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
1999-08-25
2004-01-06
Hampton-Hightower, P. (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, C525S077000, C525S09200D, C525S166000, C525S412000, C525S426000, C525S434000, C525S437000, C524S555000, C524S556000, C524S560000
Reexamination Certificate
active
06673873
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to moldable, thermoplastic multipolymer blends of an acrylic-based copolymer and a polyetheresteramide which exhibits good transparency, good chemical resistance and the enhanced dissipation of electrostatic charge.
BACKGROUND OF THE INVENTION
Transparent plastic compositions are useful for a number of applications including components for electronic and scientific equipment, point of purchase displays, packaging containers, etc., since they permit visual inspection of the items housed within the plastic. Such transparent plastic compositions are especially useful for the packaging of electronic components such as magnetic head assemblies and clean room applications. In addition, it is often desirable that the packages be reusable after cleaning. However, such transparent plastic materials typically have low conductivity and, as a result, tend to accumulate static electrical charges during their manufacture and use. Such static electrical charges may cause dust or other particles to adhere to the plastic material or even cause the plastic material to adhere to itself or other articles. Further, such static charges may also lead to functional damage in the performance of highly sensitive electronic components.
Accordingly, there is a need for substantially transparent moldable, thermoplastic multipolymer compositions which prevent the buildup of static electrical charges and can dissipate such charges in order to avoid the disadvantages of prior art compositions.
Electrostatic-dissipative multipolymer blends are known in the prior art. For example, U.S. Pat. No. 5,298,558 discloses a blend of polyvinyl chloride, a small amount of an impact modifier polymer such as ABS graft copolymer and an electrostatic dissipative amount of a chain-extended polyether. U.S. Pat. No. 4,775,716 discloses an antistatic thermoplastic composition of an ABS graft copolymer and an electrostatic dissipative composition comprising a copolymer of an epihalohydrin and an oxirane-containing comonomer.
EP 0 596 704 discloses electrostatic-dissipative polymer blends of a styrenic polymer such as ABS or MABS, an epihalohydrin copolymer and a polyalkylenelactone. WO 95/14058 discloses an antistatic thermoplastic composition comprising a MABS copolymer and an inherently antistatic thermoplastic urethane copolymer. Other prior art which mention the use of polyurethanes to confer electrostatic-dissipative properties on thermoplastic polymers include U.S. Pat. Nos. 5,159,053 and 4,179,479.
It is well known that when blending two polymers which are incompatible, the blend will contain large particles or “islands” of one polymer (the minor component) imbedded in the other polymer (the major component) with very little adhesion between the two polymers. This results in undesirable physical properties with the blend often exhibiting the worst properties of both components. It is well known that the use of a compatibilizer, i.e., a “bridge,” allows the components to accept each other, thereby resulting in much smaller particles on the minor component, with good adhesion occurring between the two components, thus allowing stress transfer and hence better physical properties.
In the present invention, no compatibilizer is required because there is good inherent compatibility between the methyl methacrylate copolymer and the polyetheresteramide. This is readily seen from the data presented below in Table III in respect to the elongation @ break which is a measure of the toughness of the blend; the data below shows a comparison of the elongation @ break for a blend of a standard grade of a polymer of methyl methacrylate containing a small amount of methyl acrylate comonomer blended with a polyetheresteramide vs. a blend of the methyl methacrylate copolymer and the polyetheresteramide of the present invention.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the invention, there is provided a substantially transparent, moldable, thermoplastic multipolymer composition comprising a blend of (a) a methyl methacrylate copolymer and (b) an effective amount of a polyetheresteramide to enhance the electrostatic charge dissipation of the copolymer, said polyetheresteramide having a refractive index within about 0.005 units of the refractive index of the copolymer. In a more preferred embodiment, an impact modifier having a refractive index within about 0.005 units of the refractive index of the copolymer is incorporated in the multipolymer composition.
In accordance with a second aspect of the present invention, there is provided a method for improving the electrostatic charge dissipation of the methyl methacrylate copolymer comprising the step of blending the methyl methacrylate copolymer (and optionally with an impact modifier having a refractive index within about 0.005 units of the refractive index of the copolymer) with an effective amount of a polyetheresteramide having a refractive index within about 0.005 units of the refractive index of the copolymer.
In accordance with a third aspect of the present invention, there is provided a method for preparing a substantially transparent, moldable, thermoplastic multipolymer composition comprising the step of melt blending the methyl methacrylate copolymer with a polyetheresteramide having a refractive index within about 0.005 units of the refractive index of the copolymer at a temperature above the melting temperatures of the copolymer and the polyetheresteramide (and above the melting temperature of the impact modifier having a refractive index within about 0.005 units of the refractive index of the copolymer if it is included).
DETAILED DESCRIPTION OF THE INVENTION
The substantially transparent, moldable, thermoplastic multipolymer composition of the invention comprises a blend of:
(a) a methyl methacrylate copolymer of a predominant amount of methyl methacrylate and a minor amount of one or more ethylenically unsaturated monomers; and styrene, acrybonitride, methyl acrylate, ethylacrylate
(b) an effective amount of a polyetheresteramide to enhance the electrostatic charge dissipation of the copolymer, said polyetheresteramide having a refractive index within about 0.005 units of the refractive index of the copolymer, such that when the composition is injection molded into a 0.125 inch thick plaque, the plaque exhibits a haze of not greater than about 25% and a light transmission of at least about 60%.
The methyl methacrylate copolymer employed in the compositions of the present invention will contain a predominant amount, e.g., about 50 to about 90 parts by weight, preferably 50 to 80 parts by weight, of methyl methacrylate and a minor amount, e.g., about 10 to about 50 parts by weight, preferably 20 to 40 parts by weight, of one or more ethylenically unsaturated monomers such as styrene, acrylonitrile, methyl acrylate, ethyl acrylate and mixtures thereof. Preferably, the ethylenically unsaturated monomer comprises a mixture of styrene and acrylonitrile or styrene and ethyl acrylate wherein the styrene is present in the copolymer in an amount of about 10 to about 40, preferably 15 to 30, parts by weight and the acrylonitrile is present in the copolymer in an amount of about 5 to about 30, preferably 5 to 20, parts by weight, based on the weight of the copolymer or the ethyl acrylate is present in the copolymer in an amount of about 3 to about 10, preferably 5 to 10 parts by weight, based on the weight of the copolymer. Such methyl methacrylate copolymers are well known in the prior art, e.g., U.S. Pat. Nos. 3,261,887; 3,354,238; 4,085,166; 4,228,256; 4,242,469; 5,061,747; and 5,290,860.
Preferably, the methyl methacrylate copolymer will have a weight average molecular weight of at least about 50,000, e.g., about 100,000 to about 300,000 and a glass transition temperature of at least about 50° C. Typically, the methyl methacrylate copolymer will have a refractive index of about 1.50 to about 1.53, preferably 1.51 to 1.52, (as measured in accordance with ASTM D-542).
The multipolymer compositions of the inve
Cyro Industries
Hampton-Hightower P.
Klauber & Jackson
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