EP0522898A1 - Improved process for transfer printing - Google Patents

Abstract

According to the invention, the process for printing a textile article by heat transfer of sublimable dyes with the aid of a carbon tissue, consists in coating at least the face of the article intended to be in contact with the carbon tissue with the aid of a polyurethane-based resin. The resin is applied for example in the form of an aqueous dispersion by means of a flat or rotating frame, a scraper and a pad (foulard) or by spraying, and then dried. The dry deposit of polyurethane-based resin is for example between 5 and 15 g/m<2>. The process of the invention allows transfer printing on any type of textile article, in particular an article made of pure or mixed cellulose.

Description

The present invention relates to the technique commonly known as transfer printing, or thermal printing or dry printing, in which dyes printed on a paper support are transferred by sublimation to a textile article. It relates more particularly to an improved process by which this technique becomes applicable to textile articles of any composition, and in particular to cellulosic articles in pure or mixed form.

Transfer printing, which was born in the 1960s, has only had industrial outlets in a limited number of materials: polyester, acrylic, triacetate, polyamide, that is to say in articles made of synthetic fibers. This limitation is due to the very principle on which the transfer-printing is based, namely the migration into the fiber of dyes which have been sublimated during a heat treatment of the order of 200 ° C. Fibers which are not likely to be dyed with dispersed dyes or those which do not withstand the corresponding temperature are therefore excluded. Consequently, natural fibers and in particular cellulosic fibers are not affected by this technique, which preferably applies to polyester.

However transfer printing has undeniable advantages: no water consumption, no pollution, little investment and little space for printing proper, very great flexibility of use since on the one hand, the same transfer paper allows the printing of articles of different contexts, and on the other hand the transfer paper can be stored and printing performed on demand.

Document JP 77/38077 discloses a process for transfer printing of fabrics of wool, cotton or a polyester-wool mixture which consists in carrying out a pretreatment of the fabric to be printed by transfer, this pretreatment consisting of an impregnation of the fabric by an aqueous dispersion of polyurethane. The transfer paper, comprising an ink containing a sublimable dye, is applied by pressure against the fabric treated at 200 ° and then sprayed for 20 minutes at 100 °. The printed fabric obtained has non-shrink properties and can be used for making golf clothing.

Such a known process, despite all the interest it presents, has not, to the knowledge of the applicants, had real industrial applications. From the observations they have been able to make, the applicants believe that the polyurethane pretreatment which is proposed in this document is not entirely satisfactory, since the printed articles thus produced do not have the solidities usually required, for all types of colors. It will be understood that the printed fabrics usually have a large number of colors on the same article and that it is important that all the dyes used for printing have acceptable behavior, such that no bleeding occurs, during the use of the article and in particular its washing.

The aim of the invention is to propose a process which overcomes the major drawback of transfer printing, namely its limitation to a few synthetic fibers, and also the aforementioned drawback of the process using a prior treatment by impregnation of polyurethane, namely the disgorgement of colors.

This object is perfectly achieved by the method of the invention. It is a process for printing a textile article by thermal transfer of sublimable dyes printed using a transfer paper, of the type comprising a pretreatment of said article using a polyurethane resin. Typically, the pretreatment, prior to the transfer operation proper, consists in coating at least the face of the article intended to be in contact with the transfer paper with a mixture of polyurethane ester resins, at least one being aromatic, another at least being aliphatic.

Thus, the applicants have unexpectedly found that it is possible to obtain an excellent quality transfer impression by implementing, in the pretreatment at polyurethane, on the one hand resins of a certain type, namely polyurethane esters, and on the other hand a mixture of at least two of these resins, namely a resin of the aromatic type and a resin of the aliphatic type . This very particular selection makes it possible to obtain the expected technical result, namely good solidity for the printed article.

Preferably, the mixture of resins, during the pretreatment, is applied in the form of an aqueous dispersion.

Excellent results have been obtained from a mixture of two polyurethane ester resins, in substantially equal proportions, the first being an aromatic polyurethane ester and the second an aliphatic polyurethane ester.

An improvement could also be obtained, concerning the fastness to washing at 50 °, by adding to the mixture of resins a formaldehyde derivative, for example melamine formaldehyde.

Of course melamine formalin is already known in the dyeing field to improve the fastness to washing of certain dyes. Up to now, however, melamine formaldehyde has been used to improve the fastness to washing of soluble dyes, in a finishing treatment of the article already dyed. In the present case, on the one hand the dyes used in transfer printing are dispersed dyes and not soluble dyes, and on the other hand the application of melamine formalin occurs during a pretreatment of the 'article, before printing, and not during a post-processing of the article already dyed. Thus, according to the applicants, it did not follow from normal knowledge of a person skilled in the art that the use of a formaldehyde derivative in the mixture of polyurethane ester resins during the pretreatment of the article to printing by transfer would improve the fastness to washing of the printed article.

Furthermore, it has been found that it is possible to improve the feel of the printed article by adding to the mixture of polyurethane ester resins a silicone compound, for example hexamethyl polysiloxane. Of course those skilled in the art know that this kind of compound can be used to improve the feel of articles, but this is usually done on the finished article and not as it is done in the present case during a pretreatment, prior to the application of the dye itself. Thus, unexpectedly, the use in the mixture of polyurethane ester resins of a silicone compound does not disturb the transfer printing proper, that is to say does not prevent the sublimable dyes from migrate inside the resin mixture and attach to it. Furthermore, it has been noted that the presence of silicone compounds further improves the washing resistance.

Preferably, the resin is applied to both sides of the article by full bath impregnation with a scarf.

According to the preferred embodiment of the process, this full bath impregnation was carried out from an aqueous dispersion containing from 2 to 4% of an aliphatic polyurethane ester resin, from 2 to 4% of a aromatic polyurethane ester resin, from 1 to 2% of melamine formaldehyde and from 1 to 2% of hexamethyl polysiloxane.

The application of the resin is followed by a drying step intended to remove the water and to obtain the partial or total polymerization of the resin.

The textile article, dried and thus coated with the mixture of polyurethane ester resins, is then subjected to the transfer operation. This operation can be carried out continuously after the steps of applying the resin and drying, or preferably discontinuously, the article dried and coated with resins being temporarily stored.

The actual transfer operation is carried out under the usual conditions, for example by means of a calender. The invention will be better understood on reading the description which will be given of several exemplary embodiments of the invention.

1st example

A transfer-printing is carried out on a polyester jersey knit of 150 g / m2, on a calender under the following conditions: temperature of 215 ° C., residence time 25 seconds.

The treatment was carried out on the one hand with a paper ink transfer to water and secondly with solvent ink transfer paper.

In both cases, the polyester knitted fabric thus printed has a very good color yield. Furthermore, the fastness to light and to washing are as follows: 4 to 7 depending on the dyes for fastness to light and from 3 to 5 for fastness to washing, according to ISO standards.

2nd example

Transfer-transfer printing is carried out under the same conditions as for the first example on a pure cotton jersey knit having the same grammage and the same texture.

The cotton fabric thus printed has a dull appearance, and the solidities are very poor both in light and in washing.

3rd example

On the same cotton knit as in Example 2, a mixture of two polyurethane ester resins is applied according to the invention, one being of the type
aliphatic and the other of the aromatic type. This application is carried out from an aqueous dispersion comprising from 2 to 4% of the aliphatic polyurethane ester resin, from 2 to 4% of the aromatic polyurethane ester resin, from 1 to 2% of melamine formaldehyde and from 1 to 2% of hexamethyl polysiloxane. In the case where the resins are in the form of ready-to-use dispersions, the percentage of active materials must be taken into account to obtain the above percentages, which are percentages by weight.

The cotton knit is continuously passed through an impregnation scarf, containing the dispersion of the resin mixture. The adjustment of the pressure of the scarf cylinders is provided to obtain a take-up rate of the order of 100%.

The cotton knit thus impregnated then passes through a drying tunnel, then is wound. The knitted fabric has a dry deposit of the order of 3 to 10%, by weight, of the mixture of resins based on polyurethane esters, aromatic and aliphatic, polymerized.

On the knitted fabric thus coated, transfer printing is carried out under the same conditions and with the same papers. transfer as in Examples 1 and 2 above.

The cotton knitted fabric thus printed has the same color yield as the polyester knitted fabric of Example 1, very good fastnesses both in light and in washing, as well as an excellent feel.

4th example

The pretreatment for impregnating the mixture of the two polyurethane ester resins is carried out using the same dispersion as in Example 3, during the manufacture of a cotton fabric on a loom of the water jet type. . To this end, the dispersion is added to the water used to propel the weft thread through the crowd. This is made possible by the fact that the products used in the dispersion are not corrosive and do not alter the behavior of the jet of water propelled under pressure. In particular, the presence of the dispersion does not significantly modify the viscosity of the water used.

Thus, the weft yarn is impregnated with the dispersion containing the mixture of aliphatic and aromatic polyurethane ester resins.

Transfer printing can also be carried out on the wet fabric leaving the water jet loom.

Although only the weft threads have been impregnated, it turns out that the aqueous dispersion migrates sufficiently during the manufacture and storage of the fabric roll, so that a substantially printed fabric is obtained. comparable to that obtained by impregnation in full bath.

The invention is not limited to the mode which has been described by way of non-exhaustive example. In particular, it is up to the person skilled in the art to determine in the range of polyurethane, aliphatic and aromatic ester resins, those which are most suitable depending on the textile article to be printed.

Of course, the invention also covers textile articles, of whatever nature and of whatever composition, which are obtained by the above-mentioned process, and which therefore comprise on the two faces or on one side only a mixture of resins, comprising at least two polyurethane ester resins, one aliphatic and the other aromatic, to which dispersed dyes are attached. It can be articles of cellulosic fibers, cotton, linen, viscose, etc. in pure form, or in a mixture, in particular with other cellulosic fibers or with elastane fibers or with acrylic fibers; these may be pure or mixed woolen articles; without this list being exhaustive.

Claims (8)

Method of printing a textile article by thermal transfer of sublimable dyes printed using a transfer paper, of the type comprising a pretreatment of said article using a polyurethane resin. characterized in that the pretreatment, prior to the transfer operation proper, consists in coating at least the face of the article intended to be in contact with the transfer paper with a mixture of polyurethane ester resins, l at least one being aromatic, another at least being aliphatic. Process according to Claim 1, characterized in that the mixture is a mixture of two polyurethane ester resins, in substantially equal proportions, the first being an aromatic polyurethane ester and the second an aliphatic polyurethane ester. Process according to either of Claims 1 and 2, characterized in that the mixture of resins, during the pretreatment, is applied in the form of an aqueous dispersion. Process according to Claim 3, characterized in that the aqueous dispersion comprises a formaldehyde derivative, for example melamine formaldehyde. Method according to one of claims 3 or 4 characterized in that the aqueous dispersion contains a silicone compound, for example hexamethyl polysiloxane. A method according to claim 1 characterized in that the application of the resin mixture is carried out on both sides of the article by full bath impregnation with a scarf. A method according to claim 6 characterized in that this full bath impregnation was carried out from an aqueous dispersion containing from 2 to 4% of an aliphatic polyurethane ester resin, from 2 to 4% of a d aromatic polyurethane ester, from 1 to 2% of melamine formaldehyde and from 1 to 2% of hexamethyl polysiloxane. Method according to claim 3, characterized in that the article being a fabric obtained on a weaving loom of the water jet type, the aqueous dispersion containing the mixture of resins polyurethane ester is used to propel the weft thread through the crowd.