Thermoplastic resin composition

0001This invention relates to a novel resin composition having improved chemical resistance of a polyphenylene ether resin . More specifically, this invention provides a resin composition suitable for use in the fields of automobiles, office appliances, and the like.

0002Polyphenylene ether resins are known resins and are high-performance engineering plastics having relatively high melt viscosity and high softening point. Since the polyphenylene ethers per se are, however, poor in chemical resistance, especially in organic solvent resistance, their use is limited. Moreover, because of high melt viscosity, it is hard to mold the polyphenylene ether resins alone, and impact resistance of molded articles is also poor.

0003In order to solve such problems, a resin composition of a polyphenylene ether resin and a rubber-modified styrene resin is disclosed in U.S. Patent No. 3,383,435. Although this resin composition improves moldability and impact resistance of the polyphenylene ether resin, improvement in chemical resistance is insufficient.

0004Japanese Laid-open Patent Application No. 99,162/1985 involves a resin composition comprising (a) a polyphenylene ether resin alone or a resin mixture of it and a polystyrene polymer and (b) at least one of liquid polybutene and liquid polybutadiene. This resin composition aims to improve solvent cracking resistance and impact resistance of the polyphenylene ether resin. Nevertheless, this resin composition is not said to improve satisfactorily enough in solvent resistance.

0005Since durability in wax removers, gasoline, kerosine, etc is required of polyphenylene ether resins when using same particularly in automobile exterior parts, the usage of conventional polyphenylene ether resins has been limited.

0006The present inventors have made assiduous investigations to further improve chemical resistance and solvent resistance of a polyphenylene ether resin alone or a resin composition of it and a styrene resin. They consequently found that the aforesaid problems are solved by blending a co-oligomer of ethylene and an alpha-olefin and further an elastomeric hydrogenated A-B-A block copolymer and an elastomeric hydrogenated A-B block copolymer. This finding has led to completion of this invention.

0007This invention is thus to provide a thermoplastic resin composition composed of: <ul id="ul0001" list-style="none" compact="compact"><li>(a) 100 parts by weight of a polyphenylene ether resin containing in the main chain a recurring structural unit of the formula <chemistry id="chem0001" num="0001"><img file="EP0469799B1_D0001.tif" /></chemistry> wherein R₁ is C₁-C₃ alkyl and R₂ and R₃, independently, are hydrogen or C₁-C₃ alkyl, optionally mixed with a polystyrene resin;</li><li>(b) 0.1 to 15 parts by weight of a co-oligomer of ethylene and an alpha-olefin containing a recurring unit of the formula <chemistry id="chem0002" num="0002"><img file="EP0469799B1_D0002.tif" /></chemistry> wherein <ul id="ul0002" list-style="none" compact="compact"><li>x is an integer of 1 to 30,</li><li>y is an integer of 1 to 10,</li><li>p is an integer of 3 to 60, and</li><li>n is an integer of 1 to 14,</li></ul> having a number average molecular weight of 500 to 5,000;</li><li>(c) 1 to 30 parts by weight of an elastomeric hydrogenated A-B-A block copolymer wherein A is a vinyl aromatic hydrocarbon polymer block and B is a polymer block of a saturated hydrocarbon compound; and</li><li>(d) 1 to 30 parts by weight of an elastomeric hydrogenated A-B block copolymer wherein A is a vinyl aromatic hydrocarbon polymer block and B is a polymer block of a saturated hydrocarbon compound.</li></ul>

0008The present invention also provides moulded articles of a resin composition according to the invention.

0009The resin composition of this invention is described in more detail below.

0010In the resin composition of this invention, a polyphenylene ether resin (PPE) or a mixture of it and a polystyrene resin is used as component (a).

0011The polyphenylene ether resin is a polymer containing as a main chain a recurring structural unit represented by the formula <chemistry id="chem0003" num="0003"><img file="EP0469799B1_D0003.tif" /></chemistry>    wherein <ul id="ul0003" list-style="none" compact="compact"><li>R₁ denotes a lower alkyl group having 1 to 3 carbon atoms, and</li><li>R₂ and R₃, independently, each denote a hydrogen atom or a lower alkyl group having 1 to 3 carbon atoms,</li></ul> and said polymer may be either a homopolymer or a copolymer. Commercially available polyphenylene ether resins can be ordinarily used.

0012Concrete examples of the polyphenylene ether resin include poly(2,6-dimethyl-1,4-phenylene) ether, poly(2,6-dimethyl-1,4-phenylene) ether, poly(2,6-dipropyl-1,4-phenylene) ether, poly(2-methyl-6-ethyl-1,2-phenylene) ether, and poly(2-methyl-6-propyl-1,4-phenylene) ether. Poly(2,6-dimethyl-1,4-phenylene) ether or a 2,6-dimethylphenol/2,3,6-trimethylphenol copolymer is especially preferable.

0013It is suitable that the polyphenylene ether resin has an intrinsic viscosity, as measured at 25°C in chloroform, of 0.2 to 0.7 dl/g, preferably 0.3 to 0.55 dl/g.

0014The polystyrene resin used in combination with the polyphenylene ether resin is a resin containing at least 25 % by weight, preferably at least 50 % by weight of a recurring structural unit represented by the formula <chemistry id="chem0004" num="0004"><img file="EP0469799B1_D0004.tif" /></chemistry>    wherein <ul id="ul0004" list-style="none" compact="compact"><li>R₄ denotes a hydrogen atom or a lower alkyl group,</li><li>Z denotes a halogen atom or a lower alkyl group, and</li><li>p is 0 or an integer of 1 to 3.</li></ul>

0015Examples of the polystyrene resin include polystyrene, a high-impact polystyrene, a styrene-butadiene copolymer, a styrene-butadiene-acrylonitrile copolymer, a styrene-acrylonitrile copolymer, a styrene-alpha-methylstyrene copolymer, a styrene-maleic anhydride copolymer, a styrene-methyl methacrylate copolymer, an ethylene-styrene copolymer, and an ethylene-propylene-butadiene-styrene copolymer.

0016Examples of the high-impact polystyrene include polybutadiene, a butadiene-styrene copolymer rubber, and a polystyrene modified with a rubber component such as EPDM. This rubber-modified polystyrene usually contains not more than 20 % by weight of the rubber component.

0017It is suitable that the polystyrene resin used as component (a) in the resin composition of this invention has a number average molecular weight, as measured by GPC, of 3,000 to 500,000, preferably 3,000 to 200,000.

0018A mixing ratio of the polyphenylene ether resin and the polystyrene resin as component (a) is that the polyphenylene ether resin is 10 to 100 % by weight, preferably 20 to 80 % by weight, and the polystyrene resin is 0 to 90 % by weight, preferably 20 to 80 % by weight.

0019The ethylene-alpha-olefin co-oligomer used as component (b) in the resin composition of this invention is a co-oligomer of ethylene and an alpha-olefin containing a recurring structural unit represented by the formula <chemistry id="chem0005" num="0005"><img file="EP0469799B1_D0005.tif" /></chemistry>    wherein <ul id="ul0005" list-style="none" compact="compact"><li>x is an integer of 1 to 30,</li><li>y is an integer of 1 to 10,</li><li>p is an integer of 3 to 10, and</li><li>n is an integer of 1 to 14,</li></ul> and having a number average molecular weight of 500 to 5,000, preferably 1,000 to 3,000. Examples of the alpha-olefin include propylene, n-butene-1, n-hexene-1 and n-octene-1. When the number average molecular weight of the co-oligomer as component (b) is lower than 500, undesirous cloudiness or silver streaks are observed in the appearance of an article obtained by injection molding.

0020On the other hand, when the number average molecular weight of the co-oligomer exceeds 5,000, a delamination phenomenon is undesirously liable to occur in the appearance of the molded article.

0021By the way, the ethylene-alpha-olefin co-oligomer is commercially available under the tradename "Lucant" (Mitsui Petrochemical Industries, Ltd.), and can be obtained with ease.

0022A mixing ratio of the ethylene-alpha-olefin co-oligomer as component (b) is 0.1 to 15 parts by weight, preferably 0.5 to 10 parts by weight per 100 parts by weight of component (a). When the ratio of component (b) is less than 0.1 part by weight, effects of improvements in chemical resistance and solvent resistance are not sufficient. When said ratio exceeds 15 parts by weight, a delamination phenomenon occurs in the surface of the molded article or heat resistance decreases. Thus, it is improper.

0023The elastomeric hydrogenated block copolymer used as component (c) in the resin composition of this invention has an A-B-A structure wherein A and B are polymer blocks. The central block B is composed of a saturated hydrocarbon compound. Before the hydrogenation, the block is a polybutadiene or polyisoprene block, and the double bond of the polybutadiene or polyisoprene block is converted into a saturated hydrocarbon by the hydrogenation.

0024Meanwhile, the terminal block A of component (c) is a a vinyl aromatic hydrocarbon polymer block, preferably a polystyrene block. The number average molecular weight of the terminal block A is usually 4,000 to 115,000, preferably 5,000 to 40,000. The number average molecular weight of the central block B is usually 20,000 to 450,000, preferably 25,000 to 150,000. The elastomeric hydrogenated block copolymer (component c) can easily be obtained on the market, and is commercially available from, e.g., Shell Chemical under the tradenames "Kraton G1650", "Kraton G1651", "Kraton G1652", etc.

0025A mixing ratio of the elastomeric hydrogenated A-B-A block copolymer as component (c) is 1 to 30 parts by weight, preferably 5 to 20 parts by weight per 100 parts by weight of component (a). Component (c) improves chemical resistance and impact resistance. When the ratio of component (c) exceeds 30 parts by weight, rigidity decreases.

0026The elastomeric hydrogenated block copolymer used as component (d) in the resin composition of this invention has an A-B structure wherein A and B are polymer blocks.

0027The block A of component (d) is a vinyl aromatic hydrocarbon polymer block, preferably a block composed of polystyrene. The number average molecular weight of the block A is usually 4,000 to 120,000, preferably 5,000 to 40,000. The block B is composed of a saturated hydrocarbon compound. Before the hydrogenation, the block B is a polybutadiene or polyisoprene block. By the hydrogenation, the double bond of the polybutadiene or the polyisoprene is converted into a saturated hydrocarbon. The number average molecular weight of the block B is usually 4,000 to 500,000, preferably 25,000 to 150,000. The elastomeric hydrogenated block copolymer [component (d)] can easily be obtained on the market, and is commercially available by Shell Chemical under the tradenames "Kraton G1702" and "Kraton G1701".

0028A mixing ratio of the elastomeric hydrogenated A-B block copolymer as component (d) is 1 to 30 parts by weight, preferably 5 to 20 parts by weight per 100 parts by weight of component (a). From the aspects of oil resistance and appearance of a molded article, it is advisable that when at least 1 part by weight of component (d) per 100 parts by weight of component (a) is used, a component (c): component (d) weight ratio is 8:2 to 2:8.

0029In components (c) and (d) of this invention, a degree of hydrogenation may be such that the double bonds contained in the blocks B in said components (c) and (d) before the hydrogenation are substantially saturated.

0030A method for producing the resin composition of this invention is not limited in particular, and the individual components may properly be compounded in a usual manner. Moreover, the resin composition of this invention may contain, as required, various additives such as a pigment, a heat stabilizer, an ultraviolet absorber, a fire retardant, and a filler. A mixture of them is kneaded and extruded in an extruder, and pelletized to a suitable size.

0031The following Examples, Reference Examples and Comparative Examples illustrate this invention specifically. This invention is however never limited thereto.

REFERENCE EXAMPLES 1 to 3 and COMPARATIVE EXAMPLES 1 to 2

0032A poly(2,6-dimethyl-l,4-phenylene) ether powder having an intrinsic viscosity of 0.50 dl/g as measured at 25°C in chloroform, a high-impact polystyrene ("Diarex YH-478": a tradename for a product of Mitsubishi Kasei Polytec Company), an ethylene-alpha-olefin co-oligomer ("Lucant HC-100": a tradename for a product of Mitsui Petrochemical Industries, Ltd.), and an elastomeric hydrogenated A-B-A block copolymer ("Kraton G1650": a tradename for a product of Shell Chemical) were compounded according to a formulation shown in Table 1, mixed by a Henschel mixer, and melt-kneaded at 250 to 270°C and extruded by a biaxial extruder (PCM-30: a tradename for a machine of Ikegai Iron Works, Ltd.) to obtain pellets. The pellets were injection-molded into various test pieces. Using the test pieces, various properties were measured, and the results are shown in Table 1.

0033Incidentally, an example of not containing the ethylene-alpha-olefin co-oligomer as component (b) and an example of using the ethylene-alpha-olefin co-oligomer as component (b) in a larger amount than that in this invention are shown in Comparative Examples 1 and 2, respectively.

EVALUATION OF CHEMICAL RESISTANCE

0034A 1.0 % bending strain was exerted to the test piece. A filter paper was attached to a portion having the maximum strain stress by a cellophane adhesive tape, and a kerosine-type wax remover (or a salad oil, or Launa oil) was then coated on the portion of the filter paper. The resulting test piece was then left to stand at room temperature for 48 hours. Subsequently, a tensile test was run and the chemical resistance was evaluated by percent retention of elongation at break. It was found that the higher the percent retention, the better the chemical resistance.

0035Evaluation of the chemical resistance: <dl id="dl0001" compact="compact"><dt>ⓞ :</dt><dd>percent retention - more than 70 %</dd><dt>○ :</dt><dd>percent retention - 40-70 %</dd><dt>X :</dt><dd>percent retention - less than 40 %</dd></dl><tables id="tabl0001" num="0001"><img file="EP0469799B1_D0006.tif" /></tables>

REFERENCE EXAMPLES 4 to 5 and COMPARATIVE EXAMPLES 3 to 4

0036The same components as in Example 1 were compounded according to a formulation shown in Table 2 except that a fire retardant was added for imparting fire retardance. Tensile test pieces were prepared as in Example 1. Using the test pieces, the test for chemical resistance to a salad oil and a Launa oil was conducted as in Example 1. The results are shown in Table 2.

0037For comparison, examples of not containing the ethylene-alpha-olefin co-oligomer are shown in Comparative Examples 3 and 4. <tables id="tabl0002" num="0002"><img file="EP0469799B1_D0007.tif" /></tables>

EXAMPLES 1 to 3 and COMPARATIVE EXAMPLES 1 to 3

(1) Production of resin composition pellets

0038A poly(2,6-dimethyl-l,4-phenylene) ether powder having an intrinsic viscosity of 0.50 dl/g as measured at 25°C in chloroform, a high-impact polystyrene ("Diarex YH-478": a tradename for a product of Mitsubishi Kasei Polytec Company), polystyrene ("Diarex HF-77": a tradename for a product of Mitsubishi Kasei Polytec Company), an ethylene-alpha-olefin co-oligomer ("Lucant HC150": a tradename for a product of Mitsui Petrochemical Industries, Ltd.), an elastomeric hydrogenated A-B-A block copolymer ("Kraton G1650": a tradename for a product of Shell Chemical), an elastomeric hydrogenated A-B block copolymer ("Kraton G1702": a tradename for a product of Shell Chemical), and brominated polystyrene and antimony trioxide as a fire retardant were compounded according to a formulation shown in Table 3, mixed with a Henschel mixer, and melt-kneaded at 250 to 270°C and extruded by a biaxial extruder (PCM-30: a tradename for a machine of Ikegai Iron Works, Ltd.) to obtain pellets. The pellets were molded into test pieces for evaluation of chemical resistance, etc.

(2) Evaluation of chemical resistance, etc.

0039A 1.0 % bending strain was exerted to the test piece (having the size described in ASTM, D638). A filter paper was attached to a portion having the maximum strain stress by a cellophane adhesive tape, and a salad oil ("Nisshin Salad Oil": a tradename for a product of The Nisshin Oil Mills, Ltd.) was then coated on the portion of the filter paper. After the resulting test piece was left to stand at room temperature for 48 hours, the tensile test was run, and the chemical resistance was evaluated by percent retention of elongation at break. It was found that the higher the percent retention, the better the chemical resistance.

0040The appearance of the molded article was evaluated by delamination of the molded article (having a length of 125 mm, a width of 12.5 mm and a thickness of 1.6 mm).

0041For comparison, an example of not containing polystyrene, the ethylene-alpha-olefin co-oligomer and the elastomeric hydrogenated A-B block copolymer was shown in Comparative Example 5. The properties were measured, and the results are shown in Table 3.

0042The appearance of the molded article and the chemical resistance in Table 3 are evaluated as follows.

0043Appearance of the molded article: <dl id="dl0002" compact="compact"><dt>ⓞ :</dt><dd>Surface delamination was not observed.</dd><dt>X :</dt><dd>Surface delamination was observed.</dd></dl> Chemical resistance: <dl id="dl0003" compact="compact"><dt>ⓞ :</dt><dd>Percent retention of elongation at break - more than 70 %</dd><dt>○:</dt><dd>Percent retention of elongation at break - 40-70 %</dd><dt>X :</dt><dd>Percent retention of elongation at break - less than 40 %</dd></dl><tables id="tabl0003" num="0003"><img file="EP0469799B1_D0008.tif" /></tables>

0044The resin composition of this invention maintains the mechanical strength and the heat resistance of the ordinary polyphenylene ether resin and is significantly improved in chemical resistance and oil resistance. Accordingly, said resin composition is well suited for use in automobile exterior parts, parts of office appliances, and the like.