Stabilized polyolefin composition

Abstract: A polyolefin composition comprising a polyolefin, and the following components: (A) a phenolic compound represented by the formula (I): wherein R¹ is hydrogen or an alkyl of 1 to 3 carbon atoms; (B) an acrylate compound represented by the formula (II): wherein R² is an alkyl of 1 to 5 carbon atoms, R³ is an alkyl of 1 to 8 carbon atoms, R⁴ is hydrogen or an alkyl of 1 to 8 carbon atoms, and R⁵ is hydrogen or methyl; and (C) at least one organic phosphorous compound such as bis(2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite. This composition is stable against thermal processing, thermal oxidation and discoloration, and it is especially useful for fibers and films. Further incorporation of a polycondensate of dimethyl succinate with 1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine is effective to improve the light stability of the composition.

Description: The present invention relates to a stabilized polyolefin composition, and more particularly it relates to a polyolefin composition which is not only stable against thermal deterioration during high temperature processing and against thermal oxidative deterioration in use but also extremely stable against discoloration by combustion gas or nitrogen oxides gas (hereinafter referred to as "NOx gas"). Since polyolefin resins, including polyethylene, polypropylene and the like, have excellent physical, chemical and electrical properties, they are widely used as materials for fibers, films, sheets and other shaped articles. However, these polyolefin resins have some problems in that they tend to deteriorate under the action of heat during processing and under the action of heat and oxygen in use, thereby degrading their mechanical properties. In order to control such deterioration, various stabilizers, such as phenolic antioxidants and organic phosphorous antioxidants, have heretofore been used. For example, the phenolic antioxidants conventionally used include 2,6-di-t-butyl-4-methylphenol, 1,3,5-tris(3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate, 1,3,5-tris(4-t-butyl-3-hydroxy-2,6-dimethybenzyl) isocyanurate, and the like. The organic phosphorous antioxidants conventionally used include distearyl pentaerythritol diphosphite, tris(2,4-di-t-butylphenyl) phosphite, bis(2,4-di-t-butylphenyl) pentaerythritol diphosphite, tetrakis(2,4-di-t-butylphenyl) 4,4'-biphenylene diphosphonite, and the like. Polyolefin compositions conventionally proposed have shown some improvements in thermal oxidation resistance in use, but they have still been of insufficient heat resistance during high temperature processing. Especially in the field of fibers, films or the like, where the polyolefin composition undergoes severe production conditions and usage conditions, there are still some problems, and the conventional technologies are not satisfactory. For example in the field of fibers, since the conditions of production and processing are severer than those for usual thick articles, the composition has in the first place to endure high temperatures in the production process. In drying after fiber formation, city gas or kerosene is often used as a heat source; since the polyolefin fibers are easily discolored by the combustion gas from the heat source, they are also desired to resist such discoloration. Further, the final fiber products are also exposed to exhaust gas, such as combustion gas from fuel of automobiles in outdoor usage and combustion gas from kerosene stove in interior usage. Since the polyolefin fibers tend to be discolored by NOx gas contained in the exhaust gas, they are also desired to resist such discoloration. Though polyolefin compositions conventionally proposed are fairly stable agaist thermal oxidation in use they are not so satisfactory in heat resistance during high temperature processing, and also they have insufficient stability against discoloration by combustion gas or NOx gas. Thus, it has been strongly desired to develop a stabilizer formulation which stabilizes the polyolefin against heat during high temperature processing and thermal oxidation in use and also shows good resistance against discoloration by combustion gas or NOx gas. We have found that the combined use of particular hindered phenolic compound, particular acrylate compound and particular organic phosphorous compound can give these stability properties; and that the use of a particular hindered piperidine compound together with the above components further improves stability against light. The present invention provides a polyolefin composition comprising polyolefin and, per 100 parts by weight of the polyolefin, the following components: (A) at least 0.01 part by weight of hindered phenolic compound of formula (I): wherein R¹ is hydrogen or an alkyl of 1 to 3 carbon atoms; (B) at least 0.01 part by weight of acrylate compound of formula (II): wherein R² is an alkyl of 1 to 5 carbon atoms, R³ is an alkyl of 1 to 8 carbon atoms, R⁴ is hydrogen or an alkyl of 1 to 8 carbon atoms, and R⁵ is hydrogen or methyl; and (C) at least 0.01 part by weight of organic phosphorous compound selected from bis(2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, bis(2,4-di-t-butylphenyl) pentaerythritol diphosphite, tris(2,4-di-t-butylphenyl) phosphite, tetrakis(2,4-di-t-butylphenyl) 4,4'-biphenylene diphosphonite, 2,2'-ethylidenebis(4,6-di-t-butylphenyl) fluorophosphite, and 2,2'-methylenebis(4,6-di-t-butylphenyl) octyl phosphite. The composition of the present invention preferably also contains the further component (D) 0.01 to 1 part by weight, per 100 parts by weight of the polyolefin, of hindered piperidine compound of formula (III): wherein n is 2 to 20. Each of components (A), (B), (C) and (D) may consist of one, two or more of the defined compounds. The invention further provides a process for producing a polyolefin shaped article by blending polyolefin with the aforementioned components (A), (B) and (C), and optionally also with component (D), and forming the resulting composition into a shaped article, thereby stabilizing the shaped article against heat and oxidation as well as against discoloration by combustion gas or NOx gas. The invention still further provides a polyolefin fiber or film prepared from the aforementioned composition. The polyolefin used in the invention may be a homopolymer of an α-olefin including ethylene, propylene, butene-1, isobutene, 3-methylpentene-1, hexene-1, 4-methylpentene-1 or the like, or a random or block copolymer obtainable from two or more of the α-olefins. Specific examples thereof are polyethylene, polypropylene, polybutene-1, polyisobutene, poly-3-methylbutene-1, polyhexene-1, poly-4-methylpentene-1, ethylene/propylene copolymer, ethylene/butene-1 copolymer, ethylene/4-methylpentene-1 copolymer, propylene/butene-1 copolymer, propylene/4-methylpentene-1 copolymer, ethylene/propylene/butene-1 copolymer, and the like; especially preferred is polypropylene including propylene homopolymer and copolymer of propylene with a small amount of ethylene. In hindered phenolic component (A) of formula (I), R¹ is hydrogen or an alkyl of 1 to 3 carbon atoms including methyl, ethyl and propyl; R¹ is preferably alkyl and most preferably methyl, for thermal oxidation resistance. In acrylate component (B) of formula (II), R² is an alkyl of 1 to 5 carbon atoms including methyl, ethyl, propyl, t-butyl, 2,2-dimethylpropyl and the like; R² is preferably methyl or ethyl, for thermal stability. R³ in formula (II) is an alkyl of 1 to 8 carbon atoms including methyl, ethyl, propyl, t-butyl, t-pentyl, t-octyl and the like ; R³ is preferably methyl, t-butyl or t-pentyl, for thermal stability, and especially preferred is t-pentyl. R⁴ in formula (II) is hydrogen or an alkyl of 1 to 8 carbon atoms including methyl, ethyl, propyl, butyl, pentyl, octyl and the like; R⁴ is preferably hydrogen or methyl, for thermal stability. R⁵ in formula (II) is hydrogen or methyl; hydrogen is preferred, for thermal stability. The organic phosphorous component (C) used in the invention is selected from the aforementioned six compounds, among which bis(2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite is especially preferred, for thermal and oxidation resistance. In the invention, all of the components (A), (B) and (C) are essential, and the amounts thereof used are preferably 0.01 to 1 part by weight for each component per 100 parts by weight of the polyolefin. When any of the components (A), (B) and (C) is used in an amount less than 0.01 part by weight, the desired effects are insufficiently achieved; use of any of them in an amount exceeding 1 part by weight may be uneconomic since concomittantly increased effects may not be achieved. Within these ranges, hindered phenolic component (A) is preferably used in an amount of from 0.02 to 0.5 part by weight, acrylate component (B) in an amount of from 0.02 to 0.5 part by weight, and organic phosphorous component (C) in an amount of from 0.02 to 0.5 part by weight, each per 100 parts by weight of the polyolefin. In the invention, it is preferred to use component (D), i.e. the hindered piperidine compound of formula (III), in combination with components (A), (B) and (C). The combined use of the hindered piperidine component contributes to further improve the stability against light. The amount of hindered piperidine component of formula (III), when used, is 0.01 to 1 part by weight, preferably from 0.02 to 0.5 part by weight, per 100 parts by weight of the polyolefin. Hindered piperidine compound represented by the formula (III) is disclosed, for example, in US-A-4,234,707, and is commercially available as "TINUVIN 622 LD" from Ciba-Geigy Corp. The polyolefin composition of the invention may further contain any other additives including antioxidants, light stabilizers, metal soaps, nucleating agents, lubricants, antistatic agents, metal deactivators, flame retardants, pigments, fluorescent brighteners and the like, so long as the additives do not adversely affect the basic characteristics of the composition. In blending the polyolefin with the components (A), (B) and (C) used in the invention, component (D) optionally used, and other optional additives incorporated in case of necessity, any and every method which is suitable for forming a homogeneous blend can be employed. Thus, the starting materials may be blended simultaneously, they may be blended separately in plural stages, or they may be blended as a masterbatch of one or more components. These materials may be kneaded in any usual manner, for instance, by using a single-screw extruder, a double-screw extruder, or the like. The polyolefin composition of the invention is useful where the composition is processed at a high temperature for the purpose of raising the productivity and in the field of fibers, films and other shaped articles which are desired to be inhibited from discoloration, especially in the field of such shaped articles which are exposed to combustion gas or NOx gas. In particular, the composition is useful for fibers. The composition can be shaped by various known methods. For example the composition can be formed into films by means of any conventional film extruder, optionally with simultaneous stretching. For fibers, such methods can be applied as melt-spinning the composition in any conventional manner and optionally stretching the resulting products, or melt-spinning the composition and thereafter subjecting the resulting products to surface treatment (e.g. with finishing agent comprising oil, antistatic agent and others) followed by stretching. The present invention is explained below in more detail with reference to Examples, which are only illustrative and not limitative of the scope of the invention. In the Examples, parts are by weight unless otherwise indicated. Test additives used in the Examples are as follows, and they will be referred to hereinunder by the indicated symbols. A-1 : 3,9-Bis[2-{3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy}-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane AO2 : 1,3,5-Tris(3,5-di-t-butyl-4-hydroxybenzyl) isocyanurate AO3 : 1,3,5-Tris(4-t-butyl-3-hydroxy-2,6-dimethylbenzyl) isocyanurate AO4 : Calcium bis(ethyl 3,5-di-t-butyl-4-hydroxybenzylphosphonate) B-1 : 2,4-Di-t-amyl-6-[1-(3,5-di-t-amyl-2-hydroxyphenyl)ethyl]phenyl acrylate B-2 : 2-t-Butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)4-methylphenyl acrylate C-1 : Bis(2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite C-2 : Bis(2,4-di-t-butylphenyl) pentaerythritol diphosphite C-3 : Tris(2,4-di-t-butylphenyl) phosphite C-4 : Tetrakis(2,4-di-t-butylphenyl) 4,4'-biphenylene diphosphonite C-5 : 2,2'-Ethylidenebis(4,6-di-t-butylphenyl) fluorophosphite C-6 : 2,2'-Methylenebis(4,6-di-t-butylphenyl) octyl phosphite D-1 : Polycondensate of dimethyl succinate with 1-(2-hydroxyethyl)-4-hydroxy-2,2,6,6-tetramethylpiperidine (TINUVIN 622 LD, produced by Ciba-Geigy Corp.) HL2 : Poly[{6-(1,1,3,3-tetramethylbutyl)imino-1,3,5-triazin-2,4-diyl}{(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}] (CHIMASSORB 944 LD, produced by Ciba-Geigy Corp.) HL3 : Poly[(6-morpholino-1,3,5-triazin-2,4-diyl){(2,2,6,6-tetramethyl-4-piperidyl)imino}hexamethylene{(2,2,6,6-tetramethyl-4-piperidyl)imino}] (CYASORB UV-3346, produced by American Cyanamid Co.) EXAMPLE 1 Formulation Unstabilized Polypropylene 100 parts Calcium Stearate 0.05 part Test Additives Shown in Table 1 The above blend was admixed for 5 minutes in a mixer and thereafter extruded at 310°C using a 40 mm⊘ extruder to pelletize the blend. The resulting pellets were subjected to melt spinning at a temperature of 340°C and under a resin discharge pressure of 100 kgf/cm³ (constant) using a 30 mm⊘ extruder having a die shape of 0.5 mm⊘ x 36 holes, and the following characteristic items were evaluated. (1) Heat Resistance In the above melt spinning step, draw-off speed for the 36 filaments flowing out of the die was varied between 400 m/min. and 900 m/min. at an interval of 100 m/min., and the speed at which the filaments could be drawn without breakage was determined to evaluate the heat resistance. Since filament breakage occurs due to deterioration of the resin caused by heat during processing, no filament breakage or a high speed draw-off capability indicates excellent heat resistance during processing. (2) Thermal Oxidation Resistance The unstretched filaments obtained by melt spinning were stretched to 2.5 times their length at 135°C to obtain fibers of 18 denier/filament. The fibers were cut into 5 cm lengths,and about 3 g thereof was bundled at the center to make a test specimen. The test specimen was put in a Geer oven at 135°C, and the period (days) until thermal discoloration occured was determined to evaluate the thermal oxidation resistance. (3) Light Oxidation Resistance Thirtysix fibers of the 18 denier/filament stretched product from (2) above were twisted to make yarn. The resulting yarn was put in a xenone fade meter having a black panel temperature of 89°C, and the tensile strength of the yarn was measured after each 50 kJ of irradiation. The light oxidation resistance was evaluated by the energy dose needed to reduce the tensile strength by 50%. (4) Resistance to Discoloration by Combustion Gas The same test specimen as in item (2) above was prepared, and it was exposed to combustion gas at 98°C generated from city gas for 30 minutes to evaluate the discoloration degree with visual judgement of the following five criteria, in which the smaller the value, the better the resistance to discoloration. 1 : No discoloration 2 : Slight discoloration 3 : Moderate discolaration 4 : Marked discoloration 5 : Severe discoloration The device utilized for the combustion gas exposure was a stainless steel cylinder having a diameter of 25 cm and a length of 70 cm, where the combustion gas was generated from the bottom and the test specimen was placed at the upper portion. (5) Resistance to Discoloration by NOx Gas The same test specimen as in item (2) above was prepared, and it was exposed to an atmosphere having an NOx concentration of 2% by volume for 24 hours in accordance with JIS L 0855 "Testing Method for Colour Fastness to Nitrogen Oxides". The discoloration degree was evaluated with the same visual judgement of the five criteria as described in item (4) above. The smaller the value, the better the resistance to discoloration. The evaluation results of the above tests are shown in Table 1 and Table 2. In the Tables, (1) to (5) appearing in the column of "Results" correspond to the characteristic items of the above evaluation tests and are as follows: (1) Heat Resistance: Draw-off speed capability (m/min.) (2) Thermal Oxidation Resistance: Thermal discoloration period at 135°C (days) (3) Light Oxidation Resistance: Energy dose until the tensile strength is reduced by half (4) Resistance to Discoloration by Combustion Gas (5) Resistance to Discoloration by NOx Gas The polyolefin composition blended with particular hindered phenolic compound, particular acrylate compound and particular organic phosphorous compound, according to the invention, has for practical purposes sufficient stability against heat during high temperature processing and against thermal oxidation in use and also it exhibits high resistance against discoloration caused by combustion gas or NOx gas. Additional incorporation of particular hindered piperidine compound further improves the stability of the composition against light oxidation. While the invention has been described in detail and with reference to specific embodiments and examples, it is to be understood for the person skilled in the art that the invention is not limited to the details given herein but may be modified and changed within the spirit and scope of the appended claims.

Claims: A polyolefin composition comprising polyolefin and, per 100 parts by weight of the polyolefin, the following components: (A) at least 0.01 part by weight of hindered phenolic compound of formula (I): wherein R¹ is hydrogen or an alkyl of 1 to 3 carbon atoms; (B) at least 0.01 part by weight of acrylate compound of formula (II): wherein R² is an alkyl of 1 to 5 carbon atoms, R³ is an alkyl of 1 to 8 carbon atoms, R⁴ is hydrogen or an alkyl of 1 to 8 carbon atoms, and R⁵ is hydrogen or methyl; and (C) at least 0.01 part by weight of organic phosphorous compound selected from bis(2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, bis(2,4-di-t-butylphenyl) pentaerythritol diphosphite, tris(2,4-di-t-butylphenyl) phosphite, tetrakis(2,4-di-t-butylphenyl) 4,4'-biphenylene diphosphonite, 2,2'-ethylidenebis(4,6-di-t-butylphenyl) fluorophosphite, and 2,2'-methylenebis(4,6-di-t-butylphenyl) octyl phosphite. A composition according to claim 1 which further contains (D) 0.01 to 1 part by weight, per 100 parts by weight of the polyolefin, of hindered piperidine compound of formula (III): wherein n is 2 to 20. A composition according to claim 1 or 2 wherein the polyolefin comprises homopolymer of an α-olefin or copolymer of two or more α-olefins, and preferably comprises polypropylene. A composition according to any preceding claim wherein the component (A) is of formula (I) in which R¹ is alkyl of 1 to 3 carbon atoms, preferably 3,9-bis[2-{3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy}-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane. A composition according to any preceding claim wherein component (B) is of formula (II) in which R² is methyl or ethyl, R³ is methyl, t-butyl or t-pentyl, R⁴ is hydrogen or methyl, and R⁵ is hydrogen, preferably 2,4-di-t-amyl-6-[1-(3,5-di-t-amyl-2-hydroxyphenyl)ethyl]phenyl acrylate or 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate. A composition according to any preceding claim wherein the component (C) is bis(2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite. A composition according to any preceding claim wherein each of components (A), (B) and (C), and component (D) when present, amounts to 0.02 to 0.5 part by weight per 100 parts by weight of the polyolefin. A process for producing a polyolefin shaped article which comprises blending polyolefin with: (A) hindered phenolic compound of formula (I): wherein R¹ is hydrogen or an alkyl of 1 to 3 carbon atoms; (B) acrylate compound of formula (II): wherein R² is an alkyl of 1 to 5 carbon atoms, R³ is an alkyl of 1 to 8 carbon atoms, R⁴ is hydrogen or an alkyl of 1 to 8 carbon atoms, and R⁵ is hydrogen or methyl; and (C) organic phosphorous compound selected from bis(2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, bis(2,4-di-t-butylphenyl) pentaerythritol diphosphite, tris(2,4-di-t-butylphenyl) phosphite, tetrakis(2,4-di-t-butylphenyl) 4,4'-biphenylene diphosphonite, 2,2'-ethylidenebis(4,6-di-t-butylphenyl) fluorophosphite, and 2,2'-methylenebis(4,6-di-t-butylphenyl) octyl phosphite; and forming the resulting composition into a shaped article, whereby the shaped article is stabilized against heat and oxidation as well as against discoloration by combustion gas or nitrogen oxides gas, the polyolefin optionally being blended also with (D) hindered piperidine compound of formula (III): wherein n is 2 to 20, whereby the resulting shaped article is further stabilized against light. A process according to claim 8 wherein the forming is effected by melt-spinning the composition followed by stretching to prepare a fiber, or by extruding the composition into a film. A polyolefin fiber or film prepared from a composition according to any of claims 1 to 7.

Inventors: IDA KANAKO, ISHII TAMAKI, KOJIMA FUMITOSHI, YACHIGO SHINICHI, IDA, KANAKO, ISHII, TAMAKI, KOJIMA, FUMITOSHI, YACHIGO, SHINICHI
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1992
Main classification: C08L23
IPC codes: C08L23, C08K5, D01F6