Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-05-20
2004-07-13
Niland, Patrick (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S210000, C524S211000, C524S227000
Reexamination Certificate
active
06762229
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a poly(arylene sulfide) resin composition in which an organic amide is compounded as a modifier, and particularly to a poly(arylene sulfide) resin composition having excellent flowability and toughness.
According to the resin composition of the present invention, its glass transition temperature and cold crystallization temperature can be lowered while retaining the high melting point inherent in a poly(arylene sulfide), and so crystallization can be facilitated upon molding even when the temperature of a mold is lower than the usual temperature, and moreover molded products having excellent strength and good surface quality can be provided.
The resin composition according to the present invention has excellent melt-flow properties, tensile elongation and tensile strength in addition to the various excellent properties inherent in the poly(arylene sulfide), such as heat resistance, flame retardancy and chemical resistance, and is hence suitable for use as not only injection-molded products but also non-woven fabrics, monofilaments and the like.
BACKGROUND ART
Poly(arylene sulfides) (hereinafter abbreviated as “PAS”) are aromatic polymers having predominant repeating units of arylene sulfide represented by the formula [—Ar—S—] in which Ar means an arylene group, and poly(phenylene sulfide) (hereinafter abbreviated as “PPS”) is representative of the PAS. PAS is excellent in heat resistance, flame retardancy, chemical resistance, dimensional stability, mechanical properties and the like, and hence used in wide application fields.
However, the PAS involves a drawback that it is low in toughness typified by tensile elongation. The toughness of the PAS is improved by heightening its molecular weight. Since its melt viscosity is also increased at the same time, however, it is difficult to injection-mold it into precise molded products, molded products of complicated forms, and the like using molds narrow in channel and complicated in form. In particular, a PAS resin composition, in which a large amount of a filler such as glass fibers has been compounded, is improved in various properties such as mechanical properties, dimensional stability, heat resistance and electrical properties, but its melt viscosity is extremely increased, and so its melt-flow properties are deteriorated to a great extent. Accordingly, there is a limit to heightening the molecular weight of the PAS from the necessity of ensuring the flowability of the PAS upon molding, and so it has have no other choice but sacrifice its toughness.
The PAS generally has high glass transition temperature (Tg) and cold crystallization temperature (Tc). For example, PPS has a Tg of about 90° C. and a Tc of about 125° C. as measured by means of a differential scanning calorimeter (DSC). Therefore, in the case where the PAS is used to obtain a molded product by injection molding, it has been necessary to use a mold heated to a high temperature of generally 120° C. or higher, often 130° C. or higher in order to facilitate its crystallization and provide a molded product having good appearance. Since the molding operation is conducted at a mold temperature of about 100° C. in the usual injection molding making use of a general-purpose resin, however, there has been a problem that special equipment and fuel must be used in order to raise the mold temperature to a high temperature of 120° C. or higher.
In addition, in order to produce a molded product excellent in hardness, dimensional stability and form stability in the injection molding of the PAS, it is preferred to achieve a high degree of crystallinity as soon as possible. However, even when the high degree of crystallinity is quickly achieved by raising a mold temperature to a comparatively high temperature, there has been a limit to the shortening of an injection molding cycle to enhance productivity, since the residence time of the resulting molded product in the mold lengthens.
As means for crystallizing the PAS at a high speed, there have heretofore been proposed, for example, a method in which a monomeric carboxylic ester is added (Japanese Patent Application Laid-Open No. 230848/1987), a method in which a thioether is added (Japanese Patent Application Laid-Open No. 230849/1987), and a method in which an aromatic phosphoric ester is added (Japanese Patent Application Laid-Open Nos. 230850/1987 and 225660/1989). However, the additives used in these methods are poor in heat resistance, and so evaporated gases or decomposed gases are generated upon molding and processing. Therefore, these methods are not preferred from the viewpoint of practical use.
The PAS is expected to develop its uses to not only a field of injection-molded products, but also a field of high-performance filters of which high heat resistance, flame retardancy, chemical resistance and the like are required, making good use of its various excellent properties.
In general, a non-woven fabric or porous body is used as a filter composed of a polymeric material. In order to obtain a high-performance filter composed of the non-woven fabric, it is preferred from the viewpoints of collection efficiency and pressure loss that the fineness of fibers making up the non-woven fabric be fine in addition to the fact that the various properties of a polymeric material itself used are excellent. Therefore, if a non-woven fabric can be produced from a PAS by a melt blow process by which a non-woven fabric composed of extremely fine fibers can be produced, the uses of the PAS can be developed to new fields of high-performance filters and the like.
Some proposals have heretofore been made on methods for producing a non-woven fabric formed of extremely fine fibers by a melt blow process in order to apply the PAS to uses such as filters. For example, Japanese Patent Application Laid-Open No. 315655/1988 discloses a melt-blow non-woven PPS fabric, wherein the non-woven fabric is composed of PPS fibers having an average fineness of at most 0.5 deniers, part of the fibers are at least fusion-bonded or entangled, and its coefficient of variation in METSUKE (mass per unit area) is at most 7%. Japanese Patent Application Laid-Open No. 22985/1989 discloses a non-woven PAS fabric, which is composed of PAS fibers having an average fiber diameter of 0.1 to 0.8 &mgr;m and has a METSUKE of 5 to 500 g/m
2
.
However, the melt-blow non-woven PAS fabrics obtained by these conventional techniques have involved drawbacks that when the degree of crystallinity of the PAS is enhanced in order to improve its chemical resistance and dimensional stability, the toughness typified by tensile elongation is deteriorated, and that sufficient strength cannot be achieved. More specifically, the conventional melt-blow non-woven PAS fabrics have involved the following problems.
In the melt blow process, a thermoplastic resin is generally melted and ejected from a minute orifice, the thus-ejected melt is blown off by a heated gas in a sonic velocity region to form fine fibers, and the fibers are collected on a moving porous drum or screen to produce a non-woven fabric. In order to form highly thinned fibers by the action of the heated gas in the sonic velocity region, it is said that to lower the melt viscosity of the thermoplastic resin used is indispensable. Accordingly, in order to produce a non-woven fabric formed of extremely fine fibers narrow in scatter of fineness by the melt blow process using the PAS, it has been necessary to use a PAS having a low melt viscosity.
On the other hand, in order to sufficiently develop excellent chemical resistance and dimensional stability, which are characteristic of the PAS, in the melt-blow non-woven fabric, it is desirable to enhance the degree of crystallinity of the PAS. However, a melt-blow non-woven fabric obtained by using a PAS having a low melt viscosity is extremely deteriorated in toughness if the degree of crystallinity of the PAS is enhanced by controlling melt-blow conditions and heat-treatment conditions, so that such a non-woven fabric cannot be
Nishihata Naomitsu
Ohuchi Kiyomi
Sato Hiroyuki
Tada Masahito
Kureha Kagaku Kogyo K.K.
McDermott & Will & Emery
Niland Patrick
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