POLYOLEFIN COMPOSITION AND METHOD OF COATING MOLDED ARTICLE OBTAINED THEREFROM

Abstract: A polyolefin composition is a blend of, by weight (1) 99.9-30 parts of a polyolefin (e.g. polyethylene or an ethylene-propylene block copolymer) and (2) 0.1-70 parts of a crystalline and/or rubbery copolymer of ethylene (10-80%) and propylene and optionally an olefin of 4 or more C atoms (e.g. butene-1) to which is graft copolymerised an unsatu­ rated dicarboxylic acid or anhydride (e.g. maleic or itaconic). The graft polymerising can be done by reacting the copolymer in an organic solvent with the acid/anhydride in the presence of a free radical generator catalyst, e.g. a peroxide. The composition is granulated and molded to shape. The product is spray coated with a urethane which adheres well without an undercoat; the surface may however be treated to improve adhesion before coating.

Description: This invention relates to a polyolefin composition which provides a molded article having improved physical properties, such as impact strength, and ease of finishing, such as coating, adhesion, filling, printing, hot-stamping and plating, and to a method of coating said molded article. More particularly, this invention relates to a polyolefin composition obtained by blending a polyolefin with a modified polymer prepared by graft-copolymerizing an unsaturated dicarboxylic acid or an anhydride thereof to a specific ethylene-propylene-based copolymer and to a method of coating a topcoat on a molded article produced from said composition without coating an undercoat. Polyolefins have been used for many purposes because of their excellent mechanical properties, such as rigidity, and tensile strength, chemical resistance and processability. However, polyolefins involve difficulty in finishing, such as coating, adhesion, filling, printing, hot-stamping , or plating, due to their non-polarity, and many attempts have been made to overcome this disadvantage. In particular, studies have been conducted on modification of a surface layer of a polyolefin molded article by physical or chemical processes prior to finishing and put into practical application. These improved processes, however, produce insufficient effects because they require complicated steps or, depending upon etching processes, accompany deformation of molded articles. Therefore, no satisfactory results can be obtained in view of increased cost. EP-A-0014018 describes a thermoplastic elastomer containing polyolefin, preferably in amount of 10 to 50 parts by weight, and a rubbery copolymer of ethylene and another alpha-alkene in amount of 50 to 90 parts by weight, which has improved ridigity, hardness, strength, toughness at low temperature and processability. EP-A-0028085 discloses a polyolefin composition which can comprise a polyolefin modified by addition of an unsaturated carboxylic acid or anhydride thereof and an unmodified polythene, and the composition must include a nucleating agent and a filler. The composition does not undergo substantial deterioration by heat or reduction of its mechanical strength during molding. Neither of these publications is concerned with the problems of the finishing of a polyolefin product. In order to eliminate the above-described problems, the present inventors have conducted extensive and intensive investigations, and, as a result, it has now been surprisingly found that a modified polymer obtained by graft-copolymerizing an unsaturated dicarboxylic acid or an anhydride thereof to a specific ethylene-propylene-based copolymer produces a remarkable effect on improvement in the above-described finishing and also improvements of impact strength. According to the present invention we provide a polyolefin composition comprising, per 100 parts of the composition:- (1) from 99 to 60 parts by weight of a polyolefin and (2) from 1 to 40 parts by weight of a modified polymer obtained by graft-polymerizing from 0.1 to 10% by weight, based on the modified polymer, of an unsaturated dicarboxylic acid or an anhydride thereof to a rubber copolymer comprising ethylene and propylene and optionally an olefin having 4 or more carbon atoms and having an ethylene content of from 10 to 80% by weight: The latter modified polymer is hereinafter referred to as an "ethylene-propylene-based copolymer". Polyolefins have a disadvantage in that they have unsatisfactory adhesiveness to a coating and, in particular, they exhibit no adhesiveness at all to a urethane coating. As a result of investigations in order to solve this problem, it has also been found that satisfactory adhesion between an olefin resin and a urethane coating can be achieved by using the above-described polyolefin composition without forming an undercoat. The polyolefin which can be used in the present invention typically includes polyethylene, polypropylene, an ethylene-propylene copolymer, a propylene-ethylene-butene terpolymer, an ethylene-butene copolymer, polybutene-1, and mixtures thereof. In the present invention, the polyolefin is blended with a modified polymer obtained by graft-copolymerizing an unsaturated dicarboxylic acid or an anhydride thereof to a rubber ethylene-propylene-based copolymer thereby to obtain a polyolefin composition. The rubber ethylene-propylene-based copolymer used in the present invention has an ethylene content of from 10 to 80% by weight. If the ethylene content is less than 10% by weight,the impact resistance of the resulting molded article becomes poor, and with an ethylene content of more than 80% by weight, the rigidity of the resulting molded article is reduced. The rubber ethylene-propylene-based copolymer can be an ethylene-propylene block copolymer or an ethylene-propylene rubber, which can be a copolymer of ethylene,propylene and a non-conjugated diene. The olefin having 4 or more carbon atoms which can be used in the rubber ethylene-propylene-based copolymer in combination with ethylene and propylene includes butene-1, pentene-1 and 4-methylhexene-1. These olefins are effective to impart viscosity to the polyolefin composition. The modified polymer used in the present invention can be prepared by known processes, such as a process comprising dissolving a rubber ethylene-propylene-based copolymer in an organic solvent, adding at least one unsaturated dicarboxylic acid or anhydride thereof and a radical generator and heating the mixture with stirring, and a process comprising supplying the above-described components to an extruder to effect graft-copolymerization. The unsaturated dicarboxylic acid or anhydride thereof which is used for modification of an ethylene-propylene-based copolymer can be selected from maleic acid, Himic Acid (a trademark,manufactured by Hitachi Chemical Co., Ltd.), itaconic acid, maleic anhydride, Himic Anhydride® ( endo-cis-bicyclo[2,2,11-5-heptyl-2,3-dicarboxylic anhydride; a trademark, manufactured by Hitachi Chemical Co., Ltd.) and itaconic anhydride. The content of the unsaturated dicarboxylic acid or anhydride thereof in the modified polymer is from 0.1 to 10% by weight. If it is less than 0.1% by weight, polar groups contributory to finishing workability are too less to obtain expected effects. On the other hand, contents more than 10% by weight bring unfavorably excessive polarity, sometimes resulting in insufficient compatibility with polyolefins. Further, it was unexpectedly found that a modified polymer of the aforesaid ethylene-propylene rubber brings about a greater effect on improving the impact strength of polyolefins than does the corresponding unmodified ethylene-propylene rubber. If necessary, the polyolefin composition according to the present invention may further contain one or more compounds selected from polyhydric alcohols, e.g., trimethylolpropane, 1,6-hexanediol, pentaerythritol or dipentaerythritol, Addition of these compounds sometimes brings about further improved finishing workability, impact resistance and the like. In addition, the composition of the present invention may furthermore contain additives, such as styrene-based elastomers, e.g., a styrene-butadiene random copolymer, a styrene-butadiene block copolymer; various fillers, e.g., glass fiber, talc, wood-meal, calcium carbonate ; antioxidants; weathering agents; and so on. Blending of the polyolefin and the modified ethylene-propylene-based copolymer can be carried out by conventional techniques, such as Banbury mixing, kneader mixing, roll mixing, continuous mixing by means of a uniaxial or biaxial screw, and the like. Prior to coating a topcoat on molded articles produced from the polyolefin composition according to the present invention, surface preparation of the molded articles may or may not be conducted. In the former case, surface preparation can be carried out by solvent treatment with halogenated hydrocarbons, low-temperature plasma treatment, corona discharge treatment, flame treatment, alkali degreasing, degreasing with aromatic hydrocarbons or aliphatic alcohols, or a combination of these techniques. The halogenated hydrocarbons used in the aforesaid solvent treatment are not desirable from the standpoint of their volatility and odor but have the merits of freedom from fire danger because of their flame retardancy or incombustibility. Examples of the halogenated hydrocarbon solvents are methylene chloride, chloroform, carbon tetrachloride, 1,1,1-trichloroethane, tetrachloroethylene, trichloroethylene, methylene bromide, bromoform, or Freon IB or; Freon BF (chloro-fluoro-alkanes diluted with ethanol). The solvent treatment with these halogenated hydrocarbons can be carried out by steaming, wiping, immersion, or the like, but it is preferable for uniform workability that the molded articles are immersed in these solvents or steamed with vapors of these solvents. In preferred embodiments, the polyolefin molded articles are treated with the halogenated hydrocarbon solvent by immersion or washing with vapors thereof at 60° to 100°C for 5 to 120 seconds, and more preferably at 70° to 90°C for 15 to 60 seconds. The low-temperature plasma treatment is carried out by exciting a gas, e.g., oxygen, nitrogen, argon, helium, etc., and preferably oxygen having a pressure of 1.3 MPa (10 mmHg) or less, and preferably from 0.0133 to 1.33 MPa (0.1 to 10 mmHg), by discharge, such as glow discharge, high-frequency discharge, etc., to generate plasma and placing a molded article obtained from the polyolefin composition in the thus produced plasma atmosphere. The strength of the plasma treatment should be such that the surface wet tension of the molded article immediately after the treatment is at least 38.10⁻⁴ J (38 dyn/cm). If the surface wet tension is less than that, the effect on adhesion cannot be manifested. If the treating strength is too high, degradation of the surface of the polyolefin molded article tends to occur, resulting in reduction of adhesive strength. Accordingly, the treating strength in the plasma treatment is preferably such that the treated surface of the molded article may have a surface wet tension ranging from 38 to 65.10⁻⁴ J (38 to 65 dyn/cm), and more preferably from 42 to 55.10⁻⁴ J (42 to 55 dyn/cm). The alkali degreasing can be effected by applying an alkaline aqueous solution to the surface of a polyolefin molded article by immersion, spraying or brushing, followed by washing with water and drying. The alkaline aqueous solution used as a degreasing agent includes an aqueous solution of a metal silicate, a metal phosphate, a metal carbonate, sodium hydroxide, potassium hydroxide, etc., with an aqueous solution of a metal silicate, sodium hydroxide or potassium hydroxide being preferred. The alkaline aqueous solution has a pH of from 9 to 14, and preferably from 11 to 14. Alkaline aqueous solutions having pH values less than 9 show weak degreasing ability so that sufficient adhesive strength to a urethane coating cannot be obtained. Improved adhesive strength to a urethane coating can be achieved by the above-described surface preparation with an alkaline aqueous solution, but a further ensured improving effect can be produced by washing the molded article with a neutral detergent after the alkali degreasing, washing and drying. The neutral detergents to be used are generally employed anionic or nonionic surface active agents. The degreasing treatment with an aromatic hydrocarbon solvent or an alcohol solvent can be performed by wiping the surface of a molded article with such a solvent. The solvent to be used includes toluene, isopropyl alcohol, etc. The coating to be applied onto the polyolefin molded article with or without surface preparation is a urethane coating having flexibility and includes acrylic urethane, polyester urethane and other coatings having a urethane structure. The present invention will now be illustrated in greater detail with reference to the following examples and comparative examples; all parts and percents are by weight unless otherwise indicated. EXAMPLE 1 An ethylene-propylene rubber (EPR) having an ethylene content of 50% was reacted with maleic anhydride (MAH) in toluene in the presence of a peroxide at 155°C to synthesize EPR containing 5% of MAH (hereinafter referred to as MAH-modified EPR-1). Twenty parts of MAH-modified EPR-1 and 80 parts of an ethylene-propylene block copolymer having an ethylene content of 7.4% and a melt index of 8 (hereinafter referred to as Block PP) were mixed in a biaxial extruder (manufactured by Ikegai Iron Works, Ltd.), granulated, and then injection-molded to prepare a resin plate having a size of 150 x 90 x 2(t) mm. The resulting resin plate was spray-coated with a spray gun with a urethane coating dissolved in 15% of a thinner (Flexthane 101, trademark, manufactured by Nippon Bee Chemical Co., Ltd). as it was or after being subjected to one of the following surface preparations followed by baking at 120°C for 30 minutes. Surface Preparation : (1) Steaming with 1,1,1-trichloroethane vapor at 74°C for 30 seconds. (2) Immersion in an aqueous solution of sodium orthosilicate (NaSiO₄) at pH 13.5 at 60°C for 3 minutes while stirring, followed by washing with water. (3) Wiping with isopropyl alcohol. Each of the thus treated plates was evaluated for initial adhesiveness and water-resistance in accordance with the following test methods. The results obtained are shown in Table 1 below. Test Method : (A) Initial Adhesiveness: The urethane coating film was cross-cut in 2 mm squares, and a celulosic tape of 24 mm in width (Cellotape, Registered trademark, manufactured by Nichiban Co., Ltd.) was stuck thereon. The tape was peeled off at a peel angle of 90°, and the percent of squares remaining on the resin plate was determined. (B) Water-Resistance: The coated article was soaked in warm water at 40°C for 240 hours and then subjected to the same peeling test as described in (A) above. It can be seen from the results of Table 1 above that the urethane coating can firmly be adhered to the surface of the resin plate without an undercoat irrespective of whether surface preparation is conducted or not and irrespective of the type of surface preparation. COMPARATIVE EXAMPLE 1 Coated resin plates (Sample Nos. 5 to 8) were produced in the same manner as described in Example 1 but using no MAH-modified EPR-1. The coated film was evaluated for initial adhesiveness in the same manner as in Example 1, and the results obtained are shown in Table 2 below. As shown in Table 2 above, the resin plates molded from Block PP alone exhibit no adhesion to an urethane coating at all irrespective of the type of surface preparation. COMPARATIVE EXAMPLE 2 The same procedures as in Example 1 were repeated except for using MAH-unmodified ethylene-propylene rubber having an ethylene content of 50% (hereinafter referred to as unmodified EPR) in place of MAH-modified EPR-1. The results obtained are shown in Table 3 below. As shown in Table 3, the resin plates molded from MAH-unmodified EPR and Block PP exhibit substantially no adhesion to an urethane coating. EXAMPLE 2 EPR having an ethylene content of 50% was reacted with MAH in toluene in the presence of a peroxide catalyst at 155°C to synthesize EPR having an MAH content of 2% (hereinafter referred as to MAH-modified EPR-2). Thirty parts of MAH-modified EPR-2 and 70 parts of Block PP were mixed, granulated and injection-molded in the same manner as described in Example 1 to prepare resin plates (150 x 90 x 2(t) mm). The resulting plate was subjected to low-temperature plasma treatment by means of a microwave plasma generator so as to have a surface wet tension of from 48 to 50.10⁻⁴ J (48 to 50 dyn/cm). The thus treated plate was spray-coated with Flexthane® #101 and baked in the same manner as in Example 1. The coated film was evaluated for initial adhesiveness and water-resistance in the same manner as in Example 1. As a result, no peeling of the coating film was observed. EXAMPLE 3 An ethylene-propylene block copolymer having an ethylene content of 14% and a melt index of 2 was reacted with MAH in toluene in the presence of a peroxide at 165°C to obtain a block copolymer having an MAH content of 2% (hereinafter referred to as MAH-modified PP). Thirty parts of MAH-modified PP and 70 parts of Block PP were mixed, granulated and injection-molded in the same manner as in Example 1. The resulting resin plate was subjected to surface preparation, coated, and evaluated in the same manner as in Example 1. As a result, no peeling of the coated film was observed. EXAMPLE 4 The same procedures as in Example 1 were repeated except for spraying a mixture of a polyester urethane, a hardener and thinner in a proportion of 4:1: 2 to 3 ("R263", manufactured by Nippon Bee Chemical Co., Ltd.) and baking the coated film at 80°C for 40 minutes. As a result, no peeling was observed in any case. EXAMPLE 5 The same resin plate as prepared in Example 1 was adhered to a polyvinyl chloride sheet using an NBR adhesive (NBR with 0-10% toluene and 10-20% n-hexane; "#545N" manufactured by Cemedine Co., Ltd.). The peel strength of the resulting laminate was determined at 23°C, at a peel angle of 180° and at a rate of pulling of 50 mm/min, and was found to be 0.7 Kg/cm² (1.8 Kg/inch). COMPARATIVE EXAMPLE 3 The same procedures as described in Example 5 were repeated except for using no MAH-modified EPR-1. As a result, the laminate showed a peel strength of 0.23 Kg/cm² (0.6 Kg/inch) at a peel angle of 180°. EXAMPLE 6 The same resin plate as prepared in Example 1 was hot-stamped using a hot stamping foil having a gold-colored deposited film (produced by Kurz Japan Co., Ltd.) and a hot stamping die having letters (5 mm in width) relief-engraved thereon at a temperature of 170°C. A cellulosic adhesive tape (Cellotape, a registered trademark, manufactured by Nichiban Co., Ltd.) having a width of 24 mm was stuck fast to the hot-stamped plate by pressure of fingers and then rapidly peeled off to evaluate adhesiveness of the foil to the plate. As a result, the percent remaining of the hot-stamped foil was 100%. COMPARATIVE EXAMPLE 4 The same procedures as described in Example 6 were repeated except for using no MAH-modified EPR-1. As a result, the percent remaining of the hot-stamped foil was 70%. EXAMPLE 7 EPR having an ethylene content of 50% was reacted with MAH in toluene in the presence of a peroxide at 155°C to synthesize MAH-modified EPR-3 having an MAH content of 0.5%. Forty parts of MAH-modified EPR-3 and 60 parts of Block PP were mixed, granulated and injection-molded in the same manner as in Example 1 to prepare a resin plate having a size of 150 x 90 x 2(t) mm. The resulting resin plate was coated, baked, and evaluated for initial adhesiveness and water-resistance in the same manner as in Example 1. As a result, no peeling of the coated film was observed. EXAMPLE 8 Twenty parts each of MAH-modified EPR-1, 2 and 3 and 80 parts of Block PP were blended and molded. Each of the resulting polyolefin molded articles was subjected to Izod impact test at 23°C (ASTM D256) (hereinafter the same) and was found to have an Izod impact strength (notched) of 44.2, 51.1 and 46.3 Kg.cm/cm, respectively. COMPARATIVE EXAMPLE 5 Twenty parts of the same unmodified EPR as used in Example 2 and 80 parts of Block PP were blended and molded. The Izod impact strength (notched) of the resulting molded article was found to be 20.9 Kg.cm/cm. EXAMPLE 9 The molded article produced from the polyolefin composition as prepared in Example 3 was found to have an Izod impact strength (notched) of 8.3 Kg.cm/cm. COMPARATIVE EXAMPLE 6 The molded article produced from Block PP alone as used in Example 1 was found to be 6.4 Kg.cm/cm.

Claims: A polyolefin composition comprising per 100 parts of the composition:- (1) from 99 to 60 parts by weight of a polyolefin and (2) from 1 to 40 parts by weight of a modified polymer obtained by graft-polymerizing from 0.1 to 10% by weight, based on the modified polymer, of an unsaturated dicarboxylic acid or an anhydride thereof to a rubber copolymer comprising ethylene and propylene and optionally an olefin having 4 or more carbon atoms and having an ethylene content of from 10 to 80% by weight. A polyolefin composition as claimed in Claim 1, wherein said polyolefin is present in an amount of from 95 to 60 parts by weight and said modified polymer is present in an amount of from 5 to 40 parts by weight. A polyolefin composition as claimed in Claim 1 or 2, wherein the polyolefin (1) is polyethylene, polypropylene, a copolymer of ethylene, propylene and butene, a terpolymer of ethylene, propylene and butene, or polybutene-1. A polyolefin composition as claimed in any preceding claim, wherein any olefin in the copolymer (2) is butene-1, pentene-1 or 4-methylhexene-1. A polyolefin composition as claimed in any preceding claim, wherein the graft polymerization was effected in the presence of a free radical generator as catalyst. A molded article made from a composition as claimed in any preceding claim. A coating method which comprises coating a polyolefin molded article as claimed in Claim 6 with a urethane coating. A method as claimed in Claim 7, which further includes surface preparation of the molded article prior to the coating. A method as claimed in Claim 8, wherein said surface preparation is by solvent treatment with a halogenated hydrocarbon, low-temperature plasma treatment, corona discharge treatment, flame treatment, alkali degreasing or degreasing with an aromatic hydrocarbon or an aliphatic alcohol.

Inventors: DOI, TOSHIKI, KURIBAYASHI, HIDEYUKI, SHINONAGA, HIDEO
Applicants: SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1985
Main classification: C08L23
IPC codes: C08L53, C08L51, C08L23