US3017236A - Hydrogen peroxide-alkali metal bicarbonate acidic bleaching process - Google Patents

Description

United States Patent i 3,017,236 HYDROGEN PEROXIDE-ALKALI METAL BICAR- BQNATE ACIDIC BLEACHING PRDfiESS Neil J. Stalter, Wilmington, Del, assignor to E. I. (lit .lont tle Nemours and t'Jompan-y, Wilmington, Del, a corporation of Delaware No Drawing. Filed Aug. 14, 1959, Ser. No. 833,710

2 Claims. (Cl. 8-111) This invention relates to the bleaching of various solid surfaces and to acidic bleaching solutions which are particularly adapted to effectively bleach solid surfaces with a minimum of attending disadvantages.

Hydrogen peroxide solutions have heretofore been employed or proposed for bleaching various solid surfaces such as those of wood, paperboard, paper and floor covering products such as linoleum and rubber tiles. The use of strongly alkaline peroxide solutions have almost invariably been regarded as necessary for bleaching such surfaces. Alkaline solutions containing caustic soda, sodium silicate or other common non-volatile alk'alies have been most widely used. Usually, leaching is effected 'by drying, e.g., by heating, such a solution on the surface to be bleached. This leaves a bleached surface coated with an objectionable gritty residue of non-volatile alkali. Such residue can be removed by further processing at extra cost, e.g. by neutralization with an acid followed by lashing. The use of ammonia as the alkaline agent has been proposed to avoid formation of such alkaline residue, but hydrogen peroxide solutions alkalized with ammonia do not give as effective bleaching as is generally desired. Furthermore, ammonia readily volatilizes with the formation of highly objectionable fumes.

It is an object of the invention to provide an improved peroxide method for bleaching such solid surfaces.

It is an additional object to provide an improved peroxide method for bleaching solid surfaces which avoids the use of strongly alkaline peroxide solutions, the formation of solid residues and objectionable fumes when the bleach solution is dried on the solid surfaces being bleached. It is another object to provide bleaching solutions which are especially Well suited for use in practicing the improved method of the invention. Still further objects will be apparent from the following description.

The objects of the invention are accomplished by the use of bleaching solutions which are aqueous acidic solutions containing 10-50% by weight hydrogen peroxide (H 0 and an alkali metal bicarbonate at a concentration of at least by weight, preferably -15% by weight. Solid surfaces can simply be wet or coated uniformly with the bleaching solution and the treated surfaces are then dried either at room or elevated temperatures.

Strong aqueous alkali bleaching solutions containing hydrogen peroxide and sufficient caustic soda to impart a relatively high pH have been successfully used to bleach wood surfaces. Generally these solutions are sprayed on wood surfaces at room temperature and thereafter the surfaces are dried at elevated temperatures until the water has been completely evaporated. A typical wood bleach contains:

Water gal 1 Caustic soda "lb... 1% Sodium silicate, 42 B oz 1 Lime oz 1 H202 gals 3 These alkali bleaching solutions have also been applied with good results to linoleum and similar hard-surface floor covering materials, such as rubber tile, which are hardened by a heat curing treatment that imparts a yellow discoloration. Unfortunately, alkaline solutions damage Patented Jan. 16, 1962 ice certain types of linoleum and cause pitting. Additionally, bleaching solutions containing caustic soda leave a gritty residue on the bleached surface.

To overcome these disadvantages a bleaching solution containing ammonium salts has been developed which has about a neutral pH (pl-l 6.5-7.5). Salts such as ammouium carbonate, bicarbonate, sesquicarbonate, hartshorn salt (NH HCO -NH COONH and the like are volatile and when applied to linoleum and subjected to elevated temperatures give off ammonia fumes. Ammonia fumes are irritating to personnel in the immediate drying area and necessitate the use of special drying controls. Another disadvantage of bleaching solutions containing the ammonia salts is that of wetting; aqueous solutions containing ammon um bicarbonate, for instance, do not satisfactorily wet linoleum, although this disadvantage is mitigated when a wetting agent is incorporated in the solution.

it has been found that if an alkali metal bicarbonate, preferably sodium bicarbonate, is used in slightly acidic peroxide bleaching solutions a more effective bleaching action is obtained when these solutions are applied to linoleum, wood, paperboard and other solid surfaces susceptible to the bleachin action of peroxide. Using the preferred bicarbonate, NaHCO in an amount of at least 5% by weight together with 10-50% hydrogen peroxide, a solution can be prepared which can be applied to practically any linoleum surface without damage to the surface. Furthermore, rapid assembly-line bleaching is possible because no noxious fumes are expelled when the treated surfaces are dried. In addition to excellent wetting characteristics, the solutions unexpectedly result in a superior bleach both in terms of the initial bleach obtained and in showing less reversion of color after being dried. In contrast to solutions containing caustic soda, the bleaching solutions of the present invention are easily prepared since they are endothermic, not exothermic.

The concentration of the preferred bicarbonate should be at least 5% by weight and preferably 10-15% by weight, although higher concentrations up to saturation concentration can be used.

The concentration of hydrogen peroxide in the bleaching composition generally should be at least 10% of the weight of the composition. Higher concentrations up to about 50% are suitable and those in the range 20 to 40% are generally preferred because of their rapid effective bleaching action, particularly when they also contain sodium bicarbonate at a concentration in the preferred range. The present compositions are readily prepared simply by dissolving the required amount of the sodium v bicarbonate compound in a commercial aqueous hydrogen peroxide, e.g., of about 27 to 50% strength. No cooling is required during their preparation to prevent peroxide decomposition.

Aqueous bleaching solutions of the above type free of reagents other than hydrogen peroxide and the alkali metal bicarbonate compound are highly effective for the present purpose and are generally preferred. They are weak acidic solutions having a pH of about 5.5-6.5.

Any of the solid surfaces heretofore known to respond to bleaching with hydrogen peroxide can in general be bleached by means of the present compositions. Illustrative are the surfaces of wood and wooden articles, paperboard, paper, fiber based acoustical tile such as wood pulp and bagasse tiles, and floor coverings such as linoleum, cork-tile, granulated cork pressed into sheets and rubber tile. These floor covering products are generally prepared from compositions which contain unsaturated materials such as drying oils or rubber which give surfaces a yellowish discoloration during the usual heat curing operation in the manufacture of such products. Such surfaces can be rapidly and effectively bleached simply by wetting or coating them uniformly with the present bleaching composition and permitting the wet surface to dry at ordinary or elevated temperatures.

Solutions were prepared as follows:

A. Ten parts of sodium bicarbonate (NaHCO were added to 90 parts of 35 aqueous hydrogen peroxide plus 1 part of a Wetting agent, alkyl aryl sodium sulfonate. This solution had a pH of 6.2.

B. Twenty parts of ammonium bicarbonate (NH4HCO3) were added to 80 parts of 35% aqueous hydrogen peroxide plus 1 part of wetting agent, alkyl aryl sodium sulfonate. This solution had a pH of 6.4.

C. One hundred twenty-eight parts of water were added to 20 parts of sodium hydroxide (NaOI-I), one-fifth of 1 part of calcium hydroxide (Ca(OH) 1 part of aque ous sodium silicate 42 B. and 1 part of the same wetting agent. This solution was then added to 450 parts of 35% aqueous hydrogen peroxide.

Each of solutions A, B and C were sponged onto separate sections of a piece of linoleum. An application of 0.12 lb./ sq. yd. was used. The samples were then dried for two minutes at 205-220 F., followed by a rinse in cold tap water.

The samples bleached with solution A had a superior bleach to samples bleached with solutions B and C. Solution A spread more easily and evenly on the linoleum than solution B, a decided advantage in the application of bleach solution on a production basis. Certain samples of linoleum showed damage in the form of pitting when bleached with solution C. There was no damage or pitting of samples bleached with solution A.

The use of a Wetting agent in solution A is not necessary but is preferred when used to bleach linoleum.

It was found that the use of solution B on a production basis created a problem due to the NH fumes given off. The fumes were irritating to personnel in the immediate area and special dryer control and construction was necessary to eliminate this problem.

Three solutions were prepared as follows:

A. Fifteen parts of solid sodium bicarbonate (NaHCO was dissolved in 85 parts of 35% hydrogen peroxide. The resulting solution had a pH of 5.5.

B. Fifteen parts of solid ammonium bicarbonate (NI-I I-ICO was dissolved in 85 parts of 35 hydrogen peroxide. The pH was 5.3.

C. A solution was prepared by adding 20 parts of caustic soda, 1 part of 42 B. aqueous sodium silicate and 1 part of calcium hydroxide, to 130 parts of water. One part of the resulting solution was then added to 3 parts of 35% aqueous hydrogen peroxide to give the bleaching solution.

Each of solutions A, B and C was sprayed onto separate marked portions of an unbleached hardboard sample. As much of each solution was sprayed on as would remain on the vertical surface. After spraying, the board was allowed to dry two minutes at room temperature and was then heated in an oven at 140 F. for five minutes. The surfaces in each case were bleached from 19 to 29 G.E. brightness but there was no reversion of brightness on standing for one month at room temperature using solution A. Reversion with solution B was. 20%.

Pine wood, was treated with each solution as above. Solutions A and B both bleached to about 45 GE. Wood bleached with NaHCO Formula A did not yellow or revert. in brightness on standing one month, whereas wood bleached with NH HCO formula yellowed up very noticeably. Formula C bleached only to 40 G.E.

'Walnut veneer was treated in a similar manner. Formula A had less yellowing after bleaching than B or C and was at a higher level of brightness.

In the above examples and throughout the specification, parts and percentages are by weight unless indicated otherwise.

Pie-cleaning of the surfaces with soap and water, a solution of an alkali or with an organic solvent which does not attack the surface, will permit employing hydrogen peroxide treating solutions free of wetting agents. However, when a linoleum surface to be treated has not been pro-cleaned to remove mold lubricants, the addition of a wetting agent to the peroxide solution will be advantageous in order to obtain uniform treatment. In such cases Wetting agent concentrations ranging from about 0.55% are suitable.

The peroxide treating solution may also contain a thickening agent for increasing its viscosity to facilitate uniform application and retention of the solution. Suitable for this purpose are the water-soluble salts of carboxymethyl cellulose and poly-acrylic acid.

The treatment with the peroxide solution is preferably effected by coating the solution onto the surface of the linoleum product. Application or" the solution can be made by any of the usual methods for applying liquids to surfaces, e.g., by dipping, spraying, sponging or brushing, or by means of roller-type applicators, the latter being generally preferred. The amount of solution to be applied will depend somewhat on the particular surface being treated and the composition of the solution used. In general, application of from 0.002 to 0.01 pound of solution per square foot of surface will be satisfactory for most purposes.

Following application of the solution to the discolored surface, the surface with the applied solution may be allowed to stand until the desired result has been accomplished. However, it is preferred to employ elevated temperatures to accelerate the decoloring action, particularly when continuous treatment is desired, as when treating continuous webs of material. Heating to dry the applied peroxide solution on the surface is particularly effective. This can readily be accomplished using radiant heaters, circulating hot air ovens or other conventional heating means. Oven temperatures of from about 300 to 700 F. have been used successfully under conditions such that the surface temperature of the product ranged from about to 180 F. Care should, of course, be used to avoid temperature suthciently high to damage the product. Another elfective heating method is to contact the coated sur face with a metal surface heated to a suitable temperature to effect rapid drying.

The invention provides a highly practical method for removing undesired yellow discoloration from floor and wall covering products such as linoleum and rubber tile. The present method is particularly well adapted for continuous operation in treating'materials of the above types. which can be processed in continuous length, with consequent important savings in time and labor over the procedure previously employed.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. The method of bleaching a solid surface responsive to bleaching with hydrogen peroxide selected from the group consisting of linoleum, rubber tile, wood, fiber based acoustical tile, and paperboard, comprising the step of coating said surface with an aqueous acidic bleaching solution having a pH about 5.5 to 6.5 and containing at least 5% by weight of an alkali metal bicarbonate and 10-50% by weight hydrogen peroxide.

2. The method of bleaching a solid surface responsive to bleaching with hydrogen peroxide selected from the group consisting of linoleum, rubber tile, wood, fiber based acoustical tile, and paperboard, comprising the step of coating said surface with an aqueous acidic bleaching solution having a pH about 5.5-65 and containing 10- 5 15% by weight of sodium bicarbonate and 20-40% by 2,166,954 Kauffmann et a1 July 25, 1939 Weight hydrogen peroxide. 2,185,632 Hill et a1. J an. 2, 1940 2,203,589 Baymiller June 4, 1940 References Cited m the file of thls patent 2, 891819 Hawkinson July 7 1959 UNITED STATES PATENTS 5 2,960,382 Kelley et a1 Nov. 15, 1960 1,986,672 Bergman Jan. 1, 1935

Claims (1)

1. THE METHOD OF BLECHING A SOLID SURFACE RESPONSIVE TO BLEACHING WITH HYDROGEN PEROXIDE SELECTED FROM THE GROUP CONSISTING OF LINOLEUM, RUBBER TILE, WOOD FIBER BASED ACOUSTICAL TILE, AND PAPERBOARD, COMPRISING THE STEP OF COATING SAID SURFACE WITH AN AQUEOUS ACIDIC BLEACHING SOLUTION HAVING A PH ABOUT 5.5 TO 6.5 AND CONTAINING AT LEAST 5% BY WEIGHT OF AN ALKALI METAL BICARBONATE AND 10-50% BY WEIGHT HYDROGEN PEROXIDE.