WO2024172789A1 - A new dyeing method including two-step mordanting for dyeing lyocell textile products with direct dyestuffs - Google Patents

Abstract

The present invention relates to a new dyeing method comprising the use of metallic mordants (chemical mordants) or bio-mordants before and after dyeing in order to improve the colour of lyocell textile products in the textile industry, to prevent discoloration due to use and external factors after dyeing and to improve wet fastness.

Description

A NEW DYEING METHOD INCLUDING TWO-STEP MORDANTING FOR DYEING LYOCELL TEXTILE PRODUCTS WITH DIRECT DYESTUFFS

Field of the Invention

The present invention relates to a new dyeing method comprising the use of metallic mordants (chemical mordants) and bio-mordants before and after dyeing in order to improve the colour of lyocell textile products in the textile industry, to prevent discoloration due to use and external factors after dyeing and to improve wet fastness.

State of the Art

Lyocell is a textile fiber product originating from regenerated cellulose. Lyocell fibers, whose trade name is Tencel®, are obtained from wood pulp. Lyocell fiber is obtained by dissolving the cellulose raw material in an organic solvent (NMMO) and spinning the fiber by wet spinning. Mostly wet or dry-jet spinning methods are used. The substance obtained by dissolving the wood pulp of plants such as birch, oak or eucalyptus in NMMO (N-methymorpholine N-oxide) solution is called 'paste'. This dissolved cellulosic paste is first extruded through a cooling air gap and then spun. When the extruder forces this paste through the nozzle holes, it is formed into long, thin fibers. In the next stage, coagulation is achieved in a dilute spinning bath. After fiber extraction, the fiber concentration is increased by evaporating the excess of the NMMO. At this stage, it forms a fibrillar tissue in the internal structure of the fibers and can also be separated from the fibers. As a result of fiber extraction and related fiber properties, a perfect longitudinally continuous filament structure such as viscose-type polynosic fibers is obtained. The resulting fibers can be cut and stapled, the fibers can be oiled and given anti-static properties and finally washed and dried. The NMMO solution used here is 99.5% recyclable. The remaining less than 1 % is biodegradable in nature. Since the fiber production process eliminates the use of toxic chemicals and reduces water and air emissions, it is a highly environmentally sensitive production. At the same time, low CO2 and SO2 emissions and low abiotic depletion have a low negative impact on terrestrial ecotoxicity and photochemically.

The production method of the cellulose solution for lyocell fibers is completely different from that of the viscose rayon. Wood pulp is formed by precipitation in organic solution, there is no displacement of the hydroxyl groups of the fiber and no chemical by-products are produced. Due to environmental concerns, researchers sought new methods for the preparation of cellulose solution and discovered NMMO. The NMMO solvent directly dissolves cellulose into wood pulp. An American company, American Enka, discovered a method of spinning regenerated cellulose fibers using NMMO solvent but failed to commercialize the process. Pat White, R&D leader at Courtaulds in the UK, has developed a new method of spinning cellulose solution with a successful engineering approach. In 1982 Courtaulds set up a small pilot factory, producing 100 kg of Lyocell fiber per week. In 1984, production capacity was increased to 1 ton per week. In 1988, a semi-commercial production line of 25 tons per week was launched in Grimbsy (UK). In 1992, production in Mobile Alabama (USA) and Courtaulds reached full commercial capacity and this new regenerated fiber was produced under the trade name TENCEL. Another large European company, Lenzing (Austria), starts the production of Lyocell fiber. Instead of lyocell fibers, which are normally produced by customizing the viscose rayon production line, Lenzing established a pilot factory to produce lyocell fibers in 1990. Lenzing's large-scale production plant in Heiligenkruz (Austria) started production in 1997. Annual capacity of 12.000 tons of lyocell staple fiber production was realized. This fiber was named Lenzing Lyocell. In 2004 Lenzing acquired the Tencel group and a plant in Mobile Alabama and a plant in Grimsby were transferred to Lenzing. By 2022, Lenzing became the world's largest producer of lyocell fiber. In March 2022, Lenzing built a new factory in Thailand with an annual capacity of 100.000 tons of lyocell fiber.

The advantage of lyocell production is that no harmful chemical derivatives are formed at the time of dissolution as in conventional viscose production. According to primary energy demand, water use and land use, lyocell fibers have the lowest environmental impact while viscose rayon has the highest environmental impact. However, the environmental impact of other regenerated cellulose fibers is lower than that of viscose. When viscose rayon and lyocell are compared; lyocell fibers, which can be recycled, have emerged as a rival fiber to viscose rayon because they have advantages such astotal energy efficiency and less dependence on fossil fuel. Wood pulp is produced by harvesting trees grown in sustainable industrial forests. Compared to viscose rayon, it has higher crystallinity and larger crystal size. Lyocell fibers have high strength in wet and dry state; its tensile strength is higher when wet and dry compared to cotton and viscose rayon. It provides good dimensional stability in clothes due to its low shrinkage in water. It has higher dyeability than cotton and viscose rayon. Its stabilization under alkaline conditions is higher than viscose. Stone washing and sand washing can be applied to the fabrics and a peach fuzz effect can also be given. It can absorb excess liquid (perspiration) and quickly release it into the atmosphere. Tencel absorbs 50% more moisture than cotton (from 65% RH to 100% RH). They are less resistant to thermal permeability compared to cotton and have higher vapor permeability (good thermal and good moisture management), resulting in high wearing comfort.

Lyocell fibers can be dyed with Direct, Reactive, Vat, Sulphur and Azoic dyes just like other cellulosic fibers. As a result of the high fibrillation property of lyocell fibers and the alkaline pre-treatment processes, the dye uptake rate, colour depth and good moisture retention properties are improved. As a result, the dye absorption abilities of lyocell fibers show some different results compared to other cellulosic fibers. Dyeing and finishing processes for products made of Lyocell fiber are of great importance, especially due to its fibrillation feature. It is expected that dyed and ready-to-use textile materials, especially those to be used for clothing, will not change colour during the period of use and that the colours will not change after washing, after perspiration, during ironing and after use under light. Lyocell fabrics are mostly dyed with reactive dyestuffs and the dyeing temperature varies according to the dyeing method used and the reactivity of the dyestuff.

Direct dyestuffs have a high affinity for cellulosic fibers such as lyocell. Direct dyestuffs can rapidly penetrate into lyocell fibers in the presence of high temperature and salt and form weak hydrogen and van der Waals bonds with the fiber. However, direct dyestuffs cannot form strong bonds in the fiber structure and can only be held in the fiber by these weak hydrogen bonds and weak forces such as van der Waals. As a result, the wet fastness of direct dyestuff applications is lower. However, after the dyeing process is completed, the water solubility of the dyestuffs on the fiber is tried to be prevented by treating in aqueous and acidic solution with synthetic mordant (fixing) chemicals, generally called cationic fixers, according to the properties of the direct dyestuffs used in dyeing. As a result, it is aimed to obtain slightly higher fastness values in wet fastnesses (washing, water, sweat, etc.). However, these processes do not always give successful results, changes in the colour of the obtained material are observed and the improvement in the targeted fastness values is limited. Due to the fibrillation properties of Lyocell fibers, colour loss and colour fading (whitening) can also be observed. For this reason, there is a need for a new dyeing method that eliminates these problems in the known state of the technique, which uses direct dyestuffs and enables the desired colour to be obtained exactly without using excess dye in lyocell textile products, increases wet fastness.

An example of the known state of the art in the research conducted in the literature is document numbered CN1 14182542A. The said document relates to a dyeing method applicable to natural fibers such as cotton, hemp, silk, wool and similar natural fibers or regenerated cellulose fibers and fibers such as viscose, modal, lyocell, soybean protein, milk protein and similar fibers. This natural/herbal dye mentioned in the document is a dye in the cutee vat dye class and is applied with the padding method in said method. However, the document does not mention a dyeing and mordanting method based on exhaust method.

Our patent application numbered 2022/018729 in the literature is related to a reactive dyeing method using metallic mordant salts for dyeing lyocell fabrics. The application discloses the method of dyeing lyocell fabrics with reactive dyestuffs in the presence of metallic mordant salts in order to increase the wet fastness values of dyed and ready-to-use textile materials and especially the products to be used for clothing purposes and to ensure that there is no colour change during the period of use, to improve the colours and to extend the service life. However, the application does not mention a new mordanting method in which pre- and postmordanting are applied together, nor does it mention the efficient application of direct dyestuffs.

As a result, due to the abovementioned disadvantages and the insufficiency of the current solutions regarding the subject matter, a development is required to be made in the relevant technical field.

Brief Description of the Invention

The present invention relates to a new dyeing method for dyeing lyocell textiles with direct dyes in the presence of metallic mordants (chemical mordants) or biomordants, which fulfills the above-mentioned requirements, eliminates all disadvantages and brings some additional advantages.

The primary aim of the present invention is to provide an alternative efficient method of direct dyeing of lyocell textiles with direct dyestuffs and metallic mordants (chemical mordants) in the presence of bio-mordants and metallic mordants by using a new two-step mordanting process in which pre- and post-mordanting are applied together. Here, the wet fastness of the product is improved by the complexation of the ions obtained from the mordant chemical directly with the molecules of the dyestuff in the product fiber and the difficulty of this complexed structure to get out of the fiber.

The aim of the present invention is to provide a novel dyeing method that prevents unsuccessful dyeing in existing methods using direct dyes for lyocell textile products, prevents the use of excess dyestuff and ensures that the target colour is obtained exactly and improves wet fastness.

One aim of the present invention is to provide a method developed to ensure that the colours of textile products dyed with direct dyestuffs do not change after dyeing because of the effects of external factors such as ironing, light, etc. and due to use (sweat, etc.). Another aim of the present invention is to develop a method in which direct dyes, which are classified as "Class A dyes", "Class B dyes" and "Class C dyes" according to their molecular size, can also be applied by pre- and post-mordanting process, which is the subject and application of the application.

A further aim of the invention is to ensure longer product life and thus reduce replacement costs. To ensure maximum benefit from the product over a long period of time.

In order to fulfil the above-mentioned aims, the invention is a dyeing method in which metallic (chemical) mordant or bio-mordant salts are used in the dyeing of lyocell textile products with direct dyestuffs, in order to improve colours, prevent colour change due to post-dyeing use and external factors, and improve wet fastness, characterized by comprising the following process steps; i. Soaking lyocell textiles in alkaline solution followed by rinsing the fabric, ii. Preparing solution containing salt compound(s) and soaking of textile products in this solution, iii. Adjusting the pH of solution to the range 4-6 and adding mordant salts iv. Application of the pre-mordanting process of the textile product, v. Adding dyestuffs directly to the solution and adjusting the pH of the solution to the range 5-10, vi. Performing the dyeing process by keeping the textile product in the solution at a temperature of 90-1 OO'C for 60-90 minutes, vii. Adjusting the pH of the dyeing solution to the range 4-6 and adding mordant salts viii. Application of the post-mordanting process to the textile product, ix. Application of washing and drying processes to the product after the dyeing process.

The structural and characteristic features of the present invention will be understood clearly by the following drawings and the detailed description made with reference to these drawings and therefore the evaluation shall be made by taking these figures and the detailed description into consideration.

Figures Clarifying the Invention

Figure 1 : Schematic illustration of a new direct dying method using pre- and postmordanting.

Description of the References:

1. Alkaline Pre-treatment

2. Pre-treatment with Salt

3. Pre-Mordanting

4. Dyeing with direct dyestuffs

5. Post-mordanting

AB: Alkaline compound

A: Acid

T: Salt compound

M: Metallic Mordant or Bio mordant salt

D: Direct dyestuff

Detailed Description of the Invention

In this detailed description, the inventive method is described only for clarifying the subject matter in a manner such that no limiting effect is created.

With the method subject to the invention, lyocell textile products dyed with direct dyestuffs are produced in which the use of excess dyestuff is prevented, the target colour is obtained exactly, the colour change due to use and external factors after dyeing is prevented, the service life is extended and the wet fastness is improved. With this method, products with a longer service life, reduced cost and maximum benefit can be obtained. Figure 1 shows a schematic view of the new direct staining method using pre- and post-mordanting. The subject of the present invention is a dyeing method in which metallic (chemical) mordant or bio-mordant salts are used in the dyeing of lyocell textile products with direct dyestuffs, in order to improve colors, prevent color change due to post-dyeing use and external factors, and improve wet fastness, characterized in that, it comprises the following process steps; i. Soaking lyocell textiles in alkaline solution followed by rinsing the fabric, ii. Preparing solution containing salt compound(s) and soaking of textile products in this solution, iii. Adjusting the pH of solution to range of 4-6 and adding mordant salts iv. Applying pre-mordanting process to textile product, v. Adding dyestuffs directly to the solution and adjusting the pH of the solution to the range 5-10, vi. Performing the dyeing process by keeping the textile product in the solution at a temperature of 90-1 OO'C for 60-90 minutes, vii. Adjusting the pH of the dyeing solution to the range 4-6 and adding mordant salts viii. Applying the post-mordanting process to the textile product, ix. Applying washing and drying processes to the product after the dyeing process.

In the aforementioned process step (i), lyocell textiles are soaked in an alkaline solution preferably at room temperature for 30 minutes and then the fabric is washed. The alkaline solution comprises alkaline (basic) compound preferably selected from sodium hydroxide, sodium carbonate, potassium hydroxide, more preferably NaOH (Sodium Hydroxide). The alkaline solution contains 0,05-4 molar and preferably 1 molar sodium hydroxide. Here, the molar expression is used to express the amounts of chemical substances (especially acids, alkalis/basics and salts) in solution. The term molar refers to the number of moles of the chemical substance considered in 1 liter of solution. The number of moles is obtained by dividing the amount of the chemical substance considered by the molecular weight of that chemical substance. When the mole value obtained is found in 1 liter of solution, the chemical considered has a molar solution with a certain numerical value. In one liter of aqueous solution in a solution of 0,05 molar NaOH (Sodium Hydroxide, molecular weight 40 grams), 2 grams of NaOH (Sodium Hydroxide) are dissolved, in 1 molar NaOH (Sodium Hydroxide) solution, 40 grams of NaOH(Sodium Hydroxide) is dissolved in 1 liter of aqueous solution and 160 grams of NaOH (Sodium Hydroxide) are dissolved in 4 molar NaOH (Sodium Hydroxide) solution. Here 2/40=0,0540/40=1 and 160/40=4 and when these amounts are found in 1 liter of solution, 0,05 molar, 1 molar and 4 molar NaOH (Sodium Hydroxide) solutions are obtained respectively.

In the mentioned process step (ii), the solution is prepared with the salt compound which selected from sodium chloride, sodium sulfate, sodium sulfate decahydrate. Lyocell textile products are kept in the solution that contains this salt compound at a temperature of 70-90 <0 for 30 minutes.

In the process step (iii), weak acid is added to adjust the pH of solution to range of 4-6 and then 0,1 -5 wt%, preferably 2,5 wt%, of metallic mordant or biomordant salts are added. Acetic acid can be used here as a weak acid, but other weak acids can also be used.

In the process step (iv), lyocell textile products are pre-mordanted at pH 4-6, preferably at a temperature range of 70-90 C for 20-40 minutes.

In the process step (v), direct dyestuffs are added to the solution at a ratio of 0.5- 8%, preferably 1 % by weight, and then the solution pH is adjusted to 5-10 by-adding the salt compound. Said salt compound is selected from sodium chloride, sodium sulfate, sodium sulfate decahydrate.

In the process step (vi), the textile product is dyed by keeping it in solution at 90- O'C and 60-90 minutes. Said dyeing takes place in the pH range of 5-10.

In the process step (vii), the pH of the solution is adjusted to the range of 4-6 by adding weak acid. Then, metallic mordant or bio-mordant salts are added at a ratio of 0,1 -5%, preferably 2,5% by weight. Acetic acid can be used here as a weak acid, but other weak acids can also be used.

In the process step (viii), the post mordanting process is applied to the dyed lyocell textile products for 20-40 minutes in the pH range of 4-6, preferably at the temperature range of 70-90 ^<C.

In the step (ix) of applying washing and drying processes to the product after the aforementioned dyeing process; firstly, the dyed and post-mordanting textile product is rinsed in water preferably at room temperature for 20 minutes. Then, washing is carried out in the presence of anionic and nonionic surfactants, preferably at 60C for 40 minutes. After the washing process, the product is preferably rinsed in water at room temperature for 20 minutes and finally it is dried in a dryer for 1 minute, preferably at 140^<C.

The said metallic mordant salts are selected from Potassium Aluminum Sulfate Dodecahydrate [KAI(SC )2 ■ I 2H2O], Iron II Sulphate Heptahydrate ((FeSCU -7H2O), L-Ascorbic acid (CeHsOe), Calcium Carbonate (CaCOa) or Tannic Acid (C76H52O46) is selected as bio-mordant.

Direct dyestuffs are dyes with anionic soluble functional groups and are used primarily and mostly in the dyeing of cellulosic (cotton, viscose rayon) products. In the dyeing of Lyocell fabrics, NaOH (Sodium Hydroxide) pretreatment followed by soaking in a solution containing salt compound, pre- and post mordanting with metallic mordant or bio-mordant salts constitute the privileged aspect of the inventive method.

Direct dyes are classified as "Class A dyes", "Class B dyes" and "Class C dyes" according to their molecular size. All these molecular size classes can be used in our inventive method. In our method subject to the present invention, direct dyestuffs are used in the amount of 0,5% - 8% of the mass (weight) of the textile material (yarn, fabric, etc.), preferably in the amount of 1 %, in the dyeing of lyocell textile products. For example, 1 % dyeing means that 100 kg of fabric (textile material) will be dyed in the dyeing solution to which 1 kg of dyestuff is added.

In the dyeing of lyocell fabrics, colouring is achieved by using metallic mordant or bio-mordant salts in the amount of 0,1 -5% of the mass of the textile material, preferably 2,5%, in addition to this colouring result, the wet fastness of the dyeing is high and colour loss is reduced. For example, the addition of 2.5% mordant means that 100 kg of fabric (textile material) will be in a dyeing solution containing 2,5 kg of mordant salt.

The acidity-basicity properties of a solution are given by the concentrations of hydrogen (H+) and hydroxyl (OH-) ions in the solution. The term 'pH' is universally used for both acidic and basic properties in the range expressed as the pH scale. pH values between 1 -7 indicate the acidic properties of the solution, and pH values between 7-14 indicate the basic properties of the solution.

In an application of our inventive method, for pretreatment with alkaline solution, lyocell textile products such as lyocell fabrics are preferably soaked in a solution containing 8 g NaOH in 200 mL for 30 minutes and then the fabrics are rinsed with water several times. Salt compound (sodium chloride, sodium sulphate, sodium sulphate decahydrate, etc.) preferably a solution containing 8 g of salt compound in 200 mL is prepared and the fabrics are kept in this solution at 8013. Afterwards, acetic acid is preferably added to the solution, pH is adjusted to 4-6 and metallic mordant or bio-mordant salts are added, preferably 2,5% of the fabric weight. The fabrics are pre-mordanted at pH 4-6, preferably at a temperature range of 70-9013 for 20-40 minutes. After pre-mordanting, direct dyestuffs are added to the solution and then salt compound is added and the pH of the solution is adjusted to the range of 5-10 for the dyeing process. Then the fabrics are kept in the solution at maximum 10013 for 60-90 minutes and the dyeing process is c arried out. After dyeing, the pH of the solution is adjusted to the range of 4-6, preferably by adding acetic acid, and then metallic mordant or biomordant salts are added. Fabrics dyed with direct dyestuffs are subjected to post-mordanting at pH 4-6, preferably at a temperature range of 70-90^<C for 20-40 minutes. After the dyein g process, washing and drying processes are applied to the product.

The high affinity of the direct dyestuff affects the dyeing behavior. At the same time, the type and amount of mordant used, dyeing pH, dyeing temperature and dyeing time are among the important parameters. The amount of NaOH (Sodium Hydroxide) used is of critical importance. The use of high amounts may increase the initial pH of the dyeing and cause destabilization of the direct dyestuff as well as precipitation of the metallic mordant salt used during the pre-mordanting process. The direct dyeing pH of Lyocell fabrics is between 5-10, and since the metallic mordant or bio-mordant salts used during post-mordanting work between pH 4-6 ranges, care must be taken to lower the appropriate pH level.

Analysis was applied to the products obtained by the method of our invention for washing fastness. For example, after the lyocell fabric dyeing was completed, the washing fastness test was applied according to the ISO 105 C06 B1 M washing fastness standard, without any pre-washing, and then the fabrics were dried. By measuring colour on a reflectance spectrophotometer, L*, a*, b*, C* h° and K/S values of the fabrics were determined before and after the washing fastness test. As a result of colour measurements made before and after the washing fastness test, L*, a*, b*, C*, h° and K/S values in reflecta nce spectrophotometer based on changes in different metallic mordant salt types with/without NaOH (Sodium Hydroxide) pretreatment are given in table 1 and table 2, respectively.

Table 1 Study results before washing fastness test

Table 2 Study results after washing fastness test

Claims

1. A dyeing method in which metallic (chemical) mordant or bio-mordant salts are used in the dyeing of lyocell textile products with direct dyestuffs, in order to improve colors, prevent discoloration due to post-dyeing use and external factors, and improve wet fastness, characterized by comprising the following process steps; i. Soaking lyocell textile products in alkaline solution and then rinsing the product, ii. Preparing solution containing salt compound(s) and soaking of textile products in this solution, iii. Adjusting the pH of the solution to 4-6 and adding mordant salts iv. Applying pre-mordanting process to textile product, v. Adding dyestuffs directly to the solution and adjusting the pH of the solution to the range 5-10, vi. Performing the dyeing process by keeping the textile product in the solution at a temperature of 90-1 OO'C for 60-90 min utes, vii. Adjusting the pH of the dyeing solution to 4-6 and adding mordant salts viii. Applying the post-mordanting process to the textile product, ix. Applying washing and drying processes to the product after the dyeing process.

2. The dyeing method according to claim 1 , characterized in that, in the process step (i), lyocell textile products are kept in alkaline solution for 30 minutes.

3. The dyeing method according to claim 1 or 2, characterized in that, in said process step (i), the lyocell textile products are soaked in alkaline solution containing alkali compounds selected from sodium hydroxide, sodium carbonate, potassium hydroxide.

4. The dyeing method according to claim 1 , characterized in that, in the process step (ii), the solution is prepared with the salt compound selected from sodium chloride, sodium sulfate, sodium sulfate decahydrate.

5. The dyeing method according to claim 1 , characterized in that, in said process step (ii), the lyocell textile products are soaked in solution containing salt compound at a temperature of 70-90^<C for 30 minutes .

6. The dyeing method according to claim 1 , characterized in that, in the process step (iii), the pH of the solution is adjusted to the range of 4-6 by adding weak acid.

7. The dyeing method according to claim 1 , characterized in that, in the process step (iii), metallic mordant or bio-mordant salt is added in the range of 0,1 -5% by weight.

8. The dyeing method according to claim 1 , characterized in that, in the process step (iv), pre-mordanting process is applied to lyocell textile products for 20-40 minutes at a temperature range of 70-90 ^<C.

9. The dyeing method according to claim 1 , characterized in that, in the process step (v), direct dyestuffs are added in the range of 0.5-8% by weight.

10. The dyeing method according to claim 1 , characterized in that, in the process step (v), the pH of the solution is adjusted to the range of 5-10 by adding salt compound.

11. The dyeing method according to claim 10, characterized in that, the said salt compound is selected from sodium chloride, sodium sulfate, sodium sulfate decahydrate.

12. The dyeing method according to claim 1 , characterized in that, in the process step (vii), the pH of the solution is adjusted to the range of 4-6 by adding weak acid.

13. The dyeing method according to claim 1 , characterized in that, in the process step (vii), metallic mordant or bio-mordant salt is added in the range 0,1 - 5% by weight.

14. The dyeing method according to claim 1 , characterized in that, in the process step (viii), dyed lyocell textiles are subjected to post-mordanting at a temperature range of 70-90 <C for 20-40 minutes.

15. The dyeing method according to claims 1 or 7-8 or 13-14, characterized in that, pre- and post-mordanting processes are carried out with metallic mordant which selected from Potassium Aluminum Sulphate Dodecahydrate, Iron II Sulphate Heptahydrate, L-Ascorbic acid and Calcium Carbonate or bio-mordant which selected from Tannic Acid and its salts.