US2733120A - Ouakum kuuivi - Google Patents

Description

eese PROCESS OF BLEACHING DURING LAUNDERING Homer L. Robson, Lewiston, N. Y., and William H. Sheltmire, Baltimore, Md., assignors to Olin Mathieson Chemical Corporation, a corporation of Virginia N Drawing. Application October 12, 1953, Serial No. 385,706

3 Claims. (Cl. 8-137) Our invention relates to improvements in laundry bleaching practice whereby calcium hypochlorite compositions are added as dry products directly to the laundry wash wheel in the presence of soap.

In commercial laundering, most of the goods to be washed are composed of white cotton goods which the laundry operator wishes to deliver in a clean, sterile condition with a high degree of whiteness. To aid in achieving this condition bleaching is employed. In commercial laundry practice, the washing cycle consists of many changes of water, usually about ten. The laundry cycle starts with a break in which the clothes are washed in a wheel in an alkaline liquor which may or may not contain soap. After several minutes of washing in this liquor, the wheel is drained and several washings follow with suflicient soap to give detergency. Normally about four such suds treatments are employed with the wash, liquor being drained from the wheel after each suds treatment. Bleaching is usually done in the last suds. Following the last suds usually about four rinses are employed, followed by a sour and blue operation.

Because of the well-known reaction of calcium salts with soap solutions by which considerable soap is consumed by reaction with the calcium salts to form calcium soaps and because of the resulting troublesome deposits and residues, calcium hypochlorite as such has not been employed in laundries for bleaching. The addition of a calcium salt, such as calcium hypochlorite, to the soap liquors containing some soap results in precipitation of calcium soaps upon the clothing. This usually shows up in the form of visible soap specs or fiecs on the cloth because of the tendency of calcium soaps under some conditions to form insoluble macroscopic curds which suggest dirt and frequently do carry a minor portion of dirt. They are also objectionable in that rancidity may develop from the calcium soaps of the washed cloth if stored for long periods of time. Not all of the calcium soap will appear in the form of specs or flees, however, but some may be in a molecularly dis persed form, distributed throughout the cloth which, when in limited amounts may be unobjectionable. The presence of soap specs or flecs, however, amounting to less than one half a per cent on the dry weight of the cloth, may make the washing treatment unsatisfactory for laundry standards. Frequently, laundry standards require a complete absence of calcium soap deposits in the form of spots. Because of this, commercial laundries employ dilute sodium hypochlorite solutions for the bleaching operation. The sodium hypochlorite bleach solution is customarily added to the wash wheel in the last of a succession of washing operations or suds. The addition of the sodium hypochlorite solution is usually fixed at 2 quarts of a one per cent available chlorine solution for each 100 pounds dry weight of wash load in the wheel.

Many methods of obtaining the sodium hypochlorite solution are available to laundries. The instability of solid sodium hypochlorite is well known so that no prep- Patented Jan. 31, 1956 aration based on this material is commercially available. The sodium hypochlorite solution may be obtained as such in concentrated form in glass carboys but is not stable, thus limiting storage time, and generally must be diluted before being added to the wash wheel to avoid damage to the cloth. More general practice, however, is to prepare a stock solution, usually at a concentration of one per cent available chlorine, from solid calcium hypochlorite. The calcium hypochlorite is converted to sodium hypochlorite by reacting it with soda ash with the simultaneous formation of highly insoluble calcium carbonate:

The precipitaed chalk is permitted to settle and then the supernatant liquid is removed by siphoning or otherwise for subsequent use in the wash wheel. The common trade practice has been for the laundry to procure the high test calcium hypochlorite and soda ash as separate items. Recently, a product has been available which provides a suitably proportioned loose mixture of calcium hypochlorite and soda ash, containing a dessicant, e. g., quickline, to inhibit decomposition of the hypochlorite, which permits the preparation of sodium hypochlorite solutions from a single product.

All these methods of utilizing sodium hypochlorite solutions are objectionable, however, because of incon venience in preparing the solution, for example, the requirement of providing settling time, subsequent disposal of sludge, and the destructive action of the solution upon operators clothes. Although it has been proposed to add the dry mixture, in an equivalent amount of available chlorine, directly to the wash wheel, the procedure has been found infeasible because of excessive soap destruction and deposition of insoluble calcium soaps. The formation of calcium soaps by reaction between the sodium soaps present in the wash wheel and the calcium ions from the quick dissolving calcium hypochlorite (and the relatively slow dissolving calcium hydroxide formed by hydration of the quicklime dessicant) occurs despite the fact that the mixture may contain more than the reactive amount of sodium carbonate required to combine with the total calcium content of the mixture to form highly insoluble calcium carbonate. This can best be explained by the fact that the sodium soaps are already in the solution and therefore grab or selectively react with a disproportionately high share of the calcium ions to form equally insoluble calcium soaps together with sodium hypochlorite. Hence, when loose mixtures of this type are added directly to the wash wheel an excessive degree of soap destruction is experienced. For example, if such a mixture, containing sodium carbonate 20 per cent in excess of the calcium reactive proportion, is directly added to a hot soap solution (1 gpl soap at 60 C.) to an amount representing a dosage quantity of p. p. m. of available chlorine, upwards of 70 per cent of the soap is destroyed.

Surprisingly, we have now found that high test calcium hypochlorite may be added in dry form directly to the laundry wash wheel in the presence of soap under cer tain conditions in amounts sufiicient to effect the desired bleaching without deposition of undesirable amounts of calcium soap in the cloth. We have found that a minimum concentration of soap is required in solution to which calcium salts are added to form calcium soap curds which would deposit on cloth in the form of undesirable specs or flees. Thus, we have found that calcium hypochlorite compositions can be added in dry form directly to the laundry wash wheel in the presence of the limited amounts of soap, i. e. about 100 to 200 p. p. m., normally present in certain stages of the rinsing cycles of laundry practice. Advantageously, the addition is made seamen more to liquors containing not more than about 150 p. p. m. of soap. The addition of calcium hypochlorite to the rinsing cycle in which such concentrations of soap are present results in the deposition of allowable amounts of calcium soaps which are distributed evenly over the cloth, and at lower levels of soap concentration calcium soaps are not deposited in any manner. Thus the process of our invention provides an advantageous, convenient and effective manner of bleaching in commercial laundry practice.

According to the process of our invention, the calcium hypochlorite compositions are added in dry form to one of the rinsing steps, other than the initial rinse, prior to the final rinse in regular laundry practice. Generally about 1 to 3 ounces of a calcium hypochlorite preparation, containing about 37 to 40 per cent available chlorine, per 100 pounds of clothes is sufiicient for good bleaching action. The second rinsing operation offers particular advantages as the soap concentration is normally between about 100 and 200 p. p. m. In washing heavily soiled materials, however, it is advantageous to provide an extra rinse to adequately reduce the larger than normal soap content caused by the larger than normal portions of soap and alkali that may be employed. In such a case, it is advantageous to add the calcium hypochlorite during a rinsing step after this extra rinse, and preferably during the third rinse. At such soap concentrations, only negligible amounts of calcium soaps will be deposited on the cloth, and these calcium soaps are not in the form of objectionable soap specs or fiecs. Such soaps as are deposited are molecularly dispersed and distributed generally throughout the cloth and have no noticeable effect on the hand or outward physical properties of the cloth. At lower soap concentrations, no calcium soaps are deposited on the cloth. It is desirable to avoid adding the calcium hypochlorite composition too late in the rinsing cycle as some available chlorine may carry over into the sour and blue operation where it may cause trouble. Thus, according to our invention dry calcium hypochlorite is added directly to the wash wheel without any deleterious effect on the whiteness rctention of the cloth.

It is important that the calcium hypochlorite be free flowing, non-lumping and quick dissolving. With a fast dissolving material, calcium soap curds are not formed whereas if large grains or slow dissolving grains are added to unstirred or slowly stirred soap solutions, some calcium soap curds may form during the process of solution and these curds may be later retained on the cloth. Therefore, it is important that the calcium hypochlorite be finely divided, but to minimize dustiness in handling while providing a rapid rate of solubility in the wash wheel, the particle sizing commercially obtained by passing calcium hypochlorite through about a 30-mesh screen with retention on about a 60-mesh screen is particularly advantageous.

The calcium hypochlorite compositions useful in the process of our invention are preferably those prepared from stable high test calcium hypochlorite which is high in available chlorine and low in lime and calcium chloride. A preferred calcium hypochlorite product is prepared as described in U. S. Patent 1,787,048 and is particularly useful. characteristically, commercial products of this type contain about 70 per cent available chlorine. The calcium hypochlorite compositions disclosed in the pending application, Serial No. 400,120, filed December 23, 1953, of James D. McMahon, which contain a minor amount of sodium tripolyphosphate, e. g. about 2 to weight per cent, are particularly useful in that the turbidity of the resulting solutions is greatly reduced.

The proportion of high test calcium hypochlorite used in the compositions may approximate 40 to 95 weight per cent but advantageously approximates 40 to about 65 weight per cent. The compositions advantageously contain quicklime or calcium oxide, e. g. about 4 to 10 weight per cent, or other dessicant, for storage stability. Advantageously, flake salt is added as a diluent to aid in the rapid dispersing and solution of the calcium hypochlorite when added to the laundry wash wheel. In addition, the compositions may contain other compatible ingredients such as sodium silicate, sodium bicarbonate, soda ash, and the like. Also, it may be desirable to incorporate a detergent of the synthetic organic type, or additives such as CMC (carboxymethyl cellulose) in order to facilitate rinsing or to add to the effectiveness of the compositions.

While I do not propose to limit the invention by the explanation of the mechanism responsible, it appears that when calcium hypochlorite is added to a soap solution containing less soap than that corresponding to the critical micelle concentration, calcium soap curds which would deposit on the cloth as specs or fiecs are not formed but instead molecularly dispersed calcium soaps form which do not precipitate on the cloth. In laundering, when soap is added to a water solution, at the temperatures normally employed in a laundry, i. c. 140 to 160 F., the first portion goes into solution in a molecular state. This molecularly dispersed soap while aiding in wetting the cloth does not have appreciable detergent power, however, and the soap concentration must be raised so that the molecules aggregate into structures commonly termed micelles, which are the effective detergent agents in washing operations. The concentration to which soap may be added While remaining molecularly dispersed will vary with the other constituents in the solution, for example soil, and the composition of the soap. The concentration may be as high as 600 p. p. in. when the soap is dissolved in pure water, but when alkaline salts or Builders are added, micelle formation is aided and the soap concentration may be reduced to below 200 p. p. m. The concentration at which micelle formation starts is termed the critical micelle concentration." Once the critical micelle concentration is reached, further addition of soap to the solution results in increased formation of micelles, with usually negligible further increase in molecularly dispersed soap. In commercial laundry operation fairly standard soap consumption has been developed. Thus, in the standard operation, the soap concentration in the first suds is about 1000 to 1500 p. p. m. and builders are added to depress the critical micelle concentration to about 250 to 350 p. p. in. More soap is added to give detergency and in the last suds the concentration of soap is normally in the range of 400 to 500 p. p. m. in the wash liquor, which is within the micelle range. In the rinsing operation the soap concentration is reduced and in the second rinse is about to p. p. m.

We have found that addition of calcium salts to soap solutions produces a moderate lowering of the critical micelle concentration, as would be expected from the addition of a water soluble salt. However, when the soap solution contains more soap than that corresponding to the critical micelle concentration, we have found that the addition of calcium salts causes the formation of soap curds. When the soap concentration is clearly below the critical micelle concentration, by an amount sufiicient to allow for the building effect of the added calcium salts, then calcium soap curds do not form. Instead, molecularly dispersed calcium soaps form which do not precipitate on the cloth and which may be repeatedly filtered through cloth without adsorption on the cloth at normal laundering temperatures of about to F.

If the temperature drops sufficiently, however, the critical micelle concentration changes and calcium soap will form insoluble particles. Also, at temperatures above about F., soap curds may form from added calcium salts at micelle concentrations which would not cause soap curd formation at normal temperatures of 140 to 160 F. At this higher temperature, a rapid treatment of the cloth may avoid the deposition of soap curds while a slower treatment will not. To avoid damage to cloth goods, however, laundries generally avoid the use of these excessive temperatures.

Thus, we have found that in normal laundry practice calcium hypochlorite can be added in dry form to wash liquors containing not more than about 200 p. p. m. of soap, advantageously not more than about 150 p. p. m., and the normal concentration of builders, i. e. below the critical micelle concentration, in suflicient amount to effect the desired bleaching without deposition of undesirable calcium soap specs or flecs on the cloth.

We claim:

1. In a process of laundering in which the wash load is subjected to a washing cycle with an aqueous solution of soap followed by a rinsing cycle consisting of a plurality of rinsing steps, the method of bleaching the wash load in the presence of soap which comprises adding a dry bleaching composition which essentially comprises a high-test calcium hypochlorite during a rinsing step, other than the first rinse, in which the soap concentration is not more than about 200 p. p. m. prior to flhe final rinse.

2. In a process of laundering in which the wash load is subjected to a washing cycle with an aqueous solution of soap followed by a rinsing cycle consisting of a plurality of rinsing steps, the method of bleaching the wash load in the presence of soap which comprises adding a dry bleaching composition which essentially comprises a high-test calcium hypochlorite during the second rinsing step in which the soap concentration is not more than about 200 p. p. m.

3. In a process of laundering in which the wash load is subjected to a washing cycle with an aqueous solution of soap followed by a rinsing cycle consisting of a plurality of rinsing steps, the method of bleaching the wash load in the presence of soap which comprises adding a dry bleaching composition which essentially comprises a high-test calcium hypochlorite during a rinsing step in which the soap concentration is not more than about 200 p. p. m. prior to the final rinse.

References Cited in the file of this patent UNITED STATES PATENTS 98,387 Jeanning Dec. 28, 1869 1,515,647 Airheart Nov. 18, 1924 1,777,858 Phair Oct. 7, 1930 1,961,606 Ells June 5, 1934 OTHER REFERENCES Procter & Gamble Co., The Washroom, 1927, pp. 74 and 75.

Claims (1)

1. IN A PROCESS OF LAUNDERING IN WHICH THE WASH LOAD IS SUBJECTED TO A WASHING CYCLE WITH AN AQUEOUS SOLUTION OF SOAP FOLLOWED BY A RINSING CYCLE CONSISTING OF A PLURALITY OF RINSING STEPS, THE METHOD OF BLEACHING THE WASH LOAD IN THE PRESENCE OF SOAP WHICH COMPRISES ADDING A DRY BLEACHING COMPOSITION WHICH ESSENTIALLY COMPRISES A HIGH-TEST CALCIUM HYPOCHLORITE DURING A RINSING STEP, OTHER THAN THE FIRST RINSE, IN WHICH THE SOAP CONCENTRATION IS NOT MORE THAN ABOUT 200 P. P. M. PRIOR TO THE FINAL RINSE.