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
2000-11-02
2002-04-16
Nutter, Nathan M. (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...
C525S192000, C525S193000, C525S222000, C525S232000, C525S240000
Reexamination Certificate
active
06372846
ABSTRACT:
The present invention relates to a polymer composition, in particular a composition comprising a base polymer which is a poly(alkyl(meth)acrylate) and a rubber toughening agent.
Base polymer such as a poly(alkyl(meth)acrylate), e.g. poly(methyl methacrylate), known as PMMA, can be a relatively brittle material. This detracts from its use in certain applications, e.g. external light clusters for automotive vehicles, where properties such as impact resistance are important. Conventionally, the properties of the base polymer can be improved by the addition of comonomers during its production and/or by the addition of toughening agents. Typically, the toughening agents are small particles having a core-shell structure, e.g. as disclosed in GB-A-2039496. The toughening agents are added as pre-made particles which are then compounded with the base polymer. Such toughening agents are prepared using emulsion phase polymerisation in which each layer is sequentially polymerised one on another. Consequently, due to the complexity of the core-shell manufacturing process, the base polymer so toughened is relatively expensive and is primarily confined for use in specialised applications.
Certain rubber toughening agents are used to improve the properties of polystyrene. EP-0818481-A2 describes a process for the manufacture of high impact polystyrene (HIPS) materials using low shear mechanical agitation such that the product produced contains large particle sizes of a rubber-like composite phase up to 12 micron for shear rates all lower than 50 rpm. These particle sizes are retained when this polymeric mixture is further extruded into an article.
It has now been found that base polymer such as a poly(alkyl(meth)acrylate) as previously described can be toughened by the addition of certain rubber toughening agents which are added during the production of the base polymer. The polymer composition so formed has improved impact resistance compared to that of the base polymer and has a unique morphology.
Accordingly, in a first aspect, the present invention provides a polymer composition comprising
(a) a base polymer which is a poly(alkyl(meth)acrylate); and
(b) a rubber toughening agent selected from the group consisting of
(i) copolymers of (alkyl)acrylate rubbers
(ii) copolymers of vinyl aromatic monomers with (alkyl)acrylates
(iii) copolymers of vinyl aromatic monomers with conjugated diolefins
(iv) copolymers of vinyl aromatic monomers with monoethylenically unsaturated monomers
wherein the rubber toughening agent is present in the polymer composition as discrete islands substantially surrounded by the base polymer and in which islands are sub-islands of the base polymer.
In a second aspect the present invention provides a process for the preparation of a polymer composition comprising
(a) a base polymer which is a poly(alkyl(meth)acrylate); and
(b) a rubber toughening agent selected from the group consisting of
(i) copolymers of (alkyl)acrylate rubbers
(ii) copolymers of vinyl aromatic monomers with (alkyl)acrylates
(iii) copolymers of vinyl aromatic monomers with conjugated diolefins
(iv) copolymers of vinyl aromatic monomers with monoethylenically unsaturated monomers
wherein the rubber toughening agent is present in the polymer composition as discrete islands substantially surrounded by the base polymer and in which islands are sub-islands of the base polymer which process comprises dissolving the rubber toughening agent in a monomer composition from which the base polymer is to be formed to form a solution, polymerising the monomer composition to form the base polymer and thereby causing the rubber toughening agent to come out of solution so as to form islands within the polymer composition in which are included sub-islands of the base polymer.
In a third aspect the present invention provides a moulded article formed from a polymer composition comprising
(a) a base polymer which is a poly(alkyl(meth)acrylate); and
(b) a rubber toughening agent selected from the group consisting of
(i) copolymers of (alkyl)acrylate rubbers
(ii) copolymers of vinyl aromatic monomers with (alkyl)acrylates
(iii) copolymers of vinyl aromatic monomers with conjugated diolefins
(iv) copolymers of vinyl aromatic monomers with monoethylenically unsaturated monomers
wherein the rubber toughening agent is present in the polymer composition as discrete islands substantially surrounded by the base polymer and in which islands are sub-islands of the base polymer.
For the rubber toughening agent (i) copolymers of (alkyl)acrylate rubbers and (ii) copolymers of vinyl aromatic monomers with (alkyl)acrylates include both saturated and unsaturated copolymers.
The base polymer may be a homopolymer or a copolymer. Preferably the base polymer contains an alkyl methacrylate, such as a C
1
-C
4
alkyl methacrylate, e.g. methyl methacrylate. Particularly preferred is when the base polymer is a copolymer of such an alkyl methacrylate and an alkyl acrylate, such as a C
1
-C
4
alkyl acrylate, e.g. ethyl acrylate.
The rubber toughening agent may be selected from a wide variety of commercially available and other copolymers. Suitable copolymers of vinyl aromatic monomers with (alkyl)acrylates include styrene-butyl acrylate (St-BA) and styrene-lauryl methacrylate (St-LMA) rubbers, preferably incorporating allyl unsaturation. Examples of monomers that can provide allyl unsaturation include allyl methacrylate (AMA) and glycidyl methacrylate (GMA) Suitable copolymers of (alkyl)acrylate rubbers include benzyl methacrylate-lauryl methacrylate (BzMA-LMA) rubber also preferably incorporating allyl unsaturation. Suitable copolymers of vinyl aromatic monomers with conjugated diolefins include styrene-butadiene rubbers such as Nipol NS210., polystyrene-polybutadiene block copolymers such as Cariflex 1184, S1509, S1013. Suitable copolymers of vinyl aromatic monomers with monoethylenically unsaturated monomers include styrene ethylene butylene styrene (SEBS) copolymer.
It is preferred that the rubber toughening agent contains at least some degree of unsaturation, for example where the rubber toughening agent is a styrene-butylacrylate rubber it is preferred that the level of allyl unsaturation is from 1.5 to 5.0% (on a molar basis), particularly from 1.5 to 4.5%, and especially about 2%. Where the rubber toughening agent is selected from saturated rubbers such as styrene-butyl acrylate (St-BA), styrene-lauryl methacrylate (St-LMA) and benzyl methacrylate-lauryl methacrylate (BzMA-LMA) rubbers we find that less of the rubber toughening agent is present in the desired island/sub-island morphology whilst a proportion is present in the form of discreet, separate phase.
The islands of rubber toughening agent are generally circular in cross section and typically up to very large average particle sizes of 250 microns or less in diameter, for example from 10 to 100 microns in diameter. However, where the optical properties of the polymer composition are especially important small diameter islands, e.g. from 2 to 5 microns, are desirable. Therefore it is surprising that when an unsaturated styrene-laurylmethacrylate rubber is used even with islands of up to 10 microns in size the optical properties of the polymer composition remain acceptable whereas a comparable polymer composition containing an unsaturated styrene-butylacrylate rubber is translucent and hazy.
Typically, the rubber toughening agent represents from 1 to 20% preferably from 1 to 10% by weight of the polymer composition. More preferably, the rubber toughening agent represents from 2 to 6% by weight of the polymer composition and in particular about 4%, for example 96% by weight of a base polymer containing methyl methacrylate and with 4% by weight of a styrene-butadiene rubber.
The polymer composition is prepared by dissolving the rubber toughening agent in a monomer composition from which the base polymer is to be formed, for example a mixture of methyl methacrylate and ethyl acrylate, so as to form a solution. The preparation of the solution may be assisted with stirring or agitation and
Emmerson Gordon Thomas
Jenkins Stephen Derek
Lindsay Christopher Ian
McGrail Patrick Terence
Gennaro Jane E.
National Starch and Chemical Investment Holding Corporation
Nutter Nathan M.
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