Patent Publication Number: US-3880579-A

Title: Thermo-printing process

Description:
United States Patent 1191 Renaut 1111 3,880,579 1 51 Apr. 29, 1975 1 THERMO-PRINTING PROCESS [75] lnventor:  
 [73] Assignee: Societe Anonyme dite:  
 &#34; Etablissements P. Lamaire &amp; Cie  
  22 Filed: Mar; 19, 197.3  
  211 Appl. No.: 342,364  
 Henri Renaut, Roubaix, France 3,454,764 7/1969 Collier et a1. 250/65 3,455,687 7/1969 Holstead et a1... 96/27 3,490,371 1/1970 Games 101/426 3.768 280 10/1973 Kanncgicsser 68/5 D CARRIER SH EET OTHER PUBLICATIONS International Dryer and Textile Printer, March 19, 1971, page 335, article title: Transfer Printing-Art or Science, by Burtonshaw. a Journal of the Textile Institute, Sept. 1971 page 1085, article: Effect of Thermal Fixation on Dyeing of Polyamide Fibres, by Supranaitite &amp; Brazauskas. 7  
 Primur Examiner-Clyde l. Coughenour Attorney, Agent, or FirmRobert E. Burns; Emmanuel J. Lobato; Bruce L. Adams [5 7] ABSTRACT Improvements to the process known as thermoprinting of fabric, consisting of carrying out a second partial vaporisation of the dyes already fixed to the material, when this material has been separated from the inert support upon which the dyes are fixed and has fallen to a temperature below the vaporisation temperature, by means of a heat flux circulating from the printed surface of the material towards the non; printed surface.  
 3 Claims, 1 Drawing Figure FABRIC FIRST THERMOPRINTING HEAT TREATMENT CARRIER SHEET REMOVED SECOND PENETRATING HEAT? PRESSURIZED GAS STRggii/l TR EATM ENT WITH  PiTEblTfinAPflzsasra 3,880,579  
 FABRIC CARRIER SH EET FIRST THERMOPRINTING HEAT TREATMENT CARRIER SHEET REMOVED SECOND PENETRATING HEAT TREATMENT WITH PRESSURIZED GAS STREAM Tl-lERMO-PRINTING PROCESS BACKGROUND OF THE INVENTION This invention relates to improvements to the process known as thermo-printing.  
  Thermo-printing. to which the improvements according to the invention are directed. consists of transfer&#39; ring dyes fixed to a temporary inert support onto fabric materials. the most common of these materials being textiles of artificial origin.  
  This method has been used with success for many years. It makes it possible to tint or to dye numerous materials reproducing. if required. patterns and designs of many colours. without the use of any water or organic solvents during the course of the dyeing processv Dyes used with satisfaction are disperseor plastosoluble dyes. often selected from among the nitroaryl amines. the azoics. or the anthraquinones. These dyes. which are obtainable commercially. have a vaporisation or sublimation temperature often lying between l and 200C. which thus makes it possible to print numerous materials which do not become altered at these temperatures.  
  The dyes. often thickened with the aid of natural rubber. are fixed or impregnated onto a temporary inert carrier support of paper. cellophane or metal. The support may be plain or may reproduce designs in one or more colours.  
  This process may be applied successfully to numer ous textile materials of artificial origin. among which there may be mentioned cellulose acetate. the polyesters and the polyamides. Mixtures of natural fibres. such as wool and cotton. and artificial fibres already referred to also give good results.  
  The transferring of the dye to the material may be carried out using apparatus such as that described in U.S. Pat. No. 3.689.350 which comprises a cylinder or calendering roll heated to the vaporisation temperature. against which the inert support and the material to be printed are applied by means of an endless belt. The inert carrier support and the fabric material are in contact at one of their faces while their other face is in contact respectively with the calendering roll and the endless belt. The temperature of the roll will depend upon the dye used, while the contact time is sufficient to allow the dye to vaporise or to sublime and to penetrate. to condense in the material to be dyed.  
  In most cases the material is thermo-printed at the surface. because the dye vapours condense rapidly and are therefore not able to penetrate into the mass of the material beyond a certain thickness. In aiming to produce a dyeing effect through a sufficient thickness, it is difficult to raise the temperature of the roll too much since there is then a loss of dye or a risk of dye and/or fabric deterioration, or to reduce its rotational speed since then the production rate becomes much too slow.  
  This lack of penetration of the dyes into the material constitutes a serious disadvantage when thermoprinting knitted fabrics. and more generally when printing woven fabrics. In fact. when thermo-printed material such as jersey is stretched. the colour becomes rapidly attenuated by the appearance of fibres which in the non-stretched state occupied a position within the thickness itself of the material.  
  Attempts have already been made to propose solutions to this problem by using a heated and perforated calendering roll to which a vacuum of greater or lesser intensity is applied. In this method. the following is the sequence from the inside to the outside of the roll: the material to be thermo-printed. the insert support for the dyes. and a heating range for example of infra-red heaters. The result is mediochre. since a static subpressure is produced in the region of the fabric. due to the fact that the inert support for the dyes is virtually impermeable. The air sucked in therefore cannot pass dynamically through the support and the material from the outside towards the inside of the roll to permit improved penetration of the dye vapours.  
  The improvements according to the invention are directed towards overcoming these disadvantages. and for this purpose one of the first objectives of the method proposed is to cause the penetration of the dyes into the thickness of the material, from its side which has just been thermo-printed right through to its virgin side. The colour of the textile materials will thus remain exactly the same even when they are stretched.  
  Another objective of the method according to the invention is to restore to the thermo-printed fabric its original texture and feel by raising the surface strands which had been flattened during the thermo-printing due to the coompressive and thermal stresses exerted between the endless belt and the roll.  
  Another objective of the method according to the invention is to make it possible to maintain high production rates in thermo-printing installations. especially for woven fabrics. while effecting perfect dyeing.  
 Another objective of the method according to the invention is to prevent any dispersion of the dye over tl&#39;lfig material, which could adversely affect the correct reproduction of the coloured patterns. by a rapid heat flux circulating perpendicularly to the material when this material has been separated from the inert support to which the dyes are fixed.  
 BRIEF SUMMARY OF THE INVENTION According to the invention there is provided in a thermo-printing process in which vaporisable dyes are caused to pass from an inert support to a surface of rnaterial by bringing dye vapours into contact with the material heated to the vaporisation temperature. the improvement in which a second partial vaporisation of the dyes already fixed to the material is then carried out when this material has been separated from the inert support and has returned to a temperature below the vaporisation temperature. by means of a heat flux circulating from the printed surface of the material towards the non-printed surface.  
 DESCRIPTION OF PREFERRED EMBODIMENTS Embodiments of the invention will now be described by way of example, several methods of carrying out the improvements to the thermo-printing process being described.  
  The installation used for the thermo-printing of the fabric is based upon that described in U.S. Pat. No. 3.689.350. The thermo-printed material circulates in contact with the major part of the periphery of a heated I drum. while the inert support is applied to this material The method according to the invention should be carried out immediately after the separation and solely upon the thermo-printed material itself, in contrast to what was previously known for improving the penetra tion by acting during the thermo-printing stage while the fabric and paper were still in contact and applied to the heating drum. The invention consists of carrying out a second sublimation, but in this case a partial one, of the dyes which have been fixed to the fabric. It is necessary to do this when the material has returned to a temperature from to below the vaporisationtemperature.  
  In order to do this. there is provided between the heating drum and the fabric rolling-up drum a heat flux in the form of an air blowing nozzle array, blowing air heated to a temperature above the sublimation temperature. and blowing through the thermo-printed face towards the virgin face. A portion only of the dyes becomes vaporised to recondense rapidly within the body itself of the material.  
  This operation may be carried out continuously upon the material, provided that the nozzle array acting across the whole width of the material, blows air through a very small portion of its length. It should also be ensured that the air is blown perpendicularly to the material. in order not to disperse the partially revaporised dyes, since such dispersion could affect the thermo-printed patterns.  
  An air flow speed which is large in relation to the speed of travel of the material is selected, in order that only a small portion of the dye is resublimated. This high speed also makes it possible to restore to the fabric its original texture by lifting up the strands at the surface which have been crushed between the drum and the belt during the thermo-printing stage.  
  Other known devices could be used for causing the heat flux to circulate from the printed surface towards the non-printed surface. and it would also be possible to do this if recycled air, passed through a reheater were used.  
  In this way materials are obtained which are better thermo-printed in the body of the material. and are of improved texture. after a second partial sublimation of the dyes has been carried out, this second partial sublimation being however carried out under dynamic conditions.  
 I claim:  
  1. An improved process for the thermoprinting of fabrics providing penetration of the printed design into and through the body of the fabric, wherein designs in vaporizable dyes are transferred by heat from a moving carrier sheet onto the surface of the moving fabric,  
 which comprises the steps of:  
 a. contacting the carrier sheet, bearing designs in vaporizable dyes, with the surface of the fabric;  
 b. heating said carrier sheet to vaporize said dyes;  
 c. transferring the design from said carrier to the surface of said fabric by condensing the vapors of said dyes thereon;  
 d. separating the carrier sheet from the designbearing surface of said fabric and cooling said fabric e. distributing the dye-design, condensed on said fabric, through the body of said fabric by a second heating step comprising the application of a pressurized heated gas stream directed substantially perpendicular to the surface and through the body of said fabric, to force vapors of said dyes from the surface of the fabric substantially perpendicularly to the surface and into the body of said cooled fabric to condense therein.  
  2. A thermo-printing process according to claim 1, in which air, from a pressurized source and raised to a temperature higher than the vaporisation temperature of the dyes, is blown through the body of said fabric from the design bearing surface of the fabric towards the virgin surface, across the whole width of the moving material, but over successively very small segments of its length as the fabric moves past said gas source.  
  3. A thermo-printing process according to claim 2 in which the flow speed of the heated gas stream through said successive fabric length segments is high relativ to the movement of the fabric. a