EP1905889A2

EP1905889A2 - Printing process on polyester or polyester-mixed textile products, and textile products thus obtained

Info

Publication number: EP1905889A2
Application number: EP07116696A
Authority: EP
Inventors: Paolo Lenzi
Original assignee: Stamperia Altair Srl
Current assignee: Stamperia Altair Srl
Priority date: 2006-09-27
Filing date: 2007-09-18
Publication date: 2008-04-02
Also published as: ITFI20060237A1; EP1905889A3

Abstract

The process according to the invention consists in applying a printing paste containing high concentrations of strong alkali on a substrate in polyester or polyester mixed. The paste is applied through a printing matrix on which there is formed a certain pattern, whereby said pattern becomes reproduced on the textile substrate as a result of a basic hydrolysis reaction produced on the polyester by the strong alkali. The resulting effect of areas with different degradation characteristics is triggered further to a drying, steaming or thermofixing step at high temperature carried out after the printing step.

Description

The present invention concerns the field of textile production. More specifically, it concerns a new process for obtaining new and peculiar surface designs through printing on textile products (fabrics or garments) made of polyester or in any case containing polyester fibers.
Textile printing, in general terms, consists of applying printing pastes - containing dyes or pigments - to textile products. This step is followed by one or more stabilization steps, comprising physical and/or chemical treatments having the purpose of stably and locally fixing the dying substances. A more precise, though brief, consideration of the various kinds of known printing systems, can be found in the introductory part of the description of European Patent Publication n. EP1591582 , in the name of the same applicant, herein incorporated for reference.
As far as the polyester fabrics are concerned, the most widely used printing processes are the direct or application printing (using colored pigments or dying substances belonging to the category of the disperse dyes), the corrosion printing, the resist printing and the thermal transfer printing. In this latter system, contrary to the more traditional technologies, the printing is not carried out directly on the textile support, but in two steps, firstly printing a support having a perfectly plane and stable surface (release paper) with appropriate colorants, and subsequently transferring the design on the fabric with processes making use of dry heat (sublimation, thermoplasticity), or wet heat (migration, steaming).
It is also known the phenomenon of the surface "decortication" due to basic hydrolysis of the polyester products. The polyester fibers can be saponified by sodium hydroxide. This is sometimes exploited to make the polyester textile products more hydrophilic, and with a feel and a looseness that are more similar to those typical of the natural fibers (namely silk). Sodium hydroxide attacks the polyester in the areas of the fiber that are more easily accessible, i. e. in the amorphous ones, and forms some surface cracks. The hydrolysis products that are formed in this way (terephthalate and glycol) pass in solution, and thus a first surface degradation stage occurs, known as "decortication", used with the aims mentioned above. A second, stronger hydrolysis stage could then bring to the total demolition of the polymeric structure of the polyester, and thus to the total dissolution of the fibers. This finishing treatments can be carried out both with continuous and discontinuous processes, among which the DEBACA^® process, developed and patented by the company Montefibre of Milan back in the eighties.
The applicant has now surprisingly identified a new process that, with a non obvious combination of the aforementioned prior art elements, allows to obtain on the textile material, in a very simple manner, aesthetical effects which are either new, or comparable with effects that can presently be achieved only with much longer operative times and higher costs.
Such a result is achieved, according to the present invention, with a printing process that can be used on a textile substrate in polyester or comprising polyester fibers, the essential features of which are defined in the first of the appended claims.
In practice, the process according to the invention consists in applying printing pastes containing high concentrations of strong alkali, such as sodium hydroxide, with appropriate thickening agents, on polyester or polyester-mixed products, in a raw condition or dyed. It is possible to carry out a simultaneous coloration of the product, by applying dyes or pigments via further and different printing cylinders or screens. After the printing step the fabric is dried at high temperature, and then undergoes washing (rope or open wide washing) and neutralization steps.
In this way, localized decortication effects are obtained, characterized by incised, carved areas (in hairy polyester fabrics such as pile fabrics), or simply degradated areas as a result of a partial solubilization of the fabric, with effects similar to those of the dévoré printing system (in fabrics having an even surface), said areas having neat and well defined borders that reproduce the design of the printing matrix through which the paste has been applied. In fact, the said areas correspond to those selectively interested by the contact with the printing paste and in which therefore, contrary to the rest of the product, the hydrolysis effect develops with consequent degradation of the polyester fibers. The pattern resulting from this contrast becomes fully evident during the drying/steaming step at high temperature, because it is in this step that the hydrolytic action (saponification) of the polyester fibers occurs.
The above mentioned effects are therefore obtained, according to the invention, with elementary and cost-effective techniques, with reduced productive times and relatively simple and commonly used devices, whereas in the prior art some somehow comparable results can be obtained only with lengthy, laborious and costly techniques (e.g. laser treatments of pile fabrics).
The features and advantages of the printing process on polyester or polyester-mixed textile products for obtaining designs defined by areas having different degradation characteristics, and of the products so obtained will be apparent from the following description of an embodiment thereof, given purely as a non-limiting example.
According to the invention, the process can be applied on textile substrates consisting of woven or knitted fabrics or of manufactured garments, made of polyester or polyester-mixed. These substrates can be in any condition and with any superficial appearance (e.g. pile fabrics, with an even surface, made of fancy yarns etc.). Moreover, they can be in a raw condition, bleached, dyed or printed. However, in case of previously died or printed fabrics, it is necessary that colorant materials and/or pigments resistant to alkaline treatments have been used.
The sequence of the processing steps can be considered, per se, analogous to a conventional printing process. Therefore, first of all there is a preparation step of the printing paste containing the strong alkali and the other auxiliary components normally present in the traditional printing pastes. The paste can then be applied with any known method (screen printing - with manual, semi-automatic or automatic systems -, hollow cylinder rotary printing, cylinder or roller printing), with a speed that may vary as a function of the technique that is used and the desired results. Also the penetration of the printing paste can be adjusted as a function of the effect one wishes to obtain. The pattern of the printing matrix, and consequently the design that will be defined on the fabric by the areas with different degradation characteristics, can be of any kind, that is, geometrical, flowery, generally fancy.
Immediately after the printing step, which as mentioned may also comprise traditional printing runs for dying the product, a drying step will follow with hot air drying machines, at high temperature (comprised between about 160°C and 185°C) depending on the kind of fabric and, also in this case, of the desired effect. It is at that stage that the actual basic hydrolysis (saponification) of the polyester will be activated. As an alternative, the drying step can be carried out at a temperature comprised between about 100°C and 120°C, and then steaming or thermofixing the material at temperatures around 160°C ÷ 180°C.
A final washing and neutralizing step will have the aim of washing away the residuals of strong alkali of the printing paste and the products of the hydrolysis (terephthalate and glycol). In case a simultaneous dying has been carried out in the printing step, the washing will also be useful for getting away with the unfixed dyeing substances and/or pigments. The washing can be carried put with continuous or discontinuous processes, depending on the devices one has available. The temperature and other washing conditions are set as a function of the type of printed textile material and of the device in use. All the above mentioned steps are obviously carried out with apparatus fully known of to the person skilled in the art.

Turning back to the core of the process, that is, to the print runs, a preferred preparation of a printing paste with strong alkali is expressed by the following recipe.

Chronological order	Products	Amount (/kg of paste)
1	Purified water	as needed
2	Strong alkali (e.g. sodium hydroxide - aqueous solution 32%)	700 ÷ 850 g
3/a	Synthetic thickening agent (e.g. dispersion of acrylic copolymers in light mineral oil) ALCOLPRINT DT-CS^® (Ciba Specialty Chemicals S.p.A.)	35 ÷ 65 g
3/b	Natural thickening agent (e.g. starch, carboxymethylcellulose, etc.)	10 ÷ 20 g

The thickening agent has obviously the function of making the paste suitably thick in view of the subsequent use. If needed, wetting substances can be added, as obvious to the skilled person. The preparation of the paste will be carried out with the mixing and agitation techniques usual in the field of the textile printing.
Variants and/or modifications can be brought to the printing process on textile products made of polyester or polyester-mixed for obtaining surface designs defined by areas having different degradation characteristics, and to the textile products thus obtained according to the present invention, without for this reason departing from the scope of protection of the invention itself as defined by the appended claims.

Claims

A process to be used on a textile substrate made of polyester or comprising polyester fibers, the process comprising a printing step in which a printing paste is directly applied on said substrate by means of a printing matrix on which there is formed a pattern to be reproduced, and at least a subsequent drying, steaming or thermofixing step at high temperature, the process being characterized by the fact that said printing paste comprises a high concentration of strong alkali for defining on said substrate, further to said printing and the subsequent drying, steaming or thermofixing step at high temperature, areas with different degradation characteristics, in accordance with said pattern of said matrix, as a result of a basic hydrolysis reaction triggered on the polyester by said strong alkali.
The process according to claim 1, wherein said strong alkali comprise sodium hydroxide.
The process according to claim 2, wherein said printing paste comprise sodium hydroxide in aqueous solution 32%, about 700 ÷ 850 g of said solution being used for obtaining each kg of printing paste.
The process according to claim 3, wherein said printing paste further comprises a thickening agent.
The process according to claim 4, wherein said thickening agent is a synthetic agent, used in a concentration comprised between about 35 and 65 g for obtaining each kg of printing paste.
The process according to claim 4, wherein said thickening agent is a natural agent, used in a concentration comprised between about 10 and 20 g for obtaining each kg of printing paste.
The process according to any of the previous claims, wherein after said printing step a drying step is carried out at high temperature, comprised between about 160° and 185°C.
The process according to any of the claims 1 to 6, wherein after said printing step said substrate undergoes a drying step at a temperature comprised between about 100°C and 120°C and a steaming or thermofixing step at a temperature comprised between about 160°C and 180°C.
The process according to claim 7 or 8, wherein said textile substrate undergoes a final washing or neutralization step in order to eliminate the residuals of strong alkali in the printing paste and the products of the hydrolysis.
The process according to any of the previous claims, wherein simultaneously to said printing step, one or more traditional printing runs are carried out for coloring the substrate by applying dying substances or pigments.