GB2043709A - Colouration of textiles - Google Patents

Abstract

A method of colouring textiles comprises pressing onto a textile fabric a flexible substrate, preferably silicone treated paper, having a removable layer thereon containing a dyestuff a polyvinyl alcohol soluble in hot water and sufficiently soluble in cold water to enable it to be washed off the fabric. After pressing, preferably carried out in a steam press, the substrate is removed leaving the layer on the fabric. The fabric and layer are then heat treated to fix the dyestuff. Surplus layer components are washed from the fabric using water below 60 DEG C containing a small quantity of detergent. The process is particularly suited to natural fibres, e.g. keratinous fibres, and in this case the dyestuffs employed may be acid, reactive or premetallised dyes.

Description

SPECIFICATION Colouration of textiles This invention relates to a method for the colouration of textiles and in particular relates to a method of transfer printing.

The term transfer printing refers to processes of decorating textile fabrics by transferring a pattern or design from a substrate onto which is has been preprinted. Possibly the best-known form of transfer printing is the "Sublistatic" process in which a paper substrate has sublimable disperse dyestuffs printed on it in a desired pattern. The "transfer paper" may then be used at some subsequent time to print a textile fabric by pressing it into contact with the fabric at a temperature in the range 1800C to 240"C for about 30 seconds. Only fabrics made from textile fibres which accept disperse dyes may be employed in this process and, in practice, it is restricted to polyester fabrics.

Another approach to transfer printing which is less fibre specific is the so-called melt transfer printing process. In the latter the dyestuffs, which may be non-sublimable, are held on the substrate in some form of resinous film. When the substrate is pressed onto a suitable textile fabric the whole film transfers from the substrate to the textile carrying the dyestuffs with it. A subsequent treatment then fixes the dystuffs on the textile.

The invention seeks to provide an improved form of melt transfer printing which is especially suitable for colouring wool textiles.

According to the present invention there is provided a method of colouring textiles which comprises pressing a flexible substrate having a removable layer thereon containing a dyestuff and a polyvinyl alcohol soluble in hot water and sufficiently soluble in cold water to enable itto be washed off, on to a textile fabric, removing the substrate leaving the layer on the fabric, heat treating the fabric carrying the layer to fix the dyestuff, and washing surplus layer components from the fabric.

There are available commercially many grades of polyvinyl alcohol but we have found that to be suitable in the process of the invention the grade selected should fulfill the following conditions, that is, it should: i) be soluble in hot water, to ensure that under the conditions of pressing it becomes tacky and adheres to the textile fabric; ii) be sufficiently soluble in cold water to ensure that surplus will be washed out of the fabric under normal washing-off rountines; and iii) be of low viscosity (preferable S 10 cp in 4% aqueous solution at 20"C), to ensure that it can easily be printed onto the substrate.

Conditions (i) and (ii) above will generally be met with grades of polyvinyl alcohol having hydrolysis mol. % figures in the range 85 to 90, i.e. containing 10-15% residual polyvinyl acetate (the latter groups tend to be soluble in cold water but not hot, whereas "pure" polyvinyl alcohol tends to be soluble only in hot water).

The textile fabric to be printed may be of any textile fibres natural or synthetic although the process is especially advantageous for natural textile fibres which have hitherto generally not been suitable for transfer printing processes. In particular the process of the invention is advantageous for keratinous fibres, especially wool.

The dyestuffs chosen will of course depend on the textile substrate to be printed. Thus for polyester disperse dyes may be used, for cotton reactive or direct dyes, for wool acid, premetallised or recactive dyes, and so on. Similarly dyeing adjuvants may be employed and incorporated into the layer together with the dyestuff. For example, using reactive dyes for cellulose fabrics alkali may be present; acid or reactive dyes for wool fabric require acid; substances such as urea or thiourea may be added to aid dyestuff solubility and/or fixation; wetting agents may be added, and so on.

The flexible substrate may be any inert sheet material capable of carrying the layer, and should preferably have release properties or at least bond less firmly to the layer than the layer does to the fabric under the conditions of pressing. Plastics material films or metal foils may be employed, but the most suitable substrate is paper. An especially advantageous substrate is paper which has been treated, e.g. with a wax, a synthetic rubber or, preferably, a suitable silicone, to render one surface hydrophobic.

The pressing step may be carried out in any of the normally available textile pressing machines, e.g. a hot head press. The pressing step should involve heat as well as pressure, and preferably the heat is introduced by means of steam. The steam also helps render tacky the transfer layer and therefore aids transfer. In the absence of steam or other moisture during the pressing step it is preferred to incorporate a suitable humectant, e.g. glycerine, in the transfer layer. The pressing step may involve temperatures in the range of, for example, 1 000C to 1 500C and times of from a few seconds to a few minutes. A typical pressing cycle might be 30 seconds at 1200C.

Often it is advantageous to cool the fabric, e.g. for 5 or 10 seconds, after pressing before removing the substrate.

After pressing, the fabric is heat treated to fix the dye. Normally the substrate is removed before heat treatment but this is not always essential. The type and duration of heat treatment will depend upon the dyestuffs employed. For instance, disperse dyes require dry heat at temperatures in the range 1 80 C to 240"C; whereas acid or reactive dyes may be fixed by steaming at temperatures of from 180 to 1 20 C.

The duration of the heat treatment is similarly related to the dyestuffs employed. Thermosol treatments are typically of short duration, e.g. g or 1 minute; whereas steaming treatments may be carried out for from 10 minutes to 2 hours, with 30 minutes being a useful average.

In order that the handle and appearance of the fabric should not be adversely affected by the process, it is desirable that the fabric be washed after dye fixation. This step removes surplus dyestuff, the polyvinyl alcohol and any other adjuvants. It is preferably carried out using water containing; for example, a small quantity of detergent, attemperatures up to 50 or 60"C. For energy and other considera tions, it is not desirable to exceed these tempera tures and it is for this reason that the polyvinyl alcohol emplpyed should be soluble in water below 60"C, i.e. "cold" water, as well as in "hot" water, i.e.

water above 60 C.

The process of the invention may be used to print patterns or designs, in which the desired design would be printed onto the substrate by normal paper printing techniques, or may be used to print solid shades.

The following Examples are for the purpose of illust ration: Example 1 A print paste was made up as follows:- Polyvinyl Alcohol (PVA) 250 gm.Kg-t Citric Acid 3 Procion Blue MX3G (ICI) 30 Water 717 1,000 gm.Kg-l The grade of PVA used was Gohensol GL05 (Nippon Gohsei) which has a viscosity in the range of 4.8 to 5.8 CP and a hydrolysis of 87-89 MO1 % and is thus soluble in both hot and cold water. The acid and dyestuff were dissolved in the water at 25"C after which the PVA was added and stirred with a paddle stirrer until well dispersed. The temperature was raised to 90"C with constant stirring and maintained at this temperature until the PVA was completely dissolved (1 hour).Sheets of silicone treated release paper (Grade PN419 - Leonard Stace Ltd.) were coated with a 60 micron layer of the paste and the paper dried at 40"C for 30 minutes.

Samples of 2 x 2 rib knitted wool fabric knitted from two ends of 2/24's w.c. yarn were provided.

One batch had been treated by chlorination followed by application of a polyamide/epochlorohydrin resin (Hercosett 57-Trade Mark) two impart shnnk- resistance and the remainer was untreated.

Samples of each batch were pressed with a coated paper in a hot head press at 1400C for 30 seconds steam followed by 5 seconds vacuum, after which the paper was peeled off the fabric. The printed samples were steamed in an autoclave at 6 Ibs in -1(1 100C) for 30 mins, after which they were washed off at 50"C and dried.

Good prints were obtained in both cases.

Example2 Example 1 was repeated with sh rink-resist treated single jersey fabric knitted from 2/28 w.c.

chlorine/Hercosett treated wool yarn. After pressing samples of the fabric were autoclaved at 3 Ib. in -2 (105"C) for 10 minutes, or at atmospheric pressure for 30 minutes.

After washing-off and drying as before good prints were obtained, with the atmospheric steaming giving better fixation.

Example 3 A print paste was made up as in Example 1 substituting 100 gms KG-1 of urea for 100 gm KG-' of the water. This paste was screen printed on silicone paper in a desired design.

Samples of the single jersey fabric of Example 2 were printed in a hot head press set to medium pres sure and 30 second steam, 5 second vacuum cycle.

This was followed by steaming at atmospheric pressure for 15 or30 minutes.

After washing-off and drying as before good clear prints of the design were obtained.

Example 4 Two pastes, with and without glycerine, were made up as follows:- Gohsenol GL 05 220 220 gm.KG-' CitricAcid 3 3 Procion MX3G 30 30 Urea 100 100 Glycerine 40 0 Matexil PN-UP 5 5 Water 602 602 1,000 gm.KG-' 1,000 gm. KG-' The paste was made up as in Example 1 with the matexil wetting agent, and glycering, when used, stirred into the hot solution after the PVA had been dissolved.

Samples of the single jersey fabric were printed in a hot-head press as before, or in a fusing press at 140"C (dry heat) for 30 seconds. The samples were steamed for 30 minutes at atmospheric pressure, washed and dried as before.

Both samples printed with the glycerinecontaining paste produced good prints; but with the sample without glycerine, printed under dry conditions on the fusing press, no transfer of the layer took place. The remaining sample, subjected to steam pressing, showed a good print.

The invention further includes a printing sheet for use in transfer printing textiles which comprises a flexible substrate having a removable layer thereon containing a dyestuff and a polyvinyl alcohol soluble in hot water and sufficiently soluble in cold water to enable itto be washed off the textile after printing.

Claims (33)

1. A method of colouring textiles which comprises pressing a flexible substrate having a removable layer thereon containing a dyestuff and a polyvinyl alcohol soluble in hot water and sufficiently soluble in cold water to enable itto be washed off, on to a textile fabric, removing the substrate leaving the layer on the fabric, heat treating the fabric carrying the layer to fix the dyestuff, and washing surplus layer components from the fabric.

2. A method as claimed in claim 1 in which the polyvinyl alcohol has a viscosity less than or equal to 10 CP in 4% aqueous solution at 20 C.

3. A method as claimed in either of claims 1 or 2 in which the polyvinyl alcohol has a hydrolysis mol.% value in the range 85 to 90 and contains 10 to 15% residual polyvinyl acetate groups.

4. A method as claimed in any of claims 1 to 3 in which the textile material comprises natural textile fibres.

5. A method as claimed in claim 4 in which the natural fibres are keratinous fibres.

6. A method as claimed in claim 5 in which the dyestuffs used are acid, reactive, or pre-metallised dyes.

7. A method as claimed in any one of claims 1 to 6 in which the flexible substrate is an inert sheet material.

8. A method as claimed in claim 7 in which the substrate is paper.

9. A method as claimed in claim 8 in which the paper has been treated with a wax, a synthetic rubber, or a suitable silicone to render one surface hydrophobic.

10. A method as claimed in any one of claims 1 to 9 in which the pressing is carried out in a textile pressing machine.

11. A process as clamed in claim 10 in which the pressing machine is a fusing press.

12. A process as claimed in claim 11 in which a humectant is incorporated into the layer.

13. A process as claimed in claim 12 in which the humectant is glycerine.

14. A process as claimed in claim 10 in which the pressing machine has the facility to enable steam to be introduced to the textile material.

15. A method as claimed in any one of claims 1 to 14 in which the pressing step is carried out at a temperature in the range of from 100 to 150"C.

16. A method as claimed in claim 15 in which the pressing step is carried out at 1200C for a time of 30 seconds.

17. A method as claimed in any one of claims 4 to 16 in which the heat treatment step is carried out by steaming at temperatures of from 100 to 120"C.

18. A method as claimed in claim 17 in which the steaming treatment is carried out for between 10 minutes and 2 hours.

19. A method as claimed in claim 18 in which the heat treatment is carried out for a period of 30 minutes.

20. A method as claimed in any one of claims 1 to 19 in which washing the surplus layer of components from the fabric is carried out using cold water, i.e. water below 60"C.

21. A method as claimed in claim 20 in which the water contains a small quantity of detergent.

22. A method of colouring textiles substantially as hereinbefore described with reference to and as illustrated in the foregoing examples.

23. Atextile whenever coloured by a method as claimed in any one of claims 1 to 22.

24. A printing sheet for use in transfer printing textiles which comprises a flexible substrate having a removable layer thereon containing dye stuff and a polyvinyl alcohol soluble in hot water and sufficiently soluble in cold water to enable itto be washed off the textile after printing.

25. A sheet as claimed in claim 24 in which the polyvinyl alcohol has a viscosity less than or equal to 10 cp in 4% aqueous solution at 20"C.

26. A sheet as claimed in either of claims 24 or 25 in which the polyvinyl alcohol has a hydrolysis mol.

% value in the range 85 to 90 and contains 10 to 15 residual polyvinyl acetate groups.

27. A sheet as claimed in any one of claims 24 to 26 in which the dye-stuffs used are acid, reactive, or premetallised dyes.

28. A sheet as claimed in any one of claims 24 to 27 in which the flexible substrate is an inert sheet material.

29. A sheet as claimed in claim 28 in which the substrate is paper.

30. A sheet as claimed in claim 29 in which the paper has been treated with a wax, a synthetic rubber, or a suitable silicone to render one surface hydrophobic.

31. A sheet as claimed in any one of claims 24to 30 in which a humectant is incorporated into the layer.

32. A sheet as claimed in claim 31 in which the humectant is glycerine.

33. A printing sheet for use in transfer printing textiles substantially as herein described with reference to and as illustrated in the foregoing examples.