US2194358A - Bleaching artificial textile fibers - Google Patents

Description

Patented Mar. 19, 1940 STATES PATNT OFFlE the-Main, Germany,

assignors to Deutsche Gold und Silber Scheideanstalt, Frankfort-on- I the-Main, Germany,

many

a corporation of Ger- No Drawing. Application May 1'7, 1938, Serial No. 208,495. In Germany May 24, 1937 9 Claims.

This invention relates to a process of bleaching textile fabrics. It is especially applicable to the continuous bleaching of textile materials and is especially valuable for the treatment of those textile fibers resulting from manufacturing processes wherein the product is of cellulosic nature such as artificial staple fibers, artificial silk and similar materials. The process utilizes active oxygen yielding compounds, more particularly peroxygen compounds such as hydrogen peroxide,

alkali metal percarbonates, alkali metal perborates and other peroxygen compounds.

Previously processes wherein the fiber is first saturated with a solution of hydrogen peroxide followed by squeezing out the excess solution and drying at elevated temperatures have been restricted in use to the bleaching of animal fibers such as wool. It was generally supposed that such a process would not be applicable in the 20 bleaching of vegetable fibrous material such as cotton because hydrogen peroxide in contact with such fibers was known to become inactive very rapidly.

We have now discovered that artificial textile 25 fibers from regenerated cellulose, such as artificial staple fiber, artificial silk formed of a cellulose base, and similar fibrous materials possess a marked accumulating capacity for hydrogen peroxide. On the basis of such knowledge We have found it possible to bleach fibrous material of this nature by saturating the fibrous material with the solution of the peroxygen compound (hydrogen peroxide for example) and subsequently drying the fibrous material which has previously been freed, if necessary, from excess bleaching liquor by a procedure such as squeezing.

The process of the invention may be carried out, for example, by treating the fibrous mate- 40 rial with the bleaching liquor which may be a solution of hydrogen peroxide, then treating the fibrous material with steam and finally drying that material. Previous to the drying step the fabric may be freed, if desired, from excess bleaching liquor by some procedure such as squeezing or centrifuging the fabric.

During the bleaching stepthe material being bleached should be contacted with a liquor which is alkaline in reaction. The pH value should preferably be between 7.5 and during the initial phase of the bleaching. Subsequently during the heating and steaming processes the pH value of the material being bleached will ordinarily be not more than 8 and preferably will fall within the pH range 6 to '7 .6 or within the narrower pH range 6.5 to 7.5. The amount of alkali required during the bleaching process depends on the quantity of alkali or acid contained in or on the fibrous material being bleached, as well as on the type and amount of impurities present in the fibrous material which tend to consume alkali. The amounts of alkali necessary for bleaching a specified fibrous material with a given hydrogen peroxide consumption in order to impart to the material being bleached the desired pI-I during the heat treatment can always be readily ascertained by preliminary experiments. The saturation or impregnation of the fibrous material being bleached with the activeoxygen yielding solution may also be accomplished by sprinkling or spraying, such as by conveying the material on a moving belt past the spraying device.

We have found that it is most desirable to utilize relatively weak alkalies or salts which yield alkali by hydrolysis. When utilizing strong alkalies such as caustic soda, especially during continuous operations, it has been observed that relatively slight excesses of these strong alkalies' impart to the material too high a pH value, thereby hindering the bleaching effect. We have therefore found relatively weak alkalies to be more desirable for use in our process and especially prefer to use salts of relatively strong bases and relatively weak acids such as the alkali metal pyrophosphates, disodium phosphate, borax, alkali metal succinates, alkali metal malonates, and similar salts. The alkali metal salts of the fatty acids, 1. e., soaps, have also been found to be especially advantageous since theamount added need not be determined with considerable exactitude since their total alkali content is relatively small. Fibrous material is also favorably influenced by the presence of soap, it being observed that a softer feel is thereby imparted thereto. be advantageously'adjusted so that the desired pH value is obtained by using a buffer mixture such as, e. g., a mixture of NaOH and monopotassium phosphate, or a mixture of sodium carbonate and sodium bicarbonate. Other buffer mixtures are also suitable.

In accordance with one method of proceeding in accordance with our invention, the fibrous material to be bleached is first impregnated with a neutral or slightly acid solution, one having a pH below 7.0. Such neutral or slightly acid solutions are utilized in place of alkaline bleaching solutions. Salts which have the property of raising the pH value of, the bleaching solu- The material to be bleached can also 1 tion to a value higher than 7.0 are added to the bleach bath, which may comprise a solution of hydrogen peroxide. Among such salts may be mentioned sodium and potassium oxalate.

We have found that a solution containing about 5 cc. of 40% (by volume) hydrogen peroxide solution and 5 grams of sodium oxalate per liter will have a pH value of approximately 6.6 at 20 C. At 100 C. the same solution, due to hydrolysis of the salt, will have a pH value of approximately 9.0. By using neutral or slightly acid bleaching solutions during the step wherein the textile material to be bleached is impregnated with the solution there has been found to occur no important loss of hydrogen peroxide even upon prolonged standing. However, at the elevated temperature, due to hydrolysis, the desired alkalinity for rapid bleaching is secured.

We have found that from 3 to 15 cc. of hydrogen peroxide solution (40% by volume) per liter provides the best bleaching bath. The consumption of hydrogen peroxide for each 100 grams of material being bleached will be-found to amount to from 0.3 to 1.5 cc. of hydrogen peroxide solution.

The amounts of bleaching agent and the total alkali content present are so controlled that the material being bleached at the conclusion of the heat treatment contained substantially no undecomposed peroxide. By regulating the temperature of drying and the pH of the goods during the heat treatment or drying step it is possible to regulate the speed of active oxygen evolution so that the process occurs either rapidly or slowly, thus carrying out the reaction in such a manner that the finished product contains no undecomposed peroxide. The steaming of the material being bleached is preferably carried out at temperatures of approximately 100 C.

After-treatment of the textile goods, involving washing and drying, may be eliminated, particularly if the bleaching is carried out so that the material being bleached is substantially free from hydrogen peroxide at the completion of the heat treatment step. The steam treatment may also be eliminated, the steaming being replaced by a drying process. It has proven advantageous under these conditions to dry the material which has been preliminarily impregnated with the bleaching liquor, first, at relatively high temperatures, followed by drying at relatively low temperatures.

Drying of the fibrous material, after it has been impregnated with the bleaching liquid, may also be carried out by exposure in the open air at room temperature. The hydrogen which has accumulated on the fiber exerts a very effective bleaching action during the course of the drying process. In this Way very satisfactorily bleached products are obtained.

The process may also be carried out by drying the fibrous material at an elevated temperature, for example, temperatures within the range to C., following-the impregnation step. In this case it is observed that surprisingly enough a marked bleaching action occurs subsequent to the V drying. In carrying out our procedure in accordance with this variation it is recommended that the dried material be subjected to an aftertreatment, for example, by allowing it to stand in the air at room temperature (15 to 20 C.). The process may be prolonged, if desired, until all hydrogen peroxide present on the fibrous material is eliminated.

One method of accomplishing our process involves passing the fibrous material continuously through a bath of hydrogen peroxide, then freeing it from excess liquid by centrifuging or squeezing, then treating it for approximately 10 to 30 minutes with steam, preferably at 100? C., and finally drying at approximately 50 to C. The material which has been freed from excess bleaching liquid'may be immediately subjected to drying, omitting the steam treatment. If this is done the drying should first be carried out at 90 to C. and subsequently the temperature of drying reduced to one within the temperature range 40 to 70 C.

In place of treating the fibrous material with hydrogen peroxide or other peroxygen compound the process may also be carried out by spraying the material with the bleaching solution. This is most expediently accomplished by passing the material on a moving band through a spraying device. If desired, the spraying may be repeated one or more times and the fibrous material may be sprayed on both sides.

In accordance with our invention the ingredients of the bleach bath are so selected that the material being bleached maintains an alkaline reaction, one within the pH'range 7.5 to 10, during the first phase of the heat treatment. Subsequently it assumes an approximately neutral or slightly alkaline or acid reaction (pH approximately between 6 to 7.6) during this treatment. The maintenance of these conditions is of considerable importance if good bleaching is to be obtained. The pH value of the goods after the steaming or drying treatment is a definite criterion as to the success or lack of success of the bleach. If the amount of alkaline materials added to the substance being bleached is adjusted so that the material being bleached remains too strongly alkaline during the entire heat treatment it Will be observed that the bleaching effect is poor and that yellowing may occur.

Determination of the pH of the material may be accomplished as follows:

50 grams of air-dried goods are moistened with 70 cc. of distilled water. 20 cc. of this liquid is squeezed from the goods. In the case of steamed goods enough distilled water is added so that 50 grams of artificial fiber being bleached contains 70 cc. of liquid. The liquid squeezed out (20 cc.) is used for the determination of the pH values. This testing method was used in the examples of our improved process which will be subsequently described. a

It is possible to employ in the solution of hydrogen peroxide or of other peroxygen compound used for bleaching purposes special agents such as emulsions of olein, Turkey red oil, fatty alcohol sulfonates, and other materials which insure softening of the goods and enlivening of the bleached color. The process may be continuously carried out in continuous operations, the impregnation, removal of excess liquor, drying, or steaming and drying, being carried out continuously on a travelling conveyor belt. It is also possible to employ our process as a single step in a combined bleaching operation such as a step in the combined chlorine-peroxide bleaching methods known to the art.

Our process permits the bleaching of artificial fibers, especially regenerated cellulose and products manufactured therefrom by a rapid, simple and inexpensive method yielding uniformly satisfactory results. Mixed fibers, mixed fabrics, and similar materials may also be similarly advantageously treated in accordance with our process, since the hydrogen peroxide accumulatedon the cellulose artificial threads exerts a bleaching influence on the neighboring threads.

After the drying step it is sometimes desirable to permit the goods to stand in the air at room temperature, i. e. at a temperature of approximately 15 to 20 C. This after-step of standing may be prolonged if desired until any residual hydrogen peroxide which may remain in the fiber is decomposed. By suitably adjusting the concentration of the hydrogen peroxide solution by the addition of suitable agents it is possible to regulate the bleaching action so that any desired bleaching effect is secured. The liquid recovered from the fibrous material by squeezing or centrifuging may, of course, be used over again in the bleaching of subsequent batches of fibers or fabrics.

As examples of our improved process for the bleaching of fibrous materials the following may be given.

Example I The fibrous material to be bleached is first passed through a container filled with dilute hydrogen peroxide solution The solution contained, per liter of solution:

Hydrogen peroxide (40% concentration by volume) cc 10 to 20 Ammonium hydroxide. cc 1 to 2 Olein gram 0. 3 to 0. 5

After passing through the solution the fibrous material was squeezed or centrifuged, and then dried in the air at ordinary room temperature, a temperature within the range 15 to 20 C. At the conclusion of this process the fibrous material was bleached to a satisfactory white c010 and the fiber had a soft smooth feel. I

Example II Fibrous material was first impregnated with a bleaching solution, as in Example I, utilizing a solution of hydrogen peroxide which contained, per liter of solution:

Hydrogen peroxide (40% concentration by volume) cc 10 to 20 Ammonium hydroxide cc 1 to 3 Sodium pyrophosphate crystals gram 1 Olein gram 0. 3 to 0.5

The fibrous material to be bleached wasimpregnated with the bleaching liquor, as, in Example I, utilizing a bath of hydrogen peroxide containing per liter of solution:

Hydrogen peroxide (40% concentration by volume) cc 10 to 20 Ammonia water cc 5 to 10 Sodium pyrophosphate cc 1 to 3 Olein gram 0. 3 to 0. 5

After squeezing out excess solution the fibrous material was conveyed on a conveyor belt through a drying apparatus and dried at temperatures of approximately'lS? C. The resulting product was bleached to a satisfactory white color and had a soft smooth feel.

Hydrogen peroxide (40% concentration by volume) cc 4 Disodium phosphates gram 0. 3 Marseilles soap grams 3 After immersion, the artificial staple fiber was squeezed in order to free it from excess solution. It was subsequently steamed for 20 minutes at a temperature of C. and then dried at a temperature of approximately 70 C. The pH value of the bleaching bath was 9.1 and the pH value of the artificial staple fibers after the steaming treatment was 7.0. The fiber was bleached very satisfactorily.

Example V 100 grams of artificial staple fiber prepared from cellulose was immersed for 5 minutes in a bleaching bath constituted as follows:

Hydrogen peroxide (40% concentration by volume) cc Disodium phosphate gram 0.

Borax grams Sufiicient water to make up 1 liter of solution.

Example VI 100 grams of artificial staple fiber prepared from cellulosewas immersed for 5 minutes in a bleaching solution which contained in a liter of solution the following ingredients:

Hydrogen peroxide solution (40% concentration by volume) cc 5 Caustic soda grams 2 Monopotassium Buffer mixture{ phosphate grams 6.6

After immersion, the fiber was withdrawn and squeezed or centrifuged to remove excess liquor. It was then subjected to steaming and subsequently dried as in Example IV. The pH value of the bleaching solution was approximately 7.7,

while the pH value of the artificial fibers, at the conclusion of the steaming step, was 6.6. The goods were bleached to a satisfactory white color.

Example VII Hydrogen peroxide of 40% by volume concentration; cc 3 Sodium oxalate grams 4 After immersion, the goods were treated as in Example IV. The pH value of the bleaching solution when cold was 6.6. When heated to a temperature of substantially 100 C., the pH of this solution became 9.0. No change in pH value of the artificial staple fiber occurred during the step of drying the fiber at the conclusion of the steaming process. The fibrous material was bleached to a satisfactory white color and had a soft smooth feel.

The foregoing details, procedures, temperatures, percentages and amounts which have been given merely as illustrative of preferred modes in which our improved process may be carried out are not to be regarded as restrictive. term heat treatment, as it may be used in the specification or claims, there should be understood either the treatment of the fibers to be bleached with the alkaline peroxide solution at substantially 100 C. in the presence of steam, or in those instances where steam treatment is not employed, the subjection of the fibers to the action of the alkaline bleaching solution at substantially 100 C. The subsequent drying of the fibers is not to be considered as part of the heat treatment. Various changes may be made in such details of our process as described which will nevertheless come within the purview of our invention. The scope of that invention is to be determined, not by the procedures and amounts indicated as merely illustrative, but in accordance with the scope of the appended claims.

We claim: 1. A process for bleaching artificial textile fibers comprising the steps of impregnating the fibrous material with a solution containing a peroxygen compound, said solution being maintained at a temperature of substantially 100 C., and then drying said fibrous material at an elevated temperature within the range 50-90" C., the pH value of said fibrous material during said drying step being maintained within the range 7.5 to 10 at the initial phase of said heat treatment at substantially 100 C. and the pH value of said fibrous material during said treatment at 100 C. falling within the pH range 6.0 to 7.6.

2. A process for bleaching artificial textile fibers, especially those prepared from regenerated cellulose such as artificial staple fiber, artificial silk and similar materials, which comprises the steps of first impregnating the fibrous material with a solution of a peroxygen compound, removing said fibrous material from said solution, squeezing to remove excess liquid therefrom, drying said fibrous material at an elevated temperature within the range 90 to 100 C. and then continuing said drying step at lower temperatures, temperatures within thfiange 40 to 70 C., the pH value of said materials being maintained below about 8.0 during substantially said entire drying step.

3. A process as defined in claim 2 wherein the pH value of said fibrous material duringsaid drying step is maintained within the range 6.0 to 7.8.

4. A process for bleaching artificial textile fibers, especially textile fibers fashioned from regenerated cellulose and products made therefrom such as artificial wool and artificial silk, which process comprises the steps of impregnating the fibrous material with a solution of an active oxygen-yielding compound, subjecting said impreg- By the 2,194.,ssa

nated fibrous material to the action of heat, and then drying said impregnated fibrous material, the pH value of said textile fibers being maintained on the alkaline side during the initial phase of said heat treatment of said impregnated fibers, and the pH value of said textile fibers at the conclusion of said heat treatment step being approximately 7.0.

5. A process for bleaching artificial textile fibers, especially textile fibers fashioned from regenerated cellulose and products made therefrom such as artificial wool and artificial silk, which process comprises the steps of impregnating the fibrous material with a solution of hydrogen peroxide, subjecting said impregnated fibrous material to the action of steam, and then drying said fibrous material, the pH value of said textile fibers being maintained on the alkaline side during the initial phase of said steam treatment step, the pH value of said textile fibers at the end of said steam treatment being substantially equivalent to that of a neutral solution.

6. A process for bleaching artificial textile fibers, more particularly textile fibers fashioned from regenerated cellulose and products made therefrom such as artificial wool and artificial silk, which process comprises the steps of impregnating said fibrous material with a solution of hydrogen peroxide, subjecting said impregnated fibrous material to the action of steam at a temperature of 100 C., and then drying said fibrous material at a temperature within the range 50 to 90 C., the pH value of said textile fibers being maintained within the range 7.5 to 10 during the initial phase of said steam treatment at substantially 100 C. and being maintained within the range 6.0 to 8.0 during said step of steam treatment at substantially 100 C.

7. A process for bleaching artificial textile fibers, more particularly textile fibers fashioned from regenerated cellulose and products made therefrom such as artificial wool and artificial silk, which process comprises the steps of impregnating the fibrous material with a solution of hydrogen peroxide containing, as an alkalinizing agent, a salt of a strong base and a weak acid selected from the group which consists of the alkali metal pyrophosphates, disodium phosphate, borax, the alkali metal succinates, the alkali metal malonates, and soap, subjecting said impregnated fibrous material to the action of heat, and then drying said impregnated fibrous material, the pH value of said textile fibers being maintained on the alkaline side during the initial phase of said heat treatment of said impregnated fibers.

8. A process as defined in claim 5 wherein a solution of hydrogen peroxide containing a butering agent for maintaining said solution alkaline is utilized as the impregnating agent.

9. A process as defined in claim 5 wherein there ing a pH value below 7 and containing an alkali metal oxalate, said solution becoming alkaline in reaction duringsaid subsequent heat treatment steps due to the action of said alkali metal oxalate.

WILLI HUNDT. HERMANN BAIER.

is utilized a solution of hydrogen peroxide hav-