Coating processes – Vacuum utilized prior to or during coating – Organic base
Patent
1984-01-27
1986-05-27
Silverberg, Sam
Coating processes
Vacuum utilized prior to or during coating
Organic base
427343, 427369, 4274191, 427440, B05D 300
Patent
active
045915156
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of impregnating wood in order to protect it against fungal decay.
Copper-chrome-arsenic (CCA) water-borne wood preservatives, typically based on a mixture of copper sulphate, sodium or potassium dichromate and arsenic pentoxide, have been available commercially for many years. Pressure impregnation techniques are usually employed to treat the wood and fix the preservatives therein. CCA preservatives are effective against basidiomycetes, which cause white and brown rot in both hard and soft woods, as has been well established over long periods in many countries. The main shortcoming of CCA preservatives is their inability to control adequately copper-tolerant soft rot fungi which attack a wide range of timber species, particularly hard woods, when they are exposed to very wet conditions, for example in ground contact.
Copper-chrome-boron (CCB) water-borne wood preservatives, typically based on a mixture of copper sulphate, sodium or potassium dichromate and boric oxide, have been used for many years where arsenic has been unavailable or its use has been considered undesirable. CCB is generally less effective than CCA in controlling basidiomycetes, partly because the boron is not fixed and is leached from the wood over a period of time. CCB, however, does provide good protection against soft rot fungi, even in hard woods.
Attempts have been made using copper-chrome-arsenic-boron (CCAB) preservatives to combine the activity of CCA and CCB wood preservatives by substituting 50% of the arsenic compound in CCA with boric acid to control both basidiomycetes decay and soft rot in hard wood. The results of trials have shown that a CCAB formulation is less effective than CCB against soft rot.
Other trials with both soft and hard woods have shown that both CCA and CCB are both more effective in controlling decay in wood than a CCAB type formulation. The poor performance of CCAB has been attributed to lack of fixation of the preservative composition in the wood.
We have found, in accordance with the present invention, that a two-stage treatment of wood involving a first stage in which the wood is impregnated with a copper preservative and with a fixative agent therefor and a second stage in which the wood is impregnated with an arsenic preservative provides a broad spectrum of activity against basidiomycetes and soft rot fungi in both soft woods and hard woods, in particular against soft rot fungi attack of hard woods.
What is novel and inventive herein is the finding that carrying out the method in two stages leads to improved resistance of woods to fungal attack. As implied in the above statement, the first stage is carried out in the substantial absence of arsenic. The omission of an arsenical preservative from the copper solution appears to increase the amount of copper which is fixed in the wood shortly after the treatment. Tests have been carried out in which birch sawdust was treated comparably with (i) CCA, (ii) CCB, (iii) CCAB, or (iv) C, i.e. copper sulphate. The treated sawdust was leached and the unleachable copper remaining in the wood was measured. These tests showed that during the period up to 8 hours after treatment the CCB and C treatments gave markedly higher percentages of unleached copper than the other two treatments. However, after that time, the unleached copper in the C treatment fell away and the results of the other 3 tests began to converge until after about 48 hours they were virtually identical. The amount of chromium fixed was initially lower in the CCB treatment than with CCA or CCAB. It is believed, therefore, that the treatment of the invention enables copper to interact better with the cell wall of the wood and that this interaction provides improved protection against soft-rot fungi. The treatment of the invention is therefore carried out so that the first stage provides for interaction of the copper within the cell wall, particularly adsorption thereof to sites within the S2 layer, unimpeded by arsenic, and the second stage provides for the arseni
REFERENCES:
patent: 3007844 (1961-11-01), Schulz
patent: 4038086 (1977-07-01), Clarke et al.
patent: 4323477 (1982-04-01), Hill
Dickinson David J.
Gray Scarlette M.
Bell Janyce A.
National Research Development Corp.
Silverberg Sam
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