GB2228199A - Insect-proof treatment of rubber wood - Google Patents

Abstract

Rubber wood is immersed in boiling water and is then immersed in water at a lower temperature containing boric acid and borax in a combined concentration of 5%-10%, in order to render the wood insect-proof and resistant to discolouration and bacterial putrefaction.

Description

A METHOD OF INSECT-PROOF TREATMENT OF RUBBER WOOD DESCRIPTION The present invention relates to a method of insect-proof treatment for rubber wood.

Rubber wood, when air-dried, has a specific gravity of 0.6 - 0.7. Its color is white or light yellow, and because of its hardness and bend-less quality, it is most suitable for furniture and building materials. In particular, since rubber trees are replanted at intervals of 25 - 30 years, there is an abundant supply of rubber wood, and besides, as rubber trees are planted on flat wand, the cutting down, collection and transportation of the trees are easy. There fore, as compared with Japanese oak, Japanese beech, "sen", "tamo", birch, and wood of other broadleaf trees, which are now being used widely in many countries, the rubber wood is in an advantageous position from the standpoint of competitiveness in cost, equality and stable availability.

Although rubber wood has such advantages, it is, unfortunately, liable to be damaged by bacteria and insects, and consequently, it has hitherto been difficult to fully utilize it by making the best use of its qualities.

The damage by bacteria and insects are caused by the following factors: 1 Damage by discoloring bacteria and putrefying bacteria The rubber wood contains in its vessels and gap portions a large amount of latex (consisting of vegetable rubber substance, starch substance, essential oil, oi3 and fat, oleic acid, and other components), and immediate after sawina into lumbers, the latex together with sqlution of other components exudes to the surface of tbe wood. The exudate is eaten away by discolorina and putrefying bacteria within a short period of time. As a result, the wood is discolored, thereby greatly lowering the usability of the wood.

The rubber wood is acidic with its pH being 4 - 5. Many of its components are starch substances such es latex, and in addition, it contains tannin. Therefore, the rubber wood is apt to easi]y turn reddish due to chemical chanvesscaused by air and ultraviolet rav of the sunliaFt, and discoloration to reddish brown occurs within a short time not only on the surface but also in all parts of the wood, and this areatly decreases commodity value of the wood.

2 Damaae by insects Latex, one of the components of the rubber wood, is present in all ports of the wood substance. It gives off a characteristic smell which insects like, and this smell attracts insects, which then eat the wood and lay eags in it. The rubber wood, even after dried and fabricated into furniture or processed into building materials, and even when used as such, is always subject to deface by insects.

For these reasons, in recent years, there have been made many studies and experiments to remove such weak points peculiar to rubber wood. However, the main method for removal was either to use chemicals with subsequent environmental pollution or to use costly, complicated pressure tanks.

In preventing the damage by insects and bacteria, the method of this invention uses neither pollution-causina chemicals nor costly pressure tanks. It is a very easy treating methdd by which the damage can be successfully prevented.

In the method of this invention, two water tanks A and B are prepared for treating rubber wood. Tank A is so desianed that water in it containing no chemical can be boiled either by direct heating or by jetting hot steam into the water.

TahkB is filled with water, to which is added an aqueous solution of boric acid and borax in such a way that the combined concentration of boric acid and borax in the tank is maintained at 5 - 10%.

First, rubber wood sawn into a suitable size is immediately taken into tank A, and is boiled. The boiling time varies with the thickness of the wood, with a standard set at 60 min for 4/4" and 120 min for 8/4". Upon finishing the boiling in tank A, the wood is transferred to tank B containing cold aqueous solution of a mixture of boric acid and borax, and there the wood is treated for a necessary period of time depending on the thickness of the wood.

When the thickness of the wood is large, and it takes a long time to treat the wood in tank B resulting in a poor treating efficiency, the treating time in tank B may be shortened, and the wood is taken out of'the tank B earlier. The wood thus taken out is piled up, and the outside of the stack of wood is covered with an airtight plastic sheet, and the wood is left there for a necessary period of time depending on the thickness of the wood. By so doing, the solution of boric acid and borax is allowed to permeate into the wood by replacement. For tank B, cold water without any heating is used.

However, when the wood treated in tank A at a high temperature is immediately taken into tank B, the temperature cf the water in tank B tends to go up to some extent. It will go up to about 250C, and when the wood is kept in water, the temperature may further go up 280C - 330C. However, the temperature increased to this much of extent may be said to be a comparatively low temperature, and therefore is allowable.

By treating rubber wood successively in tank A in which the wood is boiled and in tank B where the wood is treated in water containing boric acid and borax as in the method of this invention, the discoloration and putrefaction of the wood can be prevented completely, and thus it becomes possible to make the rubber wood insect-proof without spoiing its characteristic white or light yellow color.

As mentioned above, the treating method of this invention is a simple and easy one. It has been found that the effect of this process comes from the following factors: (a) By boiling the rubber wood in tank A, the wood is heated at.a uniform temperature, thereby dissolving substances and waste materials filling pores of the vessels and gap portions of the rubber wood; and by heating, the pressure in the wood rises, as a result of which the dissolved filling substances-and waste materials are pressed out of the wood, and this smoothens the flow of water and air in the wood substance. Moreover, when heated, the rubber wood becomes soft, thereby making it easier for the pores of cell membrane loosen and close. Also, when rubber wood thus boiled in tank A is taken out of tank A and transferred immediately, in a hot state, into tank B containing cold aqueous solution of boric acid and borax, the cold waterrcontaining a mixture of boric acid and borax, whose specific gravity is large, violently permeates into the empty spaces in the pores of vessels and gap portions of wood substance brought about by heating process in tank A. When permeating, the aqueous solution of boric acid and borax replaces hot water remaining the wood substance, and thus the aqueous solution of boric acid and borax spreads into all parts of the wood substance.

In such a way, the cold aqueous solution of a mixture of boric acid and borax becomes the bound water of the wood substance, and as a result, the mixture of boric acid and borax remains in the wood substance even after drying of wood, thereby giving an insect-proof property to the rubber wood for a long time.

(b) By this insect-proof treatment, the anti-discoloration treatment can also be accomplished at the same time.

That is to say, by the boiling in tank A, the solution of wood components that exuded to the surface of the wood, which is a factor in causing discoloration, is dissolved away, and at the same time, the wood components undergo a chemical change as a result of heating, thereby changing the latex and starch substances which bacteria like into substances the bacteria dislike. Furthermore, with the solution of a mixture of boric acid and borax having permeated into wood by replacement, the wood becomes a boric acid - borax containing material which resists any attack by discoloring and putrefying bacteria. It has also been confirmed that with this treatment, the pH of the wood changes from a strong acid pH to an alkaline pH, as a result of which the wood becomes resistant to discoloration by air or ultraviolet ray.

(c) In case the wood is of a large thickness, and it takes a long time to treat the wood in tank B, the treating time may be shortened for efficiency's sake. In this case, shortened treatment time is set beforehand for each thickness, and the wood is taken out of the tank according to this tame table. The wood taken out is piled up, and the outside of the stack is covered with an airtight plastic sheet, and the wood is lef-. there for a period of time sufficient for the solution of boric acid and borax to permeate into the wood.

By boiling wood in tank A, it becomes easy for the solution of boric acid and borax to permeate into the wood by replacement. In case of wood whose thickness is 50 mm, if it is left in the cover of the plastic sheet for 2 days after immersion in the solution of boric acid and borax, it will be possible for the solution to evenly permeate deep into the wood substance and stay there.

When the solution of boric acid and borax is applied directly to rubber wood without boiling process in tank A, and the wood is kept in the cover of the plastic sheet, the wood will discolor and-putrefy within 1 - 2 days, andsthus it becomes unfit for use.

When rubber wood has been boiled in tank A, followed by the process of immersion of the wood in the solution of boric acid and borax in tank B as in the method of this invention, there occurs neither discoloration nor putrefaction even when the wood is covered with a plastic sheet. Thus, the wood can be utilized without spoiling its sound quality and color.

As mentioned above, in the method of this invention, the method of injection under pressure in a pressure tank is not used in applying the insecticidal solution of a mixture of boric acid and borax to rubber wood, but the treatment of the wood is done by first giving hot water treatment in a tank, followed by a cold water treatment in another tank containing cold aqueous solution of insecticides. With these two steps of treatment, the insecticidal solution permeates evenly deep into all parts of the wood, and the insecticides stay in the tissues of the wood, thereby making the wood perfectly insect-proof. At the same time, the two steps also make the wood resistant to discoloring and putrefying bacteria, and also to discoloration by air and ultraviolet ray.Thus, this invention is an epoch-making one in that it has economically solved the problem of rubber wood, namely its weakness against insects and bacteria.

The results of experiments made based on the method of this invention are as shown in a separate sheet.

[Example] Into a reinforced concrete tank A 1.5 m in wideth, 3 m in length and 2 m in depth was poured water up to a depth of 1.2 m. Then, a bundle of rubber planks packed as under was put into the water in tank A with a crane: Rubber planks 25 mm and 50 mm in thickness are piled up into a stack I m in width, 1 m in length and 50 cm in height, with crosspieces 20 mm in thickness put between each piece of plank, and the stack is tied up with iron band.

Since the planks were of raw wood, they sank without a weight on them.

Hot, fresh steam generated in a boiler was jetted into the water through iron pipes set one at each of the four corners of tank. Then, the water came into a boiling state in about 30 min, maintaining 95 - 980C.

Of planks in tank A, those 25 mm in thickness were taken out after boiling for 60 min, and those 50 mm in thickness were taken out after boiling for 120 min, and the planks were immediately immersed into cold aqueous solution of boric acid and borax in tank B whose size is same as that of tank A.

In making aqueous solution of boric acid and borax for tank B, a powder mixture of 408 o; boric acid and 60% cf borax was added to the water in tank B (5.4 M3), with stirring, in such a way that the combined concentration of boric acid and borax comes to 5%. Of the planks immersed in tank B, those 25 mm in thickness were taken out after immersion for 60 min, and each plank was covered with a vinyl sheet, and left there for 24 hr. After that, planks 25 mm in thickness and those 50 mm in thickness were each halved into two portions.Half was put into an artificial drying chamber, and dried to a water content of 8%. The other half was taken to a lumber storage yard in the mill without drying, and was left there, in a piled up state, under the same conditions as those for untreated lumbers immediately after sawing.

Each of the artificially dried planks was sawn off into a 10 cm-wide piece at the lengthwide central part of the plank, and each of the 10 cm-wide piece thus prepared was further cut, with a hatchet, into a 10 cm-wide piece at its central part. With the cut side as testing surface, a 10% testing solution of curcumin-extracted alcohol was first dripped onto the cut surface with a filler. After the said testing solution dried, there was applied to the same surface, with a filler, another testing solution prepared by saturating a mixture of 10 cc of concentrated hydrochloric acid and 90 cc of alcohol with salicylic acid; and 10 min later, resulting color reaction was examined.

The test results were as follows: 10 pieces each of 25 mm-thick cut piece and 50 cm-thick cut piece were used for the color reaction test, and a red color reaction was observed in each of these test pieces.

The above red color reaction shows that over 0.2% of the insecticidal mixture of boric acid and borax is retained in the wood. According to literatures in other countries, it is recognized that the retention of over 0.2% is enough to give a satisfactory insect-proof effect.

Rubber wood to which insect-proof treatment had been given as above was stored in a testing box together with untreated rubber wood at a sawmill in Lyon Prefecture, Thailand to see how these test pieces would be damaged by insects. In about a month, the untreated.wood was damaged by insects to such an extent that the original shape of the test pieces was hardly retained. On the other hand, on treated wood, only traces of slight licking by insects were found, but no bores or other damage were observed.

Meanwhile, rubber wood treated as above was piled up in the mill without artificial trying along with untreated wood. The untreated wood was damaged by insects within 3 days, and discoloring and putrefying bacteria were growing and spreading all over the wood. On the other hand, on the treated wood, no damage by insects was seen even after 7 days, and no adhesion or growth of discoloring and putrefying bacteria was seen either. Moreover, untreated wood left outdoors turned dark brown on the surface in 24 hr, while treated wood left outdoors showed almost no discoloration, retaining its white color seen after treatment.

Test results of insect-proof treatment of rubber wood by boilling, and immersion in aqueous solution (cold water) of insecticides (Table)

Concentration of boric acid and borax in treating solution 1% 5% 10% Details of treatment Thickness of test wood (used ordinary 25 m/m 50 m/m 25 m/m 50 m/m 25 m/m 50 m/m rubber wood produced in Thailand) Boilling temperature (Tank A) 95 - 98 C 95 - 98 C 95 - 98 C 95 - 98 C 95 - 98 C 95 - 98 C 95 - 98 C Boilling time (Tank A) 30 min 60 min 60 min 120 min 30 min 60 min 120 min 30 min 60 min 60 min 120 min Temperature of solution of boric acid and horax (Tank B) 25 C 25 C 25 C 25 C 25 C 25 C 25 C 25 C 25 C 25 C 25 C 25 C Treating time with solution of boric acid and borax (Tank B) 60 min 50 min 120 min 120 min 60 min 60 min 120 min 120 min 60 min 60 min 120 min 120 min Color reaction Yellow Yellow Yellow Yellow Pink Red Pink Red Red Red Red Red (Yellow and pink - does not pass; Red - passes x x x x x0 0 x 0 0 0 0 0 30month test Test damage by insects (used wood borer and "kikul nagamushi" (long wood x x x x x 0 0 0 0 0 0 0 borer)) Growth of discoloring and putrefying bacteria (piled up indoors for 7 days) None None None None None None None None None None None None (Remarks) 1 Used a mixture of 40% of boric acid and 60% of borax 2 Since open tank was used, temperature did not go up beyond 98 C.

3 The temperature of aqueous solution of a mixture of boric acid and borax was 25 C initially, but when hot wood was immersed, it went up to 28 - 33 C.

4 As for reagents, the 1st reagent used was 10% solution of curcumin-extracted alcohol, and the 2nd reagent was a mixture of 10 cc of concentrated hydrochloric acid and 90 cc of alcohol saturerd with salicylic acid. Only red was taken as "pass". When color reaction is red, the wood is considered to have absorbed over 0.2% of insecticides.

5 For the color reaction test, the central part of the wood was used.

6 For test of damage by insects, 200 pieces of wood borer and long wood borer were put in the testing box, and they were left there to eat the test pieces.

Claims (2)

CLAINS

1. A method of insect-proof treatment of rubber wood comprising: (a) a step of boiling rubber wood in water of a high temperature, and (b) a step of immersing the rubber wood, for a certain period of time, in water of a low temperature containing boric acid and borax in a combined concentration of 5% - 10%.

2. A method of insect-proof treatment of rubber wood substantially as herein defined.