Thermoplastic compositions providing matt surface

Details Thermoplastic compositions providing matt surface Thermoplastic compositions providing matt surface

2002-09-10

2004-11-02

Mullis, Jeffrey C. (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...

C525S066000, C525S070000, C525S073000, C525S077000, C525S080000, C525S085000

Reexamination Certificate

active

06812282

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a thermoplastic composition that contains grafted acrylate rubber and more particularly to compositions suitable for making molded articles having a non-glossy surface.
SUMMARY OF THE INVENTION
A low gloss thermoplastic composition suitable for making articles having low gloss and a process for its preparation are disclosed. The composition contains a resinous component that includes (a) a (co)polyalkyl (meth)acrylate rubber characterized in that it contains no grafted phase, (b) a poly(vinyl aromatic-co-nitrile)-grafted (co)polyalkyl (meth)acrylate rubber, and (c) a poly(vinylaromatic-co-nitrile), and a gloss-reducing agent that is the reaction product of (d) a compound having two or more maleic anhydride groups per molecule, and (e) a compound having two or more terminal primary amine groups per molecule, with the proviso that the total of the maleic anhydride groups per molecule and the terminal primary amine functional groups per molecule is greater than 4. The incorporation of the gloss reducing agent in the inventive composition may be by blending the reaction product or, in the alternative, by blending the reactants (d) and (e) in the molten resinous component under process conditions designed to bring about the in situ formation of the inventive gloss reducing agent.
BACKGROUND OF THE INVENTION
Products prepared of thermoplastic molding compositions are often times glossy, yet for some applications this is not a desirable property.
There is considerable need for low-gloss compositions especially in applications such as computer housings, keyboards, appliances and automotive parts.
Acrylonitrile-styrene-acrylate interpolymers (hereinafter referred to as “ASA resins”) are well known in the art, and have many favorable features such as good strength and outstanding weathering resistance. Attempts to reduce the high gloss of these resins met with the disadvantages as discussed below.
Elimination of gloss by surface embossing has been practiced but requires a separate step and adds cost. Moreover, subsequent abrasion may remove the embossed matte surface and cause the gloss to reappear. Addition of a finely-divided filler, such as silica, silicate or aluminate or other similarly inert minerals has been demonstrated to reduce the gloss of thermoplastic molding compositions yet this is often accompanied by an undesirable reduction in the level of at least some physical and/or mechanical properties of the molded article, most notably the impact strength. In addition to the adverse effect on the impact strength, there is often a corresponding decline of the heat distortion temperature, decline in the weld line strength, deficient weathering and light stability, as well as other important properties.
U.S. Pat. No. 4,460,742 disclosed a delustered thermoplastic resin composition containing a thermoplastic resin, such as acrylic resin, and a component that contains the crosslinked polymerization product of a C
1-4
alkyl methacrylate and a copolymer of aromatic vinyl and C
1-13
-alkyl acrylate.
U.S. Pat. No. 4,894,416 disclosed a low gloss thermoplastic blend with good physical properties that contains a core-shell ASA (acrylate-styrene-acrylonitrile interpolymer) resin blended with a polymer of glycidyl (meth)acrylate.
U.S. Pat. No. 5,580,924 disclosed reduced gloss thermoplastic compositions entailing compounding a styrene-acrylonitrile copolymer (SAN) in the presence of an electrophilic reagent and an acid to form a gel, and then compounding the resultant gels with polycarbonate, SAN and ABS graft polymer to form a PC/ABS/SAN composition having reduced gloss.
U.S. Pat. No. 5,990,239 disclosed a low gloss thermoplastic blend that contains an ASA resin blended with a polyalkyl acrylate rubber containing no grafted phase.
DETAILED DESCRIPTION OF THE INVENTION
The inventive thermoplastic composition comprises
(I) a resinous component that includes:
(a) An ungrafted (co)polyalkyl (meth)acrylate rubber, preferably polybutyl (meth)acrylate rubber, which may optionally be crosslinked,
(b) A grafted rubber, which may optionally be crosslinked, containing a substrate of polyalkyl (meth)acrylate, preferably polybutyl (meth)acrylate and a phase grafted thereto (herein grafted phase) where the substrate may be homopolymeric or copolymeric and where the grafted phase contains poly(vinyl aromatc-co-nitrile), preferably styrene-acrylonitrile (SAN), and
(c) A poly(vinyl aromatic-co-nitrile), preferably styrene-acrylonitrile (SAN) having a weight-average molecular weight of about 50,000 to 200,000, preferably 80,000 to 150,000 g/mole, and
(II) a gloss-reducing agent that is the reaction product of:
(d) A compound having two or more maleic anhydride groups per molecule, and
(e) A compound having two or more terminal primary amine groups per molecule.
In a preferred embodiment, the inventive composition is further characterized in that the contents of (co)polyalkyl (methacrylate rubber is 10 to 40, preferably 15 to 35%, relative to the weight of the resinous component. In a yet further preferred embodiment, Components (a) and (b) relate by weight such that the ratio between (a) to the total of (a)+(b) is 0.1 to 0.8, preferably 0.15 to 0.7. In a still further preferred embodiment the particle size of the acrylate rubber (weight average particle size) is 0.02 to 10 microns, preferably 0.03 to 1 microns.
The ungrafted rubber, (a) of the resinous component, is (co)polyalkyl (meth)acrylate rubber, which may optionally be crosslinked, is the polymerized product of known (co)monomers, including C
1
-C
18
-alkyl acrylate and C
1
-C
6
-alkyl methacrylate, preferably, C
2
-C
8
-alkyl acrylate and C
1
-C
4
-alkyl methacrylate with or without additional comonomers. Most preferred are poly(n-butyl acrylate), poly(ethyl acrylate) and poly(2-ethyl hexylacrylate). Optionally, the rubber may contain small amounts, of about 1 to 20% by weight relative to the weight of the (met)acrylate monomer of additional monomers such as styrene, (meth)-acrylonitrile, methylmethacrylate,(meth)acrylic acid, vinylidene chloride, vinyl toluene or other ethylenically unsaturated comonomers which may be copolymerizable with the (meth)acrylate monomer.
Crosslinking as an optional characteristic of the rubber useful in the present context results in the substantial insolubility of the rubber in such solvents as tetrahydrofuran, methyl ethyl ketone, cyclohexanone or acetone. The degree of crosslinking imparted to the rubber is that which results from the incorporation therewith of about 0.1 to 2.0 parts by weight (pbw) of crosslinking agent per hundred parts by weight of rubber (pphr); preferably the crosslinking agent is present in an amount of 0.4 to 1.4 pphr. Crosslinking of the copolymer substrate may be attained during the polymerization of the rubber by including in the reaction, a crosslinking agent, for instance, di- or poly-functional ethylenically unsaturated monomer. Among the suitable crosslinking agents mention may be made of divinyl benzene, trimethylol propane triacrylate, allyl methacrylate, diallyl fumerate, diallyl maleate, 1,3-butylene dimethacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, trimethylol propane trimethacrylate, methylene bisacrylamide, diethylene glycol diacrylate, ethylene glycol diacrylate, divinyl ether, diallyl phthalate, divinyl sulfone, divinyl sorbitol, triethylene glycol dimethacrylate, trimethylene glycol diacrylate, butylene glycol diacrylate, octylene glycol diacrylate, trimethylolpropane triacrylate, tetraacrylate ester of pentaerythritol, ethylidene norbornene, vinyl norbornene, diallyl phosphonate, triallyl cyanurate and triallyl isocyanurate. The preferred crosslinking agent is diallyl maleate (DAM).
The ungrafted polyalkyl acrylate rubber has a weight average particle size of 0.02 to 10 microns, preferably 0.03 to 1 microns.
The grafted rubber, (b) of the resinous component, contains an optionally crosslinked substrate of (co)polyalkyl (meth)acrylate and a phase grafted thereto (herein “grafted phase

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