GB2236984A

GB2236984A - Image transfer process and carrier material therefor

Info

Publication number: GB2236984A
Application number: GB9021274A
Authority: GB
Inventors: Denny Damodar Kalro
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-07-13
Filing date: 1990-10-01
Publication date: 1991-04-24
Anticipated expiration: 2010-10-01
Also published as: GB9015470D0; GB9021274D0; GB2236984B

Abstract

A flexible sheet image carrier for use in transferring images to target substrates such as textiles or pro-coated non-porous bodies such as metals comprises a base material, for example limp latex-impregnated paper, with an extruded polymeric surface layer, and a thermoplastic transfer coating thereon that is separable from the polymeric surface under heat and pressure when in face to face contact with the target substrate. The transfer coating, which may be arc treated to enhance its receptivity, receives the image by a xerographic method, and the image carrier meets photocopier industry standards for copy papers. Transfer coating materials include ionomer resins, ethylene-butyl acrylate copolymers and ethylene-vinyl acetate copolymers, which together with low density polyethylene are also suitable for the polymeric surface to the paper base carrier web.

Description

IMAGE TRANSFER PROCESS AND CARRIER MATERIAL THEREFOR This invention relates to an image transfer process and to an image carrier material for use in such a process.

The invention is particularly concerned with image transfer processes in which, firstly, an image is formed on an intermediate carrier. and secondly, the image is physically transferred from the carrier to a target substrate. The image may be semi-permanent on the carrier, enabling the carrier to be handled without risk to the integrity of the image, but permitting transfer to the target substrate under particular conditions. The image is desirably substantially permanent once it has been transferred to the target.

The invention has been particularly devised for use in conjunction with photocopying technology. Accordingly, in preferred embodiments of the invention, the carrier material is furnished with the image by xerographic means. The carrier may simply replace the conventional photocopy paper in a commercially available photocopier, which may then form a black or coloured image on the carrier. Thereafter, the image is transferred from the image on the carrier to a target substrate, such as a cotton tee-shirt, under appropriate conditions.

A particularly preferred application of the invention is in printing textile materials, and a particular application is in printing images on to tee-shirts. One of the objects of the invention is to provide economical and versatile means for transferring single images to textile fabrics in a bespoke manner.

However, it will be apparent that the invention may be used far more widely, printing on to wood or even non-porous materials such as metals and ceramics, for example, although some pre-treatment of the target substrate may be needed to improve its receptivity.

According to a first aspect of the invention, there is provided an image transfer process which comprises forming an image with an image-forming medium on a thermoplastic coating on a polymeric surface of a flexible carrier web; placing the image-bearing web in face to face contact with a target substrate; and applying heat and pressure whereby to separate the thermoplastic coating from the polymeric surface of the web and to transfer it and the imageforming medium to the target substrate.

According to a second aspect of the invention there is provided an image carrier comprising a flexible web having a polymeric surface provided with a thermoplastic coating receptive to an image-forming medium, such that when bearing an image formed by a said medium and placed in face to face contact with a target substrate under suitable conditions of heat and pressure, the thermoplastic coating is capable of separating from the surface of the web and transferring the image-forming medium to the substrate.

The image can be formed on the thermoplastic coating (herein also referred to as transfer coating) in a very wide variety of ways, provided that the image is formed by means of a medium that can be transferred to the substrate with the thermoplastic coating material under particular conditions of heat and pressure. Normally it would be desired that the image should not lose its integrity during the transfer, although no doubt interesting effects could be achieved by permitting some modification of the image at this stage.

Images can be formed on the thermoplastic transfer coating by the direct application of inks, dyes or pigments or the like, such as by drawing or writing on the receptive surface; but the preferred method is to use a xerographic method and to form the image with xerographic toner. The toner is normally a fusible powder, and may be black or coloured.

The image carrier is used in a xerographic copier in place of the usual copy paper, so that the original image scanned by the copier is used as the basis of a copy in toner formed on the receptive surface of the carrier. The toner is fixed to the coating in the usual manner for the copier, normally by passing the carrier between the copier's fuser rollers. Clearly the conditions of heat and pressure at such fuser rollers must not be those conditions of heat and pressure that will cause the thermoplastic coating to separate from the carrier web.

If the copier is provided with optical or electronic image processing facilities, it may be possible to adapt or manipulate the image before forming it on the carrier. In particular, text can be reversed in the copier, so that a second reversal of the text in subsequent face to face printing on to the target substrate will restore its normal readable form.

An image carrier intended for receiving the image by xerographic methods will desirably be flat and curl free, of a weight not more than about 110 g.s.m., and able to withstand the temperature and pressure of the fuser rollers. The overall thickness and construction of the sheet should meet the norms and standards of the copier industry.

The thermoplastic transfer coating on the carrier web must separate from the polymeric surface of the web under acceptable conditions of temperature and pressure; these conditions should not be so extreme as to damage the image or the target substrate. Suitable temperatures for printing textile materials are generally not more than 195"C, and more usually in the range from 1650C to 1900C. The temperature and pressure are typically applied for between 10 and 15 seconds, but this will vary according to the actual temperature and pressure employed, the nature of the transfer coating, and the nature of the substrate. The carrier web itself will be discarded after the coating has been transferred to the substrate and its condition at that time will not be material.

The transfer coating should be compatible with the target substrate, to the extent that under the conditions of transfer it will wet the substrate and desirably flow into intimate contact with the fibres of the substrate in the case of textiles (woven or non-woven). It may be entirely or partially absorbed by the target substrate.

In the case of non-porous target substrates, including metals such as aluminium, copper, brass and bronze, and ceramics, the substrate is advantageously pre-coated with a compatible and preferably similar layer to the transfer coating. For example, acrylic plastics may provide a suitably receptive pre-coating, especially when the transfer coating on the image carrier comprises an acrylate component. The substrate pre-coating may be applied by spray, brush or dip coating methods, and dried before use.

The principal functions of the thermoplastic transfer coating include carrying the image-forming medium across to the substrate, and bonding the medium to the substrate to fix the image thereon.

Desirable properties include a high melt index, implying good flow properties and low viscosity.

A preferred thermoplastic coating comprises an ionomer, which although cross-linked at normal ambient temperatures becomes plastic at elevated temperatures. Typical ionomers are polymers of ethylene with small quantities of co-monomers containing carboxyl groups; since the cross-linking is ionic in character, it is temperature dependant and reversible. Preferred ionomer resins include those sold under the trade mark Surlyn.

Another preferred thermoplastic coating comprises an ethylene-lower alkyl carboxylate copolymer. Particularly preferred lower alkyl (up to 5 carbon atoms) carboxylate components are esters of acrylic and methacrylic acids; and especially preferred is ethylene-butyl acrylate copolymer (EBA). The lower alkyl carboxylate proportion may be up to 30%, preferably about 15% to 20% in EBA.

Other thermoplastic polymers of this general type that are suitable for coating the carrier web and receiving the image-forming medium include ethylene-vinyl acetate copolymers (EVA). In these, the proportion of vinyl acetate is desirably below 22%, and more preferably about 9%.

Although different coating techniques may be employed, such as melt, solution or emulsion coating, the thermoplastic coating is preferably applied to the carrier web by an extrusion process. The coating material is rapidly heated, extruded through a die and then immediately laminated to the carrier web. Excessive heating and air contact when hot are desirably kept to a minimum. Typical extrusion temperatures are in the range from 2600C to 3000C.

It may well be necessary or desirable to surface treat the thermoplastic coating in order to render it receptive to imageforming media. Treatment by a cold plasma or glow discharge, or by a hybrid plasma such as a corona discharge, or exposure to energetic radiation from an arc or the like, may be used to promote the wettability of, and adhesive strength to, the thermoplastic surface. Corona arc treatment is preferred.

The carrier web has a polymeric surface to which the thermoplastic transfer coating is applied. The carrier could be a flexible, uniform, polymeric sheet material. However, it may with advantage be a composite material, comprising a surface layer of polymer on a different base material. The base material can be selected to give particular major physical properties such as weight, dimensional stability and flexibility (or stiffness). The polymeric surface layer can be selected for its contribution to these qualities, and in addition for its qualities as a release agent under the image transfer conditions, having regard to its compatibility with, and the nature of, the thermoplastic transfer coating that it carries.

The carrier web preferably comprises a flexible woven or non-woven fibrous material, especially paper, and particularly paper impregnated with latex. Paper with latex saturation can be made extremely limp so that it will lie flat against the target substrate.

In the case of the composite carrier-web, typically of a paper base coated with a polymeric surface layer, the polymeric layer can be applied by the same techniques as described above for the thermoplastic transfer coating, and especially by extrusion coating, and within the same temperature range. In fact, it is preferred that that the polymer layer and the thermoplastic transfer coating be applied in succession, with just sufficient delay to ensure that the thermoplastic transfer coating can later be separated from the underlying polymer layer during the image transfer process.

In order to ensure the later separability of the thermoplastic transfer coating from the composite carrier web it may be necessary to select appropriately different materials and/or different application conditions for the polymer layer and the thermoplastic transfer coating. Preferably, the polymer layer is of a different material to the thermoplastic transfer coating, and they are applied to the web base at different temperatures; in particular, the thermoplastic transfer coating may be applied to the polymer layer at a higher temperature than the polymer layer was applied to the web base.

The polymeric surface may be of the same materials (including ionomers and polyethylene-lower alkyl carboxylic esters such as EBA and EVA) as were identified above as suitable for the thermoplastic transfer coating, although preferably not the same material for each in one and the same composite web carrier material. A suitable alternative polymeric surface material is low density polyethylene (LDPE).

Table 1 shows suitable combinations of materials in image carrier materials according to the invention.

Table 1

Ueb Base Polymeric Surace Transfer Coating Surlyn ionomer EBA Surlyn ionomer EVA Paper or paper EBA Surlyn ionomer impregnated EVA Surlyn ionomer with latex LDPE Surlyn ionomer LDPE EBA LDPE EVA Whether the carrier web is a simple flexible polymer web carrying the thermoplastic transfer coating directly, or a composite of a base material and a polymeric surface layer on which the transfer coating is carried, the image-forming medium is first applied to the transfer coating, and the thermoplastic transfer coating together with the image-forming medium are secondly transferred from the web to the target substrate, with separation of the thermoplastic transfer coating under heat and pressure from polymeric surface of the carrier web.

The invention is illustrated in the following examples.

Example 1 A paper web is fed past two laminating extrusion dies spaced a short distance apart on the same side of the web. From the first die a melt of Surlyn ionomer resin is extruded at 2800C or preferably 290"C and laminated to the paper at a coating weight between about 7 and 12 g.s.m. to form the carrier web. From the second die a melt of ethylene-vinyl acetate copolymer is extruded at the slightly higher temperature of 300"C or preferably 3100C to form a thermoplastic coating of about 20 to 30 g.s.m. weight over the ionomer polymer layer on the paper web base. The carrier web so formed has a weight of 105 g.s.m.

The surface of the thermoplastic coating is exposed to a corona arc at an intensity of at least 45 dynes, preferably 50 dynes or more, to render it receptive to photocopier toner powder, and the image carrier material so formed is then cut into sheets.

A single sheet of this carrier material is fed into a Canon colour laser copier (eg model CLC 1, CLC 200 or CLC 500) where it receives a full colour image in fused toner powder. The image-bearing sheet is then placed in face to face contact with a white cotton teeshirt as the target substrate, against which it is pressed for about 12 seconds at between 165"C and 1900C.

On peeling off the carrier web it is found that the EVA thermoplastic layer has separated cleanly from the ionomer resin layer on the paper base of the composite carrier, and has been absorbed by the cotton, transferring the colour toner image and fixing it to the cotton. The image is substantially unaffected by subsequent laundering.

Example 2 The procedures of Example 1 are repeated in coating a 70 g.s.m.

paper base with 10 g.s.m. of Surlyn ionomer resin followed by 20 g.s.m. of ethylene-butyl acrylate copolymer (EBA) containing 17% butyl acrylate to give an image carrier of 100 g.s.m. weight, +3 g.s.m.

A full colour image is transferred to a white cotton tee-shirt in the same manner as in Example 1. It is noted that while the same actual transfer temperature of 187"C, within the given range of 165-190"C, is preferred for reasons of consistency, image-bearing EBA coatings can readily be transferred at temperatures around 20"C lower that those used for EVA based image transfer.

It is further observed that in the photocopier, the image carrier with an EBA transfer coating shows enhanced friction properties, particularly with regard to improved registration with the photocopier transfer drum. The acetate-free thermoplastic transfer coating is less corrosive to coating machinery and in the photocopier, where elevated temperatures are met. In terms of durability after repeated laundering, the image transferred in EBA shows superior life and resistance to cracking.

By using a paper base with a polymeric surface as the web, to which a thermoplastic coating acting as the transfer coating is applied, as described, much improved separation of the image-bearing layer is achieved, in comparison with a transfer coating carried directly by paper. Furthermore, the image carrier as a whole can be made of a weight, such as 100 g.s.m., and with other properties, which directly match the specifications of the xerographic copier industry, with corresponding advantages in terms of versatility and compatibility with existing photocopier equipment.

It will be apparent from the foregoing description that while the particularly preferred process comprises xerographic reproduction of an image on to a carrier followed by heat and pressure transfer of the image on to a textile, a carrier in accordance with the invention does lend itself to image transfer techniques beyond these applications.

Furthermore, while the invention has been described with reference to specific features and combinations, these are not limiting and each feature may be combined with any one or more others. No feature is necessarily indispensable to the invention, and alternatives may be employed. What is defined as the invention is not to be construed as limiting the disclosure of this description.

Claims

1. An image carrier comprising a flexible web having a polymeric surface provided with a thermoplastic coating receptive to an image-forming medium, such that when bearing an image formed by a said medium and placed in face to face contact with a target substrate under suitable conditions of heat and pressure, the thermoplastic coating is capable of separating from the surface of the web and transferring the image-forming medium to the substrate.

2. An image carrier as claimed in claim 1 wherein the thermoplastic coating is receptive to xerographic toner as the image-forming medium.

3. An image carrier as claimed in claim 1 or claim 2 wherein the flexible web is normally flat and curl free and of a weight not more than about 110 g.s.m.

4. An image carrier as claimed in any one of the preceding claims wherein either the thermoplastic coating or the polymeric surface of the web comprises an ionomer.

5. An image carrier as claimed in claim 4 wherein the ionomer is a polymer of ethylene with a minor proportion of co-monomer containing carboxyl groups.

6. An image carrier as claimed in any one of the preceding claims wherein either the thermoplastic coating or the polymeric surface of the web comprises an ethylene-lower alkyl carboxylate copolymer.

7. An image carrier as claimed in claim 6 wherein the lower alkyl carboxylate moiety is an ester of acrylic or methacrylic acid.

8. An image carrier as claimed in claim 6 or claim 7 wherein the lower alkyl carboxylate comprises up to 30% of the copolymer.

9. An image carrier as claimed in claim 6 wherein either the thermoplastic coating or the polymeric surface of the web comprises ethylene-butyl acrylate copolymer.

10. An image carrier as claimed in claim 9 wherein the copolymer comprises about 15% to 20% butyl acrylate.

11. An image carrier as claimed in claim 6 wherein either the thermoplastic coating or the polymeric surface of the web comprises an ethylene-vinyl acetate copolymer.

12. An image carrier as claimed in claim 11 wherein the copolymer comprises below 22% vinyl acetate.

13. An image carrier as claimed in any one of the preceding claims wherein the polymeric surface of the web comprises low density polyethylene.

14. An image carrier as claimed in any one of the preceding claims wherein the thermoplastic coating has been surface treated whereby to render it receptive to image-forming media.

15. An image carrier as claimed in claim 14 wherein the thermoplastic coating has been surface treated by exposure to a corona arc.

16. An image carrier as claimed in any one of the preceding claims wherein the flexible web is a composite comprising a surface layer of polymer on a different base material.

17. An image carrier as claimed in claim 16 wherein the base material comprises paper.

18. An image carrier as claimed in claim 17 wherein the paper is impregnated with lastex.

19. An image carrier as claimed in any one of claims 16 to 18 wherein the polymeric surface layer of the flexible web has been applied to the base material by extrusion coating.

20. An image carrier as claimed in any one of the preceding claims wherein the thermoplastic coating has been applied to the web by extrusion coating.

21. An image carrier as claimed in claim 20 when dependent upon claim 18, wherein the polymeric surface layer of the web has been applied to the base, and the thermoplastic coating has been applied to the polymeric surface coating, in succession, at different temperatures, and with just sufficient delay to ensure that the thermoplastic coating is capable of separating from the surface of the web as aforesaid.

22. An image transfer process which comprises forming an imageforming medium on a thermoplastic coating on a polymeric surface of a flexible carrier web; placing the image-bearing web in face to face contact with a target substrate; and applying heat and pressure whereby to separate the thermoplastic coating from the polymeric surface of the web and to transfer it and the imageforming medium to the target substrate.

23. An image transfer process as claimed in claim 22 wherein the image is formed on the thermoplastic coating on the carrier web by a xerographic method.

24. An image transfer process substantially as herein described with reference to either of the specific Examples.

24. An image transfer process as claimed in claim 22 or claim 23 wherein the target substrate is a textile material.

25. An image transfer process as claimed in claim 24 wherein the thermoplastic coating and the image-forming medium are transferred to the target substrate at a temperature from 1650C to 195"C.

26. An image transfer process as claimed in any one of claims 22 to 25 wherein the thermoplastic coating wets the target substrate under the conditions of transfer thereto.

27. An image transfer process as claimed in claim 22 or claim 23 wherein the target substrate is non-porous and is pre-coated with a receptive layer compatible with the thermoplastic coating transferred from the web.

28. An image transfer process as claimed in claim 27 wherein the pre-coating layer comprises an acrylic resin.

29. An image transfer process as claimed in any one of claims 22 to 28 wherein the flexible carrier web having a thermoplastic coating on a polymeric surface thereof comprises an image carrier as claimed in any one of claims 1 to 21.

30. An image carrier substantially as herein described with reference to either of the specific Examples.

31. An image transfer process substantially as herein described with reference to either of the specific Examples.

Amendments to the claims have been filed as follows CLAIMS 1. An image carrier sheet for use in an image transfer process, in which an image in xerographic toner is formed on the carrier sheet by a xerographic process and fixed thereto, and thereafter the carrier sheet is placed in face to face contact with a target substrate of textile material and the toner image transferred thereto under suitable conditions of heat and pressure, wherein the said carrier sheet comprises a flexible web base having a surface layer of polymeric material, and on the said surface layer of the base a thermoplastic coating receptive to xerographic toner, the polymeric layer on the base and the thermoplastic coating being selected so that under the said conditions of heat and pressure the thermoplastic coating is capable of separating from the polymeric layer and transferring the toner image to the textile substrate, wetting the substrate and flowing into intimate contact with the fibres thereof.

2. An image carrier as claimed in claim 1 wherein the flexible web is normally flat and curl free and of a weight not more than about 110 g.s.m.

3. An image carrier as claimed in claim 1 or claim 2 wherein either the thermoplastic coating or the polymeric surface layer of the web comprises an ionomer.

4. An image carrier as claimed in claim 3 wherein the ionomer is a polymer of ethylene with a minor proportion of co-monomer containing carboxyl groups.

5. An image carrier as claimed in any one of the preceding claims wherein either the thermoplastic coating or the polymeric surface layer of the web comprises an ethylene-lower alkyl carboxylate copolymer.

6. An image carrier as claimed in claim 5 wherein the lower alkyl carboxylate moiety is an ester of acrylic or methacrylic acid.

7. An image carrier as claimed in claim 5 or claim 6 wherein the lower alkyl carboxylate comprises up to 30% of the copolymer.

8. An image carrier as claimed in claim 5 wherein either the thermoplastic coating or the polymeric surface layer of the web comprises ethylene-butyl acrylate copolymer.

9. An image carrier as claimed in claim 8 wherein the copolymer comprises about 15% to 20% butyl acrylate.

10. An image carrier as claimed in claim 5 wherein either the thermoplastic coating or the polymeric surface layer of the web comprises an ethylene-vinyl acetate copolymer.

11. An image carrier as claimed in claim 10 wherein the copolymer comprises below 22% vinyl acetate.

12. An image carrier as claimed in any one of the preceding claims wherein the polymeric surface layer of the web comprises low density polyethylene.

13. An image carrier as claimed in any one of the preceding claims wherein the thermoplastic coating has been surface treated whereby to render it receptive to xerographic toner.

14. An image carrier as claimed in claim 13 wherein the thermoplastic coating has been surface treated by exposure to a corona arc.

15. An image carrier as claimed in any one of the preceding claims wherein the flexible web is a composite comprising a surface layer of polymer on a base material which comprises paper.

16. An image carrier as claimed in claim 15 wherein the paper is impregnated with latex.

17. An image carrier as claimed in any one of the preceding claims wherein the polymeric surface layer of the flexible web has been applied to the base material by extrusion coating.

18. An image carrier as claimed in any one of the preceding claims wherein the thermoplastic coating has been applied to the surface layer of the web by extrusion coating.

19. An image carrier as claimed in claim 18 when dependent upon claim 17, wherein the polymeric surface layer of the web has been applied to the basle, and the thermoplastic coating has been applied to the polymeric surface coating, in succession, at different temperatures, and with just sufficient delay to ensure that the thermoplastic coating is capable of separating from the surface layer of the web as aforesaid.

20. An image transfer process which comprises providing an image carrier sheet comprising a flexible web base having a surface layer of polymeric material, and on the said surface layer of the base a thermoplastic coating; forming an image in xerographic toner by a xerographic process on the thermoplastic coating on the carrier sheet and fixing the image thereto; placing the image-bearing carrier sheet in face to face contact with a target substrate of textile material; and applying heat and pressure whereby to separate the thermoplastic coating from the polymer surface -layer of the web and to transfer it and the toner image to the textile substrate, wetting the substrate and flowing into intimate contact with the fibres thereof.

21. An image transfer process as claimed in claim 20 wherein the thermoplastic coating and the image-forming medium are transferred to the textile substrate at a temperature from 1650C to 1950C.

22. An image transfer process as claimed in claim 20 or 21 wherein the flexible carrier web having a thermoplastic coating on a polymeric surface layer thereof comprises an image carrier as claimed in any one of claims 1 to 19.

23. An image carrier substantially as herein described with reference to either of the specific Examples.