WO2003024680A1

WO2003024680A1 - Wood-preserving agent containing crude tall oil

Info

Publication number: WO2003024680A1
Application number: PCT/SE2002/001661
Authority: WO
Inventors: Bengt Carlsson
Original assignee: Bengt Carlsson
Priority date: 2001-09-14
Filing date: 2002-09-16
Publication date: 2003-03-27
Also published as: SE0103074L; SE0103074D0; SE520125C2

Abstract

Wood-preserving agent based on crude tall oil with addition of at least 10 % resin acids. Use of crude tall oil with addition of resin acids as wood-preserving agent. Method for pressure impregnation with the wood-preserving agent according to the invention. Method for after-treatment of impregnated wood by prolonged impregnation at elevated temperature or by cooking in water.

Description

WOOD-PRESERVING AGENT CONTAINING CRUDE TALL OIL

The present invention relates to a wood-preserving agent based on crude tall oil.

Prior art

Crude tall oil is recovered from sulphate cooking of both softwood and hardwood.

Crude tall oil from softwood has the approximate composition: 50% resin acids, 30% fatty acids and, the remainder, 20% more or less non- saponifiable extractive substances.

Tall oil from hardwood contains no resin acids.

By mixing softwood and hardwood, a tall oil of varying composition is obtained: - resin acids 0-70%

- fatty acids 20-70% remainder 10-30%

Tall oil is distilled (in Sweden by Arizona Chem.) to resin acids for coating paper and to fatty acids for alkyd production. The remainder is burned.

Tall oil is an interesting alternative wood-preserving agent. It is known to use tall oil for impregnating wood. A problem which has not yet been solved is that the products impregnated with tall oil "sweat" oil and are "sticky" for an unacceptably long time. The technique is therefore not employed at the present time.

SE-C2-509 980 describes a method for impregnating a wood product, in which method a solid acid anhydride, a vegetable oil, for example tall oil, and an alcohol are used as impregnating agent. The treated wood product is heated at a temperature of above 150°C in order to bind the oil. To avoid tackiness from the tall oil, it is therefore necessary, according to said patent specification, to add both solid anhydride and alcohol and to heat at a high temperature. However, the method has not been found to give sufficiently good results and has therefore not gained commercial application (6 years after the priority date).

SU 1555131 describes an impregnating agent for fibre boards which contains 58- 75%o tall oil pitch and in addition higher fatty acids from tall oil. Admixture of the fatty acids improves the penetration and shortens the impregnation time. There is no indication as to how the impregnated product is intended to be made non-tacky.

SE 9401356-2 describes a wood-preserving method in which a "crude tall oil composition" is used. The aim is to obtain a tall oil which contains more fatty acids than resin acids in order to achieve a lower viscosity. The weight ratio between fatty acids and resin acids is to be at least 1 :1 and can be up to 10:1. Moreover, a solvent is expediently added. Seeping of crude tall oil from the treated wood can be substantially reduced or even eliminated by addition of siccatives or organic compounds, for example pinene turpentine.

Swedish patent application 9903126-2 describes in purely general terms the pressure-impregnation of wood with tall oil which can contain a penetrating agent and also other additives, mention also being made of fractions of tall oil soap or sulphate soap. To obtain a dry surface, after-treatment is carried out using a fixing agent which is preferably a solution of alkaline phosphates in water.

Object of the invention

It is an object of the invention to make available an effective wood-preserving agent which provides a dry and usable surface on the impregnated wood item.

A further object is to permit use of crude tall oil in an impregnating agent for wood, without the above-described problems occurring. A further object is to provide a method for non-stick treatment of wood which has been impregnated with a tall oil product and is not completely free from tackiness.

Brief description of the invention

These objects are achieved by means of a wood-preserving agent in which crude tall oil with an admixture of resin acids is used for impregnating wood. Thus, it has been surprisingly found that a usable impregnating agent is obtained simply by increasing the crude tall oil's content of resin acids. The addition can vary from 10 to 95 percent by weight, although preference is given to using an addition of at least 15%), suitably at least 20%> and in particular at least 30%. The addition is suitably at most 80%, preferably at most 70% and in particular at most 60%, all of these figures being based on the weight of the tall oil. A maximum added amount of 50% is particularly preferred. The amount of resin acids which has to be added is dependent on the resin acid content of the original oil. For each crude tall oil, a skilled person will easily be able to determine how much resin acid is needed in order to ensure that a treated product will be non-tacky.

The invention also relates to a method for pressure-impregnation using the present wood-preserving agent. The invention further relates to a method of after-treatment in which the wood is left in the wood-preserving agent after reduction of the pressure, or, after removal from the wood-preserving agent and possible drying, is again immersed in a wood-preserving agent according to the invention, the wood- preserving agent maintaining a temperature of at least 100°C during the after- treatment. Another possibility is to cook the impregnated wood in water, preferably for at least 5 minutes.

Detailed description of the invention

The wood-preserving agent according to the invention preferably consists of only tall oil and an addition of resin acids. No siccative, such as Mn, is included. Turpentine or other natural or synthetic substances which increase the wood- preserving effect can be added, but this is not necessary.

To dissolve the resin acids in the crude tall oil, these have to be heated. A temperature of about 120°C is preferably used. It is not necessary to use a vacuum. It suffices to pressure-impregnate the wood products to obtain the desired result.

The invention is described in more detail below with reference to illustrative embodiments. Test specimens have been impregnated and tested for possible bleeding by being subjected to heat for 1 week through exposure to the sun when placed against a wall. The test specimens are judged to have been exposed to a temperature of 25-40°C.

Examples

Tall oil from AssiDoman Frδvifors and resin acids from Arizona Chemicals were used in the tests.

Test l : 5841 g of tall oil and 1543 g of resin were used in the test. This corresponds to an admixture of 26% based on the amount of tall oil or 21% based on the amount of finished mixture. The resin acids were dissolved in the tall oil at about 120°C from solid form. The whole mixture was heated to about 175°C. The pieces of wood were impregnated for 20 minutes at a pressure of 7 kp/cm . The result is shown in Table 1 below. Table 1

This gives an average weight increase of 256 g or the equivalent of 409 kg/m sapwood.

Test piece No. B45 was tested under a heating lamp for 2 hours at 70°C. The test piece bled, and the excess of tall oil and resin ran down towards the short end. Where bleeding occurred, the surface dried after the heating lamp was removed.

After week 1, the test pieces in test series 45 did not have a surface completely free from tackiness. This, therefore, was not a completely satisfactory result.

Test 2

In this test, the content of resin was increased to 35%, based on the amount of tall oil (26%o of the total amount). Amount of tall oil 6079 g, resin 2148 g. The temperature at the start of the pressure phase was 135°C and at the end of the pressure phase it was 88°C. Impregnation pressure 7 kp/cm for 20 minutes. The result is shown in Table 2. Table 2

This gives an average weight increase of 225 g or the equivalent of 306 kg/cm sapwood. The test pieces A and C were afterwards subjected to a vacuum of 0.9 kp/cm² for 30 minutes, without any noticeable result. After 1 week, the test pieces in test series 46 had a dry, slightly sticky surface. However, the surface was non- tacky.

Test 3

In this test, the content of resin was increased to 42%, based on the amount of tall oil used (30% of the total weight). Amount of tall oil 6342 g, resin 2661 g. The temperature at the start of the pressure phase was 140°C and at the end of the pressure phase it was 85°C. Impregnation for 20 minutes at a pressure of 7 kp/cm . The result is shown in Table 3.

Table 3

This gives an average weight increase of 198 g or 317 kg/cm sapwood. After 1 week, the test pieces in test series 47 had a dry and fine surface which was non- tacky.

Test 4

In this test, the same mixture was used as in test 3. The temperature at the start of the pressure phase was 145°C and at the end of the pressure phase it was 100°C. The impregnation was carried out for 15 minutes at a pressure of 10 kp/cm . The result is shown in Table 4.

Table 4

This gives an average weight increase of 299 g or 478 kg/cm sapwood. After 1 week, the test pieces in test series 49 had a dry and fine surface which was non- tacky.

In the above-described tests with admixture of resin in tall oil, it was found that in cases of admixture of resin of less than 30%» of the amount of tall oil, the result obtained was a surface not completely free from tackiness (test No. 1) or a slightly sticky surface (test No. 2). However, for an oil which from the outset contains a larger amount of resin acids, a lower addition can suffice to achieve a non-tacky surface. Tests for subsequently obtaining a completely dry surface on the test pieces

In these tests, test specimens from previous tests 1 and 2 were used. The test specimens were still tacky or slightly sticky on the surface.

Test 5 was carried out so that 2 test specimens from test series 1 and 2 (piece Nos. B45 and B46) were immersed in boiling water for 10 minutes. After heating, the test specimens were left to cool at room temperature. After about 5 minutes, all the test specimens had a very dry and fine surface. All the test specimens decreased slightly in weight after the cooking.

Test 6 was carried out so that 3 test specimens from test series 1 and 2 (piece Nos. A45, C45 and C46) were put in a heated mixture of tall oil and resin (same mixture as was used in the pressure phase during the impregnation). The oil had been heated beforehand to 120°C. During the test, the temperature was maintained at this level.

The test specimens were left to lie in the mixture of tall oil and resin for 2 hours. After this, the test specimens were allowed to stand and cool at room temperature. After about 5 minutes, these test specimens too had a very dry and fine surface. All the test specimens in this test also decreased slightly in weight.

The test specimens Nos. C45 and B46 were tested with a heating lamp for a total of VΔ hours. Not until the wood surface had attained a temperature of 70°C, did the test specimens begin to bleed. The bleeding intensified during the 40 minutes for which the specimens were exposed to further heating up to 82°C. After the heat was removed, the test specimens recovered their dry and fine surface. Conclusion

All the test specimens in tests 2, 3 and 4 show that it is possible to obtain a non- tacky surface by impregnation with a mixture of crude tall oil and resin acids. According to these tests, the added amount of resin should be at least 30-35%), based on the amount of tall oil, to obtain a completely satisfactory result. However, this amount depends on how much resin the crude tall oil contains from the outset.

The test specimens in tests 5 and 6 show that it is possible to obtain a non-tacky and completely dry surface on the test specimens which have been impregnated with an agent with a resin addition of less than 30%> of the amount of tall oil if, after impregnation, these test specimens are either cooked in water or are left to lie in the oil mixture which is then heated to above 100°C. In addition, these test specimens acquired a more even shade of colour than the test specimens which did not undergo after-treatment with heat.

The invention is defined in the attached patent claims and must not be seen as being limited to the above illustrative embodiments. All modifications and variations within the scope of the claims are possible.

Claims

1. Wood-preserving agent containing a tall oil product, characterized in that it contains crude tall oil which has been enriched with resin acids by addition of at least 10%> thereof, based on the amount of tall oil.

2. Wood-preserving agent according to Claim 1, characterized in that the added amount of resin acids is at most 95 percent by weight, based on the tall oil.

3. Wood-preserving agent according to Claim 2, characterized in that the added amount of resin acids is at least 15%, preferably at least 20%> and in particular at least 25%, based on the amount of tall oil.

4. Wood-preserving agent according to Claim 3, characterized in that the added amount of resin acids is at least 30%, preferably at least 35%, based on the amount of tall oil.

5. Wood-preserving agent according to any of Claims 1-4, characterized in that the added amount of resin acids is at most 80%>, preferably at most 70%, based on the amount of tall oil.

6. Wood-preserving agent according to any of Claims 1-4, characterized in that the added amount of resin acids is at most 60%>, preferably at most 50%>, based on the amount of tall oil.

7. Use of crude tall oil with addition of resin acids according to any of Claims 1-6 for impregnation of wood.

8. Method for impregnation of wood, characterized in that wood is pressure- impregnated with a wood-preserving agent according to any of Claims 1-6 at a temperature, at the start of the pressure phase, of at least 70°C, preferably at least 90°C and in particular at least about 110°C, the impregnated wood being removed from the oil after normalization of the pressure.

9. Method according to Claim 8, characterized by an after-treatment in which the wood is left in the wood-preserving agent after reduction of the pressure, or, after removal from the wood-preserving agent and possible drying, is immersed again in a wood-preserving agent according to any of Claims 1-6, the wood-preserving agent being maintained at a temperature of at least 100°C during the after-treatment.

10. Method according to Claim 8, characterized by an after-treatment in which the impregnated wood, after removal from the wood-preserving agent, is cooked in water, preferably for at least 5 minutes.