry weight of at least 10 g/m2, more preferably 15 to 25 g/m2, and most preferably 17 g/m2 to 24 g/m2. At lower dry weight of the base layer, any increased coalescence that is observed may be compensated further by adjusting the base layer composition to increase absorption capacity of the base layer or to improve wetability of the receiver. For example, the addition of flurorosurfactant to the base layer can reduce coalescence at low base-layer coverage. Also, coalescence may be reduced by adding absorption capacity in the form of an intermediate layer. Other possible adjustments to the composition of the base layer can include changing the surface area of the particles and/or the addition of other particulate materials.
The base layer is located under the other porous ink-retaining layers, at least the gloss layer, and absorbs a substantial amount of the liquid carrier applied to the inkjet recording element, but substantially less dye or pigment, if any, than the overlying layer or layers.
In one embodiment of the present inkjet recording element, the base layer is at least two times, preferably 3 times, more preferably at least 6 times, most preferably at least 9 times the thickness of the upper gloss layer.
The inorganic particles in the base layer can comprise a mixture of two different populations of fumed silica that are separately made and then admixed.
Preferably, the anionic fumed silica (or mixed-oxide fumed particle containing silicon) in the base layer comprises at least about 70 percent, more preferably at least about 90 percent by weight of the total weight of inorganic particles in the base layer.
The base layer may further comprise a minor amount of one or more other non-cationic inorganic particles in addition to the fumed silica, if any, for example, colloidal silica, titanium oxide, tin oxide, zinc oxide, and the like, and/or mixtures thereof. Examples of other useful non-cationic inorganic particles include clay or calcium carbonate. Preferably, any optional non-aggregated colloidal particles comprise anionic colloidal (non-aggregated) silica, as described above for the porous gloss layer, other than particle size.
In addition to the inorganic particles mentioned above, the base layer may independently contain non-cationic organic particles or beads such as poly(methyl methacrylate), polystyrene, poly(butyl acrylate), etc. Preferably, substantially all the particles in the base layer have a median primary or secondary particle size of not more than 300 nm.
Preferably, the one or more other non-cationic inorganic materials in the base layer comprise particles of a silicon-oxide containing material in which at least 70 percent, preferably at least 80 percent, of the metal or silicon atoms are silicon, in combination with oxygen or other non-metallic or metallic atoms.
In a preferred embodiment, the base layer comprises between 5 and 15.0 weight percent binder. The base layer can comprise both hydrophilic and hydrophobic binder. Most preferably, the binder in the base layer comprises poly(vinyl alcohol). In addition, it is preferred that the base layer further comprises crosslinker crosslinking the poly(vinyl alcohol).
In one embodiment, the base layer further comprises fluorosurfactant, suitably in the amount of 0.1 to 5%, preferably 0.8 to 2% of the total weight of the coating composition. Preferred fluorosurfactants are non-ionic, linear, perfluorinated polyethoxylated alcohols, as disclosed in US Patent Publication No. 2005/0013947, hereby incorporated by reference. In some embodiments, such fluorosurfactants can improve gloss and coalescence.
The porous layers above the base layer contain interconnecting voids that can provide a pathway for the liquid components of applied ink to penetrate appreciably into the base layer, thus allowing the base layer to contribute to the dry time. A non-porous layer or a layer that contains closed cells would not allow underlying layers to contribute to the dry time.
The inkjet recording element preferably comprises, in the base layer, fumed silica having an average primary particle size of up to 50 nm, preferably 5 to 40 nm, but which is aggregated having a median secondary particle size preferably up to 300 nm, more preferably 150 to 250 nm.
The base layer is characterized by the absence of cationic materials that affect the surface charge or zeta potential of the anionic silica particles in the invention such as cationic polymer, a hydroxyl-containing polyvalent metal salt, for example aluminum chlorohydrate, or a silane coupling agent. “Absence” is defined herewith as below a limit in which there are sufficient cationic groups to critically change the zeta potential of the anionic silica particles, rendering the zeta potential more positive than negative 15 mv. The term “cationic polymer,” for example, includes polymers with at least one quaternary ammonium group, phosphonium group, an acid adduct of a primary, secondary or tertiary amine group, polyethylene imines, polydiallylamines or polyallylamines, polyvinylamines, dicyandiamide condensates, dicyandiamide-polyamine co-condensates or polyamide-formaldehyde condensates, and the like.
Preferably, the fumed silica, like the colloidal silica in the present invention, is characterized by at least 70, preferably at least 90 percent of the metal or silicon atoms in the particles being silicon, in combination with oxygen or other non-metallic non-silicon atoms. For example, various dopants, impurities, variations in the composition of starting materials, surface agents, and other modifying agents may be added to the silicon oxide in limited amounts during its preparation, as long as the resulting surface is anionic. Fumed silica can include mixed metal oxides, as long as the zeta potential requirements are met. See, for example, U.S. Pat. No. 7,015,270 to Scharfe et al. and U.S. Pat. No. 6,808,769 to Batz-Sohn et al., both hereby incorporated by reference. Silicon-oxide-mixed oxide particles can include, for example, titanium, aluminum, cerium, lanthanum, or zirconium atoms. Mixed oxides include intimate mixtures of oxide powders at an atomic level with the formation of mixed oxygen-metal/non-metal bonds.
Silicon-oxide particles can be divided roughly into particles that are made by a wet process and particles made by a dry process (vapor phase process). The latter type of particles is also referred to as fumed or pyrogenic particles. In a vapor phase method, flame hydrolysis methods and arc methods have been commercially used. The term “flame hydrolysis” is understood to mean the hydrolysis of metal or non-metal compounds in the gas phase of a flame, generated by reaction of a fuel gas, preferably hydrogen, and oxygen. Highly disperse, non-porous primary particles are initially formed which, as the reaction continues, coalesce to form aggregates, and these aggregates may congregate further to form agglomerates. In a preferred embodiment, the BET surface of area of these primary particles are 5 to 600 m2/g. Fumed silica is produced in a vapor phase process, whereas colloidal silica is not and can be distinguished from both fumed silica made by a dry process and other silicas made by a wet process such as relatively more porous silica gel.
Fumed particles exhibit different properties than non-fumed or wet-process particles, which are referred to herein as “colloidal silica.” In the case of fumed silica, this may be due to the difference in density of the silanol group on the surface. Fumed particles are suitable for forming a three-dimensional structure having high void ratio.
Fumed or pyrogenic particles are aggregates of smaller, primary particles. Although the primary particles are not porous, the aggregates contain a significant void volume, and hence are capable of rapid liquid absorption. These void-containing aggregates enable a coating to retain a significant capacity for liquid absorption even when the aggregate particles are densely packed, which minimizes the inter-particle void volume of the coating. For example, fumed silica, for selective optional use in the present invention, are described in U.S. Pat. No. 6,808,769 to Batz-Sohn et al., U.S. Pat. No. 6,964,992 to Morris et al. and U.S. Pat. No. 5,472,493 to Regan, all hereby incorporated by reference. Examples of fumed silica are provided in the Examples below and are commercially available, for example, from Cabot Corp. under the family trademark CAB-O-SIL silica, or Degussa under the family trademark AEROSIL silica.
Fumed silicas having relatively lower surface area are preferred for their lower binder requirement, but fumed silicas with surface areas that are too low decrease gloss. In one embodiment, a range of 150 to 350 m2/g is preferred, more preferably 170 to 270 m2/g.
Coated over the base layer is the upper gloss layer. The voids in the gloss layer provide a pathway for an ink to penetrate appreciably into the base layer, thus allowing the base layer to contribute to the dry time. It is preferred, therefore, that the voids in the gloss-producing ink-receiving layer are open to (connect with) and preferably (but not necessarily) have a void size similar to or slightly larger than the voids in the base layer for optimal interlayer absorption.
In one embodiment, the upper gloss layer comprises less than 10 weight percent binder, based on total solids in the layer. The binders in the upper gloss layer can be selected from the same binders as in the base layer. Poly(vinyl alcohol) is again the preferred binder.
The gloss layer is characterized by the absence of cationic materials that affect the surface charge or zeta potential of the silica particles in the invention such as cationic polymer, a hydroxyl-containing polyvalent metal salt, for example aluminum chlorohydrate, or a silane coupling agent. “Absence” is defined herewith as below a limit in which there are sufficient cationic groups to critically change the zeta potential of the anionic silica particles, rendering the zeta potential more positive than negative 15 mv.
Preferably, the colloidal silica in the gloss layer comprises at least about 80 percent, more preferably 90 percent, by weight of the inorganic particles in the gloss layer.
The term “colloidal silica” refers to particles comprising silicon dioxide that are dispersed to become colloidal. Such colloidal particles characteristically are primary particles that are substantially spherical. Larger particles, aggregates of primary particles relatively limited in number and aggregation, may be present to a minor extent, depending on the particular material and its monodispersity or polydispersity, but the larger particles have relatively minor effect on the number weighted median particle size. Examples of these colloidal silica are described in the Examples below and are commercially available from a number of manufacturers, including Nissan Chemical Industries, Degussa, Grace Davison (for example under the family trademarks SYLOJET and LUDOX), Nalco Chemical Co., etc. Typically, colloidal silica naturally has an anionic charge, resulting from the loss of protons from silanol groups present on the particles' surface. Such particles typically originate from dispersions or sols in which the particles do not settle from dispersion over long periods of time. Most commercially available colloidal silica sols contain sodium hydroxide, which originates at least partially from the sodium silicate used to make the colloidal silica.
The average metallic composition of said colloidal particles comprises at least 70 percent, more preferably at least 90 percent silicon, wherein silicon is considered a metallic element for this calculation, as described above for the fumed silica in the base layer.
The gloss layer may further comprise a minor amount of one or more other non-cationic inorganic particles, if any, for example, fumed silica, titanium oxide, and/or mixtures thereof. Preferably, any optional aggregated particles comprise anionic fumed silica, as described above for the porous base layer, other than particle size. Also suitable are anionic colloidal particles of zinc oxide, tin oxide, and the like.
In addition to the inorganic particles mentioned above, the gloss layer may independently contain non-cationic organic particles or beads such as the ones mentioned above for the base layer. Preferably, substantially all the particles in the base layer have an average primary particle size of not more than 45 nm, except for particles used as matte beads.
Preferably, the one or more other non-cationic inorganic materials in the gloss layer comprise particles of a silicon-oxide containing material in which at least 80 percent of the metal or silicon atoms are silicon, in combination with oxygen or other non-metallic or metallic atoms.
Conventional additives may be included in the ink-receiving layers in the present invention, which may depend on the particular use for the recording element. Such additives that optionally can be included in the ink-receiving layers of the inkjet recording element include cross-linkers, rheology modifiers, surfactants, UV-absorbers, biocides, lubricants, dyes, optical brighteners, and other conventionally known additives. Additives may be added in light of the fact that the inkjet recording element may come in contact with other image recording articles or the drive or transport mechanisms of image-recording devices, so that additives such as matte particles and the like may be added to the inkjet recording element to the extent that they do not degrade the properties of interest. Also the additives must be compatible with anionic silica.
The inkjet recording element can be specially adapted for either pigmented inks or dye-based inks, or designed for both. In the case of pigment-based inks, the upper gloss layer can function as a pigment-trapping layer. In the case of dye-based inks, both the upper gloss layer and the lower base layer, or an upper portion thereof, may contain the image, depending on the particular embodiment, thickness of the layers, particle composition, binder, etc.
The term “pigment-trapping layer” is used herein to mean that, in use, preferably at least about 75% by weight, more preferably substantially all, of the pigment colorant in the inkjet ink composition used to print an image remains in the pigment-trapping layer.
The support for the coated ink-retaining layers may be selected from plain papers or resin-coated paper. Preferably the resin-coated paper comprises a polyolefin coating on both sides, more preferably polyethylene. The thickness of the support employed in the invention can be from about 12 to about 500 μm, preferably from about 75 to about 300 μm.
If desired, in order to improve the adhesion of the base layer to the support, the surface of the support or a subbing layer may be corona-discharge-treated prior to applying the base layer to the support.
The inkjet recording element of the present invention can be manufactured by conventional manufacturing techniques known in the art. In a particularly preferred method, the subbing layer is coated in a single layer at a single station and all the additional coating layers, comprising the base and gloss layers, are simultaneously coated in a single station. In one embodiment, the entire inkjet recording element is coated in a single coating pass.
The term “single coating pass” or “one coating pass” refers to a coating operation comprising coating one or more layers, optionally at one or more stations, in which the coating operation occurs prior to winding the inkjet recording material in a roll. A coating operation, in which a further coating step occurs before and again after winding the inkjet recording material on a roll, but prior to winding the inkjet recording material in a roll a second time, is referred to as a two-pass coating operation.
The term “post-metering method” is defined herewith as a method in which the coating composition is metered after coating, by removing excess material that has been coated.
The term “pre-metering method,” also referred to as “direct metering method,” is defined herewith as a method in which the coating composition is metered before coating, for example, by a pump.
Pre-metered methods can be selected from, for example, curtain coating, extrusion hopper coating, slide hopper coating, and the like.
In a preferred embodiment, the two ink-receiving layers are simultaneously coated, preferably by curtain coating.
In a preferred embodiment, the method of manufacturing an inkjet recording element comprises the steps of:
(a) providing a support;
(b) simultaneously coating in order over the support;

    
    
        (i) a first coating composition, for a base layer, comprising particles of anionic fumed silica and a hydrophilic binder capable of being substantially cross-linked by crosslinking compound not contained in the first composition; and
        (ii) a second coating composition, for a gloss layer, comprising particles of anionic colloidal silica and a binder;
    
    


wherein said particles of fumed silica and colloidal silica exhibit a zeta potential below negative 15 mv, wherein the percent of binder to total solids in the first and second coating compositions is between 5% and 15.0% by weight (not including 15.0 percent); and
(c) treating the support prior to step (b) with a subbing composition comprising a crosslinking compound that diffuses into at least the base layer to substantially crosslink at least the hydrophilic binder in the base layer.
The subbing composition can optionally comprise a binder or may simply comprise a liquid carrier such as water.
Preferably, the crosslinking compound contains boron, for example, the crosslinking compound can be borax or borate.
In a preferred embodiment of the method, the hydrophilic binder in the base layer comprises poly(vinyl alcohol) or a derivative or co-polymer thereof
The binder in the gloss layer can also be capable of being substantially cross-linked by crosslinking compound not contained in the second composition and wherein said crosslinking compound also diffuses into the gloss layer to substantially crosslink the binder in the gloss layer.
Thus, in one embodiment, the support is treated prior to step (b) with a subbing composition comprising a crosslinking compound that diffuses into at least the base layer to substantially crosslink at least the hydrophilic binder in the base layer. In this case, the crosslinking compound may migrate to some extent into the upper gloss layer, depending on various factors such as the thickness of the base layer.
Further intermediate layers between the base layer and the upper gloss layer, etc. may be coated by conventional pre-metered coating means as enumerated above. Preferably, the base layer and the gloss layer are the only two layers having a dry weight over 1.0 g/m2 in the ink-receiving element.
Inkjet inks used to image the recording elements of the present invention are well known in the art. The ink compositions used in inkjet printing typically are liquid compositions comprising a solvent or carrier liquid, dyes or pigments, humectants, organic solvents, detergents, thickeners, preservatives, and the like. The solvent or carrier liquid can be solely water or can be water mixed with other water-miscible solvents such as polyhydric alcohols. Inks in which organic materials such as polyhydric alcohols are the predominant carrier or solvent liquid may also be used. Particularly useful are mixed solvents of water and polyhydric alcohols. If dyes are used in such compositions, they are typically water-soluble direct or acid type dyes. Such liquid compositions have been described extensively in the prior art including, for example, U.S. Pat. Nos. 4,381,946; 4,239,543; and 4,781,758.
Typically the colorants used in inkjet printing are anionic in character. In dye based printing systems, the dye molecules contain anionic moieties. In pigment based printing systems, the dispersed pigments are functionalized with anionic moieties. Colorants must be fixed near the surface of the inkjet receiver in order to provide the maximum image density. In the case of pigment based printing systems, the inkjet receiver is designed with the optimum pore size in the top layer to provide effective trapping of ink pigment particles near the surface. Dye-based printing systems known in the conventional art require a fixative or mordant in the top layer or layers of the receiver. Polyvalent metal ions and insoluble cationic polymeric latex particles provide effective mordants for anionic dyes. Both pigment and dye based printing systems are widely available. For the convenience of the user, a universal porous inkjet receiver known in the conventional art will comprise a dye fixative in the topmost layer or layers.
Although the recording elements disclosed herein have been referred to primarily as being useful for inkjet printers, they also can be used as recording media for pen plotter assemblies. Pen plotters operate by writing directly on the surface of a recording medium using a pen consisting of a bundle of capillary tubes in contact with an ink reservoir.
Another aspect of the invention relates to an inkjet printing method comprising the steps of: (a) providing an inkjet printer that is responsive to digital data signals; (b) loading the inkjet printer with the inkjet recording element described above; (c) loading the inkjet printer with a pigmented inkjet ink; and (d) printing on the inkjet recording element using the inkjet ink in response to the digital data signals.
Yet another aspect of the invention relates to a packaged product set comprising the inkjet receiver of the present invention in combination with an inkjet ink set comprising at least three colored ink compositions, for example, cyan, yellow, and magenta. Such a product set can conveniently be made commercially available to customers for use in printing photo-quality images, so that the ink compositions and the inkjet receiver are desirably matched during printing of images. The inkjet recording element of the present invention can further be characterized by the presence, on the backside thereof, of indicia that are capable of being detected by an inkjet printer. Such indicia can be detected by an optical detector or other such means in order to further improve the desired result by ensuring the recommended printer settings for a particular inkjet receiver are used when printing an image. This system allows the user to achieve higher print quality more conveniently.
In a preferred embodiments the inkjet ink composition is applied onto the inkjet recording element at a rate of at least 5.0×10−4 mL/cm2/sec without loss of image quality. This ink flux corresponds to printing a photograph at an addressable resolution of 1200 by 1200 pixels per inch with an average ink volume of 10.35 picoliters (pL) per pixel in 42 seconds, wherein the printing of a given pixel by multiple coating passes is complete in less than 4 seconds.
The following examples further illustrate the invention.
EXAMPLE 1
A support comprising a paper with polyethylene resin coating on both sides was treated on one side by coating with an aqueous composition comprising poly (vinyl alcohol) (PVA, CELVOL 103), a styrene-butadiene latex (DOW CP692NA), and sodium tetraborate in a ratio of 1:1:2, at a total solids of 0.6% and dried to provide a dry coverage of 0.32 g/m2.
A first aqueous coating composition (17.9% solids) for a base layer comprising a dispersion (DEGUSSA W7520) containing anionic fumed silica (AEROSIL 200), 7.5% PVA (NIPPON GOHSEI KH20), 0.75% (1,4-dioxane-2,3-diol (DHD)), 1% fluorosurfactant (ZONYL FS300), and a second aqueous coating composition (10% solids) for a gloss layer comprising a dispersion of anionic colloidal silica (1:1 mixture of Grace Davison SYLOJET 4000 A and LUDOX TM-50), 8% succinylated gelatin (GELITA IMAGEL MS), a crosslinker (0.8% 1,4-dioxane-2,3-diol (DHD)), and a coating aid (1% ZONYL FS300) were simultaneously coated on the subbing layer to provide layers of dry weight 21.5 g/m2 and 2.2 g/m2, respectively, and dried to form inventive Sample I-1.
Comparative Samples C1 to C5 employed an identical treated support as described above. A first aqueous coating composition (17.9% solids) for abase layer comprising a dispersion (DEGUSSA WK7330) containing cationic fumed silica (cationically modified AEROSIL 130); PVA (NIPPON GOHSEI KH20), 2.5% (1,4-dioxane-2,3-diol (DHD)), 0.5% boric acid and 1.85% coating aid (10 G, DIXIE CHEMICAL) and a second aqueous coating composition (10% solids) for a gloss layer comprising a dispersion of cationic colloidal silica (Grace Davison SYLOJET 4000 C); 3.5% polyvinyl alcohol (NIPPON GOHSEI GH23); 1% 1,4-dioxane-2,3-diol and 1% ZONYL FS300 were coated simultaneously on the subbing layer to provide layers of dry weight 21.5 g/m2 and 2.2 g/m2 respectively. The fimned silica-containing layer was varied with respect to PVA level, and the fumed silica level was adjusted to compensate. The amounts of PVA used in Comparative Samples C1 to C5 are given in Table 1 below.
Cracking of the coated samples was assessed visually. The gloss of the unprinted samples was measured at 20 and 60 degrees. The samples were printed using a KODAK EASYSHARE 5100 Inket Printer with a driver setting selected such that print speed and ink laydown were maximized (KODAK ULTRA PREMIUM STUDIO GLOSS PAPER selection). Coalescence, or local density non-uniformity in solid color patches, was assessed visually and rated on a scale of 1 (none visible) to 5 (significant coalescence observed under conditions in which the selected printer mode provides a very high ink flux, up to, but not including “flooding”). Ratings up to 4 may be considered acceptable for some printing applications. Samples that were flooded with ink as well as coalesced were rated higher than 5. The samples were also printed with an EPSON R320 dye-based printer, and densities of solid color patches were measured. Averages of densities for cyan, magenta, and yellow were compared, as well as average values for red, green, and blue patches and pure black patches. The results are shown in Table 1 below.














TABLE 1









Pig-
Dye-
Dye-







ment-
based
based
Dye-




Base

based
Ink
Ink
based




Layer

Ink
Density
Density
Ink


Sam-
Silica
Binder
Crack-
Coales-
(Ave of
(Ave of
Density


ple
Type
(%)
ing
cence
CMY)
RGB)
(K)






















C-1
Cationic
9
Yes
3
1.88
1.66
2.38


C-2
Cationic
11
Slight
2.5
1.84
1.67
2.36


C-3
Cationic
13
No
3
1.84
1.63
2.34


C-4
Cationic
15
No
5
1.85
1.63
2.19


C-5
Cationic
16.4
No
7
1.82
1.66
2.19


I-1
Anionic
7.5
No
1.5
2.18
1.69
2.38









As demonstrated by the results in Table 1, the present inventors have discovered that a recording element of the present invention comprising anionic fumed silica in the ink receiving layer and anionic colloidal silica in the gloss layer may be coated with a lower binder content in the ink-receiving layer without cracking. As a result, reduced coalescence is obtained with pigment-based inks. Surprisingly, the color density of dye-based inks is improved as well. In the art, standard practice for inkjet receivers is to employ cationic particles such as alumina or cationically modified silica, and optionally to incorporate cationic mordants compatible with the cationic particles, in order to fix the standard anionic ink colorants near the receiver surface for maximum color density. In the present invention, essentially no cationic particles or additives are employed in the receiver, but superior results are obtained for printing with inks comprising standard anionic colorants.
EXAMPLE 2
The present invention comprises an uppermost gloss layer comprising colloidal silica. For comparison, an Comparative Sample C-6 was prepared as in the Inventive Sample I-1, except that instead of coating the gloss layer, the dry coverage of the ink-receiving layer was increased by a corresponding dry weight. Samples C-6 and I-1 were evaluated as in Example 1 and the results are reported in Table 2.














TABLE 2






Coverage
Coverage
Gloss
Gloss
Density
Density



Sam-
(Base
(Gloss
(20
(60
(Ave of
(Ave of
Density


ple
Layer)
layer)
Deg)
Deg)
CMY)
RGB)
(K)






















I-1
21.5
2.2
21.4
47.3
2.18
1.69
2.38


C-6
23.7
0
6.1
17.0
1.42
1.09
1.72









The results shown in Table 2 demonstrate a dramatic gloss improvement when a gloss layer is provided on top of the ink-receiving layer. In addition, the densities of all colors are substantially improved when printed with a dye-based ink.
EXAMPLE 3
The present invention comprises a porous base layer comprising particles of anionic fumed silica. Inventive Samples I-2, I-3, and I-3A were prepared identically to inventive coating Sample I-1, except the topcoat coverage was increased to 3.2 grams/m2; and anionic colloidal silica (Grace Davison SYLOJET 4000A) was partially substituted for the fumed silica in the bottom layer in the amounts described in Table 3 below. Samples were evaluated as in Example 1













TABLE 3






%

Density
Density





Fumed

(Ave of
(Ave of
Density
20 degree


Sample
Silica
Coalescence
CMY)
RGB)
(K)
gloss





















I-2
0
1.5
2.20
1.80
2.38
32


I-3
10
2.5
2.18
1.77
2.33
30


I-3A
20
5
2.15
1.77
2.39
33









The results of Table 3 demonstrate that a base layer comprising anionic fumed silica provides excellent printed color density with dye-based inks without unacceptable coalescence of pigment-based inks even with the addition of other compatible anionic inorganic particles.
EXAMPLE 4
A series of coatings was prepared according to the procedure for coating Sample I-1 of Example 1, except that the coating composition of the gloss layer was changed to 15% solids and the laydown was varied. Samples of the coating were evaluated as in Example 1 and the test results are reported in Table 4 below.













TABLE 4






Gloss layer

Density
Density





coverage,
Coales-
(Ave of
(Ave of
Density
20 degree


Sample
g/m2
cence
CMY)
RGB)
(K)
gloss





















I-4
4.3
2
2.21
1.83
2.45
32


I-5
3.2
1.8
2.17
1.69
2.37
33


I-6
2.2
1.5
2.02
1.55
2.28
31


I-7
1.1
1.5
1.73
1.34
1.95
24









As demonstrated in Table 4, at lower gloss layer weight, the printed color density may decline. A slight increase in coalescence appears for gloss layer dry weight above 5 g/m2.
EXAMPLE 5
A series of coatings was prepared according to the procedure for Coating Sample I-1 in Example 1, except that the mixture of anionic colloidal silica types of the gloss layer was replaced by a single component, Grace Davison SYLOJET 4000A, and the gelatin binder in the gloss layer was replaced by poly(vinyl alcohol). The poly(vinyl alcohol) level in the gloss layer was adjusted through a range of 4% by weight to 10% by weight. The level of crosslinker in the gloss layer was adjusted to 10% by weight of the binder level. The base layer was prepared at a constant binder level of 6% by weight.
Bronzing occurs when a printed dark area exhibits enhanced gloss with the appearance of a bronze color. A visual assessment of bronzing was made by observing an imaged black area printed by an EPSON R260 printer with dye-based inks.












TABLE 5








Density





Gloss layer binder

(Ave of
Density (Ave
Density


Sample
level (weight %)
Bronzing
CMY)
of RGB)
(K)




















I-8
10
Poor
1.73
1.49
1.94


I-9
7.5
Good
1.73
1.45
1.92


I-10
5.6
Good
1.69
1.42
1.90


I-11
4
Good
1.64
1.39
1.82









The data in Table 5 demonstrates that a binder proportion in the gloss layer up to 10% provides excellent printed dye density. For inks prone to bronzing, lower binder proportions are preferred in the gloss layer.
EXAMPLE 6
A series of coatings was prepared according to the procedure of Example 5, except that the binder level in the ink-receiving layer was 7% by weight. The coat weights of the gloss layer and the ink-receiving layer were varied as shown in Table 6 below.












TABLE 6








Total





Base Layer
Gloss Layer
layer





coverage,
coverage,
coverage,
Coales-



Sample
g/m2
g/m2
g/m2
cence
Cracking




















I-12
21.5
4.3
25.8
2
Slight


I-13
21.5
3.2
24.7
2
Very slight


I-14
21.5
2.2
23.7
2.5
Good


I-15
19.4
4.3
23.7
3
Very slight


I-16
19.4
3.2
22.6
4
Good


I-17
19.4
2.2
21.6
3
Good


I-18
16.1
4.3
20.4
6
Good


I-19
16.1
3.2
19.3
6
Good


I-20
16.1
2.2
18.3
6
Good









The results shown in Table 6 show preferred ranges for some embodiments of the invention, and demonstrate that an ink-receiving layer comprising at least 17 g/m2 reduces coalescence compared with layers of less dry weight. The increased coalescence observed at lower base-layer dry weight may be compensated further by adjusting the base layer composition to increase absorption capacity or wetting. For example, as indicated in Example 18 below, increasing the amount of fluorosurfactant in the base layer can reduce coalescence at low base-layer coverage. As total dry weight of the combined base layer and gloss layer increases beyond 25 g/m2, the receiver may be more prone to cracking during manufacture. The gloss coat coverage has a relatively larger effect on cracking, while the ink-receiving dry layer weight has a relatively larger influence on image quality.
EXAMPLE 7
A series of coatings was prepared according to the procedure for coating Sample I-1 in Example 1, except that the mixture of anionic colloidal silica types of the gloss layer was replaced by a single component, Grace Davison SYLOJET 4000A and the gloss layer dry weight was set at 3.2 g/m2. The binder level for the ink-receiving layer was varied as shown in Table 7 below.











TABLE 7






Base Layer
Base Layer




Sample
coverage, g/m2
binder level
Coalescence
Cracking



















I-21
19.4
7.5%
3
Good


I-22
19.4
 10%
4
Good


I-23
19.4
12.5% 
5
Good


I-24
28
7.5%
1.5
Poor


I-25
28
 10%
2
Slight


I-26
28
12.5% 
2.5
Very






slight









The results shown in Table 7 demonstrate that base layer dry weights above 24 g/m2 may result in increased cracking, whereas increasing relative dry binder content tends to increase coalescence.
EXAMPLE 8
A treated support was prepared according to the procedure for coating Sample I-1 in Example 1, except that the borax-containing treatment layer comprised a 1:1 mixture of polyvinyl pyrrolidone (K-90, ISP Corp) and sodium tetraborate. A series of coatings was prepared with dispersions of cationic fumed silica for the ink-receiving layer. Aqueous cationic coating composition A (total solids 17.9%) was prepared to yield 82.6% cationic silica from a commercial dispersion WK7330 (dispersion of AEROSIL 130, Degussa); 12.5% poly(vinyl alcohol) (KH-20); 2.5% Dihydroxy dioxane; 0.5% boric acid; and 1.9% 10 G surfactant.
Cationic coating composition B was prepared according to the same formula as Composition A, except WK7525 (a cationic dispersion of AEROSIL 200 from Degussa) was used in place of WK7330 and cationic coating Composition C was prepared according to the same formula as composition B, except that the poly(vinyl alcohol) binder level was raised to 15%; and the level of silica was lowered to compensate. An aqueous cationic coating composition for the gloss layer was prepared at 10% solids, comprising 83.8% cationic colloidal silica (from SYLOJET 4000C dispersion available from Grace Davison); 10% cationic fumed silica (WK7330; Degussa); 4% poly(vinyl alcohol) (KH20); 1.1% dihydroxy dioxane and 1.1% ZONYL FS300 surfactant.
A series of coating Samples C-13 to C-15 was prepared by simultaneously coating the cationic coating compositions for the ink-receiving layer and the cationic coating composition for the gloss layer in combination to yield dry coating weights of 21.5 g/m2 for the ink-receiving layer and 2.2 g/m2 for the gloss layer. In addition, an anionic coating identical in composition to Example 1 was prepared, except that the binder in the gloss layer was changed to poly(vinyl alcohol), and the layers were coated on the same borax treatment layer used for the cationic comparative examples to provide coating Sample I-27. The samples were evaluated as in Example 1 and the results are shown in Table 8.















TABLE 8






Gloss
Base
Base

Ave
Density





layer
layer
layer

density
(Ave
Density



Sample
type
type
binder
Cracking
(CMY)
of RGB)
(K)
Coalescence























C-13
Cationic
Cationic A
12.5%
Good
1.83
1.62
2.39
3.5


C-14
Cationic
Cationic B
12.5%
Flaked
(N/A)
(N/A)
(N/A)
(N/A)






off






C-15
Cationic
Cationic C
  15%
Poor
1.65
1.52
2.95
3.5


I-27
Anionic
Anionic
 7.5%
Good
2.19
1.77
2.36
3  









The results shown in Table 8 show that a larger particle size is preferable for the ink-receiving layer containing cationic silica than is preferred for a layer containing anionic silica, along with increased binder content relative to the formula employing anionic silica. While coalescence and cracking levels can approach those seen for the anionic layers of the invention, dye density is not as high.
EXAMPLE 9
The Example demonstrates zeta potentials of silica particles used in various examples and comparative examples of the invention. The zeta potentials were measured using a Malvern Zetasizer Nano-ZS. The results are shown in Table 9 below.










TABLE 9





Dispersion
Silica
Type
Zeta (mV)







SYLOJET 4000A silica
Colloidal
Anionic 
−40.1


SYLOJET 4000C silica
Colloidal
Cationic
+36.1


W7520 (AEROSIL 200) silica
Fumed
Anionic
−31.5


W7330 (AEROSIL 130) silica
Fumed
Cationic
+33.8









As seen by the results in Table 9, anionic silica dispersions of the invention have zeta potentials more negative than negative 15 mv. The cationic silica dispersions have zeta potentials greater than +15 mv.
EXAMPLE 10
Anionic coating compositions for the base layer and gloss layer were prepared corresponding to those used in Example 5. Cationic coating compositions for the base layer and gloss layer were prepared corresponding to those used in Example 8. The melts were combined with stirring at room temperature to assess compatibility. The observations are recorded in Table 10.











TABLE 10







Base Layer
Gloss Layer
Result



Composition
Composition
upon combining









Anionic
Anionic
Compatible



Anionic
Cationic
Particles formed



Cationic
Cationic
Compatible



Cationic
Anionic
Agglomeration










These observations suggest that the particles in the coating compositions must possess like charges in order to be compatible for successful simultaneous coating
EXAMPLE 11
A coating was prepared identically to Example 1, except that the dry weight of the gloss layer was increased to 3.2 g/m2. A comparison coating was prepared by a sequential coating method, that is, the image-receiving layer was coated and dried and then the gloss layer was coated on top and dried. The printed gloss was evaluated using a KODAK EASYSHARE 5100 printer. Patches of cyan, magenta, yellow, and protective ink were printed and then the 20-degree gloss of each patch was measured and the values averaged. The results are shown in Table 11.











TABLE 11








Printed





Unprinted
20 deg gloss


Sample
Coating type
20 deg gloss
(Ave CMY)
Coalescence







I-28
Simultaneous
31
79
2


I-29
Sequential
21
57
3









The results of the simultaneous and sequential coating methods for anionic silica coating compositions shown in Table 11 demonstrate that the unprinted gloss and printed gloss are superior for the preferred simultaneous coating method and the coalescence is reduced. While not wishing to be bound by any particular theory, the inventors surmise that the simultaneous coating method sufficiently alters the microstructure at the interface of the gloss and base layers of the receiver that it significantly improves the printed gloss and reduces coalescence with pigmented inks.
EXAMPLE 12
Anionic coating compositions for the base and gloss layers were prepared as for Example 5, and cationic coating compositions for the base and gloss layers were prepared as in Example 8. The base layers were each coated over a borax-containing subbing layer as described in Example 1 and dried. The dried anionic base layer was subsequently coated with the cationic gloss composition and dried, while the cationic base layer was subsequently coated with the anionic gloss composition and dried. For comparison, the anionic base and gloss layer compositions were also coated simultaneously and dried, as were the cationic base and gloss layer compositions. The samples were evaluated as in Example 1 and the results are shown in Table 12.













TABLE 12









Density





Base
Gloss
20 deg
(Ave of
Density



Sample
Layer
Layer
gloss
RGB)
(K)
Coalescence





















C-16
Anionic
Cationic
43
1.43
2.40
4


C-17
Cationic
Anionic
23
1.54
2.28
3


C-18
Cationic
Cationic
41
1.56
2.33
4


I-30
Anionic
Anionic
32
1.80
2.38
1.5









The results shown in Table 12 demonstrate that the anionic structure I-30 of the invention provides the best composite color density and least amount of coalescence with very good gloss, compared to structures C-16 to C-18 comprising cationically modified silica.
EXAMPLE 13
A series of coatings were prepared identical to sample I-27, except that alternative anionic fumed silica dispersions from anionic fumed silica particles of different surface areas were used and with the exception of the highest surface area silica (sample I-34) that the binder level in the base layer was increased to 10%. The dispersions (all from Degussa) and their corresponding silica particle identity were, respectively, W7525 (AEROSIL 90), W7330N (AEROSIL 130), and W7622 (AEROSIL 300). The samples were evaluated for cracking and unprinted gloss and the results are shown in Table 13.












TABLE 13








Silica Specific

Unprinted




Surface area,

20 degree



Sample
m2/g
Cracking
gloss





















I-31
90
Good
3



I-32
130
Good
8



I-33
200
Good
31



I-34
300
Poor
13










The results shown in Table 13 demonstrate that preferred specific surface areas of anionic fumed silica useful in the ink-receiving layer are between 150 m2/g and 350 m2/g for glossy receivers. The poor cracking behavior and low gloss of sample I-34 could be resolved by increasing the binder level, but this option may be less attractive from a manufacturing standpoint as it is likely that increased viscosity would require that the solid weight of the coating composition be reduced, hence slower coating, less productive drying speeds would be required.
EXAMPLE 14
A series of coatings was prepared according to the procedure for Sample I-1 in Example 1, except that the relative weight of binder in the ink-receiver was lowered from 7.5 to 7.0% and a series of commercially available anionic colloidal silica particles were substituted in the coating composition for the gloss layer. The identity and particle size as provided by the manufacturer are given below in Table 14. In some cases, the commercially available colloidal silica dispersions comprise more than one particle size.













TABLE 14








Unprinted
Ave






Colloidal silica
20 deg
density
Density
Density


Sample
Colloidal silica
particle size, nm
gloss
(CMY)
(Ave of RGB)
(K)





















I-35
SYLOJET 4000A
22
29
1.75
1.46
2.01


C-19
NALCO 2329
75
22
1.58
1.31
1.74


I-36
FUSO PL-3
35
18
1.77
1.48
2.05


C-20
FUSO PL-7
70
7
1.39
1.19
1.54


C-21
NALCO 1060
60
12
1.65
1.40
1.85


I-37
NALCO 1140
15
21
2.09
1.70
2.62


I-38
LUDOX TM-50
22
20
1.98
1.67
2.19


I-39
LUDOX LS
12
22
1.84
1.60
2.36









The results shown in Table 14 demonstrate that colloidal silica particles of median particle size smaller than 37 nm provide improved unprinted gloss and printed color density. A combination of colloidal silica dispersions of different median particle sizes below 37 nm may be most preferred, as it can offer a balance of better porosity (lower coalescence) with acceptable gloss and dye-density performance.
EXAMPLE 15
A further series of coatings was made according to the procedure of Example 1 except that, as in Example 14, the binder in the base layer was lowered from 7.5% to 7%, and the colloidal silica in the coating composition was replaced by an equivalent weight of a mixture of colloidal silica particle types of different median particle size. The combinations tested are shown in Table 16 below. Samples of the coatings were printed with the EPSON R320 printer using Epson recommended dye-based ink. The unprinted gloss and the printed color density were measured and the results are shown in Table 15.












TABLE 15







Unprinted
Ave
Density



Sam-

20 deg.
density
(Ave of
Density


ple
Particles in gloss layer
gloss
(CMY)
RGB)
(K)







C-22
NALCO
16.1
1.78
1.62
2.10



1060/NALCO 1140 1:1






I-40
LUDOX TM50/LUDOX
27.1
1.87
1.73
2.33



LS 3:1






I-41
LUDOX TM50/LUDOX
24.0
1.88
1.63
2.41



LS 1:1






I-42
LUDOX TM50/LUDOX
22.5
1.90
1.60
2.37



LS 1:3









The results shown in Table 15 demonstrate that mixtures of anionic colloidal silica particles in the gloss layer provide excellent unprinted gloss and printed color density when the median particle size falls below 37 nm as in Samples I-28 through I-30, whereas the unprinted gloss and color print density are reduced for the Sample C-22 in which the median particle size is 37 nm.
EXAMPLE 16
This Example shows that crosslinking of the binder in the base layer and gloss layer can be accomplished by diffusion of crosslinker from a subbing layer. A fumed silica base layer and gloss layer were prepared as in Example 5 except that the base layer binder level was 8% and the gloss layer binder level was also 8%. The total PVA level was about 1.6 g/m2. A subbing layer was prepared as in Example 8, but the borax concentration in the subbing layer was adjusted so that varying amounts of sodium tetraborate were deposited. Coating quality and gloss were assessed.











TABLE 16






Sodium
Weight Ratio of





Tetraborate,
Sodium Tetraborate

20 degree


Sample
g/m2
to PVA
Cracking
gloss







I-43
0.11
0.06
Very slight
13


I-44
0.16
0.19
Good
30


I-45
0.22
0.14
Good
31


I-46
0.32
0.20
Slight
11









The results shown in Table 16 demonstrate that preferred borate levels between 0.14 and 0.27 g/m2 of binder provide improved imprinted gloss and reduced cracking. Preferred borate levels are correspondingly between 6% and 20% by weight of binder.
EXAMPLE 17
A series of coatings were made identical to those in Sample I-27 of Example 8, except the amounts of PVA, fluorosurfactant ZONYL FS300, and total weight were varied. Gloss was measured and coalescence was assessed by printing with a KODAK EASYSHARE 5100 printer.












TABLE 17









20 deg



Sample
PVA g/m2
Coverage, g/m2
FS
gloss
Coalescence




















I-47
8
21.5
Yes
26
1.5


I-48
8
19.4
Yes
29
2


I-49
8
17.2
Yes
27
2


I-50
8
21.5
No
15
1


I-51
8
19.4
No
15
2


I-52
8
17.2
No
16
7


I-53
10
21.5
Yes
24
1.5


I-54
10
19.4
Yes
28
2


I-55
10
17.2
Yes
24
3.5


I-56
10
21.5
No
18
2.5


I-57
10
19.4
No
20
2.5


I-58
10
17.2
No
21
4


I-59
12.5
21.5
Yes
24
1.5


I-60
12.5
19.4
Yes
24
2.5


I-61
12.5
17.2
Yes
21
3.5


I-62
12.5
21.5
No
21
2.5


I-63
12.5
19.4
No
19
3.5


I-64
12.5
17.2
No
19
7









This data shows the complex relationship between binder level, fluorosurfactant level, gloss, and coalescence. As binder level increases, gloss decreases in the presence of fluorosurfactant, but slightly decreases without it. Fluorosurfactant always improves coalescence, but at some binder levels coalescence and gloss may be sufficient for some applications even without fluorosurfactant.
EXAMPLE 18
A series of coatings was prepared according to the procedure of Example 1, except that the base layer coverage was 23.7 g/m2, the gloss layer coverage was 3.2 g/m2, and poly(vinyl alcohol) type used in the ink-receiving layer was varied with respect to degree of hydrolysis and molecular weight. The molecular weight is typically characterized in the art by the viscosity of a 4% solution in water at 20° C., the values of which are supplied by the manufacturer. The degree of cracking was visually assessed and the unprinted gloss was measured. The results are given in Table 18 below.












TABLE 18






PVA







trademark

Degree





(Nippon
Viscosity
of
Unprinted



Sample
Gohsei)
(cP)
Hydrolysis
20 deg gloss
Cracking




















I-65
KH20
44-52
78.5-81.5
31
Good


I-66
KH17
32-38
78.5-81.5
30
Very slight


I-67
KP-08
6-8
  71-73.5
2
Poor


I-68
GH23
48-56
86.5-89  
24
Good


I-69
AH22
50-58
97.5-98.5
10
Poor









The results presented in Table 18 demonstrate that the preferred poly(vinyl alcohol) binders have a molecular weight high enough to provide a viscosity 30 cP or more in a 4% solution in water at 20° C.; and a degree of hydrolysis of approximately 90 or less in order to provide preferred cracking resistance, gloss and compatibility with dispersions of anionic fumed silica without making other changes in the coating compositions such as limiting the thickness of the base layer or increasing the amount of binder.
The invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention.

## Claims

1. An inkjet recording element having a support and the following ink-receiving layers:
(a) a porous base layer comprising particles of anionic fumed silica and hydrophilic hydroxyl-containing polymer as the primary binder crosslinked with crosslinker comprising boron-containing compound, wherein the porous base layer has a dry weight of about 10 to 35 g/m2, wherein the weight percent of total binder to total solids in the porous base layer is greater than 5.0 percent and less than 15.0 percent; and
(b) an uppermost porous gloss layer above the porous base layer comprising particles of colloidal silica and hydrophilic binder and having a dry weight of about 1.0 to 7.5 g/m2, wherein the median particle size of the particles of colloidal silica is about 10 to under 45 nm, and wherein the uppermost porous gloss layer is characterized by the absence of cationic polymer;
wherein the particles of anionic fumed silica and the particles of colloidal silica exhibit a zeta potential below negative 15 mv, and the base layer is characterized by the absence of cationic materials in an amount that would render the zeta potential of the anionic silica particles more positive than negative 15 mv.

2. The inkjet recording element of claim 1 wherein the median primary particle size of the particles of anionic fumed silica is under 30 nm.

3. The inkjet recording element of claim 1 wherein the porous base layer is at least two times the dry weight of the uppermost porous gloss layer.

4. The inkjet recording element of claim 1 wherein the particles of colloidal silica in the uppermost porous gloss layer comprise a mixture of two different populations of colloidal silica that are separately made and then admixed.

5. The inkjet recording element of claim 1 wherein the anionic fumed silica in the porous base layer comprises at least about 70 percent by weight of the total inorganic particles in the porous base layer.

6. The inkjet recording element of claim 1 wherein the porous base layer comprises less than 12 weight percent binder.

7. The inkjet recording element of claim 1 wherein the polymer in the porous base layer comprises modified or unmodified poly(vinyl alcohol) or copolymers thereof.

8. The inkjet recording element of claim 1 wherein the polymer in the porous base layer comprises poly(vinyl alcohol).

9. The inkjet recording element of claim 8 wherein the poly(vinyl alcohol) has a degree of hydrolysis of at least 70-percent.

10. The inkjet recording element of claim 1 wherein the porous base layer further comprises fluorosurfactant.

11. The inkjet recording element of claim 1 wherein the median primary particle size of the particles of colloidal silica is under 30 nm.

12. The inkjet recording element of claim 1 wherein the uppermost porous gloss layer comprises less than 10 weight percent binder, based on total solids in the uppermost porous gloss layer.

13. The inkjet recording element of claim 1 wherein the particles of colloidal silica in the uppermost porous gloss layer comprise at least about 70 percent by weight of the total inorganic particles in the uppermost porous gloss layer.

14. The inkjet recording element of claim 1 wherein the support comprises cellulosic paper.

15. The inkjet recording element of claim 1 wherein the support comprises resin-coated paper.

16. The inkjet recording element of claim 1 consisting of the porous base layer and the uppermost porous gloss layer, over the support and any optional subbing layer.

17. An inkjet printing process comprising the steps of:
(A) providing an inkjet printer that is responsive to digital data signals;
(B) loading the inkjet printer with an inkjet recording element as described in claim 1;
(C) loading the inkjet printer with an inkjet ink composition; and
(D) printing on the inkjet recording element using the inkjet ink composition in response to the digital data signals.

18. The inkjet printing process of claim 17 wherein the inkjet ink composition comprises anionic dye-based ink.

19. A packaged product comprising the inkjet recording element of claim 1 and an inkjet ink set comprising at least three colored ink compositions.