US2397193A - Wood bleach and process of making same - Google Patents

Description

Patented Mar. 26, 1946 um'rso mm, auteur asses 2,391,193 woon unseen an: masses or assume Gustavus Harry Miller, Portland, Urea.

No Drawing.

Application May 115, 1M2, Serial No. 4%,170

' 3 Claims. (on. ass-as) This invention relates to bleaching wood and more particularly to bleaching the surfaces of plywood and hardwood veneers used in the woodworking and'iurn'iture industries, the principal object being to provide a bleach that will lighten dark wood surfaces to a uniform color, at ordinary temperatures without distorting the wood surface or unduly raising the grain, or otherwise rendering the surface unfit for application of finishing coatings immediately following the bleaching operation.

Another object of this invention is to provide an economical, quick acting and quick-drying odorless bleach which, when sprayed, will penetrate the surface of the wood sumciently to provide a permanently and uniformly bleached surface, in one operation, which does not require cleaning or the application of alcohol as a neutralizer before applying the finishing materials.

Such simple methods of application as spraying,

,shing', or dipping are used without regard to e and temperature regulation. soaking or immersing the material tor long periods of time as'in former bleaching processes is definitely unnecessary and furthermore is undesirable since deep penetration of the liquid into the wood tends to raise the grain thereof.

- A further object of this invention is to provide a simple prepared bleaching solution which comprises adding one part by volume hydrogen peroxide solution to an equal portion by volume of an alkali solution and, this combination as an active ouidizins= agent will remain relatively stable at normal temperatures for four hours.

In prior art, wooden articles were bleached by the oxidizing action of hydrogen peroxide in a closed system usually at elevated temperatures, together with added amounts of sodium silicate, Dil'ophosphate, or potassium permanganate, and often in the presence of ammonia. Unevenness of color resulted in the harder portions of the grain and the softer wood fiber, and over-absorption of the bleach solution invariably required after-drying of the wood at additional expense, with a tendencyto checking, before finishes could be applied. Wood surfaces were also bleached by the use of a solution containing three parts'hydroge'n peroxideilioya by weight).

to one part by volume an alkali solution composed of sodium silicate and lime. The early methods were not able to provide a definite pH' control and therefore the surface of the wood was either too alkaline or too acid; and, for this reason, alcohol was often used as a neutralizer. Furthermore, due to the sodium tetrasilicate contained in the alkali mixture, a crystallized iorma tion resulted on drying which would not respond satisfactorily to the finishing material.

Another well known process is to use three parts by volume of hydrogen peroride to one part by volume of ammonium hydroxide.

When ammonia is used as the alkaline solution and hydrogen peroxide as the acid solution, the obnoxious ammonia fumes must he guarded against with proper equipment (masks) to protect the operator from the intolerable irritatinl!r fumes.

Now, in accordance with the present invention and as hereinafter described and set forth in the examples of this invention, the bleaching solution composed of a mixture oi one part by volume of aqueous hydrogen peroxide by weight), and in equal portion by volume of an alkali solution, an active oxygen producing agent is provided to realize a uniformly bleached sur face, without external aids, ready for finishing: material, which is relatively stable from four to five hours at normal temperatures (Iii-475 This practically odorless solution can he applied. to the wood surface by either brush, spray, or dip in. the usual manner, and although the surface is generally wet sufilciently to obtain a penetra tion of about one-twentieth inch, it will dry at room temperature in about an hour. Preferred results are obtained at V5 to 85 iii, without the aid of ammonia vapor. sin itional application is an improvement when sen hard or badly stained and difiioult types of wood. are encouu tered.

The desired results are obtained within narrow The borax is added to an 800 cc. beaker with'the caustic sodaon top; six ounces of water are slow ly added with constant stirring; when dissolved, add the sodium tetrasilicate and follow with the balance of the water. cool and clear up. crystal-clear liquid.

Let stand over night to Decant or syphon oil the The foregoing eoueous slimline solution with a pH of 10.? is added in equal volume to. en aqueoushydrogen perorzide solution (see, weight) with a pH of 2.5 immediately prior to epplication to the wood surface. The combined solutions have an initial pH of 9.7 end will retain their bleaching properties for four hours at normal temperatures; applied as a. bleach to the wood,

the surface, when dry, will be free from residue and require no neutralizing before applying the finishing materials.

is prepared in u, ten gallon mixing tank provided with an agitator; such eqiupment should be made to withstand the corrosive action oi on ueous caustic solution and the agitator geared to a. speed sufiicientto keep the materials from set= tling to the bottom until dissolved.

Add the water to the mixing tank and start the agitator, then slowly add the boron, sodium hydroxide, and sodium tetrasilicnte; when dissolved, draw off the aqueous alkaline solution" into a settling tank to cool and clear up before filling into stock containers which ere usually glass bottles closed with a rubber stopper.

Twenty-four pounds of the above alkaline solution is added to twenty-four pounds of an aqueous hydrogen peroxide solution by weight) immediately prior to application to the wood surface as a colorless, odorless wood bleach to provide a bleached surface free from residue that does not require neutralizing before applying such finishing materials as woodstains, fillers,

clear primers. varnish, or lacquer.

Example II! An aqueous solution containing:

Pounds Borax (sodium tetraborate)..-.. .c......- 1 Caustoc sode. (sodium hydromdel ,2 Sodium tetrosilicate 1 Water 21 is prepared in e. mixing tank provided with a. spigot two inches from the bottom and equipped with an agitator, the speed of which shall be sumcient to keep the materials from settling to the bottom while mixing. Such equipment should be made of material that will withstand the corrosive action of an aqueous caustic solution.

The water is added to the tank eud'the borax, sodium hydroxide, and sodium tetrasillcate slowly added with constant agitation; when dissolved. the solution is allowed to cool and clear up before filling into stock containers which are often rubber or glass lined or glass bottles with rubber stoppers.

.The above composition is added in equal proportion by weight to aqueous hydrogen peroxide solution (30% by weight) to provide a colorless, odorless wood bleach, which, applied to the wood surface by either spray, brush, or dip, will provide e. bleached surface from residue that requires no neutral n before opplg 52in ishing motorists.

Example IV An equecus solution containing: Borax (sodium tetraborate from the bottom. so that the clear liquid can be drawn of! without disturbing the residue left on the bottom. A wooden paddle may be used as a stirrer. I

The borax is added to the mixing tank and the sodium hydroxide is put on jtop. Eighteen gallons of water are slowly added with constant stirring; whendissolved, add the sodium tetrasilicate and follow with thebalance of the water. Let stand over night to cool and clear up. It is now ready to draw off into suitable containers. The above described solution with a pH of 10.9 is added to an equal volume of an aqueous hydrogen peroxide solution with a pH of 2.5; at the time the two solutions are combined as a' bleach, they will have a pH of 9.7; one hour later, a, pH of 9.8; two hours later, a. pH of 9.9 which remains quite constant for three hours at a room temperature of 68-72? F. usually after twenty-four hours, the bubbling subsides and theflnal pH value is 10.9; applied to either hard or soft wood surfaces, the combined solutions apparently un-, dergo an accelerated reaction whereby the oxidation or bleaching is accomplished in less than an hour at 75-80 15'. within a pH range from 9.7 at the time of application to a pH of 10.9 at the time of exhaustion. The definite action in the bleaching process is achieved by reason of the materials used in the proportions as prescribed in the examples and set forth in the claims; the sodium ion activates the oxidation at the surface when in solution with hydrogen peroxide and the sodium ion is greatlyenhanced when a hydrogen ion is also in solution. Borax and sodium tetrasllicate in the proportions indicated in the examples are both used as mild activators of hydrogen peroxide and as buffering agents to retard the action of thesodium ion on the cellulose and DOIYPSSCOhI-OSB compounds in wood.

The reaction, when completed, leaves no ash or residue on the wood surface which has the final appearance of having been cleaned and bleached is prepared by adding the borax and caustic soda to a suitable mixing tank; fifty-one gallons of water are slowly .added with constant stirring until the materials are completely dissolved; the sodium tetrasilicate is dispersed in the solution, and the agitator is stopped to allow the liquid to cool and clear up.

The mixing tank may be made of iron or steel and lined with a non-corrosivematerlal such as Pyrex glass or synthetic rubber, equipped with a suitable agitator of a corrosion-proof metal with provision made for drawing oil th liquid so that the impurities as sediment which collects on the bottom of the tank are not disturbed. The residue is removed and the tank i washed aft-er each operation.

The above described solution with a pH of 10.5-11 is added to an equal volume of hydrogen peroxide solution with a pH of 4-5; within five minutes from the time of combining the two solutions, a fairly constant pH of 9.5- is reached and shows little change for about four hours. After a period of twenty-four hours, the oxygen has been practically expelled and the solution has a PH of 10541.

By reason of the buffer action brought about by the given proportions of waterglass and borax,

' the action of the sodium ion on the wood fibre is such as to bring about the optimum conditions for an oxidizing action on the wood surface. The definite action in the bleaching process is achieved by the admixture of the materials in the proportions as prescribed in the examples and set forth in the claims.

Although the present invention has been described in the foregoing examples with specific details, it is not intended that such details shall be regarded as limitations upon the scope of the in vention, except insofar as is included in th accompanying claims.

What I claim is:

l. A method of bleaching smooth wood surfaces which have been otherwise finally conditioned for receiving finishing coatings without adversely affecting such surfaces which comprises applying a thin film of a bleach solution consisting of about one volume of an alkali component consisting substantially of one part by weight borax, two parts by weight caustic soda, one part by weight 42 B. waterglass, twenty parts by weight water, and a second component consisting of a substantially equal volume of hydrogen peroxide (30% by weight), said two components having been mixed together substantially immediately before the application thereof to said wood surface. permitting said wood surface to dry at room temperature after the application of said film thereto whereby said wood surface is left smooth, free from residue, and in condition for immediately receiving finishing coatings.

2. A method of bleaching a smooth wood surface which will leave the surface clean, free of rough crystalline residue, substantially neutral and otherwise unaltered as concerns the application of finishing coatings onto the bleached surface, which method comprises spraying onto the wood surface a thin film of a bleach solution consisting substantially of a freshly mixed mixture of equal volumes of hydrogen peroxide (30% by weight) and an alkaline solution consisting of one part by weight borax, two parts by weight caustic soda, one part by weight 42 B. waterglass, and twenty parts by weight water, and allowing s id wood surface to dry thereafter at room temperature to minimize penetration of the solution into the wood whereby the grain of the wood is not raised and the surface of the wood left clean and smooth.

3. A bleaching solution for bleaching smooth wood surfaces which have been otherwise finalhr conditioned for receiving finishing coatings which solution consists of a mixture of two substantially equal volumes of previously prepared components, one of said components consisting substantially of one part by weight borax, two parts by weight caustic soda, one part by weight 42 B. waterglass, 20 parts by weight water, the second component consisting of hydrogen peroxide (30% by weight), said solution being adapted for spray application onto said wood surface immediately after the mixing of said two components and being characterized by the fact that upon drying of said wood surface at room temperature following such application, said wood surface is left smooth, free from residue and in condition for immediately receiving finishing coatings.

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