Recording material for water-dilutable inks

A recording material, more particularly for ink-jet printers, comprises an inking layer formulated to locally receive a water-soluble pigment solution and containing an epoxy cross-linkable, carboxyl-grouped cationic mixed polymer, an epoxidized metal oxide and a water-soluble polymer.

The invention relates to a recording material for water-dilutable inks, 
more particularly for use with ink-jet printers, and a method for 
producing same. 
Image recording and reproduction by means of ink-jet printers is a method 
in wide use since it permits direct and speedy conversion of electronic 
image data. Modern printing technology permits imaging with a resolution 
corresponding to the resolution in imaging in conventional silver halide 
photography employing greatly differing print media such as paper media or 
transparent films. The quality of the images, more particularly the 
resolution, depends on both the capabilities of the printer used and 
decisively on the properties of the recording material, it being the 
recording material which furthermore dictates handling and applicational 
possibilities of the finished images. The recording material needs to 
satisfy the following requirements: good inking to achieve high color 
density; low diffusion of the ink (dye solution) in the recording material 
to maintain the droplet size small and thus to achieve good contour 
acutance and resolution; fast drying and good smudge resistance after 
inking; low tack even at high air humidity; high transparency of the 
recording material when configured as a projection film; and low 
sensitivity to water and thus suitable for outdoor applications. 
Conventional recording materials fail to come up to these requirements and 
are thus restricted in their application. 
In the case of paper media recording materials, fast inking and smudge 
resistance is achieved by modifying an inking layer by high pigmentation 
(DE 3 024 205, EP 379 964), this resulting, however, in heavy clouding so 
that such modified recording materials are not suitable as projection 
films. It is known to provide inking layers of water-soluble polymers such 
as e.g. polyvinyl alcohol, polyvinylpyrrolidone, gelatine etc. (U.S. Pat. 
No. 4,503,111, U.S. Pat. No. 4,680,235, U.S. Pat. No. 4,555,432, DE 4 405 
969). Under influence of humidity these polymers exhibit, however, high 
tack and lack of imperviousness to water. Employing cationic polymers as 
binding agents for fixing the pigments in an inking layer and to enhance 
smudge resistance is known from DE 3 707 624 or EP 514 633. Polymer blends 
of polyvinyl alcohol or polyalkyloxides with cationic polymers may also be 
employed (EP 379 964, EP 634 284, JP 56-84992, JP 59-20696). 
Employing metal oxide sols as fillers is described in EP 524 626 and DE 4 
405 969. To improve smudge resistance it is known to add silanes to the 
binding agent solutions to form matrix polymers (see EP 583 141, EP 482 
837). To prevent sensitivity to water it is proposed in EP 233 703 to use 
acidic, water-insoluble polyacrylates and polyvinylpyrrolidones as the 
inking layer. 
It is also known to produce 2-layer systems comprising a microporous 
polyvinyl acetate cover layer to improve smudge resistance. Due to this, 
however, the transparency is impaired so that an application as projection 
film is impossible. For film media it is thus proposed to cross-link 
water-soluble mixed polymers on the basis of acrylic acid or p-styrene 
sulfonic acid with polyfunctional aziridines (EP 482 838). This 
cross-linking has a negative effect on the drying time of the applied ink, 
however. 
The known recording materials fail to satisfy the above requirements, they 
not being suitable, more particularly, for applications in which contact 
with moisture or water is possible, since pigment is extracted from the 
layer with swelling or dissolution of the inking layer (water-logging) so 
that the achieved inking densities are reduced and contour acutance is 
lacking. 
It is the object of the invention to define a new recording (printing) 
material featuring improved resistance to moisture and water, and to 
define a method of producing same. More particularly, the intention is to 
provide a recording or printing material having a broader range of 
application and featuring practically acceptable drying times after 
inking. 
This object is achieved by a material as set forth in claim 1 and a method 
as set forth in claim 8. Advantageous embodiments read from the 
sub-claims. 
A recording or printing material in accordance with the invention comprises 
an inking layer (or ink recepting layer) containing an epoxy 
cross-linkable, carboxyl-grouped, cationic mixed polymer, a water-soluble 
polymer and an epoxidized metal oxide sol. The percentages by weight are 
preferably 30 to 60% by weight of the mixed polymer, 30 to 60% by weight 
of the metal oxide and 10 to 40% by weight of the water-soluble polymer in 
each case. 
The epoxy cross-linkable, carboxyl-grouped, cationic mixed polymer has the 
structure formula: 
##STR1## 
where M: carboxylic acid monomer 
Z: vinyl monomer 
A: oxygen or nitrogen 
R1: H, CH.sub.3 
R2: alkylene group of C2 to C8 
R3: CH.sub.3, C.sub.2 H.sub.5, C.sub.3 H.sub.7, C.sub.4 H.sub.9 
X: chloride, bromide, and 
a: 10 to 50 mol %, 
b: 0 to 20 mol %, 
c: 50 to 90 mol %. 
Examples of such cross-linkable polymers having the cited general structure 
formula are: 
Acrylic acid methacryloxyethyl-trimethyl ammonium chloride copolymers: 
##STR2## 
Acrylic acid ethylacrylate-methacryloxyethyl-trimethyl ammonium chloride 
terpolymers: 
##STR3## 
Acrylic acid methacrylamidopropyl-trimethyl ammonium chloride copolymers 
##STR4## 
The components of the cross-linkable polymer may also contain a 
combination of various polymers according to the general structure 
formula. 
As the carboxylic acid monomer module, acrylic acid, methacrylic acid or 
itaconic acid is preferred. In this case the percentages in the polymer 
component are preferably 20 to 35 mol %. In addition to ethylacrylate all 
known vinyl monomers, such as vinyl pyrrolidone, styrene, acryl amide or 
vinyl acetate may function as the comonomer module. The molecular weight 
of this polymer component is typically 10000 D to 500000 D. 
The metal oxide sol component is produced in a known way by sol/gel 
technologies from epoxidized metal oxide sols with an organic solvent 
(e.g. methanol, ethanol)--see U.S. Pat. No. 3,955,035, H. I. Schmidt et 
al. "Non-Cryst. Solids" 80 (1989) 557. Preferably hydrolysates of epoxy 
silanes are employed. Examples of hydrolyzable epoxy silanes are: 
glycidoxypropyltrimethoxysilane, 
glycidoxypropyltriethoxysilane, and 
(3,4 epoxycyclohexylethyltrimethoxysilane). 
Hydrolysis and condensation can be implemented in the presence of 
tetraalkoxysilanes, alkyltrialkoxysilanes or diakyldialkoxysilanes, as a 
result of which the epoxy content of the metal oxide sol can be 
specifically controlled. In accordance with the invention metal oxide 
mixtures may also be employed, whereby alkoxylates of boron, aluminum or 
titanium function as the comodules in producing the sol. 
In cross-linking the epoxy groups or in forming the gel (during drying) the 
epoxidized metal oxide sols react with the free carboxyl groups of the 
polymers and thus result in a water insoluble network of metal oxide and 
cationic polymer. To accelerate this reaction, epoxy catalysts can be 
additionally added to the composition. 
Examples of epoxy catalysts are triethylamine, dimethylbenzylamine and 
N-methylimidazol. Their concentration relative to the epoxidized metal 
oxide sol is preferably 1 to 5% by weight. 
The second water-soluble polymer component soluble is preferably a 
non-ionic or cationic polymer soluble in water. This can be formed, for 
example, by polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide, 
cationic polyacrylamide, cationic polyacrylester or combinations thereof. 
The recording material in accordance with the invention may furthermore 
contain in the inking layer means for controlling film homogenity and 
surface tension. For this purpose more particularly non-ionic or cationic 
tensides are suitable, preference being given especially to 
hexadecyltrimethyl ammonium bromide. 
The recording material in accordance with the invention may contain as the 
base a flexible base suitable for printing by an ink-jet printer. Paper or 
transparent plastic films are used preferably for this purpose. It is, 
however, also possible to use rigid or non-flexible materials such as 
plates of glass or plastics as the base. The base may be substantially 
flat or also in any shape, applying the inking layer being possible to any 
surfaces of the base. In conclusion, it is possible to produce the inking 
layer in such a thickness that a freely-carrying (unsupported) recording 
material is formed. 
Producing a recording material in accordance with the invention is done by 
applying a coating solution for the formation of an inking layer on the 
base. Formulating the coating solution is done by preparing a metal oxide 
sol in accordance with the composition as cited above and adding the 
polymer components. Formulating is done preferably in aqueous-organic 
solvents, e.g. in a mixture of water and ethanol. Applying the coating 
solution to the base is done by a pouring technique as is known, for 
example, from photochemical coating techniques. As an alternative the base 
may also be coated by dipping, spraying or some similar method of 
application. Subsequently the coating solution is gelled on the base, this 
procedure possibly being accelerated by applying heat. 
The recording material in accordance with the invention features the 
following advantages. The recording material contains a novel inking layer 
which is insoluble in water, forms no tacky surface in contact with 
moisture and features a practicable drying time. The inking layer is 
transparent and thus suitable for both paper and film base. The inking 
layer can be combined with known layers of conventional recording 
materials by employing the new inking layer as the cover layer. Following 
position-selective inking (pigment solution) the ink pigments are firmly 
anchored in the cross-linked polymer composition of the inking layer and 
are not bleached out by coming into contact with water. Due to this, using 
the recording material is not restricted to printing material for ink-jet 
printers, it instead also being suitable outdoors or in open air. There is 
no bleed of the ink droplets so that the recording material in accordance 
with the invention is suitable for recording techniques (printing 
processes) with high requirements on the resolution as in modern printing 
devices for producing overhead projector films or color prints of 
photographs. 
Embodiments

EXAMPLE 1 (COMATIVE EXAMPLE) 
With a 10% by weight solution of water and alcohol (40/60) a 7.8 .mu.m 
thick layer having the following composition: 
45% by weight gelatine (bone gelatine dissolved in alkaline) 
35% by weight polyvinylpyrrolidone (K 90) 
20% by weight epoxy-functional metal oxide sol, produced from 80% by weight 
tetraethoxysilane and 20% by weight glycidooxypropyl-trimethoxysilane 
is applied to a 100 .mu.m thick base of polyester in a known way by means 
of a ductor pourer. 
After drying the layer at 85.degree. C. the film is printed by means of an 
ink-jet printer, type HP Descjet 690C. To characterize the properties the 
optical density is established, contour acutance (Crispness) visually 
appreciated and both transparency and tack of the surface assessed. 
Furthermore, for testing its resistance to water the film is brought into 
contact with flowing water for 30 min. at 25.degree. C., after which the 
optical density and quality of the coating inspected. The results are as 
follows: 
______________________________________ 
Contour acutance good, after watering fuzzy 
Drying time 7.5 min 
Surface quality (85% rh): slightly tacky, heavy 
swelling in water contact 
Transparency clear film. 
______________________________________ 
opt. density 
D1 (before watering) 
D2 (after watering) 
______________________________________ 
(magenta) 1.9 1.3 
(cyan) 1.7 0.9 
(yellow) 0.95 0.6 
______________________________________ 
Coating not impervious to water. Pigment bleaches out and diffuses also in 
the coating. 
EXAMPLE 2 (COMATIVE EXAMPLE) 
Analogous to example 1 an 8.5 .mu.m thick coating having the following 
composition: 
35% by weight Na-polyacrylate 
59% by weight polyacylic acid (cross-linked in the presence of silanes as 
per EP 583 141) 
8% by weight metal oxide sol of tetraethoxysilane is applied. 
The results are as follows: 
______________________________________ 
Contour acutance: good, after watering fuzzy 
Drying time: 6.5 min 
Surface quality (85% rh): non-tacky, coating swells 
heavily in water contact 
Transparency clear film. 
______________________________________ 
opt. density 
D1 (before watering) 
D2 (after watering) 
______________________________________ 
(magenta) 1.1 1.1 
(cyan) 1.4 0.4 
(yellow) 0.6 0.3 
______________________________________ 
Coating not impervious to water. Pigment diffuses in coating and is 
bleached out considerably. 
EXAMPLE 3 
Analogous to example 1 an 11.5 .mu.m thick coating having the following 
composition: 
45% by weight coplymer of acrylic acid and methacryloxyethyl-trimethyl 
ammonium chloride (20/80), molecular weight 130000 D, 
45% by weight metal oxide sol, produced from 75% by weight 
tetraethoxysilane and 25% by weight glycidoxypropyltrimethoxysilane, and 
10% by weight polyvinylalcohol (fully saponified, molecular weight 95000 D) 
is applied. 
The results are as follows: 
______________________________________ 
Contour acutance: good, even after watering 
Drying time: 7.0 min 
Surface quality (85% rh): non-tacky, coating non-tacky, 
insoluble in water contact 
Transparency: clear film. 
______________________________________ 
opt. density 
D1 (before watering) 
D2 (after watering) 
______________________________________ 
(magenta) 1.9 1.85 
(cyan) 1.6 1.5 
(yellow) 0.9 0.9 
______________________________________ 
The coating is impervious to water. No appreciable bleaching of pigment in 
contact with water. Crisp images reattained after drying. 
EXAMPLE 4 
Analogous to example 1 an 12.5 .mu.m thick coating having the following 
composition: 
55% by weight mixed polymer of acrylic 
acid/ethylacrylate/methacryloxyethyl-trimethyl ammonium chloride 
(28/12/60), molecular weight 140000 D, 
35% by weight metal oxide sol of 50% by weight 
glycidoxypropyltriethoxysilane and 50% by weight tetraethoxysilane, and 
10% by weight polyvinylpyrrolidone (molecular weight 320000 D) 
is applied. 
The results are as follows: 
______________________________________ 
Contour acutance: 
good, even after watering crisp images 
Drying time: 7.0 min 
Surface quality (85% rh): non-tacky, clear, non-tacky 
coating in water contact 
Transparency: clear film. 
______________________________________ 
opt. density 
D1 (before watering) 
D2 (after watering) 
______________________________________ 
(magenta) 2.1 2.0 
(cyan) 1.8 1.7 
(yellow) 0.9 0.85 
______________________________________ 
The coating is impervious to water. No appreciable bleach-out of pigment 
when watered. Crisp images reattained after drying. 
EXAMPLE 5 
Analogous to example 1 a 10.5 .mu.m thick coating having the following 
composition: 
48.5% by weight coplymer of acrylic acid and acrylamidopropyl-trimethyl 
ammonium chloride (35/65) (molecular weight 195000 D), 
40% by weight metal oxide sol of 80% by weight tetraethoxysilane and 20% by 
weight glycidoxypropyltrimethoxysilane, 
10% by weight poly-methacrylamidopropyl-trimethyl ammonium chloride 
(molecular weight 85000 D), and 
1.5% by weight hexadecyltrimethylammonium bromide 
is applied. 
The results are as follows: 
______________________________________ 
Contour acutance: 
good, even after watering crisp images 
Drying time: 7.5 min 
Surface quality (85% rh): non-tacky, even in water 
contact 
Transparency: clear film. 
______________________________________ 
opt. density 
D1 (before watering) 
D2 (after watering) 
______________________________________ 
(magenta) 2.0 1.95 
(cyan) 1.9 1.8 
(yellow) 0.8 0.8 
______________________________________ 
The coating is impervious to water. No appreciable bleach-out of pigment 
when watered. Crisp images reattained after drying. 
As compared to conventional comparitive examples these examples exhibit 
high constant density even after water contact, dry, non-tacky surfaces 
and high transparency even after water contact and a repeat drying. The 
inking layer features a composition which is practically non-toxic.