Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2000-05-30
2002-04-16
Michl, Paul R. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
active
06372862
ABSTRACT:
The present invention relates to a phenolic resin-based adhesive composition which is excellent in adhesive strength, especially adhesive strength after heating, and operability, and which does not generate volatile solvents or waste water, and to a process for producing the same.
Conventional phenolic resin-based adhesives are generally those of solvent type which are prepared by dissolving, in solvents such as alcohols or ketones, phenolic resins (novolak type phenolic resins and hexamethylenetetramine or resol type phenolic resins) or mixtures of phenolic resins with polyvinyl butyral, polyvinyl acetate or the like, and those of aqueous type which are prepared by emulsifying or completely water-solubilizing them (the solvent type or aqueous type phenolic resin adhesives are disclosed, for example, in “Adhesive Data Book” pages 13-18, edited by Japan Adhesive Society and published from Nikkan Kogyo Shinbun-sha, in 1990; and “Adhesive Application Techniques” pages 218-219, edited by Limited Company N.N. and issued by Nikkei Gijutsu Tosho Co., in 1991). Use of these solvent type and aqueous type phenolic resin-based adhesives needs to coat the adhesives on materials to be bonded, dry the coat and hot-press the materials. The drying step requires a long time to volatilize the solvent or water, resulting in deterioration of operability, and furthermore the volatilized solvent or water must be recovered or abandoned.
On the other hand, powder type phenolic resin-based adhesives which require no drying step and produce no industrial wastes, have been investigated. When the novolak type phenolic resins are used as such adhesives, in many cases, they are mixed with pulverized hexamethylenetetramine (see, for example, “Adhesive Handbook” pages 250-251, edited by Japan Adhesive Society, published from Nikkan Kogyo Shinbun-sha, in 1971), and a uniform coat cannot be formed in coating of the adhesives on materials to be bonded, and no sufficient adhesive strength can be obtained. They suffer from further problems that adhesive strength of the adhesives after being heated is not sufficient, and the adhesive strength deteriorates upon exposure to thermal history in use environment to cause separation of the bonded materials.
The present invention has been accomplished as a result of intensive research conducted in an attempt to solve the above problems of the conventional phenolic resin-based adhesives, and the object of the present invention is to provide phenolic resin-based adhesives which are excellent in adhesive strength, especially adhesive strength after being heated, and operability, and which do not produce volatile solvents or waste water.
The present invention relates to a phenolic resin-based adhesive composition which contains a polyvinyl butyral, a novolak type phenolic resin or a novolak type phenolic resin and a resol type phenolic resin, and hexamethylenetetramine and which is prepared by melt-mixing these components, and to a phenolic resin-based adhesive composition which contains a polyvinyl butyral, an epoxy resin, a novolak type phenolic resin or a novolak type phenolic resin and a resol type phenolic resin, and hexamethylenetetramine and which is prepared by melt-mixing these components.
Preferred is a phenolic resin-based adhesive composition which contains a polyvinyl butyral, an epoxy resin, a novolak type phenolic resin, a resol type phenolic resin, and hexamethylenetetramine and which is prepared by melt-mixing these components. Furthermore, a phenolic resin-based adhesive composition which is excellent in operability and adhesive strength, especially adhesive strength after being heated, can be obtained when the hexamethylenetetramine as a hardener forms an adduct with the phenolic resin.
That is, it has been confirmed that a composition containing an epoxy resin, a novolak type phenolic resin and a resol type phenolic resin as essential components is effective for improvement of adhesive strength after being heated.
The present invention will be explained specifically below.
In the present invention, a polyvinyl butyral is added to improve peeling strength and adhesive strength under shear at room temperature of the phenolic resin-based adhesives. Its polymerization degree is preferably 200-3000. If the polymerization degree is less than 200, sufficient adhesive strength cannot be obtained, and if it exceeds 3000, viscosity of the adhesives at melting increases and it is sometimes difficult to obtain a uniform adhesive coat. Content of the polyvinyl butyral in the phenolic resin-based adhesive compositions of the present invention is 1-50 parts by weight, preferably 5-30 parts by weight based on 100 parts by weight of the phenolic resin. If the content is less than 1 part by weight, sufficient adhesive strength cannot be obtained, and if it exceeds 50 parts by weight, viscosity of the adhesives at melting increases and it is difficult to obtain a uniform adhesive coat.
The epoxy resins used in the present invention are those which have at least two epoxy groups in one molecule, and which may be solid or liquid at room temperature. Examples of the epoxy resins are those of bisphenol A type, bisphenol S type, phenol novolak type, cresol novolak type, biphenyl type, naphthalene type and aromatic amine type, which do not limit the epoxy resins used in the present invention. These can be used each alone or in combination of two or more. In the present invention, the epoxy resins are added to improve adhesive property of the phenolic resins. Content of the epoxy resins is 1-50 parts by weight, preferably 3-30 parts by weight based on 100 parts by weight of the phenolic resin. If the content is less than 1 part by weight, sufficient effect to improve the adhesive property cannot be obtained, and if it exceeds 50 parts by weight, curability of the adhesives deteriorates and sufficient adhesive strength cannot be obtained.
In the present invention, the phenolic resins are excellent in heat resistance, superior in adhesive force, and especially great in the action to absorb thermal stress at high temperatures, and as a result, have an effect to increase adhesive strength at high temperatures. The phenolic resins include novolak type phenolic resins and combinations of novolak type phenolic resins and resol type phenolic resins. Preferred are novolak type cresol-modified phenolic resins or combinations of novolak type cresol-modified phenolic resins and resol type cresol-modified phenolic resins, since they are superior in adhesive strength, particularly adhesive strength after being heated. These phenolic resins can be used in any form of liquid, solid or powder. When a novolak type phenolic resin and a resol type phenolic resin are used in combination, ratio of them is preferably 100 parts by weight or less of the resol type phenolic resin for 100 parts by weight of the novolak type phenolic resin. If amount of the resol type phenolic resin exceeds 100 parts by weight, there is caused the problem that the powdered resin is apt to absorb water or it is apt to aggregate.
As to the hardener for the novolak type phenolic resins, hexamethylenetetramine which is generally used as the hardener for novolak type phenolic resins is sometimes not used because when a resol type phenolic resin is used in combination, this also has an action as a hardener. However, in the present invention, hexamethylenetetramine is used as the hardener. Amount of the hexamethylenetetramine is 3-20 parts by weight, preferably 7-17 parts by weight based on 100 parts by weight of the novolak type phenolic resin, though it depends on the amount of the resol type phenolic resin. If the amount is less than 3 parts by weight, the adhesive hardens insufficiently, and if it exceeds 20 parts by weight, it becomes difficult to obtain a uniform adhesive layer due to the decomposition gas of hexamethylenetetramine.
When only the novolak type phenolic resin is used, similarly hexamethylenetetramine is used, and amount thereof is 3-20 parts by weight, preferably 7-17 parts by weight based on 100 parts by weigh
Michl Paul R.
Smith , Gambrell & Russell, LLP
Sumitomo Durez Company Ltd.
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