Patent Publication Number: US-4321054-A

Title: Oxidizing medium for dyes

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation of application Ser. No. 136,582, filed Apr. 1, 1980, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to an improved oxidant and more in particular to an acidic, aqueous, oxidizing agent containing bromate and iodate ions. 
     Dying of various fabrics to impart a color to the fiber has been practiced for many centuries. The color must generally be permanently and uniformly distributed throughout the fiber and not merely superficially applied to the fiber as in painting. Many different types of natural and regenerated cellulosic fibers have been dyed to impart a color. For example, natural fibers, such as the vegetable fibers cotton, linen, jute, and flax have been dyed. Regenerated cellulosic fibers, such as viscose rayon and cellulose acetate, are those produced from natural materials which were altered by man to produce a desired textile material. 
     It has become accepted, and common, practice to color these materials with well-known sulfur and vat dyes. These dyes are water insoluble substances which are readily converted to a water soluble or leuco form by reducing the sulfur or vat dye in, for example, a solution containing an alkali and sodium sulfide or hydrosulfite. 
     The leuco forms of sulfur and vat dyes are water soluble and well known to be substantive to cellulosic fibers. After application to the fiber, the leuco dye must be oxidized to permanently color the fabric. The process of U.S. Pat. No. 3,775,047 oxidized the dye with an aqueous oxidizing solution including acetic acid and sodium or potassium iodate. U.S. Pat. No. 4,042,319 disclosed similar oxidation with an aqueous oxidant containing acetic or formic acid, an alkali bromate and an alkali iodate. Such oxidizing solutions are operable; however, it is desired to provide an improved material suitable to oxidize leuco forms of sulfur and vat dyes. 
     SUMMARY OF THE INVENTION 
     The oxidant of the present invention is an acidic, aqueous material including ionized bromate, iodate and a soluble molybdenum containing material. In one use, leuco sulfur or vat dyes on fibers are contacted with the oxidant for a sufficient time to oxidize a desired or predetermined amount of the leuco material to impart a suitable color to the fibers or fabric. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The improved herein described oxidant is readily made by mixing together at least one water soluble bromine-containing compound with at least one water soluble iodine-containing compound and at least one water soluble molybdenum-containing compound in water. An acid, such as, for example, hydrobromic, hydrochloric, trifluoroethanoic and preferably a lower aliphatic acid containing 1 to 4 carbon atoms, is, preferably, thereafter admixed with the solution. 
     Suitable water soluble bromine-containing compounds are, for example, alkali metal bromates, such as lithium bromate, sodium bromate, potassium bromate, hydrogen bromate, and alkaline earth metal bromates such as magnesium bromate, calcium bromate and strontium bromate. Suitable iodine-containing compounds are, for example, alkali metal iodides, such as lithium iodide, sodium iodide, and potassium iodide; alkaline earth metal iodides such as magnesium iodide, calcium iodide and strontium iodide; ammonium iodide; hydrogen iodide; iodine monobromide and tribromide; and iodine oxides such as dioxide (IO 2 ), pentoxide (I 2  O 5 ), and nonoxide (I 4  O 9 ). 
     Addition of a soluble molybdenum compound to the solution, desirably before addition of the acid, has been found to improve the performance of the solution as an oxidant. The soluble molybdenum compound is believed to, at least initially, form a molybdate ion such as MoO 4   --  and Mo 2  O 7   -- . Although it is not necessary to the present invention, and in no way limits such invention, it is known in theory that iodates may complex with molybdates to form more complex iodine-molybdate structures. It is possible that such complexes are formed after the molybdate ion-forming compound is added to the solution. 
     Other bromine-, iodine- or molybdenum-containing materials may be employed providing such material will form the respective bromate, iodate or molybdate ion in the solution. 
     The described oxidizing material is an aqueous solution with an acidic pH. Oxidation of the leuco sulfur and vat dyes on fibers will occur at any pH below 7, but the rapidity of the oxidation is more commercially acceptable when the pH is about 5 or less. When the pH is lower than about 2.5, there may be a tendency for the oxidizing solution to cause some deterioration of the fibers. Therefore, it is preferred that the oxidizing solution of the present invention have a pH within the range of about 2.5 to about 5. A number of acids are quite satisfactory to impart the acidity to the solution; however, it is preferred that at least one of the lower aliphatic acids, i.e., acetic acid, propionic acid and butyric acid, be employed in an amount sufficient to produce the desired pH. Acetic acid is readily available and has been determined to be commercially satisfactory in solutions for oxidizing leuco dyes. 
     It is desired, and preferred for optimum performance, that the oxidizing solution, when initially made, contain about 0.4 to about 42 grams per liter (gpl) BrO 3   - , about 0.03 to about 12 gpl IO 3   31 , and about 0.02 to about 8 gpl molybdate ion. More preferably, the acidic solution contains about 0.4 to about 25 gpl BrO 3   - , about 0.03 to about 7 gpl IO 3   - , and sufficient molybdate ion to produce an about 0.5:1 to about 1:1 weight ratio with respect to IO 3   -  present in the solution. Additional molybdate can be used, but will not affect the performance of the oxidizing solution. 
     Following is illustrative of one method of making the oxidizing solution. About 0.05 to about 5 (preferably about 0.1 to about 3 ) weight percent (based on the final weight of the solution) of sodium or potassium bromate is added to water. Sodium or potassium iodide is added to the water in an amount adequate to produce a concentration equal to about 1 to about 25 (preferably about 5 to about 20) weight percent of the sodium or potassium bromate added to the water. 
     The soluble molybdenum compound, such as alkali metal molybdates, such as sodium and potassium molybdates, ammonium molybdate [(NH 4 ) 2  MoO 4] , ammonium paramolybdate [(NH 4 ) 6  MoO 7  O 24 .4H 2  O], MoO 3 .H 2  O and H 2  MoO 4  is preferably added in an amount equivalent to at least about 20 (preferably about 50 to about 120) weight percent of the sodium or potassium iodide. It is theorized that the molybdate ion, or a more complex molybdenum structure present in the solution, acts as a catalyst in the oxidation of iodides to iodates and periodates, and in the oxidation of a leuco sulfur or vat dye. 
     After the leuco sulfur- or vat dye-treated fibers are prepared for the oxidation step, the dye can be oxidized by procedures well known to those skilled in the art and which are used for other existing oxidizing agents. The temperature of the solution is not critical, but temperatures lower than about room temperature, i.e. about 20° C., may reduce the speed of oxidation sufficiently to be unfeasible in a commercial dying operation. Temperatures in excess of about 95° C. may require special equipment and/or begin to cause some deterioration of the fiber. Accordingly, it is preferred that oxidation be carried out within a temperature range of about 20° to about 95° C. Generally, however, temperatures of about 65° to about 75° C. have proven to be acceptable from a rate of oxidation standpoint and minimal deterioration of the fabric. 
     The normal fabric treatment procedures well known to those skilled in the art to be carried out before and after oxidation of the leuco sulfur- or vat dye-treated fabric are satisfactory in the present process. 
     The following examples are illustrative of the present invention. 
    
    
     EXAMPLES 1-19 
     The compositions of Examples 1-19 were formed by mixing with water the amounts of bromate, iodide and molybdate shown in the following table. After thoroughly mixing such compounds with the water to form a solution thereof, acetic, propionic or trifluoroethanoic acid was added to the solution in the amounts shown in the table. The solutions were again mixed to obtain a uniform composition and heated to about 70° to 75° C. for a sufficient time (about 4 to about 8 minutes) to produce substantially visually clear solutions. 
     The oxidizing solution was tested by applying Sodyesul Liquid Brown 7RCF dye (Sodeco Division of Martin Marietta Chemicals Company) to a sample of a standard finely woven 100 percent 80×80 bleached cotton print cloth style number 400 (available from Test Fabrics, Inc., Middlesex, N.J.). The cloth was steamed for one minute and thereafter rinsed in warm water to remove excess dye. Pressure was applied to the fabric to remove excess water. The fabric was then oxidized by dipping in the bromate solution a sufficient number of times to oxidize the dye. Each &#34;dip&#34; cycle time, i.e. the total time of cloth immerison in the solution and time the cloth was in the air between immersions, was about three seconds. 
     It was determined that the oxidizing solutions of Examples 1-19 were suitable for oxidizing leuco sulfur dyes. In a manner similar to that described above, the composition of the present invention was employed to oxidize the following Sodyesul liquid dyes on cotton fabric: Brown FCF and CRCF, Blue 2GBCF, Navy GFCF, Orange RDCRF, and Yellow ECF. 
     COMPARATIVE EXAMPLES A AND B 
     Examples A and B are identical to the compositions of Examples 18 and 19 , respectively, with the exception that Examples A and B do not contain a catalytic amount of a molybdate as in Examples 18 and 19. It was observed in Example A that the color of the fabric was not completely developed after oxidizing for a total of 30 to 35 seconds whereas the catalyst containing solution of Example 18 oxidized the leuco dye sufficiently in 12 to 15 seconds to produce a color of good depth. In a like manner, the catalyst-free composition of Example B resulted in oxidation of the dye to produce a good color depth only after oxidizing for 18 to 21 seconds. In contrast, the solution of Example 19 oxidized the leuco dye on the cotton fabric sufficiently in only 6 to 9 seconds to produce a very good color depth. 
     
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                                            Time To                       
                                            Complete                      
                                Oxidation   Oxidation of                  
Example (a)                                                               
       NaBrO.sub.3                                                        
            KI    H.sub.2 MoO.sub.4                                       
                       Na.sub.2 MoO.sub.4 . 2H.sub.2 O                    
                                Temp. °C.                          
                                      No. of dips                         
                                            Dye (Sec.)                    
__________________________________________________________________________
1      1.0  0.1   0.1  (none)   70    5-6   15-20                         
2      1.0  0.1   0.1  &#34;        27    7-9   21-27                         
3      1.0   0.05  0.05                                                   
                       &#34;        70     8-10 24-30                         
4      1.0   0.05  0.05                                                   
                       &#34;        30    12-18 36-42                         
5      1.0  0.1   0.1  &#34;        26    5-7   15-21                         
6      1.0  (0.1 NaI)                                                     
                  (none)                                                  
                       0.1      70    3-6    9-18                         
7(b)   1.0  0.2   &#34;    0.2      70    3     9                             
8      1.0  0.2   &#34;    0.2      26    4      12                           
9(c)   1.0  0.2   &#34;    0.2      26    3-4    9-12                         
10(d)  1.0  0.1   &#34;    0.1      70    3-4    9-12                         
11(d)  1.0  0.1   &#34;    0.1      80    5-6   15-18                         
12     1.0  (0.1 NH.sub.4 I)                                              
                  &#34;    0.1      70    3-4    9-12                         
13     1.0  (0.1 NH.sub.4 I)                                              
                  &#34;    0.1      28    5-6   15-18                         
14     1.0  (0.1 CaI.sub.2)                                               
                  &#34;    0.1      70    3-4    9-12                         
15     1.0  (0.1 CaI.sub.2)                                               
                  &#34;    0.1      32    5-6   15-18                         
16(e)  1.0  0.1   &#34;    0.1      25    4-5   12-15                         
17(e)  1.0  0.1   &#34;    0.1      70    2-3   6-9                           
18     1.0  (0.11 KIO.sub.3)                                              
                  &#34;    0.1      25    4-5   12-15                         
19     1.0  (0.11 KIO.sub.3)                                              
                  &#34;    0.1      70    2-3   6-9                           
A      1.0  (0.11 KIO.sub.3)                                              
                  &#34;    (none)   25    10-11 30-35                         
B      1.0  (0.11 KIO.sub.3)                                              
                  &#34;    &#34;        70    6-7   18-21                         
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 (a) All quantities are based upon grams per liter of oxidizing solution; 
 unless otherwise noted, 7.5 gpl of acetic acid (CH.sub.3 COOH) was added 
 to the oxidizing solution (pH of the solution was about 3.9).            
 (b) Differential pulse polarography analysis showed the solution included
 0.86 gpl NaBrO.sub.3, 0.22 gpl KIO.sub.3 and 0.029 gpl KIO.sub.4 ;       
 molybdate, and other ions not affecting the basic characteristics of the 
 solution as an oxidizing agent were also present.                        
 (c) pH was adjusted to 3.2 with acetic acid.                             
 (d) The solution was acidified by adding 9.25 gpl of propionic acid      
 (CH.sub.3 CH.sub.2 COOH).                                                
 (e) The solution was acidified by adding 0.6 gpl of trifluorethanioc acid
 (CF.sub.3 COOH) to provide a pH of about 4.0.