Process for obtaining a diffusion resistant lenticular element

A process of forming a diffusion resistant lenticular element comprising: PA1 a) contacting at least one dye-donor element comprising a support having thereon a dye layer comprising an image dye in a binder having an infrared-absorbing material associated therewith, the image dye comprising a nonionic dye capable of being converted to a cationic dye by means of an acid, with a lenticular element comprising a first support having thereon a lenticular array on the opposite side thereof; PA1 b) imagewise-heating the dye-donor element by means of a laser; PA1 c) transferring a dye image to the first support of the lenticular element; PA1 d) contacting the dye image with a mordanting element comprising a second support having thereon in order, a release layer and an adhesive layer of an acidic polymer having a Tg less than about 80.degree. C., the adhesive layer of the mordanting element being in contact with the side of the first support which contains the dye image, forming a composite laminate; PA1 e) heating the composite laminate to cause the nonionic dye to convert to a cationic dye which is mordanted in the adhesive layer and to cause the adhesive layer to adhere the mordanting element to the lenticular element; and PA1 f) removing the second support from the composite laminate, thus forming a diffusion resistant lenticular element.

CROSS REFERENCE TO RELATED APPLICATIONS
 Reference is made to commonly-assigned copending U.S. patent application
 Ser. No. 09/404,564, filed of even date herewith pending, entitled
 "Diffusion Resistant Lenticular Element", of Tutt et al; and copending
 U.S. patent application Ser. No. 09/404,062, filed of even date herewith
 pending, entitled "Diffusion Resistant Lenticular Element", of Tutt et al;
 the teachings of which are incorporated herein by reference.
 FIELD OF THE INVENTION
 This invention relates to the laser printing of stereoscopic, multiple
 images or motion images which will be used in conjunction with a
 lenticular element.
 BACKGROUND OF THE INVENTION
 Lenticular arrays or overlays are a known means to give images the
 appearance of depth or motion. A lenticular image is created using a
 transparent upper layer having narrow parallel lenticules (half
 cylindrical lenses) on the outer surface and an image containing substrate
 or lower layer which projects images through the lenticules. The two
 layers form a lenticular system wherein each image is selectively visible
 as a function of the angle from which the system is viewed. A depth image
 is a composite picture made by bringing together into a single composition
 a number of different parts of a scene viewed from different angles. When
 the lenticules are vertically oriented, each eye of a viewer will see
 different elements and the viewer will interpret the net result as depth
 of field. The viewer may also move his head with respect to the image
 thereby observing other views with each eye and enhancing the sense of
 depth. Each lenticule is associated with a plurality of image lines or an
 image line set and the viewer is supposed to see only one image line (or
 view slice) of each set with each eye for each lenticule. It is imperative
 that the line image sets be registered accurately with the lenticules, so
 that the proper picture is formed when the assembly is viewed.
 This process can be used to generate a three-dimensional effect at a proper
 viewing distance or multiple images by viewing from different angles. When
 the lenticules are oriented horizontally, each eye receives the same
 image. In this case, the multiple images upon moving the lenticular can be
 used to generate the illusion of motion. For whichever orientation the
 lenticules are oriented, each of the viewed images is generated by lines
 from an image which has been interlaced substantially at the frequency of
 the lenticular array, number of lenticules per length and with the desired
 number of images.
 One method of recording of linear images on a lenticular recording material
 is accomplished with a stereoscopic image recording apparatus (hereunder
 referred to simply as "a recording apparatus") that relies upon optical
 exposure (printing). With this recording apparatus, original transmission
 images are projected from a light source. The light transmitted through
 the original images passes through the projection lenses of the recording
 apparatus to be focused on the lenticular recording material via a
 lenticular sheet. The original images are thereby exposed as linear
 images.
 Another method of image recording uses scanning exposure which requires
 comparatively simple optics and yet has great flexibility in adapting to
 various image-processing operations and to alterations in the
 specifications of the lenticular sheet.
 In the article entitled "Development of Motion Image Printer", by H.
 Akahori et al., IS&T 50th Annual Conference Proceedings, page 305, there
 is a disclosure of a printer for printing stereoscopic images using a
 thermal head and thermal dye transfer in registration with the lenticular
 material. The receiver sheet must be heated to achieve the necessary
 stability for registration of the images with the lenticular material. The
 resolution is six images on 100 DPI lenticular material with a 300 DPI
 thermal head. However, there is a problem with this method in that low
 resolution images are obtained, since heat transferred from the resistive
 head "spreads" through the support during printing.
 EP 0 596 629A2 and EP 0 659 026A2 disclose a method and apparatus for
 directly printing on lenticular supports using lasers. This method
 generates an image in contact with the lenticular material. There is a
 problem with this method, however, in that the dyes can continue to
 migrate after transfer, resulting in unacceptable image ghosting (adjacent
 views bleeding through). In addition, if it is desired to add a reflective
 backing to the element, then trimming or a very accurate alignment is
 required.
 An object of this invention is to provide a process for obtaining a high
 resolution lenticular image which is resistant to thermal dye diffusion.
 It is another object of this invention to provide a process for obtaining
 a high resolution lenticular image which is resistant to abrasion and does
 not require trimming or accurate alignment. Another object of the
 invention is to provide a process for obtaining a high resolution
 lenticular image which has a reflection layer underneath the image.
 SUMMARY OF THE INVENTION
 These and other objects of the invention are obtained in accordance with
 the invention which relates to a process of forming a diffusion resistant
 lenticular element comprising:
 a) contacting at least one dye-donor element comprising a support having
 thereon a dye layer comprising an image dye in a binder having an
 infrared-absorbing material associated therewith, the image dye comprising
 a nonionic dye capable of being converted to a cationic dye by means of an
 acid, with a lenticular element comprising a first support having thereon
 a lenticular array on the opposite side thereof;
 b) imagewise-heating the dye-donor element by means of a laser;
 c) transferring a dye image to the first support of the lenticular element;
 d) contacting the dye image with a mordanting element comprising a second
 support having thereon in order, a release layer and an adhesive layer of
 an acidic polymer having a Tg less than about 80.degree. C., the adhesive
 layer of the mordanting element being in contact with the side of the
 first support which contains the dye image, forming a composite laminate;
 e) heating the composite laminate to cause the nonionic dye to convert to a
 cationic dye which is mordanted in the adhesive layer and to cause the
 adhesive layer to adhere the mordanting element to the lenticular element;
 and
 f) removing the second support from the composite laminate, thus forming a
 diffusion resistant lenticular element.
 By use of the invention, a high resolution lenticular image is generated
 efficiently which is resistant to thermal dye diffusion, has a high
 abrasion resistance and does not require trimming.
 DESCRIPTION OF THE PREFERRED EMBODIMENTS
 The support for the mordanting element used in the invention can include
 polyesters such as poly(ethylene terephthalate); polyamides;
 polycarbonates; cellulose esters such as cellulose acetate; fluorine
 polymers such as poly(vinylidene fluoride) or
 poly(tetrafluoroethylene-co-hexafluoropropylene); polyethers such as
 polyoxymethylene; polyacetals; polyolefins such as polystyrene,
 polyethylene, polypropylene or methylpentene polymers; and polyimides such
 as polyimide-amides and polyether-imides. The support generally has a
 thickness of from about 5 to about 200 .mu.m.
 As noted above, dyes useful in the invention are nonionic dyes capable of
 being converted to cationic dyes by means of an acid. A cationic dye
 diffuses much less readily than a nonionic dye due to electrostatic forces
 retarding movement. An example of an nonionic dye which converts to a
 cationic dye in the presence of an acid is the following (Since the
 chromophore is involved in the reaction, there is a color change
 indicating the state of the dye molecule):
 ##STR1##
 Examples of such dyes which may be used in the invention are of many
 classes. For example, the dye may be a deprotonated cationic dye which is
 capable of being reprotonated to a cationic dye having an N--H group which
 is part of a conjugated system. Additional examples of such dyes are
 disclosed in U.S. Pat. No. 5,523,274, the disclosure of which is hereby
 incorporated by reference, and include the following:
 ##STR2##
 Another class of dyes useful in the invention is a pendant basic dye
 capable of being protonated to a cationic dye, as disclosed in U.S. Pat.
 Nos. 5,512,532, 5,744,422, and 5,804,531, the disclosures of which are
 hereby incorporated by reference. An example of a pendant basic dye which
 converts to a cationic dye in the presence of an acid is the following:
 ##STR3##
 Additional examples of such dyes include the following:
 ##STR4##
 Another class of dyes useful in the invention is a lactone leuco dye
 capable of being protonated to a cationic dye, as disclosed in U.S. Pat.
 No. 5,830,823 and copending U.S. Ser. No. 08/996,388, the disclosures of
 which are hereby incorporated by reference. An example of a lactone leuco
 dye which converts to a cationic dye in the presence of an acid is the
 following:
 ##STR5##
 An additional example of such dyes includes the following:
 ##STR6##
 Another class of dyes useful in the invention is a carbinol dye capable of
 being protonated to a cationic dye, as disclosed in U.S. Pat. No.
 5,804,531, the disclosure of which is hereby incorporated by reference. An
 example of a carbinol dye which converts to a cationic dye in the presence
 of an acid is the following:
 ##STR7##
 As noted above, the adhesive layer of an acidic polymer used in the
 invention has a Tg less than about 80.degree. C. If the Tg is greater than
 80.degree. C., then low or very little adhesion of the lenticular element
 to the protective element is obtained. Examples of acidic adhesive
 polymers useful in the invention include condensation polymers such as
 polyesters, polyurethanes, polycarbonates, etc.; addition polymers such as
 polystyrenes, vinyl polymers, etc.; and copolymers of more than one type
 of monomer covalently linked together, provided such polymeric material
 contains acid groups as part of the polymer chain. In a preferred
 embodiment of the invention, the acidic adhesive comprises an acrylic
 polymer, an olefinic polymer, an olefin acrylic copolymer, a
 sulfopolyester or a styrenic polymer. The adhesive layer can be used at a
 coverage of from about 0.1 to about 10 g/m.sup.2.
 The release layer used in the invention can be any polymer which will
 enable the lenticular element to separate from the support of the
 mordanting element. The release can occur at the interface of the release
 layer and the support, within the release layer itself, or at the
 interface of the release layer and the next adjacent layer. In a preferred
 embodiment of the invention, the release occurs at the interface of the
 release layer and the support.
 Examples of release layers which can be used in the invention include
 hydroxyethyl cellulose, gelatin, polyvinylbutyral, etc. The release layer
 may be used at a coverage from about 0.2 to about 10 g/m.sup.2. In
 embodiments where the release layer remains with the lenticular element,
 the release layer can provide additional strength, abrasion resistance,
 rigidity, ink receptivity for backside printing and prevention of the
 adhesive layer from sticking to an undesired surface.
 Between the release layer and the acidic adhesive polymer there may be
 located one or more interlayers to give reflection capability, strength,
 extra abrasion resistance, or rigidity. These layers may be a polymeric
 binder containing reflective materials such as TiO.sub.2, barium sulfate,
 hollow beads, etc. In a preferred embodiment of the invention, separation
 occurs at the interface between the release layer and its support. Thus,
 the lenticular element will have a reflection layer located between the
 acidic adhesive polymer and the release layer.
 The dyes of the dye-donor element used in the invention can optionally be
 dispersed in a polymeric binder such as a cellulose derivative, e.g.,
 cellulose acetate hydrogen phthalate, cellulose acetate, cellulose acetate
 propionate, cellulose acetate butyrate, cellulose triacetate or any of the
 materials described in U.S. Pat. No. 4,700,207; polyvinyl butyrate;
 copolymers of maleic anhydride with vinyl ethers such as methyl vinyl
 ether; polycyanoacrylates; a polycarbonate; poly(vinyl acetate);
 poly(styrene-co-acrylonitrile); a polysulfone or a poly(phenylene oxide),
 gelatin, etc. The binder may be used at a coverage of from about 0.1 to
 about 5 g/m.sup.2.
 Any material can be used as the support for the lenticular array of the
 invention provided it is dimensionally stable. Such materials include
 polyesters such as poly(ethylene terephthalate); polyamides;
 polycarbonates; cellulose esters such as cellulose acetate; fluorine
 polymers such as poly(vinylidene fluoride) or
 poly(tetrafluoroethylene-co-hexafluoropropylene); polyethers such as
 polyoxymethylene; polyacetals; polyolefins such as polystyrene,
 polyethylene, polypropylene or methylpentene polymers; and polyimides such
 as polyimide-amides and polyether-imides. The support generally has a
 thickness of from about 50 to about 5000 .mu.m. While the lenticular array
 may be provided on a separate support, generally the support and the array
 are in one integral element.
 Infrared-absorbing materials which may be used in the invention include
 carbon black, cyanine infrared-absorbing dyes as described in U.S. Pat.
 No. 4,973,572, or other materials as described in the following U.S. Pat.
 Nos. 4,948,777; 4,950,640; 4,950,639; 4,948,776; 4,948,778; 4,942,141;
 4,952,552; 5,036,040; and 4,912,083, the disclosures of which are hereby
 incorporated by reference.
 A laser is used to transfer dye from the dye-donor element used in the
 invention. It is preferred to use a diode laser since it offers
 substantial advantages in terms of its small size, low cost, stability,
 reliability, ruggedness, and ease of modulation Lasers which can be used
 to transfer dye from dye-donors employed in the invention are available
 commercially. There can be employed, for example, Laser Model SDL-2420-H2
 from Spectra Diode Labs, or Laser Model SLD 304 V/W from Sony Corp.
 A thermal printer which uses the laser described above to form an image on
 a thermal print medium is described and claimed in U.S. Pat. No.
 5,268,708, the disclosure of which is hereby incorporated by reference.
 Spacer beads may be employed in a separate layer over the dye layer of the
 dye-donor element in the above-described laser process in order to
 separate the donor from the receiver during dye transfer, thereby
 increasing the uniformity and density of the transferred image. That
 invention is more fully described in U.S. Pat. No. 4,772,582, the
 disclosure of which is hereby incorporated by reference. Alternatively,
 spacer beads may be employed in the receiving layer of the receiver as
 described in U.S. Pat. No. 4,876,235, the disclosure of which is hereby
 incorporated by reference. The spacer beads may be coated with a polymeric
 binder if desired.
 As noted above, in the process of the invention, the lenticular element
 with the transferred dye is heated to cause the nonionic dye to convert to
 a cationic dye which is mordanted in the adhesive layer and to cause the
 adhesive layer to adhere the mordanting element to the lenticular element.
 This heating may be accomplished, for example by passing the element
 between a pair of heated rollers. Other methods of heating could also be
 used such as using a heated platen, use of pressure and heat, external
 heating, etc.
 During the heating step, the adhesive layer contacts the lenticular element
 and only adheres in the desired area. Upon separation of the mordanting
 element support from the composite laminate, areas of the mordanting
 element which was not in contact with the lenticular element maintain
 their integrity. In areas of the mordanting element which was in contact
 with the lenticular element, the release layer allows separation without
 the need for a separate trimming step.
 The following examples are provided to illustrate the invention.

EXAMPLES
 Example 1
 Dye Donor Element 1
 The donor element was coated with a laydown of 0.22 g/m.sup.2 carbon black,
 Cabot Black Pearls 700.RTM. (Cabot Corp.), 0.54 g/m.sup.2
 polyvinylbutyral, (Butvar.RTM. 76, Monsanto Co.), 0.01 g/m.sup.2 Fluorad
 FC 431.RTM. surfactant (3M Co.), 0.02 g/m.sup.2 crosslinked
 polydivinylbenzene beads, 5.4 .mu.m, and 0.54 g/m.sup.2 of Dye 1
 (illustrated above) from methyl isobutyl ketone on a 104 .mu.m thick
 poly(ethylene terephthalate) support.
 Dye Donor Element 2
 The donor element was the same as Dye Donor Element 1 except that it
 contained Dye 6 (illustrated above).
 Mordanting Element 1 of the Invention
 A 36 .mu.m thick poly(ethylene terephthalate) support was coated with a
 release layer of polyvinylbutyral, (Butvar.RTM. 76, Monsanto Co.), 0.108
 g/cm.sup.2, from acetone. On top of said release layer was coated a
 mordanting adhesive layer of an aqueous coating of 3.24 g/m.sup.2 of the
 ammonia salt of poly{isophthalic acid-co-5-sulfoisophthalic acid (90:10
 molar ratio)-diethylene glycol (100 molar ratio)}, MW=20,000 (ammonium
 salt of AQ29D, Eastman Chemical Co.) and 0.02 g/m.sup.2 Dispex N-40.RTM.
 surfactant (Ciba Specialty Chemicals).
 Mordanting Element 2 of the Invention
 This element was the same as Mordanting Element 1 of the Invention except
 that between the release layer and the mordanting adhesive layer was
 coated a reflective layer of an aqueous coating of TiO.sub.2 (R706, Dupont
 Inc), 32.4 g/cm.sup.2, and an aqueous coating of 3.24 g/m.sup.2 of the
 ammonia salt of poly{isophthalic acid-co-5-sulfoisophthalic acid (90:10
 molar ratio)diethylene glycol (100 molar ratio)}, MW=20,000 (ammonium salt
 of AQ29D, Eastman Chemical Co.) and 0.02 g/m.sup.2 Dispex N-40.RTM.
 surfactant (Ciba Specialty Chemicals).
 Mordanting Element 3 of the Invention
 This element was the same as Mordanting Element 1 of the Invention except
 that the release layer was hydroxyethyl cellulose (0.32 g/m.sup.2) and 10
 G surfactant (Olin Corp.) (0.03 g/cm.sup.2) and the mordanting adhesive
 layer was an ethylene/acrylic acid (15% acrylic acid) copolymer (1.62
 g/m.sup.2) (Scientific Polymer Products Inc.) from tetrahydrofuran.
 Mordanting Element 4 of the Invention
 This element was the same as Mordanting Element 1 of the Invention except
 that the release layer was gelatin (1.08 g/m.sup.2), 10 G surfactant (Olin
 Corp.) (0.011 g/cm.sup.2) and bis(vinylsulphonyl)methane, (0.022
 g/cm.sup.2).
 Mordanting Element 5 of the Invention
 This element was the same as Mordanting Element 3 of the Invention except
 that the release layer was gelatin (1.08 g/m.sup.2), 10 G surfactant (Olin
 Corp.) (0.011 g/cm.sup.2) and bis(vinylsulphonyl)methane, (0.022
 g/cm.sup.2).
 Control 1 Mordanting Element
 This element was the same as Mordanting Element 1 of the Invention except
 that there was no release layer.
 Control 2 Mordanting Element
 This element was the same as Mordanting Element 3 of the Invention except
 that there was no release layer.
 Lenticular Array
 A polycarbonate lenticular material which consisted of cylindrical lenses
 on one face and a flat rear face was used. This lenticular material had a
 pitch of 1.973 lines/mm and a thickness of 1.27 mm. The lens curvature was
 such that focus was on the rear of the lenticular material.
 Printing
 A dye-donor element was placed dye side to flat rear side of the lenticular
 array and vacuum was applied to hold the donor to the array. Printing was
 accomplished using an SDL 23-S9781 1 watt c-mount laser diode (Spectra
 Diode Labs, Inc.). Approximately 700 mw was delivered to the element in a
 spot approximately 13 .mu.m by 80 .mu.m using the technique of beam
 folding as disclosed in copending application U.S. Ser. No. 09/175,735 of
 Kessler, filed Oct. 20, 1998. Scanning of the spot was accomplished using
 a galvanometer with the beam oriented with the long axis parallel to the
 scan direction as described in the copending application U.S. Ser. No.
 09/128,077, of Kessler et al., filed Aug. 3, 1998. Dwell time was
 approximately 9 microseconds.
 A target image was written onto the back of the donor causing the donor dye
 to be transferred to the lenticular material. The resulting image was
 magenta.
 Mordanting of the dyes and lamination of the mordanting element was
 accomplished by passing the card through a laminator with the adhesive
 layer of the mordanting element in contact with the flat side of the
 lenticular array. The lamination was conducted with a feed rate of 0.36
 cm/sec at a temperature of 133.degree. C. The laminator was a modified GMP
 Co. LTD (Kyoungki-Do, Korea) laminator model Passport-175LSI. The
 modification was to adjust the gap thickness to accommodate the 1270 .mu.m
 lenticular material and the lower roller heating was disabled.
 The support was then peeled from the back of the lenticular material. The
 peeling was evaluated as to difficulty and as to whether the dye image on
 the lenticular support was removed, which is undesirable. The following
 results were obtained:
 TABLE
 Mordanting Element Peelability Dye Image Removal
 1 Good None
 2 Good None
 3 Good None
 4 Good None
 5 Good None
 Control 1 Poor/Support tore Some
 Control 2 Poor Complete
 The above results show that the mordanting elements of the invention peeled
 easily and did not cause any of the image dye layer to be removed, in
 contrast to the control elements
 The invention has been described in detail with particular reference to
 preferred embodiments thereof, but it will be understood that variations
 and modifications can be effected within the spirit and scope of the
 invention.