Patent Publication Number: US-5294588-A

Title: Sheet for sublimation transfer

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sheet for sublimation transfer to be used in a thermal transfer recording apparatus, such as a thermal printer, a thermal typewriter, a laser printer and so forth. 
     2. Description of the Prior Art 
     In such kind of a sheet for sublimation transfer, a lubricative heat resisting layer is provided on the backside of a material sheet. An ink layer is formed on the surface of the sheet by coating an ink containing dispersing dyes or the like which sublimate by heating. From the backside of the sheet where the lubricative heat resisting layer is formed, thermal transfer corresponding to an image information is performed by means of a thermal head, laser or so forth to transfer the image on to an object, to which the image is to be transferred. 
     Conventionally, the ink contains a binder in addition to sublimation type dyes. As such binder, in addition to a saturated polyester resin, polycarbonate resin, cellulosic resin, polyvinyl acetoacetal resin (Japanese Patent Laid Open (Kokai) No. 63-151484) and polyvinyl butyral resin (Japanese Patent Laid Open (Kokai) No. 60-101087) among polyvinyl acetal resins are used. 
     Namely, in the following formula (I) expressing a vinyl acetal group (X), polyvinyl acetoacetal resin contains CH 3  as alkyl group R and polyvinyl butyral resin contains C 3  H 7 . ##STR2## 
     Among the conventional binders saturated polyester resin or polycarbonate resin have relatively high capability of dispersing dyes. However, these resins are defective in a tendency of melting on a printing paper during thermal transfer. On the other hand, polyvinyl acetoacetal resin, polyvinyl butyral resin, or the cellulosic resin, such as ethyl cellulose, propyl cellulose and the like have a property of hardly melting on the printing paper. However, these binder materials have a defect in insufficient holding capability of the dispersing dyes. For instance, the above-mentioned binders are added to respective inks of yellow, magenta, and cyan. Then, respective ink is coated on a material sheet in order of yellow, magenta and cyan to prepare a sheet for sublimation transfer. Then such sheet is wound on a tube of vinyl chloride having a diameter of 1 inch for a plurality of turns, and maintained within a thermostatic chamber at 60° C. for 96 hours. Then, there is observed a dye transferring phenomenon to transfer the dispersing dyes forming yellow, magenta and cyan in the ink layer to the lubricative heat resisting layer on the backside of the material sheet. 
     SUMMARY OF THE INVENTION 
     Therefore, it is an object of the present invention to provide a sheet for sublimation transfer which will not melt on a printing paper during thermal printing, and in which ink will never be transferred to a lubricative heat resisting layer on the backside of the material sheet even when it is left in piled condition by being wound for a plurality of times, under higher temperature condition which is higher than a room temperature. 
     In order to accomplish the above-mentioned object, a sheet is provided for sublimation transfer, having a lubricative heat resisting layer on one side of a material sheet and an ink layer formed on the other side of the material sheet, which ink layer is formed by coating a sublimation transfer ink containing binder composed of vinyl acetal group (X), vinyl alcohol group (Y), and vinyl acetate group (Z) as expressed by the following formula (I): ##STR3## wherein R of said polyvinyl acetal resin is H, C 2  H 5  or an alkyl group of 4 or more carbon atoms. 
     The sublimation transfer ink to be used for forming the ink layer of the present invention is prepared by solving a sublimation type dispersing dye with the above-mentioned binder and then coating it on one side of the material sheet by a solvent. 
     The binder may be selected from polyvinyl formal having H as group R, polyvinyl propyral having C 2  H 5  as alkyl group, or polyvinyl pental (R=C 4  H 9 ), polyvinyl hexal (R=C 5  H 11 ), polyvinyl heptal (R=C 6  H 13 ) or polyvinyl acetal having a greater number of carbon atoms, as the alkyl group R. When an isocyanate compound is preferably mixed with the binder, isocyanate group of the isocyanate compound forms urethane coupling with hydroxyl group of the binder to enhance capability of holding dyes. 
     Composition of the ink is preferred to contain, with respect to total amount of ink 100 wt part, 3˜15 wt part of dyes, 1˜50 wt part of the binder, 0 to 50 wt part of the isocyanate compound, 96˜50 wt part of the solvent. 
     Further preferably, an anchor coating is preliminarily provided on the surface, on which the ink is to be coated. The anchor coating agent is preferably prepared by solving the binder with a solvent. Also, it is further preferred to include isocyanate compound with the binder. 
     As the solvent for the ink, the lubricative heat resisting agent or the anchor coating agent, a known solvent, such as toluene, methyl ethyl ketone or so forth can be used. 
     As the material sheet for the present invention, a plastic film in a thickness approximately 2 to 25 μm, such as polyester, polyimide, polysulfone, polystyrene, polycarbonate or so forth, can be used. 
     It is known to those skilled in the art that a glass transition point becomes higher as a greater number of carbon atoms is present in the alkyl group R in the vinyl acetal group (X), namely as there is a greater molecular weight per vinyl acetal monomer, and as a greater number of the vinyl acetal groups (X) is present, namely as there is a greater polymerization degree. By providing a composition ratio greater than or equal to 15˜20% of vinyl alcohol group (Y) in the molecular chain, hydroxyl group (--OH) in the vinyl alcohol group may promote stabilization of electron density in the dye molecule and act to maintain coupling of polar component of the dye molecule and hydrogen. However, in case of vinyl acetoacetal (R=CH 3 ) or vinyl butyral (R=C 3  H 7 ) having number of carbon atoms, n=1 or n=3, or in case of vinyl formal (R=H) or vinyl propyral (R=C 2  H 5 ) having number of carbon atoms, n=0 or n=2, among normally known vinyl acetal group (X), number of carbon atoms is less than or equal to 3which results in a small molecular weight and low glass transition point. Also, at the same time, there is a tendency to lower content ratio of hydroxyl group (--OH) in vinyl alcohol group to make shelf life unstable. Among vinyl acetal group (X) containing carbon atoms less than or equal to 3 in alkyl group, vinyl formal (R=H) and vinyl propyral (R=C 2  H 5  at n=0 or n=2), the polymerization degree is required to establish molecular chain to maintain the polymerization degree greater than or equal to 1000, and to have content ratio of the hydroxyl group (--OH) in the vinyl alcohol group (Y) greater than or equal to approximately 10 to 15%. In case of the polyvinyl acetal having greater than or equal to 4 carbon atoms in alkyl group R in vinyl acetal group (X), the composition may have high glass transition point. In addition, in case of vinyl acetal group having 0 or 2 carbon atoms in alkyl group R, high glass transition point can be obtained by making the polymerization degree greater than or equal to 1,000, at least. Also, it becomes possible to select binder for ink having high holding ability of dyes by hydrogen coupling between appropriate amount of hydroxyl group (--OH) in the vinyl alcohol group (Y) in the molecular chain, and molecule of the dyes. Accordingly, with high glass transition point or high polymerization degree, thermal transfer can be easily done without causing melting of the binder component onto the printing paper during thermal printing. Furthermore, according to the present invention, improved shelf life can be provided. According to rising temperature by heating during transfer, respective dye molecules initiates vaporization behavior by weakening of hydrogen coupling force with hydroxyl group (--OH) in vinyl alcohol group (Y) of the molecular chain. Then, the distance between molecules is progressively expanded. At this time, with hydrophilic activation behavior of hydroxyl group (--OH) in vinyl alcohol group (Y), the polar energy acts as reacting force for vaporizing non-polar dye molecules to promote sublimating behavior of the dye molecules. Therefore, sublimation transfer force for transferring dyes onto the printing paper is activated to obtain high density transferred image with high efficiency. In addition, the sheet for sublimation transfer according to the present invention will never cause transfer of ink to the lubricative heat resisting layer on the backside of the material when the sheet is rolled to pile a plurality of sheets even under higher temperature condition than the room temperature. 
     Particularly, by mixing isocyanate compound with the binder, isocyanate group in isocyanate compound establishes urethane coupling with hydroxyl group of the binder to further increase dye holding force to further completely avoid dye transferring phenomenon. 
    
    
     EXAMPLES 
     Discussion will be given herebelow with respect to examples implementing the present invention. In the following discussion, the unit &#34;part&#34; represents &#34;weight part&#34;. 
     EXAMPLE 1 
     After coating an ink having the following composition on one side of a polyester film having thickness of 6 μm by 200 mesh gravure coating, the film is left at 40° C. for one week to form a lubricative heat resisting layer of 0.4 μm thickness. 
     
         ______________________________________                                    
BINDER                                                                    
A801 (Dainippon Ink Kagaku K.K., Acryl Polyohol)                          
                           4      parts                                   
ISOCYANATE COMPOUND                                                       
Takenate D-110N (Takeda Yakuhin K.K.)                                     
                           1      part                                    
SURFACTANT AND LUBRICANT                                                  
Homogenol L-18 (Kao K.K.)  0.5    parts                                   
PHOSPHATE METAL SALT                                                      
Gafac RD-720 (Toho Kagaku K.K.)                                           
                           0.5    parts                                   
SOLVENT                                                                   
methyl ethyl ketone        94.0   parts                                   
______________________________________                                    
 
    
     Next, on the opposite side of the polyester film, an anchor coat agent having the following composition was coated by a gravure coater, and dried to form an anchor coat layer of 0.2 μm thickness. 
     
         ______________________________________                                    
BINDER                                                                    
Denka polyvinyl propyral BY-111 (Denki Kagaku                             
                           2.0 parts                                      
K.K.)                                                                     
ISOCYANATE COMPOUND                                                       
Takenate D-110N (Takeda Yakuhin K.K.)                                     
                           2.0 parts                                      
SOLVENT                                                                   
ethyl acetate              96.0 parts                                     
______________________________________                                    
 
    
     After coating the anchor coat agent, the film is left at the room temperature for three days. After sufficient aging, four kinds of inks blended with the following materials were coated for respective 17.3 cm length over overall width in order of yellow, magenta, cyan and black to obtain the thermal printing sheet. 
     
         ______________________________________                                    
(a) Yellow Ink                                                            
DYES                                                                      
MS Yellow VP (Mitsui Toatsu Senryo K.K.)                                  
                           2.0    parts                                   
DYES                                                                      
Macrolex Yellow 3G         2.0    parts                                   
(C.I. Solvent Yellow 93) (Byer)                                           
BINDER                                                                    
Denka polyvinyl propyral BY-111 (Denki Kagaku                             
                           4.0    parts                                   
K.K.)                                                                     
ISOCYANATE COMPOUND                                                       
Takenate D-110N (Takeda Yakuhin K.K.)                                     
                           1.0    part                                    
COAT PROMOTING SURFACE IMPROVING                                          
AGENT                                                                     
Defenser MCF-323 (Dainippon Ink K.K.)                                     
                           0.2    parts                                   
SOLVENT                                                                   
Toluene                    90.8   parts                                   
(b) Magenta Ink                                                           
DYES                                                                      
Resirene Red TB            2.0    parts                                   
(C.I. Disperse Red 60) (Byer)                                             
DYES                                                                      
Macrolex Red Violet R      1.0    part                                    
(C.I. Disperse Violet 31) (Byer)                                          
DYES                                                                      
MS Magenta VP (Mitsui Toatsu Senryo K.K.)                                 
                           2.0    parts                                   
BINDER                                                                    
Denka polyvinyl pental AY-20 (Denki Kagaku K.K.)                          
                           3.0    parts                                   
ISOCYANATE COMPOUND                                                       
Takenate D-110N (Takeda Yakuhin K.K.)                                     
                           0.5    parts                                   
COAT PROMOTING SURFACE IMPROVING                                          
AGENT                                                                     
Defenser MCF-323 (Dainippon Ink K.K.)                                     
                           0.2    parts                                   
SOLVENT                                                                   
Toluene                    91.3   parts                                   
(c) Cyan Ink                                                              
DYES                                                                      
MS Cyan VP (Mitsui Toatsu Senryo K.K.)                                    
                           3.0    parts                                   
DYES                                                                      
MS Cyan VPG (Mitsui Toatsu Senryo K.K.)                                   
                           1.0    part                                    
DYES                                                                      
Ceres Blue GN              3.0    parts                                   
(C.I. Solvent Blue 63) (Byer)                                             
DYES                                                                      
Foron Brilliant Blue S-R PIPK                                             
                           0.5    parts                                   
(C.I. Disperse Blue 354) (Sando)                                          
BINDER                                                                    
Denka polyvinyl hexal AY21 (Denki Kagaku K.K.)                            
                           4.0    parts                                   
ISOCYANATE COMPOUND                                                       
Takenate D-110N            2.0    parts                                   
SOLVENT                                                                   
methyl ethyl ketone        40.0   parts                                   
SOLVENT                                                                   
toluene                    46.5   parts                                   
(d) Black Ink                                                             
DYES                                                                      
Foron Brilliant Blue S-R PIPK                                             
                           5.0    parts                                   
(C.I. Disperse Blue 354) (Sando)                                          
DYES                                                                      
Foron Rubine SE-GFL PIPK   2.5    parts                                   
(C.I. Disperse Red 73) (Sando)                                            
DYES                                                                      
Foron Brilliant Yellow S-6GL PIPK                                         
                           2.5    parts                                   
(C.I. Disperse Yellow 23l) (Sando)                                        
BINDER                                                                    
Denka polyvinyl heptal AY22 (Denki Kagaku K.K.)                           
                           2.0    parts                                   
Denka polyvinyl Propyral BY-111 (Denki Kagaku                             
                           2.0    parts                                   
K.K.)                                                                     
ISOCYANATE COMPOUND                                                       
Takenate D-110N (Takeda Yakuhin K.K.)                                     
                           1.0    part                                    
SOLVENT                                                                   
dichloromethane            85.0   parts                                   
______________________________________                                    
 
    
     EXAMPLE 2 
     After coating an ink having the following composition on one side of a polyester film having thickness of 6 μm by 200 mesh gravure coating, the film is left at 40° C. for one week to form a lubricative heat resisting layer of 0.4 μm thickness. 
     
         ______________________________________                                    
BINDER                                                                    
A815-45 (Dainippon Ink Kagaku K.K., Acryl                                 
                         2.00    parts                                    
Polyohol)                                                                 
silicon oil L-722 (Shin-etsu Kagaku K.K.)                                 
                         0.05    parts                                    
ISOCYANATE COMPOUND                                                       
Takenate D-110N (Takeda Yakuhin K.K.)                                     
                         1.00    part                                     
PHOSPHATE METAL SALT                                                      
Gafac RD-720 (Toho Kagaku K.K.)                                           
                         1.00    part                                     
SOLVENT                                                                   
methyl ethyl ketone      95.95   parts                                    
______________________________________                                    
 
    
     Next, on the opposite side of the polyester film, an anchor coat agent having the following composition was coated by a gravure coater, and dried to form an anchor coat layer of 0.2 μm thickness. 
     
         ______________________________________                                    
BINDER                                                                    
Denka polyvinyl propyral BY-111 (Denki Kagaku                             
                           2.0    parts                                   
K.K.)                                                                     
ISOCYANATE COMPOUND                                                       
Takenate D-110N (Takeda Yakuhin K.K.)                                     
                           2.0    parts                                   
SOLVENT                                                                   
methyl ethyl ketone        96.0   parts                                   
______________________________________                                    
 
    
     After coating the anchor coat agent, the film is left at the room temperature for three days. After sufficient aging, three kinds of inks blended with the following materials were coated for respective 32.6 cm length over overall width in order of yellow, magenta, and cyan to obtain the thermal printing sheet. 
     
         ______________________________________                                    
(a) Yellow Ink                                                            
DYES                                                                      
MS Yellow VP (Mitsui Toatsu Senryo K.K.                                   
                           3      parts                                   
BINDER                                                                    
Denka polyvinyl propyral BY-111 (Denki Kagaku                             
                           4      parts                                   
K.K.)                                                                     
ISOCYANATE COMPOUND                                                       
Takenate D-110N (Takeda Yakuhin K.K.)                                     
                           1      part                                    
SOLVENT                                                                   
1,4-dioxane                92     parts                                   
(b) Magenta Ink                                                           
DYES                                                                      
MS Magenta VP (Mitsui Toatsu Senryo K.K.)                                 
                           3      parts                                   
BINDER                                                                    
Denka polyvinyl propyral BY-111 (Denki Kagaku                             
                           4      parts                                   
K.K.)                                                                     
ISOCYANATE COMPOUND                                                       
Takenate D-110N (Takeda Yakuhin K.K.)                                     
                           1      part                                    
SOLVENT                                                                   
1,4-dioxane                92     parts                                   
(c) Cyan Ink                                                              
DYES                                                                      
MS Cyan VPG (Mitsui Toatsu Senryo K.K.)                                   
                           4      parts                                   
BINDER                                                                    
Denka polyvinyl propyral BY-111 (Denki Kagaku                             
                           5      parts                                   
K.K.)                                                                     
ISOCYANATE COMPOUND                                                       
Takenate D-110N (Takeda Yakuhin K.K.)                                     
                           1      part                                    
SOLVENT                                                                   
1,4-dioxane                90     parts                                   
______________________________________                                    
 
    
     The sheets for sublimation transfer obtained through the examples 1 and 2 were wound on a vinyl chloride tube having 1 inch diameter for a plurality of turns to form samples. The samples were placed in a thermostatic chamber and left for continuous hours at 60° C. of temperature. As a result, it has been found that no dyes transfer to the lubricative heat resisting layer on the backside of the sheet. This demonstrates high performance of holding dyes. In the thermal printing, melting of the binder component had not been caused. 
     Although the invention has been illustrated and described with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without departing from the spirit and scope of the present invention. Therefore, the present invention should not be understood as limited to the specific embodiments set out above but to include all possible embodiments within a scope encompassed, and equivalents thereof, with respect to the features set out in the appended claims.