GB2345653A - Receiver medium for ink jet printing - Google Patents

Abstract

A receiver medium for use with oil-based ink jet printing ink comprises a substrate having an ink receiving surface bearing a coating of plasticised acrylic polymer, that preferably has a Tg below 0{C and a high butyl acrylate content. The coating is capable of absorbing oil and can thus enable oil-based inks to be printed successfully onto non-absorbent substrates, including optically transparent polyethylene terephthalate films for use in OHPs. The substrate may alternatively absorb some of the oil from applied ink. The acrylic polymer may be plasticised by a polyoxyethylene amine and/or an unsaturated long chain alcohol or ester thereof, applied in admixture therewith or as a layer thereon. The coating may include a further acrylic polymer of Tg at least 20{C.

Description

Title: Receiver medium for ink iet printing Field of Invention This invention concerns a receiver medium for use in ink jet printing, particularly for use with oil-based ink jet printing inks, and also relates to a method of making such a medium and a method of printing using such a medium. The term"oil-based ink"is used to mean a substantially non-aqueous ink composition employing solvents or diluents other than water and containing one or more oils.

Background to the Invention Ink jet printing is a widely used printing technique. In general, ink jet printing inks are water-based compositions, and such inks are widely used in a range of different ink jet printers, for commercial, office and domestic use, including desk-top printers.

Oil-based ink jet printing inks comprising a low viscosity dispersion of pigment in non-volatile non-aqueous diluent comprising a major amount of aliphatic hydrocarbon (oil) and a minor amount of oleyl alcohol are also known ; see WO 96/24642. Such oil-based inks have the advantages of enabling printing to be performed very rapidly and also producing a water-resistant end product. Such inks are not, however, widely used commercially, and currently the only commercially available ink jet printers designed to use oil-based inks are wide-format printers designed to print on large rolls of paper, typically about 1 metre in width. Because oil-based inks are non-volatile, the diluent must be absorbed or otherwise permanently accommodated by the receiver medium to produce an acceptable print. Such oil-based inks produce good results when printing on paper and similar absorbent materials, with the oil being rapidly absorbed by the porosity of the paper or other material while leaving the pigment near the surface. However, such oil-based inks are not capable of providing adequate prints on non-absorbent media eg transparent media (which cannot have macroscopic pores as these scatter light and render the material opaque), and so cannot be used, for example, in production of transparency sheets for use in overhead projectors (OHPs).

They are also unsuitable for use with currently available glossy media.

US Re 34933 concerns receiver sheets for use in offset lithography and similar printing techniques using solvent-based inks containing oil. The receiver sheets may comprise a transparent substrate, eg of transparent polyester such as polyethylene terephthalate, carrying a transparent ink-receptive polymeric layer comprising one or more polymers or copolymers, eg a copolymer of n-butyl methacrylate and isobutyl methacrylate. Such receiver sheets may be used to produce transparent printed images, eg by offset lithography. The receiver sheets are not, however, suited to use in ink jet printing using oil-based printing inks. For use with mechanical printing techniques, such as offset lithography, a receiver medium requires properties of mechanical stability and abrasion resistance that are not necessary when printing using ink jet techniques. Further, the solvent-based inks used for this purpose are rather different from oil-based ink jet printer inks, typically being high viscosity compositions with high solids content, and having a much smaller content of oil as compared with oil-based ink jet printer inks. These prior art receiver sheets are not capable of absorbing the high oil content of oil-based ink jet printer inks, nor of adequately coping with the low viscosity properties of such inks.

The present invention thus aims to provide a novel receiver medium suitable for use with ink jet printers using oil-based printing ink.

Summarv of the Invention According to one aspect of the invention there is provided a receiver medium for use with oil-based ink jet printing ink, comprising a substrate having an ink-receiving surface bearing a coating of plasticised acrylic polymer.

Acrylic polymer coatings do not generally have the ability to absorb oil in appropriate manner to be able to cope with oil-based ink applied by ink jet printing. However, plasticised acrylic polymers, having a reduced glass transition temperature (Tg), are softer and also have a more open polymer structure, and have enhanced oil absorption properties. Preferred coatings at least are able rapidly to absorb large quantities of oil on application of oil-based ink, having good pigment adhesion with the dispersed pigment being permanently fixed on the surface, and being reasonably robust and resistant to damage.

Because the coating is capable of absorbing oil, there is no need for the substrate itself to be able to absorb oil. By applying such a coating to non-absorbent substrates it is thus possible for oil-based inks to be printed successfully onto non-absorbent substrates such as glossy white film materials in a way that has not hitherto been possible. In preferred embodiments, the coatings are optically transparent and so can be used on transparent substrates eg for the production of transparency sheets for use in OHPs. The substrate may alternatively be of other materials including metal, plastics, wood etc, and materials having metallised or other non-absorbent finishes.

There is, however, no need for the substrate to be non-absorbent, and the coating can be equally well applied to an absorbent substrate, including absorbent paper, card etc.

In this event the substrate itself may also act to absorb some of the oil from ink applied in use, in which case the coating may be made thinner than would be required on a non-absorbent substrate.

The substrate may be pre-treated, eg in known manner, prior to application of the coating. For example, the substrate may be pre-treated with an adhesion-promoting priming layer, eg of parachlorometacresol (PCMC).

It will thus be apparent that the substrate can be selected from a very wide range of materials.

The substrate is typically in the form of a film or sheet, but the physical form is not important as the coating can be applied to substrates of a wide variety of physical forms.

Typical substrate materials include polymeric materials having suitable properties including dimensional stability, optical transparency, translucency or opacity, tensile strength, adhesion characteristics, thermal stability, hardness etc for the intended purpose. Transparent polymeric substrate materials suitable for use in the production of transparencies include sheets or films of polyester eg poly (ethyleneterephthalate) (PET) such as Melinex (Melinex is a Trade Mark) or poly (ethylenenaphthalate) (PEN). Polycarbonate sheets may also be used for this purpose. Such transparent sheets typically have a thickness of about 50 to about 15011m. Other possible polymeric materials include polysulphones, polyvinyl chloride, polystyrene, polyimides, polyolefins, polymethyl methacrylate, cellulose esters such as cellulose acetate etc. A wide range of paper and card materials may also be used as the substrate.

The acrylic polymer of the polymer (in unplasticised condition) suitably has a Tg below 0 C, preferably below-20 C.

The acrylic polymer may comprise a mixture of polymers. Suitable materials are readily available commercially. Acrylic polymers are generally available in the form of either polymer emulsions or solutions in organic solvent.

Good results have been obtained with acrylic polymer having a high butyl acrylate content, eg in the form of Esi-cryl 752 from ESI/Kromachem (Esi-cryl 752 is a Trade Mark) which is an acrylic polymer emulsion having a high butyl acrylate content and a Tg of-22 C.

There may be advantages in using a mixture of an emulsion of the acrylic polymer together with an emulsion of another polymer of higher Tg, say having a Tg of at least 20 C. A different acrylic polymer emulsion of higher Tg may be used for this purpose. Use of such a mixture results in deposition of a soft polymer and a harder polymer as an interpenetrating network, resulting in a porous polymer matrix. The harder polymer provides the resulting coating with mechanical robusmess, with the soft polymer providing oil-absorption properties. The two emulsions must be mixed under well controlled conditions to produce a stable, well-mixed coating solution.

Acrylic polymers may be readily plasticised in known manner, by use of known plasticisers as is well known in the art. Plasticisers are usually organic materials in the form of moderately high molecular weight liquids or low melting point solids.

Most commonly plasticisers comprise esters of carboxylic acids or phosphoric acid, although hydrocarbons, halogenated hydrocarbons, ethers, glycols, polyglycols and hydrogenated or epoxidised oils (eg soya bean oil) may also be employed, as described in EP-A-0232040. Currently preferred plasticisers include polyoxyethylene amine, unsaturated long chain alcohols and their esters, especially oleyl alcohol and its esters, and oleates, such as sorbitan trioleate, sorbitan oleate and polyoxyethylenesorbitan trioleate. A mixture of plasticisers may be used.

Good results have been obtained with the acrylic polymer Esi-cryl 752 and polyoxyethylene amine plasticisers, eg in the form of Atmer 163 from ICI (Atmer 163 is a Trade Mark).

Plasticiser should be used in an appropriate amount to give a coating having desired properties. This amount will depend, inter alia, on the Tg of the polymer and hence the degree of plasticisation required. Appropriate proportions of plasticiser and polymer in any particular case can be readily determined by experiment. In general, plasticiser is suitably used in an amount in the range 2 to 50%, preferably 5 to 30%, more preferably 10 to 20%, based on the weight of polymer.

Acrylic polymer and plasticiser, where compatible in solution, may be mixed together and the resulting mixture applied to the ink-receiving surface of the receiver medium and dried. Where the acrylic polymer and plasticiser are not compatible, a layer of polymer may be applied to the ink-receiving surface and dried, and a separate, usually thinner, layer of plasticiser (preferably in solvent solution) laid down on the polymer layer and dried. In either case, materials in question are dried for a suitable time at a suitable temperature to achieve plasticisation of the polymer to give a coating having desired properties as discussed above. Drying of the polymer prior to application of plasticiser is generally necessary to avoid damage thereto during subsequent coating with plasticiser, although this may not be necessary where non-contact coating techniques such as curtain coating are used.

Suitable drying conditions (time and temperature) can be readily determined by experiment for any combination of chemicals and coating thickness. A temperature in the range 110 to 140 C, preferably in the range 120 to 130 C, is generally suitable, with times at up to 240 seconds generally being appropriate.

The coating materials may be applied by any suitable coating technique, including those known in the field, eg by use of a Meier bar, by roller coating, rod coating, slide coating, curtain coating, doctor coating etc.

The coating may be applied to the entire surface of the substrate or to only selected areas of the substrate surface. In the case of a sheet or film of substrate, the coating will typically be applied to at least one surface and possibly both surfaces (to enable double-sided printing).

The coating thickness will typically be in the range 30 to 100pu for non-absorbent substrates, eg about 80pm, with thinner coatings, eg about 5pm, being suitable for absorbent coatings, with coating thickness being selected depending on substrate properties and desired characteristics of the receiver medium.

Where the plasticiser is applied in a separate layer, this is usually relatively thin, up to say 15pm thick and typically 12pm or 6m thick. After the plasticiser layer has been thermally treated, it is totally absorbed into the acrylic polymer, and does not persist as a separate layer.

The coating desirably includes particulate filler material to increase surface roughness of the coating, thus reducing the tendency of the coating to block, ie stick by wetting action to adjacent surfaces: this tendency arises from the low Tg of the coating.

Suitable materials for this purpose include inorganic, organic or polymeric particulates such as silica including amorphous silica, crystalline silica, fumed silica, aluminium trihydrate, aluminium hydroxide, calcium carbonate, glass, sesquisiloxanes, clays, aluminium silicates, polyolefin particulates, organic pigments and mixtures thereof. It is preferred to use porous inorganic particulate material for this purpose, eg silica; in this event the porous filler material may also functional to absorb some of the oil from ink applied to the receiver medium. Particulate filler material has a tendency to increase light scattering, reducing coating transparency, so this factor must be taken into consideration in relation to transparent substrates and coatings, while being of no relevance to opaque receiver media. Filler material particles suitably have a primary size in the range 5nrn-50pm. Filler with a dimension much smaller than the wavelength of light can be used at higher loadings than larger fillers (because of their lower scattering) and therefore make a greater contribution to the mechanical properties of the coating, but are less efficient at creating surface roughness than are fillers with a major dimension of comparable size to the coating thickness. It is often desirable to incorporate fillers of two different sizes in order to optimise the overall properties of the coating.

Particulate filler material is desirably included in a separate relatively thin layer of plasticiser, as discussed above, by being mixed with the plasticiser material prior to application and drying. During the course of the drying process, the plasticiser is completely absorbed into the acrylic layer, and leaves the filler embedded in the surface of the coating. Alternatively, filler may be included in a separate, thin antiblocking coat applied on top of the plasticised acrylic polymer coating.

Particulate filler material may additionally or alternatively be included with the acrylic polymer material, to increase coating stiffness ; this may be desirable with a highly plasticised coating which would otherwise be susceptible to mechanical damage.

The receiver medium may include an optional top coat (or supercoat) over the plasticised acrylic polymer coating. A top coat desirably has the following characteristics: 1) The top coat should be capable of absorbing oil from applied oil-based ink reasonably rapidly.

2) The top coat should be of higher Tg than the coating so as to reduce the tendency of the receiver medium to block.

3) The top coat should exhibit good adhesion to pigment of applied ink.

The top coat conveniently comprises one or more polymers, and one example of a top coat formulation is a mixture of polybutadiene, styrene butadiene rubber and polystyrene.

The top coat is typically much thinner than the plasticised acrylic polymer coating, eg having a thickness in the range 0.2 to 5llm.

The top coat desirably includes particulate filler material, eg as discussed above, to improve anti-blocking properties and possibly also to improve pigment adhesion and other receiver medium properties. Again the light-scattering effect of particulate filler materials must be borne in mind when dealing with transparent receiver media. By use of a relatively thin top coat containing filler, the anti-blocking effect can be maximised without introducing too much light scattering, as smaller particles can be used than would be required in the thicker plasticised acrylic polymer coating.

A top coat may be applied by any suitable coating technique, for example those discussed above.

A crosslinked structure (not involving the acrylate) may optionally be included in the plasticised acrylic polymer coating, to make the coating more robust, although this may also have the disadvantageous effect of reducing the rate of oil absorption.

Where the polymer is in the form of a solution, components capable of producing a crosslinked structure, eg a hydroxylated polymer and melamine-formaldehyde resin, with suitable catalyst, may be added to the solution. Where the polymer is in the form of an emulsion, a self-crosslinking emulsion may be used, as is known in the art, with bonds being formed between individual particles of the emulsion during or after coalescence, by bonding to surfactant on the surface of the polymer emulsion particles.

Other additives may optionally be included in the coating to improve properties of the coating. For example, lubricants and release agents, such as waxes and silicones, may be included to reduce friction and/or adhesion at the coating surface.

In a further aspect, the invention provides a method of making a receiver medium for use with oil-based ink jet printing ink, comprising applying to an ink-receiving surface of a substrate a coating of plasticised acrylic polymer.

The receiver medium is used by oil-based ink jet printing ink being applied thereto by an inkjet printing technique, eg in known manner, using known ink-jet printing apparatus. The ink may be, eg, generally as described in WO 96/24642 discussed above. On impingement on the receiver medium, the oil of the ink is rapidly absorbed by the ink-receiving surface (ie the coating of plasticised acrylic polymer and possibly also by the anti-blocking layer or the top coat if present) and may also in part be absorbed by the substrate if absorbent, as discussed above.

In another aspect, the invention thus provides a method of printing, comprising applying oil-based ink to the ink-receiving surface of receiver medium in accordance with the invention by an ink jet printing technique.

The coatings described in the present application may optionally be used in conjunction with coatings described in the specifications of our co-pending UK applications filed on even date herewith under references C268.00/I, C270.00/I and C275.00/I.

The invention will be further described, by way of illustration, in the following examples.

Examples Samples of experimental receiver media were made and tested for their ability to absorb oil-based ink (comprising organic pigments dispersed in aliphatic hydrocarbon oil with oleyl alcohol, generally as described in WO 96/24642 by placing a few drops of ink on the edge of the coating, and drawing a Meier bar (24 p. m unless otherwise stated) over the surface. The ink was then viewed obliquely in order to determine the drying time. The ability of the prints to withstand abrasion was also determined by drawing a rubber-gloved finger lightly over the printed area. Transparency was normally judged simply by looking at the samples, and this was confirmed from time to time by placing representative samples on an OHP.

The acrylate emulsions giving the best absorption were found to be ones containing a high proportion of butyl acrylate. In particular, Esi-cryl 752 was promising. It was found that the performance with ink, tested as described above, depended greatly on the ink colour; cyan and yellow gave much better performance than magenta (thought to be due to the magenta ink containing little or no plasticiser). It was found that the rate of absorption could be greatly increased for all colours by incorporation of a suitable plasticiser additive. This could take the form of an aqueous dispersible material put down in a mixture with the acrylate emulsion, or alternatively an oily material put down as a separate coating.

Example 1 Esi-cryl 752 was coated onto Melinex O transparent PET film using a 150 llm Meier bar, and dried in an oven at 110 C for 180 seconds. This resulted in a coating about 801lu thick, after solvent evaporation.

The coating was either left untreated or over coated with a 12 um layer of plasticiser additive, applied using a 12, ut Meier bar, followed by a 60 seconds incubation at 110 C.

Testing with a 24 pm layer of magenta ink, by the technique described above, gave the following results:

Additive Dry time/s Composition Manufacturer none 280 Atmer 163 50 Polyoxyethylene amine ICI oleyl alcohol 80 Span 85 100 Sorbitan trioleate ICI Span 80 140 Sorbitan oleate ICI Similar results to those for oleyl alcohol were obtained by mixing a 20 % solution of Tween 85 (polyoxyethylene-sorbitan trioleate from ICI) with the Esi-cryl 752 (1: 3) before coating as described above.

Within 60 seconds of being visually dry, the ink layer was resistant to abrasion, but the surface of the coating was slightly tacky before the ink was applied, and very tacky after application.

Atmer 163 was chosen for further investigation. It was found that the coat quality of the overcoat could be greatly improved by applying the Atmer coating from a 20 to 80% solution in methanol or butan-2-one, as this gives a more even coating.

Example 2 In order to reduce the blocking tendency of the coatings, various filler layers were applied on top of Esi-cryl/Atmer coatings, produced generally as described in Example 1, but with the Atmer applied from a 50% solution in methanol using a 24m Meier bar. This gave a 12 m layer after solvent evaporation. Drying temperatures and times were as in Example 1.

Antiblock coat Thickness Dry time Composition Manufacturer Comments (ILM) (seconds) 1. Cerasol 4 100 Alumina sol Alcan crazed but Chemicals reduced tack 2. Cerasol 6g 6 55-65 crazedbut Apyral 0.7 g Aluminium Nabaltec less tack than hydroxide for sample 1 Tween 85 0.1 g Water 1.2 g 3. As 2 above 24 65-85 still crazed but less than for sample 1 4. Cerasol 5 g 6 65-70 similar tack Tospearl 0.2 g 12 pm Toshiba to sample 2 sesquisiloxane sphere Tween 85 0.2 g Water 1.1 I All the above overcoats seemed to be effective in reducing tack and blocking, but all showed visible crazing of the overcoat and increased drying time.

Example 3 As the Cerasol seemed to be causing visible defects (crazing) and was acting as a barrier, it was decided to investigate the application of other filler materials directly to the surface of the acrylate, mixed with the plasticiser. 1 50Fum wet coatings of Esi-cryl 752 were dried at 110 C for 240 s and then coated with the following.

Antiblock coat Thickness Dry time Composition Manufacturer Comments (Rm) (seconds) at I 10 C 1. Atmer 163 6g 6 60 Overcoat crazed. methanol 2 g Slightly tacky to Aerosil OX50 silica Degussa touch. Ink part dry Neosyl AC silica Crosfield after 35 seconds, but completion slow 2. As sample 1,6 60 Coat quality better. substituting 5g Ink dried 40 to 60 of methanol seconds. Smudge free 120 seconds.

3. As sample 1, 6 60 Surface still crazed. but with No bloclang against addition of 1 g polyester film. Ink Apyral 16. drying slow ( > 50 seconds).

4. Atmer 163 5g 6 60 No crazing of methanol 5 g overcoat. Slight Apyral 16 1 g blocking against polyester. Ink dries 45 to 70 seconds. Aerosil OX50 has a particle size of 40nm and is non-porous. Neosyl AC has a particle size of 17pro and is porous.

Projection of the films gave some problems because in heavily inked areas the colour looked grey. This was found to be caused by the coating separating into small (about 0.1 mm) islands that scattered the light. It was found that by limiting the topcoat to a 4 m wet coat of 50% solution of Atmer 163 in methanol laid down on a layer of Esicryl 752 formed as described above, the effect could be almost avoided; however the ink drying of such films was relatively slow (40 to 70 seconds). There is thus a trade-off between maximum rate of uptake and film coherence.

An alternative acrylic emulsion having a Tg of-12 C was investigated (Texicryl 13802, from Scott-Bader). This provided slower initial absorption, and was more prone to crazing by the Atmer 163.

Example 4 The best overall performance was obtained from a receiver coat put down from a 150 m layer of Esi-cryl 752 with an overcoat of 6 gm of : Atmer 163 1 g methanol 1 g Aerosil OX 50 0.4 g

Claims (19)

1. Claims 1. A receiver medium for use with oil-based ink jet printing ink, comprising a substrate having an ink-receiving surface bearing a coating of plasticised acrylic polymer.
2. 2. A receiver medium according to claim 1, wherein the substrate comprises a film or sheet of transparent material.
3. 3. A receiver medium according to claim 2, wherein the substrate comprises polyethylene terephthalate.
4. 4. A receiver medium according to claim 1, wherein the substrate is capable of absorbing oil.
5. 5. A receiver medium according to any one of the preceding claims, wherein the acrylic polymer has a Tg below 0 C, preferably below-20 C.
6. 6. A receiver medium according to any one of the preceding claims, wherein the acrylic polymer has a high butyl acrylate content.
7. 7. A receiver medium according to any one of the preceding claims, wherein the coating comprises a mixture of polymers.
8. 8. A receiver medium according to claim 7, wherein the coating includes a further acrylic polymer having a Tg of at least 20 C.
9. 9. a receiver medium according to any one of the preceding claims, wherein the acrylic polymer is plasticised by use of a plasticiser.
10. 10. A receiver medium according to claim 9, wherein the plasticiser used in an amount in the range 2 to 50%, preferably 5 to 30%, more preferably 10 to 20%, based on the weight of polymer.
11. 11. A receiver medium according to claim 9 or 10, wherein the plasticiser comprises a polyoxyethylene amine and/or an unsaturated long chain alcohol or ester thereof.
12. 12. A receiver medium according to any one of the preceding claims, further comprises a top coat over the plasticised acrylic polymer coating.
13. 13. A receiver medium according to claim 12, wherein the top coat includes particulate filler material.
14. 14. A receiver medium according to any one of the preceding claims, wherein a crosslinked structure is included in the plasticised acrylic polymer layer.
15. 15. A method of making a receiver medium for use with oil-based ink jet printing ink, comprising applying to an ink-receiving surface of a substrate a coating of plasticised acrylic polymer.
16. 16. A method according to claim 15, wherein a mixture of acrylic polymer and plasticiser is laid down on said surface and dried.
17. 17. A method according to claim 15, wherein a layer of acrylic polymer is laid down on said surface, and a layer of plasticiser is laid down on the polymer layer, followed by drying.
18. 18. A method according to claim 17, wherein the plasticiser layer includes particulate filler material.
19. 19. A method according to any one of claims 15 to 18, wherein a top coat including particulate filler material is formed on the plasticised acrylic polymer coating. 2u. A method of printing, comprising applying oil-based ink to the ink-receiving surface of a receiver medium in accordance with any one of claims 1 to 14 by an ink jet printing technique.