Avoiding Stains in Dyed Cationically Modified Cotton Fabrics

The current disclosure pertains to a process for improving the stain resistance of a cationically modified fabric containing natural fibers (e.g., cotton-based).

Textile dyeing is the process of applying pigments or dyes on textile materials such as fabrics, yarns, and fibers. Desirably, the dyeing process is efficient and rapid, and provides the dyed textile with a desired degree of coloring, and resistance to fading and running of the dye (color fastness). Further, the dyeing process and the materials used therein preferably do not adversely affect the aspects of the textile, such as its flexibility, durability, and tactile properties like softness, smoothness, stiffness.

Creating “cationic cotton” by introducing a positive charge to a cotton fabric or textile for increased dye uptake is well known. One of the most common methods to cationically modify natural fibers such as cotton is to use epoxy-based ammonium compounds, such as 3-chloro-2-hydroxypropyltrimethylammonium chloride, to add a charge to the natural fiber's cellulose polymer backbone. Other agents, such as the ether amino salts described in U.S. Pat. No. 9,493,398 have also been proved to be effective in creating cationic fibers such as cotton.

Ammonium quaternary suppliers typically suggest the use of different amounts of the cationic agent, depending on the desired color shade after dyeing, with darker shades demanding a higher content of the agent, and lighter shades demanding a lower content. However, the use of different amounts of the agent complicates the production and handling and therefore is not desired by textile mills. A single cationic agent recommended content for all shades is becoming a reality, with high amounts of ammonium quaternaries on cationic cotton. However, it has been observed that this single content of cationic agents tends to allow light and medium shades of dyed cationic fabric to be more subject to staining during home washes, which is believed to be due to the released dye from darker clothes produced from conventional dyeing methods in the same wash.

It is desired to have a process to prevent such staining.

To avoid this staining, a method of applying acrylic polymers in cationic fabrics is presented involving the step of having an acrylic polymer in contact with a cationic cotton. For a longer life cycles of the staining resistance, the pH of the environment with a modified dyed natural fiber which has previously been reacted with cationic agent should be similar to the regular pH of the acrylic polymer sample. However, for shorter life cycles, the staining resistance does not present significant relationship with the standard pH of the acrylic polymer sample and the pH of the environment with a modified dyed natural fiber which has previously been reacted with cationic agent.

It is proposed to have an acrylic polymer in contact with a modified dyed cotton or other natural fiber, which fiber had previously been reacted with cationic agent to avoid staining in the cationic material. For long lasting life cycles of the staining resistance, the environment pH should be similar to the regular pH of the acrylic polymer sample. It has been observed that when the acrylic polymer is contacted with the cationized fabric at a pH which is similar to the standard pH of the acrylic polymer, the acrylic polymer tends to attach to the fabric more robustly. When the acrylic polymer molecule attaches to the cationic cotton, it is believed that it will block spots susceptible to dye staining from the fabric, thereby avoiding the stains during different process, like home washes. However, for short lasting (or “short term”) life cycles, the staining resistance does not strongly present significant relationship between the standard pH of the acrylic polymer sample and the environment, being more related with the contact between the acrylic polymer and the cationic cotton.

The proposed solution is believed to be effective with all of the different cationic agents currently applied in cationic fabric, but it is recommended to use the ether amino salt type of cationic reagents disclosed in US patent U.S. Pat. No. 9,493,398B2.

Cationic cotton (or other natural fiber) is prepared either by continuous or jet exhaust application. These processes use sodium hydroxide aqueous solution maximum 50% wt., and a cationic reagent (preferably of the sort identified in U.S. Pat. No. 9,493,398B2). With that, a cationic cotton is obtained.

The cationic cotton (or other natural fiber) is then dyed in a latter process step as is known in the art.

In the method of the present invention, for long lasting life cycles, either during dyeing or after it, the fiber is allowed to be in contact with an acrylic polymer under a pH environment similar to the regular pH of the acrylic polymer sample, controlled by the addition of sodium carbonate or other basic substance, to increase the pH, or citric acid or other acidic substance to decrease the pH. Also, the method of this application can also be with acrylic polymer by itself or in mixture with common chemistries present in textile process, such as softener agents in finishing steps.

The embodiments of the present invention described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art can appreciate and understand the principles and practices of the present invention.

All publications and patents mentioned herein are hereby incorporated by reference to the full extent permitted under the relevant laws. The publications and patents disclosed herein are provided solely for their disclosure. Nothing herein is to be construed as an admission that the inventors are not entitled to antedate any publication and/or patent, including any publication and/or patent cited herein.

The term “about” used preceding any numerical value of the disclosure or appended claims allows some slight imprecision in that stated numerical value, which imprecision may either be understood in the art, or may result from methods of measuring to obtain such numerical values (e.g., such as with chemical or physical measurements), and any numerical value not preceded by the term “about” of the disclosure or appended claims may also be understood the same way.

Methods and compositions of the disclosure described as “comprising” or “including” can include those recited step and compounds, respectively, and optionally can include other steps and components. If methods or compositions of the disclosure are described as “consisting of,” those methods or compositions have the recited steps or compounds but do not include steps or compounds that are not recited. The term “consisting essentially of” generally refers to compositions that include the recited compounds and may include other non-recited compounds, but in unsubstantial amounts. For example, such compositions can include one or more other non-recited components but not in an amount that is greater than about 1% (by weight), greater than about 0.5% (by weight), or greater than about 0.1% (by weight) of the total composition. In a composition “consisting of” the recited components there is no other measurable amount of component other than the recited component, or a method “consisting” of certain steps includes no other steps than those ones recited.

For the purposes of the present invention, it should be understood that “textiles” includes yarns, fabrics, as well as articles made from fabric or yarns such as garments or linens.

In its broadest sense, the present invention is a method for improving the stain resistance of a cationized fiber or textile comprising natural fiber. The method comprises the steps of immersing the cationized fiber or textile in an aqueous solution having a given pH and then contacting the fabric immersed in the aqueous solution with an acrylic polymer having or not a standard pH under conditions sufficient to allow at least a portion of the acrylic polymer to attach to the fiber or fabric. Notably, the aqueous solution has been selected or adjusted to have a pH that is similar to the standard pH of the acrylic polymer prior to the addition of the acrylic polymer. The adjustment or not of the environment pH to a similar standard pH of the acrylic polymer will depend on the desire or not of the long lasting staining resistance of the cationic fabric material. If a shorter staining resistance shelf life is desired, no pH adjustments are necessary. However, if a longer staining resistance shelf life is desired, the environment pH should be similar to the standard pH of the acrylic polymer.

The present invention involves modifying a natural fiber which has been cationized and dyed. The cationization can be done using agents known in the art. It is preferred that the ether amino salts described in US U.S. Pat. No. 9,493,398B2 be used. As is known in the art, the cationization process typically involves reacting the natural fiber or textile with the cationic agent in a continuous (e.g., cold pad bath) or jet exhaust application in the presence of an aqueous sodium hydroxide solution have no more than about 50 weight percent sodium hydroxide. Time and temperature of such cationization process as well as the identity and amount of cationization agent used, may be varied as is generally known in the art.

After the cationization step, the fiber or textile is typically washed and neutralized with an aqueous solution of up to 5 grams per liter acetic or citric acid. After neutralization the fiber or textile may optionally be dried and then subjected to an aqueous dying process, as per the recommendations of the dye manufacturers.

In the present invention, the fiber or textile is kept in contact with an acrylic polymer. This contact may be conducted simultaneously with the dying or in a separate step after the dying, like in finishing step. This step involves placing the fiber or textile in an aqueous solution having a pH similar to the original pH of the acrylic polymer additive that will be used for long lasting staining resistance cycles. For shorter staining resistance cycles, the pH of the environment does not need a previous modification, as there is no significant dependence on the standard pH of the acrylic polymer being used as antistaing additive. The terms “regular”, “original” or “standard” pH are used interchangeably in the present application, and are meant to denote the pH of the acrylic polymer as produced or if purchased, the sales specification, which may be stated as a range. For purposes of this application, the term “similar” means a pH with a value within plus or minus 1, preferably plus or minus 0.5, even more preferably plus or minus 0.25, of the regular pH of the acrylic polymer. If the aqueous solution used in this step does not naturally have a pH which is similar to the acrylic polymer which will be used, then the pH can be adjusted prior to the addition of the acrylic polymer. To increase the pH of the aqueous solution, sodium carbonate, or other alkaline substance, like soda ash, sodium hydroxide, etc., can be added, and to decrease the pH, citric acid, acetic acid or other acidic solution can be added. The amount of substance added in order to adjust the pH of the aqueous solution will depend on the target pH desired to be achieved, as is generally known in the art.

As textile processes in mills tend to be conducted under alkaline conditions, it may be preferred that acrylic polymers having a higher standard pH be used, such that less adjustment of an aqueous solution resulting from a previous process will be needed. In other circumstances though, the use of acrylic polymers having a more neutral pH will be preferred as the more neutral aqueous solutions may require less care in handling.

For long lasting staining resistance cycles, when the desired pH for the aqueous solution has been achieved, the fiber or textile is contacted with an acrylic polymer with a standard pH which is then similar to the reactive environment. The acrylic polymer can be any polymer derived from acrylic acid or methacrylic acid, including acrylate or methacrylate esters, and salts thereof. Thus, the monomers can advantageously include acrylic acid, t-butyl acrylate, or methyl methacrylate and mixtures thereof. The acrylic polymer can be a homopolymer or may contain two or more monomers. It is generally preferred that the acrylic polymer have a molecular weight in the range of from 2,000, 2,500, 3,000 or even 3,300 to 4,500, 4,300, 4,100 or even 3,900 g/mol. These polymers can be produced as is generally known in the art or can be commercially obtained.

The amount of acrylic polymer in the aqueous solution can be in a range of from 5 g/L, 20 g/L, 30 g/L, 50 g/L or even 90 g/L up to a maximum of 100 g/L, 90 g/L. 80 g/L or even 70 g/L. For example, for some applications it may be beneficial to have a concentration of acrylic polymer in the aqueous solution in the range of from 90 to 100 g/L while in other application it may be desirable to have a concentration of acrylic polymer in the aqueous solution in the range of from 30 to 70 g/L.

The fiber or textile is contacted with the acrylic polymer under conditions to allow the polymer to become at least partially attached to the fiber or textile the contact between the acrylic polymer and the cationic cotton. This can advantageously be done at room temperature for a period of up to an hour, preferably from 10 to 30 minutes.

For long lasting staining resistance cycles, the fiber or textile is then neutralized by the addition of an acidic solution, which can be citric acid, acetic acid or any other acidic substance. Typically, this neutralization is carried out by the addition of 5-100 g/L of the acidic substance.

Different methodologies are proposed to evaluate the method of the present invention efficacy against stain which, in general, they depend on: dyed cationic cotton with or without the additive is left in contact with an aqueous solution of dark dye for a period of time, after which the fabric is removed and both the fabric's color and the bath's color are evaluated. Unchanged fabric and darker bath are both indications that the additive was successful at preventing staining because it keeps the dye from attaching to the cationic fabric.

The process of the current invention is demonstrated in the following examples.

Table 1A presents a table of materials used in the Examples:

Examples to Understand Acrylic Polymers Efficacy and the Interaction Between the pHs—

In a set of experiments, fabric which has been cationized with 75 g/L of Cationic Reagent A in continuous (cold pad batch) application and then dyed using NOVACRON™ Yellow P-6GS dye at a concentration of 250 μL per 10 g swatch, is treated with different “stain resisting” materials. To achieve this, the dyed fabric is added to an aqueous bath in a bath ratio of 10 (water):1 (fabric) by weight. The pH of the bath is then adjusted with sodium carbonate to achieve more alkaline conditions or with citric acid to achieve more acidic conditions in order to bring the bath to the standard pH of the anti-staining additive to be used as necessary (the starting pH and concentration of acidic or alkaline material will determine the amount to be added). After the pH was adjusted (if necessary) to the desired pH, the reaction between the anti-stain additive and the cationized fabric is allowed to proceed for 10 minutes at 30° C. These fabrics are then placed in a bath containing an aqueous solution with NOVACRON™ Black C-NN dye in order to simulate a staining condition in a home washing activity. All the examples in Tables 1-10 use the same black dye at the same concentration (0.1% on weight of goods (OWG) in 200 g of water), same bath ratio (20:1 wt.) for the same amount of time (30 minutes per “wash”) at the same temperature (30° C.). Color analysis is then done on a quantitative basis for both the fabric and the bath. For the quantitative analysis a spectrophotometer is used to measure the L, a*, and b* parameters to measure the color intensity of the fabric (reflectance mode) and those parameters were used to calculate dE (delta E, ΔE) as known in the art.

Acrylic Polymer A has a 2,000 g/mol as molecular weight (MW). Table 1 presents the results for the application of Additive A at 25 g/L. As it can be observed, L parameter reduces and dE parameter increases with the increase in staining washes. This means that the cationic cotton with the anti staining additive become more stained with the increase of staining washes. This result was similar in all pH conditions (acid, neutral or alkaline) and in all staining washes, so it is understood that acrylic polymers with up to 2,000 g/mol as MW and applied at 25 g/L will not work in avoiding the stains.

In order to evaluate if the low Acrylic Polymer A concentration was the cause for the results presented in Table 1, the study was replicate for the same additive, but with 100 g/L instead. The obtained results are presented in Table 2 and the conclusions are as similar to the previous example, with a small increase in the staining resistance at the initial staining washes. This corroborates to the conclusion that acrylic polymers with up to 2,000 g/mol as MW will not work in avoiding the stains, even in higher concentration applications, but this concentration will support a short lasting staining resistance with application at any proposed pHs

Acrylic Polymer B has a 4,500 g/mol as molecular weight (MW) and it is produced in an acid pH. Table 3 presents the results for the application of Acrylic Polymer B at 100 g/L. As it can be observed, L parameter generally reduces and dE parameter increases with the increase in staining washes. When we compare the L or dE parameters after several washes, with the data before contamination (“dye+treat”), there is a modification in those parameters for the cases where the additive was applied in neutral or alkaline pHs, which indicates that the fabric do not present a long lasting staining resistance at those application pHs. However, there was no significant modification in the L and dE parameters for the case when the Acrylic Polymer B was applied at an acidic pH, which is a similar pH for the pH of the production of Acrylic Polymer B. It is concluded that Acrylic Polymer B was effective in avoiding stains after several staining washes when the application was in acid pH, which is a similar pH of the production of Acrylic Polymer B. It is concluded that Acrylic Polymer B was effective in presenting a long lasting resistance to stains at 100 g/L in acid pH, which is a similar pH of the production of Acrylic Polymer B.

However, there was not significant modification in L and dE parameters for the initial staining washes when the application was at an acid pH (similar to the pH of the acrylic polymer) or neutral pH (different than the pH of the acrylic polymer). This indicates that for desired short lasting staining resistance, the application does not need to be in a pH too close to the acrylic polymer pH. For acid acrylic polymers, short lasting staining resistance present better results for acid or neutral application pH, but depending on the qualitative criteria, alkaline application pH can also be applied.

Acrylic Polymer C has a 4.500 g/mol as molecular weight (MW) and it is produced in an acid pH.

Table 4 presents the results for the application of Acrylic Polymer C at 100 g/L. L parameter generally reduces and dE parameter increases with the increase in staining washes. When we compare the L and dE parameters after several washes, with the data before contamination (“dye+treat”), there is a modification in those parameters for the cases where the additive was applied in neutral or alkaline pHs, which indicates that the fabric do not present a long lasting staining resistance at those application pHs. However, there was no significant modification in the L and dE parameters for the case when the Acrylic Polymer C was applied at an acidic pH, which is a similar pH for the pH of the production of Acrylic Polymer C. The Acrylic Polymer C was effective in avoiding stains after several staining washes when the application was in acid pH, which is a similar pH of the production of Acrylic Polymer C. It is concluded that Acrylic Polymer C was effective in presenting a long lasting resistance to stains at 100 g/L in acid pH, which is a similar pH of the production of Acrylic Polymer C.

However, there was not significant modification in L and dE parameters for the initial staining washes, when the application was at an acid pH (similar to the pH of the acrylic polymer) or neutral pH (different than the pH of the acrylic polymer). This indicates that for desired short term staining resistance, the application does not need to be in a pH too close to the acrylic polymer pH. For acid acrylic polymers, short lasting staining resistance present better results for acid or neutral application pH, but depending on the qualitative criteria, alkaline application pH can also be applied.

Acrylic Polymer D has a 3,600 g/mol as molecular weight (MW) and it is produced in an acid pH. Table 5 presents the results for the application of Acrylic Polymer D at 25 g/L. L parameter generally reduces and dE parameter increases with the increase in staining washes. When we compare the L and dE parameters after several washes, with the data before contamination (“dye+treat”), there is a modification in those parameters for the cases where the additive was applied in neutral or alkaline pHs, which indicates that the fabric do not present a long lasting staining resistance at those application pHs. However, there was no significant modification in the L and dE parameters for the case when the Acrylic Polymer D was applied at an acidic pH, which is a similar pH for the pH of the production of Acrylic Polymer D The Acrylic Polymer D was effective in avoiding stains after several staining washes when the application was at 25 g/L in acid pH, which is a similar pH of the production of Acrylic Polymer D. It is concluded that Acrylic Polymer D was effective in presenting a long lasting resistance to stains at 25 g/L in acid pH, which is a similar pH of the production of Acrylic Polymer D.

However, there was not significant modification in L and dE parameters for the initial staining washes, when the application was at an acid pH (similar to the pH of the acrylic polymer) or neutral pH (different than the pH of the acrylic polymer). This indicates that for desired short term staining resistance, the application does not need to be in a pH too close to the acrylic polymer pH, even when the application needs only 25 g/L of the additive. For acid acrylic polymers, short lasting staining resistance present better results for acid or neutral application pH, but depending on the qualitative criteria, alkaline application pH can also be applied.

In order to evaluate if an increase in the content of the Acrylic Polymer D would change the results presented in Table 5, the study was replicate for the same additive, but with 100 g/L instead. The obtained results are presented in Table 6 and it can be concluded that, even after 4 contamination washes, the change in L and dE parameters were even lower than the previous case, for all pH conditions, with acidic pH being the best application pH. It can be concluded that a higher concentration of the additive, 100 g/L in this case, is a better application conditions, probably because there will be more polymer avoiding the contamination dye to be attached to the fabric.

Also, for short lasting resistance to stain, as data presented after one staining wash, the difference in L and dE parameters are not significant, when we compare different application pHs. So for short lasting staining resistance, the application pH does not need to be too close to the standard pH of the acrylic polymer, but higher differences in L and dE parameters, indicating a worse staining protection, occur when the application pH is more different than the acrylic polymer pH (alkaline application pH is worse than neutral or acidic application pHs).

Acrylic Polymer E has a 3,500 g/mol as molecular weight (MW) and it is produced in a neutral pH. Table 7 presents the results for the application of Acrylic Polymer E at 100 g/L. As it can be observed, when we compare the L and dE parameters after several washes, with the data before contamination (“dye+treat”), there is a higher modification in those parameters for the cases where the additive was applied in acidic or alkaline pHs, which indicates that the fabric was stained after the four contamination washes. This indicates that for long lasting staining resistance, the application should be in a neutral pH, similar to the standard pH of the acrylic polymer E, because this application conditions present the lowest modification in L and dE parameters. It is concluded that Acrylic Polymer E was effective in presenting a long lasting or resistance to stains at 100 g/L in neutral pH, which is a similar pH of the production of Acrylic Polymer E.

However, for a short lasting resistance to stains, as noticed by comparing L and dE parameters before any staining wash with after one staining wash significant difference was noticed. It can be concluded that for demands with short lasting resistance to stains, the application pH being close to the standard pH of the acrylic polymer result in an application at any pH for a neutral acrylic polymer, because a close pH to a neutral pH are both acid or alkaline pHs. So, for a short lasting resistance, if the standard pH of the acrylic polymer is neutral, the application pH can be any.