Styrene resins are inexpensive and excellent in mechanical properties such as mechanical strength and rigidity and in moldability, and accordingly, they are widely used in a variety of fields. However, styrene resins are likely to cause problems due to the development of electrostatic charge when they are used in parts of electronic or electric equipment such as video casettes, IC cards, copying machines, televisions etc., or to cause a staining problem by sticking of the dust caused by electrostatic charges when used in housings of household appliances, office automation equipment, etc.
On the other hand, acrylic resins are excellent in transparency and rigidity and hence are in wide use as the material of various parts of electronic devices, household appliances, office automation equipment, etc., including, for example, lighting fixtures, instrument nameplates and meter covers.
However, similarly to styrene resins, acrylic resins have a high specific surface resistance and are readily electrified by friction etc., so that they are likely to present a poor appearance due to the sticking of the dust and dirt, or cause problems due to the development of electrostatic charge when they are used in parts of electronic instruments or the like.
Accordingly, there has been a desire for the development of a material based on vinyl resins, such as styrene resin and acrylic resin, which has been imparted good antistatic property, while retaining the excellent characteristic properties which are inherent to these resins.
As to the method for imparting an antistatic property to said vinyl resins, it is well known, for example, to incorporate a surface active agent into the resin or coating the agent on the resin surface. In such methods, however, the antistatic agent present on the surface is likely to be removed by water-washing, rubbing, etc., and to impart a permanent antistatic property to a surface is difficult.
Methods comprising adding a polyamide elastomer to a styrene resin to improve the impact resistance and antistatic property of the styrene resin have been proposed in Japanese Patent Application Kokai Nos. 59-193,959, 60-23,435, 63-95,251 and 63-97,653, etc.
The polyamide elastomers used in the above methods include a polyetheresteramide wherein the hard segment is polyamide, the soft segment is polyether and the two segments are connected by an ester linkage; a polyetheramide wherein said two segments are connected by an amide linkage; and a polyesteramide wherein the soft segment is polyester. However, the compatibility of these polyamide elastomers with styrene resins is poor.
Japanese Patent Application Kokai No. 59-193,959 discloses the use of a vinyl copolymer, obtained by copolymerizing a vinyl monomer containing a carboxyl group, to improve the compatibility thereof with a polyamide elastomer and to improve the impact resistance of the composition formed. However, since 40% by weight or more of a polyamide elastomer is used in this case, the resulting composition has a decreased rigidity.
Japanese Patent Application Kokai No. 60-23,435 discloses a composition comprising 5-80 parts by weight of a polyetheresteramide and 95-20 parts by weight of a vinyl copolymer containing a carboxyl group. Although the composition is improved in compatibility and antistatic property, a large amount of the polyetheresteramide must be added in order to obtain a practically useful antistatic property, which resulted in the flexural modulus being unsatisfactory.
Japanese Patent Application Kokai No. 63-95,251 discloses a composition comprising a polyetheresteramide, a rubber-modified styrene resin and a vinyl copolymer containing a carboxyl group, which gives molded products having good antistatic property and gloss.
Further, Japanese Patent Application Kokai No. 63-97,653 discloses a composition obtained by finely dispersing a polyamide elastomer having a size of 0.01-10 .mu.m into a styrene resin to eliminate laminar peeling and to impart an antistatic property.
Polyamide elastomers hitherto investigated for incorporation into styrene resins are polyetheresteramides, polyetheramides, and polyesteramides. However, polyetheramides are disadvantageous with regard to cost because the process for the production of polyetherdiamines is complicated and expensive when polyetherdiamines are used. Polyesteramides have a low hydrophilicity and exhibit an antistatic effect with difficulty.
Among these, polyetheresteramides are advantageous with regard to cost since they can be obtained from relatively inexpensive polyoxyalkylene glycols, as the raw material. Accordingly, an attempt has been made to use them and to improve also the flexural modulus (Japanese Patent Application Kokai No. 63-95,251). However, polyetheresteramides are not fully satisfactory in thermal resistance and, when blended into styrene resins and exposed to high temperatures for a long period of time in molding operations, etc., the resulting molded products would sometimes undergo deterioration in properties including mechanical properties and antistatic property.
On the hand, with regard to the methods for imparting a permanent antistatic property to acrylic resins, there have been disclosed, for example, (1) a method comprising blending into acrylic resins, a vinyl copolymer having a polyoxyethylene chain and a structure of sulfonic acid salt, carboxylic acid salt or quaternary ammonium salt (Japanese Patent Application Kokai Nos. 55-36,237 and 63-63,739) and (2) a method comprising blending a polyetheresteramide into methyl methacrylate-butadiene-styrene copolymers (i.e., MBS resin) or methyl methacrylate-acrylonitrile-butadiene-styrene copolymers (i.e., MABS resin) (Japanese Patent Application Kokai No. 62-119,256).
In method (1) mentioned above, however, the vinyl copolymer to be blended uses a special vinyl monomer and hence is expensive, so that the production cost of the acrylic resin blended with said copolymer becomes inevitably high. Moreover, in the method described in Japanese Patent Application Kokai No. 55-36,237, the amount of the vinyl copolymer blended is large and the deterioration of thermal resistance, etc., which is inherent in an acrylic resin, cannot be avoided. On the other hand, in method (2) mentioned above, the amorphous polyetheresteramide and the MBS or MABS resins are so selected that the difference in their refractive indices is 0.02 or less to ensure the transparency of the resulting composition. This restricts the degree of freedom of the combination and in the case of polymethyl methacrylate, a typical acrylic resin, the refractive index can be difficultly adapted, resulting in lowered transparency.
A prominent feature of acrylic resins is their excellent transparency. When a polymer is blended into acrylic resin to impart a permanent antistatic property thereto, however, the polymer is frequently poor in compatibility with the acrylic resin, resulting in a product of lowered transparency; or even when a product of good transparency is obtained, the product shows an insufficient antistatic effect or a decreased thermal resistance. Further, when a polymer of a complicated structure is prepared to obtain a satisfactory antistatic effect it leads to a high production cost, and an acrylic resin which is inexpensive and has a good antistatic property cannot be obtained.