Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Organic compound containing
Reexamination Certificate
2002-06-26
2003-05-27
Bell, Mark L. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Organic compound containing
C502S164000, C156S324000, C156S351000, C252S182110, C252S183110, C524S047000, C524S052000, C524S535000, C524S555000, C524S563000, C524S013000, C524S417000, C524S291000, C524S320000
Reexamination Certificate
active
06569801
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of adhesives and more particularly to adhesives made by cross-linking liquid catalysts with amino resins.
BACKGROUND OF THE INVENTION
Amino resins are used in the area of wood products including particleboard, hardwood, plywood, decorative laminate, furniture assembly, etc. Amino resins are supplied in liquid form and are combined with a catalyst at the time of use to form an adhesive substance that is applied to the wood product. This adhesive substance provides adhesion between wood surfaces.
The catalysts are either acidic substances or other materials capable of liberating free acid upon addition to the amino resin. The acidic property of the catalyst promotes cross-linking amino resins and accordingly, the cross-linking or setting of the adhesive substance so that the adhesive substance has the necessary high strength, water resistance and cold flow resistance in order to meet its necessary applications. For example, hardwood floors used for flooring in truck trailer, truck bodies and shipping containers are laminated using a catalyst/amino resin with high strength cross-linking. The quality of lamination can then be verified using Fruehauf Engineering Standards, with one of the most important criteria being the wet shear strength.
The amount and type of catalyst used determines whether the adhesive bond can be cured at room temperature or at higher temperatures. Cure time may vary from a few minutes at high temperatures to a few hours at room temperature. In an application where high frequency heating is required, as for example with laminated pieces of wood flooring, it is common to reduce the time required to cure the adhesive substance.
Current catalysts used in combination with amino resins are in powder form.
A major drawback with a powder catalyst is that powders are not easy to manipulate. Mass transfer of powder materials requires special equipment and/or more human manipulations.
Also, powder catalysts pose certain problems in terms of dust formation during transfer, which may cause toxic effects on humans (irritating mucous membranes and upper respiratory tract).
Care must always be taken to mix homogeneously the blend of powder catalyst and liquid amino resin to avoid any lumping of powder, which will cause a burn or an arc if high frequency heating is used.
While the use of a high level of powder catalyst imparts lower setting time, the amount of powder catalyst mixed with the amino resin is limited to about a maximum of 15% by weight. Increasing the amount of powder catalyst above 15% by weight increases the viscosity and reduces the pot life of the mixture, but decreases the adhesivity and strength of the mixture. Moreover, powder catalysts do not contribute any adhesive property to the mixture and a higher concentration of powder catalyst reduces the relative amount of amino resin in the mixture and therefore reduces the adhesive performance of the resulting mixture.
When properly cured, the resulting bond of the amino resin cross-linked with a powder catalyst is hard and brittle and is characterized by a low impact strength and low elongation point prior to breakage.
Accordingly, there remains a need to develop a catalyst that is commercially beneficial for the wood glue industries and which can be easily mixed at a relatively high concentration with a liquid amino resin to provide a resulting adhesive substance with an adequate viscosity, pot life, and setting time. There also remains a need to provide a catalyst that reduces the cycle time of a high frequency heating press, while contributing adhesive properties to the final adhesive substance.
SUMMARY OF THE INVENTION
It is an object of one aspect of the present invention to provide an adhesive with improved properties.
It is a further object of one aspect of the present invention to provide a catalyst with improved cross-linking capabilities and properties that facilitate mixing with an amino resin.
According to one aspect of the present invention, there is provided an adhesive substance made from mixing a liquid catalyst comprising between 52 and 93% of a copolymer, between 3 and 14% of an acid, and, between 4 and 14% of an ammonium salt, with an amino resin.
In a preferred embodiment of the present invention, the liquid catalyst provides adhesive properties to the catalyst/amino resin mixture and it provides excellent bond strength and excellent water resistance to the adhesive substance.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention provides an adhesive made by cross-linking a liquid catalyst with an amino resin. The liquid catalyst is a composition comprised of a copolymer, acid, and ammonium salt. In a preferred embodiment, the liquid catalyst has a storage life of a minimum of three months.
In a preferred embodiment of the present invention, the liquid catalyst composition comprises the following components (all percentages are in weight % to a total of 100%):
Copolymer emulsion >
52% to 98%
Acid
14% to 0.01%
ammonium salt
14% to 2%
ionisable salt
3% to 0%
inert filler
1% to 0%
adjusting water
16% to 0%
(A) Copolymer:
The copolymer is the primary component of the liquid catalyst. It is preferably present in an amount ranging from about 52 to 98 weight %. Most preferably, it is present in an amount of 70 to 78 weight %.
In a preferred embodiment, the copolymer is comprised of vinyl acetate and a comonomer capable of crosslinking. An example of a suitable comonomer is N-methylolacrylamide, which shows improved crosslinking capabilities with polyvinyl acetate.
The polyvinyl acetate and comonomer form an emulsion that is self-crosslinkable. The emulsion functions as a water resistant adhesive, thereby improving the adhesivity and impact strength of the liquid catalyst over the non-adhesive powder catalysts used in the prior art.
A commercially available source of copolymer is the self cross-linking poly-vinyl acetate dispersion available under the trade-mark P-1036™ from Dural, a division of Multibond Inc. This copolymer is a dispersion in water having a solids content of about 51% (51±1%), a pH of 4.0 to 5.0, a Brookfield viscosity at 25° C. (spindle 5 at 20 rpm) of 8,000 to 12,000 cps, an average particle size of 0.8&mgr;, and a minimum film forming temperature of +15.6° C. The copolymer dispersion is non-ionic with a density of 1.07 g/cm
3
. It has a stabilization system based on polyvinyl alcohol.
N-methylolacrylamide is purchased at a concentration of 48%. The amount of N-methylolacrylamide based on the weight of vinyl acetate may vary from 3 to 10%.
It will be apparent to one skilled in the art that other copolymers may be used within the confines of the invention without deviating from the invention as claimed. For example, a self-crosslinking polyvinyl acrylic or polyacrylic may be used as part of the copolymer dispersion.
(B) Acid:
In a preferred embodiment, the liquid catalyst includes an acid such as citric acid, commercially available under the name citric acid anhydrous. It is present in the liquid catalyst in an amount ranging from 1 to 14 weight %, and preferably in an amount of from 4 to 7 weight % of the liquid catalyst.
The acid is useful in the liquid catalyst because it initiates hardening of the catalyst-amino resin mixture by improving the cross-linking reaction with the amino resin.
A commercially available source of citric acid anhydrous is available from ADM Food Additive Division. It has a solubility in water of 162 g/100 ml at 25° C., with a maximum water content of 0.5%, and a maximum lead content of 0.5 ppm. Another suitable acid is salicylic acid.
(C) Ammonium Salt:
In a preferred embodiment, the liquid catalyst also includes an ammonium salt. The preferred ammonium salts are ammonium salts derived from strong acids, such as, ammonium chloride and ammonium sulfate. The ammonium salt cross-links with the amino resin and improves the overall cross-linking of the liquid catalyst. It is preferably present in an amount ranging from about 2 to 14 weigh
Berube Serge
Cutt John
Bell Mark L.
Clarizio Dino P.
Diomck Stratton Clarizio
Hailey Patricia L.
Multibond Inc.
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