GB2450165A

GB2450165A - Imaging Material

Info

Publication number: GB2450165A
Application number: GB0711710A
Authority: GB
Inventors: Jonathan James Osborn; Jayne Maura Woosey
Original assignee: Harman Technology Ltd
Current assignee: Harman Technology Ltd
Priority date: 2007-06-15
Filing date: 2007-06-15
Publication date: 2008-12-17
Anticipated expiration: 2027-06-15
Also published as: GB2450165B; GB0711710D0

Abstract

There is provided a glossy image receiving material suitable for recording using the ink jet printing process comprising: <UL ST=" Ò "> <LI> a supporting substrate comprising a baryta-coated paper base; <LI>on at least one side of the supporting substrate at least one porous ink-receptive recording layer comprising alumina pigment, polyvinyl alcohol, and boric acid or salt thereof; and <LI>an upper protective porous layer comprising cationic colloidal silica pigment with little or no binder.

Description

Imaging Material

Field of the Invention

The present invention relates to a glossy image receiving material suitable for recording using the ink jet printing process.

Background of the Invention

Ink jet recording is a non-impact printing method wherein droplets of a recording fluid, the ink, are formed by forcing the fluid through a tiny nozzle (or a series of nozzles) under computer control and deposited on a recording material such as paper. There are several classes of ink jet printer, for instance thermal drop-on-demand printers, piezo drop-on-demand printers, and continuous ink jet printers. Ink jet recording has undergone extensive development in recent years, and has found broad application as output for personal computers in the office and the home becau3c of its accessible price, low noise characteristic, capability of high speed printing, facility of multi-colour printing, reliability, and achievable image quality.

Inks for ink jet printers generally comprise: a colorant, which may be a dye, a pigment, or a coloured resin particle; and a carrier liquid, which typically is made up mainly of water, together with at least one water miscible organic cosolvent such as a polyhydric alcohol.

Frequently the ink also comprises other addenda such as one or more surfactants. By the term dye is meant a colorant which is present as a solution in the ink. Any suitable dye may be used, but anionic dyes such as acid dyes and direct dyes are commonly used in aqueous ink jet inks. By the term pigment is meant a colorant which is provided in an insoluble particulate state. Suitable pigments for ink jet inks are well known, and include so-called self dispersing pigments and conventional pigments stabilised by the presence of one or more dispersants. It is of course possible to use more than one colorant in the ink. It has become more conmion recently to use pigments as the colorants for ink jet inks instead of, or sometimes in addition to, dyes. Typically, in most commercial ink jet printers a set of at least four inks is provided comprising the three subtractive primary colours cyan, magenta, and yellow, together with a black ink.

Increasingly severe requirements are being set for the image receiving materials for use with the ink jet recording process. For instance, the material must be robust and resistant to mechanical damage during printing and display. Furthermore, the print produced by means of an ink jet process is required to have, for example, good water and smear resistance, high resolution, good colour density, sufficient ink gradation, and good light fastness. An additional feature of particular interest is compatibility of the recording material with a wide variety of printers employing both dyed and pigmented inks.

It has become common to provide ink jet image receiving materials comprising a suitable sheet-like supporting substrate having on at least one surface thereof at least one ink-receptive recording layer. Use of paper as supporting substrate for ink jet image receiving materials intended for viewing by reflection is well known. It is also known to employ coated paper, for instance polyethylene-coated paper and baryta-coated paper, as a supporting substrate for an ink jet image redèiving material.

Baiyta-coated paper is well known and has been in use for many years as supporting substrate in the conventional silver halide photographic industry. It comprises a paper substrate and a base layer comprising barium sulphate pigment and a binder, typically gelatin, together optionally with a hardener and other additives. There is especial interest in using baryta-coated paper as supporting substrate for ink receiving materials as it may provide prints that have image quality, appearance, and feel equivalent to that achieved by conventional photography.

In general, two types of ink-receptive recording layer are in use in ink jet image receiving systems: so-called swelling polymer types and so-called porous types. For many applications the porous types are preferred, especially when printing using modem high-speed ink jet printers, because prints on such materials are quickly dry to the touch after printing as the liquid phase of the ink absorbs very rapidly into the open pores, providing the pore volume and thickness of the coated layer are sufficient to contain the liquid ink. Porous ink jet image receiving materials may also provide excellent image quality, and also tend to have better compatibility with pigmented ink jet inks than swelling polymer type materials.

Typically, the ink-receptive recording layer of a porous type recording system comprises fine particles of one or more colourless filler or pigment in combination with a polymeric binder.

Typically the fine particles are particles of an inorganic pigment such as silica, alumina, or alumina hydrate, and the binder is polyvinyl alcohol. Commonly, there is also present a crosslinicing agent or hardener for the binder. Crosslinking allows for the modification of the physical properties of the layer, in particular in robustness and in resistance against physical damage especially when wet, and also improves printing properties. Further it is common to provide a cationic fixative for the dyes that are generally anionic dyes in aqueous ink jet inks. This cationic fixative may be a cationic additive such as a polyvalent metallic cation or a cationic polymer, or may take the form of a cationising treatment of the surface of the pigment particles.

Porous type ink jet image receiving materials on baryta-coated base are known. For example, ink jet image receiving materials comprising a baryta-coated base support and an image receiving layer comprising fine particles of alumina or alumina hydrate are disclosed by European Patent Application 1 236 582 A and by United States Patents 6,200,670, 6,502,935, and 6,696,118.

However there are disadvantages with these known materials. For instance it is difficult to achieve adequate robustness to handling in use, such as scuffing of the surface by contact with parts of the printing apparatus.

It is known that resistance to scuffing may be improved by use of a thin surface layer on the porous coating. For instance, European Patent Application 1 464 511 A discloses an ink jet recording sheet having a main pigment layer comprising amorphous silica, a cationic inducing compound, and a binder; and an upper layer comprising a spherical silica with little or no binder. Similarly, PCT WO 2006/119202 discloses a porous ink jet recording material wherein the main pigment layer comprises a fumed silica or alumina that has been treated with a silane coupling agent and the upper layer comprises and colloidal inorganic oxide.

However it is found that the cationic treatment of the pigment in such systems can give rise to poor rheological properties and unstable coating formulations, particularly in the presence of additional functional additives such as for example an Optical Brightening Agent (OBA) or a toning coloured pigment to control the appearance such as brightness and base tint of the material. On the other hand, the presence of these functional additives is desirable to equal the appearance of conventional photographic materials.

We have developed improved ink jet image receiving materials that are compatible with a variety of printers employing both dyed and pigmented inks, rapid to dry, and provide feel, appearance, and image quality equivalent to that achieved by conventional photography.

$iimmary of the Invention According to this invention there is provided a glossy image receiving material suitable for recording using the ink jet printing process comprising: * a supporting substrate comprising a bazyta-coated paper base; * on at least one side of the supporting substrate at least one porous ink-receptive recording layer comprising alumina pigment, polyvinyl alcohol, and boric acid or salt thereof, and * on top of the ink-receptive layer an upper protective porous layer comprising cationic colloidal silica pigment with little or no binder.

Detailed Description of the Invention

The baryta-coated paper supporting substrate for the image receiving materials of the invention is well known in the art, and comprises a paper substrate and a base layer comprising barium sulphate pigment and a gelatin binder, together with a hardener for the binder, for example an aldehyde hardener or chrome alum. The barium sulphate improves the opacity and whiteness of the print. The paper substrate may contain other additives as are known in the art, such as sizing agents, opacif'ing white fillers or pigments, and optical brightening agents. The ink receiving layer is coated on top of the baryta layer.

The thickness of the supporting substrate is not pat ticularly restricted, but may be up to 500 j.tm, especially between approximately 200.Lm and approximately 300.im including the baryta layer.

The pigment of the ink-receptive recording layer is alumina, that is to say aluminium oxide.

Preferably the alumina is a fumed aluminium oxide having a primary particle size of less than 50 nm, preferably between 10 and 50 nm, especially between 10 and 20 nm. The particles may be aggregated; average aggregate particle size is less than 500 nm, preferably between 100 and 500 nm, especially between 100 and 200 nrn. Fumed alumina in this size range suitable for use in ink jet receiving layers is commercially available.

The poly vinyl alcohol binder of the ink-receptive recording layer may be frilly saponified or partially saponified, but is prçferably at least 80% saponified, and most preferably at least 88% saponified. The molecular weight of the polyvinyl alcohol is not particularly restricted, but is typically greater than 100,000. Further, mixtures of two or more types of polyvinyl alcohol may be used in the ink-receptive recording layer.

It is normally preferred to minimise the proportion of binder in the ink-receptive recording layer to increase the speed of absorption of the ink and the quantity of ink that may be absorbed, but if insufficient binder is present the coated layer becomes fragile and powdery.

The pigment: binder ratio of the ink-receptive recording layer may be up to 10: 1 by dry weight, preferably between 4: 1 and 7: 1.

The boric acid or salt thereof in the ink-receptive recording layer is a cross-linking agent or hardener for the poly vinyl alcohol binder. By the term boric acid or salt thereof is meant boric acid; a suitable water soluble salt, for example sodium metaborate; or a condensed borate, for example sodium tetraborate. Boric acid is preferred. Hardening the binder improves the physical and printing properties of the material.

Herein, weight ratios of boric acid are expressed as weight of boric acid itself, and includes also an equivalent weight if a salt thereof is employed. The quantity of boric acid may be up to 15% by dry weight of the polyvinyl alcohol, preferably between 8% and 12% by dry weight or an equivalent weight if a salt thereof is employed.

The coated amount of the ink-receptive recording layer may be determined mainly according to the quantity of ink laid down by the printing apparatus in use. If the coating weight is too low the ink absorptivity of the recording layer is insufficient and the material is slow to dry, also leading to image problems such as coalescence, puddling, and blurring.

A suitable total dry coating weight of the ink-receptive layer is from approximately 10 gm2 to approximately 30 gm-2, preferably from approximately 20 gm-2 to approximately 30 gm-2.

The cationic colloidal silica pigment of the upper protective porous layer is not aggregated and preferably comprises substantially spherical silica having an average particle size between 30 nm and 90 nm, preferably between 40 nm and 80 nm.

The silica pigment may be cationised by treatment with a cationising substance, such as by forming a surface treatment with a polyvalent metallic salt such as aluminium chlorohydrate, by surface treatment of the pigment with a silane coupling agent, or by treatment with a cationic polymer. Cationic colloidal silica suitable for ink recording layers is commercially available. Preferably the silica is a spherical cationic colloidal silica of average particle size approximately 50 nm.

The upper protective porous layer comprises little or no binder, but preferably no binder is included in the formulation of this layer. Preferably the dry coating weight of the upper protective layer is from 0-1 gm-2 to 5 gm2, especially from 05 gm2 to 15 gm-2.

It is in general necessary that one pr more surfactants be present in the coating formulations for the materials of the invention to allow for smooth coating and evenness of the layers and to improve printing properties.

The surfactant used is not particularly limited as long as it is compatible with the other components of the assembly, but nonionic surface active agents are particularly preferred.

Examples of suitable surfactants include: alkylene oxide derivatives, for example acetylenic alcohol polyethylene glycol ethers, polyethylene glycol alkyl or alkylaryl ethers, polyethylene glycol esters, or polyethylene glycol! polypropylene glycol condensates; glycidol derivatives; and aliphatic esters of polyhydric alcohols or sucrose. Further, silicone surfactants such as polyether modified polydimethylsjloxane are also suitable.

Mixtures of two or more of the above mentioned surfactants may also be used. Such surfactants are well known in the art. Preferably the surfactant is a polyethylene glycol alkylaryl ether.

In addition to the components already mentioned, the ink-receptive recording layer may advantageously also contain further auxiliary agents as are known in the art, such as plasticisers, lubricants, dye fixatives, latexes, antistatic agents, toning agents, fungicides, dispersants, antifoams, stabilisers, biocides, antioxidants, ultraviolet absorbers, pH buffers, and optical brighteners. The recording layer may also comprise one or more additional hydrophilic binders compatible with the poly vinyl alcohol. Further, the p1-I of the layer formulations may be adjusted if necessary by suitable addition of acid or alkali.

According to one preferred embodiment of the invention, the formulation for the ink-receptive layer comprises at least one optical brightener or fluorescent whitening agent.

Optical brighteners increase the visual brightness of the material. The optical brightener is not particularly limited, but is preferably a stilbene type optical brightener, and most preferably a cationic type stilbene optical brightener complex as disclosed in United States Patents 6,426,382 and 7,019,134.

According to another preferred embodiment of the invention, the formulation for the ink-receptive layer comprises at least one toning agent. By toning agent is meant a colorant to control base tint, that is to say the visual hue of the unprinted material. In particular the material may be slightly bluer than neutral, described as cold toned, or may be slightly browner than neutral, described as warm toned. The toning agent or agents may be dyes or pigments, but pigments are preferred. The exact toning agents used depend on the desired visual appearance, but suitable cold-toning pigments include blue or violet pigments, especially copper phthalocyanines as blue pigments and triphenodioxazjnes as violet pigments. Suitable warm-toning pigments include many of the pigments listed in the Colour Index as yellow, orange, brown, or red pigments. It is of course possible to mix more than one pigment as toning agent. An especially preferred warm-toning agent comprises a combination of CI Pigment Yellow 83 and CI Pigment Red 112.

The upper protective layer may advantageously also contain additional components as are known in the art, such as plasticisers, lubricants, antistatic agents, antiblocking agents, fungicides, dispersants, antifoams, stabiljsers, biocides, antioxidants, ultraviolet absorbers, and pH buffers. Further, the pH of the layer formulation may be adjusted if necessary by suitable addition of acid or alkali.

In particular, the upper protective layer may comprise an antiblocking agent. By antiblocking agent is meant a particulate solid comprising particles which are sufficiently large that they protrude from the surface of the recording material and prevent intimate contact of sheets on stacking the material. A suitable average particle size for the antiblocking agent is from I p.m to 10 p.m, especially from 3 p.m to 5 jLm. Monodisperse polystyrene beads prepared according to the method disclosed in European Patent Application EP 0 341 200 A are especially preferred.

One of the advantages of the recording materials of the present invention is that the ink-receptive and upper protective layers may conveniently be provided for coating as aqueous formulations. Deionised water is commonly used. The formulations may be coated on to the substrate by any suitable coating means, but a slide bead coaler is particularly preferred at it permits simultaneous coating of the two layers of the materials of the invention, which is preferred from a manufacturing economic perspective. Such apparatus is well known in the imaging industry and is described in United States Patent Specification 2,761,791 and on pages 120 and 121 of the book Modern Coating and Diying Technology, edited by E.D.Cohen and E.B.Gutoff and published by VCH in 1992.

The back surface of the substrate may be left uncoated, may have a coating for lay-flat properties, or may be treated for anticurl properties to promote transport in the printing apparatus.

The materials of the invention provide the weight, visual appearance, and feel equivalent to conventional photographic materials. Furthermore, they provide gloss equivalent to conventional glossy photographic materials without the need for a mechanical process such as cast coating or calendering of the coated material. The gloss of the inventive materials is at least 40% measured at 60 , especially between 40% and 50%, measured at 60 .

Another advantage of the materials of the invention is that they provide good printing properties without requiring a high addition level of cationic additive in the ink receiving layer, and thus are compatible with variety of further components in this layer that would be unstable in the presence of a large amount of cationic additive.

The materials of the invention are suitable as ink jet image receiving materials for use with a variety of ink jet printers, for instance a thermal drop-on-demand printer, a piezo drop-on-demand printer, or a Continuous ink jet printer. The printer may be a desk top ink jet printer or a wide format ink jet printer. The materials are suitable for use with inks comprising dyes or pigments as colorants. Preferably the ink is an aqueous ink, that is to say an ink in which the carrier liquid is predominantly water, but may also comprise one or more water soluble organic cosolvents such as a polyhydric alcohol. The ink may also comprise other components that are commonly added to aqueous ink jet inks, such as surfactants, viscosity modifiers, metal-sequestering agents, and biocides. Such inks are well known in the art and are supplied for use with many commercially available ink jet printers.

Although the image receiving materials disclosed herein have been referred to primarily as being useful as receiving media for ink jet printers, they may also be used as printing media for other recording devices such as pen plotter assemblies.

The following examples will serve to illustrate the invention.

Exami,le I An image receiving material according to the invention was prepared as follows. A coating solution for a ink-receptive lower recording layer was prepared using the following components: Component -Quantity (grams) 1 1ater 7.5 LAlumina (30% suspension) 57 jçlyvinyl alcohol (10% solution) 342 jOBA (22% solution) 4.5 Boric acid (4% solution) 86 LSurfactant (3% solution) 025 LIcal 112 The alumina was Aerodisp' W630 from DegussaR fumed aluminium oxide having a primary particle size of 13 nm and average aggregate particle size of 140 nm. The polyvinyl alcohol was MowioVTM 40-88 that is 88% saponified. The surfactant was TritonR X-100.

The OBA was a stilbene type optical brightener available from Clariant as LeucophorM FTS, diluted to provide a 22% solution. The OBA, boric acid, and surfactant were added immediately before coating to give a formulation with a solids content of 21%. The weight ratio of alumina to polyvinyl alcohol is 5:1 by dry weight and of boric acid to polyvinyl alcohol is 994: 1.

A coating solution for the upper layer was prepared using the following components: [IComponent Quantity (grams) LWater 8275 -lycerol 46 urfactant (3% solution) 2S5 ationic colloidal silica 855 [jo1ystyrene antiblock 155 is Ltal -100 The surfactant was as above. The silica was Cartacoat K303 C cationic colloidal silica of average particle size 50 mn available from Clariant as a 30% dispersion. The antibiock was a 20% dispersion of spherical 4 tm polystyrene beads stabilised with Olinm lOG surfactant.

The coating formulations were coated simultaneously Onto a conventional baryta coated photographic paper base support of thickness 270 j.tm using a slide bead coater to give a dry coating weight of 28 gm2 for the ink-receptive layer and of I gm2 for the upper layer.

The coated product was compared with commercially available ILFORDR MultigradeRTM TV FB black and white photographic printing paper coated on a baryta base, unexposed and processed to reveal the base. The experimental ink receiving coating had a good photo-like appearance and feel.

The base tint of the material was measured with a GretagMacbethRTM SpecrolinoTM scanning reflectance spectrophotometer using D65 illuminant and 2 Standard Observer.

The results according to the CIELAB L* a* b* colorimetry system are shown in table I below. In this system L* is a measure of the brightness of the coating, the a* value is a measure of the colour along the green/red axis, with a negative value being greener, and the b* value is a measure of the colour along the blue/yellow axis, i.e. warm or cold toned, with a negative value being bluer or cold toned. A neutral tone has both a* and b* zero.

Table 1.

CIELAB colorimetiy values L* a* b* Example 1 9842 0l I -14 MG IV PB (Comparison) 9793 l6..3.34 It is seen that the figures for both materials are closely comparable. The inventive material is visually similar to the comparison. The a* and b* values for both are sufficiently close to zero that they are visually neutral in tone.

The gloss of the materials was measured using a Dr Lange' gloss meter at 20 , 60 , and 80 . The results are given in Table 2:

Table 2.

I Gloss (%) 1 20 60 80 Examp1e I l47 455 750 LMG IV FB (Comparison) 140 53.3 57.5 Visually, the coating has similar gloss to the comparison.

Test images and test charts comprising patches of various colours were printed on the inventive material with the following commercial ink jet printers: HP 7960, HPR B9180, HPR 8750, EpSORR R300, EPSOnR R800, Epson 1290, Epson' 1400, Epson 2100, EPSOflRTM 2400, EpsonRT 3800, Epson' 4000, Epson 4800, EpsonR 7600, Canon'M Pixma' iP 6220D, Canon' S900, and Canon 19950. The material printed well to give good quality images with all printers, thus showing the compatibility of the inventive material for use with a variety of printers using both dyed and pigmented inks.

The test chart printed with the HPR 7960 printer that uses dyed inks was exposed to light for 120 hours in a Xenotest apparatus. The density of yellow, magenta, and cyan test patches before and after exposure was measured, and the percentage loss calculated. The results are shown in table 3 below, compared with the figures for a commercial glossy ink receiving material on resin-coated base.

Table 3.

_________ Density -L Cyan Magenta Yellow I Example I (Invention) unexposed 1 23 -1 56 I 36 jxamp1e I after exposure 078 -128 129 loss -368 18*4 51 LComparison unexposed 121 174 162 Lcomparison after exposure 062 096 -l53 [ 483 451 5.5 It is seen that the dyes printed on the inventive material are more stable than those on the comparison commercial material, showing the advantage of the invention.

xample 2 An image receiving material according to the invention was prepared following example I except that the OI3A was omitted from the formulation for the lower layer. The material was coated as in example I and printed on a variety of printers. The material printed well on all printers tested.

Example 3

An image receiving material according to the invention was prepared comprising an ink-receptive recording layer formulated as in example I except that the OBA solution was at 33% instead of 22%. A formulation for the upper layer was prepared as in example 1, and the formulations were coated simultaneously on the same baryta coated photographic paper base support as in example 1 using a slide bead coating apparatus to provide a dry coating weight ink-receptive recording layer of 28 gm2 and for the upper layer of I gm2.

The base tint of the material was measured as in example 1, and the results are given in Table 4 below. The coating is visually neutral, but is slightly brighter and bluer than that of example 1 because of the increased addition of OBA.

Table 4.

L CIELAB colonmetry values [ L* a* b* LExample 3 9851 0-57 -284 Bxample4 A coating solution for an ink-receptive lower recording layer was prepared using the following components: Component I Quantity (gram Water 7.7 Alumina (30% suspension) 588 Polyvinyl alcohol (10% solution) 35.3 Toning pigment I Boric acid (4% solution) 8-9 Surfactant (3% solution) 025 Total -112 The toning pigment is a 1% dispersion of an orange pigment mixture comprising commercial samples of Colanyl Yellow HRD and ColanyI' Red FGRX. The other components are as in example I. The toning pigment, boric acid, and surfactant were added immediately before coating.

An image receiving material according to the invention was coated on a conventional baiyta coated photographic paper base support of thickness 270 tm using a slide bead coating apparatus as in example I provide to provide a dry coating weight for the ink-receptive recording layer of 28 gm-2, and for the upper layer formulated as in example 1 of 1 gm2 The material was compared with commercially available ILFORDR MultigradeM FB Warmtone black and white photographic printing paper coated on a baryta base, unexposed and processed to reveal the base. The experimental ink receiving coating had a good photo-like appearance and feel, and similar slightly warm visual base tint to the comparison. The base tint of the material was measured as in example 1, and the results are given in Table 5 below. The small positive b* value shows the slightly warm base tint.

Table 5.

L CIELAB colorimetry values L L* a* b* [Example 4 9769 067 065 Exami,le 5 The coatings of example 4 were repeated, except that the addition of the toning pigment was varied from 0% to 2% of the formulation for the lower layer. Each formulation with a different addition of pigment was coated with an upper layer as in example 4, and the base tint was measured. The results are shown in figure 1. The straight line relationship between the a* and b* values and the addition level shows the compatibility of the pigment with the other formulation components. Is

Claims

Claims I. A glossy image receiving material suitable for recording

using the ink jet printing process comprising: * a supporting substrate comprising a baryta-coated paper base; * on at least one side of the supporting substrate at least one porous ink-receptive recording layer comprising alumina pigment, polyvinyl alcohol, and boric acid or salt thereof, and * an upper protective porous layer comprising a cationic colloidal silica pigment with little or no binder.
2. An image receiving material according to claim 1 wherein the alumina pigment in the ink-receptive recording layer comprises fumed aluminium oxide having a primary particle size between 10 and 50 nm, and an average aggregate particle size between 100 and 500 nm.
3. An image receiving material according to either of claims I or 2 wherein the pigment: binder ratio of the ink-receptive recording layer is between 4: 1 and 7: 1 by dry weight, and the quantity of boric acid is between 8% and 12% of the polyvinyl alcohol by dry weight.
4. An image receiving material according to any of claims 1 -3 wherein the cationic colloidal silica pigment of the upper protective porous layer is not aggregated and comprises spherical particles of average particle size between 30 nm and 90 nm.
5. An image receiving material according to any of claims I -4 wherein the ink-receptive layer additionally comprises at least one stilbene type optical brightener.
6. An image receiving material according to any of claims I -5 wherein the ink-receptive layer additionally comprises at least one toning agent.
7. An image receiving material according to claim 6 wherein the toning agent is a warm-toning agent comprising a combination of CI Pigment Yellow 83 and CI Pigment Red 112.
8. An image receiving material according to any of claims I -7 wherein the upper protective layer additionally comprises an antiblocking agent.
9. An image receiving material according to claim 8 wherein the antiblocking agent comprises monodisperse polystyrene particles having an average particle size from ljimtol0j.tm.
10. An image receiving material according to any of claims I -9 wherein the gloss is at least 40% measured at 60 .