Reactive Dyeing

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Reactive Dyeing Q: In the dyeing of cotton/silk/polyurethane union weave (45/50/5) using acid or direct dyestuff, we have been asked to take measures against insufficient fastness to rubbing and washing that occurs in cases of deep-dyeing. We have tried the addition of fixing agents but found it ineffective, and are now considering the use of reactive dyestuff. What dyeing methods are recommended for this? A: As you mentioned in your question, it is considered difficult to improve fastness in acid or direct-dyed goods through fixing treatment. As a possible, practical countermeasure, there is a method in which only the silk and cotton component, and not polyurethane (which is contained in a small amount and not visible on the surface), is dyed with reactive dyestuff so that minimum staining on polyurethane would result. recommend the use of the following one-bath, two-step dyeing method using Sumifix HF dyes. Note: The temperature of dye exhaustion in the first stage should be adjusted according to the dyeability of substrate used as it affects the distribution of dyestuff to cotton and silk. The higher the temperature, the more dyestuff is distributed to silk. In the program above, the pH value is around 5.0-5.5 at the start of dyeing, 5.5-6.0 in the second stage before the addition of soda ash and 10-10.1 at the time the dyeing is completed. Recommended dyestuff: The following are recommended trichromatic dyestuffs capable of uniform distribution to both cotton and silk, and which are superior in tone-in-tone dyeing. Sumifix HF Yellow 3R 1

Transcript of Reactive Dyeing

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Reactive Dyeing

Q:

In the dyeing of cotton/silk/polyurethane union weave (45/50/5) using acid or direct dyestuff, we have been asked to take measures against insufficient fastness to rubbing and washing that occurs in cases of deep-dyeing. We have tried the addition of fixing agents but found it ineffective, and are now considering the use of reactive dyestuff. What dyeing methods are recommended for this?

A: As you mentioned in your question, it is considered difficult to improve fastness in acid or direct-dyed goods through fixing treatment.

As a possible, practical countermeasure, there is a method in which only the silk and cotton component, and not polyurethane (which is contained in a small amount and not visible on the surface), is dyed with reactive dyestuff so that minimum staining on polyurethane would result.

recommend the use of the following one-bath, two-step dyeing method using Sumifix HF dyes.

Note:

The temperature of dye exhaustion in the first stage should be adjusted according to the dyeability of substrate used as it affects the distribution of dyestuff to cotton and silk. The higher the temperature, the more dyestuff is distributed to silk.

In the program above, the pH value is around 5.0-5.5 at the start of dyeing, 5.5-6.0 in the second stage before the addition of soda ash and 10-10.1 at the time the dyeing is completed.

Recommended dyestuff:

The following are recommended trichromatic dyestuffs capable of uniform distribution to both cotton and silk, and which are superior in tone-in-tone dyeing.

Sumifix HF Yellow 3R Sumifix HF Scarlet 2G Sumifix HF Blue BG

The amount of dyeing auxiliary used:

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Dye concentration(o.w.f.) X < 2% 2%< X <4% 4% < X

Glauber’s salt calc. 50g/L 70g/L 90g/L

Soda ash 2g/L 3g/L 3g/LNote that the amount of soda ash used is smaller than that in the usual dyeing conditions for 100% cotton. After the dyeing process, rinsing and soaping are carried out.

Soaping conditions: Soaping agent 2g/L

(e.g. Adekanol TS800 or any auxiliary withgood polyurethane-stain-removing effects)

Temperature & time 80°C x 20minAfter the soaping process, rinsing and drying are carried out.

Q: Reactive dyes are used in the dyeing of cotton knits. Could you point out the basic points that should receive attention in this kind of dyeing?

A: Reactive dyes are the best dyes for dyeing cotton knits. While most dyeing is through exhaustion dyeing, some is also carried out with the cold pad batch method.

In the preparatory processing of cotton knits, the knitting oil that is used during the knitting must be sufficiently removed at the same time as the scouring and bleaching that removes impurities from the cotton takes place.

In the use of auxiliaries during dyeing, the simultaneous use of a dyebath lubricant is effective in preventing the fixing of wrinkles and the appearance of penetration blotches. If the water used in dyeing is hard, there is the possibility that the solubility of the dyes will deteriorate, and to avoid this, a sequestering

agent can be used.

Because each dye has its own ideal temperature and pH conditions, it is best to consult the manufacturer's recommendations when deciding upon the dye recipe.

After dyeing, any unfixed dye should be removed, and thorough soaping carried out. Deep colors should undergo fixing, but care must be taken due to the possibility of the deterioration of the fastness to light and the fastness to chlorine treatment water.

Recipes for exhaustion dyeing

Q: What are some important points to consider during the determination of a dye recipe for exhaustion dyeing with reactive dyes?

A: The optimum dyeing temperatures and dyeing conditions for reactive dyes differ according to the type of reactive group involved, so the first thing that must be decided is the type of dye that will be used.

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The substantivity to cellulose of reactive dyes is lower that that of direct dyes, but the addition of inorganic salts to the dye bath can raise its substantivity. Usually, Glauber's salt is used at a rate of 50g/L, but this rate should be increased in the dyeing of deep shades, and can be reduced with dyes that can be used in low salt dyeing. Inorganic salts can be added incrementally to dye baths for level dyeing, and the preliminary addition of Glauber's salt, that is, implementation of a dye bath with this pre-dissolved inorganic salt, can be used for dyes with low primary exhaustion rates and with dyeing machinery that provide effective agitation and circulation in the dye bath. Alkali is employed as the catalyst in the reaction between the dye and the fiber and the important point here is not the type of alkali used but the need for the pH of the bath after addition of the alkali to be around 11.5. Soda ash is easily used as the alkali because the addition of 20g/L yields a pH of around 11.5. Caustic soda is also convenient, but because it is a strong alkali, adjusting the pH to around 11.5 is extremely difficult, and recently, in consideration of this, a liquid alkali has been in use with reactive dyes.

Because the dyeing rate of reactive dyes depends on a combination of exhaustion through substantivity and fixing through reaction, quantitative adjustments through the control of the dyeing rate by adjusting the rate of temperature increase, as are used for other classes of dyes, are not effective, but adjustments with the incremental addition of inorganic salts or alkalis (pH) are effective. Consequently, isothermal dyeing through the incremental addition of alkali or alkali dosing is used. The specifics of incremental addition and dosing are decided by the agitation efficiency of the dyeing apparatus. To prevent rope marks in the use of piece-dyes, a dyebath lubricant can be used in the bath, and if hard water is used in the dyeing process, a sequestering agent can be added.

Levelness in cheese dyeing

Q: How can level dyeing best be achieved in the case of cheese dyeing in which color differences for the inner and outer layer often occur?

A: In cheese dyeing, it is difficult to achieve level dyeing through dye migration, and so control of the dyeing rate is necessary. In the use of a cheese-dyeing machine, the number of circulations of the dye liquor is decided by the flow rate of the dye liquor and the liquor ratio, so, for example, the dyeing speed is adjusted to around 1% of the dyeing per circulation.

Total volume of dye liquor=material weight to be dyed x liquor ratio

Liquor circulations per minute=dye liquor flow rate/total volume of dye liquor

Dye uptake per minute=number of liquor circulations per minute x coefficient

This coefficient is usually set at 1, but for more accurate calculations, the concept of regional replacement ratio is used. Note: For the concept of regional replacement ratio, please refer to the following:Y. Matoba, Senshoku nouhau no rironka ("The Theorization of Dyeing Know-How"), Senshoku Keizai Shimbun, 1985, p.25

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Q: Br.Blue R (C.I. Reactive Blue 19) is being considered for use as the blue of the trichromatic colors in reactive dyes, but level dyeing with this dye is difficult to achieve. Are there any good techniques for achieving level dyeing with this dye?

A: C.I. Reactive blue 19 (Br. Blue R) is a blue reactive dye with special dye strength and dye fastness characteristics. It is a representative blue dye that is widely used throughout the world. This dye is vinyl sulfone-based, and is used in dyeing in the form of sulfate ethyl sulfone, but with the addition of alkali, it becomes vinyl sulfone and fixes to the fiber by reacting with it.

Because Blue 19 in the form of sulfate ethyl sulfone has a high solubility and a very low affinity, it displays a low primary exhaustion rate, but in the form of vinyl sulfone, its solubility decreases dramatically and it displays a high affinity, and thus the exhaustion rate increases rapidly. Consequently, under typical dyeing conditions, dyeing advances rapidly after the addition of alkali, giving the use of this dye a high risk of uneven dyeing.

In order to ensure level dyeing, an anion surfactant can increase the solution stability of the vinyl dye, and the incremental addition or dosing of inorganic salt and alkali can prevent the rapid exhaustion of the dye.

Dyes of a special type (eg. Sumifix Br. Blue R special) with improved stability in alkali baths have been developed, and in the use of these dyes, the initial incremental addition of alkali, Glauber's salt or soda ash is effective. This method is limited to dyes of this special type, and conventional application methods of Blue 19 are not recommended because precipitation of the dye occurs after the first addition of alkali, thus causing uneven dyeing.

Below is an example dyeing program for a method including the initial addition of alkali.

Levelness in jet dyeing

Q: What are some important points for achieving level dyeing in jet dyeing with reactive dyes?

A: In dyeing with a jet-dyeing machine, proper control of the exhaustion rate and migration contributes to level dyeing. Effective control of the dyeing rate is possible through the incremental addition, or dosing, of inorganic salt (Glauber's salt) and alkali, but quantitative control is difficult using only heat program settings. Isothermal dyeing is being increasingly adopted with reactive dyes because a higher dyeing temperature during primary exhaustion promotes effective migration.

The exchange conditions of the dye liquor and the circulation rate of the fabric are important factors in the dyeing machinery's conditions, and new dyeing machines with improved dye-liquor exchange at the jet nozzle (eg. Sclavos, Greece), or that allow fabric loops to pass through jet nozzles an increased number of times (eg. MCS Multiflow, Italy),

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have been receiving much attention recently.

The specific conditions chosen for machinery must be checked against the circulation rate of the fabric and the number of circulations of the fabric per minute. In the case of reactive dyes, the dyeing rate is decided by both the exhaustion and fixing rates, but the exhaustion rate is important in the setting of dyeing conditions for achieving level dyeing. (Conditions like those relating to the number of circulations can be set according to the same principles as in the rapid dyeing of polyester fibers with disperse dyes using the exhaustion rate.)

Because jet-dyeing machines conduct rope dyeing, rope marks tend to occur easily, but these can be prevented through the use of an auxiliary, a dyebath lubricant being effective.

Dyeing mercerized yarn

Q: Recently, the yarn-mercerization of cotton yarn has been emphasized as a way of raising quality and increasing the variety of products. What points are important in the dyeing of mercerized cotton yarn?

A: The common methods of mercerizing yarn include hank mercerization, cheese mercerization, single-end mercerization, and tow mercerization. Because the adjustment of the physical (mechanical) conditions, like the uniformity of tension, is difficult, even mercerization is more difficult to achieve in the mercerization of yarn than in the conventional mercerization of weaves. Hank mercerization is often applied in practice because of the treatment's effectiveness and evenness. New hank-mercerization apparatus featuring automatic control of the alkali solution's concentration and temperature, of the adjustment of the yarn's tension, and of the rinsing conditions, allow very few variations and have become increasingly popular recently. (For example, see the NS200-PC of Nishinakajima Precision Machinery Co., Ltd., at http://www.textileinfo.com/, under "IT & Machines".)

The first point to consider in the dyeing of cotton yarn that has been yarn mercerized is whether the mercerization is even or not because level dyeing of cotton yarn that has been unevenly treated is not easy. In comparison with unmercerized cotton yarn, mercerized cotton yarn that has been evenly treated exhibits the following dyeing properties:

1. Visibly deeper colors (less dyestuff is required for color matching with the same color sample).

2. Faster absorption and dyeing rates.

To control the rate of exhaustion, it is important that the practical dyeing program, including the incremental addition of inorganic salt and alkaline, is determined according to the type of mercerized cotton yarn. In the dyeing of mercerized cotton yarn, the amount of inorganic salt and alkaline added in the first addition should be reduced and the number of times addition occurs should be increased. The standard amount of alkali used in dyeing with common reactive dyes is determined in consideration of the preservation of a stable pH for the dyebath and general safety conditions, but with mercerized cotton, the amount of alkali can be reduced. (For example, the amount of soda ash used is 20g/L for unmercerized yarn but 15g/L for mercerized yarn. In addition, when the amount of alkali has been reduced, the pH of the residual bath after dyeing should also be checked.)

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Level dyeing with phthalocyanine Turq Blue

Q: C.I. Reactive Blue 21 is now being used as turquoise blue, but the inferior reproducibility of this dye in comparison to other reactive dyes can cause problems. What measures can be taken to tackle these problems?

A: The chromophore in brilliant turquoise blue reactive dyestuffs is usually copper (occasionally nickel) phthalocyanine. Some of the characteristics of phthalocyanine dyes are as follows:

1. Large molecular weight in comparison to other reactive dyes.

2. Associate easily while also being water soluble, but do not completely dissolve in the dyebath, existing in a colloidal state.

3. Chemically, include a large number of isomers, and even for dyestuffs with the same color index number, the structure and composition can vary according to maker or lot. (While inexpensive dyestuffs have been introduced recently, the use of dyestuffs of consistent quality is recommended.)

Because of these characteristics, these are some of the more difficult dyestuffs to use. For example, the well-known C.I. Reactive Blue 21 is an effective dyestuff that is widely used for producing turquoise blue and green. This dyestuff is vinyl sulfone-based and has copper phthalocyanine as its chromophore. Because is has a chemical structure similar to that of C.I. Direct Blue 86, a direct dyestuff, it has a high affinity and displays a high primary exhaustion rate. Furthermore, a characteristic common to copper phthalocyanine dyes is that they associate easily, and their low solubility has a negative effect on level dyeing. The prior addition of alkali is effective in increasing the stability of the dyestuff in solution, and for C.I. Reactive Blue 21, the dyeing temperature is set not at 50°C, the standard temperature for vinyl sulfone-based dyes, but at the higher temperature of 70°C. The absorption rate is adjusted through the incremental addition of Glauber's salt. The incremental addition of alkali is not very effective because the level of absorption in the primary absorption process is great and the contribution of the secondary absorption is minimal.The following diagram displays an example dyeing program including the initial addition of alkali.

The role of alkali in reactive dyeing

Q: When dyeing with reactive dyestuffs, soda ash is often used as the alkali in dyestuff manufacturers' recipes. Recently, however, a synthetic alkali has appeared. What is the role of alkalis in reactive dyeing and what should be considered when choosing one?

A: In the dyeing of cellulose with reactive dyes, alkali is necessary because it acts as a catalyst in the reaction between the dyestuff and the fiber. The important point is not the type or amount of alkali but rather the pH of the dyebath, which must be closely supervised.

The most suitable pH for dyeing varies with the temperature, being approx. 11.5 for

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common warm dyeing (dyeing at approx. 60 ), 10-11 for hot dyeing (80 ) and 12.5 for cold dyeing (40 ). The relationship between temperature and the optimum pH is shown in the following graph.

Soda ash is often used because 20g/l usually produces a pH of around 11.5. However, it can be used with sodium phosphate or caustic soda when a higher pH is required, or with sodium bicarbonate (baking soda) when a lower pH is required. Caustic soda is not often used because it is a strong alkali and achieving a pH in the range of 10-12 is difficult. Nothing prevents it from being used, however, if the pH can be adjusted accurately with automatic equipment.

Recently introduced alkaline agents specifically for use with reactive dyes adjust the pH of the dyebath to a level suitable for dyeing with reactive dyestuffs and are easy to use because they come in liquid form, but the alkaline agent to be used should be chosen in consideration of the optimum pH for the temperature at which the dyestuff is to be used. The pH of the first bath is often checked to determine the pH for the dyeing, but attention should be paid to the pH after dyeing because if alkali is not added in sufficient quantity, the pH at the conclusion of dyeing may be considerably lower.

Low-salt dyeing

Q: Low-salt dyeing has recently become a popular topic for discussion. What is the role of inorganic salts in exhaustion dyeing with reactive dyestuffs, and how should they be used?

A: Inorganic salts have two main functions in exhaustion dyeing with reactive dyestuffs:

1. Improving the affinity of the dyestuff 2. Acceleration of the dyestuff's association and lowering of its solubility.

Improving the affinity and thus the exhaustion of dyestuff during primary exhaustion serves to raise the exhaustion rate of reactive dyestuffs. Because reactive dyestuffs have a lower affinity than direct dyestuffs, more inorganic salt is required when using reactive dyestuffs in order to accelerate absorption. Thus, while around 10g/l of Glauber's salt is usually appropriate for dyeing with direct dyes, an average of 50g/l is used with reactive dyes.

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While the amount of inorganic salt used varies according to the type of dyestuff used, recently developed high-fixation dyestuffs with improved affinity allow the amount of inorganic salt to be reduced. The amount of inorganic salt used can also be reduced when the concentration of the dyestuff is low. The following displays the amount of Glauber's salt used, the exhaustion rate and the fixing rate for a conventional dye and a high-fixation dye (Sumifix Supra E-XF).

Because inorganic salts accelerate the association of water-soluble dyestuffs and lower the solubility of dyestuffs, an excess of inorganic salt may in fact impede the absorption of some dyestuffs, and so care is necessary when one is used. Due to considerations of effectiveness and cost, both Glauber's salt and common salt (sodium chloride) are used in dyeing. In terms of their role as an inorganic salt, these two are effectively the same because of the sodium cation active in both. In respect to their molecular weights, 1kg of Glauber's salt contains 324g of sodium while 1kg of common salt contains 393g of sodium, and thus an advantage of common salt is that the quantity required is only 82% of that of Glauber's salt. However, the use of common salt can easily result in the lowering of the solubility of the dyestuff and can also cause the metal in the dyeing equipment to corrode due to the presence of chlorine ions, and it is due to these problems that Glauber's salt is commonly used in Japan. Overseas, however, common salt is often used because of its low cost. Rock salt is sometimes used, but care is required because impurities in rock salt (metallic ions other than those of sodium) can negatively effect dyeing.

The effectiveness of the inorganic salt is not decided by the ratio of its quantity to the quantity of fabric (o.w.f.) but rather by its concentration in the dyebath (g/l), and so it is by lowering its concentration that the effect of an The importance of surfactants in

reactive dyeing

Q: The standard recipes for reactive dyestuffs given in the examples provided by dyestuff manufacturers often do not include the addition of surfactants such as dyebath lubricants. Doe this mean that they are not required?

A: In the dyeing of cotton with reactive dyes, because hydrophilic fibers are dyed with water-soluble dyestuffs, the dyeing itself does not require the use of surfactants. However, in the dyeing of cloth, it is difficult to spread the cloth out in the dyebath, and so it is often dyed in rope-form, but because it is sometimes difficult to circulate the liquid over the cloth, rope marks can easily form. The use of a dyebath lubricant is recommended as a method for dealing with this problem. The use of cold and warm dyeing dyestuffs when the temperature of the dyeing is below 55 means the fiber is dyed while it is in a hard state, making a dyebath lubricant especially important for improving the quality of the dyeing. When dyeing is conducted at a temperature above 60 with warm and hot dyeing reactive dyestuffs, however, the fiber itself softens and spreads easily, so the use of a dyebath lubricant is not as important.

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However, when the solubility of a reactive dyestuff is reduced due to factors such as association, the use of a surface-active dyebath lubricant can result in a dispersion effect. Furthermore, when a small amount of wax still remains on the substrate due to insufficient scouring, the use of a dyebath lubricant can promote the permeation of the dye liquid. Thus to lower the degree of risk in dyeing, the use of an appropriate dyebath lubricant is recommended.

inorganic salt can be reduced.

The role of sequestering agents in reactive dyeing

Q: Is the use of a sequestering agent required when dyeing with reactive dyes?

A: When the water of the dyebath contains metallic ions, there is the danger that uneven dyeing, such as specking, or reduction of the concentration of the dye will be caused by the dyestuff's coagulation and reduced solubility. Aside from in the water, metallic ions can also be introduced by impurities in Glauber's salt or common salt, so even when soft water is used in the dyeing, the presence of metallic ions can lead to problems. In Japan, the water quality is generally very good and the chemicals used contain very few impurities, so sequestering agents are often not used. Overseas, however, the use of sequestering agents is very important.

In the past, traditional thinking has been that "if the chromophore of a dyestuff is a metallic complex salt, then sequestering agents should not be used." Recently, however, it has been ascertained that sequestering agents added to the dyebath have practically no effect on the metal in the chromophore of the dye.

Sequestering agents effective in neutral to alkaline conditions are preferable, and agents combining the effects of sequestering agents with those of anionic surfactants and marketed for use with reactive dyes are now being developed.

Obverse and reverse side color differences in the dyeing of cotton knits

Q: When reactive dyes are used in the dyeing of circular cotton knits, there is sometimes a color difference between the obverse and reverse sides. Are there any measures that can be taken to prevent this?

A: In the dyeing of a tubular knit, the substrate is fed into the dyeing machine inside out, with the obverse surface on the inside. Reasons for color differences between the two sides can exist in either the scouring and bleaching process, or in the dyeing process itself.

When scouring and bleaching have not been conducted properly, a difference between the levels of scouring on the two surfaces can have a direct influence on the results of the dyeing. Recently, rationalization has been common in the scouring and bleaching process, including the introduction of machinery using lower bath ratios, but sufficient amounts of water should be used to ensure the effectiveness of the process. In identifying the problem, it is the condition of the fabric after scouring and bleaching that should be checked first.

The reason can lie also in the dyeing process if the dyestuff used does not have good penetration. If this is the case, the penetration of the dyestuff will differ between the surface on the outside, which comes into direct contact with the circulating dye solution,

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and the surface on the inside, where the dye solution is not being exchanged to such an extent, resulting in a color difference between the two sides.

This problem is related to differences in the affinities of the dyestuffs used. If dyestuffs with high affinity that are easily absorbed by the surface of the fabric are used with other dyestuffs that are not, color differences will result. While differences in affinity can be avoided by the correct selection of dyestuffs, problems may also arise due to the use of hard water in the process which will lower the solubility of the dyestuff resulting in surface dyeing, or the solubility of the dyestuff might alternatively be reduced by the addition of alkali. In a process that has previously been free of problems, any problem that arises

suddenly is often related to the hardness of theDispersing leveling agents

Q: When dyeing cotton with reactive dyestuffs, in some cases the use of a dispersing leveling agent is recommended. Why use a dispersing leveling agent with water-soluble reactive dyes? What are the benefits?

A: Specialized dyebath lubricants that have been developed for use as surfactants in reactive dyeing are effective in preventing rope marks and in promoting penetration of the dyestuff.

Since reactive dyestuffs are water-soluble, anionic surfactants, which are common dispersing agents, are not used. In alkaline baths, however, the solubility of some dyestuffs is reduced and some products may tend to suffer some degree of coagulation. In these cases, the use of a dispersing leveling agent can be advantageous.

In an alkaline bath, a typical dyestuff that suffers reduced solubility is C.I. Reactive Blue 19. While this dyestuff displays good solubility in its commercial form of sulfate ethyl sulfone, in its vinyl-sulfone form after the addition of alkali to the dyebath, its solubility is dramatically reduced and it may coagulate.

Fig. 1

The structural transformation of C.I. Reactive Blue 19 in an alkaline bath

In this case, use of an anionic dispersing leveling agent produces even dispersion and good solubilization, ensuring level dyeing and good reproducibility.

An example of a typical dyestuff which tends to coagulate is phthalocyanine-based Turq Blue. (eg. C.I. Reactive Blue 21). Use of a dispersing leveling agent raises the level of solubility and improves the levelness of dyeing. For dyes of this type, however, since dispersing leveling agents display a large retarding effect, addition of too much dispersing leveling agent can reduce the concentration of the dye fixing. Due to this, the

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quantity used should be carefully supervised.

In addition, when the water used in the dyebath contains metal ions, reactive dyestuffs in general tend to suffer reduced solubility due to their influence. In this case too, use of a dispersing leveling agent is advantageous.

An example of a dispersing leveling agent that can be used for realizing the above effects is Sumipon SE.

water.

To overcome these problems, the dyestuffs used should be chosen carefully, but the use of a sequestering agent or a dyebath lubricant that improves penetration can also be effective.

: Some new reactive dyestuffs can be used in hot dyeing (dyeing at a temperature of around 80 ) even though their reactive group is vinyl sulfone. How can the optimum dyeing temperature for reactive dyestuffs be determined?

A: In exhaustion dyeing with reactive dyestuffs, the reactivity is usually decided by the reactive group. Thus optimum dyeing temperatures can be divided into the following three groups:

Cold dyeing (30-40 ): eg. dichlorotriazine, difluorochloropyrimidine dyestuffs Warm dyeing (50-60 ): eg. vinyl sulfone, monofluorotriazine dyestuffs Hot dyeing (80-90 ): eg. monochlorotriazine, trichloropyrimidine dyestuffs

(Steaming and baking are used in continuous dyeing and in printing, but in this case, treatment time is adjusted depending on the reactivity of dyestuffs under constant temperature conditions, because dyestuffs with lower dyeing temperatures fix faster.) Traditional reactive dyestuffs use a chromophore of relatively low molecular weight similar to that of acid dyestuffs. Thus while the dyeing temperature for most dyestuffs can still be decided according to the reactant as outlined above, some recently developed dyestuffs have higher molecular weights approaching those of direct dyestuffs and increased affinity which results in a higher degree of fixation. For these dyes, the temperature as traditionally determined according to the type of reactive group may not necessarily be the most suitable. A basic formula concerning the efficiency of dyeing with reactive dyestuffs is as follows:

where E: efficiency of reactive dyeing, [D]s: dyestuff concentration in solution, [D]f : dyestuff concentration in the fiber, D: diffusion coefficient, Ka: first-order rate constant of fixation reaction with the fiber, Kw: first-order rate constant of the hydrolysis, L: liquor ratio, S: surface area of the fiber In formula (1), the factors influenced by the dyeing temperature are Ka, Kw and D. Since the values of Ka and Kw are dependent on the reactivity of the reactive group, a general range for these values can be determined according to the type of reactive group. The diffusion coefficient, however, is specific for each dyestuff because it is linked to the dyestuff's molecular weight. The value of E can be improved by increasing the diffusion coefficient D, and for some dyestuffs with large molecular weights, raising the temperature is an effective way of achieving this. The result is that dyeing will be more effective at a temperature higher than that as decided by the reactive group. This principle is illustrated by the favorable dyeing results that can be achieved at a dyeing temperature of 70 , as opposed to 50 , when using phthalocyanine Turq. Blue dyestuff with vinyl sulfone (eg. C.I. Reactive Blue 21). While this phthalocyanine dyestuff has long been subject to special

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treatment, now the number of dyestuffs requiring this special treatment has increased due to the recent appearance of many new products. Good examples of this are Sumifix HF and Cibacron LS dyestuffs, both of which have been attracting a lot of attention recently. Thus, although these dyestuffs have the same reactive group as traditional warm-dyeing dyestuffs, hot dyeing is recommended. In determining the optimum dyeing temperature for each reactive dyestuff, it is best to focus on the dyeing temperature recommended by the manufacturer. However, when dyeing is to be conducted at a temperature higher than that recommended by the manufacturer, a lower pH should be set, and when it is to be conducted at a lower temperature, a higher pH should be set.

Liquor ratio and dyeing properties

Q: Atmospheric low liquor ratio jet dyeing machines for the dyeing of cotton knits have recently been introduced in dyeing mills overseas. To what extent is the low liquor ratio dyeing of cotton knits possible with reactive dyes?

A: Reactive dyestuffs tend to have a low substantivity and are thus readily influenced by the liquor ratio. Setting the liquor ratio as low as possible will raise the fixing rate to make most effective use of the dyestuff.

The relationship between the liquor ratio and the dyestuff exhaustion rate can usually be expressed by formula 1.

where E: degree of exhaustion, K: partition coefficient, [D]s: dyestuff concentration in solution, [D]f : dyestuff concentration in the fiber, L: liquor ratio, Ws: weight of dye liquor, Wf: weight of fiber

As can be seen from formula 1, as long as the partition coefficient, K, is constant, any rise in the liquor ratio, L, will lower the degree of exhaustion. Furthermore, the larger the partition coefficient, K, the less effect the liquor ratio has. Reactive dyestuffs have a lower substantivity and a lower value for K than other types of dyestuffs, and thus dyeing with these dyes tends to be more readily influenced by the liquor ratio. Efforts have been made to increase the partition coefficient of some reactive dyestuffs and products resulting from this have recently become available. The influence of the liquor ratio in dyeing with these new dyestuffs is less than that in dyeing with conventional dyestuffs.

In wince and jet dyeing, the liquor ratio must be decided in view of the fact that any reductions in the liquor ratio increase the risk of uneven dyeing. Since cotton knits are held at conditions of low tension during the jet dyeing process, the weight of dye solution held by the substrate is twice the weight of the substrate itself. This means that dyeing cannot be conducted at liquor ratios lower than 1:2. A volume of dye solution equal to that necessary to fill the pipes, pumps and heat exchanger is also necessary. Furthermore, in order to enhance the efficacy of the dye circulation to achieve an evenly dyed surface, the volume of dye solution must be sufficient for it to move freely over the surface of the fabric. Calculation of the minimum volume of dye-bath required with consideration given to these factors will yield the lower limit for the liquor ratio.

Some atmospheric low liquor ratio jet dyeing machines are marketed as being capable of dyeing at liquor ratios of 1:4, but in reality dyeing at a liquor ratio of 1:4 is likely to lead to many problems including that of uneven dyeing. Within the limits set by modern technology, a ratio of at least 1:6 is necessary for achieving high-quality dyeing. It is

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important to note that problems can easily arise if pretreatment is conducted in the same low liquor ratio dyeing equipment.

When the substrate is wound in a compact form as in cheese dyeing, the substrate holds less dye solution and efforts to reduce the internal volume of the dyeing equipment can make dyeing at a liquor ratio of around 1:3 possible. In this case, lowering of the liquor ratio leads to an increased number of circulations which allows level dyeing to be achieved.

Dyestuffs for post-dyeing mercerization

Q: While mercerization that is conducted after dyeing and weaving of the yarn is attracting attention as a high-grade treatment, it is said that vinylsulfone-based reactive dyestuffs cannot be used in this form of treatment. Is this the case?

A: It is common knowledge that the stability of the chemical bond between the reactive group of reactive dyestuffs and the cotton varies according to the type of reactive group. The following table shows the known relationships concerning the stability of the bonds between fibers and dyestuffs according to the type of reactive group.

(Click for enlargement)

The question asked here arises from the fact that, in items dyed with vinylsulfone-based dyestuffs, cleavage can be caused between dye-fiber chemical bonds if treated in high-temperature, alkaline conditions, i.e. boiling.

However, the conditions of industrial post-dyeing mercerization are set out below (please refer to the conditions used in testing of post-dyeing mercerization). Under such practical conditions, the chemical bonds between cellulose and dyestuffs will suffer practically no recognizable breakage, and there is more likelihood of problems concerning bleeding into the mercerizing bath or staining arising from residue of a dyestuff with poor wash-off properties.

Results of testing of post-dyeing mercerization with dyed items (based on JIS methods) are shown below.

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(Click for enlargement)

Test method:Dyeing (fixing) sewn to white cloth of same size post-dyeing mercerization (22°Bé NaOH, 20°C, 2 min) rinsing hot rinsing (70°C, 2 min) neutralization (acetic acid) rinsing hot rinsing (70°C, 3 min) rinsing drying

From these results it can be seen that the level of staining on white cloth and bleeding into the solution is not related to the type of reactive group. Monochlorotriazine-based products with high levels of staining correspond to those used in exhaust dyeing that have high affinity and poor wash-off properties.

When testing conditions for the post-dyeing mercerization includes insufficient neutralization and rinsing while the fabric still has an alkalinity of over pH 9, and followed by drying using a cylinder drying machine, vinylsulfone-based dyestuffs sometimes display poor results.

In addition, when dyeing black, due to considerations of economy in relation to dyeability and colorfastness, sometimes one cannot avoid using the vinyl sulfone-based dyestuff C.I. Reactive Black 5 or mixed dyestuffs composed mainly of Black 5. Due to this, the actual conditions for neutralization and soaping during post-dyeing mercerization should accommodate use of C.I. Reactive Black 5.

From the above is can be said that selected vinyl sulfone-based dyestuffs (such as C.I. Reactive Black 5) and hetero-bifunctional dyestuffs of vinyl sulfone/monochlorotriazine have good wash-off properties and are suitable for use in post-dyeing mercerization.

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Fluorescent whitening of cotton knits

Q: I have been investigating one-bath fluorescent bleaching for cotton yarn with hydrogen peroxide but have not been able to achieve as high a level of whiteness as I expected. Remembering that chlorine bleaching is not possible due to the material from which the machinery is made, what points should I check?

A: The process outlined below is recommended as a standard for the scouring and bleaching of cotton yarn.Scouring → bleaching → fluorescent whitening → washing (softening) → drying

Example scouring recipe

Scouring agent 1~3g/L

Caustic soda (or sodium carbonate) 1~3g/L

Liquor ratio 1:10~20

Temperature & time 95~100°C x 30~60min

Example recipe for peroxide bleaching

Hydrogen peroxide (35%) 8~30g/L

Sodium silicate 3~5g/L

Sodium tripolyphosphate 1~3g/L

Magnesium sulfate 0.1g/L

pH 10.5~11.0

Liquor ratio 1:10~20

Temperature & time 90~100°C x 60~90min

Example recipe for fluorescent whitening

Fluorescent whitening agent 0.2~0.5% o.w.f.

Glauber's salt calc. 0~10% o.w.f.

Liquor ratio 1:10~20

Temperature & time 40~50°C x 30min

The most suitable conditions differ for each of the processes above as outlined in the table below.

 Dyeing temperature

pH Effect of bleaching agent

Scouring 95~100°C >11 None

Bleaching 90~100°C 10.5~11 -

Fluorescent whitening 40~50°C Neutral Selection of durable whitening agent

While it is relatively easy to combine the scouring and the bleaching in a one-bath recipe due to the similarity of treatment temperatures and bath pH, careful consideration is required in the selection of a whitening agent if fluorescent whitening is also to be included

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in a one-bath method.

A fluorescent whitening agent used in these circumstances requires the following characteristics.

1. Stable in the presence of hydrogen peroxide 2. Stable in an alkaline bath 3. Stable at high temperatures (boiling)

Fluorescent whitening agents that fulfill these conditions include Whitex BF (C.I. Fluorescent Brightener 90) and Whitex BO (C.I. Fluorescent Brightener 84). An example recipe for one-bath scouring, bleaching and fluorescent whitening is as follows: Hydrogen peroxide (35%) 8~30g/L

Caustic soda 1g/L

Sodium silicate 3g/L

Scouring agent 3g/L

Sequestering agent 0.1g/L

Fluorescent brightener (Whitex BF cc.)

0.5% o.w.f.

Liquor ratio 1:10~20

Temperature & time

The recipe above can be used to achieve a practical level of whiteness, but if a higher level of whiteness is required, conduct testing with a process composed of separate baths.

Reactive dyestuffs for ground color in discharge printing

Q: I have heard that vinyl sulfone-based dyestuffs are suitable for use as reactive dyestuff for ground color in discharge printing. Why is this so?

A: Discharge printing with reducing agents is a method that uses a reducing agent to decompose and decolor dyestuffs with azo groups as shown in the following diagram.

The original color of the azo-based dyestuff disappears due to the decomposition of the azo group of the chromophore brought about by the reducing agent in discharge printing. The amine component that is produced after decomposition (the groups remaining from the decomposed chromophore) cause a yellow to orange coloration. If amines remain bound to

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the fiber, white discharge printing is not possible, making such dyestuffs unsuitable for ground dyeing. It is in this way that a dyestuff's suitability in printing is influenced by chemical structure. In white discharge printing, the level of whiteness produced and color changes over time are influenced by the molecular structure of the components combined with reactive groups that remain on the surface of the fabric. For example, the structure of red reactive dyestuffs and the possibility of white discharge printing are outlined below.

In the following example with a monochloro triazine-based dyestuff, since the amine remaining after reduction decomposition is a colored amine with a high molecular weight containing naphthalene, the cloth will retain an orange coloring. Thus this dyestuff is unsuitable for use in ground dyeing in discharge printing.

*White discharge printing not possible

In the following example with a monochlorotriazine-based dyestuff, after reduction decomposition the remaining amine is a colored amine with relatively low molecular weight. Since the degree of coloring is low, it can be used for pale shades in ground dyeing in discharge printing, but is not suitable for use with medium and dark shades.

 *White discharge printing

possible with pale shades

In the following example with a vinyl sulfone-based dyestuff, since, the amine remaining after reduction decomposition is a colorless amine with a low molecular weight, this dyestuff is suitable for ground dyeing in discharge printing.

 *White discharge printing possible

even with dark shade

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Although the suitability of reactive dyestuffs for discharge printing is not related to the original reactive group, since triazine-based and pyrimidine-based reactive dyestuffs are often used with the reactive group introduced into the coupling component, colored amines with high molecular weight remain on the fibers after discharge printing with the result that many of these types of dyestuff are unsuitable for ground dyeing in discharge printing. In vinyl sulfone-based azo dyestuffs, however, the reactive group is introduced directly to a benzene-based amine of low molecular weight and is used as a diazo component. Thus even when a component that retains coloring is used as the coupling component, the component remaining on the fibers after discharge printing has a low molecular weight and practically no coloring. As a result, many of these dyestuffs are suitable for use in ground dyeing in discharge printing.

As can be seen here, a dyestuff's suitability for discharge printing is related to its chemical structure. However since commercial dyestuffs are industrially produced, they may contain isomers or shading components, the result being that dyestuffs with the same color index number may produce different results in discharge printing. When selecting dyestuffs for ground dyeing in discharge printing, please refer to the reference material supplied by each manufacturer.

Reactive dyeing of silk

Q: We are considering a switch in methods of silk yarn dyeing, from fast-color dyeing with metal complex dyestuff to one that uses reactive dyestuff. What methods are there that use reactive dyestuff and what are the points to keep in mind?

A: Because of a circumstance that chemical structures originally developed for acid dyestuff are often diverted as chromophore in reactive dyestuff, there are many reactive dye products that display a high degree of exhaustion on silk under acidic dyeing conditions. However, when using reactive dyestuff, setting of appropriate dyeing conditions for silk is necessary as it is important to ensure fast fixation through a chemical reaction with the fiber.

The reaction that takes place between reactive dyestuff and silk fiber is similar to that of hydroxyl groups in cellulosic fiber and is believed to be a chemical bonding of the dyestuff's reactive groups with the hydroxyl groups of oxyamino acid, such as tyrosine and serine, contained in silk protein. In contrast to this, the reactive dyeing of wool, while being another kind of animal fiber, will require different conditions as the reaction is different in that it is with the amino terminal group of wool protein.

The following is an example of a silk dyeing recipe using Sumifix Supra dyes.

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The most important point to remember is that the reactive dyeing of silk involves alkaline treatment and is therefore prone to problems such as hardening of fabric hand and the generation of friction marks. As the enquiry here concerns yarn dyeing, the generation of friction marks is less likely, however, it should be noted that the reserved use of alkali, as little as 3g/L in the recipe above, is still preferred.

The dyeing temperature is set to 75°C on the premise that as little as 3g/L of soda ash is used. While 60°C is the temperature required for the case of using as much as 10g/L, dyeing at 75°C with less alkali is recommended in respect to the resultant fabric hand.

The following are examples of dyestuffs that exhibit good applicability to silk in terms of dyeability and fastness.

Sumifix Supra Br.Yellow 3GF 150% gran.Sumifix Supra Yellow GRNF 150% gran.Sumifix Supra Yellow 3RF 150% gran.Sumfix Supra Yellow E-XF gran.Sumifix Supra Br.Red 3BF 150%gran.Sumifix Supra Red E-XF gran.Sumifix Supra Blue BRF 150% gran.Sumifix Supra Blue E-XF gran.Sumifix Supra Blue 2BNF gran.Sumifix Supra Navy Blue BF gran.Sumifix Supra Navy Blue 3GF 150% gran.

Method of testing the effect of bleaching on cotton knits

Q: Uneven dyeing results are sometimes produced in the dyeing of cotton knits, possibly because of insufficient bleaching. Tell us if there are any methods to determine whether sufficient bleaching is carried out prior to dyeing.

A: In the dyeing of cotton knits, pretreatment, such as scouring and bleaching, is carried out in order to remove impurities and colorants contained within the fiber as well as fats and oils such as knitting oil and other impurities that exist on the fiber surface because any insufficient removal may result in uneven dyeing. To see whether pretreatment is sufficient, ie. to see if there is any possibility of hindrance being caused in dyeability, the following tests are carried out.

1. The detection of knitting oil and other fat/oil residuals

(1) Quantitative examination is carried out based on extraction with methanol. Chloroform is sometimes used as a solvent, in which case care is required with polyester/cotton blends as chloroform may dissolve polyester oligomer, causing fluctuations in the test result.

(2) Qualitative examination is carried out based on the presence of fluorescence in dyed fabric in exposure to UV rays (black light). Fluorescence will be detected if there is any oil or fat remaining.

2. Water absorbency

This is to examine if there is any oil or surfactant remaining on the fiber. The following three test specimens, a, b and c, are used. Each specimen is cut vertically into a 20 x 2cm strip, hung longways with the bottom end dipped in water in order to

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measure the length of fabric by which water is absorbed in 5 minutes.

a. Pretreated fabric b. Pretreated fabric, put in 1L, 90°C water for 30 minutes, thoroughly rinsed and dried c. Pretreated fabric, re-treated under scouring conditions, thoroughly rinsed and dried

Examination will be based on comparison of the length of the three specimens by which water is absorbed. a≒b≒c Ready for dyeing, with little oil/surfactant remaining on fiber

a>b≒c Thorough warm/cold rinsing required, with surfactant remaining on fiber

a≒b<c Scouring insufficient, with much oil remaining on fiber

3. Fabric pH 10g pretreated fabric is put in 100ml boiling water for 5 minutes in order to observe the pH of the liquor after being cooled to an ambient temperature. Neutral pH ranges are desired.

The effect of resin treatment on reactive-dyed fabric

Q:

We are planning to carry out dyeing of cotton woven fabric for postcure finishing and have been asked to use reactive dyestuff that produces minimum color change in the subsequent resin finishing. Please advise us what points to bear in mind when selecting dyestuff for this.

A: Color change and fading sometimes occur in reactive-dyed cotton due to resin finishing which can also be a cause of adverse effects in rubbing and light fastnesses.

Possible causes of these phenomena include the influence of chemical bonding between dyestuff and a cellulose-reactive resin finishing agent or formaldehyde, as well as the influence of metallic ions contained in catalysts used, acidic catalysts affecting pH, the hydrolysis of dyestuff, color changes in resin finishing agents themselves and the effect of surfactants contained in such agents.

Thus, choosing the optimum resin finishing recipe and conditions are important apart from selecting dyestuffs from which a minimum color change is expected, moreover, consideration of possible color change in resin finishing, and due preliminary testing, is sometimes required in the color matching stage.

The effect of resin finishing is produced by the cross-linking of the hydroxyl group of cellulose fiber and formaldehyde or the formal group of a resin finishing agent. However, chemical reactions between functional groups (amino groups etc.) that are present in the molecules of dyestuffs and aldehyde groups sometimes take place simultaneously, in which case color change is caused as well as deterioration in fastness.

Among dyestuffs that are easily affected by resin treatments, there is one kind in particular with a structure in which its amino group remains unsubstituted, for example, H-Acid-based disazo type dyestuffs in the range of navy blue and black shades. This range of dyestuff is easily influenced by formaldehyde because of the amino group of H Acid remaining unsubstituted.

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With C.I. Reactive Black 5, which is the most widely used black dyestuff and typical of the H-Acid-based disazo type dyestuffs, color change is caused due to chemical reactions such as shown in Fig. 1. There are many cases where the use of this dyestuff is not regarded as problematic in deep-black dyeing since color alteration is not so visible, however, when used as the blue component of trichromatic dyes, care is required as considerable influences can be expected.

Fig. 1 Reactions between C.I. Reactive Black 5 dyestuff and formaldehyde

Such influences can be reduced even with H-Acid-based disazo type dyestuffs through the introduction of bulky substituents, such as the sulfonic acid group, in the ortho position of the azo group which is present on the side of the amino group, as the amino group is then protected due to the effect of steric hindrance.

(Click to enlarge)

The following are examples of the type of dyestuffs with their amino group being protected by the effect of steric hindrance.

Sumifix Supra Navy Blue 3GF 150% gran.Sumifix Supra Navy Blue BF gran.Sumifix Supra Marine BNF gran.Sumifix HF Navy 2G gran.

As has been discussed so far, the degree of influences due to resin treatment differs according to the structure of the dyestuff used, it is therefore important to select dyestuffs from which minimum influence is expected.

As for the extent to which each dyestuff is influenced by resin finishing, please refer to

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technical information provided by dyestuff manufacturers.

In addition, deterioration in light fastness may sometimes result from the influence of catalysts used in resin finishing, however, improvements can be expected from conducting post-treatment soaping.

Reactive dyeing of cotton/silk/polyurethane union weaves

Q:

In the dyeing of cotton/silk/polyurethane union weave (45/50/5) using acid or direct dyestuff, we have been asked to take measures against insufficient fastness to rubbing and washing that occurs in cases of deep-dyeing. We have tried the addition of fixing agents but found it ineffective, and are now considering the use of reactive dyestuff. What dyeing methods are recommended for this?

A: As you mentioned in your question, it is considered difficult to improve fastness in acid or direct-dyed goods through fixing treatment.

As a possible, practical countermeasure, there is a method in which only the silk and cotton component, and not polyurethane (which is contained in a small amount and not visible on the surface), is dyed with reactive dyestuff so that minimum staining on polyurethane would result.

recommend the use of the following one-bath, two-step dyeing method using Sumifix HF dyes.

Note:

The temperature of dye exhaustion in the first stage should be adjusted according to the dyeability of substrate used as it affects the distribution of dyestuff to cotton and silk. The higher the temperature, the more dyestuff is distributed to silk.

In the program above, the pH value is around 5.0-5.5 at the start of dyeing, 5.5-6.0 in the second stage before the addition of soda ash and 10-10.1 at the time the dyeing is completed.

Recommended dyestuff:

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The following are recommended trichromatic dyestuffs capable of uniform distribution to both cotton and silk, and which are superior in tone-in-tone dyeing.

Sumifix HF Yellow 3R Sumifix HF Scarlet 2G Sumifix HF Blue BG

The amount of dyeing auxiliary used: Dye concentration(o.w.f.) X < 2% 2%< X <4% 4% < X

Glauber’s salt calc. 50g/L 70g/L 90g/L

Soda ash 2g/L 3g/L 3g/LNote that the amount of soda ash used is smaller than that in the usual dyeing conditions for 100% cotton. After the dyeing process, rinsing and soaping are carried out. Soaping conditions: Soaping agent 2g/L

(e.g. Adekanol TS800 or any auxiliary withgood polyurethane-stain-removing effects)

Temperature & time 80°C x 20minAfter the soaping process, rinsing and drying are carried out.

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