FILLER-CONTAINING POLYPROPYLENE RESIN COMPOSITIONS

Abstract: A filler-containing polypropylene resin composition comprises (a) from 30 to 90% by weight of a polypropylene resin, (b) from 2.5 to 38% by weight of an ethylene copolymer composed of from 82 to 98.7 mol% of ethylene, from 1 to 15 mol% of an ester selected from alky acrylate and alkyl methacrylates having from 1 to 8 carbon atoms in the alkyl moiety thereof, and from 0.3 to 3 mol% of an unsaturated dicarboxylic acid anhydride, and (c) from 5 to 50% by weight of filler. Molded products obtained from the composition have improved surface properties, such as adhesibility, coatability and printability.

Description: This invention relates to polypropylene resin compositions containing filler and having improved surface properties, such as adhesibility, coatability and printability. The non-polarity of polypropylene resins often causes difficulty. It is well known to add fillers to polypropylene resins in order to improve their finishing properties. By taking advantage of the excellent mechanical and thermal properties of filler-containing polypropylene resins, their application in automobile parts and in appliances has been markedly broadened. In such applications, for instance, interior components, such as instrument boards, trims, and pillars, the surface of the component is often covered with non-woven fabric, foamed fabric or leather cloth made of polyvinyl chloride to produce a high-class effect. Further, there is a tendency in decorative styling to coat a bumper in color harmony with the body. In appliance parts, also, printing is commonly employed for decoration. Thus, incorporation of fillers into polypropylene resins improves surface properties to some extent depending on the kind and amount of the filler, but such an improvement is still insufficient for practical purposes. In order to further improve surface properties, i.e., compatibility between polypropylene and adhesives or coatings, a medium known as a "primer", which typically comprises chlorinated polypropylene and toluene, is usually applied to the surface of the polypropylene. However, since the primer itself is expensive and an extra coating step is required, the cost of the final product is increased. Therefore, further improvements have been demanded. In an attempt to improve surface properties, physical or chemical etching of the surface of polypropylene molded products prior to finishing has been studied and applied in practice. However, this process involves more complicated steps than the primer coating, and moreover some etching conditions cause deformation of the molded products or produce insufficient effect. The process of coating a primer is being replaced by a process comprising oxidatively polarizing the surface of a molded article by irradiation with plasma to improve coating reception. At present, however, this process does not always achieve satisfactory results because the plasma irradiation should be effected in a batch system and the polarity obtained is non-uniform depending on the shape of the molded article. Attempts have also been made to impart polarity to polypropylene per se . For example, there has been proposed a process in which polypropylene is modified by grafting with an unsaturated carboxylic acid or an anhydride thereof, e.g., acrylic acid or maleic anhydride, in the presence of an initiator, e.g., organic peroxide; and a process in which the above-described grafted polypropylene is blended with unmodified polypropylene, as disclosed in Japanese Patent Application (OPI) No. 76149/75 (the term "OPI" herein used means "unexamined published application"), Japanese Patent Publication No. 10264/77, etc. According to these processes, the grafting is accompanied by decomposition of polypropylene with the peroxide so that the amount of the unsaturated carboxylic acid or the anhydride thereof that can be incorporated is limited. As a result, the surface modifying effect is insufficient. If any useful effect is achieved, the mechanical properties are impaired due to degradation of polypropylene to the low molecular weight side. An aim to this invention is to provide a filler-containing polypropylene resin composition having excellent adhesibility, coatability, printability and the like. Another aim of this invention is to provide from such a composition molded products having, besides excellent finishing properties, excellent mechanical characteristics, thermal characteristics and the like. As a result of extensive investigations, it has now been found that the above aims can be accomplished by a composition comprising a polypropylene resin, an ethylene copolymer composed of ethylene units, ester units selected from alkyl acrylates and alkyl methacrylates,and unsaturated dicarboxylic acid anhydride units, and a filler. According to the present invention there is provided a filler-containing polypropylene resin composition comprising: (a) from 30 to 90% by weight of a polypropylene resin, (b) from 2.5 to 38% by weight of an ethylene copolymer having a melt index of from 0.5 to 300 and composed of from 82 to 98.7 mol% of an ethylene repeating unit, from 1 to 15 mol% of an ester repeating unit selected from alkyl acrylates and alkyl methacrylates having from 1 to 8 carbon atoms in the alkyl moiety thereof and from 0.3 to 3 mol% of an unsaturated dicarboxylic acid anhydride repeating unit, and (c) from 5 to 50% by weight of a filler. The polypropylene resins which can be used in the present invention include crystalline polypropylene, crystalline propylene-ethylene block or random copolymers, crystalline propylene-α-olefin copolymers wherein the α-olefin has from 4 to 10 carbon atoms, and mixtures thereof. The polypropylene resin usually has a melt index (as determined according to JIS K6758) ranging from 0.5 to 100, and preferably from 1 to 50. Monomers for providing the ester repeating unit in the ethylene copolymer of the invention include methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, ethyl methacrylate, 2-ethylhexyl methacrylate and butyl methacrylate (hereinafter referred to unsaturated ester compounds). The ester repeating unit is present in the ethylene copolymer of the invention in a proportion of from 1 to 15 mol%, and preferably from 3 to 12 mol%. Proportions outside this range impair compatibility of the ethylene copolymer with the polypropylene resin or reduce the effect of improving mechanical characteristics, such as impact strength. Monomers for providing the unsaturated dicarboxylic acid anhydride repeating unit include maleic anhydride, citraconic anhydride, itaconic anhydride and tetrahydrophthalic anhydride, with maleic anhydride being particularly preferred. The proportion of the unsaturated dicarboxylic acid anhydride repeating unit in the ethylene copolymer ranges from 0.3 to 3 mol%, and preferably from 0.5 to 2.8 mol%. With proportions lower than 0.3 mol%, the amount of polar groups which contribute to surface effects is too small to produce satisfactory improved effects. Proportions higher than 3 mol% impair compatibility with polypropylene resins due to excessively strong polarity. Processes for producing the ethylene copolymer are not particularly restricted and include known processes, such as a solution polymerization process and emulsion polymerization process, and a high-pressure bulk polymerization process. Of these processes, the most common is the high-pressure polymerization process, in which ethylene is copolymerized in the presence of a radical generator at a temperature of from 100 to 300°C under a pressure of from 4903 to 29418.10⁴ Pa (500 to 3000 atm.) in the presence or absence of an appropriate solvent or a chain transfer agent. The high-pressure polymerization process is suitably carried out by dissolving the above-described unsaturated dicarboxylic acid anhydride in the above-described unsaturated ester compound, elevating the pressure of the solution by means of a pressure pump, and introducing the solution directly into a vessel type reactor or a tubular reactor. The thus obtained ethylene copolymer has a melt index (as determined according to JIS K6760) of from 0.5 to 300, and preferably from 1 to 200. If the melt index is smaller than the above-described lower limit, the ethylene copolymer lacks compatibility with the polypropylene resin. Melt indexes higher than the upper limit greatly reduce rigidity, heat resistance and surface hardness of the resulting resin composition. Fillers to be used in the present invention, either organic or inorganic, are not particularly restricted, and preferably include inorganic fillers, such as calcium carbonate, talc, clay, silica, diatomaceous earth, alumina, zinc white, magnesium oxide, mica, calcium sulfite, calcium sulfate, calcium silicate, glass powders, glass fibers (inclusive of silane-treated glass fibers), asbestos and gypsum fibers; and organic fillers, such as various kinds of woodmeal, cellulose fiber and melamine powders. These fillers may be used either individually or, if desired, in combination. In view of a favorable balance between impact resistance and heat resistance of the resulting filler-containing polypropylene resin composition, talc and/or mica are preferably used as fillers. The filler-containing polypropylene resin composition according to the present invention contains from 2.5 to 38% by weight, and preferably from 5 to 30% by weight, of the ethylene copolymer (b). If the proportion of the ethylene copolymer (b) is less than 2.5% by weight, the effects of improving surface properties, such as adhesion, coating properties and printability are insubstantial. On the other hand, if it exceeds 38% by weight, not only is no further improving effect obtained but also physical properties of the resulting resin composition, such as rigidity and heat resistance are impaired. The filler-containing polypropylene resin composition of the present invention contains from 5 to 50% by weight, and preferably from 10 to 40% by weight, of the above-described filler (c). If the proportion of the filler (c) is less than 5% by weight, improved thermal characteristics, e.g. heat deformation temperature, that are essential conditions of the resin composition according to the present invention cannot be ensured. Proportions exceeding 50% by weight seriously reduce impact resistance of the composition, resulting in poor utility as materials for interior and exterior automobile parts. No further effects in improving thermal characteristics are produced by such an excess of filler. If desired, the filler-containing polypropylene resin composition comprising the above-described components can further contain various styrene-based elastomers, such as styrene-butadiene random copolymer, a styrene-butadiene block copolymer or hydrogenated products thereof; various polyolefin elastomers, such as a non-crystalline ethylene-propylene copolymer or an ethylene-propylene-dicyclopentadiene copolymer; and, in addition, various functional group-containing polyolefins, such as maleic anhydride-grafted modified polypropylene or a glycidyl group-containing ethylene copolymer; as long as various characteristics possessed by the resin composition of the invention are not essentially impaired. Further, it is possible to add to the resin composition of the invention appropriate amounts of various additives, such as antioxidants, weathering agents, antistatic agents, foaming agents and colorants. The method of preparing the filler-containing polypropylene resin composition of the present invention is not particularly restricted. Kneading machines commonly employed for plastics or rubbers, such as a Banbury mixer, a single-screw extruder, a twin-screw extruder or a roll mill, can be used. The resulting resin composition can be molded into desired molded products by injection molding, extrusion molding, blow molding, etc. in a known manner. The filler-containing polypropylene resin compositions in accordance with the present invention have the following characteristics, as well as excellent surface properties, such as adhesibility, coatability and printability, and excellent mechanical properties: (1) The resin composition can provide thin injection molded products having a complicated shape under conventional molding conditions while substantially retaining the flowability inherent in filler-containing polypropylene resins; (2) The resin composition does not suffer from great reduction in mechanical characteristics, such as rigidity; in particular, the composition has greatly improved impact strength; and (3) Weldlines (a defect of molded products caused by incomplete fusion of two or more of molten resins) are not so conspicuous as in the case of using the conventional filler-containing polypropylene resins. Since the filler-containing polypropylene resin compositions according to the present invention bring about excellent effects as set forth above, they can be utilized in the fields requiring adhesion, coating and printing. Typical examples of their use include exterior parts of automobiles, e.g. bumpers and bumper corners, interior parts of automobiles, e.g. instrument boards, meter cases, glove compartments, console boxes, trims and pillars; motorcycle parts, e.g. fenders and leg seals; and appliance parts, e.g. lids of washing machines, bodies of vacuum cleaners, stands of electric fans and frames of ventilating fans. This invention is illustrated in greater detail with reference to the following Examples, but it should be understood that they are not intended to limit the present invention as claimed. EXAMPLES l TO 6 AND COMPARATIVE EXAMPLES l TO 3 Preparation of Ethylene Copolymer: Ethylene containing a small amount of propane as a chain transfer agent and maleic anhydride were dissolved in an unsaturated ester compound shown in Table l below, and the solution was continuously fed under pressure to a l.2 liter-volume reaction vessel equipped with a stirrer. Copolymerization was effected at a polymerisation temperature controlled to 180°C under a pressure of 1600.9.806.10⁴ Pa (l600 kg/cm²) at a rate of l.5 to 3.2 Kg/hr to obtain Ethylene Copolymer Samples (a) to (d) as shown in Table l below. Comonomer Content (mol%) Melt Index (190°C) Sample No. Maleic Anhydride Unsaturated Ester Compound (g/10 min) (a) 1.22 butyl acrylate 5.34 150 (b) 1.10 2-ethylhexyl methacrylate 2.81 5 (c) 2.21 ethyl acrylate 7.52 41 (d) 1.95 methyl methacrylate 14.4 24 A polypropylene resin (Sumitomo Noblen ® AW564 produced by Sumitomo Chemical Co., Ltd.), an ethylene copolymer (Sample (a), (b), (c) or (d)) and as a filler (talc having a mean particle diameter (corresponding to a 50% cumulative distribution by the sedimentation-type particle size distribution measurement) of 3.0 pm or mica having a mean particle diameter of 3.5 pm) were blended at a compounding ratio shown in Table 2, and 0.2 part by weight of Irganox ® 1010 (produced by Chiba-Geigy AG), 0.05 part by weight of calcium stearate and 0.05 part by weight of Ultranox ® 626 (produced by Borg-Warner Corp.) per 100 parts by weight of the resin blend were added thereto. The resulting compound was mixed in a dry blender. The dry blend was melt-kneaded in a vented extruder having a diameter of 65 mm (L/D = 28, manufactured by Ikegai Iron Works, Ltd.) at a die temperature of 220°C to obtain a resin composition in the form of pellets. Determination of Physical Properties : Physical properties of molded products of the above prepared resin compositions were evaluated in accordance with the following methods: l) Wet Tensile Strength: Measured in accordance with JIS K6768-l977 at 23°C. Specimens under test were prepared by molding the resin composition into a plate of l50 mm × 90 mm × 2 mm by the use of an in-line screw type injection molding of 99g (3.5 oz.) (manufactured by Nissei Jushi Kogyo K.K.). 2) Adhesive Strength: The same specimen as used in l) above was coated with about l50g/m² of an adhesive comprising 97% by weight of G250 (produced by Cemedine Co., Ltd.) and 3% by weight of Desmodur ® (produced by Bayer AG) with an air-spray gun, followed by drying at 80°C for 2 minutes. A skin material (PPX , produced by Toray Industries, Inc.) was heated at ll0°C for 2 minutes and, immediately thereafter, adhered to the adhesive-coated test plate under a planer pressure of 0.2.9.806.10⁴ Pa (0.2 kg/cm²) . After the laminate was allowed to stand at 23°C and 65±5% RH (relative humidity) for 7 days, peel test was conducted at a peel angle of l80° at a peel rate of 300 mm/min to measure a peel strength. 3) Initial Adhesion: The same specimen as used in l) above was cleaned with l,l,l-trichloroethane vapors (74°C) for 30 seconds, followed by drying at room temperature. A urethane coat (Flexthane ® #l0l, produced by Nippon Bee Chemical Co., Ltd.) was directly spray-coated on the plate and then baked in an oven at l20°C for 30 minutes. The coating film was cross-hatched with a blade to make 2-millimeter squares (l00 squares; l0 by l0). A 24 mm wide adhesive tape (Cellotape ® , produced by Nichiban Co., Ltd.) was adhered thereon by pressing with fingers, and one end thereof was rapidly peeled off. The number of the squares remaining on the plate was counted to determine the percentage remaining. 4) Izot Impact Strength: Measured in accordance with JIS K7ll0 at 23°C. The specimens were prepared by molding the resin composition by the use of an in-line screw type injection molding machine of 283g (l0 oz) (manufactured by Sumitomo Heavy Industries, Ltd.). 5) Heat Deformation Temperature: Measured in accordance with JIS K7207 at a bending stress of 4.6 kg/cm². The specimens were prepared in the same manner as in 4) above. The results of these measurements are shown in Table 3. It can be seen from Table 3 that the molded products obtained from the filler-containing polypropylene resin compositions according to the present invention have an excellent balance of various physical properties as compared with the comparative samples. As described above, the present invention provides filler-containing polypropylene resin compositions and molded products thereof exhibiting excellent surface properties, such as adhesibility, coatability and printability as well as high impact strength and high heat resistance.

Claims: A filler-containing polypropylene resin composition characterised in that the composition comprises (a) from 30 to 90% by weight of polypropylene resin, (b) from 2.5 to 38% by weight of an ethylene copolymer having a melt index of from 0.5 to 300 and composed of from 82 to 98.7 mol% of ethylene, from 1 to 15 mol% of ester selected from alkyl acrylates and alkyl methacrylates having from 1 to 8 carbon atoms in the alkyl moiety thereof, and from 0.3 to 3 mol% of unsaturated dicarboxylic acid anhydride, and (c) from 5 to 50% by weight of filler. A composition as claimed in Claim 1, wherein said ester is present in an amount of from 3 to 12 mol% based on the ethylene copolymer (b). A composition as claimed in Claim 1 or 2, wherein said unsaturated dicarboxylic acid anhydride is maleic anhydride. A composition as claimed in Claim 1, 2 or 3, wherein said unsaturated dicarboxylic acid anhydride is present in an amount of from 0.5 to 2.8 mol% based on the ethylene copolymer (b). A composition as claimed in any preceding claim, wherein said ethylene copolymer (b) is present in an amount of from 5 to 30% by weight based on the composition. A composition as claimed in any preceding claim, wherein said filler (c) is talc and/or mica. A composition as claimed in any preceding claim, wherein said filler (c) is present in an amount of from 10 to 40% by weight based on the composition. A component part for a vehicle or appliance, molded from a composition as claimed in any preceding claim.

Inventors: DAIMON, AKIO, KOYAMA, TERUHISA, MITSUNO, TATSUYUKI, SHINONAGA, HIDEO
Applicants: SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1986
Main classification: C08L23
IPC codes: C08L53, C08L33, C08K7, C08L51, C08L23, C08K3, C08L77, C08L101