Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-08-28
2004-05-04
Thexton, Matthew A. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
Reexamination Certificate
active
06730718
ABSTRACT:
The present invention relates to water-resistant, polyvinyl ester-based, aqueous dispersion adhesives with a long pot life and good color constancy of their bonds on storage, to processes for preparing these dispersion adhesives, and to their use for bonding porous and semiporous substrates.
Polyvinyl ester dispersions, whose films exhibit increased water resistance, normally comprise reactive monomers or additives which decrease the hydrophilicity of the adhesive by crosslinking the polyvinyl alcohol which is used for stabilizing the dispersion. Crosslinking additives of high efficiency which are employed in water-resistant adhesive dispersions based on polyvinyl ester includes free aldehydes or their adducts with nucleophiles, which are able to undergo crosslinking reactions either inherently or, following removal of masking agents, by way of reactive aldehyde groups that have been released.
As crosslinking catalysts it is common to use hardener salts. Hardener salts disclosed by U.S. Pat. No. 3,563,851 and DE-C-26 20 738 include specific metal salts, examples being those of aluminum or those of transition group elements with the oxidation states III or IV.
DEB-22 61 402 describes water-resistant adhesive bonds based on a polyvinyl ester dispersion to which a urea-formaldehyde resin with crosslinking activity, in combination with a free organic or inorganic acid or an acidic metal salt, is admixed.
EP-A0 413 136 describes adhesives with cold water resistance based on polyvinyl alcohol and polyvinyl esters. Crosslinking adducts used include N-nucleophiles with glyoxal, examples being cyclic ureas or copolymerized reaction products of acrylamide. Through the addition of acidic metal salts, based preferably on aluminum, the water resistance can be improved.
EP-B-0 686 682 describes aqueous dispersion adhesives of increased water resistance, comprising homopolymeric or copolymeric polyvinyl esters, protective colloids, compounds which can be complexed with the protective colloids, and at least partly masked polyaldehydes having al least 3 carbon atoms which controlledly release aldehyde groups in acidic media. A subgroup of the complexible compounds is formed by metal salts, aluminum salts or zirconium salts for example. The resulting adhesives give rise advantageously to pale gluelines and satisfy relevant test standards, especially the DIN EN 204 durability classes D2 and D3 (cold water resistance) and DIN EN 204 D4 (hot water resistance). The pot lives following admixture of the ingredients are at least 8 hours.
For the end user of these adhesives, a long pot life, i.e., a slow increase in the viscosity of the dispersion following activation with the acidic metal salts, is fundamentally a desirable feature. Another desirable feature is high color constancy of the pale gluelines following application. The use of transition metal salts or aluminum salts as crosslinking catalysts has the disadvantage of a gradual darkening of the gluelines, caused by the reaction of the metal salts with polyvinyl alcohol or any substances contained in wood that may be present. The effect is observed on aging of the adhesive bond at room temperature, and is accelerated on exposure to heat.
One attempted solution to improving the discoloration of wood adhesive dispersions based on polyvinyl esters and comprising hardeners is described by DE-A-196 49 419. According to DE-A-196 49 419, the addition of low molecular mass polyvinyl alcohols having Höppler viscosities of from 2 to 6 mPa·s (measured in 4% strength aqueous solution) reduces the discoloration tendency in the case of cold water resistant adhesive bonds of durability class D3. A disadvantage is that the addition of sizable amounts of polyvinyl alcohol, which acts as a hydrophilicizing agent, decreases the hot water resistance of bonds.
The object accordingly was to provide polyvinyl ester dispersions for adhesives which possess a high, user-compatible pot life and whose adhesive bonds exhibit high color constancy with a high level of water resistance.
It has now surprisingly been found that aqueous dispersion adhesives comprising at least
a) one homopolymeric and/or copolymeric polyvinyl ester,
b) one polymeric protective colloid,
c) one water-soluble compound which can be complexed with the polymeric protective colloids, and
d) two, at least partly masked polyaldehydes which release aldehyde groups again in acidic media, wherein at least one masked polyaldehyde is a glyoxal derivative and at least one other masked polyaldehyde is a derivative of a polyaldehyde having at least 3 carbon atoms,
feature a long, user-compatible pot life and a high level of water resistance and color constancy of their gluelines.
The polyaldehydes having at least 3 carbon atoms are aldehydes having a functionality of at least two.
Suitable monomeric units for the homopolymeric and copolymeric polyvinyl esters include preferably vinyl acetate, vinyl formate, vinyl propionate, vinyl isobutyrate, vinyl pivalate, vinyl 2-ethylhexanoate, vinyl esters of saturated, branched monocarboxylic acids having 9 to 10 carbon atoms in the acid radical, vinyl esters of relatively long-chain, saturated or unsaturated fatty acids such as, for example, vinyl laurate, vinyl stearate, and also vinyl esters of benzoic acid and/or substituted derivatives of benzoic acid such as, for example, vinyl p-tert-butylbenzoate. Vinyl acetate is of particularly preferred suitability.
The weight fraction of vinyl ester(s) in the copolymer of polyvinyl esters is preferably at least 50% by weight and with particular preference at least 75% by weight.
The copolymeric vinyl esters contain, where appropriate, as further monomer units
a) up to 50% by weight, preferably up to 25% by weight, of one or more monomers from the following group: ethylene, &agr;-olefins having from 3 to 18 carbon atoms (e.g., propylene, butylene), styrene, vinyltoluene, vinylxylene, halogenated, unsaturated, aliphatic hydrocarbons (e.g., vinyl chloride, vinyl fluoride, vinylidene chloride, vinylidene fluoride) and/or
b) up to 25% by weight, preferably between 1 and 5% by weight, of one or more monomers from the following group: &agr;,&bgr;-unsaturated acids (e.g., acrylic acid, methacrylic acid), esters of &agr;,&bgr;-unsaturated acids with primary or secondary, saturated, monohydric alcohols having from 1 to 18 carbon atoms (e.g., methanol, ethanol, propanol, butanol, 2-ethylhexanol, cycloaliphatic alcohols, and relatively long-chain fatty alcohols), &agr;,&bgr;-unsaturated dicarboxylic acids (e.g., maleic acid, fumaric acid, itaconic acid, citraconic acid), monoesters and/or diesters of &agr;,&bgr;-unsaturated dicarboxylic acids with saturated, monohydric, aliphatic alcohols having from 1 to 18 carbon atoms and/or
c) up to 10% by weight, preferably up 2% by weight, of one or more monomers from the group consisting of polyethylenically unsaturated monomers, such as diallyl phthalate, diallyl maleate, triallyl cyanurate, tetraallyloxyethane, divinylbenzene, butan-1,4-diol dimethacrylate, triethylene glycol dimethacrylate, divinyl adipate, allyl (meth)acrylate, vinyl crotonate, methylenebisacrylamide, hexanediol diacrylate, pentaerythritol diacrylate, trimethylolpropane triacrylate and/or
d) up to 15% by weight, preferably up to 10% by weight, of one or more nitrogen-containing monomers containing N-functional groups, such as (meth)acrylamide, allyl carbamate, acrylonitrile, N-methylol(meth)acrylamide, N-methylolallylcarbamate, N-methylol esters, N-methylol alkyl ethers or Mannich bases of N-methylol(meth)acrylamide or N-methylolallylcarbamate, acrylamidoglycolic acid, methyl acrylamidomethoxyacetate, N-(2,2-dimethoxy-1 -hydroxyethyl)acrylamide, N-dimethylaminopropyl(meth)-acrylamide, N-methyl(meth)acrylamide, N-butyl(meth)acrylamide, N-cyclohexyl(meth)acrylamide, N-dodecyl(meth)acrylamide, N-benzyl(meth)acrylamide, p-hydroxyphenyl(meth)acrylamide, N-(3-hydroxy-2,2-dimethylpropyl)methacrylamide, ethyl imidazolidonylmethacrylate, N-vinylformamide, N-vinylpyrrolidone anchor
e) up to 25% by weight, preferably up to 15% by weight,
Celanese Emulsions GmbH
Thexton Matthew A.
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