Highly antioxidant resin composition

Abstract: A highly antioxidant resin composition containing a resin, a solution of a hypophosphite compound in an organic solvent, a heat stabilizer and a hindered amine base weathering stabilizer, which has improved heat stability and weather resistance.

Description: The present invention relates to a highly antioxidant resin composition. More particularly, the present invention relates to a highly antioxidant resin composition comprising a resin, a heat stabilizer and a hindered amine base weathering stabilizer and having good heat stability and weather resistance. An amount of the resins which are used outdoors is increasing year by year. Such resins for outdoor use are required to have weather resistance according to the applications. To this end, various weathering stabilizer have been developed. Recently, hindered amine base weathering stabilizers, which are so-called hindered amine light stabilizers (HALS) are often used, since they can prevent decrease of the mechanical properties or change of color tone of the resin compositions when subjected to the outdoor weathering much better than the conventional weathering stabilizers (cf. JP-A-86645/1984). Since the weathering stabilizer cannot impart processing stability or heat stability to the resins, a heat stabilizer (e.g. hindered phenol base heat stabilizers, sulfur base heat stabilizers and phosphite ester base heat stabilizers) is generally added to the resin composition. However, under certain conditions, the resin composition containing both the heat stabilizer and the hindered amine base weathering stabilizer may suffer from deterioration due to poor heat stability such as gellation or seizure during processing or discoloration after processing. Further, when exposed to the outdoor atmosphere, the resin composition may be degraded due to poor weather resistance such as decrease of mechanical properties or changes of gloss or color tone. Accordingly, the conventional resin compositions are not satisfactory in both the heat stability and the weather resistance. Though the heat stability and the weather resistance may be improved to some extent by the addition of larger amounts of the heat stabilizer and the hindered amine base weathering stabilizer to the resin, the resin composition may be yellowed, or the heat stabilizer and/or the hindered amine base weathering stabilizer may bleed out on the surface so that appearance of a molded article is deteriorated. In particular, it is known that, when the hindered phenol base heat stabilizer and the hindered amine base weathering stabilizer are used in combination, the hindered phenol base heat stabilizer causes yellowing of the resin and the hindered amine base weathering stabilizer interferes the antioxidant action of the hindered phenol base heat stabilizer. In EP-A-0 38964 the heat stability of such stabilizer systems has been improved by the addition of hypophosphite to the hindered phenol base heat stabilizer and the hindered amine base weathering stabilizer combination. An object of the present invention is to further improve heat and weather stability of a highly antioxidant resin composition which comprises a resin, a heat stabilizer, a hindered amine base weathering stabilizer and a hypophosphite. According to the present invention, there is provided a highly antioxidant resin composition comprising a resin, a solution of a hypophosphite compound in an organic solvent, a heat stabilizer and a hindered amine base weathering stabilizer. As the heat stabilizer to be used in the present invention, are exemplified hindered phenol compounds such as 2,6-dialkylphenol derivatives and 2-alkylphenol derivatives, sulfur-containing compounds having a thiol or thioether linkage containing a divalent sulfur atom, or compounds having a phosphite ester linkage containing a trivalent phosphorus atom. Examples of the hindered phenol base heat stabilizer are following compounds (1) to (8): Examples of the sulfur-containing heat stabilizer are following compounds (9) - (16): (C₁₂H₂₅-SCH₂CH₂COOCH₂)₄C wherein R is an alkyl group having 12, 13 or 14 carbon atoms Examples of the phosphite ester base heat stabilizer are following compounds (17) through (33): P(O-C₁₀H₂₁)₃ P(O-C₁₃H₂₇)₃ wherein R is an alkyl group having 12 through 15 carbon atoms The above heat stabilizer may be used independently or as a mixture thereof. The hindered amine base weathering stabilizer is preferably a 2,2,6,6-tetralkylpiperidine derivative having a substituent at the 4-position and a molecular weight of at least 250. As the substituent at the 4-position, are exemplified a carboxylic acid residue, an alkoxy group, an alkylamino group and the like. The N-position may be substituted with, for example, an alkyl group. Specific examples of the hindered amine base weathering stabilizer are following compounds (34) through (41): The hypophosphite compound to be used in the present invention is expressed by the formula (A): X a (H₂PO₂) b wherein X is a metal ion, an ammonium ion or a quaternary phosphonium ion, a and b are positive numbers provided that they satisfy the equation: a x c = b in which c is a valency of X. Specific examples of the compound (A) are lithium hypophosphite, sodium hypophosphite, potassium hypophosphite, magnesium hypophosphite, calcium hypophosphite, zinc hypophosphite, titanium hypophosphite, vanadium hypophosphite, molybdenum hypophosphite, manganese hypophosphite, cobalt hypophosphite, ammonium hypophosphite, butylammonium hypophosphite, diethylammonium hypophosphite, triethylammonium hypophosphite, tetraethylammonium hypophosphite, tetrabutylphosphonium hypophosphite and tetraphenylphosphonium hypophosphite. As the organic solvent in which the hypophosphite compound is dissolved, any solvent in that the hypophosphite can be dissolved and that has a boiling point higher than a processing temperature of the resin is preferably used. Examples of the organic solvent are protic polar solvents such as polyhydric alcohols, preferably those having a molecular weight of not more than 50,000, and polyamines and aprotic polar solvents such as alkylsulfones. Specific examples of the protic solvent are ethylene glycol, diethylene glycol, polyethylene glycol (having a molecular weight of 150 to 50,000), polypropylene glycol (having a molecular weight of 134 to 50,000), glycerin, diglycerin, hexaglycerin, trimethylolpropane and hexamethylenediamine. A specific example of the aprotic solvent is dimethylsulfoxide. Examples of the resin to be used in the present invention are olefin polymers such as olefin homopolymers (e.g. polyethylene, polypropylene, poly-1-butene and poly-4-methyl-1-pentene), olefin copolymers (e.g. ethylene-propylene block copolymer, ethylene-propylene random copolymer, ethylene-1-butene copolymer, ethylene-1-hexene copolymer, ethylene-4-methyl-1-pentene copolymer, ethylene-1-octene copolymer and propylene-1-butene copolymer), copolymers of an olefin and a polar vinyl compound (e.g. ethylene-vinyl acetate and ethylene-methyl methacrylate copolymer) and ionomer resins; acrylic resins such as polymethyl methacrylate; polyester resins; polyamide resins; polycarbonate resins; phenol resins; polyvinyl chloride resins; and polyurethane resins. Amounts of the components contained in the resin composition of the present invention are as follows: The heat stabilizer is used in an amount of 0.01 to 10 parts by weight, preferably 0.05 to 1 part by weight per 100 parts by weight of the resin. When this amount is less than 0.01 part by weight, the heat stability is not effectively improved. When this amount exceeds 10 parts by weight, the heat stability is not significantly improved and such larger amount is not economical. In addition, the heat stabilizer may unpreferably bleed out or discolor. The hindered amine base weathering stabilizer is used in an amount of 0.01 to 10 parts by weight per 100 parts by weight of the resin. When this amount is less than 0.01 part by weight, the weather resistance is not effectively improved. When this amount exceeds 10 parts by weight, the weather resistance is not further improved and such larger amount is not economical. In addition, the weathering stabilizer may unpreferably bleed out or discolor. The added amount of the hypophosphite compound is usually from 0.001 to 100 part by weight per one part by weight of the hindered amine base weathering stabilizer. When this amount is less than 0.001 part by weight, the heat stability and the weather resistance are not effectively improved. When this amount exceeds 100 parts by weight, the heat stability and the weather resistance are not significantly improved, such larger amount is not economical, and further the solution of the hypophosphite compound tends to bleed out due to a too large amount of the solution to be added to the resin. An amount of the organic solvent is selected so that 0.01 to 30 parts by weight of the solution containing the hypophosphite compound in an amount of less than a saturation amount is used per 100 parts by weight of the resin. When the amount of the solution is less than 0.01 part by weight, the amount of the hypophosphite compound to be added to the resin is not sufficient so that the heat stability and the weather resistance are not satisfactorily improved. When the amount of the solution exceeds 30 parts by weight, the solution tends to bleed out. The resin composition of the present invention may contain a UV light absorber, an anti-fogging agent, an antistatic agent, a lubricant, a filler, a flame retardant and/or a pigment in such amount that the effects of the present invention are not deteriorated. The compounding manner of the above components is not critical, and the components are compounded by a usual means such as Banbury mixer, a mixing roll or an extruder. According to the present invention, by the addition of the solution of the hypophosphite compound in the resin composition containing the heat stabilizer and the hindered amine base weathering stabilizer, the heat stability and the weather resistance of the resin composition are significantly improved. The resin composition of the present invention is molded in the form of a film, a sheet, fibers and a molded article and used in various fields such as an agricultural film and an automobile parts material. In particular, the film produced from the resin composition of the present invention comprising, as the resin, the polyolefin such as polyethylene or the ethylene-1-butene copolymer, or the ethylene-vinyl acetate copolymer is very useful as a wrapping film and a covering material for agricultural green houses or tunnels. The resin composition of the present invention is useful as a material for outdoor use which is required to have high weather resistance such as an automobile parts, for example, a bumper, or construction materials such as a roof of a garage. The present invention will be illustrated by the following Examples, which do not limit the scope of the present invention. The test methods in Examples are as follows: Heat stability test With a test sample of 1mm in thickness (1 g), an induction period for oxygen absorption is measured by a measurement apparatus for polymer deterioration (manufactured by Shibayama Scientific Co., Ltd.) at a predetermined vessel internal temperature with an oxygen amount of 40 ml in a dark place. The induction period for oxygen absorption is expressed by a time period till the oxygen amount decreases by 0.9 ml or the internal oxygen volume indicates the minimum volume when decomposed gases are generated, after the vessel temperature is stabilized. The longer induction period for oxygen absorption means better resistance to oxidative degradation, namely better heat stability. Weathering test A test sample in the form of a JIS No. 3 dumbbell is aged with an Eye Super UV Tester (trademark) SUV-W 11 (manufactured by Eye Graphics Co., Ltd.) with a luminous energy of 100 mW/cm², at a distance of 24 cm from a light source, at a blowing air temperature of 600C and a relative humidity of 33 %. The aged sample is subjected to tensile test with an Autograph (trademark) DSS 100 (manufactured by Shimadzu Co.) to measure elongation (%) and then the weathering test time at which the elongation decreases to a half of the original value (a half value period of weather resistance) is recorded. The larger half value period means better weather resistance. Various solutions of the hypophosphite compounds are listed in Table 1. Examples 1-4 A resin, a heat stabilizer, a hindered amine base weathering stabilizer and a solution of a hypophosphite compound as shown in Table 2 were compounded and kneaded with a Banbury mixer at 150°C for 5 minutes. Then, the mixture was granulated with an extruder to produce pellets. The pellets were molded by press molding to form a sheet of 1 mm in thickness or by inflation molding to form a film of 50 µm in thickness, which were subjected to the heat stability test (a vessel internal temperature of 210°C) and the weathering test, respectively. The results are shown in Table 2. Each resin composition had good antioxidant properties. Comparative Examples 1-4 In the same manner as in Examples 1-4 but using no solution of a hypophosphite compound, the sheet and the film were molded and subjected the heat stability test and the weathering test. The results are shown in Table 2. None of the resin compositions had good antioxidant properties. Examples 5-13 A resin, a heat stabilizer, a hindered amine base weathering stabilizer and a solution of a hypophosphite compound as shown in Table 3 were compounded and kneaded with a Laboplast Mill (manufactured by Toyo Seiki Seisakusho) at 160°C and 60 rpm for 5 minutes and then press molded to form a sheet of 1 mm in thickness. The sheet was subjected to the heat stability test (a vessel internal temperature of 210°C). The results are shown in Table 3. Each resin composition had the good antioxidant property. Comparative Examples 5-9 In the same manner as in Examples 7-12 but using components in a composition of Table 3, a sheet was produced and subjected to the heat stability test. The results are shown in Table 3. None of the resin compositions had a good antioxidant property. Example 14 A resin, a heat stabilizer, a hindered amine base weathering stabilizer, an anti-fogging agent and a solution of a hypophosphite compound as shown in Table 4 were compounded and kneaded with a Banbury mixer at 150°C for 5 minutes and then granulated by an extruder to produce pellets. The pellets were molded by inflation molding to form a film having a thickness of 75 µm. The film was subjected to the weathering test. The results are shown in Table 4. The resin composition had the good antioxidant property. Comparative Example 10 In the same manner as in Example 14 but using components in a composition of Table 4, a film was produced and subjected to the weathering test. The results are shown in Table 4. The resin compositions had a poor antioxidant property.

Claims: A resin composition comprising a resin, a solution of a hypophosphite compound in an organic solvent, a heat stabilizer and a hindered amine base weathering stabilizer. The resin composition according to claim 1, wherein said resin is an olefin polymer. The resin composition according to claim 1, wherein said hypophosphite compound is at least one selected from the group consisting of lithium hypophosphite, sodium hypophosphite, potassium hypophosphite, magnesium hypophosphite, calcium hypophosphite, zinc hypophosphite, titanium hypophosphite, vanadium hypophosphite, molybdenum hypophosphite, manganese hypophosphite, cobalt hypophosphite, ammonium hypophosphite, butylammonium hypophosphite, diethylammonium hypophosphite, triethylammonium hypophosphite, tetraethylammonium hypophosphite, tetrabutylphosphonium hypophosphite and tetraphenylphosphonium hypophosphite. The resin composition according to claim 1, wherein said organic solvent is a polyvalent alcohol having a molecular weight of not more than 50,000.

Inventors: KOTANI KOZO, SAKAYA TAIICHI, KOTANI, KOZO, SAKAYA, TAIICHI
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1991
Main classification: C08K13
IPC codes: C08L101, C08K5, C08L23, C08K3, C08K13