Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-05-03
2003-03-04
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S804000, C524S819000
Reexamination Certificate
active
06528567
ABSTRACT:
This application is a 371 application of PCT/JP99/06100, filed Nov. 2, 1999.
TECHNICAL FIELD
The present invention relates to an improvement in resin composition having permanent antistatic property.
BACKGROUND ART
As plastics generally have a large electrical resistivity and a strong chargeability, static electricity induced thereon by contact, friction, peeling, etc., is difficult to dissipate and thus attracts dust and dirt, thus resulting in troubles, such as impaired appearance on shaped articles, sheets, films and fibers formed from the plastics. For obviating these drawbacks, the following methods, roughly classified, have been investigated.
1. Method of kneading an antistatic agent into. plastics.
2. Method of applying an antistatic agent on the surface of the plastics.
3. Method of surface application of a silicone compound.
4. Method of chemically reforming the structure of plastics.
Among these, the method of kneading an antistatic agent is accompanied with drawbacks such that it is not sufficient for providing permanent antistatic property, so that the antistatic effect is lost if the antistatic agent present on the surface is removed by means of washing with water, rubbing, etc.; that the adhesion of dust and dirt is liable to occur if the antistatic agent excessively bleeds to the surface; and that it impairs the transparence.
The method of surface application of an antistatic agent causes a remarkable lowering in antistatic effect by washing the plastic product.
The method of surface application of a silicone compound can provide a semipermanent antistatic effect but is liable to be economically disadvantageous.
The method of chemically reforming the plastic structure is a method of introducing a hydrophilic group into the plastics as by polymerization or other methods. However, a substantially large amount of hydrophilic group is generally required to be incorporated in order to exhibit antistatic effect, so that the mechanical properties and other properties are adversely affected by moisture absorption.
In contrast to the above, the present applicant already developed a thermoplastic resin composition having permanent antistatic property by incorporating an anionic surfactant into a thermoplastic resin comprising a graft copolymer of a rubber trunk polymer having an alkylene oxide group (Japanese Patent Publication (JP-B) 59-2462; corr. to GB-A 2070046). Herein, “permanent antistatic property” is unlike a non-persistent antistatic property which may be obtained by application of an antistatic agent or bleeding-out to the surface of a shaped article of an antistatic agent kneaded into an ordinary thermoplastic resin and can be remarkably reduced by wiping of the surface, but means a permanently and persistently exhibited antistatic property which is developed by an antistatic agent stably held inside a thermoplastic resin constituting a shaped product and is not essentially reduced by wiping of the shaped product.
While the function mechanism of the above-mentioned thermoplastic resin composition exhibiting permanent anionic surfactant property has not been fully clarified as yet, it is considered that a rubber trunk polymer comprising a monomer having an alkylene oxide group and a conjugated diene or an acrylate ester as one component is dispersed, at the time of processing, in the graft component resin or a mixture of the graft component resin and a thermoplastic resin as the matrix component in the form of mutual bridges, and an antistatic agent added thereto is selectively, adsorbed principally by the rubber trunk polymer, so that when a charging member contacts the shaped body, electric charges of the opposite polarity are moved principally through the rubber trunk polymer phase adsorbing the antistatic agent to be quickly accumulated at the contact surface, thereby dissipating and neutralizing the charges given by the charging member. It is further considered that as the rubber trunk polymer comprises a monomer having an alkylene oxide group, the movement of the charges are extremely promoted to remarkably enhance the addition effect of the antistatic agent.
However, several problems have been found with the above-mentioned antistatic resin composition based on he rubber trunk polymer having an alkylene oxide group, from practical points of view. For example, the above-mentioned resin composition is characterized by an ability of providing a shaped product having good transparence in addition to the antistatic property, but the shaped products were sometimes accompanied with haze or discoloration. Further, in some cases, the shaped products failed to exhibit the expected permanent antistatic property.
Accordingly, an object of the present invention is to provide an antistatic resin composition that can stably retain beautiful appearance and permanent antistatic property.
DISCLOSURE OF INVENTION
According to our study, it has been found possible to achieve the above-mentioned object by adding an improvement in composition to the above-mentioned antistatic resin composition developed by the present applicant from a viewpoint of commercial production process thereof.
More specifically, according to the present invention, there is provided an antistatic resin composition, comprising: (a) 7-100 wt. parts of a graft copolymer formed by graft-polymerizing an ethylenically unsaturated monomer onto a rubber trunk polymer having an alkylene oxide group which has been obtained by using a carboxylic acid-type surfactant as an emulsifier for polymerization, (b) 0-93 wt. parts of a thermoplastic resin, and (c) 0.1-5 wt. parts of an anionic surfactant having a thermal weight loss initiation temperature (as defined by JIS K7120) of at least 250° C.; wherein the rubber trunk polymer occupies 5-80 wt. parts within 100 wt. parts in total of (a) and (b).
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.
The above-mentioned problems of the haze or discoloration of shaped products found with respect to the antistatic resin composition developed by the present applicant (JP-B 59-2462, corresponding to U.S. Pat. No. 4,315,081) were found in a stage of pursuing an improvement in mass productivity. More specifically, an anionic surfactant used as an antistatic agent in the above-mentioned antistatic resin composition already has a fairly good thermal resistance, but it has been found that such an anionic surfactant is still liable to cause a thermal degradation with respect to a portion thereof subjected to heating for a long residence time in the case of elevating the extruder temperature for injection molding or using a large-capacity extruder, thus causing haze or discoloration of the shaped products in some cases, and thus failing to exhibit an expected level of permanent antistatic property in some cases. Further, it has been also found that the above-mentioned problem is caused accompanying the use of a graft copolymer of a rubber trunk polymer having an alkylene oxide group as a base resin. More specifically, such a graft copolymer is generally recovered in a solid powdery form by subjecting latex after emulsion polymerization to precipitation by salt addition (salting-out) or by acid addition (acid precipitation). The salting-out and the acid precipitation can exhibit substantially equivalent effects for ordinary graft copolymers, such as MBS resin and ABS resin, but the graft copolymer used in the present invention comprises a rubber trunk polymer having an alkylene oxide group functioning as a kind of nonionic surfactant, and a strict control of condition becomes necessary for the salting-out thereof. More specifically, in the case of using a monovalent salt, it is necessary to use a salt solution in an amount and at a concentration which exceed ordinary levels, and this is impractical. For this reason, the salting-out has been performed by using a divalent or higher-valent salt and a solution thereof at a concentration which is still higher than an ordinary le
Arai Shiro
Watabe Teruhide
Cain Edward J.
Kureha Kagaku Kogyo Kabushiki Kaisha
Wenderoth , Lind & Ponack, L.L.P.
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