Stock material or miscellaneous articles – Composite – Of aldehyde or ketone condensation product
Reexamination Certificate
1998-12-11
2002-09-03
Gallagher, John J. (Department: 1733)
Stock material or miscellaneous articles
Composite
Of aldehyde or ketone condensation product
C156S331300, C524S127000, C524S239000
Reexamination Certificate
active
06444329
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for preserving plywood and particle board against undesirable reactions caused by microorganisms, particularly those caused by fungi and moulds, resulting in decay, mould and blue-stain deterioration of wood.
According to the present method, a wood composite product is made from separate wood pieces by joining said pieces together with an adhesive or binder. The wood pieces may comprise planar wood veneer sheets or smaller wood particles (chips, sawdust or wood powder). The preserving additive possessing growth- and spreading-inhibiting properties against microorganisms is mixed into the base adhesive used in the method.
The invention also concerns an adhesive composition with particularly advantageous properties for producing plywood and particle boards, as well as methods for preparing such an adhesive composition.
2. Description of Related Art
Rot fungi and other microorganisms use the structural components of wood in their metabolism or degrade wood by the growth of their colonies. Wood degradation, particularly in the form of an essential loss of its strength properties, is chiefly caused by rot fungi, of which brown-rot, white-rot and cubical dry-rot fungi deserve mentioning. Further, the species of these fungi causing the greatest damages are those of the brown-rot fungi including dry-rot fungus (
Serpula lacrymans
), cellar fungus (
Coniophora puteana
) and white-pore fungi (Poria sp., Antrodia sp., Fibroporia sp.). Brown-rot fungi decompose the polysaccharides of wood causing rapid deterioration of wood strength properties already during the initial state of rot, even prior to a detectable weight loss of the wood.
Damage to wood is also caused by blue-stain and mold fungi mostly causing discolouration defects. The blue-stain fungi may in some cases bring about a minor weight loss in the wood, however, generally less than 3%. When occurring in great abundance, blue-stain fungi modify the permeability properties of wood, whereby wood becomes more permeable to water, whereby favourable growth conditions may be formed for the actual rot fungi.
The most common blue-stain fungi found in wood are those of the Ambrosiella, Aureo-basidium, Ceratocystis, Cladosporium, and Phialosphora families. Blue-stain fungi most frequently occurring in pine wood material are Aureobasidium pullulans, and the species of the Ceratocystis family such as
C. pilifera.
In addition to these, blue-staining of sawn spruce is caused by such species as, e.g.,
Ceratocystis piceae
and
C. coerulens.
In addition to the fungi of the families mentioned above, blue-staining of sawn pine is also caused by species of the Sclerophoma family such as
Sclerophoma entoxylina.
Of fungi causing mould damage, the most important to mention are species of the Cladosporium, Altenaria, Helminthosporium, Penicillium, Aspergillus, Epicoccus and Rhizopus families. Mold fungi belonging particularly to the Penicillium and Aspergillus families cause extensive damage in indoor spaces and structures.
To preserve wood against decay and damage caused by microorganisms, different types of methods and preservative compositions have been developed. The most common method is to subject wood to pressure impregnation with preservatives (e.g., salt preservatives and creosote oil), which are capable of preventing growth of microorganisms in wood. With plywood and other similar wood composite materials, the most commonly used preservation treatment comprises admixing the preservative into the adhesive during the manufacture of the composite sheet. Typically, the active preservative compound to be admixed into the adhesive is selected from the group of chlorinated phenols, organic tin compounds, fluorides, and today, Xyligen, moraside and xylasane compounds. Besides using a preservative in the adhesive, wood composite products may be protected by spraying the wood veneer sheets or chips with a preservative solution. Veneer sheets may also be treated by immersion. Ready-laminated sheets can be protected by pressure or vacuum impregnation, whereby the preservatives are selected from the groups of salt preservatives and oil-based preservative formulas containing organic tin compounds.
A disadvantage of preservatives used for impregnating sawn goods is their general toxicity necessitating the handling of such preservative residues and wood blocks treated with them as hazardous waste. Also the other above-mentioned preservative compositions used for preserving wood composite products are handicapped by the same problem.
FI Patent No. 90,951 discloses a wood preservation method capable of overcoming the problems associated with conventional preservation of sawn wood material. In the method disclosed therein, complexing agents are used to bind in the wood into chelates at least a portion of the metals, which are essential to the metabolism of the decaying microorganisms. Preservation of wood in the method is carried out in a conventional manner by impregnating the wood being treated with a solution of the complexing agent.
Up to now, the use of complexing agents in the preservation of plywood and similar wood composite products has not been considered in the art. In particular, the preservation of plywood and particle board or similar wood composite products made from wood pieces/particles and a binder used to adhere such pieces/particles together against decay and moulds by means of admixing complexing agents into the binder used in the fabrication of said products during the manufacturing process for the specific purpose of improving the resistance of the wood product to deterioration and decay due to fungi and mold has not been considered. According to the prior knowledge of the art, this has not been considered possible, because the adhesives used in the process are two-component formulations, in which the hardeners contain metals capable of reacting with the complexing agents. For instance, the hardener of conventional plywood bonding adhesive contains, among other components, wood bark extract and chalk, whereby large amounts of heavy metals and other metallic compounds are contained therein. On the basis of such knowledge, a conclusion has been made in the art that the admixture of complexing agents into the adhesive of plywood and similar materials would decisively deteriorate the properties of the adhesive resulting in the precipitation, change of pH and inhibition of gel formation in the adhesive.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the drawbacks of the above-described prior-art techniques and to provide an entirely novel method for preserving plywood, particle board and similar wood composites against rot, mould and other similar decay and quality-degrading reactions.
It is another object of the present invention to provide a wood composite product which is protected against rot, mould and other similar decay and quality-degrading reactions.
It is a third object of the present invention to provide a binder composition for use in the manufacture of wood composite products, and it is still a further object of the present invention to provide a method of producing a binder suited for use in the manufacture of plywood, particle board and similar wood composite products.
These and other objects of the invention are achieved through preserving the wood composite against the undesirable reactions caused by the above-mentioned microorganisms by admixing into the adhesive or binder compound used in the manufacture of plywood and particle board such complexing agents that are capable of forming chelates with metals essential to the rot mechanisms and general metabolism of fungi. In fact, the invention is based on an unexpected discovery that, contrary to a general belief, a chelate-forming agent admixed into the adhesive can migrate from the adhesive due to the moisture released from the adhesive and the processing conditions of sheet products into the veneer sheet or chips of the product without causing
Korpela Jaakko
Lähteenmäki Markku
Lehtonen Markku
Ritschkoff Anne-Christine
Gallagher John J.
UPM-Kymmene Oy
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