METHOD FOR BLEACHING FABRICS

Abstract

A method for the localized or diffuse bleaching of colored fabrics and garments by applying an accelerating substance comprising quaternary ammonium salts and subsequent treatment with ozone.

Description

METHOD FOR BLEACHING FABRICS Field of Invention The present invention relates to the field of treatments for bleaching textile products, in particular, but not exclusively, garments made of denim fabrics. More specifically, the invention relates to a method for bleaching or discoloring colored fabrics, in order to give such fabrics a worn and aged appearance similar to that which would be obtained after years of use. In particular, the objective of the present invention is a method for bleaching textile products thanks to the synergistic action of a quaternary ammonium cation and ozone. Background of the Invention As is well known, there are different chemical products and treatment methods used both industrially and domestically for aging textiles in order to give certain garments greater appeal and aesthetic value. The aged effect is produced by a discoloration of the fabric which, depending on the case, can spread over the entire surface of the garment or be localized in specific areas of the garment itself. -2It should be noted that, although the following text refers to denim fabric, i.e., a fabric made of cotton, the method of the present invention can be applied to any textile product. It should also be noted that, in this text, the term textile product refers interchangeably to a fabric or a made-up garment. In this patent text, the terms bleaching and decolorization are used interchangeably to refer to treatment processes that are capable of altering the color of the textile product, generally making it paler and more white. In the textile industry, methods for localized bleaching of jeans, denim, or similar fabrics have been known for a long time; i.e., methods that achieve a particularly limited bleaching of specific areas of the product. Currently, the most commonly used bleaching method employs a potassium permanganate solution that is sprayed by an operator onto specific areas of the fabric to be treated, particularly, in the case of trousers, the knee and thigh areas. Potassium permanganate is a strong oxidizing agent that reacts with the fabric's color, causing it to bleach and accentuating the worn and aged appearance. qq / rnn / zznz / E / YiAi -3However, this solution has the drawback of exposing the operator to obvious risks to their health and safety in case of inhalation of the aerosols formed during the spraying of potassium permanganate onto the fabric. At the same time, diffuse bleaching treatments of denim textiles are known that are used to obtain a substantially homogeneous aged effect over the entire surface of the product, i.e., without significantly non-homogeneous areas. In currently known solutions of this type, the textiles to be treated are placed in industrial washing machines whose washing liquid is supplemented with chemical compounds such as potassium permanganate, sodium hypochlorite, hydrogen peroxide, laccase, etc. These solutions for the diffuse bleaching of textiles require large quantities of chemical additives to achieve a sufficiently strong bleaching effect. The use of these substances has a high environmental impact, and the wash water must be treated to reduce the contaminant content. Another drawback of these processes is the high water consumption in the various washing and rinsing phases. To overcome the aforementioned problems, processes for bleaching textiles using ozone have been developed several years ago. Ozone is generated in situ using special machinery and introduced into hermetically sealed washing machines where the textiles to be treated are placed; the treatment can be carried out dry or in water. In the case of denim fabrics, ozone treatment provides fabric cleaning from the re-deposition of indigo and in some cases also a slight bleaching. To enhance the bleaching effect of ozone, the fabric is moistened with water to accelerate the oxidizing action of the ozone. US patent application US20140068871 describes a method for bleaching denim fabric by wetting it with water and then subjecting it to a second ozone bath. A similar solution is described in Japanese patent application JPH04100987A. International patent application WO2018065388A1 discloses a method of localized bleaching of a denim fabric using ozone, after soaking certain areas of the fabric with a hygroscopic substance, i.e., a substance that absorbs moisture. All the solutions described above use water to enhance the oxidizing action of ozone, but the results obtained are unsatisfactory. In particular, the bleaching effect is weak to moderate, and it is not possible to selectively bleach the fabric to achieve the strong color contrasts that are currently in high demand. -5 in the fashion sector. The aforementioned USA application US20140068871 also describes a method for locally bleaching fabric by spraying water only on certain areas of the fabric before treating it in the ozone bath. However, this solution also has the same disadvantages as the other known solutions described above, namely, that the bleaching achievable using only water as an ozone accelerator is not sufficiently pronounced. Furthermore, this method is not in line with the requirements of the modern textile industry, where dozens or hundreds of garments are treated simultaneously in the ozone machine, but prior to this stage, they must be manually pre-treated by spraying water on limited areas of the fabric. Only a small number of garments can be pre-treated at a time, so that by the end of this phase, before the ozone treatment, many of the garments have completely dried, rendering the subsequent ozone treatment useless. Other, more expensive and complicated treatment processes have been developed for the localized bleaching of textiles using ozone, such as that described in document EP0554648A1, where differential bleaching is achieved through additional pre-treatments such as the application of substances that block the bleaching action of ozone on part of the fabric or qq / enn / zznz / E / YiAi -6 dyeing of the fabric with dyes that have different sensitivity to ozone. None of the ozone textile bleaching methods described above achieve a comparable anti-aging effect to that obtained with traditional treatment methods, which, however, use potentially harmful or polluting chemicals. In the case of selective bleaching, none of the methods described above achieve a pronounced color contrast between bleached and unbleached areas. Summary of the Invention Therefore, the objective of the present invention is to provide an ozone treatment method for bleaching colored textile products, in particular denim fabrics, that is effective and fast and does not involve high water consumption. Another important objective of the present invention is to reduce the ozonation treatment time of textile products, while providing a pronounced and effective bleaching effect. Another objective of the present invention is to provide a method of localized bleaching of textiles that is safe for the health of the operators. A no less important objective of the present invention qq / enn / zznz / E / YiAi is to locally bleach a textile product producing a strong chromatic contrast between the treated and unbleached areas. These and other objectives, which will become clear to the expert in the field from reading this document, are achieved through a method of bleaching textile products that involves an initial pre-treatment stage, in which the fabric is moistened with an accelerating substance containing a quaternary ammonium salt and then the pre-treated textile product is placed in an ozonizing fluid. Surprisingly, it has been observed that quaternary ammonium salts improve the oxidizing action of ozone, so that when the textile product pretreated with this accelerator is subjected to an ozonation treatment, a much more pronounced bleaching is obtained than with treatment with ozone alone. Preferably, the quaternary ammonium salt that constitutes said accelerator is cetrimonium chloride, also known as cetyltrimethylammonium chloride, or hexadecyltrimethylammonium chloride or cetrimide or CTAC. Alternatively, the quaternary ammonium salt used is benzalkonium chloride, also called alkyldimethylbenzylammonium chloride. Conveniently, these quaternary ammonium salts are mixed with other adjuvant components, such as qq / rnn / zznz / E / YiAi -8 surfactants (wetting agents, antifoaming agents, deaerating agents, etc.), pH buffering substances and any other substance useful to facilitate the application of the product. A mixture of cetrimonium chloride and benzalkonium chloride and / or other quaternary ammonium salts may also be used. The accelerator used in this method can be conveniently applied with a brush or impregnated glove, without the risk of creating unwanted halos and / or stains on the finished product, unlike potassium permanganate, which can only be applied by spraying in the form of tiny particles due to its high reactivity. The ability to apply the product even without spraying it onto the fabric significantly reduces the risk of inhalation by the operator. In a first version of the bleaching method of the present invention, particularly suitable for obtaining diffuse and substantially uniform bleaching, the textile product is placed in a bath comprising the accelerating substance based on quaternary ammonium salts, and is then at least partially dried, and subsequently placed inside the ozone treatment machine. In a second version of this method, particularly suitable for localized bleaching of qq / rnn / zznz / E / YiAi products In textiles, the accelerating agent is selectively applied only to specific areas of the textile product, for example, the thigh and knee area in the case of jeans. Once the accelerating agent is applied, the textile product is optionally dried to prevent moisture from affecting the next stage. It is then placed in the ozone machine and subjected to ozonation treatment, resulting in more pronounced bleaching in the areas where the accelerating agent was applied. There are different ways to apply the accelerator. For example, in the case of localized discoloration, the accelerator can be applied with a brush or impregnated glove, or by localized spraying. In the case of diffuse application, the accelerator can be applied using cloths impregnated with the same substance or by spraying it inside sealed washing machines. In both versions of the method, there may be a final stage of neutralizing residual ozone by applying a reducing product to the bath, or more simply by one or more rinses followed by drying. Very advantageously, the combined action of ozone with the accelerating substance applied to the textile product provides a more pronounced bleaching than that obtained by the ozone bleaching methods known to date. qq t enn / zznz / E / YiAi - 10 Unlike known solutions, the method of the present invention employs an accelerating substance based on ammonium salts capable of reacting with ozone in the presence of moisture or once said substance has completely dried. In the solutions already known, very strict planning is required, therefore difficult to control, of the execution times of the different stages of the process because the bleaching effect of ozone varies significantly depending on the degree of residual moisture and consequently on the time elapsed since the pre-treatment phase; in these solutions the accelerator used is in fact only water or a hygroscopic substance capable of attracting moisture. In comparison with known solutions, in the objective method of the present invention the bleaching effect given by the synergistic effect of ozone and quaternary ammonium salts is not affected by humidity or by the time elapsed between the pre-treatment phase of the product and the ozonation phase, therefore the advantages that the present solution is able to achieve are evident. Detailed Description of the Invention In the text of this patent, the term ozonation refers to a treatment process with ozone that consists of placing the textile product inside an ozone-enriched fluid. In the textile industry, the ozonation process is carried out by placing the textile product to be treated inside a sealed machine, similar to an industrial washing machine, into which ozone produced by an ozone generator is introduced. The ozonation process can be carried out dry, that is, without using water, by pumping the ozone gas into the machine or, alternatively, by immersing the textile product in an aqueous bath in which the ozone dissolves. The objective method of the present invention essentially comprises the following main phases: (a) Pre-treatment: In this first pre-treatment stage, the textile product is at least partially moistened with an accelerating substance comprising quaternary ammonium salts, preferably cetrimonium chloride and / or benzalkonium chloride; (c) Ozonation: In this phase, the pre-treated product is placed inside an ozone machine of a known type and kept there for a certain period of time immersed in an atmosphere rich in this gas. After the pre-treatment phase (a) but before the ozonation phase (c), the following intermediate phase may optionally be carried out: qq / rnn / zznz / E / YiAi - 12 (b) Drying: In this phase, the textile product is dried according to known processes, in order to eliminate moisture that could affect the next ozone treatment phase. Finally, in certain versions of the method, after the ozonation phase (c) an additional step is performed: (d) Neutralization: In this phase, the residual ozone is neutralized by means of a known reducing product applied in the bath or by a series of successive rinses of the product, followed by additional drying. During the ozonation phase (c), the oxidizing action of ozone, combined with the accelerating substance composed of ammonium salts, applied in the previous pre-treatment phase (a), causes discoloration of the fabric. In other words, the ammonium salt compound intensifies the bleaching action of ozone in the areas of the fabric to which it has been applied. The method described in the present invention can be used to achieve localized bleaching of the textile product or diffuse bleaching. In the first case, the areas where the accelerator has been applied show a visibly more pronounced bleaching than the areas where the accelerator has not been applied. If the pre-treatment is applied diffusely over the entire textile product, a substantially uniform but more pronounced bleaching is obtained than if ozone alone were used. Preferably, the accelerating agent used is a cetrimonium chloride solution. The weight percent concentration of solute is preferably between 1% and 30%, although solutions with lower or higher solute concentrations may be used; excellent results are obtained with a concentration of 3%. Instead of cetrimonium chloride, a solution of benzalkonium chloride may be used, or alternatively, a mixture of the above compounds of quaternary ammonium salts or other quaternary ammonium salts. In some versions of the invention, said accelerating substance further comprises at least one adjuvant compound, such as a surfactant or a pH buffer substance or other similar substance, useful to facilitate application to the textile product. According to a possible version of the invention, aimed at achieving localized bleaching or discoloration only in specific areas of the textile product, during the pre-treatment stage (a) the quaternary ammonium salt compound is applied by an operator directly to one or more circumscribed surface areas of the textile product so that these areas, and only these areas, become impregnated with said compound. In this case, the operator applies the mixture directly onto the fabric using a brush or an impregnated glove, or by spraying it with an airbrush, or more generally by any other method that selectively wets one or more circumscribed areas of the product in a desired shape or pattern. In a second version of the method, during the pre-treatment phase (a) the accelerating solution is diffusely applied over the textile product, thus obtaining a non-localized bleaching effect, extended to the entire surface of the textile product. The diffuse application of the accelerator according to this second version of the objective method of the invention can be carried out, for example, by placing the textile product in an aqueous bath inside a washing machine, in whose washing liquid the same accelerating substance is dissolved. Other alternative solutions can be used, such as nebulizing the accelerating substance inside the drum of a washing machine using nozzles incorporated into the machine, where the product to be treated is deposited; in this case the treatment cycle does not include an aqueous bath. Another technique that can be used to achieve diffuse surface bleaching, although with more accumulated stains, is that of impregnated cloths. These cloths, pre-cut to size, are impregnated with the accelerating substance, then, after a light extraction, they are... - 15 spin together with the textile product inside the washing machine (without a water bath), releasing traces of accelerating substance by contact on the surface of the product. It should be noted that although the description refers to a textile product, the objective method of the invention can be applied equally to a plurality of textile products that are subjected to pre-treatment (a) simultaneously or separately and that are subsequently subjected simultaneously to ozonation (c) and optionally, depending on the versions of the method, to the other drying (b) and neutralization (d) treatments.

Claims

1. A method for bleaching a textile product characterized in that it comprises the following steps: (a) pre-treatment, by applying an accelerating substance comprising quaternary ammonium salts to at least a portion of said textile product; (c) ozonation, by introducing and maintaining said textile product in an ozonizing fluid.

2. A method according to claim 1 above, characterized in that it is applied to a textile product comprising colored cotton of the denim type.

3. A method according to one of the preceding claims, characterized in that it comprises, between the pre-treatment stage (a) and the ozonation stage (c), the drying stage (b) of said textile product.

4. A method according to one of the preceding claims, characterized in that said ozonation step (c) is followed by the step (d) of neutralizing the residual ozone on the textile product, by using a reducing compound applied in a bath or by subsequent rinses, which is followed by the drying step.

5. A method according to one of the 17 preceding claims, characterized in that in the pre-treatment stage (a), said accelerating substance is selectively applied locally to one or more circumscribed areas of the textile product.

6. A method according to claim 5 above, characterized in that in the pre-treatment stage (a) the accelerating substance is applied manually by an operator using a brush or impregnated glove or by nebulizing it with an airbrush.

7. A method according to any one of claims 1 to 4 above, characterized in that in the pre-treatment stage (a), said accelerating substance is diffusely applied to said textile product by means of an aqueous bath, by nebulization or by contact with a plurality of pre-cut impregnated cloths.

8. A method according to any of the preceding claims, characterized in that said accelerating substance is a solution of quaternary ammonium salts with a concentration between 1% and 30%, preferably 3%.

9. A method according to one of the preceding claims, characterized in that said quaternary ammonium salts comprise cetrimonium chloride.

10. A method according to one of the preceding claims, characterized in that said qq / rnn / zznz / E / YiAi quaternary ammonium salts comprise benzalkonium chloride.

11. A method according to one of the preceding claims, characterized in that said accelerating substance comprises at least one adjuvant compound, such as for example a surfactant or a pH buffer substance or other similar substance, useful to facilitate application to the textile product.