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
2001-10-18
2003-12-02
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S079000, C525S070000, C524S515000
Reexamination Certificate
active
06657005
ABSTRACT:
TECHNICAL FILED
The present invention relates to a non-black thermoplastic resin composition which can provide a shaped product showing a sufficiently short static decay time (time in which an applied voltage is attenuated to a prescribed voltage) and is suitable for use as an ESD (electrical static dissipative) material.
BACKGROUND ART
A synthetic resin having a surface resistivity of 10
6
to 10
11
ohm/square (ohm/□) is strongly desired as an ESD control material in a field of industry where static electricity has to be removed.
Hitherto, for providing anti-static synthetic resins, there have been used a method of surface-application of an antistatic agent or a silicone compound, and a method of shaping a composition containing an antistatic agent or a filler material having a low electrical resistivity.
Among the above, the method of surface-application of an antistatic agent or a silicone compound is accompanied with a practically great problem that the antistatic effect is markedly reduced by washing or rubbing.
On the other hand, the method of shaping a composition containing an antistatic agent as an additive is not sufficient for permanent static prevention and is accompanied with problems such that the antistatic effect is lost when the antistatic agent present at the surface is removed by washing with water or rubbing, and excessive bleeding to the surface of the antistatic agent not only causes adhesive sticking of refuse or dust but also is liable to soil the environment due to elution or vaporization of the antistatic agent. JP-B 59-2462 (corr. to GB-A 2070046) has disclosed a thermoplastic resin composition showing a permanent antistatic function obtained by adding an anionic surfactant to a thermoplastic resin containing a graft-copolymer based on a rubber trunk polymer having an alkylene oxide group, but the antistatic function is insufficient for use as an ESD control material.
In the method of shaping a composition containing a filler material having a low electrical resistivity, a mixture comprising a good-conductivity filler material having a low electrical resistivity, such as electroconductive carbon black, graphite, carbon fiber, metal fiber or metal powder, and a synthetic resin, is formed into a synthetic resin composition. In this case, as the electrical resistivities of the filler and the synthetic resin are remarkably different, the electrical resistivity of the resultant resin composition remarkably varies depending on a content of the filler. Particularly, in a surface resistivity range of ca. 10
6
-10
11
ohm/square of a resin composition, the electrical resistivity of a resin composition sharply varies depending on the filler content. Accordingly, it has been difficult to stably produce a synthetic resin composition having a surface resistivity of 10
6
-10
11
ohm/square. Among the above-mentioned good-conductivity filler materials, carbon materials such as electroconductive carbon black, graphite and carbon fiber, are suitably used for providing a surface resistivity in a range of 10
6
-10
11
ohm/square, but the application thereof is necessarily confined since the hue of the resultant resin composition is restricted to “black”.
A principal object of the present invention is to provide a non-black thermoplastic resin composition which shows a sufficiently short static decay time for use as an ESD control material and can be colored into arbitrary hues.
DISCLOSURE OF INTENTION
According to our study, it has been found possible to accomplish the above-mentioned object by a non-black thermoplastic resin composition comprising: (A) 30-84.9 wt. % of a crystalline thermoplastic resin, (B) 15-65 wt. % of a graft-copolymer formed by graft-polymerizing an ethylenically unsaturated monomer onto a rubber trunk polymer having an alkylene oxide group and (C) 0.1-5 wt. % of an anionic surfactant. As a result, according to another aspect, it is possible to obtain a non-black thermoplastic resin composition providing a shaped article exhibiting a very short decay time from 5000 volts to 50 volts of at most 10 sec and a surface resistivity of at least 10 ohm/square.
Some history and details as to how we have arrived at the present invention as a result of study for achieving the above object, will now be briefly described.
It is understood that the excellent antistatic effect of the thermoplastic resin composition of the present invention relies on the function of the anionic surfactant selectively adsorbed onto the rubber trunk polymer of the graft copolymer (B). This is the same as in the antistatic resin composition disclosed in the above-mentioned JP-B 59-2462. The same JP-B 59-2462 also describes that a portion of the graft copolymer can be replaced with a thermoplastic resin compatible with the graft copolymer (A), and examples of the thermoplastic resin disclosed therein include some specific examples of crystalline thermoplastic resin used in the present invention. However, 31 compositions disclosed in Examples of the same JP-B 59-2462 exhibited a static decay time from 5000 volts to 50 volts and a surface resistivity which were larger by one digit or more than those of the composition of the present invention and failed to exhibit the necessary ESD property, according to our measurement (see Examples and Comparative Examples appearing hereinafter). Thus, the present invention corresponds to a selection invention which has succeeded in a remarkable improvement in ESD property by selecting a crystalline thermoplastic resin which has been included in examples of the thermoplastic resin compatible with the graft copolymer but not specially noted in the JP-B 59-2462.
There is one reason why a crystalline thermoplastic resin was not selectively used in combination with the graft copolymer in the JP-B 59-2462 unlike in the present invention. More specifically, the invention of the JP reference aimed at providing an antistatic resin composition having a good transparency as is understood from enumerated products or usage, such as covers of electrical appliances or accessories, as an object. (In fact, the compositions described in Examples are those exhibiting a whole-ray light transmittance of ca. 90% and a haze of ca. 3-5%). For such a viewpoint of transparency, it is preferred to use an amorphous thermoplastic resin having a better compatibility or an amorphous thermoplastic resin having a refractive index identical to that of the graft copolymer compared with a crystalline thermoplastic resin. A crystalline thermoplastic resin used in the present invention has a compatibility with the graft copolymer in a sense that it is thermally mixable with the graft copolymer but does not have a microscopic mutual solubility (miscibility or a good level of compatibility) with the graft copolymer sufficient to provide a good transparency. Accordingly, the resultant composition becomes semi-transparent, or milky-white, milky-yellow or milky brownish, but can be colored in arbitrary hues, of course, unlike the case of blending with carbon black. The thermoplastic resin composition of the present invention may be referred to as an invention which has been arrived at by parting from the transparency, an objective property aimed at by the invention of the above JP reference.
The reason why a remarkable improvement in ESD property compared with not only the case of using an amorphous thermoplastic resin but also the case of combining a graft copolymer (B) alone with an anionic surfactant (C), has not been clarified as yet, but it is at least believed to be certain that a crystal reproduced in the course of shaping and cooling after thermal mixing of a crystalline thermoplastic resin and a graft copolymer, is deeply concerned with development of the ESD property. It is also presumed that the added anionic surfactant (C) is not mutually soluble with such a reproduced crystal but is preferentially adsorbed onto the rubber trunk polymer of the graft copolymer (B) or the anionic surfactant (C) is present at the crystal boundaries, to contribute to the development of the
Arai Shiro
Nishihata Naomitsu
Onodera Chikau
Tada Masahito
Hu Henry S
Kureha Kagaku Kogyo Kabushiki Kaisha
Wenderoth , Lind & Ponack, L.L.P.
Wu David W.
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