TECHNICAL FIELD

The present invention deals with a thickener and textile printing pastes based on tamarind gum and an enzyme with proteolytic activity.

The textile materials printed with the textile printing pastes of the present invention show a deeper dye penetration and a better uniformity of dye distribution, as easily verified by visual assessment of the final article and by instrumental colour analysis.

PRIOR ART

Textile printing pastes serve to transfer dyes onto a textile material in a controlled way through a silk-screen, in order to have the correct formation of the desired pattern and decoration.

The textile printing paste composition is critical and largely determines the quality of the final article.

Printing pastes are prepared by solubilising a thickener (thickening agent) in water and, successively, by adding the dye and other possible chemical auxiliaries useful to the process (such as pH regulators, antifoam agents, stabilisers and others) and have a solid content comprised between 4 and 20% by weight.

Commonly used thickeners are mainly composed by one or more water soluble natural (gums) or semisynthetic polymers of varying molecular weight, such as polygalactomannans and their derivatives, starch and its derivatives, alginates, tamarind derivatives, cellulose derivatives; polygalactomannans in general and polygalactomannans from guar seeds and their derivatives are particularly preferred.

The main function of thickeners is to guarantee the viscosity to the paste in order to allow a better control in the design pattern reproduction onto the textile material.

The thickener, however, can give to the a paste a very high dye holding capability which cause the dye to be mostly applied to (or formed on) only onto the surface of the textile material to be printed, presenting a new problem of the dye failing to penetrate fully into its inside. This results in an un-dyed inner surface and an unacceptable dyed appearance when the textile material is stretched, due to lack of dye penetration between yarns.

Moreover commercially available natural thickeners, in particular the tamarind gum, always contain a variable high amount of proteins usually comprised between 1 and 20% by weight deriving from the germ of the seeds that is not possible to remove completely before or during milling of the vegetable structure containing them. These proteins are potentially able to combine with dyes, thus forming complexes, which can aggregate the colour in microscopic masses, giving rise to spots and dots which affects the dye yield and the uniformity of printing (dotting) .

Many different solutions have been proposed in the past in order to solve these problems, but, usually, they work out only one problem at the time.

For example, in WO 2005/080668 the Applicant discloses a textile printing thickener containing one or more polygalactomannan derivatives and an enzyme, in particular a protease. The enzyme hydrolises the proteins and permits to obtain printing pastes free from dotting effect, but no mention is made about the penetration of the dye into the textile material.

Now, it has been surprisingly found that the addition of an enzyme with a proteolytic activity to a tamarind gum allows the preparation of textile printing pastes which show increased uniformity of printing and at the same time deeper penetration of the dye into the textile material.

The experts in the field always acknowledged that tamarind gums has good characteristics of stability in the typical printing process and can be promptly removed in the final washing phase, but, compared to other thickeners, they showed inferior performance of superficial fixation and homogeneous distribution of the dye. Now these limitations, thank to the inventive solution, are absent or less prominent and tamarind gums can be used also in the printing of valuable, high quality textile articles.

With "depolymerized tamarind gum" we mean a tamarind gum whose average molecular weight has been sensibly educed using a degrading treatment.

DESCRI PTI ON OF THE I NVENTI ON

It is therefore an essential object of the present invention a thickener comprising a tamarind gum and an enzyme protein having proteolytic activity, characterised by the fact that the tamarind gum has a Brookfield® RVT viscosity at 20°C and 20 rpm of 20.000 mPa-s at a concentration comprised between 3 and 13% by weight in water.

It forms a further essential object of this invention a textile printing paste comprising a tamarind gum and an enzyme protein having proteolytic activity. DEDULED DESCRIPTION OF THE INVENTION

Preferably, the thickener of the invention comprises from 40 to 99.9% by weight of said tamarind gum and from 0.0001 to 5 % by weight, preferably from 0.001 to 0.5% by weight, of said enzyme protein having proteolytic activity.

Suitable proteolytic enzyme proteins include the proteases, which can be of animal, vegetable or microbial origin. Microbial origin is preferred. Purified or non purified forms of this protein may be used.

The proteolytic enzyme protein may be a serine protease or a metallo protease. A preferred proteolytic enzyme protein for the present invention is a serine protease of the subtilisin family of microbial origin.

Preferred commercially available protease enzyme formulations include those sold under the trade names MAXATASE®, MAXACAL® , MAXAPEM® , OPTIMASE®, PROPERASE® PURAFECT®, PURAFECT® OXP (Dupont-Genencor) and those sold under the trade names ALCALASE®, SAVINASE®, PRIMASE®, DURAZYM®, RELASE® , POLARZYME® and ESPERASE® (Novozymes). Examples of single products are: PURAFECT® 4000L and PURAFECT® 4000E by Dupont- Genencor; POLARZYME® 12T and SAVI NASE® 12Tby Novozymes.

Preferably the protease of the invention shows a low a-amylase secondary enzymatic activity, below 1.5 KNU/g, preferably below 0.5 KNU/g, allowing the use of the tamarind gum in combination with starch as additional thickening agent.

One Kilo Novo α-amylase Unit (KNU) is defined as the amount of enzyme which, under standard conditions (at 37 °C +/- 0.05; 0.0003 M Ca ²⁺ ; and pH 5.6) dextrinizes 5260 mg starch dry matter Merck soluble Amylum Erg. B. 6, batch no.: 6380528 (definition batch) per hour.

This analytical method is described in more detail in the standard operating procedure EB-SM-0009.02/01 , which is available from Novozymes A/S, Denmark. Tamarind (Tamarindus Indica) is a leguminous evergreen tall tree produced in the tropics. Tamarind gums, a xyloglucan polysaccharide, are obtained by extracting and purifying the seed powders, obtained by grinding the seeds of tamarind from which the testa is removed.

The tamarind gums useful for the present invention are those normally available on the market for use in the textile printing sector. The suitable tamarind gum has Brookfield® RVT viscosity measured at 20°C and 20 rpm of about 20,000 mPa-s at a concentration comprised between 3 and 13 % by weight, preferably between 7 and 12% by weight, in water. Preferably the tamarind gum useful for the present invention is a depolymerised tamarind gum. It can be prepared by using any of the methods known in the art. The tamarind gum can be depolymerized by oxidation, for example with alkali or hydrogen peroxide, or by other depolymerization reactions, such as enzymatic or thermal depolymerisation, or acid hydrolysis. The depolymerized tamarind gum used in this invention is preferably prepared by oxidation and has a Brookfield® RVT viscosity of about 20,000 mPa-s (20 rpm and 20 °C) at a concentration comprised between 7 and 12 % in water.

The thickener of the invention can comprise one or more polymers commonly used in textile printing pastes and having thickening function, such as alginates, starch and its derivatives, tamarind derivatives, synthetic polymers, cellulose derivatives, polygalactomannans and their derivatives, such as guar, hydroxypropyl guar and carboxymethyl guar. The preferred additional polymers are starch and its derivatives.

Preferably, the thickener of the invention comprises from 90% to 99.9% by weight of a tamarind gum and from 0.0001 to 5% by weight, preferably from

0.001 to 0.5 % by weight, of a protease enzyme.

The thickener of the invention can be prepared by simply mixing the tamarind gum with the enzyme protein and, optionally, the additional polymer.

Preferably, the thickener is provided as a powdery solid.

The tamarind gums and the enzyme proteins with proteolytic activity useful for the preparation of the textile printing pastes of the present invention are those mentioned above.

Preferably, the textile printing paste of the invention comprises from 0.0001 and 0.3% by weight of an enzyme protein having proteolytic activity and from 0.1 to 10 % by weight of a tamarind gum having a Brookfield® RVT viscosity at 20°C and 20 rpm of 20,000 mPa-s at a concentration comprised between 3 and 13% by weight, preferably between 7 and 12% by weight, in water.

The textile printing paste of the invention can include at least a dye. Dyes differ from pigment colorants in that usually dyes are completely soluble or easily dispersible in water whereas pigment colorants are not. Acid dyes and disperse dyes are particularly compatible with the printing paste of the invention.

According to a preferred embodiment, the textile printing paste comprises acid dyes. More preferably, the textile printing paste comprises from 0.1 to 10% by weight of one or more acid dyes. Examples of suitable acid dyes can be chosen among the group of anthraquinone type dyes, such as Colour Index (CI) Acid Blue 43 or CI Acid Blue 129, the azo- dyes, such as CI Acid Red 88 or CI Acid Red 114, and triphenylmethane dyes, such as CI Acid Violet 17, CI Acid Blue 15, CI Acid Blue 7 and CI Acid Green 3. Particularly preferred are premetalized acid dyes, for example CI Acid Blue 193 or CI Acid black 194.

According to another preferred embodiment, the textile printing paste comprises one or more disperse dyes. The disperse dye is a dye that is used for dyeing hydrophobic synthetic fibers, such as polyester and nylon, and is water-insoluble or low water-soluble. Accordingly, they are used in fine particle forms by being dispersed in aqueous media.

The disperse dyes used in the invention are not particularly limited, and any disperse dye commonly used in the textile field can be utilized for the realization of the invention.

Example of suitable disperse dyes are CI Disperse Yellow 114, CI Disperse Yellow 163, CI Disperse Orange 73, CI Disperse Red 15, CI Disperse Red 91, CI Disperse Red 92, CI Disperse Blue 60, CI Disperse Blue 165, CI Disperse Violet 23, CI Disperse Violet 36, CI Disperse Green 9, CI Disperse Brown 19, CI Disperse Black 3, etc.

Usually, the textile printing paste contains from 0.1 to 10% by weight of one or more disperse dyes.

The textile printing paste according the invention can further comprise one or more polymers having thickening function, chosen among alginates, starch and its derivatives, tamarind derivatives, synthetic polymers, cellulose derivatives, polygalactomannans and their derivatives, such as guar, hydroxypropyl guar and carboxymethyl guar; preferably in a quantity not higher than 5 % by weight. The preferred additional polymers are starch and its derivatives.

The textile printing paste according to the invention can further comprise textile printing additives familiar to the expert, such as wetting agents, emulsifiers, dispersing agents; solubilizing agents; defoamers; reducing agents, oxidizing agents, resist agents, pH regulators, complexing agents, preservatives; and mixture thereof.

Wetting agents, emulsifiers, dispersing agents can be anionic, cationic or nonionic in a known manner. Examples of these are: reaction products of aliphatic, araliphatic or aromatic hydroxy compounds, carboxylic acids, carboxylic acid amides or amines with ethylene oxide; sulfuric acid half esters or phosphoric acid partial esters thereof; fatty acid esters of mono- or polysaccharides or fatty acid sorbitan esters and ethoxylation products thereof; C ₁₀ -C ₂₀ -alkanesulfonates, C ₈ - C ₁₂ alkylbenzene sulfonates; C ₈ -C ₁₈ alky I sulfates or phosphates; or condensed aromatic sulfonic acids, such as naphthalene-formaldehyde-sulfonates. Substances of the type mentioned can also serve as leveling agents.

Solubilizing agents as further additives are, for example, glycols, mono- to tetra- alkylene glycols and ethers or esters thereof with C1-C4 alcohols or Ci-C ₄ carboxylic acids. They are particularly useful when disperse dyes are utilized for the realization of the present invention.

Defoamers are, for example, compositions comprising vegetable oils or mineral oils or, in particular, propylene oxide/ethylene oxide block polymers.

The textile printing additives mentioned in the preceding paragraphs can be present in an amount of 0 to 10% by weight, based on the total weight of the pastes according to the invention.

The textile printing pastes of the invention can be prepared according to the usual procedures, by slowly adding the thickener(s) to water, under mechanical stirring, until complete dissolution is achieved, and by adding to the thickener solution the additives (pH regulators, antifoam, and so on) and the dye, and finally by adding water up to the desired concentration of active substances.

In the printing process according to the invention, the textile materials are subjected to printing using essentially any textile screening techniques known in the art. One common technique is silk screen printing where the paste is applied to the surface of the textile material by pressing the paste through screens. The screens are conventionally made of silk, but any screen suitable for silk screen printing can be utilized, for example in nylon or polyester. Rotary screen printing and flat (bed) screen printing are examples of industrially applicable printing techniques. Inkjet printing for textile material is also suitable for the realization of the invention.

Textile materials which can be printed using the pastes according to the invention are fiber materials of loose fibers, woven or knitted goods or those in the form of nonwovens, based on natural or synthetic fibers or mixtures thereof. Examples of natural fibers are wool, silk, linen, as well as jute. Examples of synthetic fibers are polyamides, polyacrylon itriles or polypropylenes.

According to an essential aspect of the present invention the presence of an enzyme in the printing pastes has no negative effect on the printed textile materials at the end of the printing cycle. The commonly used drying and dye fixing conditions guarantee the complete inactivation of the enzyme and its transformation into soluble products that are eliminated from the printed textile materials during the final washing phase, along with the products derived from the proteins they were able to decompose. EXAMPLES

Example 1 (Comparative)

200 g of tamarind gum was depolymerised by oxidation, adding to the gum 6.0 g NaOH and 5.0 g of hydrogen peroxide 80%. The reaction occurs for 45 min at 55 °C. Then the product was cooled at 30 °C and the pH was adjusted to 7 with sulfuric acid.

After that, the product was dried and milled.

The depolymerized tamarind gum has a residual moisture content of 6 % by weight and Brookfield® RVT viscosity of about 20,000 mPa*s at 20 rpm and 20 °C at a concentration of 10 % by weight in water.

Example 2

The thickener of the present invention was prepared by carefully mixing 100 g of depolymerised tamarind gum of Example 1 with 1 g of Savinase 12T (commercialized by Novozymes).

Protein Determination

10 g of a 2.5% solution in deionized water of the thickener of Example 1 and 2 were centrifuged at 9000 rpm for 30 minutes in order to separate the insoluble matter (pellet) and the soluble matter (the supernatant).

The content of soluble proteins (in the supernatant) and insoluble proteins (in the pellet) was determined with PIERCE BCA Protein Assay KIT by Thermo Scientific. The calibration curve was prepared with Bovine Serum Albumin.

Table 1 reports the content, as % by weight of the thickener, of insoluble and soluble of proteins of Example 1 and 2.

Table 1

^* Comparative

Printing Tests.

The amount of thickeners of Examples 1 and 2 required to reach a viscosity of 20,000 mPa-s were added, under mechanical stirring, to 900 g of water and mixed until complete dissolution (about 40 min). The thickener solutions were allowed to rest for about two hours at room temperature.

30 g of Dark Blue Tiasolan LB (acid dye commercialized by Lamberti SpA), 30 g of thiodiglycol and 50 g of urea were weighed in a 1000 ml beaker and carefully mixed. The mixture was dissolved by pouring under stirring 900 g of boiling deionized water. This solution was then filtered on a polyester canvas of 54 m icron.

600 g of thickener solution were carefully homogenized with 400 g of the colour solution under mechanical stirring. Subsequently 20 g of (NH ₄ ) ₂ S0 ₄ were added under stirring.

A white silk fabric was printed with the printing pastes using a 77 threads/cm silk screen (5 stripes 5x40 cm design) and a Zimmer laboratory printing machine set at speed 4 and pressure 2. A 4 mm steel rod was used.

The fabric so obtained was then dried at a temperature of 90°C for 1 minute in oven and treated for 40 minutes, for colour fixing, in an Arioli vaporising machine set at 102 °C. The printed fabric was washed at 30 °C in the presence of soap, dried and finally ironed.

The appearance of the printed fabrics were evaluated both visually and instrumentally using a DataColor Int. reflectance spectrophotometer (Spectral Test SE600 PLUS-CT) under a DL65/10 ⁰ illuminant. The (K/S) values were calculated according to AATCC Evaluation Procedure 6.

The area printed with the paste according to the invention clearly shows, under the visual inspection, a more homogeneous dye distribution and a better penetration than the area printed with the comparative paste.

Table 2 shows the colour strenght (K/S) of the silk fabric printed using the paste of Example 1 (front area and back area) and of the fabric printed using the paste of comparative Example 2 (front area and back area) with the percentage of penetration calculated with the following formula :

% penetration = 200.(K/S) _B /((K/S) _F + (K/S) _B ).

Table 2

^* Comparative