Process for preparing adhesives having improved adhesion

Details Process for preparing adhesives having improved adhesion Process for preparing adhesives having improved adhesion

2001-10-24

2003-09-09

Knable, Geoffrey L. (Department: 1733)

Adhesive bonding and miscellaneous chemical manufacture

Methods

Surface bonding and/or assembly therefor

C524S823000, C524S832000

Reexamination Certificate

active

06616798

ABSTRACT:

BACKGROUND OF THE INVENTION
1) Field of the Invention
The invention relates to a process for preparing adhesives having improved adhesion and to the use of the adhesives obtainable by this process in adhesive compositions for paper, packaging, wood and textiles and in structural adhesives.
2) Background Art
Polyvinyl alcohol-stabilized vinyl acetate-ethylene copolymers in the form of their aqueous dispersions are frequently employed to bond paper and packaging materials. A disadvantage, however, is that the adhesion is often inadequate to bond to surfaces of plastic. To improve the adhesion, it is common to add plasticizing additives to modify the adhesive with polyacrylate dispersion or to lower the glass transition temperature of the vinyl acetate-ethylene copolymer by incorporating larger amounts of ethylene into it. A disadvantage of these measures, however, is the marked reduction in the cohesion of the adhesives.
It is therefore an object of the invention to improve the adhesion of adhesives, especially those based on polyvinyl alcohol-stabilized vinyl acetate-ethylene copolymers, without having to deal with the above-mentioned disadvantages.
It has surprisingly been found that by copolymerization with vinyl esters of alpha-branched tertiary monocarboxylic acids of 11 carbon atoms, the adhesion of the adhesives can be increased considerably without a dramatic drop in the cohesion.
The use of vinyl esters of alpha-branched tertiary monocarboxylic acids to prepare terpolymer dispersions with vinyl acetate and ethylene is known. The patent literature to date has described the use of vinyl esters of alpha-branched carboxylic acids of 5, 9 or 10 carbon atoms (VeoVa5®, VeoVa9® and VeoVa10®, trade names of Shell), especially for improving the alkali stability and light stability, and for reducing the water absorption of the polymers.
JP-A 07113069 (Derwent Abstract AN 95-196794) discloses VeoVa9®/ethylene copolymer dispersions for bonding polypropylene surfaces and JP-A 05025449 (Derwent Abstract 93-080621) discloses aqueous VeoVa10®/ethylene copolymer dispersions for bonding polyethylene foams. JP-A 58149970 (Derwent Abstract AN 83-786760) discloses aqueous vinyl ester/ethylene copolymer dispersions as adhesives for bonding hydrophobic materials, the vinyl esters used preferably being vinyl acetate, vinyl propionate, vinyl laurate and VeoVa10®. Adhesive blends of alkylphenolic resins and aqueous vinyl esters/ethylene copolymer dispersions are known from JP-A 57207662 (Derwent Abstract AN 83-11223K), the preferred vinyl esters being vinyl acetate, vinyl propionate and VeoVa10®. The bonds produced with the adhesives of the invention are notable for increased water resistance. JP-A 01126251 (Derwent Abstract AN 89-188346) describes improving the properties of cementious compositions by adding aqueous dispersions of terpolymers of ethylene/vinyl acetate/Versatic acid vinyl esters of 9 to 11 carbon atoms.
EP-A 315278 describes vinyl acetate copolymers with VeoVa9® or VeoVa10®, EP-A 431656 acrylate copolymers with VeoVa9® and, optionally, VeoVa10®, EP-A 486110 acrylate-VeoVa10® copolymers, and EP-A 516202 acrylate-VeoVa5® copolymers, in each case as coating materials.
SUMMARY OF THE INVENTION
The invention provides a process for preparing adhesives having improved adhesion, in the form of their aqueous dispersions or water-redispersible dispersion powders, by emulsion polymerization in the presence of polyvinyl alcohol with or without drying of the dispersion obtainable by this process, which comprises polymerizing a comonomer mixture comprising
a) one or more monomers from the group consisting of the vinyl esters of unbranched and branched carboxylic acids of 1 to 10 carbon atoms, the esters of acrylic acid and methacrylic acid with branched and unbranched alcohols of 1 to 12 carbon atoms, vinylaromatic compounds, vinyl halides and alpha-olefins, and
b) from 0.01 to 50% by weight, based on the overall weight of the comonomers, of a vinyl ester of alpha-branched tertiary monocarboxylic acids of 11 carbon atoms, in the presence of
c) from 0.1 to 15% by weight, based on the overall weight of the comonomers, of polyvinyl alcohol.
The vinyl esters of alpha-branched tertiary monocarboxylic acids of 11 carbon atoms are produced by Shell Chemicals under the name VeoVa®11 and are vinyl esters of versatic acid.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Based on the overall weight of the comonomers, it is preferred to copolymerize from 2 to 15% by weight of a vinyl ester of alpha-branched tertiary monocarboxylic acids of 11 carbon atoms with one or more monomers from the group consisting of vinyl esters of unbranched or branched alkylcarboxylic acids of 1 to 10 carbon atoms, methacrylates and acrylates of unbranched or branched alcohols of 1 to 12 carbon atoms, dienes such as butadiene or isoprene, olefins such as ethene or propene, vinylaromatic compounds such as styrene, methylstyrene and vinyltoluene, and vinyl halides such as vinyl chloride, in the stated amounts.
Preferred vinyl esters 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 5 to 10 carbon atoms, such as VeoVa9®, VeoVa10® (trade names of Shell). Vinyl acetate is particularly preferred.
Preferred methacrylates or acrylates are methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, n-butyl acrylate, t-butyl acrylate, n-butyl methacrylate, t-butyl methacrylate, and 2-ethylhexyl acrylate. Methyl acrylate, methyl methacrylate, n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferred.
If desired, it is also possible to copolymerize from 0.05 to 10.0% by weight, based on the overall weight of the monomers, of auxiliary monomers from the group consisting of ethylenically unsaturated mono- and dicarboxylic acids and their amides, such as acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid, acrylamide, and methacrylamide; ethylenically unsaturated sulfonic acids and their salts, preferably vinylsulfonic acid and 2-acrylamidopropanesulfonate, and N-vinylpyrrolidone.
Further examples of auxiliary monomers in the stated amounts are hydrophobicizing and pro-crosslinking alkoxysilane-functional monomers such as acryloxypropyltri(alkoxy)silanes and methacryloxypropyltri(alkoxy)silanes, vinyltrialkoxysilanes and vinylmethyldialkoxysilanes, the alkoxy groups present possibly being, for example, methoxy, ethoxy, methoxyethylene, ethoxyethylene, methoxypropylene glycol ether and ethoxypropylene glycol ether radicals. Preference is given to vinyltriethoxysilane and gamma-methacryloxypropyltriethoxysilane.
Further examples of auxiliary monomers in the stated amounts are additional crosslinkers such as acrylamidoglycolic acid (AGA), methacrylamidoglycolic acid methyl ester (MAGME), N-methylolacrylamide (NMA), N-methylolmethacrylamide (NMMA), N-methylol allyl-carbamate, alkyl ethers of N-methylolacrylamide or N-methylolmethacrylamide and also the isobutoxy ethers or n-butoxy ethers thereof.
The polymer composition is generally chosen so as to give a glass transition temperature Tg of from −30° C. to +40° C. The glass transition temperature Tg of the polymers can be determined in a known manner by means of Differential Scanning Calorimetry (DSC). The Tg can also be calculated approximately in advance by means of the Fox equation. According to Fox T. G., Bull. Am. Physics Soc. 1, 3, page 123 (1956) it holds that: 1/Tg=x
1
/Tg
1
+x
2
/Tg
2
+ . . . + x
n
/Tg
n
, where x
n
is the mass fraction (% by weight/100) of the monomer n and Tg
n
is the glass transition temperature in degrees Kelvin of the homopolymer of the monomer n. Tg values for homopolymers are listed in Polymer Handbook 3rd Edition, J. Wiley & Sons, New York (1989).
Preferred comonomer mixtures comprise the comonomer b) in the stated amount and also:
vinyl acetate,
vinyl acetate and ethylene with from 30 to 95% by weight of vinyl ac

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