Materials which can be thermally coated with a polymerizable...

Details Materials which can be thermally coated with a polymerizable... Materials which can be thermally coated with a polymerizable...

2000-05-08

2001-09-11

Seidleck, James J. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

C526S318410, C526S325000, C526S309000, C526S329700, C525S193000, C525S301000, C525S309000, C525S451000, C427S384000, C427S388100, C427S389900

Reexamination Certificate

active

06288190

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to so-called reactive plastisols, i.e. thermally film-forming polymers based on (meth)carylates and/or styrene that contain a low molecular weight or oligomeric plasticizer and a reactive monomer component.
2. Description of the Background
Plastisols are suspensions or dispersions of finely divided polymer particles in certain liquid.
STATE OF THE ART
Plastisols are suspensions or dispersions of finely divided polymer particles in certain liquid organic media, so-called plasticizers. The polymer particles microdispersed in the plasticizer phase at room temperature form a paste at room temperature. However, they melt in a “gelling process” typical of plastisol processing, usually at temperatures>100° C., ordinarily>150° C., and form a homogeneous plastic matrix with the plasticizer being absorbed by the polymers.
Typical representatives of thermoplastic finely divided synthetics for the preparation of plastisols are:
Polyvinyl chloride (PVC)
Polymethyl methacrylate (PMMA)
Polyalkyl methacrylate (PAMA), e.g. Polymethyl methacrylate copolymers
Polyvinyl chloride copolymers (PVC/PVAc)
Plastisols based on PVC are widely used because of their desirable practical properties (mechanical strength, adhesion to substrates, etc.), especially in the coatings sector. (Cf. Kunststoff-Handbuch [
Plastics Manual],
2nd Edition, Ed. H. K. Felger, Vol. 2/2, pp. 1077-1124; 854-869, Hanser-Verlag 1985).
Plastisols with beneficial properties based on poly(meth)acrylate have also been developed recently as so-called PAMA plastisols (DE-A 24 54 235, U.S. Pat. No. 4,071,653; DE-A 40 30 080, U.S. Pat. No. 5,120,795).
Esters of phthalic acid, citric acid esters, and also oligomeric compounds are known as plasticizers.
The stability of the pastes formed of plasticizer and polymer at storage temperature is characteristic of plastisols. The standard here is usually >30 days. After application to the substrate to be coated, thermal filming is usually brought about within a few minutes by heating to >150° C.
It is also known how to add a polymerizable crosslinking compound such as a (meth)acrylic ester of a polyfunctional alcohol, for example trimethylolpropane trimethacrylate, to the plastisols to impart adhesion to metallic substrates and to modify strength and hardness. However, the amounts of such additives that can be used are limited since when large amounts are added, for example more than 5 wt. %, there is severe embrittlement of the gelled coating composition.
The reason for this effect lies in the crosslinking nature of the compounds added. Polymerization of such additives occurs by thermal polymerization at the same time as the physical gelling upon heating. The dissociation properties of the initiators added are matched to the gelling temperature used.
DE-PS 25 43 542 (Röhm GmbH) describes a method for producing a plastisol by emulsion polymerization of a monomeric mixture of methyl methacrylate, monomers with a basic nitrogen atom, and other monomers copolymerizable with them. The composition differs from the plastisols pursuant to this invention by the presence of monomers with a basic nitrogen atom.
U.S. Pat. No. 5,298,542 (Nippon Ceon Coop.) describes acrylic ester plastisol compositions. In this case also, the special monomer of the invention as described in Component (B) is not mentioned.
U.S. Pat. No. 5,324,762 (ICI) describes a plastisol from mixtures of methyl methacrylate and isobutyl methacrylate copolymers. Other monomeric components, for example isobornyl methacrylate, and their specific advantages, are not disclosed.
Drawbacks of the plastisols of the state of the art that have been recorded in particular are.
PROBLEM AND SOLUTION
Drawbacks of the plastisols of the state of the art that have been recorded in particular are their deficient hardness and abrasion resistance, which are correlated directly with their high plasticizer content, nominally about 60 wt. %. This drawback also applies particularly to polyalkyl (meth)acrylate plastisols. Raising the solids content with the intention of achieving improved mechanical characteristics, however, is opposed by the severely elevated viscosity of high-solids plastisols.
The problem therefore existed of making available plastisols based on polyalkyl (meth)acrylate with improved practical properties, especially improved mechanical properties and adequate storage stability.
SUMMARY OF THE INVENTION
It has now been found that this invention solves this problem to a great extent, especially.
It has now been found that this invention solves this problem to a great extent, especially since it permits a wide range of variation in setting the plasticizer content, and with it the mechanical properties, without viscosity problems becoming important. It is surprising that storage stability is not impaired in spite of the high percentage of reactive monomers. The term “Reactive Plastisols” is proposed for the object of this invention for immediately understandable reasons.
This invention thus relates to reactive plastisols containing
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
This invention thus relates to reactive plastisols containing:
(A) Thermally film-forming polymers P as the base polymer for plastisols, especially polystyrene and polyvinyl esters, copolymers or poly(meth)acrylic esters, in particular dispersed poly(meth)acrylic esters P-M, preferably in the form of a spray-dried emulsion polymer,
(B) a reactive monomeric component consisting of at least one monofunctional (meth)acrylate monomer RM, especially one with a molecular weight of >150 Daltons,
(C) at least one low molecular weight or oligomeric plasticizer W compatible with the thermally film-forming polymer,
(D) optionally other crosslinking monomers VM,
(E) optionally conventional fillers, pigments, and auxiliaries.
As already described above, thermally film-forming polymers P in themselves are known as base polymers for plastisols. This invention is especially important with regard to the so-called PAMA plastisols formed from poly(meth)acrylic esters P-M. The polymeric component is preferably in dispersed form, especially in the form of a spray-dried emulsion polymer.
Component (A)
The principal monomeric component of the thermally film-forming polymer P is methyl methacrylate or styrene, which as a rule amounts to more than 60 wt. %, especially >70 wt. %, and preferably 80-99 wt. % based on P-M.
A content of 0-20 wt. % of polar comonomers based on P-M is also preferred. Polar comonomers that may be mentioned in particular are those that contain nitrogen and/or oxygen heteroatoms, or less preferably sulfur, particularly when they have hydrogen bonded to them at the same time.
The polar comonomers preferably consist of compounds with Formula II
wherein
R′ stands for hydrogen or methyl, and
R
1
stands for —OH or —NHR
2
, wherein R
2
stands for hydrogen or an alkyl group with 1 to 6 carbon atoms, which can also be branched, or a hydroxyester —O—R
3
—OH, wherein R
3
stands for an alkylene group with 1 to 6 carbon atoms, which can also be branched, or are selected from the group consisting of maleic acid, maleic anhydride, fumaric acid, or itaconic acid.
(Meth)acrylic acid and (meth)acrylamide may be mentioned in particular.
Besides methyl methacrylate and the polar comonomer, the poly(meth)acrylic esters P-M can also contain other monomers with Formula III different from MMA
wherein
R″ stands for hydrogen or methyl, and
R
2
stands for an alkyl group with 1 to 10 carbon atoms, which may optionally be branched, and as well stands for a cycloalkyl group with 3-7 ring members.
The monomers with Formula III are preferably C4-alkyl esters of acrylic acid or of methacrylic acid, for example isobutyl (meth)acrylate or n-butyl (meth)acrylate, or ethylhexyl methacrylate, isobornyl methacrylate, or cyclohexyl methacrylate.
Poly(meth)acrylic esters P-M with a core-shell structure are of special interest.
As a standard for the content of thermally film-forming polymers

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