Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-11-23
2002-08-27
Yao, Sam Chuan (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S062200, C156S296000, C156S332000, C156S335000, C264S112000, C264S122000
Reexamination Certificate
active
06440255
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
This invention is directed to a process for producing fast curing bonded with phenolic resin by employing, molding compounds together with pulverulent phenolic resins, pulverulent addition polymers selected from the group consisting of polyvinyl alcohols and addition polymers stabilized by hydroxyl-containing protective colloids.
2) Background Art
The importance of thermosetting phenol-formaldehyde resins, for example, hexa novolaks or resoles, as binders for a very wide variety of applications has greatly increased in recent years. Typical applications are, for example, binders in filter papers, foundry sand, ceramics, fiber mats and wood fiber boards. The use of phenol-formaldehyde resins as a thermosetting binder in most cases requires a thermally initiated, intensive crosslinking of the polymer chains to form a three-dimensional, molecular network.
In the interests of industrial use, where fast cycle times are important, development work has concentrated in particular on accelerating the crosslinking reaction, the curing, of these polymer systems.
Many prior artisans were concerned with catalyst systems which accelerate the condensation of phenol functions with aldehyde functions and were particularly interested in achieving a chemical reaction in the ortho position of the phenol ring. Examples thereof are known from WO-A 93/08223, which describes solvent-free, solid hotmelt adhesive systems with divalent metal salts as catalysts. The disadvantage here is the excess of up to 1.7 mol% of free formaldehyde which can lead to environmental problems.
U.S. Pat. No. 4,112,188 describes a process for accelerating the cure of resoles by means of boron compounds. But this process utilizes not solid, but liquid systems in aqueous solution.
The curing reaction of binder mixtures based on phenolic resin can also be accelerated by ester compounds. For example, DE-A4331656 (Derwent Abstract AN 94-286789), discloses that triacetin is useful as a cure accelerator. However, this system works only in aqueous solution and in the presence of lignin. Similarly, the Australian patent specification AU-B-22974/88 describes ester compounds, especially lactones, organic carbonates and carboxylic esters as useful cure accelerators for the liquid phenolic resins known as resoles.
Polymeric cure accelerators are likewise known. U.S. Pat. No. 5,223,587 claims a binder for wood fibers which is comprised of a powdery mix of highly condensed phenolic resins, incompletely cured phenolic resins (hexanovolaks) and optionally, coconut shell powder. U.S. Pat. No. 4,426,484 discloses accelerating the curing of solid resoles by adding solid novolak resins comprising resorcinol. The disadvantage with either process is the increased emission of formaldehyde and phenol from the starting materials used. In contrast, the use of powdered green tea, as known from U.S. Pat. No. 4,109,057, offers an environmentally benign alternative to accelerating the cure of phenolic resins by means of polymeric compounds. However, the high cost is a decisive bar to industrial use.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process whereby the curing of solid phenolic resins, especially hexanovolaks, is accelerated.
It has now been found, surprisingly, that polyvinyl alcohols and addition polymers stabilized by hydroxyl-containing protective colloids accelerate the curing of phenolic resins.
The invention accordingly provides a process for producing fast curing bonded with phenolic resin, molding compounds which comprises pulverulent phenolic resins being mixed with or applied to the substrate to be adhered together with pulverulent addition polymers selected from the group consisting of polyvinyl alcohols and addition polymers, stabilized by hydroxyl-containing protective colloids, of one or more monomers from the group of the vinyl esters of branched or unbranched carboxylic acids of 1 to 12 carbon atoms, the esters of acrylic acid and methacrylic acid with branched or unbranched alcohols of 1 to 12 carbon atoms, vinylaromatics, vinyl halides, olefins and dienes, and subsequently, by the employment of elevated temperature and optionally elevated pressure, cured and processed into a shaped article.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Suitable polyvinyl alcohols are partially or fully hydrolyzed polyvinyl alcohols, preferably having a degree of hydrolysis of 85 to 100 mol% and a Höppler viscosity of 1 to 60 mPas, measured in 4% strength aqueous solution (method of Höppler at 20° C., DIN 53015). It is also possible to use vinyl alcohol copolymers which, in addition to the vinyl alcohol and vinyl acetate units, contain other monomer units, for example 1-methylvinyl acetate or 1-methylvinyl alcohol units, preferably in an amount of 0.5 to 10% by weight, based on the total weight of the copolymer. The vinyl alcohol homo- and copolymers mentioned are commercially available or obtainable in a manner known to one skilled in the art, by hydrolysis or alcoholysis of the corresponding vinyl acetate homo- and copolymers.
Vinyl esters preferred for the protective colloid-stabilized addition polymers are vinyl acetate, vinyl propionate, vinyl butyrate, vinyl 2-ethylhexanoate, vinyl laurate, 1-methylvinyl acetate, vinyl pivalate and vinyl esters of alpha-branched monocarboxylic acids of 9 to 11 carbon atoms, for example VeoVa9® or VeoVa10® (trade names of Shell). Vinyl acetate is particularly preferred.
Methacrylic esters or acrylic esters preferred for the protective colloid-stabilized addition polymers are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, n-butyl methacrylate, 2-ethylhexyl acrylate. Particular preference is given to methyl acrylate, methyl methacrylate, n-butyl acrylate and 2-ethylhexyl acrylate.
Preferred vinylaromatics are styrene, methylstryene and vinyltoluene. The preferred vinyl halide is vinyl chloride. The preferred olefins are ethylene and propylene and preferred dienes are 1,3-butadiene and isoprene. Optionally, 0.05 to 10.0% by weight, based on the total weight of the monomers, or comonomers can be present in addition, for example acrylic acid, acrylamide, vinylsulfonic acid, 2-acrylamidopropanesulfonate, vinyltriethoxysilane, gamma-methacryloyloxypropyltriethoxysilane, N-methylolacrylamide (NMA).
Preferred protective colloid-stabilized addition polymers are vinyl ester polymers, (meth)acrylic ester polymers, vinyl chloride polymers and styrene polymers.
The hereinbelow recited polymers are particularly preferred, the weight percentages, if necessary, including the comonomer fraction, adding up to 100% by weight:
from the group of the vinyl ester polymers: vinyl acetate polymers, vinyl acetate-ethylene copolymers having an ethylene content of 1 to 60% by weight; vinyl acetate-ethylene vinyl chloride copolymers having an ethylene content of 1 to 40% by weight and a vinyl chloride content of 20 to 90% by weight; vinyl acetate copolymers with 1 to 50% by weight of one or more co-polymerizable vinyl esters such as vinyl laurate, vinyl pivalate, vinyl esters of an alpha-branched carboxylic acid, especially vinyl versatates (VeoVa9®, VeoVa10®, VeoVa11®), which optionally contain 1 to 40% by weight of ethylene in addition; vinyl acetate-acrylic ester copolymers containing 1 to 60% by weight of acrylic ester, especially n-butyl acrylate or 2-ethylhexyl acrylate, which optionally contain 1 to 40% by weight of ethylene in addition;
from the group of the (meth)acrylic ester polymers: polymers of n-butyl acrylate or 2-ethylhexyl acrylate;
copolymers of methyl methacrylate with n-butyl acrylate and/or 2-ethylhexyl acrylate;
from the group of the vinyl chloride polymers (in addition to the abovementioned vinyl ester/vinyl chloride/ethylene copolymers): vinyl chloride-ethylene copolymers and vinyl chloride/acrylate copolymers;
from the group of the styrene polymers: styrene-butadiene copolymers and styrene-acrylic ester copolymers such as styrene-n-butyl acrylat
Kohlhammer Klaus
Schmidt Claudia
Brooks & Kushman P.C.
Wacker-Chemie GmbH
Yao Sam Chuan
LandOfFree
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