EP1228889A2

EP1228889A2 - Ink-receiving material and recording method

Info

Publication number: EP1228889A2
Application number: EP02002349A
Authority: EP
Inventors: Anthony Martin Lannon; Jeffrey Ronald King; David Rowland; Karen Taylor
Original assignee: Ilford Imaging Switzerland GmbH; Ilford Imaging UK Ltd
Current assignee: Ilford Imaging Switzerland GmbH
Priority date: 2001-02-02
Filing date: 2002-01-31
Publication date: 2002-08-07
Anticipated expiration: 2022-01-31
Also published as: GB0102646D0; DE60206305T2; EP1228889A3; DE60206305D1; GB2371769A; EP1228889B1

Abstract

There is provided a recording material comprising in order:-

1) a sheet-like paper substrate;

2) at least one hydrophobic barrier layer;

3) at least one ink-receptive layer;

4) at least one porous sealing layer which comprises a dispersion of a particulate polymer characterised by a film forming temperature of between 60°C and 140°C and an average particle size between about 1 µm and about 50 µm together with at least one water-soluble polymer binder.

There is also provided a method wherein an image printed with the ink jet printing process on the recording materials of the invention is heated after printing to seal the porous sealing layer by partly melting and softening the particulate polymer dispersion sufficiently for it to form a film to provide a image protecting coating.

Description

Field of the Invention

The present invention relates to a recording material and to a method of treatment for images produced therewith. It particularly relates to a recording material for the ink jet printing process.

Background of the Invention

Ink jet recording is a non-impact method that in response to a digital signal produces droplets of ink that are deposited on a substrate such as paper or transparent film. There are several classes of ink jet printer, for instance piezoelectric and thermal drop on demand printers and continuous ink jet printers. The ink jet process is now a widely used printing process since it can be carried out using relatively cheap and reliable printers without noise and with high quality, in particular in the case of colour printing, and has found broad application as output for personal computers in the office and the home. With increasing improvement in the availability and mode of operation of ink jet printers there is great interest in using the ink jet process in many imaging and display applications and as an alternative to conventional photographic imaging and printing. Consequently, increasingly severe requirements are being set for the recording materials and for the prints produced. The recording produced by means of an ink jet processes is required to have, for example, good water and smear resistance, high resolution, high colour density, sufficient ink gradation, and good light fastness. There is also interest in providing prints with a glossy image surface. On the other hand there is great interest in achieving high image quality from cheap recording materials rather than by using expensive materials.
However the cheapest recording materials, such as so-called plain paper, generally provide poor prints from ink jet printers, particularly those using mainly aqueous inks, due to problems such as bleeding, feathering, and cockling. Consequently it has become common to provide recording materials comprising a substrate such as plain paper and at least one ink-receptive recording layer arranged thereon. The recording layer frequently consists of a mixture of a water-accepting binder and a pigment or filler. The composition of the ink receiving layer is arranged such that the ink droplets sprayed on to the recording material during the image forming process are rapidly absorbed in the ink receiving layer without excessive lateral flow, so that sharp image edges free of bleeding and feathering can be obtained. The colorant from the inks must also rapidly be fixed, preferably in a thin portion of the ink receiving layer, in order to provide images of adequate contrast, clean colour tints, and high optical density. Consequently the image receiving layer commonly may contain cationic additives in order to bind the dyes from the inks, which are generally anionic. Typical cationic additives are quaternary ammonium compounds and polymers or copolymers which bear quaternary ammonium groups.
Such ink jet recording papers generally have a low surface gloss and are adequate for printing text. However they can still show deficiencies when printing images. For instance the low gloss is not liked as the appearance is unattractive when compared with conventional glossy photographic images. Furthermore defects such as cockling can still be a problem due to the greater quantity of ink laid down, particularly when printing a multi-colour image in which very dark or dense tints are to be reproduced. When paper based receiving materials are used, cockling arises because the liquid ink medium penetrates into the paper support via the ink receiving layer, and here it is absorbed by the paper fibres so that the latter swell and the paper bulges locally. This may cause the prints to jam in the printer and they may even bulge sufficiently to contact the printing head during printing. Moreover the bulges remain even after the print is dry because the paper fibres do not shrink to their original dimension, giving rise to an unattractive poor quality final print.
It is known that the problem of cockling can to a large extent be overcome by interposing between the paper base and the ink receiving layer a so-called barrier layer which is a layer which is coherent and hydrophobic such that transfer of the aqueous ink medium into the paper is sufficiently hindered. For instance United States Patent Specification 5,141,599 discloses an image receiving material for ink jet printing wherein the substrate is a polyolefin coated paper base, and European Patent Application 0 893 271 A discloses an image receiving paper suitable for printing with aqueous ink jet inks, comprising a paper support provided on at least one side with a water-repellent barrier layer and an ink receiving layer or set of ink receiving layers.
It is also known to coat between the paper base and the barrier layer a so-called precoat or primer layer which is a thin layer comprising a binder and a pigment or filler. The primer layer aids adhesion of the barrier layer, and incorporation of the white pigment in the primer layer also improves the whiteness and opacity of the base. The primer also improves the smoothness of the material. For instance United States Patent Specifications 5,670,242, 5,741,584, 5,952,051, and 6,096,157 disclose a cast coated paper support for ink jet receiving materials comprising a base paper, an undercoating layer comprising a pigment and an adhesive, and an overcoating layer comprising a thermoplastic polymer. The wet-coated surface is then pressed against a heated metal drum having a highly polished mirror-finished surface to provide a cast coated paper of high surface gloss and good surface smoothness after drying the coated surface. It is also known to produce similar materials by calendering or super calendering to control the flatness and smoothness of the paper.
However prints on such materials are still susceptible to staining and are poorly robust to handling and scratching, particularly when wet since the binder components in the ink-receptive layer are normally water soluble or water swellable. It is known to improve the robustness of printed images by lamination or encapsulation. By lamination is meant the combination of a printed image with a transparent overlay, this combination usually being accomplished with an adhesive activated by heat, pressure, or both. The overlay acts as a physical protection for the image and completely seals it from ingress of water. By encapsulation is meant the combination of a printed image layer between two laminating sheets, that on the image surface being transparent, the combination being accomplished with an adhesive activated by heat, pressure, or both. Encapsulation is most effective if the laminating sheets extend beyond the printed image and are bonded to each other at the extremities, thus preventing ingress of water through exposed edges of the image. Highly glossy and robust images may be produced by suitable choice of the laminating sheets.
However lamination and encapsulation are both expensive because additional materials are required together with additional handling and equipment. Thus there is still a need for an ink jet printing method using a simple and cheap receiving medium but which can provide robust good quality images. There is a particular need for such a method which will additionally provide prints of good gloss. We have devised a suitable medium and method.

Summary of the Invention

It is therefore the object of the present invention to provide a recording material and method which provides water-resistant images of good quality and stability. This object is achieved by providing a recording material comprising in order:-
1) a sheet-like paper substrate;
2) at least one hydrophobic barrier layer;
3) at least one ink-receptive layer;
4) at least one porous sealing layer which comprises a dispersion of a particulate polymer characterised by a film forming temperature of between 60° and 140° and an average particle size between about 1 µm and about 50 µm together with at least one water-soluble polymer binder.
The paper substrate to be used in the present invention may be any conventional paper base, for example, paper produced by various apparatus such as a Fourdrinier paper machine, a cylinder paper machine, or a twin wire paper machine from a wood pulp including, for example, a chemical pulp, a mechanical pulp, or a waste paper pulp. The paper may be manufactured from a pulp comprising in addition optionally at least one of various conventional additives as are known in the art, for example including a filler or pigment, a binder, a sizing agent, a fixing agent, a yield-improving agent, a cationic agent and a paper strength- increasing agent. The filler content in the paper is preferably not more than 25% by weight, based on dry matter. Suitable fillers include, for example, starch or an inorganic pigment such as calcium carbonate. The paper may optionally have internal and/or surface sizing with known sizes. A suitable paper substrate material is paper having a basis weight of from 40 to 500 gm^-2, preferably from 80 to 250 gm^-2, most preferably from 100 to 200 gm^-2. A suitable paper is white bond paper.
Other additives may be present in the paper base as the case requires such as a wet strength agent, a dry strength agent, a foam supressant, a defoaming agent, a biocide, or other functional additives useful in the manufacture of coating basepapers known to those skilled in the art.
The hydrophobic barrier layer may comprise almost any water repellent resin polymer. Preferably the resin is a polymer of an ethylenically unsaturated monomer, i.e., a monomer having an ethylenically unsaturated bond. Examples of the ethylenically unsaturated monomer giving the polymer include acrylates having a C₁-C₁₈ alkyl group, such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, 2-hydroxyethyl acrylate, and glycidyl acrylate; methacrylates having a C₁ -C₁₈ alkyl group, such as methyl methacrylate, ethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and glycidyl methacrylate; and other ethylenically unsaturated monomers, such as ethylene, styrene, α-methylstyrene, vinyltoluene, acrylonitrile, vinyl chloride, vinylidene chloride, vinyl acetate, vinyl propionate, acrylamide, N-methylolacrylamide, ethylene and butadiene. The polymer may be a copolymer of two or more ethylenically unsaturated monomers. Alternatively the resin polymer may be a polyurethane. The resin polymer of the barrier layer may preferably have a glass transition point of at least 40° C, more preferably approximately 50° C.
The barrier layer may additionally comprise a proportion of between about 5% and about 60% of the dry weight of the total barrier coating formulation of an inorganic filler. Suitable fillers for the barrier layer include any inorganic pigment having a plate like structure suitable for the formation of coherent barrier layers as known to those skilled in the art, for example kaolin, talc, or calcined clay. The polymer of the barrier layer may optionally also comprise other additives such as, for example, a UV absorber, a light stabiliser such as a hindered amine, a optical brightening agent, or a tinting agent.
The coating composition for the barrier layer may generally be formulated as an aqueous coating composition. Preferably the resin polymer of the barrier layer is provided in the form of a latex of a film-forming polymer comprising fine particles of the polymer prepared by emulsion polymerisation of suitable monomers suspended in an aqueous carrier in the presence of surfactants and initiators. The coating composition for the barrier layer may be applied by any suitable coating means, such as a blade coater, an air knife coater, a roll coater, a brush coater, a bar coater, or a gravure coater, and is allowed to form a film during the drying process. The dry coating weight of the hydrophobic barrier layer may be between about 4 and about 20 gm^-2, preferably between about 5 and about 10 gm^-2.
Further, a calendering apparatus may be employed to control the flatness of the base paper after coating the barrier layer.
The ink-receptive layer may be any of the ink receiving layers known in the art. For instance the ink receiving layer may comprise one or more water-soluble or swellable binders, optionally in combination with one or more absorbent filler or pigment, and further optionally in combination with one or more cationogenic substance. Suitable binders include poly (vinyl alcohol) and copolymers and derivatives thereof; carbohydrates such as tragacanth gum, sodium alginate, or water-soluble starch derivatives; water-soluble cellulose derivatives such as hydroxyethyl cellulose, methyl hydroxypropyl cellulose, or carboxymethyl cellulose; polyalkylene oxides such as polyethylene oxide and polypropylene oxide; water-soluble acrylate, methacrylate, or maleate polymers and copolymers and derivatives thereof; poly (vinyl pyrrolidone) and copolymers and derivatives thereof; gelatin, casein, and mixtures of such binders. Suitable fillers include clay, kaolin, talc, silica, calcium carbonate, diatomaceous earth, barium sulphate, titanium dioxide, aluminium oxide, zinc oxide, porous boehmite, synthetic fillers, and mixtures of two or more of the above fillers. A preferred filler is synthetic amorphous silica. Suitable cationogenic substances include quaternary ammonium and phosphonium polymers; basic polymers such as polyethyleneimine or polymers and copolymers comprising monomers such as vinyl pyridine, vinyl imidazole, and amine containing (meth)acrylates; quaternised reaction products from such basic polymers; or a reaction product of a low molecular weight polyfunctional amine with a compound polyfunctional to amino groups such as epichlorohydrin. The cationogenic substances best known for this purpose are polymeric quaternary ammonium compounds. The coated amount of the ink-receptive layer or layers may be determined by the printing apparatus, the quantity of ink to be printed, and the components used. A suitable dry coating weight for the ink-receptive layer is from about 5 gm^-2 to about 50 gm^-2.
One preferred ink-receptive system comprises a combination of a binder, an inorganic pigment, and a cationogenic polymer. A hydrophilic acrylate binder with a porous inorganic pigment is particularly preferred, such as porous non-crystalline synthetic silica, porous magnesium carbonate, porous boehmite, or porous alumina. Porous synthetic non-crystalline silica having a large pore volume is especially preferred. A preferred cationogenic polymer is a copolymer of vinyl imidazole with vinyl pyrrolidone. A preferred dry coating weight for an ink-receptive layer comprising a combination of a binder, an inorganic pigment, and a cationogenic polymer is from about 20 gm^-2 to about 40 gm^-2.
Furthermore the ink-receptive layer may comprise two or more layers. In an ink-receptive system comprising two or more layers each of the layers may comprise the components hereinbefore described. A preferred ink-receptive system consisting of two layers comprises a lower layer consisting of gelatin and an upper layer comprising a combination of gelatin and a water soluble or water swellable cellulose derivative. Suitable cellulose derivatives are hydroxyethyl cellulose, methyl hydroxypropyl cellulose, or carboxymethyl cellulose, of which methyl hydroxypropyl cellulose is preferred. A preferred total dry coating weight for an ink-receptive system consisting of two or more layers is from about 5 gm^-2 to about 15 gm^-2.
In addition to the components already mentioned, the ink-receptive layer or layers may contain further auxiliary agents as are known in the art, such as, for example, surfactants, cross linking agents, fungicides, lubricants, plasticisers, dispersants, antifoams, ultraviolet absorbers, and optical brighteners.
The particulate polymer dispersion provided in the porous sealing layer may comprise any film-forming thermoplastics dispersion, for example dispersions of polyurethane, low density polyethylene, high density polyethylene, polypropylene, polyvinyl acetate, polyvinyl acetate copolymers, styrene/butadiene copolymers, styrene/butadiene/acrylonitrile terpolymers, styrene/(meth)acrylate copolymers, (meth)acrylic polymers, ethylene/(meth) acrylic acid copolymers, ethylene/vinyl chloride copolymers, ethylene/(meth) acrylate/maleic terpolymers, polyamides, and mixtures thereof. A preferable size for the particulate polymer is between about 5 µm and about 20 µm. The particulate polymer should have a melt flow index of at least 5, preferably between about 10 and about 100. A particularly suitable particulate polymer comprises low density polyethylene microspheres having an average diameter of about 12 µm and a melt flow index of 75. Another particularly suitable particulate polymer comprises microspheres of a 7% acrylic acid/ polyethylene copolymer having an average diameter of about 10 µm and a melt flow index of 9. Another suitable particulate polymer comprises low density polyethylene particles of random shape and a particle size of about 13 µm and a melt flow index of 70. These polymers have melting points of 105-107°C.
The polymer of the film forming dispersion may optionally contain other additives such as, for example, UV absorbers, light stabilisers such as hindered amines, optical brightening agents, or tinting agents.
The other component of the porous sealing layer is a film-forming water soluble binder. All water-soluble polymers whose use as binders is known may in principle be used, and suitable examples include poly (vinyl alcohol) and copolymers thereof; carbohydrates such as tragacanth gum, sodium alginate, or water-soluble starch derivatives; water-soluble cellulose derivatives such as hydroxyethyl cellulose or carboxymethyl cellulose; water-soluble acrylate polymers containing hydroxyl groups and copolymers thereof; poly (vinyl pyrrolidone) and copolymers thereof; gelatin, casein, and mixtures of such binders. A preferred hydrophilic binder is poly (vinyl alcohol) which has a degree of hydrolysis of at least 85%. A particularly suitable binder is poly (vinyl alcohol) which has a degree of hydrolysis of between about 98% and about 99%.
The dry coating weight of the porous sealing layer may be between about 3 gm^-2 and about 50 gm^-2. A preferred dry coating weight is between about 8 gm^-2 and about 40 gm^-2, most preferably between about 15 gm^-2 and about 35 gm^-2. Depending on the use of the recording material, the ratio of the particulate polymer dispersion to the water soluble binder in the porous recording layer may be varied in the range from about 15:1 to about 1:1, with a ratio between approximately 5:1 and approximately 10:1 being preferred. This ratio and the overall coating weight can be used to adjust the ease of coating, the image quality of the final print, and resistance to scratching, abrasion, and water.
In addition to the components already mentioned, the sealing layer may contain further auxiliary agents as are known in the art, such as, for example, surfactants, cross linking agents, anti static agents, dye fixing agents, fungicides, inorganic pigments, lubricants, dispersants, antifoams, ultraviolet absorbers, and optical brighteners.
Optionally there may also be present additional layers in the assembly. Specifically, there may be present a primer layer comprising a white pigment or filler between the paper base and the hydrophobic barrier layer or between the hydrophobic barrier layer and the ink receiving layer. Suitable white pigments include starch and inorganic pigments such as light calcium carbonate, heavy calcium carbonate, kaolin, talc, calcium sulphate, barium sulphate, titanium dioxide, zinc oxide, zinc sulphide, zinc carbonate, satin white, aluminium silicate, diatomaceous earth, calcium silicate, magnesium silicate, synthetic non-crystalline silica, colloidal silica, colloidal alumina, pseudo boehmite, aluminium hydroxide, alumina, lithopone, hydrolysed halloysite, montmorillonite, magnesium carbonate, basic magnesium carbonate, magnesium hydroxide, and zeolite and clay-based pigments. It is also possible to use mixtures of these pigments. Preferably the pigment is calcium carbonate.
The primer layer may also comprise a binder or adhesive. The binder may be any film-forming polymer. Preferably the binder is a water dispersible latex binder. Suitable examples include styrene/butadiene copolymers and styrene/acrylic copolymers. Suitable water soluble binders include poly (vinyl alcohol), copolymers of poly (vinyl alcohol); carbohydrates such as tragacanth gum, starch, modified starch, and water-soluble starch derivatives; proteins, such as gelatin, casein, soybean protein and synthetic protein; water-soluble cellulose derivatives such as hydroxyethyl cellulose or carboxymethyl cellulose; water-soluble acrylate and methacrylate polymers and copolymers; poly (vinyl pyrrolidone); and mixtures of such binders. A particularly suitable hydrophilic binder is poly (vinyl alcohol). The primer layer may also advantageously comprise one or more dispersants. The dry coating weight of the primer layer may be between 2 gm^-2 and 50 gm^-2, preferably between about 5 gm^-2 and about 20 gm^-2, and most preferably between about 15 gm^-2 and about 20 gm^-2.
In addition to the components already mentioned, the primer layer may contain further auxiliary agents as are known in the art, such as, for example, a wetting agent, a defoaming agent, a cross linking agent, a cationic polymer, a biocide, an anti static agent, an optical brightening agent, or a thickening agent.
The back surface of the paper may be left uncoated or may have a coating for lay-flat properties, for example comprising polyvinyl chloride or starch. Substances such as lubricants, which promote paper transport in the printing apparatus, may be added to the back layer. Alternatively the back of the paper may be provided with the barrier layer like the front, or may optionally be provided with both the barrier layer and the primer layer, and may additionally be provided with the ink-receptive layer and the sealing layer like the front. As a further alternative the back surface of the paper may be coated with an adhesive and the adhesive may be protected with a release sheet. The release sheet is releasably adhered to the rest of the material, and is selected on such a basis that the release sheet has an adhesive force sufficiently strong not to be peeled during transportation in an ink jet recording apparatus or during heating but weak enough to peel easily when it is desired to attach the printed image to a suitable surface. Suitable materials for a release sheet include wood free paper, kraft paper, glassine paper, impregnated paper, or a plastic film such as a polyester film or a polyamide film which may be coated with a silicone resin or ptfe as a release agent.
Suitable adhesives include solvent type and aqueous type adhesives. Preferably the adhesive is an organic solvent type adhesive such as a rubber type adhesive or an acrylic resin type adhesive. The main material of the rubber type adhesive is natural rubber or styrene-butadiene rubber. To the natural rubber, a resin or a plasticiser may be incorporated, and a suitable solvent for coating such as n-hexane. Further, a pigment such as silica, kaolin, clay, calcium carbonate, aluminium hydroxide, zinc oxide, titanium dioxide, melamine resin particles or starch particles, may be incorporated to the above material. Depending upon the particular purpose for which the recording material is employed other additives may be incorporated in the adhesive layer including a water soluble polymer, a petroleum type resin, a paraffin wax, a fatty acid or its derivative, a higher alcohol, a metal soap, or a silicone as well as an antistatic agent, a thickener, a dispersant, a preservative, an antioxidant or a defoaming agent.
In general the whiteness of the material should be as high as possible, and it may therefore be advantageous to include components such as optical brightening agents, dyes, or pigments in the paper base or in one of the layers coated thereon to improve the brightness and whiteness of the material. However the invention may also be used with coloured or tinted papers.
The recording materials of the invention are particularly suitable for use in a printing process wherein the printed image is heated after printing to seal the sealing layer by melting or partially melting and softening the particulate polymer dispersion sufficiently for it to form a film to provide a robust image protecting coating.
Therefore according to this aspect of this invention, the printed image is heated after printing to seal the sealing layer. The heating process may use any convenient method, such as direct contact with a heated surface, heated air, or infra red or microwave radiation. Alternatively the print may be heated under pressure by passing it through a nip between a pair of heated rollers. The recording layer may be heated at temperatures between about 80°C and about 160°C, preferably between about 100°C and about 120°C.
It is important that the other components of the assembly are not affected by this heating process. One of the advantages of the preferred particulate polymers of the sealing layers of the invention is that the softening points are relatively low and thus the temperature and time needed to seal them are minimised.
According to another aspect of the invention, the printed image is heated under pressure with the image surface in contact with a second, inert sheet which is held against the image protective layer of the material. The inert sheet does not adhere to the material, but protects it from the means used to apply the pressure. Suitable inert sheets include polyester films, polyamide films, and casting papers. The inert sheet may be treated with silicones or ptfe to enhance the release properties. Furthermore a suitable choice of the inert sheet may be used to produce a desired appearance to the final image such as the use of a smooth inert sheet which will impart a high gloss to the image or a textured sheet which will produce a textured finish.
Preferably according to this aspect of this invention, the printed image is heated by a device which comprises a means of heating and pressing together the image and the cover sheet by passing them through a nip between a pair of heated rollers. Devices of this general type are in wide commercial use as laminators, which are normally used for the lamination of printed images.
It is found that images produced on the materials of the invention become significantly brighter and denser in appearance after the image has been heated and sealed. Hitherto it has been difficult to achieve adequate brightness and density of ink jet prints to compete with photographic printing quality without so increasing the ink load that the resulting prints are slow to dry and show defects such as puddling, coalescence, and incomplete absorption of the ink. Therefore the materials and method of the invention are particularly useful in so called photofinishing applications used for providing the output from imaging devices. After printing and sealing the final image has a pleasing appearance and feel, and may be provided with a glossy or other desired texture and used as an alternative to conventional photographic prints.
Many types of barrier coated paper are readily available and in wide commercial use. One of the advantages of the present invention is that the ink-receptive layer and sealing layer may be produced as aqueous formulations and coated on to a commercially available barrier coated paper by any suitable coating means, such as a slide bead coater, a curtain coater, a blade coater, an air knife coater, or a bar coater. In addition, the ink-receptive layer or layers can in principle be applied together with the porous sealing layer to the paper support in one machine operation, this being favourable for considerations of cost. Thus a high quality final image is easily and cheaply produced by the printing and heat treatment method of the invention.
The recording materials of the invention are particularly suitable for use with the ink jet printing process. Therefore according to this aspect of the invention there is provided an ink-jet printing process comprising ejecting inks from an ink-jet printing apparatus to print on a recording material, wherein the recording material described above is used as said recording material, and then heating the recording material to seal the sealing layer. Any convenient ink jet printer may be used for printing on the materials of the invention, for example a continuous printer or a piezoelectric or thermal drop-on-demand printer. No particular limitation is imposed on the inks used, and suitable jetting inks include aqueous inks and those based on organic solvents such as 2-butanone (MEK), ester solvents, and mineral oils. Suitable colorants for these inks include dyes or pigments. Preferred inks for the invention are aqueous inks.
The recording materials and method of the invention may also be used with other printing methods as are known in the art, or as writing or drawing materials for use with felt tipped pens and the like.
The following examples will serve to illustrate the invention.

Example 1

A recording material according to the invention was prepared having the following layers:-
1) A back coat of oxidised potato starch having a dry coating weight of 0·5 gm^-2;
2) A paper base of substance 141 gm^-2;
3) A primer layer having a dry coating weight of 16 gm^-2;
4) A barrier layer having a dry coating weight of 7 gm^-2;
5) A first ink-receptive layer having a dry coating weight of 3·2 gm^-2;
6) A second ink-receptive layer having a dry coating weight of 1·5 gm^-2;
7) A third ink-receptive layer having a dry coating weight of 1·5 gm^-2;
8) A porous sealing layer having a dry coating weight of 36·75 gm^-2.
The paper base was a prepared from white, bleached pulp, and also comprised a calcium carbonate filler, an alkaline sizing agent, starch, and an optical brightener.
The primer layer was composed of china clay and calcium carbonate pigments stabilised by a polyacrylate dispersant, carboxymethyl cellulose, and a styrene/butadiene latex binder, and also comprised calcium stearate, a melamine-formaldehyde resin, and a silicone based antifoaming agent.
The barrier layer was composed of a blended styrene acrylate based copolymer including talc as a filler available under the trade name Proman MR90 from Proman Chemicals.
The substrate comprising the back coat, paper, primer, and barrier layers was supercalendered before the ink-receptive layers were applied.
The first ink-receptive layer was coated from a formulation comprising the following components, with all parts given by weight:-

Component Weight %

Deionised water 84·04

Deionised ossein gelatin 12

4% sodium hydroxide solution 3·2

Glycerol 0·16

Surfactant A 0·6

Surfactant A was Olin 10G commercially available from Olin Chemicals.

The second ink-receptive layer was coated from a formulation composed of the following components, with all parts given by weight:-

Component	Weight %
Deionised water	90
Deionised ossein gelatin	2·65
4% sodium hydroxide solution	0·9
Surfactant B	1·2
Surfactant C	0·7
Methyl hydroxypropyl cellulose	2·65
Cross linking agent	1·9

Surfactant B was a 3% solution of an alkyl phenol ethoxylate (average 9 to 10 moles ethylene oxide) commercially available under the trade name Triton X-100 from Union Carbide Chemicals and Plastics Company Inc. Surfactant C was a 5% solution of a fluorinated surfactant commercially available under the trade name Lodyne S-107 from Ciba. The cross linking agent was a hardener comprising a 1% aqueous solution of 1-dimethylcarbamoyl-4-(2-sulphoethyl) pyridinium inner salt.

The third ink-receptive layer was coated from a formulation composed of the following components, with all parts given by weight:-

Component Weight %

Deionised water 91·8

Deionised ossein gelatin 2·7

4% sodium hydroxide solution 0·9

Surfactant B 1·2

Surfactant C 0·7

Methyl hydroxypropyl cellulose 2·7

The porous sealing layer was coated from a formulation prepared from the following components, with all parts given by weight:-

Component Weight %

Deionised water 34·8

Surfactant D 0·2

98% polyvinyl alcohol 10% solution 40·0

Polyethylene particles 25·0

The polyvinyl alcohol was a commercial sample from Harco available under the trade name Mowiol 56-98. Surfactant D was a silicone surfactant commercially available from Byk chemie under the trade name Byk 348. The polyethylene particles comprised low density polyethylene particles of random shape with an average particle size of about 13 µm and a melt flow index of 70 available under the trade name Coathylene HX1681 from duPont Polymers.
An image was printed with pigmented inks using an Epson Stylus Photo 2000P Ink Jet printer. After the prints had dried, the sealing layer was sealed by passing through a GBC 1200 laminator at a heat setting corresponding to a temperature of 120°C with the image face contacted with a smooth sheet of polyester film available under the trade name Melinex O as an inert sheet. The resulting prints had a bright glossy surface and very good print quality.

Example 2

The inventive recording sheet of example 1 was printed with an image using an Epson Stylus Photo 870 printer and aqueous dye-based inks. The print was allowed to dry and sealed as in example 1. A clear glossy high quality image was produced.

Claims

A recording material comprising in order:-

1) a sheet-like paper substrate;

2) at least one hydrophobic barrier layer;

3) at least one ink-receptive layer;

4) at least one porous sealing layer which comprises a dispersion of a particulate polymer characterised by a film forming temperature of between 60°C and 140°C and an average particle size between about 1 µm and about 50 µm together with at least one water-soluble polymer binder.
A recording material according to claim 1 wherein the hydrophobic barrier layer is provided in the form of a latex of a film-forming polymer which is allowed to form a film during the coating and drying process.
A recording material according to claim 1 or claim 2 which comprises two or more ink-receptive layers.
A recording material according to any of claims 1 - 3 wherein the particulate polymer dispersion of the porous sealing layer comprises at least one of polyurethane, low density polyethylene, high density polyethylene, polypropylene, polyvinyl acetate, polyvinyl acetate copolymers, styrene/butadiene copolymers, styrene/butadiene/acrylonitrile terpolymers, styrene/(meth)acrylate copolymers, (meth)acrylic polymers, ethylene/(meth)acrylic acid copolymers, or ethylene/vinyl chloride copolymers.
A recording material according to any of claims 1 - 4 which also comprises a primer layer between the paper substrate and the hydrophobic barrier layer.
A recording material according to any of claims 1 - 4 which also comprises a primer layer between the hydrophobic barrier layer and the ink-receptive layer.
A recording material according to any of claims 1 - 6 wherein the back surface of the paper is coated with an adhesive and the adhesive is protected with a release sheet.
A printing method whereby an image printed on a recording material according to any of claims 1 - 7 is heated after printing to seal the porous recording layer to provide a protective surface.
A printing method according to claim 8 whereby the printed material is heated under pressure with the image surface in contact with a second, inert sheet which is held against the image protective layer of the material.
A printing method according to claim 9 whereby the printed material and inert sheet are heated under pressure by passing them through a nip between a pair of heated rollers.