POLYMERIC BINDER FOR AMINO-MODIFIED SILICONE SLIPPING LAYER FOR DYE-DONOR ELEMENT USED IN THERMAL DYE TRANSFER

Abstract: 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 comprising a lubricating material dispersed in a polymeric binder, the lubricating material comprising a linear or branched aminoalkyl-terminated poly(dialkyl, diaryl or alkylaryl siloxane) such as an aminopropyldimethyl-terminated polydimethyl­ siloxane and said polymeric binder comprises cellulose acetate propionate, cellulose nitrate or cellulose acetate hydrogen phthalate. The particular binders used minimize sticking and dye crystalliza­ tion when the dye-donor element is wound up upon itself.

Description: This invention relates to dye-donor elements used in thermal dye transfer, and more particularly to the use of particular binders in an amino-modified silicone slipping layer on the back side thereof. 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. Patent No. 4,621,271 by Brownstein entitled "Apparatus and Method For Controlling A Thermal Printer Apparatus," issued November 4, 1986. 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. It is an object of this invention to eliminate such problem in order to have a commercially acceptable system. In EP-A-0,295,484 of Vanier et al., amino-modified silicone slipping layers are disclosed and claimed (EP-A-0,295,484 belongs to the prior art according to Article 54(3)(4)EPC). While these materials have good slipping layer properties, a problem has developed when the dye-donor element is wound up on itself. There is a tendency for sticking and dye crystallization in the dye-binder layer to occur when certain binders are used for the slipping layer. It is an object of this invention to lessen or eliminate those problems. These and other objects are achieved in accordance with this invention which 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 comprising a lubricating material dispersed in a polymeric binder, characterized in that the lubricating material comprises a linear or branched aminoalkyl-terminated poly(dialkyl, diaryl or alkylaryl siloxane) and said polymeric binder comprises cellulose acetate propionate, cellulose nitrate or cellulose acetate hydrogen phthalate. Use of these particular binders lessens the sticking and dye crystallization problems described above. In a preferred embodiment of the invention, the polysiloxane is present in an amount of from 0.0005 to 0.05 g/m², representing approximately 0.1 to 10% of the binder weight. Any polysiloxane can be employed in the slipping layer of the invention providing it is a linear or branched poly(dialkyl, diaryl or alkylaryl siloxane) containing one or more aminoalkyl terminal units. In a preferred embodiment of the invention, the siloxane is an aminopropyldimethyl-terminated polydimethylsiloxane such as one having the formula: wherein n is from 10 to 2000. This material is supplied commercially from Petrarch Systems, Inc. Bartram Rd. Bristol, Pennsylvania 19007 as PS513®. In another embodiment of the invention, the siloxane polymer is a T-structure polydimethylsiloxane with an aminoalkyl functionality at the branchpoint, such as one having the formula wherein m is from 1 to 10 and n is from 10 to 1000. This material is supplied commercially from Petrarch Systems, Inc. as PS054®. As noted above, the polymeric binder used in the slipping layer of the invention comprises cellulose acetate propionate, cellulose nitrate or cellulose acetate hydrogen phthalate. In the cellulose acetate propionate, the acetyl content preferably ranges from 2 to 3%, the propionyl content preferably ranges from 35 to 50%, and the hydroxyl content preferably ranges from 1.5 to 7%. In the cellulose nitrate, the nitration preferably ranges from 60 to 80%. In the cellulose acetate hydrogen phthalate, the acetyl content preferably ranges from 18 to 25% and the phthalyl content preferably ranges from 25 to 40%. In a preferred embodiment of the invention, the binder is cellulose acetate propionate since it is available in a variety of viscosities and does not require chlorinated solvents for coating. The amount of polymeric binder used in the slipping layer of the invention is not critical. In general the polymeric binder may be present in an amount of from 0.1 to 2 g/m². 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 such as or any of the dyes disclosed in U.S. Patent 4,541,830. The above dyes may be employed singly or in combination to obtain a monochrome. The dyes may be used at a coverage of from 0.05 to 1 g/m² and are preferably hydrophobic. The dye in the dye-donor element 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; a polycarbonate; poly(styrene-co-acrylonitrile), a poly(sulfone) or a poly(phenylene oxide). The binder may be used at a coverage of from 0.1 to 5 g/m². 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; fluorine polymers; polyethers; polyacetals; polyolefins; and polyimides. The support generally has a thickness of from 2 to 30 µm. It may also be coated with a subbing layer, is desired. 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®. In a preferred embodiment, polyester with a white pigment incorporated therein is employed. 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 a concentration of from 1 to 5 g/m². As noted above, the dye-donor elements of the invention are used to form a dye transfer image. Such as 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 thereon or may have alternating areas of different dyes, such as sublimable cyan, magenta, yellow, black, etc., as described in U.S. Patent 4,541,830. 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 sequential repeating areas of cyan, magenta and yellow 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. 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 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 example is provided to illustrate the invention. Example A cyan dye-donor element was prepared by coating on a 6µm poly(ethylene terephthalate) support: 1) a subbing layer of a titanium alkoxide (duPont Tyzor TBT®) (0.12 g/m²) 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/m²) and duPont DLX-6000 Teflon® micropowder (0.016 g/m²), in a cellulose acetate propionate (2.5% acetyl, 45% propionyl) binder (0.44 g/m²) coated from a toluene, methanol and cyclopentanone solvent mixture. On the back side of the dye-donor was coated: 1) a subbing layer of titanium alkoxide (duPont Tyzor TBT®) (0.12 g/m²) from a n-propyl acetate and 1-butanol solvent mixture, and 2) a slipping layer of the siloxane described below (0.016 g/m²) neutralized with 0.0004 g/m² p-toluene sulfonic acid in the binders, each at 0.54 g/m², indicated below. J = -(CH₂)₃NH₂ Available commercially from Petrarch Systems, Inc. : PS-513 (viscosity: 2000 ctsk. ∼2300 mw) Control Binders (coated toluene and 3-pentanone solvent mixture) A) Cellulose acetate butyrate (2.8% acetyl, 50% butyryl) B) Ethyl cellulose (Hercules Corp. type 50) C) Poly(styrene-co-acrylonitrile) (30:70 wt. ratio) D) Poly(vinyl alcohol-benzal) (Butvar 76® Monsanto Corp.) E) Poly(vinyl acetate) F) Poly(methyl methacrylate) Invention Binders (coated from toluene and 3-pentanone solvent mixture) 1) Cellulose acetate propionate (2.5% acetyl, 45% propionyl, 2.8% hydroxyl) 2) Cellulose acetate propionate (2.5% acetyl, 40% propionyl, 5.0% hydroxyl) 3) Cellulose nitrate (an ester of cellulose and nitric acid, 77% nitrated 4) Cellulose acetate hydrogen phthalate (19-24% acetyl, 30-36% phthalyl) The coated dye-donors were rolled with moderate tension on a 22 mm diameter cylindrical wooden dowel (60g) and incubated for three days at 60°C, 60% RH. After this period of time, the ease of unwinding of the dye-donor and visual observance of dye crystals that formed within the dye layer were recorded using the following categories: Sticking 1. Roll unwound freely by holding one end and letting it fall by gravity. 2. Roll unwound but with a slight cracking noise. 3. Roll unwound but with distinct cracking noise. 4. Roll barely unwound. 5. Roll failed to unwind. Dye Crystallization 1. No crystals visible. 2. Barely noticeable crystal formation. 3. Moderate crystal formation. 4. Substantial crystal formation. 5. Virtual complete crystal formation. The following results were obtained: Binder Sticking Dye Crystals A (Control) 4 5 B (Control) 4 3 C (Control) 3 5 D (Control) 5 5 E (Control) 5 5 F (Control) 3 5 1 1 3 2 2 2 3 1 2 4 2 1 The above results indicate that the polymeric binders of the invention have less front to backside sticking or dye crystals or both than other closely-related polymeric binders.

Claims: 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 comprising a lubricating material dispersed in a polymeric binder, said lubricating material comprising a linear or branched aminoalkyl-terminated poly(dialkyl, diaryl or alkylaryl siloxane) and said polymeric binder comprising cellulose acetate propionate, cellulose nitrate or cellulose acetate hydrogen phthalate. The element of Claim 1 characterized in that said polysiloxane is present in an amount of from 0.0005 to 0.05 g/m², representing approximately 0.1 to 20% of the binder weight. The element of Claim 1 characterized in that said polymeric binder is cellulose acetate propionate. The element of Claim 1 characterized in that said siloxane is an aminopropyldimethyl-terminated polydimethylsiloxane. The element of Claim 4 characterized in that said polysiloxane has the formula: wherein n is from 10 to 2000. The element of Claim 1 characterized in that said support comprises poly(ethylene terephthalate). The element of Claim 6 characterized in that said dye layer comprises sequential repeating areas of cyan, magenta and yellow dye. A thermal dye transfer assemblage comprising: a) a dye-donor element comprising a support having on one side thereof a dye layer and on the other side a slipping layer comprising a lubricating material dispersed in a polymeric binder, and b) a dye-receiving element comprising a support having thereon a dye image-receiving layer, said dye-receiving element being in a superposed relationship with said dye-donor element so that said dye layer is in contact with said dye image-receiving layer, said lubricating material comprising a linear or branched aminoalkyl-terminated poly(dialkyl, diaryl or alkylaryl siloxane) and said polymeric binder comprising cellulose acetate propionate, cellulose nitrate or cellulose acetate hydrogen phthalate. The assemblage of Claim 8 characterized in that said polysiloxane is present in an amount of from about 0.0005 to about 0.05 g/m², representing approximately 0.1 to 10% of the binder weight. The assemblage of Claim 8 characterized in that said polymeric binder is cellulose acetate propionate and said siloxane is an aminopropyldimethyl-terminated polydimethylsiloxane.

Inventors: VANIER, NOEL RAWLE C/O EASTMAN KODAK COMPANY
Applicants: EASTMAN KODAK COMPANY (A NEW JERSEY CORPORATION)
Application year: 1988
Main classification: B41M5
IPC codes: C08L1, B41M5