FI57361C - FOERFARANDE FOER BEHANDLING AV VIRKE GENOM IMPREGNERING MED KONSERVERINGSMEDEL - Google Patents

Description

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Patent · och registrerttyralsan 'AraMcan uthgd ech utijkrifun pubitcund 30.04.o0 (32) (33) (31) Pyyrf-tty privilege-Begird prioriwt (71) Hager Aktiebolag, Kryssarvägen 17, 183 52 Täby, Sweden-Sverige (SE) (72) ) Bror Olof Eager, Djursholm, Sweden-Sweden (SE) "(74) Berggren Oy Ab (54) Method for treating wood by impregnation with preservative -Förfarande för behandling av virke genom impregnering med konserverings-medel v

Finnish patent 45,626 describes a wood treatment method. It involves impregnation with an aqueous solution containing a preservative and drying and surface treatment in warm oil under vacuum. Impregnation provides rot protection. the oil provides surface protection against moisture and cracking, etc. If the oil is pigmented, the wood will get color. Drying is very fast, it saves time and brings other savings, it is also very gentle.

The method is facilitated if the oil and water - impregnation solution - are not miscible. This promotes evaporation.

Experiments have shown that a similar process can be carried out when wood is impregnated with substances dissolved in organic solvents, provided that certain requirements are met and that the special possibilities which arise are exploited.

The present invention therefore relates to a process for treating wood by impregnating a solvent with a preservative dissolved in a solvent and then drying out the solvent by treating the wood with a high boiling liquid having a boiling point of at least 250 ° C at atmospheric pressure, vacuum and at a temperature such that the solvent boils. after which the treatment liquid is removed from the vessel, and the invention is characterized in that the solvent is an organic product soluble in the treatment liquid, having a boiling point of 200 ° C and a low heat of vaporization compared to water.

The different parts of the method are as follows.

The impregnation is preferably carried out as pressure impregnation in a steel cylinder. To minimize the amount of solvent evaporating from the wood, an "empty cell" method such as Lowry or Rtiping must be used. In this case, about 150-80 liters of solution / m 2 of wood are used for Swedish pine, compared to 300 liters obtained in the "full cell" method. All methods distribute the substance well into the wood, the amount of preservative applied to the wood is adjusted by keeping the concentration of the substance in the solution in the opposite proportion to the amount of the impregnating solution applied to the wood.

In the case of impregnation using organic solvents, these empty cell impregnations can be considered as a condition, as is the case when using aqueous solutions. The problem is the expensive solvent and its consumption must be kept to a minimum. Under conventional impregnation, the solvent cannot be recovered. After impregnation, when it has done its job, it evaporates from the wood and is thus wasted.

More rarely, it can be argued that in the present method - in which Lowry and Rilping are recommended as part - the causes against ful cell are not as severe as in conventional impregnations. In the present method, the solvent is recovered, only the recovery costs have to be borne. As will be seen later, they are not particularly high.

In order for the process to be carried out with good results, the solvent and the oil in which the wood is heated must have certain different properties, in particular special requirements for their boiling points or boiling range.

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It is then important for the solvent.

The solvent must be able to evaporate easily. However, solvents that boil too low should generally not be used due to the risk of fire, hygienic and other hazards, risk of leakage and other losses, etc. Volatile substances have been present in impregnation, but have caused considerable difficulty. Due to rational work, the substances must be fluid and their vapor pressure must be low at normal temperature. When the boiling point is below and about 125 degrees, they must consist of or contain non-combustible substances. The boiling point must be limited to about 200 degrees from the top, taking into account evaporation. Preferably it should be about 150 degrees.

As the solvent, petroleum products with a limited boiling point range are preferably used. Pure products such as toluene and xylene can be used, but are more expensive. The advantage of such uniform products is distillation at the exact boiling point, or if they are impure in a very narrow area.

Hardly combustible products, such as certain chlorinated substances, can be used advantageously in certain ways. Examples are dichlorobenzene, dichlorobutane, trichloropropane, tetrachlorethylene, tetrachloroethane and pentachloroethane. It is best to use a rock oil product and, if necessary, part of a chlorinated product. This proportion can generally be limited to 10 to 20% by weight of the solvent.

As the preservative, for example, penta-, tetra- or trichlorophenol, nitrophenols, chloronaphthalenes, cresols, naphthols, etc. can be used, but, for example, a tin compound such as tributyltin oxide or well-known oil-soluble copper compounds, etc. can also be used. has 6 to 12 carbon atoms - especially caprylic and capric acids - or their copper salts. A flame retardant such as tricresyl phosphate and chloroparaffin may also be added.

In some cases, these substances are not sufficiently directly soluble in the solvent, but certain additives are required. The concentrations and additions of the substances used do not differ from what can be considered as previously known.

Thus, such a solution is added to the wood, preferably by the Lowry or RUping method. These end in a vacuum. Preferably, it is maintained during the addition of the oil. If the vacuum is interrupted, otherwise there must be an opportunity for air to penetrate the wood, otherwise the oil may penetrate the wood in excessive amounts. The vacuum must also be maintained due to the fact that further processing preferably takes place under vacuum.

Thus, the oil fed to the cylinder must have the following properties.

In view of the role of the oil as a thermal medium for evaporating the solvent, it must be separated from the solvent so that it has a boiling point of at least 250 degrees. However, another aspect comes into play here. Some of the oil is intended to remain on the surface of the wood and provide long-term protection. Therefore, in order not to evaporate too quickly during the use of the wood, its boiling point should not be as low as about 250 degrees. the boiling point of the oil should therefore be at least about 300 degrees.

the oil may be different depending on the conditions. It may be a non-dry species such as paraffin oil or less refined oils of this type, fatty oil, etc., it may be desiccant or partially desiccant such as linseed oil, pine oil or alkyd. It can also be a mixture of drying and non-drying oil.

pigment may be added to the oil if desired. The wood then stains. Other agents, such as flame retardants such as tricrylyl phosphate and chloroparaffins, may also be added. Conventional anti-rot and anti-blueing agents normally present in the solvent may also be included in the drying oil.

the composition of the oil or oil mixture depends on the use of the wood and the substances added. By way of example, the decomposition of the pigment is more permanent if aromatics are present in the oils, if drying oils are to be included in the mixture, if the pigment is used, the degree of drying of the oils must be limited so that the oil can follow the wood without cracking. In general, non-drying oil alone can only be used when only surface protection against air and moisture is desired.

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As mentioned above, the oil is preferably added to the treatment cylinder while maintaining a vacuum. the oil is now kept warm. This can be done in various conventional ways, by means of coils in the cylinder or by a jacket through which a warm medium, such as steam or a warm liquid, is passed. Drying temperature - oil temperature - can normally vary between 60 and 110 degrees. Preferably it is maintained at 80 degrees. The vacuum used must be high, maintained at a pressure of 200 mm Hg or below. A lower temperature and / or a lower vacuum may be used at the beginning of the cycle to limit the evaporation of the strong solvent at the beginning.

Now the solvent evaporates quickly from the wood, it boils off under low pressure. The wood thus "dries", i.e. is released from the solvent. Although the distillation conditions are not as ideal here as when using an aqueous solution for impregnation, the conditions are very favorable. This is because the solvent has such a low heat of vapor formation. Usually it is at most 1/5 of the corresponding heat of water. This means faster distillation, low heat consumption and simple cooling for subsequent recovery. In about 3 hours, a 25 mm thick wood can usually be dried almost free of solvent, for double thickness it takes 4-5 hours.

The fact that the solvent and the oil are soluble in each other and theoretically give a worse starting point for the distillation of the solvent is thus practically replaced by a suitable choice of solvent and oil and by the fact that the solvent has a low heat of vapor formation.

The solvent can be distilled off relatively completely from the wood. If heating is used more restrictively, some of the solvent may remain in the oil until equilibrium is reached. The solvent concentration therefore remains constant in the oil if the routine of the method is kept unchanged. However, at the given boiling point ranges, it is not at all difficult to get the oil practically free of solvent at the end of the process.

As previously mentioned, the solvent is recovered. This is preferably done by cooling. It is simple when the heat of steam generation is low. Water and even air can be used as the coolant. The condenser is preferably placed between the treatment cylinder and the vacuum generating pump. In this way, the load on the pump remains low.

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Solvent recovery is, of course, very important. This is an expensive product. The recovered material can be used as received. In general, no special solvents are wasted. When the impregnation is carried out with an aqueous solution, the situation may be slightly different, in the latter case, for example, ammonia and carbon dioxide may evaporate, which may be difficult or impossible to recover.

When this happens, the surface of the wood gets an effective treatment with warm oil.

When the method is performed as shown, the processing is stopped. This is done by pumping the oil out of the cylinder where the wood is. This should be done by maintaining a vacuum, otherwise the external air pressure will press too much expensive oil on the wood.

As mentioned earlier, the oil left on the surface of the wood provides protection against air and moisture. When pigment is used, the wood becomes discolored. Generally, the oil consumption is about 40 kg oil / m 2 wood, calculated for the case of handling 25 mm thick boards. More oil per m 2 is consumed when treating thinner wood, less when handling thicker wood.

The wood is then removed from the cylinder. It is then pre-processed. To allow any used drying oils to solidify, storage for a few days is required.

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Example 4.3 m ^ of board boards measuring 25 x 100 mm and a length of about 4 m were treated.

The impregnation solution consisted of a petroleum product boiling just above 150 ° C and 3 'by weight of pentachlorophenol dissolved in tall oil.

Impregnation was performed according to the Lowry method. The solution was first pressed into the timber under a pressure of 8 kg for 90 minutes. After the solution was removed from the cylinder, a high vacuum was drawn for 30 minutes during which part of the impregnation solution was sucked out of the timber. While maintaining the vacuum, a warm, high-boiling oil mixture of drying and non-drying oils was introduced into the treatment cylinder. A fine red pigment was dispersed in the mixture.

Treatment with a high boiling oil mixture was started at 60 ° C. After 60 minutes, the temperature had risen to 80 ° C, where it was kept constant until the treatment was stopped, which occurred after 4 hours and 15 minutes. The vacuum was maintained at about 100 mm Hg. 650 liters of solvent evaporated from the timber, which was recovered after compaction.

After two hours of evaporation, the high boiling oil contained 4% by weight of solvent.

After the oil mixture was removed from the cylinder while maintaining a vacuum, the cylinder was opened, after which the timber was taken out. It was virtually solvent free,

The timber was then pre-treated. It had been impregnated, freed from solvent (recovered !, by the action of high-boiling pigmented oil on the surface, the wood had acquired a surface protection against water on the one hand and a very durable color (in this case red !.

After a few days, the oil mixture on the surface of the wood had hardened so that the surface of the wood was no longer sticky.