Slipping Layer Containing Functionalized Siloxane and Wax for Dye-Donor Element Used in Thermal Dye Transfer

This invention relates to dye-donor elements used in thermal dye transfer, and more particularly to the use of a certain polysiloxane and wax slipping layer on the back side thereof to prevent various printing defects and tearing of the donor element during the printing operation.

In recent years, thermal transfer systems have been developed to obtain prints from pictures which have been generated electronically from a color video camera. According to one way of obtaining such prints, an electronic picture is first subjected to color separation by color filters. The respective color-separated images are then converted into electrical signals. These signals are then operated on to produce cyan, magenta and yellow electrical signals. These signals are then transmitted to a thermal printer. To obtain the print, a cyan, magenta or yellow dye-donor element is placed face-to-face with a dye-receiving element. The two are then inserted between a thermal printing head and a platen roller. A line-type thermal printing head is used to apply heat from the back of the dye-donor sheet. The thermal printing head has many heating elements and is heated up sequentially in response to the cyan, magenta and yellow signals. The process is then repeated for the other two colors. A color hard copy is thus obtained which corresponds to the original picture viewed on a screen. Further details of this process and an apparatus for carrying it out are contained in U.S. Pat. No. 4,621,271 by Brownstein entitled "Apparatus and Method For Controlling A Thermal Printer Apparatus," issued Nov. 4, 1986, the disclosure of which is hereby incorporated by reference.

A problem has existed with the use of dye-donor elements for thermal dye-transfer printing because a thin support is required in order to provide effective heat transfer. For example, when a thin polyester film is employed, it softens when heated during the printing operation and then sticks to the thermal printing head. This causes intermittent rather than continuous transport across the thermal head. The dye transferred thus does not appear as a uniform area, but rather as a series of alternating light and dark bands (chatter marks).

Another defect called "smiles", which are crescent shaped low density areas, is produced in the receiving element by stretch-induced folds in the dye-donor.

Another defect is produced in the receiving element when abraded or melted debris from the back of the dye-donor builds up on the thermal head and causes steaks parallel to the travel direction and extending over the entire image area. In extreme cases, sufficient friction is often created to tear the dye-donor element during printing.

Another defect called "pops" occurs when printing images that have lines or edges parallel to the heat-line of the print head. This results in a significant number of heater elements across the head changing from hot to cold at the same time. These sudden hot to cold transitions may result in sticking of the thermal head to the donor and a jerking motion. The jerking motion causes skipped printing lines and misregistration of the image usually results. At times, the release of this sticking may be so severe as to create a popping noise, or "pops". It would be desirable to eliminate or lessen the above such problems in order to have a commercially acceptable system.

U.S. Pat. No. 4,738,950 of Vanier and Evans, issued Apr. 19, 1988, relates to the use of particular amino-modified silicone materials for use as a slipping layer in thermal dye transfer systems. While this material has been good in many respects, any improvement in lessening any of the above problems would be highly desirable. As will be shown by comparative tests hereinafter, the slipping layer of the invention has improved lubricity resulting in minimized "pops".

U.S. Ser. No. 214,364 filed July 1, 1988 by Vanier entitled "Slipping Layer Containing Acyloxy-Terminated Siloxane For Dye-Donor Element Used In Thermal Dye Transfer" relates to certain siloxanes useful in this invention.

Accordingly, this invention relates to a dye-donor element for thermal dye transfer comprising a support having on one side thereof a dye layer and on the other side a slipping layer, and wherein the slipping layer comprises a functionalized poly(dialkyl, diaryl or alkylaryl siloxane) and a hydrocarbon, ester or amide wax.

A functionalized polysiloxane is a poly(dialkyl, diaryl or alkylaryl siloxane) with at least one terminal group that is different from the group or groups that comprise the polymer backbone. For example, there may be employed in the invention a methyldiacetoxy-terminated polydimethylsiloxane, a methylmonoacetoxy-terminated polydimethylsiloxane or an aminopropyldimethyl-terminated polydimethyllsiloxane. In a preferred embodiment of the invention, the polysiloxane has the formula: ##STR1## wherein n is an integer of from 1 to 3;

m is an integer of from 0 to 2;

n+m=3;

p is from about 10 to about 2000;

each R is independently a substituted or unsubstituted alkyl group having from 1 to about 18 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, pentyl, hexyl, methoxyethyl, benzyl, 2-methanesulfonamidoethyl, 2-hydroxyethyl, 2-cyanoethyl, methoxycarbonylmethyl, etc.; or a substituted or unsubstituted aryl group having from about 6 to about 10 carbon atoms, such as phenyl, pyridyl, naphthyl, p-tolyl, p-chlorophenyl, m-(N-methyl sulfamoyl)phenyl, etc.; and

each R.sub.1 is independently a substituted or unsubstituted alkyl group having from 1 to about 7 carbon atoms, such as methyl, ethyl, propyl, isopropyl, n-butyl, t-butyl, s-butyl, n-pentyl, n-hexyl, 3-hexyl, methoxyethyl, benzyl, 2-methanesulfonamidoethyl, 2-hydroxyethyl, 2-cyanoethyl, methoxycarbonylmethyl, etc.; or a substituted or unsubstituted aryl group having from about 6 to about 10 carbon atoms such as those listed above for R.

In another preferred embodiment of the invention, the polysiloxane is a methyldiacetoxy-terminated polydimethylsiloxane, such as one having the formula: ##STR2## wherein q is from about 10 to about 2000, having a molecular weight of about 36,000. This material is supplied commercially from Petrarch Systems, Inc. Bartram Rd. Bristol, Pa. 19007 as PS368.5.RTM..

In still another preferred embodiment of the invention, the polysiloxane is a methylmonoacetoxy-terminated polydimethylsiloxane, such as one having the formula: ##STR3## wherein r is from about 10 to about 2,000, having a molecular weight of about 36,000. This material is supplied commercially from Petrarch Systems, Inc. Bartram Rd. Bristol, Pa. 19007 as PS363.5.RTM..

In yet still another preferred embodiment of the invention, the polysiloxane is an aminopropyldimethyl-terminated polydimethylsiloxane, such as one having the formula: ##STR4## wherein s is from about 10 to about 2000. This material is supplied commercially from Petrarch Systems, Inc. Bartram Rd. Bristol, Pa. 19007 as PS513.RTM..

The polysiloxane may be present in any amount which is effective for the intended purpose. In a preferred embodiment of the invention, the polysiloxane is present in an amount of from about 0.0005 to about 0.05 g/m.sup.2.

A polymeric binder may also be used in the slipping layer of the invention. In a preferred embodiment, thermoplastic binders are employed. Examples of such materials include, for example, poly(styrene-co-acrylonitrile) (70/30 wt. ratio); poly(vinyl alcohol-co-butyral) (available commercially as Butvar 76.RTM. by Monsanto Corp.; poly(vinyl alcohol-co-acetal); poly(vinyl alcohol-co-benzal); polystyrene; poly(vinyl acetate); cellulose acetate butyrate; cellulose acetate propionate; cellulose acetate; ethyl cellulose; bisphenol-A polycarbonate resins; cellulose triacetate; poly(methylmethacrylate); copolymers of methyl methacrylate; poly(styrene-co-butadiene), etc. In a preferred embodiment of the invention, the thermoplastic binder is cellulose acetate propionate.

When the above acyloxy-terminated siloxane material is coated in a polymeric binder, certain reactions may take place. The siloxane may react with moisture and the acyloxy groups may be hydrolyzed off. In addition, the siloxane groups may react with each other or with a hydroxyl group from the binder to give a cross-linked silicone.

When a polymeric binder is used in the slipping layer of the invention, the amount is not critical. In general, the polymeric binder may be employed in an amount of from about 0.1 to about 2 g/m.sup.2.

Any hydrocarbon, ester or amide wax may be used in the invention. Generally speaking, a wax is a substance which is a solid at ambient temperature and which has a low viscosity at just above the melting point. Such wax materials useful in the invention include carnauba wax, bees wax, paraffin wax, petrolatum, pentaerythritol tetrastearate, micronized polyethylene particles, a blend of polyethylene and carnauba waxes, erucylerucamide or erucamide.

The wax may be employed at any concentration useful for the intended purpose. In general, good results have been obtained at a concentration of from about 0.005 to about 0.5 g/m.sup.2.

U.S. application Ser. No. 173,345 of Vanier filled Mar. 25, 1988 relates to the use of organic lubricating particles in a slipping layer. Such particles are also useful in the slipping layer of this invention and the above application is hereby incorporated by reference.

Any dye can be used in the dye layer of the dye-donor element of the invention provided it is transferable to the dye-receiving layer by the action of heat. Especially good results have been obtained with sublimable dyes. Examples of sublimable dyes include anthraquinone dyes, e.g., Sumikalon Violet RS.RTM. (product of Sumitomo Chemical Co., Ltd.), Dianix Fast Violet 3R-FS.RTM. (product by Mitsubishi Chemical Industries, Ltd.), and Kaylalon Polyol Brilliant Blue N-BGM.RTM. and KST Black 146.RTM. (products of Nippon Kayaku Co., Ltd.); azo dyes such as Kayalon Polyol Brilliant Blue BM.RTM., Kayalon Polyol Dark Blue 2BM.RTM., and KST Black KR.RTM. (products of Nippon Kayaky Co., Ltd.), Sumickaron Diazo Black 5G.RTM. (product of Sumitomo Chemical Co., Ltd.), and Miktazol Black 5GH.RTM. (product of Mitsui Toatsu Chemicals, Inc.); direct dyes such as Direct Dark Green B.RTM. (product of Mitsubishi Chemical Industries, Ltd.) and Direct Brown M.RTM. and Direct Fast Black D.RTM. (products of Nippon Kayaku Co. Ltd.); acid dyes such as Kayanol Milling Cyanine 5R.RTM. (product of Nippon Kayaku Co. Ltd.); basic dyes such as Sumicacryl Blue 6G.RTM. (product of Sumitomo Chemical Co., Ltd.), and Aizen Malachite Green.RTM. (product of Hodogaya Chemical Co., Ltd.); ##STR5## or any of the dyes disclosed in U.S. Pat. No. 4,541,830, the disclosure of which is hereby incorporated by reference. The above dyes may be employed singly or in combination to obtain a monochrome. The dyes may be used at a coverage of from about 0.05 to about 1 g/m.sup.2 and are preferably hydrophobic.

A dye-barrier layer may be employed in the dye-donor elements of the invention to improve the density of the transferred dye. Such dye-barrier layer materials include hydrophilic materials such as those described and claimed in U.S. Pat. No. 4,716,144 by Vanier, Lum and Bowman.

The dye in the dye-donor element of the invention is 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 of Vanier and Lum; a polycarbonate; poly(styrene-co-acrylonitrile), a poly(sulfone) or a poly(phenylene oxide). The binder may be used at a coverage of from about 0.1 to about 5 g/m.sup.2.

The dye layer of the dye-donor element may be coated on the support or printed thereon by a printing technique such as a gravure process.

Any material can be used as the support for the dye-donor element of the invention provided it is dimensionally stable and can withstand the heat of the thermal printing heads. Such materials include polyesters such as poly(ethylene terephthalate); polyamides; polycarbonates; glassine paper; condenser paper; cellulose esters such as cellulose acetate; fluorine polymers such as polyvinylidene fluoride or poly(tetrafluoroethylene-co-hexafluoropropylene); polyethers such as polyoxymethylene; polyacetals; polyolefins such as polystyrene, polyethylene, propylpropylene or methylpentane polymers; and polyimides such as polyimides-amides and polyetherimides. The support generally has a thickness of from about 2 to about 30 .mu.m. It may also be coated with a subbing layer, if desired, such as those materials described in U.S. Pat. No. 4,695,288 of Ducharme or U.S. application Ser. No. 079,613 of Henzel, filed July 30, 1987.

The dye-receiving element that is used with the dye-donor element of the invention usually comprises a support having thereon a dye image-receiving layer. The support may be a transparent film such as a poly(ether sulfone), a polyimide, a cellulose ester such as cellulose acetate, a poly(vinyl alcohol-co-acetal) or a poly(ethylene terephthalate). The support for the dye-receiving element may also be reflective such as baryta-coated paper, polyethylene-coated paper, white polyester (polyester with white pigment incorporated therein), an ivory paper, a condenser paper or a synthetic paper such as duPont Tyvek.RTM..

The dye image-receiving layer may comprise, for example, a polycarbonate, a polyurethane, a polyester, polyvinyl chloride, poly(styrene-co-acrylonitrile), poly(caprolactone) or mixtures thereof. The dye image-receiving layer may be present in any amount which is effective for the intended purpose. In general, good results have been obtained at concentration of from about 1 to about 5 g/m.sup.2.

As noted above, the dye-donor elements of the invention are used to form a dye transfer image. Such a process comprises imagewise-heating a dye-donor element as described above and transferring a dye image to a dye-receiving element to form the dye transfer image.

The dye-donor element of the invention may be used in sheet form or in a continuous roll or ribbon. If a continuous roll or ribbon is employed, it may have only one dye or may have alternating areas of other different dyes, such as sublimable cyan and/or magenta and/or yellow and/or black or other dyes. Such dyes are disclosed in U.S. Pat. Nos. 4,541,830; 4,698,651 of Moore, Weaver and Lum; 4,695,287 of Evans and Lum; and 4,701,439 of Weaver, Moore and Lum; and U.S. application Ser. Nos. 059,442 of Byers and Chapman, filed June 8, 1987; 059,443 of Evans and Weber, filed June 8, 1987; 095,796 of Evans and Weber, filed Sept. 14, 1987; and 123,441 of Byers, Chapman and McManus, filed Nov. 20, 1987, the disclosures of which are hereby incorporated by reference. Thus, one-, two-, three- or four-color elements (or higher numbers also) are included within the scope of the invention.

In a preferred embodiment of the invention, the dye-donor element comprises a poly(ethylene terephthalate) support coated with a sequential repeating areas of yellow, cyan and magenta dye, and the above process steps are sequentially performed for each color to obtain a three-color dye transfer image. Of course, when the process is only performed for a single color, then a monochrome dye transfer image is obtained.

Thermal printing heads which can be used to transfer dye from the dye-donor elements of the invention are available commercially. There can be employed, for example, a Fujitsu Thermal Head (FTP-040 MCS001), a TDK Thermal Head F415 HH7-1089 or a Rohm Thermal Head KE 2008-F3.

A thermal dye transfer assemblage of the invention comprises

(a) a dye-donor element as described above, and

(b) a dye-receiving element as described above,

the dye-receiving element being in a superposed relationship with the dye-donor element so that the dye layer of the donor element is in contact with the dye image-receiving layer of the receiving element.

The above assemblage comprising these two elements may be preassembled as an integral unit when a monochrome image is to be obtained. This may be done by temporarily adhering the two elements together at their margins. After transfer, the dye-receiving element is then peeled apart to reveal the dye transfer image.

When a three-color image is to be obtained, the above assemblage is formed on three occasions during the time when heat is applied by the thermal printing head. After the first dye is transferred, the elements are peeled apart. A second dye-donor element (or another area of the donor element with a different dye area) is then brought in register with the dye-receiving element and the process repeated. The third color is obtained in the same manner.

The following examples are provided to illustrate the invention.

A cyan dye-donor element was prepared by coating on a 6 .mu.m poly(ethylene terephthalate) support:

(1) a subbing layer of a titanium alkoxide (duPont Tyzor TBT.RTM.) (0.12 g/m.sup.2) from a n-propyl acetate and n-butyl alcohol solvent mixture, and

(2) a dye layer containing the cyan dye illustrated above (0.28 g/m.sup.2) and Micropowders, Inc. Fluo-HT.RTM. micronized polytetrafluoroethylene (0.05 g/m.sup.2), in a cellulose acetate propionate (2.5% acetyl, 45% propionyl) binder (0.44 g/m.sup.2) coated from a toluene, methanol and cyclopentanone solvent mixture.

On the back side of the dye-donor was coated:

(1) a subbing layer of a titanium alkoxide (duPont Tyzor TBT.RTM.) (0.12 g/m.sup.2) coated from a n-propyl acetate and n-butyl alcohol solvent mixture, and

(2) a slipping layer of a terminally modified polysiloxane or the control material identified below with and without different waxes at either 0.016 or 0.032 g/m.sup.2 in a cellulose acetate propionate binder (2.5% acetyl, 45% propionyl) (0.54 g/m.sup.2) coated from a toluene and 3-pentanone solvent mixture.

The control slipping layers were prepared by omission of the silicone material, omission of the wax or substitution of the terminally-modified silicone with a non-modified silicone or with mineral oil.

The following terminally-modified polysiloxanes were evaluated:

PS368.5.RTM. Polysiloxane (Petrarch Systems, Inc. Bartram Rd. Bristol, Pa. 19007), illustrated above.

PS513.RTM. Polysiloxane (Petrarch Systems, Inc. Bartram Rd. Bristol, Pa. 19007), illustrated above, neutralized with p-toluene sulfonic acid.

PS043.RTM. Polysiloxane (Petrarch Systems, Inc. Bartram Rd. Bristol, Pa. 19007), having the formula: ##STR6## wherein n is from about 10 to about 2000, m.wt. 28,000

The following waxes were evaluated in combination with the above polysiloxanes:

Carnauba wax (Kodak L & R Products)

Bees wax (Kodak L & R Products)

Paraffin wax (mp 63.degree. C.) (Fisher Scientific)

Petrolatum (Kodak L & R Products)

Hexawax (Kodak L & R Products), pentaerylthritol tetrastearate, an ester wax

Micronized polyethylene particles (S-395N5.RTM. Shamrock Technologies Inc.), average particle size 12.5 .mu.m and m.p. 125.degree. C.

Micronized polyethylene wax (MPP-620XF.RTM. from Micro Powders Inc.), average particle size 2 .mu.m and melting point of 116.degree. C.

Micronized blend of polyethylene and carnauba waxes (S-232.RTM. Shamrock Technologies), 5 .mu.m avg. particle size

Erucylerucamide (an amide wax) (Humko-Sheffield Co. Kemamide E-221.RTM.)

Erucamide (an amide wax) (Humko-Sheffield Co. Kemamide E.RTM.)

A dye-receiving element was prepared by coating the following layers in the order recited on a titanium dioxide-pigmented polyethylene-overcoated paper stock which was subbed with a layer of poly(acrylonitrile-co-vinylidene chloride-co-acrylic acid) (14:79:7 wt. ratio) (0.08 g/m.sup.2) coated from 2-butanone:

(1) Dye-receiving layer of Makrolon 5705.RTM. (Bayer Ag Corporation) polycarbonate resin (2.9 g/m.sup.2), Tone PCL-300.RTM. polycaprolactone (Union Carbide) (0.38 g/m.sup.2), and 1,4-didecoxy-2,6-dimethoxyphenol (0.38 g/m.sup.2) coated from methylene chloride; and

(2) Overcoat layer of Tone PCL-300.RTM. polycaprolactone (Union Carbide) (0.11 g/m.sup.2), FC-431.RTM. surfactant (3M Corp.) (0.016 g/m.sup.2) and DC-510.RTM. Surfactant (Dow Corning) (0.016 g/m.sup.2) coated from methylene chloride.

The dye side of the dye-donor element strip approximately 10 cm.times.13 cm in area was placed in contact with the dye image-receiving layer of the dye-receiver element of the same area. The assemblage was clamped to a stepper-motor driven 60 mm diameter rubber roller and a TDK Thermal Head (No. L-231) (thermostatted at 26.degree. C.) was pressed with a force of 8.0 pounds (3.6 kg) against the dye-donor element side of the assemblage pushing it against the rubber roller.

The imaging electronics were activated causing the donor/receiver assemblage to be drawn between the printing head and roller at 6.9 mm/sec. Coincidentally, the resistive elements in the thermal print head was pulsed for 29 .mu.sec/pulse at 128 .mu.sec intervals during the 33 msec/dot printing time. A test pattern of alternating D-max and D-min bars, 1.5 mm in width, was generated by varying the number of pulses/dot from 0 to 255. The voltage supplied to the print head was approximately 23.5 volts, resulting in an instantaneous peak power of 1.3 watts/dot and a maximum total energy of 9.6 mjoules/dot.

As each "test pattern" of alternating density bars was being generated, the force required for the pulling device to draw the assemblage between the print head and roller was measured using a Himmelstein Corp. 3-08TL(16-1) Torquemeter.RTM. (10inch-lb. range) and 6-205 Conditioning Module.RTM.. The force was tabulated at the edge of the passage from a D-max area to a D-min area. A low force at this boundary is desirable to minimize "pops" and misregistration. The lower the force, the better. The following results were obtained:

The above results indicate that the slippling layer according to the invention gave superior performance as compared to nonfunctionalized polysiloxanes or mineral oil in combination with various waxes. In addition, the total weight of polysiloxane and wax generally improved the performance over the same weight of each component individually.

Cyan dye donors were prepared as described in Example 1, but two organic lubricating particles were also added to the slipping layers as follows:

A. Emralon 329.RTM. (Acheson Colloids Corp.) described by the manufacturer as a dry-film lubricant of poly(tetrafluoroethylene) particles in a thermoplastic resin supplied as a liquid concentrate. The thermoplastic resin is cellulose nitrate in a n-propylacetate, toluene, 2-propanol and 1-butanol solvent. The approximate particle size of the irregular shaped particles is 1 to 5 .mu.m; no particles are larger than 10 .mu.m. The fluorocarbon represents approximately 50% of the total weight. (In this slipping layer, no cellulose acetate propionate binder was used since the cellulose nitrate served as the binder.)

B. Fluo HT.RTM. (Micro Powder Inc.) fluorocarbon powder of micronized polytetrafluoroethylene, 2 .mu.m average particle size.

Each wax and lubricant was coated at 0.016 g/m.sup.2.

Dye-receivers was prepared as in Example 1. The evaluation procedure of Example 1 was also used with the following results:

The above results indicate that the use of lubricating particles in addition to the combination of functionalized polysiloxane and wax gave superior printing performance.

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.