Transfer sheet
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is directed to a porous transfer sheet for use in a sublimation printing process. 
     2. Description of the Prior Art 
     The transfer sheet herein requires that it have an adequate porosity to allow a desired air flow so that the transfer sheet may be used to print carpet. The state of the art is such that most transfer sheets being used are non-porous. The known transfer printing operations require the printing of a dye on a non-porous transfer sheet, placing the sheet adjacent to a fabric, and then transferring the image from the transfer sheet to the fabric by the application of heat to the back of the transfer sheet along with the pulling of a vacuum on the opposite side of the fabric to draw the dyes from the transfer sheet to the fabric. 
     SUMMARY OF THE INVENTION 
     The invention is directed to a transfer sheet which will be printed with a sublimable dye. The sheet will have a porous construction such that it will have an air permeability over the surface of the sheet of between 40 to 300 standard cubic feet per minute per square foot at 1/2 inch water. The transfer sheet will be of an indeterminable length and a width of at least 3 feet, with a tear strength of at least 100 grams. Its tensile strength will be of at least 850 psi at 450°. The sheet will be used in a continuous printing operation and must be capable of use within a temperature range of 300° to 450° F. without a loss of its structural integrity and a dimensional change of more than 1/2%. Finally, the transfer sheet must be capable of releasing at least 50% of the sublimable dye printed thereon during the printing operation. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The transfer sheet to be described below is particularly useful in carrying out the manufacturing process set forth in U.S. application Ser. No. 612,773 now U.S. Pat. No. 4,007,003. Herein, a transfer sheet is placed against the back of a carpet structure and air passes through the transfer sheet and carpet to move the dye from the transfer sheet to the carpet structure. The operation is a continuous operation in that the carpet and transfer sheet are continuously moving through an area whereby the dye transfer is carried out. This must be contrasted against many state of the art processes which are carried out as an intermediate process wherein a transfer sheet and fabric structure are stationary, and a heated plate comes down against the transfer sheet to vaporize the dye of the transfer sheet. A vacuum action then pulls the dye into the fabric. 
     The commercial requirements for a continuous process using a transfer sheet requires that the transfer material should be available in widths of at least 3 and up to 14 feet for the dyeing of carpet fabric. The transfer sheet must be strong enough to go through the continuous processing operation. The transfer sheet must be able to withstand the required operating temperatures for at least 2 minutes without the transfer sheet losing its structural integrity and having an excessive dimensional change. Also, cost must be considered in the selection of a transfer sheet. The transfer sheet must have a surface which should be relatively smooth and continuous and capable of being printed by the rotogravure printing process with an acceptable definition of 120 lines per inch. Finally, the transfer sheet should have a uniform air permeability over the surface of the sheet. The air permeability must be registered by the ASTM D-737-46 Test and should range between 50 and 300 standard cubic feet per minute per square foot. 
     A transfer sheet for use in the continuous process should be of a porous construction, such that it will have an air permeability over the surface of the sheet of between 40 to 300 standard cubic feet per minute per square foot at 1/2 inch water. The sheet should be of an indeterminable length since it is being used in a continuous manufacturing process. It should be of a width of at least 6 feet so that it can be used to print commercially available carpet goods of that width. It should be capable of being used in widths of up to 14 feet without any loss of its structural integrity. The transfer sheet should have a tear strength of at least 100 grams both machine and across machine direction (Elmendorf Test ASTM-D689-62), and a tensile strength of at least 850 psi at 450°. The transfer sheet should be capable of use in a temperature range of 300° to 450° F. without a loss of its structural integrity and without a dimensional change of more than 1/2%. Finally, the transfer sheet should be capable of releasing at least 50% of the sublimable dye printed thereon during the printing operation with the transfer sheet. 
     The following chart sets forth different types of materials formed in different manners as a transfer sheet. The air permeability of the different sheets is set forth and various comments are provided relative the efficiency of each of the materials. The comments generally apply to the different types of materials. 
     
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                       Air Permeability                                   
Type     Identification                                                   
                       SCFM/Ft.sup.2 at .5&#34; H.sub.2 O                     
                                         Comment                          
__________________________________________________________________________
Jute   22 × 22 count - 7 oz                                         
                       295        1.                                      
                                    Jute stands up well at temperature,   
                                    and releases the dye well.            
       13 × 15 count - 9 oz                                         
                       335                                                
                                  2.                                      
                                    The surface is not uniform enough     
       18 × 15 count                                                
                       258          for printing and the through holes    
                                    leave white spots on the carpet       
       16 × 16 count - 7 oz                                         
                       277          surface.                              
       20 × 20 count                                                
                       236        3.                                      
                                    Cost is high (22 to 30                
                                    cents/yd.sup.2).                      
       18 × 18 Special Weave                                        
                       23                                                 
       17 × 17 Special Weave                                        
                       112                                                
       19 × 19 Special Weave - 7 oz                                 
                       450                                                
Reemay 2016 - 1.3 oz/yd.sup.2                                             
                       505        1.                                      
                                    Reemay stands up well at the tem-     
(spun- (13.9 ¢/yd.sup.2)       perature (very slight shrinkage).     
bonded                                                                    
polyester)                                                                
       2421 - 1.8 oz/yd.sup.2                                             
                       615        2.                                      
                                    The Reemay holds the dye strongly     
                                    and                                   
       (26.4 ¢ /yd.sup.2)      results in reduced dye                
                                    efficiency-30%.                       
       2024 - 2.1 oz/yd.sup.2                                             
                       282        3.                                      
                                    &#34;Printability&#34; was better than jute,  
       (22.9 ¢/yd.sup.2)       but less than E-35-S61-58 Glass       
                                    paper.                                
       2416 - 1.5 oz/yd.sup.2                                             
                       578                                                
       (20 ¢/yd.sup.2)                                               
       2014 - 1 oz/yd.sup.2                                               
                       814                                                
       (11.7 ¢/yd.sup.2)                                             
Cellulose                                                                 
       Strathmore Grade                                                   
                       50         1.                                      
                                    Cellulose paper had shrinkage of      
       7411-25-52                   1/8&#34; over 11&#34; length for 7411-25-53   
       (8.5 ¢/yd.sup.2)        and 1/64&#34; over 11&#34; for 73-25-4.       
       Strathmore Grade                                                   
                       75         2.                                      
                                    Good printing resolution with roto-   
       753-25-4                     gravure printing.                     
       Haines 3783     347        1.                                      
                                    Shrinkage was approximately 1/32&#34;     
                                    on 12&#34; length.                        
       Haines 3018     217                                                
                                  2.                                      
                                    Wrinkled slightly when printed with   
       Haines 1808     390          water-base inks.                      
       Haines 1635     53.7       3.                                      
                                    Air permeabilities of 347 and 390     
                                    did not provide good print defini-    
       Haines 186 Flat 32.2         tion.                                 
       Dexter 1148T    20.0-40.0  1.                                      
                                    Good dye release.                     
       Paper toweling with Diamond                                        
                       615                                                
       Holes in Surface                                                   
Nonwoven                                                                  
       Made by Armstrong at Ford Co.                                      
Glass                                                                     
       Number 1 E-35-S61-58                                               
                       208        1.                                      
                                    Nos. 3, 4, and 5 are heavy for        
       Number 2 E-42-U              practical use.                        
       Number 3 H-66-U                                                    
       Number 4 H-66-S61-84       2.                                      
                                    Nos. 4, 5, and 6 turned very brown    
       Number 5 K-42-S61-70         in color and transferred color to     
       Number 6 E-27-S61-44         carpet fibers.                        
                                  3.                                      
                                    Nos. 1 and 2 were the best materials  
                                    tested, but No. 2 does not print on   
                                    surface as well as E-35-S61-58        
                                    (cost - $.27/yd.sup.2).               
Woven Glass                                                               
       100% Woven Glass                                                   
                       60         1.                                      
                                    Woven glass does not print well.      
       Warp - 39 yarn Count                                               
           300 Denier                                                     
       Type DE-150 Glass Yarn                                             
       Warp - 28 Yarn Count                                               
           600 Denier                                                     
       Type DE-75 Glass Yarn                                              
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     The paper-type products, such as non-woven glass, should have a smooth surface and these seem to have the best capability of being printed by the rotogravure process with an acceptable definition of 120 lines per inch. Rough surface materials, such as jute, cannot be printed with suitable detail and are not recommended where printing detail is important. An air flow of lower than 10 standard cubic feet per minute per square foot could be utilized, but cannot particularly secure good transfer of the dye. Air permeability of below 40 provides a very large pressure drop through the transfer sheet and, thus, excessive energy use is required to move air through the transfer sheet. Air permeability over 300 is secured in sheets which have a very porous structure, and such sheets have a surface which is not capable of receiving fine line detail printing and, therefore, yield sharp detail on the material to be printed. The best materials for use as a transfer sheet are certain types of non-woven glass materials and certain types of cellulosic papers. 
     With regard to dye release (amount of free dye released from the transfer sheet), Dexter paper released 70%-90% of its dye and non-woven glass released 50%-70%. 
     A dimensional change at printing temperature of more than 1/2% will tend to blur fine line detail. 
     With regard to tear strength, paper at a tear strength of 53 grams machine direction (MD) and 48 grams across machine direction (AMD) and paper at 80 grams MD and 75 grams AMD tear strength did not work well. Dexter paper 1148T at 187 grams MD and 139 grams AMD tear strength worked very well. It appears that 100 grams tear strength is the best minimum workable value to use. 
     A certain level of tensile strength is needed so that the transfer sheet will not tear apart during processing. Tensile strength needs vary based upon machine direction and across machine direction stresses. Temperature of processing also effects tensile strengths needed. Dexter paper 1148T was successfully used in the manufacturing process of application Ser. No. 612,773, and this has a tensile strength of 850 psi AMD and 2100 psi MD at 450°, and, 5150 psi MD and 1725 psi AMD at room temperature. All other transfer sheets used exceeded 850 psi at 450° F.