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
1999-09-14
2001-05-22
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S057000, C525S125000, C526S312000, C528S069000, C428S425100
Reexamination Certificate
active
06235843
ABSTRACT:
The invention relates to a process for the preparation of crosslinkable dispersion powders which are redispersible in water and contain isocyanate groups.
The preparation of aqueous dispersions which contained masked isocyanate groups was already a research subject which was paid much attention in the 1960s. Aqueous dispersions of copolymers which contain masked isocyanates are employed, above all, for the preparation of crosslinkable coating compositions, to which low or high molecular weight crosslinking agents with hydroxyl, carboxyl or amine groups, which react with the masked isocyanate function, are added for crosslinking.
An isopropenyl-dimethylbenzyl isocyanate (TMI) was mentioned for the first time in 1966. This molecule, which in general is present as a meta or para derivative, can be copolymerized, on the basis of its polymerization parameters, by free radicals by the customary methods, for example with vinylaromatics, (meth)acrylic acid compounds, dienes and maleic and fumaric acid derivatives, but not, for example, with ethylene, vinyl esters and vinyl chloride. For preparation of copolymers of isopropenyl-dimethylbenzyl isocyanate (TMI) with monomers with unfavourable copolymerization parameters, U.S. Pat. No. 5,314,964 proposes grafting of TMI onto polymers of these monomers.
Other isocyanates which are suitable for the preparation of aqueous polymer dispersions are described by the general formula (I) CH
2
═CR
1
—CO—O—R
2
—CR
3
R
4
—N═C═O where R
1
=H or CH
3
and R
2
=an alkylene group having 1 to 18 C atoms, and R
3
and R
4
=identical or different alkyl groups having 1 to 4 C atoms. Their preparation is described in DE-B 4302084. These (meth)-acrylic acid derivatives containing isocyanate groups can also be copolymerized with vinyl esters, vinyl chloride and ethylene. Their polymerization in an aqueous emulsion in the presence of an anionic and/or nonionic emulsifier by the preemulsion process is described in DE-A 4433874. With the aid of core/shell polymerization—the isocyanate in the core and the functional groups intended for the crosslinking, for example hydroxyl, in the shell—it was possible to dispense with additional bi- or polyfunctional crosslinker molecules. It was also proposed to block the isocyanate groups, for example with carbamates, presumably because the storage stability of the polymers was still not adequate. The copolymers can be obtained as solid substances from the aqueous polymer dispersions obtainable by this process by drying processes, such as spray or freeze drying. However, the products obtained by this procedure are not redispersible in water.
The object of the invention was thus to provide crosslinkable polymers which contain isocyanate groups, have an adequate storage stability, and above all are readily redispersible in water.
Surprisingly, it has been possible to achieve the object by carrying out the preparation of the copolymers containing isocyanate groups and the drying thereof in the presence of protective colloids. It is surprising that the isocyanate groups do not react immediately with crosslinking, although the polymerization and drying are carried out in the presence of polyvinyl alcohol or other protective colloids which contain hydroxyl groups or other reactive H atoms, and at elevated temperature.
The invention relates to a process for the preparation of crosslinkable dispersion powders which are redispersible in water and contain isocyanate groups by free-radical emulsion polymerization of one or more ethylenically unsaturated monomers in the presence of 0.2 to 6% by weight, based on the total weight of the monomers, of one or more compounds from the group consisting of meta- and para-isopropenyl -alpha,alpha-dimethylbenzyl isocyanate and isocyanates of the general formula (I) CH
2
═CR
1
—CO—O—R
2
—CR
3
R
4
—N═C═O where R
1
=H or CH
3
and R
2
=an alkylene group having 1 to 18 C atoms, and R
3
and R
4
=identical or different alkyl groups having 1 to 4 C atoms, and drying of the dispersions obtained by this polymerization, characterized in that the emulsion polymerization and the drying are carried out in the presence of 5 to 70% by weight of a protective colloid, based on the total weight of the monomers.
Preferred isocyanates are meta- and para-iso -propenyl-alpha,alpha-dimethylbenzyl isocyanate (TMI) and 2-methyl-2-isocyanatopropyl methacrylate. The isocyanates are preferably copolymerized in an amount of 0.5 to 5% by weight, based on the total weight of the monomers. If appropriate, the isocyanate groups of the compounds mentioned can also be blocked, for example with phenol, salicylic acid esters, ketoximes, caprolactam, malonic acid dialkyl esters, acetoacetic acid alkyl esters, 2,2-dimethyl-1,3-dioxane-4,6-dione, hydroxamic acid esters and amine-imides.
Suitable comonomers are one or more monomers from the group consisting of vinyl esters of unbranched or branched alkylcarboxylic acids having 1 to 18 C atoms, methacrylic acid esters and acrylic acid esters of unbranched or branched alcohols having 1 to 18 C atoms, olefins, vinylaromatics and vinylhalogen compounds.
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 having up to 11 C atoms, for example VeoVa9
R
, VeoVa10
R
or VeoVa11
R
. Vinyl acetate is particularly preferred. Preferred acrylic acid esters or methacrylic acid esters are their methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, t-butyl, hexyl, ethylhexyl, cyclohexyl and dodecyl esters. Preferred olefins are ethylene, propylene, butadiene or isoprene. Preferred vinylaromatics are styrene, methylstyrene and vinyltoluene. Vinyl chloride is the preferred vinyl halide.
For the copolymerization of TMI, the copolymerization parameters are to be taken into account in the choice of comonomers. TMI is a methylstyrene derivative and therefore cannot be copolymerized with vinyl esters, ethylene, propylene and vinyl halides in the customary manner. If copolymers are nevertheless to be prepared with such monomers, the known measures for the preparation of graft polymers or of core/shell polymers must be used, for example those described in U.S. Pat. No. 5,314,964 and DE-B 4433874.
If appropriate, monomers which contain one or more reactive H atoms can also be copolymerized. Monomers with reactive H atoms are, for example, hydroxyalkyl (meth)acrylates, such as hydroxypropyl (meth)-acrylate, hydroxybutyl (meth)acrylate and hydroxyethyl (meth) acrylate; ethylenically unsaturated carboxylic acids, such as (meth)acrylic acid, fumaric acid, maleic acid and itaconic acid, amides thereof, the half-esters of fumaric and/or maleic acid, the hydroxyalkyl esters of the carboxylic acids mentioned, and their monoesters with polyalkylene glycols having 2 to 10 recurring alkylene oxide units. The equivalent ratio of active H atoms to NCO groups can be 0.2 to 3, preferably 0.6 to 1.4. If a particularly good storage stability is required, the comonomers containing active H atoms can be copolymerized in a core/shell polymerization, TMI and/or the compounds of the general formula (I), if appropriate in blocked form, being copolymerized into the core and the monomers containing a reactive H atom being copolymerized into the shell, or vice versa. The weight ratio of core to shell can be 20:80 to 70:30; ratios of 40:60 to 60:40 are advantageous.
Possible comonomers are also compounds from the group consisting of ethylenically unsaturated sulphonic acids and salts thereof, preferably vinylsulphonic acid; and/or silanes which can be polymerized by free radicals or silanes containing mercaptan or Si—H groups. Preferred silicon-containing monomers are vinyltri-methoxy- and vinyltriethoxysilane, gamma-methacryloxy-propyltriethoxysilane and vinylmethyldi-methoxy-, -di-ethoxy-, -dibutoxy- and -di-l-methyl-2-methoxy-silane and (partial) hydrolysates thereof. Other comonomers having a crosslinking acti
Bagwell Melanie D.
Brooks & Kushman P.C.
Seidleck James J.
Wacker-Chemie GmbH
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