There has been an interest in printing images such as photographic images onto plastic substrates. It would be particularly desirable to use liquid toner-based electrophotographic printing for this purpose because this printing technique produces high quality images. It would also be desirable to provide articles having printed images visible on two opposing surfaces.

Summary of the Invention In general, the invention features a process for preparing a printed article that includes: (a) forming an ink-bearing image using a printer on a major surface of a first polymeric substrate to form a first polymeric substrate having a printed major surface and an unprinted major surface opposite the printed major surface; (b) forming an ink-bearing image using the same printer on a major surface of a second polymeric substrate to form a second polymeric substrate having a printed major surface and an unprinted major surface opposite the printed major surface; and (c) laminating the printed major surface of the second polymeric substrate to the unprinted major surface of the first polymeric substrate to form the article. Following lamination, the article may be subjected to further operations, including slitting, cutting, hole punching and drilling, foil stamping, sewing and grommeting, perforation, folding, surface texturing, and the like.

In one preferred embodiment, one of the polymeric substrates (preferably the first substrate) is substantially opaque prior to printing. In another preferred embodiment, one of the polymeric substrates (preferably the second substrate) is substantially transparent prior to printing. One or both substrates may be pre-printed.

The process may further include laminating a major surface of a third polymeric substrate to the printed major surface of the first polymeric substrate.

Preferably, the third polymeric substrate is substantially transparent prior to lamination. Alternatively, a coating (e. g., a photopolymerizable or thermally polymerizable coating) may be applied to the printed major surface of the first polymeric substrate.

A variety of printing techniques may be used to form the image.

Examples include ink jet printing, dye diffusion printing, thermal transfer printing, dye sublimation printing, liquid toner-based electrophotographic printing, and dry toner-based electrophotographic printing. Preferably, however, the printer includes an electrophotographic photoreceptor (e. g., an organophotoreceptor) and the image is created electrophotographically by: (i) charging the surface of the photoreceptor; (ii) imagewise exposing the charged surface of the photoreceptor to radiation to dissipate charge in selected areas and thereby form a latent image on the photoreceptor surface; (iii) contacting the latent image with a toner to form a toned image; and (iv) transferring the toned image to the major surfaces of the polymeric substrates. The toned image may be transferred directly to the polymeric substrates or indirectly, e. g., by initially transferring the toned image to a transfer medium, e. g., rollers, belts, elastomers and thereafter transferring the toned image from the transfer medium to the polymeric substrates.

Examples of suitable electrophotographic toners include both dry and liquid toners, with liquid toners being preferred. The liquid toner may include a film-forming polymer may have a Tg no greater than about 30°C. Alternatively, the polymer may have a Tg greater than about 30°C.

One suitable liquid toner includes a gel organosol dispersion featuring: (a) a carrier liquid (e. g., an aliphatic hydrocarbon carrier liquid having a Kauri- Butanol number less than 30) and (b) a (co) polymeric steric stabilizer having a molecular weight greater than or equal to 50,000 Daltons and a polydispersity less

than 15 covalently bonded to a thermoplastic (co) polymeric core that is insoluble in the carrier liquid. The core preferably has a Tg no greater than about 30°C. The toner may further include a colorant and a charge director.

Examples of preferred liquid toners and related electrophotographic printing processes are described, e. g., in Baker et al., U. S. 5,652,282; Baker et al., U. S. 5,698,616; and Baker et al., U. S. 5,886,067. The first two patents describe gel organosol-containing liquid toners, while the third patent describes a non-gel organosol-containing liquid toner.

Additional examples of suitable liquid toners are described in Landa et al., U. S. 4,794,651; Landa et al., U. S. 4,842,974; Landa et al., U. S. 5,047,306; Landa et al., U. S. 5,047,307; Landa et al., U. S. 5,192,638; Landa et al., U. S.

5,208,130; Landa et al., U. S. 5,225,306; Landa et al., U. S. 5,264,313; Landa et al., U. S. 5,266,435; Landa et al., U. S. 5,286,593; Landa et al., U. S. 5,346,796; Landa et al., U. S. 5,407,771; and Landa, W092/17823 published October 15,1992 entitled"Polymer Blends." Each substrate may be provided in the form of a sheet or continuous web. Suitable materials for the first polymeric substrate include polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, polyesters, polyolefins, polycarbonates, and combinations thereof. Also suitable are microporous substrates such as that available under the trade designation TESLIN, commercially available from PPG, Inc. of Pittsburgh, PA. A suitable material for the second and third polymeric substrates is polyester (e. g., polyethylene terephthalate or polyethylene naphthalate).

The two substrates are preferably laminated together using an adhesive.

Preferably, the adhesive is selected such that the peel strength between the two substrates builds to at least 6 N/cm within a period of no greater than about 1 hour following lamination between a pair of lamination rollers at a line speed of about 0.2-10 inch/sec., a temperature of about 65-150°C, and a nip pressure of about 15- 110 lbs/in. 2.

The invention provides a simple and effective method for preparing multilayer articles having printed images visible from two sides.

Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.

Brief Description of the Drawings Fig. 1 is a schematic drawing of a continuous process according to the invention in which both polymeric substrates are in the form of discrete sheets.

Fig. 2 is a schematic drawing of a continuous process according to the invention in which one of the polymeric substrates is in the form of a discrete sheet and one of the substrates is in the form of a continuous web.

Description of the Preferred Embodiments The invention features a process for preparing multilayer polymeric laminates having printed images visible from two different sides of the laminate.

Liquid toner-based electrophotographic printing is used to form the printed images.

The process preferably is a continuous process in which printing and laminating steps are performed in-line. It is also possible, however, to prepare articles in a batch process.

In the case of continuous processes, it is preferred to use an adhesive to bond the polymeric substrates together. Preferred adhesives are those which rapidly build bond strength following lamination. Nevertheless, it is also possible to prepare articles in which the substrates are laminated together without an adhesive.

Fig. 1 illustrates one embodiment of a continuous process in which the polymeric substrates are provided in the form of discrete sheets. As shown in Fig.

1, a plurality of core substrates 10 (e. g., polyvinyl chloride core substrates) are provided in the form of individual sheets arranged in a stack. A plurality of transparent overlay films 12 (e. g., polyester films) are provided in the form of

individual sheets in a separate stack. Each of the overlay films includes an adhesive layer. The overlay films 12 are stacked adhesive side down. Release liners or coatings may be used to separate individual films from each other within the stack.

Both stacks are designed to alternately or alternatively feed individual sheets of core 10 and overlay film 12 to a printing station, as described below.

A latent electrophotographic image is generated using an organic photoreceptor 14 and transferred to a transfer roll 16 according to the techniques described in the aforementioned Baker et al. patent. The photoreceptor may be in the form of a drum or flexible belt, with belts being preferred. One sheet of core 10 is fed between transfer roll 16 and a back up roll 18 to transfer the latent image resident on transfer roll 16 onto one surface of core 10. The resulting sheet features an ink-bearing, printed image 20 on one surface of core 10.

Next, a sheet of overlay film 12 is likewise fed between transfer roll 16 and back up roll 18 to transfer a latent image onto one surface of overlay film 12, thereby forming a sheet featuring an ink-bearing, printed image 22 on one surface of overlay film 12. Image 22 may be the same as, or different from, image 20.

The two printed sheets are then conveyed to the nip formed between a pair of laminating rollers 24,26. An additional polymer overlay film 28 (e. g., a transparent polyester film) in the form of a continuous web stored on a roll 30 is likewise fed into the nip region. The three materials are then laminated together between rollers 24,26 to form a multilayer article 32 having a pair of printed images 20,22 on opposite sides of the article. Because overlay films 12 and 28 are preferably selected from transparent materials, a printed image is visible from each side of the article.

Lamination preferably is effected using a line speed of about 0.2-10 inch/sec., a temperature of about 65-130°C, and a nip pressure of about 15-110 lbs/in. 2. Following lamination, the articles may be subjected to further operations.

Fig. 2 shows another continuous process which is similar to the process shown in Fig. 1 except that the adhesive-coated overlay film is provided in the form of a continuous web 11 dispensed from a back-up roll 13 and continuously fed to

the printing station. A back-up roll 15 assists in the feeding of individual sheets of core 10 to the printing station.

It is also possible to supply core 10, rather than overlay film 11, in the form of a continuous web. Alternatively, both the core and the overlay film may be supplied in the form of continuous webs.

Other embodiments are within the following claims.