Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-12-05
2002-08-06
Henderson, Christopher (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S503000, C526S202000
Reexamination Certificate
active
06429251
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The invention relates to polyvinyl alcohol-stabilized copolymers of 1,3-dienes with methacrylates and/or acrylates in the form of their aqueous polymer dispersions or polymer powders redispersible in water, and to a process for their preparation and their use.
2) Background Art
As explained in WO-A 97/15603, polymer dispersions which are stabilized with polyvinyl alcohol (PVA1) have characteristic rheology and tack properties, so that, in contrast to emulsifier-stabilizer dispersions, they are particularly suitable for coating and adhesive applications. For example, paper packaging adhesives prepared using emulsifier-stabilized copolymer dispersions have poor machine running properties compared with PVA1-stabilized copolymer dispersions, owing to the fine particles (particle size in general <400 nm), the rheology and the low surface tension of the emulsifier-stabilized dispersion. A disadvantage of the adhesives prepared using vinyl ester-based or acrylate-based copolymer dispersions is that, owing to their generally relatively high glass transition temperature (Tg) or the minimum film formation temperature (MFT), the addition of plasticizer for processing is necessary.
Using vinyl acetate/ethylene copolymer dispersions, it is possible to prepare plasticizer-free paper packaging adhesives which have improving adhesion properties with increasing ethylene content and hence associated declining Tg. A disadvantage of the adhesives prepared using polyvinyl alcohol-stabilized vinyl acetate/ethylene copolymer dispersions is that the reduction in Tg due to copolymerization with ethylene is subject to limits owing to the crystallization of the vinyl acetate/ethylene copolymers.
By copolymerizing 2-ethylhexyl acrylate, glass transition temperatures Tg down to below −50° C. can be achieved with polymer dispersions based on acrylate polymers. However, pure acrylate dispersions on an alkaline substrate release the corresponding alcohol at pH>9, owing to hydrolysis of the ester group. Thus, 2-ethylhexyl alcohol is released from 2-ethylhexyl acrylate and may be released into the surrounding air. Moreover, by oxidation of 2-ethylhexyl alcohol to the corresponding acid, secondary products which are not toxicologically safe can be produced. A further side effect is that polyacrylic acid domains having a very high Tg are obtained by hydrolysis of the ester group. The high Tg in turn has an adverse effect on the viscoelastic modulus of the resin and hence a negative effect on a number of performance characteristics such as wetting and adhesion.
It was therefore the object to provide a hydrolysis-stable dispersion or powder type whose polymer resin can be prepared in a wide Tg range (−80° C.<Tg<+100° C.). The aqueous dispersion or redispersion should have the advantageous Theological properties (machine running properties) of polyvinyl alcohol-stabilized vinyl ha ester or acrylate dispersions and should have good adhesion to a very wide range of substrates such as paper, plastics and minerals, even in the case of low Tg and in the absence of plasticizer.
This object was achieved by a process by means of which polyvinyl alcohol-stabilized copolymers of 1,3-dienes with methacrylates and/or acrylates are obtainable in the form of their aqueous polymer dispersions or polymer powders redispersible in water.
DE-A 2442121 (GB-A 1438449) disclosed that polyvinyl alcohol is not effective as a sole dispersant in the preparation of polymers of (meth)acrylates or butadienes and has therefore always been used as a mixture with emulsifiers. DE-A 2442121 therefore recommends the use of a polyvinyl alcohol modified with alkali metal olefin sulfonate for the preparation of polyvinyl alcohol-stabilized polymers of (meth)acrylate or butadiene monomers. The disadvantage is that this too is an ionic stabilizer and the disadvantages occurring in the case of emulsifiers and described above therefore also occur.
WO-A 97/15603 describes butadiene/(meth)acrylate copolymers which are stabilized with polyvinyl alcohol and emulsifiers and are obtained by grafting the polyvinyl alcohol moiety onto the copolymer by means of a functionalized silane, especially mercaptotrialkoxysilane.
U.S. Pat. No. 5,200,459 recommends copolymerization in the presence of a stabilizing solvent, in particular from the group consisting of the alcohols, for the preparation of polyvinyl alcohol-stabilized, aqueous butadiene copolymer latices.
WO-A 99/28360 discloses the preparation of polyvinyl alcohol-stabilized styrene/butadiene copolymer dispersions or dispersion powders. However, styrene-containing copolymer dispersions have the disadvantage of having viscoelastic polymer properties disadvantageous for many applications (for example in adhesives) (poor deformability). In the copolymer styrene produces polymer domains having a high Tg; these lead to relatively disadvantageous viscoelastic resin properties. This results, for example in the case of adhesives, in poorer wetting properties and poorer tack.
DE-A 19548313 (U.S. Pat. No. 5,733,944) and EP-A 744418 (U.S. Pat. No. 5,733,944) disclose processes for the preparation of aqueous dispersions of butadiene/(meth)acrylate copolymers which are prepared in the presence of a protective colloid and an emulsifier.
The invention relates to emulsifier- and solvent-free copolymers, stabilized with nonionic polyvinyl alcohol as protective colloid, of 1,3-dienes with methacrylates and/or acrylates in the form of their aqueous polymer dispersions or polymer powders redispersible in water, obtainable by emulsion polymerization and optionally drying of the polymer dispersions obtained thereby, from 10 to 100% by weight of the amount of polyvinyl alcohol being initially introduced before the initiation of the polymerization and the remaining amount being metered in during polymerization, and the addition of polyvinyl alcohol and the comonomers being controlled in such a way that, during the polymerization, the amount of protective colloid is always from 1 to 70% by weight of the total amount of free comonomers.
The invention furthermore relates to a process for the preparation of emulsifier- and solvent-free copolymers, stabilized with polyvinyl alcohol as a protective colloid, of 1,3-dienes with methacrylates and/or acrylates in the form of their aqueous polymer dispersions or polymer powders redispersible in water, by emulsion polymerization of a mixture containing one or more comonomers from the group consisting of the 1,3-dienes and one or more comonomers from the group consisting of the methacrylates and acrylates, in the presence of from 1 to 15% by weight, based on the total weight of the monomers, of one or more polyvinyl alcohols and optionally drying of the polymer dispersions obtained thereby, from 10 to 100% by weight of the amount of polyvinyl alcohol being initially introduced before the initiation of the polymerization and the remaining amount being metered in during polymerization, and the addition of polyvinyl alcohol and of the comonomers being controlled in such a way that, during the polymerization, the amount of protective colloid is always from 1 to 70% by weight of the total amount of free comonomers.
Suitable 1,3-dienes are 1,3-butadiene and isoprene, 1,3-butadiene being preferred. Suitable methacrylates and acrylates are those of straight-chain and branched alcohols having 1 to 10 carbon atoms. Preferred methacrylates are methyl methacrylate, ethyl methacrylate, propyl methacrylate and n-butyl methacrylate. Methyl methacrylate is particularly preferred. Preferred acrylates are methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, tert-butyl acrylate t-butylmeth acrylate and 2-ethylhexyl acrylate. Methyl acrylate, n-butyl acrylate and 2-ethylhexyl acrylate are particularly preferred.
If required, from 1 to 30% by weight, based on the total weight of the monomer mixture, of further monomers copolymerizable with 1,3-dienes and with the (meth)acrylates such as ethylene, vinyl chloride or vinyl e
Härzschel Reinhard
Mayer Theo
Brooks & Kushman P.C.
Henderson Christopher
Wacker Polymer Systems GmbH & Co. KG
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