US1766606A - Impregnated wood and process of treating wood - Google Patents

Description

Patented June 24, 1930 JOSEPH R. COOLIDGE, 31), OF BROOKLINE,

I PATENT OFFICE MASSACHUSETTS, ns'srenon T MONTAN,

INCL, OF BOSTON, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS IMPREGNATED WOOD AND PROCESS OF TREATING 'W OOD No Drawing.

This invention relates to the impregnation of wood with agents designed to render it resistant to fire or decay, or for the purpose of improving the characteristics of the wood in other respects.

' Thenatunal inflammability of wood, its susceptibility to decay and to attack by wood boring animalcule are serious objections to its use for many purposes. In order to m overcome these objections it is now a common practice to impregnate wood with various materials depending upon the properties which are to be imparted to'it. For example, it is a usual practice to impregnate Wood with creosote or toxic salts such as zinc chloride, copper sulphate, and the like, in order to render it resistant to decay. The impregnation of wood with certain salts to reduce its combustibility is also well known,

although not as widely practiced. Such salts as borax, ammonium sulphate, ammonium chloride, and others, have been used exten sively for this purpose, and a considerable number of salts which are commonly used for wood impregnation are valuable both for their fireproofing properties and also as preservative agents. A very serious objection, however, to any impregnation with water soluble materials is the fact that the impregnating medium leaches rapidly from the wood when it is exposed to the weather. For example, shingles impregnated with fireproofing or preservative salts lose these agents very rapidly so that in a relatively short time they are no better, from a practical standpoint, than shingles which have I not been treated. It has also been found that when flooring and interior finish are impregnated with any of the common fireproofing 49 salts, such saltsabsorb moisture from the atmosphere in damp weather, notwithstanding the presence of finish coatings of varnish, shellac, or the like, and the solutions resulting from such absorption frequently attack the finish, and in any event leave discolored spots or streaks whichare highly objectionable from the standpoint of appearance.

The present invention deals with this prob- 50 lem, and it aims to devise a thoroughly prac- Application filed June 3, 1927. Serial No. 196,394.

tical method of impregnating wood to protect it either from fire, decay, or the like, which will eifectually overcome the objections above described.

Some of the more common fireproofing salts, such as ammonium chloride and ammonium sulphate, depend for their fireproofing properties upon the fact that when heated to temperatures somewhat below the combustion point of the wood they give off non- 6o combustible vapors or gases. Other fireproofing salts, such as borax, lose their water of crystallization, or partially decompose at high temperatures, and the water vapor or steam which results from such decomposition mixes with and dilutes the combustible gases created by the heating of the wood. It is preferable to make use of both types of salts, and for this reason, and also from considerations of economy, it is preferable 7 to use borax as one of the constituents of the impregnating medium. However, almost any impregnatiomin order to proceed ethciently, must be carried on at elevated temperatures, and if borax is present in the impregnating solution it produces a very ob jectionable discoloration of the wood. While this discoloration may be reduced materially by conducting the process at a lower temperature, this involves an increased treating period and therefore a greater expense. Ac-

cordingly, it is 'a further object of this invention to prevent such discoloration while still carrying onthe process at elevated temperatures. 5 Still another objection to the use of borax is the fact that if present in high concentrations it attacks the intercellular structure of the wood .and weakens it materially. I have found, however, that this objection can be avoided by using ammonium chloride or ammonium sulphate with the borax. A further advantage derived from this combination is that notwithstanding the fact that ammonium chloride and ammonium sulphate are very corrosive and attack the linings of the cylinders of the treatin plants, and

even in the treated wood pro uce corrosion of the nails and metal parts in contact with it, still when either ammonium chloride or 1011 ammonium sulphate is used with borax the objectionable features of both salts are substantially neutralized. Consequently, an impregnation with this combination of salts does not weaken the structure of the wood to any material degree, and the corrosive action of the ammonium chloride or ammonium sulphate is practically eliminated.

Considering first the problem of preventing discoloration of the wood, I have found after a long series of experiments that this objectionable action can be avoided by using ammonium phosphate with the borax. For fireproofing treatments satisfactory results can be produced by using ammonium chloride or ammonium sulphate (these two chemicals being equivalents so far as this invention is concerned) borax, and ammonium phosphate in approximately equal proportions.

However, I have further discovered that if common rock salt, or. sodium chloride, is used with the above, or a similar mixture of fireproofing salts, the penetration of the entire salt mixture is improved very surprisingly. In other words, if a typical fireproofing treatment is made with borax, ammonium chloride and ammonium phosphate, and a second treatment then is made under the same conditions with the same salts plus a considerable percentage of rock salt, it will be found that a very much higher concentration of salts has been forced into the wood in the second treatment than in the first. And this is true notwithstanding the fact that the concentration of salts in the treating solution is the same in both cases and that the same time, temperature and pressure conditions are maintained in making both treatments. This is a very important advantage, especially when high concentrations of salts must be introduced into the wood. While this action may not be produced in all species of woods, it does occur in a large number of our common species, such as white and red cedar, white and red oak, hemlock, and others.

A further advantage attending the use of rock salt is that it reduces the expense of the treatment. Both the borax and ammonium chloride are cheap, while the ammonium phosphate is too expensive to use alone, but the rock salt is so much cheaper than any of the other ingredients, that by using all four of these salts in approximate- 1y equal proportions, the expense of the mixture is brought down to very reasonable limits.

For fireproofing treatments a solution of from 20% to 40% of these salts by weight in water is suitable. I prefer to make the solution by mixing the salts in the proportion of one pound of salts to two pounds of water, and to force this solution into the wood at a fairly high temperature, say for example, 180 to 200 F. Assuming that the wood under treatment is dry red oak flooring, an entirely satisfactory impregnation may be produced by forcing the solution into the wood at a temperature of say 190 F. under two hundred pounds pressure for a period of from two to three hours.

This impregnation should be performed in F. This results in introducing a high concentration of the salts in the wood.

It should be understoodthat the impregnation could be performed in other ways, and that the exact procedure adopted will necessarily depend upon the equipment available, the kind of wood being treated,

the size of the pieces of wood under treatment, and various other practical considerations well understood by those skilled in this art.

The process above described produces a very complete impregnation of the wood, makes it highly resistant to fire, can be practiced economically, and avoids any objectionable discoloration of the wood. The wood so treated is either air dried or kiln dried, as desired, and it is then ready for certain uses.

However, the process so far described deals simply with the problem of devising an effective and entirely practical method of rendering wood resistant to fire while avoiding discoloration and certain of the other ob ectionable features of prior practices. Vhile wood treated in this manner is entirely satisfactory for some purposes, it would not be suitable for use in wet locations, or where exposed to the weather, for the reason that the salts, being soluble in water, would leach from the wood and its resistance to fire thus would gradually be lessened. A further feature 0 this invention, therefore, deals with the sealing of these salts in the wood so that they will be protected from any harmful action of moisture.

The discovery of a material which will effectively hold the salts in the wood without, at the same time, reducing its fireproofing properties has proved to be a very difficult matter. After a long series of experiments I have discovered that an impregnation with ordinary soap satisfies these requirements.

In order to prepare the wood for this soap impregnation, it is preferable to remove the excess water which has been forced into the wood during the impregnation above described with the salt solution. This may be done by removing the wood from the cylinder and allowing it to partially dry out, but preferably this object is accomplished by subjecting the wood to a vacuum while it still remains in the treating cylinder and immediately at the conclusion of the salt impregnation. It is necessary to remove only about of the water which has been introduced in the first impregnating step, and whether this is done by air or kiln drying, or by subjecting the wood to a vacuum while still in the cylinder will depend largely upon conditions obtaining at the treating plant.

According to this invention the wood which has previously been impregnated with salts is now impregnated with a solution of soap, ordinary laundry soap being satisfactory. A solution of one part ordinary soap with five parts of water can be used with good results. In view of the fact, however, that ordinary soap contains considerable water, in some cases as high as 4.0%, it is preferable to use soap from which the water has been practically eliminated, and a solution made by dissolving one part, by weight,

' of dry soap in ten parts of water is satisfactory. This impregnation is best performed in a pressure cylinder, the solution being kept hot at, say 150 F., and forced into the wood under a pressure of from 150 to 200 pounds for a period of one hour. The temperature, pressure, and the length of the treatment will be determined by the size of the pieces being treated and other practical considerations. The wood then is removed from the cylinder and stacked where it can drain and dry out.

While the action which takes place in the wood is somewhat obscure, it seems clear that the impregnation with the fireproofing salts results in the .deposit of these salts on and in the-walls of the pores and tracheids of the wood. The subsequent impregnation with soap results in coating the walls with this material, some of the soap solution preferably also entering the cell walls. A considerable part of this soap apparently combines with ingredients in the salts and produces an insoluble metallic soap. It may be also that some of the soap, either soluble or insoluble, plugs or seals the tracheids. In any event the soap, does protect the water soluble salts from dissolving in moisture which is absorbed by the wood. The salts above mentioned are of the ordinary commercial variety, as distinguished from the chemically pure salts, so that there are doubtless associated with them, as impuri-' ties, various metal salts which will combine with the soap to produce an insoluble soap. Dyes also can be mixed with the treating 65 solution.

It is preferable, however, for most purposes not to rely on the presence of such impurities to produce an insoluble soap in the wood, and consequently, I prefer to mix with the salts which are used in making the first impregnation some salt, such as aluminum sulphate,-copper sulphate, or the like, which definitely will combine with the soap introduced in the subsequent treatment to produce an insoluble metallic soap. For this reason I prefer in making the fireproofing treatment above described to use with the borax, ammonium chloride, ammonium phosphate and comomn salt, a proportion of aluminum sulphate equal to approximately one-half the weight of the borax. While many salts other than aluminum sulphate could be used for this purpose, as will be obvious to those familiar with the manufac ture of insoluble soaps, I prefer this particular salt because it is cheap and it combines with the soap to make an excellent ofiicial tests prescribed by the city of New York. An extremely important advantage of wood fireproofed in this manner is that it retains its fire resistant characteristics indefinitely, even when exposed to the weather,

whereas wood treated by the comomn commercial processes gradualy loses its fireproofing salts when used out of doors or in damp locations. A very important. practical advantage of this process is the fact that it can be practiced in the ordinary commercial treating plants without requiring any material change in equipment.

The fireproofing properties of the soap'may be further increased by adding to the soap solution a small proportion, say 25% of the weight of the soap, of some material such as aradichlorbenzene. Usually, however, this is not"necessary.

Wood treated as above described, in addition to being fireproofed, is also highly resistant to decay. But it contains a much higher concentration of salts than is neces sary simply to preserve it from decay. That is, .it may be necessary to add as much as nine or ten pounds of dry salts to a'cubic foot of wood of some species to protect it efi'ectually from fire, whereas a very much lower weight of salts would be sufficient to preserve it from decay. Where, therefore, the fundamental object in treating the wood is to preserve it, the same process above described can 'be followed and with the same salts, (although the ammonium chloride is not necessary) but the concentration can be reduced materially. Also, in making a preservative treatment the process may be somewhat simplified by stopping the first impregnation when a sufiicient quantity of the reservative has been forced into the w to give it the desired degree of toxicity. Assuming, for example, that the solution consists of borax, ammonium phosphate, and aluminum sulphate, and that the wood under treatment is dry red oak, the first step could be stopped when the weight of the wood had been increased by a proximately The cylinder then shou d be washed out, some pressure being maintained during this washing 0 eration, and the soap solution then can be admitted to the cylinder and the second step of the process started atonce. A suflicient wei ht of the soap solution should be forced into the wood so that the dry weight of the soap introduced will be about three times the dry weight of the aluminum sulphate. While this process thus involves two steps or movements,-

it, uires but a single handlin of the wood, and the intermediate step a ve de scribed of removin the excess water introduced in the first impregnation is avoided. While the borax is a ood toxic preservative, it can be replaces by other preservatives, such as zinc chloride, copper sulphate, sodium fluoride, and others.

Man variations of the method above describe may be practiced within the scope of the invention. For exam 1e, under some circumstances it may be su cient simply to make an impregnation with insoluble soap, the metallic soap being formed in the wood by subjecting it to successive impregnations of salt and soluble-soap. Obviously the soluble soap also could be produced in the wood but this would involve additional expense with no advantage.

Essentially the same process can also be used in protecting other impregating agents than those particularly mentioned. For example, wood can be given an empty cell treatment with creosote and some of the disagreeable features of the wood so treated. can be eliminated by sealing the creosote in with an insoluble metallic soap. Either the soluble soap or the aluminum sulphate, or other salt which is to unite with the soap, can be combined with the creosote in giving the first impregnation, a subsequent impregnation being made with the ingredient necessary to act on the soap or salt to produce an insoluble soap.

In some cases, also, it may be referable to confine the impregnation with t e insoluble soap to the outer strata of the wood where its function as a sealing agentis more essential. In such cases the soap impregnation can be made by the open tank process.

The methods above described can also be used to advantage in treating wall board, fibre board, and the like, whichconsist chiefly or largely of fibre of a woody nature, and they are particularly valuable in fireproofing products of this character. Some of these wall boards or fibre boards have a relatively o 11 structure, as for example that known as lotex, so that no impre ation problem is involved, while others require substantially the same treatment as wood.

I have found it entirely possible. also, to mold articles of pulp or wood fibre. the fibre bein thoroughly moistened with aluminum sulphate, then to impregnate the molded article with a soap solution. When this product dries out it is very firmly bonded to gether, is hard and stable, and is thereafter extremel resistant to the action of moisture. It shoul be understood therefore, that the term wood is used in t e a pended claims, to include fibre articles 0 the character above described.

-It should also be understood that the, word impregnation is intended to designate a treatment which penetrates the pores and tracheids of the wood for a substantial depth, as distinguished from a mere superficial treatment or surface coating which probably never penetrates the wood for a depth of more t an one sixty-fourth of an inch.

This application is a continuation in part of my pending applications Serial Nos. 155,- 766, filed December 18, 1926, and 181,276, filed April 5, 1927, but the claims in this case are limited to subject matter not claimed in said earlier applications.

Having this described my invention, what I desire to claim as new is:

1. An article of the character described comprising wood impregnated for a substantial depth with borax and ammonium phosphate.

2. An article of the character described comprising wood, the pores and cells of which for a substantial depth are impregnated with a mixture of borax, ammonium chloride and ammonium phosphate.

3. That improvement in processes of treating wood which consists in impregnating the wood at elevated temperatures with a solution containing borax associated with a sufiicient quantity of ammonium phosphate to prevent discoloration of the wood.

4. That improvement in processes of treating wood which consists in impregnating the wood at elevated temperatures with a water solution of borax, ammonium phosphate and ammonium chloride in substantial proportions.

5. That im rovement in processes of treating wood which consists in forcing into the pores and cells of the wood a hot watersolution of protective salts including borax v and ammonium phosphate, the solution having a concentration of from 15% to 410%.

6. That improvement in processes of fireproofing wood, which consists in impregnating the wood with water soluble fireproofing salts including a sufficient percentage of common salt to promote the penetration of the entire solution.

7. That improvement in processes of treating wood which consists in impregnating the wood at elevated temperatures with a water solution of fireproofing salts including borax, ammonium phosphate and common salt.

8. That improvement in processes of treating wood which consists in impregnating the wood at elevated temperatures with a water solution of borax,- ammonium phosphate and ammonium chloride and sodium chloride. I

9. An article of the character described comprising wood, the pores and cells of which for a substantial depth are impregnated with a mixture of borax, ammonium "chloride, ammonium phosphate and common salt.

JOSEPH R. COOLIDGE, III.