Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Patent
1993-01-04
1996-09-17
Michl, Paul R.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
524 47, 524462, 1563313, 1563317, 1563319, 156335, C08K 502, C09J 400, C09J10100, C09J20100
Patent
active
055569064
DESCRIPTION:
BRIEF SUMMARY
This invention relates to adhesives and in particular to aqueous adhesives for use with porous materials. The invention is also concerned with methods for bonding porous material and for reducing cure times and bonding at higher moisture content.
In aqueous adhesive systems such as the phenolic type resins used for bonding wood products such as plywood, a certain degree of water removal from the glueline is necessary for the formation of a good bond. Without wishing to limit the present invention in any way, we believe that bond failure may be caused by the presence of excessive moisture in or near the glueline at the time of application of pressure. When heat is applied to the product to set the resin, steam is formed at the interface resulting in a weak bond. In extreme cases, the bonded articles may be blown apart by the steam pressure generated during the heating step. Excessive resin loss from the glueline during hot pressing may also occur. To avoid this situation very long assembly times may be required to allow water to migrate from the glueline into the porous substrate. Another problem that may be encountered is excessive resin penetration into the substrate so that insufficient resin remains for bonding.
It is an object of the present invention to provide an improved adhesive system which facilitates more rapid removal of water from the glueline.
We have found, surprisingly, that the objective of the present invention can be achieved by either incorporating one or more hydrophilic surfactants in the adhesive formulation, or by applying a hydrophilic surfactant to the surface of the porous material prior to the application of an adhesive.
Accordingly, in one aspect, the present invention provides an adhesive composition for bonding porous material, said composition comprising an aqueous based thermosettable resin and one or more hydrophilic anionic surfactant(s) having an HLB value of at least about 10.
In a further form, the present invention provides a method of bonding a porous material, said method including the steps of: 10 to at least a portion of a surface of the porous material; and surfactant treated surfacer.
In yet a further aspect, the present invention provides a method of bonding a porous material, said method including the step of applying an adhesive composition in accordance with the invention.
The invention is applicable to porous material of any form, for example, it may be sheet-like as in the case of plaster sheeting or timber veneer or it may be particulate. The porous material may be a combination of porous materials or it may be a combination of porous and non-porous material (such as metal or plastic). The formed product may be, for example, any bonded composite product, examples of which are particle board, plywood and various fibre boards.
Suitable adhesives are thermosettable resins including phenolic resins, resorcinol resins, melamine resins, urea resins, urethane resins and starch-type adhesives. The adhesive may also be of the addition polymer type. Preferably the adhesive is an aqueous phenol-formaldehyde resin. For the purpose of this specification the term hydrophilic surfactant extends to fluorochemical surfactants even though, technically, they may not be regarded as such.
The hydrophilic anionic surfactants may be selected from the group comprising fluorochemical type surfactants which may sufficiently lower the surface tension of water in the adhesive composition to result in water phase surface tensions lower than that of the surface energy of the porous material and hydrophilic hydrocarbon-derived surfactants with HLB numbers of about 10 or greater.
Mixtures of surfactants may be used provided they are self-compatible. Some surfactants are unstable or are degraded under the alkaline or acidic conditions commonly encountered in gluing wood, and for this purpose we prefer to use stable surfactants. The amount of surfactant to be used depends largely on the type of surfactant chosen, the moisture content of the porous material (and in the case of wood, the sp
REFERENCES:
patent: 3538031 (1970-11-01), Rice
patent: 4026856 (1977-05-01), Jahnke
patent: 4197219 (1980-04-01), Damico
Collins Peter J.
Yazaki Yoshikazu
Chemplex Australia Limited
Commonwealth Scientific and Industrial Research Organisation
DeWitt LaVonda
Michl Paul R.
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