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.

Once the image has been printed onto the surface of the plastic substrate, it is necessary to apply a protective film over the printed ink-bearing surface. The bond strength between the protective film and the printed surface must be sufRcient to resist delamination under typical use conditions.

Summary of the Invention In a first aspect, the invention features an article that includes (a) a first polymeric substrate having a major surface; (b) a second polymeric substrate different from the first substrate having a major surface; and (c) a photopolymerized adhesive bonding the major surface of the first polymeric substrate to the major surface of the second polymeric substrate such that the peel strength between the polymeric substrates is at least 6 N/cm. At least one of the major surfaces includes an ink-bearing image. It is also possible for the major surfaces of both substrates to include ink-bearing images.

The ink preferably is an electrophotographic ink. Examples of suitable electrophotographic inks include those that contain a polymer having a Tg no greater than about 30°C, while in other embodiments the ink includes a polymer having a Tg greater than about 30°C.

One example of a suitable ink is derived from gel organosol-containing, liquid toner compositions described, e. g., in Baker et al., U. S. 5,652,282 and Baker et al., U. S. 5,698,616. These toners include (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. Also suitable are non-gel organosol-containing liquid toner compositions described, for example, in Baker et al., U. S. 5,886,067.

Another example of a suitable ink is derived from liquid toners 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. 5,407,771; and Landa, W092/17823 published October 15,1992 entitled "Polymer Blends." Also useful are ink jet inks and lithographic inks. Any of these inks may be used alone or in combination with each other. For example, the ink-bearing surface may include electrophotographically printed areas featuring an electrophotographic ink and offset printed areas featuring a lithographic ink.

Preferably, however, all the printed areas of the article are electrophotographically printed areas featuring electrophotographic ink.

One example of a useful adhesive is the photopolymerization product of : (a) a reactive, acid functional polymer of the formula B (X) (Y), where B represents an organic backbone, each X independently is an acid group or salt thereof present in an amount of between 0.02 and 0.8 equivalent parts per hundred parts resin (ephr), and each Y independently is a photopolymerizable group present in an amount of between 0.35 and 1.0 equivalent parts per hundred parts resin (ephr) ; (b) a multi-functional acrylate or methacrylate crosslinking agent; and (c) a photoinitiator.

A number of polymeric substrates may be used. In one preferred embodiment, the first polymeric substrate features a rigid core layer and the second polymeric substrate features a flexible overlay film. Preferably, at least one of the substrates is substantially transparent to permit viewing of the printed image on the ink-bearing substrate surface.

The polymeric substrates may be the same as, or different from, each other. Examples of suitable polymeric substrates are selected from the group consisting of 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 films commercially available from PPG, Inc. of Pittsburgh, PA. One preferred construction includes a polyvinyl chloride substrate adhesively bonded to a substantially transparent polyester overlay film.

The article may include more than two substrates. For example, the article may include a core substrate having a pair of opposed major surfaces, each of which is bonded to a separate overlay film. Such constructions are particularly useful for articles having printed images on two different surfaces.

In a second aspect, the invention features a process for preparing an article that includes: (a) forming an ink-bearing image on a major surface of a first polymeric substrate; (b) combining the first polymeric substrate and a second polymeric substrate having a major surface with a photopolymerizable composition such that the photopolymerizable composition is intermediate the major surfaces of the polymeric substrates; (c) laminating the major surfaces of the first and second substrates together through the photopolymerizable composition to form a laminate; and (d) exposing the laminate to actinic radiation (e. g., ultraviolet radiation) to polymerize the composition to form an adhesive bonding the two substrates together.

The ink-bearing image is preferably formed according to an electrophotographic process that includes: (i) charging the surface of an electrophotographic 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 surface of the first polymeric substrate.

The toner preferably is a liquid toner. The liquid toner, in turn, preferably includes a film-forming polymer. In some embodiments, the film- forming polymer has a Tg no greater than about 30°C, while in other embodiments the film-forming polymer has a Tg greater than 30°C. Following lamination, the article may be subjected to a number of operations, including slitting, cutting, hole punching and drilling, foil stamping, sewing and grommeting, foil stamping, perforation, folding, surface texturing, and the like.

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

Detailed Description The invention will now be described further by way of the following examples.

The black, positive-acting, film-forming, electrophotographic ink used in the examples was prepared at an organosol/pigment ratio of 6 following the procedure described in Example 40 of U. S. 5,652,282 modified as follows.

The gel organosol prepared according to the procedure of Example 22 of U. S. 5,652,282 was mixed using a Silverson mixer (Model L2R, Silverson Machines, Ltd.) operated at the lowest speed setting. After mixing for five minutes, 1912 g of the homogenized organosol at 16.14% (w/w) solids in NORPAR 12 were combined with 1031 g of NORPAR 12 (Exxon Chemical Co.,

Houston, TX), 51 g of MONARCH 120 carbon black (Cabot Corp., Billerica, MA), and 6.08 g of Zirconium HEX-CEM (OMG Chemical Company, Cleveland, OH) in a 4.0 liter polyethylene container. This mixture was then milled in ten vertical bead mills, each having a capacity of 0.5 liter (Model 6TSG-1/4, Aimex Co. Ltd., Tokyo, Japan) by placing 300 g of millbase and 390 g of 1.3 mm diameter Potters glass beads (Potters Industries, Inc., Parsippany, NJ) in each mill.

Each mill was operated at 2,000 rpm for 1.5 hours without cooling water circulating through the cooling jacket of the milling chamber.

A portion of the 12% (w/w) solids toner concentrate thus formed was diluted to approximately 3% (w/w). This dilute toner sample exhibited the following properties, as determined using the test methods described in U. S.

5,652,282: Number Mean Particle Size: 0.261 micron Bulk Conductivity: 149 picoMhos/cm Percent Free Phase Conductivity: 5% Dynamic Mobility: 0.0402 micron-cm/ volt-second This 3% toner was tested on the toner plating apparatus described in U. S. 5,652,282. The reflection optical density (ROD) was greater than 1.47 at plating voltages greater than 400 volts.

EXAMPLES Example 1 A coating solution was prepared by adding Irgacure 1700 photoinitiator (3 g, available from Ciba-Geigy), a 15 wt. % solution of a 2-isocyanato ethyl methacrylate-modified polyacrylic acid photopolymer in Dowanol PM (Dow Chemical Co.) (240 g, prepared as described in published PCT application no.

PCT/US96/03542, and Sartomer SR 259 polyethylene glycol diacrylate (21.0 g of neat liquid, available from Sartomer, Inc.) to 104. 5 g of Dowanol PM. The solution was then knife-coated onto polyethylene naphthalate film (available from

Teijin Films, LTD) at a wet coating coverage of approximately 200 g/square meter and then dried for 3 minutes at 80°C to give a u. v.-curable adhesive-coated film.

The dry thickness of the adhesive layer was 1.0 mil.

The adhesive portion of the film was area printed using a liquid toner- based, black, positive-acting, film-forming, electrophotographic ink (prepared as described above) to a net optical density of 1.6. The net optical density is equal to the white light optical density minus the white light optical density of the unprinted film, measured in reflectance mode with a Macbeth densitometer. The net optical density corresponded to an ink net optical density of 1.3 for a paper substrate printed under identical conditions.

After printing, the adhesive-coated film was laminated to a white polyvinyl chloride substrate. Lamination took place between two heated rollers (roll surface temperature = 135-138°C) at a rate of 0.4 inches/second to give a laminated, printed article.

Following lamination, the adhesive was cured by exposing the printed, laminated article to ultraviolet radiation in air (40 units exposure using a Burgess Controlux Exposure Unit, available from Burgess Industries, Minneapolis MN).

The article was then cut into strips measuring one inch wide. Adhesive tape (No.

396 adhesive tape commercially available from 3M) was applied to the exposed polyethylene naphthalate surface of the article and the 180 degree peel force required to cause delamination of the polyethylene naphthalate film from the polyvinyl chloride substrate was measured using an Instron Tester (Model 5542).

The crosshead speed was 12 inches/minutes. The peel force was determined to be in excess of 3.5 pounds/inch (6.1 N/cm).

In a separate experiment, unprinted adhesive film was laminated to an identical white polyvinyl chloride substrate in an identical manner, and the peel strength measured. The peel strength was sufficiently high to cause tearing of the polyethylene naphthalate film.

Example 2 An adhesive-coated polyethylene naphthalate film was prepared following the procedure of Example 1 except that Sartomer SR 610 polyethylene glycol diacrylate was used in place of Sartomer SR 259 polyethylene glycol diacrylate. The dry thickness of the adhesive layer was 1.0 mil. The film was then used to prepare a laminated article as described in Example 1 except that the temperature of the heated rollers used for lamination was 95-120°C. The resulting article had a peel strength in excess of 3.5 pounds/inch (6.1 N/cm), which is sufficient to meet the requirements of ISO/IEC Standard No. 7810: 1995 (E).

In a separate experiment, unprinted adhesive film was laminated to an identical white polyvinyl chloride substrate in an identical manner, and the peel strength measured. The peel strength was sufficiently high to cause tearing of the polyethylene naphthalate film.

Example 3 The procedure of Example 2 was followed except that the adhesive was coated onto a polyethylene terephthalate film (1 mil thick E2Q film available from Teijin Films, Ltd.). In addition, instead of Sartomer SR 610 polyethylene glycol diacrylate, Sartomer CN 966 A80, a urethane acrylate blended with tripropylene glycol diacrylate, was used. The 180 degree peel force required to cause delamination was determined to be in excess of 3.5 pounds/inch (6.1 N/cm).

In a separate experiment, unprinted adhesive film was laminated to an identical white polyvinyl chloride substrate in an identical manner, and the peel strength measured. The peel strength was sufficiently high to cause tearing of the polyethylene terephthalate film.