JP5179915B2 - Resin tank and manufacturing method thereof - Google Patents

Description

  The present invention relates to a resin tank having high durability even when hot water is stored, and a method for manufacturing the same.

  Conventionally, there are two types of hot water heaters: an instantaneous type and a hot water type, and the hot water type hot water heater is provided with a tank for storing hot water. Examples of the tank include a cylindrical tank made of metal (such as stainless steel). This metal tank is manufactured by rounding a metal plate into a cylindrical shape and welding the ends. Furthermore, it is necessary to attach a hot water outlet after welding the end plates to both ends of the metal tank. Due to soaring material prices and manufacturing costs, application of inexpensive resin tanks is required. However, the resin tank has heat resistance that can withstand warm water of 80 ° C. or higher, and rigidity that can withstand the weight of the hot water, and also ensures creep performance by internal pressure, has a large capacity of 50 L or more, and has a durable life. Performance such as 10 years or more is required, and it is difficult for conventional resin tanks to satisfy these requirements.

In order to solve such problems, for example, Japanese Patent Application Laid-Open No. 2007-152712 (Patent Document 1) discloses a multilayer hollow container including an outermost layer, a burr recovery layer, an adhesive layer, a barrier layer, and an innermost layer. The outermost layer is made of an ethylene polymer that satisfies specific conditions, the innermost layer is made of an ethylene polymer that satisfies specific conditions, and the iron and aluminum contents are each 10 ppm by weight or less. A multilayer hollow container is disclosed. This document describes that the ethylene polymer preferably contains no additives other than the ethylene polymerization catalyst deactivator, and one or more hindered phenolic antioxidants can be used. It is described that the content of the hindered phenol-based antioxidant with respect to the ethylene-based polymer is 100 to 2500 ppm by weight. However, when such a multilayer hollow container is stored with warm water, the antioxidant bleeds out to the surface (inner surface and outer surface) of the multilayer hollow container, and the effect of the antioxidant cannot be maintained for a long period of time. Is low.
JP 2007-152712 A (claim 1 and paragraph number [0028])

  Accordingly, an object of the present invention is to provide a resin tank having high durability even when hot water is stored and a method for producing the same.

  Another object of the present invention is to provide a resin tank having high rigidity and a method for manufacturing the same.

  Still another object of the present invention is to provide a method capable of producing a resin tank with high moldability.

  As a result of diligent studies to achieve the above-mentioned problems, the inventors of the present invention have configured a resin tank with a high molecular weight polyethylene-based resin having a wide molecular weight distribution and a large amount of a high molecular weight antioxidant to store hot water. The present inventors have found that a resin tank having excellent durability can be obtained with high moldability, and the present invention has been completed.

That is, the resin tank of the present invention includes at least a resin layer composed of a polyethylene resin and an antioxidant, and is a resin tank for storing hot water of a hot water supply system, wherein the polyethylene resin has a weight It is composed of a first polyethylene resin having an average molecular weight (Mw) of 300,000 to 1,000,000 and a molecular weight distribution of 10 to 50 and a high molecular weight and a wide molecular weight distribution, and the antioxidant is a high molecular weight antioxidant. It is comprised and content of the said high molecular weight antioxidant is 3,000-10,000 ppm in weight conversion with respect to the said polyethylene-type resin. The first polyethylene resin may have a number average molecular weight (Mn) of about 15,000 to 100,000. The intrinsic viscosity of the first polyethylene resin may be about 2.5 to 5 dl / g. The first polyethylene resin has a melt flow rate of 0.1 to 0.91 under conditions of (1) density of 0.940 to 0.980 g / cm ³ , (2) temperature of 190 ° C. and load of 212 N (21.6 kgf). The circumferential notch tensile creep rupture time may be 80 to 5000 hours under the conditions of 100 g / 10 minutes, (3) a temperature of 90 ° C., and a nominal stress of 4.0 MPa. The first polyethylene resin may have a long chain branch chain. When the first polyethylene-based resin has a long-chain branched chain, the melt tension is large, which is suitable for blow molding. The polyethylene resin may further contain a second polyethylene resin having a high molecular weight and a narrow molecular weight distribution. When the second polyethylene resin is included, the moldability can be improved. The ratio of the second polyethylene resin may be about 0.1 to 60% by weight with respect to the entire polyethylene resin.

  The high molecular weight antioxidant is at least one selected from phenolic compounds, phosphorus compounds, sulfur compounds, and amine compounds, and the content of the high molecular weight antioxidant is in terms of weight relative to the polyethylene resin. Or about 3,200-9,000 ppm. The high molecular weight antioxidant is composed of a phenolic compound, a phosphorus compound, and at least one selected from a sulfur compound and an amine compound, a total amount of the phenolic compound and the phosphorus compound, a sulfur compound, and The ratio (weight ratio) with at least one selected from amine compounds may be about the former / the latter = 30/70 to 90/10. The resin layer may further contain a low molecular weight antioxidant. The total content of the high molecular weight antioxidant and the low molecular weight antioxidant may be about 5,000 to 10,000 ppm in terms of weight with respect to the polyethylene resin. Thus, even if the content of the antioxidant is large, the durability of the resin tank can be improved because the predetermined polyethylene resin is used. The ratio (weight ratio) between the high molecular weight antioxidant and the low molecular weight antioxidant may be about the former / the latter = 50/50 to 99/1. The resin tank has a capacity of 50 to 300 L, and the resin layer may have a rib. The resin tank (or a resin layer composed of a polyethylene resin and an antioxidant) may have a temperature of 210 ° C. and an oxidation induction time in an oxygen atmosphere of 30 to 250 minutes. The hot water supply system may be at least one selected from a single hot water supply system (a hot water supply system having only a hot water supply function), a hot water supply / heating system, and a bath cooking system.

  The resin tank may have a multilayer laminated structure including a resin layer and a foamed layer formed on the outer surface of the resin layer. The foam layer may be composed of a recycled product of the resin tank. The foam layer may contain a recycled product of the resin tank in a proportion of 0.01 to 50% by weight with respect to the foam layer.

  The manufacturing method of the said resin tank including the process of blow-molding the resin composition comprised with the said polyethylene-type resin and the said antioxidant is also contained in this invention. The present invention also includes a cylindrical resin layer obtained by melting the resin composition composed of the polyethylene resin and the antioxidant, and the resin composition and the foaming agent formed on the outer periphery of the resin layer. And a method for producing a resin tank having the multilayer laminated structure including a step of blow-molding a melt composed of a foamed layer obtained by melting the foamed composition composed of 1.

  Since the resin tank of the present invention includes at least a resin layer composed of a first polyethylene resin having a high molecular weight and a wide molecular weight distribution and a large amount of a high molecular weight antioxidant, it is durable even when hot water is stored. Excellent. Furthermore, the resin tank is excellent in rigidity. Furthermore, in the method of the present invention, the resin tank can be manufactured with high moldability.

  The present invention will be described in detail with reference to the accompanying drawings as necessary. The resin tank of the present invention includes a resin layer composed of a polyethylene resin and an antioxidant.

[Resin layer]
(Polyethylene resin)
The polyethylene resin is composed of a first polyethylene resin having a high molecular weight and a wide molecular weight distribution. Examples of the first polyethylene resin include ethylene homopolymers and copolymers. Examples of the homopolymer of ethylene include polyethylene [low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene, high density polyethylene (HDPE), etc.], and HDPE is usually used. Many.

The first polyethylene resin may be a copolymer of ethylene and a copolymerizable monomer. Examples of the copolymerizable monomer include α-olefins [chain olefins (propylene, butene-1, pentene-1, hexene-1, octene-1, decene-1, dodecene-1, tetradecene-1, hexadecene-1, C _3-20 α-linear olefins such as octadecene-1 and eicosene-1; 3-methyl-butene-1, 3-methyl-pentene-1, 3-ethyl-pentene-1, 4-methyl-pentene- C _3- such as 1,4-methyl-hexene-1,4,4-dimethyl-hexene-1,4,4-dimethyl-pentene-1,3-ethyl-hexene-1,4-ethyl-hexene-1 ₂₀ α-branched olefins etc.]; alkadienes (1,4-hexadiene, 1,7-octadiene, 4-methyl-1,4-hexadiene, 5-methyl-1,4- Non-conjugated alkadienes such as hexadiene, conjugated alkadienes such as butadiene and isoprene); ethylenically unsaturated carboxylic acids and acid anhydrides thereof ((meth) acrylic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, crotonic acid, Isocrotonic acid, mesaconic acid, angelic acid, etc.]; (meth) acrylic acid esters [(meth) acrylic acid alkyl esters, glycidyl (meth) acrylates, etc.]; carboxylic acid vinyl esters (saturated carboxylic acids such as vinyl acetate and vinyl propionate) Vinyl ester, etc.). These copolymerizable monomers can be used alone or in combination of two or more. Among the copolymerizable monomers, C _3-10 α-linear olefins such as propylene, butene-1, and hexene-1, particularly C _4-8 α-linear olefins such as butene-1 and hexene-1. Etc. are preferable.

  In the copolymer, the proportion (content) of the copolymerizable monomer unit is 10 wt% or less (about 0.1 to 10 wt%), preferably 0.2 to 8 wt%, more preferably 0.3 to It may be 5% by weight, usually about 0.1 to 5% by weight.

Among these first polyethylene resins, polyethylene [high density polyethylene (HDPE) and the like], copolymers of ethylene and copolymerizable monomers (ethylene-butene-1 copolymer, ethylene-hexene-1 copolymer) Such as ethylene-C _3-10 α-linear olefin copolymer). These polyethylene resins may be used alone or in combination of two or more.

  The copolymer may be a random copolymer or an alternating copolymer.

  The first polyethylene-based resin may be linear, but usually has a branched chain, and particularly preferably has a long-chain branched chain. When the first polyethylene-based resin has a long-chain branched chain, the melt tension is large, which is suitable for blow molding. Further, when the first polyethylene-based resin has a branched chain (particularly, a long-chain branched chain), an antioxidant described later is held by the branched structure of the first polyethylene-based resin, and the resin inner surface This may improve the durability of the resin tank.

The average number of branches of the first polyethylene resin may be 1 to 10, preferably 2 to 9, and more preferably about 3 to 8 per 1000 carbon atoms. The average length of the branch can be selected from 3 or more carbon atoms (for example, about 3 to 10000), preferably 4 or more (for example, 4 to 8000), more preferably 5 or more (for example, 30 to about 6000). The average number of branches and the average length of branches of the first polyethylene resin are measured using, for example, FT-NMR (manufactured by JEOL Ltd., 400 MHz FT-NMR (ECX-400), etc.) ¹³ C , Solvent o-dichlorobenzene-d4, under the conditions of a measurement temperature of 140 ° C., it can be measured by a proton decoupling method.

  The weight average molecular weight (Mw) of the first polyethylene resin is about 300,000 to 1,000,000, preferably about 400,000 to 900,000, and more preferably about 500,000 to 800,000. The number average molecular weight (Mn) of the first polyethylene resin is 15,000 or more (for example, about 15,000 to 100,000), preferably 17,000 or more (for example, about 18,000 to 70,000). ), More preferably about 20,000 or more (for example, about 21,000 to 50,000).

  The first polyethylene-based resin may have a single peak or a plurality of peaks in the analysis by the GPC method. In addition, the first polyethylene resin may have a peak in the ultrahigh molecular weight region (for example, the weight average molecular weight is about 1,000,000 to 2,000,000) in the analysis by the GPC method.

  The molecular weight distribution (Mw / Mn) of the first polyethylene resin is wide and is usually 10 or more (for example, about 10 to 50), preferably 13 or more (for example, about 14 to 45), more preferably 15 or more (for example, , About 16 to 40), particularly about 10 to 40.

  The intrinsic viscosity of the first polyethylene resin may be 2.5 to 5 dl / g, preferably 2.8 to 4.8 dl / g, and more preferably about 3 to 4.6 dl / g.

The density of the first polyethylene resin is about 0.940 to 0.980 g / cm ³ , preferably about 0.945 to 0.975 g / cm ³ , and more preferably about 0.946 to 0.970 g / cm ^3. May be. With such a density, a resin tank excellent in rigidity and buffer performance can be obtained. The density of the polyethylene resin can be adjusted by controlling the type of polymerization catalyst, the polymerization conditions, the type of copolymerizable monomer, the content of the copolymerizable monomer, and the like.

  The melt flow rate of the first polyethylene-based resin is 0.1 to 100 g / 10 minutes, preferably 0.15 to 90 g / 10 minutes, more preferably, under conditions of a temperature of 190 ° C. and a load of 212 N (21.6 kgf). May be about 0.2 to 80 g / 10 minutes. Within such a range, it is possible to obtain a resin tank that maintains durability and has low mold resin drawdown and excellent moldability.

  The all-round notch-type tensile creep rupture time of the first polyethylene-based resin is 80 hours or longer (for example, about 80 to 5000 hours), preferably 85 hours or longer (at a temperature of 90 ° C. or higher and a nominal stress of 4.0 MPa). For example, it may be about 88 to 4000 hours), more preferably 90 hours or more (for example, about 92 to 3000 hours), and usually about 80 to 3000 hours. The all-around notch tensile creep rupture time is measured in accordance with JIS K6774. Within such a range, the resin has sufficient durability against residual stress during molding of the resin tank, stress generated by its own weight when hot water is stored, stress concentrated in the recesses and steps of the resin tank, etc. A tank is obtained.

  The melting point or softening point of the first polyethylene resin may be about 70 to 200 ° C, preferably about 80 to 170 ° C, more preferably about 90 to 150 ° C (particularly 100 to 140 ° C).

  The first polyethylene resin may be prepared by a conventional polymerization method (for example, addition polymerization using a Ziegler type catalyst, addition polymerization using a metallocene catalyst, etc.). It is preferable to prepare by addition polymerization using chromium or the like. Usually, when a Ziegler-type catalyst, a metallocene-based catalyst, or the like is used, a linear polyethylene-based resin is obtained. When a chromium-based catalyst is used, a first polyethylene-based resin having a branched chain (particularly, a long-chain branched chain) is obtained. Is obtained. When a chromium-based catalyst is used, side chains are generated by chain transfer during polymerization, and long chain branching can be formed. Furthermore, when the polymerization is carried out under high temperature and high pressure conditions, long chain branching tends to be formed. Further, after polymerization, long-chain branching can be formed by molecular crosslinking by special means such as electron beam irradiation.

  The polyethylene resin may further contain a second polyethylene resin having a high molecular weight and a narrow molecular weight distribution. The first polyethylene-based resin may have high rigidity and lower fluidity, but if the second polyethylene-based resin is included, the moldability of the resin tank can be improved.

  Examples of the second polyethylene resin include ethylene homopolymers and copolymers exemplified in the section of the first polyethylene resin, and polyethylene (LDPE, LLDPE, HDPE, etc.) is often used. The second polyethylene-based resin may be linear or branched.

  The second polyethylene resin can be prepared by a conventional polymerization method exemplified in the section of the first polyethylene resin.

  The number average molecular weight (Mn) of the second polyethylene resin may be about 5,000 to 100,000, preferably 7,000 to 80,000, and more preferably about 10,000 to 60,000. The weight average molecular weight (Mw) of the second polyethylene resin is 50,000 or more (for example, 50,000 to 1,000,000, preferably 70,000 to 800,000, more preferably 100,000 to 600). The molecular weight distribution (Mw / Mn) of the second polyethylene resin is narrow, 1 to 10 (for example, 1 to 9, preferably 2 to 8, and more preferably 3 to 7). It may be a degree.

  The ratio of the second polyethylene resin is 0 to 60% by weight (for example, 0.1 to 60% by weight), preferably 0.2 to 50% by weight, and more preferably 0.3% with respect to the entire polyethylene resin. It may be about ˜40% by weight (particularly 0.4 to 35% by weight).

  The second polyethylene resin may have a single peak in the analysis by the GPC method, and when combined with the first polyethylene resin, the second polyethylene resin overlaps with the peak of the first polyethylene resin. One peak may be formed and may have a peak different from the peak of the first polyethylene resin.

  The molecular weight of the polyethylene resin can be measured by a gel permeation chromatography method (GPC method) using o-dichlorobenzene as a solvent at a measurement temperature of 140 ° C.

(Antioxidant)
Examples of the antioxidant include high molecular weight antioxidants such as radical chain inhibitors (phenolic compounds, amine compounds, etc.), peroxide decomposers (phosphorous compounds, sulfur compounds, etc.), and the like. These antioxidants can be used alone or in combination of two or more.

Examples of phenolic compounds include hindered phenolic compounds {1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane and other tris (2-alkyl-4-hydroxy-5- Tris (3,5-di) such as branched C _3-8 alkylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene -Branched C _3-8 alkyl-4-hydroxybenzyl) benzene, 1,3,5-trimethyl-2,4,6, -tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, etc. 1,3,5-trialkyl-2,4,6-tris (3,5-di - branched _{C 3-8} alkyl-4-hydroxybenzyl) benzene; tetrakis [methylene-3- (3,5-di - - butyl-4-hydroxyphenyl) propionate] tetrakis methane [alkylene-3- (3,5-di - branched _{C 3-8} alkyl-4-hydroxyphenyl) _{propionate] C 1-4} alkanes, pentaerythrityl tetrakis Pentaerythrityltetrakis [3- (3,5-di-branched C _3-8 alkyl-4-hydroxyphenyl) propionate such as [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] ] Etc.}. A phenol type compound can be used individually or in combination of 2 or more types. Phenol compounds are available, for example, as trade names “Irganox 1010”, “Irganox 1076”, “Irganox 1330”, etc., manufactured by Ciba Japan.

  Examples of amine compounds include tetracarboxylic acid tri- or tetrapiperidyl esters [eg, tetrakis (2,2,6,6-tetramethyl-4-piperidyl) ester such as 1,2,3,4-butanetetracarboxylic acid ester]. Carboxylic acid tetrakis (tetramethylpiperidyl) ester; poly [[6-[(1,1,3,3-tetramethylbutyl) amino] -1,3,5-triazine-2,4-diyl] [(2, Hindered amine compounds (HALS) such as 2,6,6-tetramethyl-4-piperidinyl) imino]] and the like. In addition, an amine compound can be obtained as, for example, trade names “Chimassorb944LD”, “Chimassorb2020FDL”, “Tinuvin622LD”, etc., manufactured by Ciba Japan Co., Ltd.

Examples of phosphorus compounds include tris (2,4-branched C _3-8 alkyl-butylphenyl) phosphite [such as tris (2,4-di-t-butylphenyl) phosphite]; tetrakis (2,4-di Tetrakis (2,4-di-branched C _3-8 alkylphenyl) -4,4′-C _2-4 alkylene phosphite such as —t-butylphenyl) -4,4′-biphenylene phosphite. . The phosphorus compound is available, for example, as trade name “Irgafos168” manufactured by Ciba Japan Co., Ltd.

High molecular weight antioxidant, t- butyl branched C _3-8 alkyl phenyl group which may be substituted with groups such as groups, which may be substituted by branched C _3-8 alkyl group such as t-butyl group At least 3 functional groups (for example, 3) in one molecule such as a hydroxyphenyl group, an aminophenyl group that may have a substituent on the nitrogen atom of the amino group, and a piperidyl group that may be substituted with a methyl group ~ 5)) in many cases.

Among these high molecular weight antioxidants, hindered phenol compounds {1,3,5-trimethyl-2,4,6, -tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene and the like 1,3,5-trialkyl-2,4,6-tris (3,5-di-branched C _3-8 alkyl-4-hydroxybenzyl) benzene, tetrakis [methylene-3- (3 ′, 5 ′ -Di-t-butyl-4'-hydroxyphenyl) propionate] tetrakis [alkylene-3- (3,5-di-branched C _3-8 alkyl-4-hydroxyphenyl) propionate] C _1-4 alkane such as methane , Pentaerythrityltetrakis [3- (3,5-pentaerythrityltetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] and the like. - such branched _{C 3-8} alkyl-4-hydroxyphenyl) propionate}, hindered amine compounds {poly [[6 - [(1,1,3,3-tetramethylbutyl) amino] -1,3,5-triazine -2,4-diyl] [(2,2,6,6-tetramethyl-4-piperidinyl) imino]] and the like} are often used.

  The molecular weight of the high molecular weight antioxidant is, as a rough guide, 600 to 10,000, preferably 620 to 9,000 (for example, 700 to 8,500), more preferably 640 to 8,000 (for example, 800 to It may be about 7,500).

  The high molecular weight antioxidant can be used alone or in combination, and the content of the high molecular weight antioxidant is 3,000 to 10,000 ppm, preferably 3,200 to 9, in terms of weight relative to the polyethylene resin. It may be about 3,000 ppm, more preferably about 3,500 to 8,000 ppm.

  When a large amount of high molecular weight antioxidant is used in this way, a high antioxidant effect is obtained for a long period of time, and the durability of the resin tank is improved.

  The antioxidant may further contain a low molecular weight antioxidant. Examples of the low molecular weight antioxidant include phenolic compounds, amine compounds, phosphorus compounds, sulfur compounds, and the like.

  Examples of phenolic compounds include dibutylhydroxytoluene (BHT), butylated hydroxyanisole (BHA), 2,6-di-t-butyl-p-cresol, 2,6-di-t-butyl-4-ethylphenol, 2,6-di-t-butylphenol, 2,4-dimethyl-6-t-butylphenol, 2-methyl-4,6-di-nonylphenol, butylhydroxyanisole, styrenated phenol, 2,4,6-tri- monophenol compounds such as t-butylphenol and 4,4′-dihydroxydiphenyl; 2,2′-methylenebis (4-methyl-6-t-butylphenol), 2,2′-methylenebis (4-ethyl-6-t) -Butylphenol), 4,4'-butylidenebis (3-methyl-6-t-butylphenol), 4,4 ' Butylidenebis (2,6-di-t-butylphenol), 1,1′-bis (4-hydroxyphenyl) cyclohexane, 2,2′-dihydroxy-3,3′-di (α-methylcyclohexyl) -5,5 Bisphenol compounds such as' -dimethyldiphenylmethane; hydroquinone compounds such as 2,5-di-t-butylhydroquinone, hydroquinone monomethyl ether, 2,5-di- (tertiary amyl) hydroquinone; n-octadecyl-3- ( And hindered phenol compounds such as 4'-hydroxy-3 ', 5'-di-t-butylphenol) propionate.

  In addition, the phenolic compound includes a metal such as a hydrazine compound having a hindered phenol structure {N, N′-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyl] hydrazine}. Inactive agents are also included, and can be obtained, for example, as “Irganox MD1024” manufactured by Ciba Japan Co., Ltd.

Examples of amine compounds include naphthylamine compounds such as phenyl-α-naphthylamine, phenyl-β-naphthylamine and androle-α-naphthylamine; p-isopropoxydiphenylamine, p- (p-toluenesulfonylamide) -diphenylamine, bis (phenyl Isopropylidene) -4,4′-diphenylamine, diphenylamine compounds such as N, N′-diphenylpropylenediamine; N, N′-diphenyl-p-phenylenediamine, N-isopropyl-N′-phenyl-p-phenylenediamine P-phenylenediamine compounds such as N, N′-bis (1-methylheptyl) -p-phenylenediamine and N, N′-bis (1-ethyl-3-methylpentyl) -p-phenylenediamine; 2,4-dihydroxybenzopheno Benzophenone compounds such as 2-hydroxy-4-methoxy-benzophenone and 2-hydroxy-4-n-octoxy-benzophenone; 2- (2′-hydroxy-5′-t-butylphenyl) benzotriazole, 2- ( Benzotriazole compounds such as 2′-hydroxy-5′-methylphenyl) benzotriazole; hindered amine compounds (HALS) such as bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate; , 3,4-Butanetetracarboxylic acid bis (2,2,6,6-tetramethyl-4-piperidyl) -bis (tridecyl) ester, 1,2,3,4-butanetetracarboxylic acid bis (N-methyl) Tetracarbos such as -2,2,6,6-tetramethyl-4-piperidyl) -bis (tridecyl) ester Bis (tetramethyl piperidyl) - bis (tri _{C 8-20} alkyl) _{esters], C 1-4} alkylene bis (tetraalkylammonium piperazinone) [1,1'-ethylenebis (3,3,3 ', 3 C _1-4 alkylenebis (tetramethylpiperazinone) such as ', 5,5,5', 5'-octamethylpiperazine-2,2'-dione)]; N, N'-diphenyl-1, 4-phenylenediamine, N-phenyl-N′-cyclohexyl-1,4-phenylenediamine and the like can be mentioned.

  Examples of phosphorus compounds include triphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, tris (nonylphenyl) phosphite; tri-2,4-dimethylphenylphosphine, tri-2,4,6-trimethylphenyl. Examples include phosphine compounds such as phosphine, tri-o-tolylphosphine, tri-m-tolylphosphine, tri-p-tolylphosphine, tri-o-anisylphosphine, and tri-p-anisylphosphine.

Examples of sulfur compounds include di-lauryl-3,3′-thiodipropionic acid ester (DLTDP), di-stearyl-3,3′-thiodipropionic acid ester (DSTDP), and di-myristyl-3,3 ′. - such thiodi _{C 2-4} carboxylic acid di _{C 10-20} alkyl esters such as thiodipropionate (DMTDP) and the like. In addition, a sulfur type compound can be obtained as a product name "Irganox PS802FD", the Sumitomo Chemical Co., Ltd. product, the brand name "Sumilyzer TPS" etc. by Ciba Japan Co., Ltd., for example.

Low molecular weight antioxidants, t- butyl branched C _3-8 alkyl phenyl group which may be substituted with groups such as groups, which may be substituted by branched C _3-8 alkyl group such as t-butyl group There are cases in which one or two functional groups such as a hydroxyphenyl group, an aminophenyl group which may have a substituent on the nitrogen atom of the amino group, or a piperidyl group which may be substituted with a methyl group are contained in one molecule. Many.

  Low molecular weight antioxidants include hindered phenol compounds [n-octadecyl-3- (4′-hydroxy-3 ′, 5′-di-t-butylphenol) propionate, etc.], phosphorus compounds (triphenyl phosphite, Diphenyl isodecyl phosphite, phenyl diisodecyl phosphite, etc.) are often used.

  The molecular weight of the low molecular weight antioxidant may be about 100 to 700 (usually 100 or more and less than 600), preferably 100 to 500 (for example, 120 to 450), more preferably about 150 to 400, as a rough guide. Good. Depending on the type of low molecular weight antioxidant, the molecular weight of the low molecular weight antioxidant (eg, low molecular weight sulfur antioxidant) may overlap the molecular weight of the high molecular weight antioxidant, but as described above, In many cases, one or two groups are contained in one molecule.

  The ratio (weight ratio) between the high molecular weight antioxidant and the low molecular weight antioxidant can be selected from the range of the former / the latter = about 40/60 to 100/0 (for example, 70/30 to 100/0). 50/50 to 99/1, preferably 60/40 to 98/2, and more preferably about 70/30 to 97/3.

  The content of the low molecular weight antioxidant may be about 500 to 5,000 ppm, preferably 700 to 4,500 ppm, and more preferably about 800 to 4,000 ppm in terms of weight with respect to the polyethylene resin.

  Further, the total content of the high molecular weight antioxidant and the low molecular weight antioxidant is 5,000 to 10,000 ppm, preferably 5,300 to 9,500 ppm, more preferably, in terms of weight relative to the polyethylene resin. It may be about 5,500 to 9,000 ppm.

  When a plurality of antioxidants are used, (i) the high molecular weight antioxidant is a phenolic compound (such as a hindered phenolic compound), an amine compound (such as a hindered amine compound), a phosphorus compound, and a sulfur compound. A combination of at least two selected from compounds, (ii) a high molecular weight antioxidant selected from a phenolic compound (such as a hindered phenolic compound), an amine compound (such as a hindered amine compound), and a phosphorus compound A combination in which the low molecular weight antioxidant is at least one selected from a phenolic compound and a sulfur compound, and (iii) the high molecular weight antioxidant is at least a phenolic compound (hindered phenolic). Compounds) and amine compounds (hindered amine compounds) The combination is such), (iv) high molecular weight antioxidant is at least phenolic compounds (such as hindered phenol compounds), such as a combination low molecular weight antioxidant is a sulfur-based compounds are preferable.

  When the antioxidant contains a high molecular weight phenol compound (high molecular weight phenol compound) and a high molecular weight phosphorus compound (high molecular weight phosphorus compound), the high molecular weight phenol compound and the high molecular weight phosphorus compound The ratio (weight ratio) can be selected from the range of the former / the latter = 20/80 to 95/5, for example, 30/70 to 90/10, preferably 40/60 to 85/15, and more preferably 50/50. About 80/20 may be sufficient.

  When the antioxidant contains a high molecular weight phenol compound and a high molecular weight amine compound (high molecular weight amine compound), the ratio (weight ratio) between the high molecular weight phenol compound and the high molecular weight amine compound is the former. The latter can be selected from the range of 10/90 to 95/5, for example, 20/80 to 90/10, preferably 30/70 to 85/15, more preferably about 40/60 to 80/20. Also good.

  When the antioxidant contains a high molecular weight phenol compound and a low molecular weight sulfur compound (low molecular weight sulfur compound), the ratio (weight ratio) of the high molecular weight phenol compound to the low molecular weight sulfur compound is the former. The latter can be selected from the range of 5/95 to 95/5, for example, 10/90 to 90/10, preferably 20/80 to 80/20, more preferably about 30/70 to 70/30. Also good.

  Antioxidants are usually used in combination with at least a high molecular weight phenolic compound and a high molecular weight phosphorus compound, and a high molecular weight phenolic compound, a high molecular weight phosphorus compound, a high molecular weight amine compound, and a low molecular weight compound are often used. You may use in combination with at least 1 type selected from the sulfur type compound. In particular, it is preferable to use a combination of a high molecular weight phenol compound (for example, a high molecular weight hindered phenol compound), a high molecular weight phosphorus compound, and a low molecular weight sulfur system. When a high molecular weight phenol compound and / or a low molecular weight sulfur compound and a high molecular weight phosphorus compound are used in combination, a great synergistic effect is obtained as an antioxidant. Further, when a high molecular weight phenol compound (for example, a high molecular weight hindered phenol compound) and a high molecular weight amine compound (high molecular weight hindered amine compound) are used in combination, the antioxidant property may be improved. The ratio (weight ratio) between the total amount of the high molecular weight phenolic compound and the high molecular weight phosphorus compound and at least one selected from the low molecular weight sulfur compound and the high molecular weight amine compound is the former / the latter = 20/80 to 95. For example, it may be 30/70 to 90/10, preferably 40/60 to 85/15, and more preferably about 50/50 to 80/20.

  Combining a high molecular weight antioxidant and a low molecular weight antioxidant can prevent early deterioration due to local heating such as deterioration due to heat history during molding and fusion, and high oxidation resistance over a long period of time. An effect is acquired and the durability of a resin tank improves. Further, when an antioxidant is contained in a large amount as described above, an antioxidant effect can be obtained for a long period of time. If a large amount of antioxidant is contained (for example, if it exceeds 10,000 ppm in terms of weight with respect to polyethylene resin), the antioxidant aggregates inside the resin and the strength of the resin tank May decrease.

  For example, oxidation induction time (OIT) can be used as an index for quantitatively evaluating the effect of the antioxidant. The oxidation induction time is measured according to the thermal stability test method of JIS K6774. The oxidation induction time is a time measured by holding a test piece containing an antioxidant in an oxygen atmosphere at a specific test temperature and suppressing the oxidation of the test piece by the antioxidant. The oxidation induction time of the resin tank may be about 30 to 250 minutes, preferably 40 to 250 minutes, more preferably about 50 to 250 minutes under the conditions of a temperature of 210 ° C. and an oxygen atmosphere. In order to ensure long-term durability (for example, durability of 10 years or more), it is preferable that the oxidation induction time is long. However, if it is too long, the antioxidant will aggregate and segregate inside the resin. The strength of is reduced.

  The average thickness of the resin layer can be selected according to the capacity of the resin tank, and may be, for example, about 1 to 15 mm, preferably 2 to 10 mm, more preferably about 3 to 8 mm (particularly 4 to 7 mm). .

[Foamed layer]
The resin tank of the present invention does not necessarily include a foam layer, but may have a multilayer laminated structure including the resin layer and a foam layer formed on the outer surface of the resin layer. With such a multilayer laminated structure, the heat insulation of the resin tank can be improved. The foam layer may be formed on a part of the outer surface of the resin layer, or may be formed on the entire outer surface. The foamed layer may or may not have the rib.

  Although the component which comprises a foamed layer is not restrict | limited in particular, Usually, it is comprised with the component (at least polyethylene-type resin and high molecular weight antioxidant) similar to the said resin layer.

  The resin layer and / or the foam layer may be composed of a recycled product of the resin tank (particularly, resin layer), and in particular, the foam layer is composed of a recycled product of the resin tank (particularly, resin layer). There are many cases. Examples of the recycled resin tank include waste materials (burrs and the like) generated during processing of the resin tank.

  The resin layer and / or foam layer (especially foam layer) is 50% by weight or less (about 0 to 45% by weight) of the recycled product of the resin tank with respect to the resin layer and / or foam layer (particularly foam layer). ), Preferably 0.01 to 40% by weight, more preferably 0.1 to 30% by weight, and usually 0.01 to 50% by weight.

  Thus, even if the resin tank is a recycled product of the resin tank (for example, burrs), the characteristics of the resin tank can be maintained.

  The foamed layer has a closed cell ratio of 50% or more (for example, 55 to 100%), preferably 60% or more (for example, 65 to 95%), more preferably 70% or more (for example, about 75 to 90%). It may be.

  The expansion ratio of the foam layer can be selected from about 2 to 100 times, for example, 2 to 90 times (for example, 2.5 to 80 times), preferably 3 to 70 times, more preferably 4 to 65 times).

  The foam layer may have an average thickness of 1 to 30 cm, preferably 2 to 25 cm, and more preferably about 3 to 20 cm. The ratio (B / A) of the average thickness (B) of the foam layer to the average thickness (A) of the resin layer is 0.2 / 1 to 10/1, preferably 0.3 / 1 to 9/1. More preferably, it may be about 0.5 / 1 to 8/1.

  The resin layer and / or the foamed layer may contain an additive as necessary. Examples of the additives include fillers, stabilizers (heat stabilizers, weathering stabilizers, etc.), foaming aids, flame retardants, colorants (dyes, pigments, etc.), dispersants, mold release agents, lubricants, A plasticizer, an anti-shrink agent, an antistatic agent, an antibacterial agent, an antiseptic agent, an antifungal agent and the like may be contained. These additives may be used alone or in combination of two or more.

  The ratio (weight ratio) of the additive is 0.01 to 30 parts by weight, preferably 0.05 to 20 parts by weight, and more preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the polyethylene resin. It may be about a part.

  FIG. 1 is a schematic view of an example of the resin tank of the present invention. The resin tank 1 is formed of a resin layer having a hollow rectangular parallelepiped shape, and a convex portion (a bulging portion) 2 extending in the height direction along one side surface of the tank is formed on an upper portion thereof. Yes. That is, the resin tank 1 has a shape in which a heat source device or the like can be disposed in the concave portion or the space portion formed by the convex portion 2. An insertion pipe 3 that extends in the lateral direction of the resin tank 1 and allows hot water to flow into (or flow out) into the resin tank 1 is provided at the lower portion of the resin tank 1 and the upper portion of the convex portion 2. The insertion tube 3 has a plurality of outflow holes for introducing the hot water flowing in from the end thereof into the resin tank 1. In addition, at the upper end portion of the convex portion 2, a take-out port 4 for taking out unnecessary objects in the resin tank 1 (for example, resin debris generated during cutting or cutting of the resin tank) and the take-out port 4 A lid (cap) 5 is provided for closing the cover. In addition, the resin tank 1 is provided with a plurality of ribs 6 along the outer periphery at intervals in the height direction from the middle part to the lower part.

  FIG. 2 is a cross-sectional view showing an example of a resin tank provided with the foam layer 7. The resin tank of this example includes the resin tank 1 and a foam layer 7 that covers the entire surface of the resin tank 1 with a predetermined thickness according to the shape of the resin tank 1.

  The shape of the resin tank is not particularly limited, and may be a hollow cylindrical shape, a hollow elliptical shape, a polygonal cross section [a cross-sectional quadrangular prism shape (a cross-sectional cube shape, a cross-sectional cuboid shape, etc.)], or the like. The resin tank may have a recess, a step, or the like for disposing a heat source device or the like.

  The horizontal inner diameter of the resin tank may be, for example, about 10 to 60 cm, preferably about 13 to 50 cm, and more preferably about 15 to 40 cm. The longitudinal inner diameter of the resin tank may be, for example, about 30 to 100 cm, preferably about 35 to 90 cm, and more preferably about 40 to 80 cm. The inner diameter of the resin tank in the height direction may be, for example, about 50 to 300 cm, preferably about 70 to 250 cm, and more preferably about 100 to 200 cm. The capacity of the resin tank is 50L or more (for example, about 55 to 400L), preferably 60 to 350L, more preferably 70 to 250L (particularly 100 to 200L), and usually about 50 to 300L. Even if the resin tank of the present invention has such a large capacity (large size), it is excellent in durability and can be manufactured with high moldability.

  In the resin tank, the resin layer may or may not have ribs. If the resin layer has ribs, the rigidity and strength of the resin tank can be improved. Further, when the resin tank has a multilayer laminated structure, the resin layer and / or the foamed layer may have ribs, and usually at least the resin layer has ribs in many cases.

  The ribs may be formed in any of the resin tanks, and are usually formed on the side portions (side surfaces) of the resin layer and / or the foamed layer (particularly the resin layer) in many cases. The shape of the rib may be convex or concave. The cross-sectional shape of the rib may be a cross-sectional circle shape, a cross-sectional elliptical shape, a cross-sectional triangle shape, a cross-sectional U-shape, a cross-sectional trapezoidal shape, or the like.

  The ribs can be formed not only in the circumferential direction of the resin tank but also in the height direction, the lateral direction, and the oblique direction, and may be in a lattice shape. In addition, the number of ribs, the width, and the like are not particularly limited, and can be appropriately selected depending on the application.

[Production method of resin tank]
The said resin tank can be manufactured through the process of blow-molding the resin composition comprised by the polyethylene-type resin and antioxidant.

  Blow molding (or blow molding) usually involves melting a resin composition, extruding a cylindrical melt (parison) from an extruder die, sandwiching it with a mold, closing one of the melts, and compressing from the other. Blow air and solidify by cooling. Since the resin composition is composed of a specific polyethylene-based resin and a high molecular weight antioxidant, the melt draw-down property is low, and a resin tank can be easily manufactured by blow molding. Also, a melt comprising a cylindrical resin layer in which the resin composition is melted and a foam layer formed on the outer periphery of the resin layer and in which a foam composition composed of the resin and a foaming agent is melted. A resin tank having a multilayer laminated structure can be manufactured by blow molding (multilayer parison).

  Examples of the foaming agent in the foam layer include conventional foaming agents such as inert or incombustible gases (nitrogen, carbon dioxide, chlorofluorocarbons, alternative chlorofluorocarbons, etc.), water, organic physical foaming agents [for example, aliphatic hydrocarbons ( Propane, n-butane, isobutane, pentane (such as n-pentane, isopentane), hexane (such as n-hexane), aromatic hydrocarbon (such as toluene), halogenated hydrocarbon (such as trifluorochloromethane), Ethers (such as dimethyl ether), ketones (such as acetone)], degradable foaming agents [inorganic carbonates such as sodium bicarbonate and ammonium carbonate or salts thereof; organic acids such as citric acid or salts thereof (such as sodium citrate) ) Etc.]; 2,2'-azobisisobutyronitrile, azo compounds such as azodicarbonamide (ADCA); dinitrosope Such data tetramine (DPT) nitroso compounds such as and the like. These foaming agents may be used alone or in combination of two or more. The decomposition temperature of the foaming agent may be 180 ° C. or higher (for example, about 200 to 300 ° C.).

  The ratio of the foaming agent may be 0.1 to 50 parts by weight, preferably 0.5 to 40 parts by weight, and more preferably about 1 to 30 parts by weight with respect to 100 parts by weight of the polyethylene resin.

  The foaming agent may be preliminarily contained in the resin composition, or may be added or pressed into the resin composition in the process of blow molding. In addition, you may add the above-mentioned additive etc. to a resin composition and / or a foaming composition in the suitable stage of blow molding as needed.

  Blow molding may be performed using a conventional blow molding machine (for example, an extrusion blow molding machine, an injection blow molding machine, a stretch blow molding machine, a multilayer blow molding machine, etc.).

  The molding temperature may be, for example, about 120 to 300 ° C, preferably about 140 to 280 ° C, and more preferably about 150 to 260 ° C.

  Since the resin tank of the present invention has high durability even when storing hot water as well as cold water, a hot water supply system having a temperature difference between cold water and hot water [a single hot water supply system, a household cogeneration system (gas engine) Gas hot water / heating system with power generation function, hot water / heating system such as gas hot water / heating system with power generation function equipped with fuel cells (solid polymer fuel cell, solid oxide fuel cell, etc.), bath cooking system, water heater (Electric water heaters such as natural refrigerant heat pump type electric water heaters).

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples.

  The polyethylene resins and antioxidants used in the examples and comparative examples are shown below.

[Polyethylene resin]
(First polyethylene resin)
Polyethylene resin A: manufactured by Nippon Polyethylene Co., Ltd., 70 parts by weight of the first polyethylene resin (HB217RW, number average molecular weight 26,800, weight average molecular weight 511,000, molecular weight distribution 19.1), Nippon Polyethylene Co., Ltd. ) Made, second polyethylene resin (HJ221, number average molecular weight 45,000, weight average molecular weight 310,500, molecular weight distribution 6.9) blend with 30 parts by weight, number average molecular weight 35,300, weight average molecular weight 588,000, molecular weight distribution 16.6
Polyethylene resin B: manufactured by Prime Polymer Co., Ltd., Hizex 8800BS, number average molecular weight 21,300, weight average molecular weight 783,000, molecular weight distribution 36.8
Polyethylene resin C: manufactured by Nippon Polyethylene Co., Ltd., HB216R, solar water tank resin, contains antioxidants in the proportions shown in Table 1, number average molecular weight 28,000, weight average molecular weight 550,000, molecular weight distribution 19.6
(Second polyethylene resin)
Polyethylene resin D: manufactured by Prime Polymer Co., Ltd., SP4030, rotational molding resin, containing an antioxidant at the ratio shown in Table 1, number average molecular weight 8,500, weight average molecular weight 70,000, molecular weight distribution 8.2
Polyethylene resin E: manufactured by Mitsui Chemicals, Inc., NZ4004M, gas pipe resin, containing antioxidants in the proportions shown in Table 1, number average molecular weight 17,000, weight average molecular weight 150,000, molecular weight distribution 8.8
[Antioxidant]
(High molecular weight antioxidant)
High molecular weight antioxidant a (phenolic compound): pentaerythrityltetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, manufactured by Ciba Japan, Irganox 1010, molecular weight 1177. 7
Polymer antioxidant b (phenolic compound): 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, Ciba Japan ), Irganoz 1330, molecular weight 775.2
Polymer antioxidant c (phosphorus compound): Tris (2,4-di-t-butylphenyl) phosphite, Ciba Japan Co., Ltd., Irgafos 168, molecular weight 646.9
Polymeric antioxidant d (amine compound): poly [[6-[(1,1,3,3-tetramethylbutyl) amino] -1,3,5-triazine-2,4-diyl] [( 2,2,6,6-tetramethyl-4-piperidinyl) imino]], manufactured by Ciba Japan Co., Ltd., Chimassorb 944LD, molecular weight 2500 or more (low molecular weight antioxidant)
Low molecular weight antioxidant e (phenolic compound): dibutylhydroxytoluene (BHT), manufactured by Sumitomo Chemical Co., Ltd., BHT, molecular weight 220.4
Low molecular weight antioxidant f (phenolic compound): octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propinate, manufactured by Ciba Japan, Irganox 1076, molecular weight 530.9
Low molecular weight antioxidant g (sulfur compound): di-stearyl-3,3′-thiodipropionic acid ester, manufactured by Sumitomo Chemical Co., Ltd., Sumilizer TPS, molecular weight 683.

Example 1
5 parts by weight of an antioxidant masterbatch was mixed with 100 parts by weight of the polyethylene resin A to finally obtain a resin composition containing an antioxidant at a ratio shown in Table 1. This resin composition was blow-molded using a large blow molding machine (DA-G, manufactured by Plako Co., Ltd., extrusion nozzle diameter 120 mm, accumulator capacity 40 L), and a resin tank (inner diameter of about 150 cm in height direction) The inner diameter in the vertical direction was about 43 cm × the inner diameter in the horizontal direction was about 19 cm, and the capacity was about 100 L).

(Example 2)
10 parts by weight of an antioxidant masterbatch was mixed with 100 parts by weight of polyethylene resin B to finally obtain a resin composition containing an antioxidant at a ratio shown in Table 1. This resin composition was blow molded in the same manner as in Example 1 to form a resin tank (height inner diameter of about 150 cm × vertical inner diameter of about 43 cm × lateral inner diameter of about 19 cm, capacity of about 100 L).

(Comparative Example 1)
Polyethylene resin C was blow molded in the same manner as in Example 1 to obtain a resin tank (height inner diameter of about 150 cm × vertical inner diameter of about 43 cm × lateral inner diameter of about 19 cm, capacity of about 100 L).

(Comparative Example 2)
Polyethylene resin D was blow molded in the same manner as in Example 1 to obtain a resin tank (height inner diameter of about 150 cm × vertical inner diameter of about 43 cm × lateral inner diameter of about 19 cm, capacity of about 100 L).

(Comparative Example 3)
Polyethylene resin E was blow-molded in the same manner as in Example 1 to obtain a resin tank (height inner diameter of about 150 cm × vertical inner diameter of about 43 cm × lateral inner diameter of about 19 cm, capacity of about 100 L).

  The characteristics of the resin tank were measured by the following method.

(density)
In accordance with JIS K7112, a polyethylene resin pellet was melted by a hot compression molding machine at a temperature of 160 ° C., and then cooled at a rate of 25 ° C./min to form a sheet having a thickness of 2 mm. This sheet was conditioned in a room at a temperature of 23 ° C. for 48 hours and then placed in a density gradient tube to measure the density of the polyethylene resin.

(Melt flow rate (MFR))
Based on JIS K7210, the melt flow rate of the polyethylene resin was measured under the conditions of a temperature of 190 ° C. and a load of 212 N (21.6 kgf).

(All-around notch tensile creep strength)
In accordance with JIS K6774, a test piece having a length of 6 mm, a width of 6 mm, and a length of 70 mm was cut out from a 6 mm-thick polyethylene resin press sheet, and a 1.0 mm depth was formed in the center using a notching jig. I put a notch around. A temperature of 90 ° C. and a nominal stress of 4.0 MPa were applied, and the time until fracture was measured.

(Oxidation induction time (OIT))
A 5 mg sample of a resin tank is placed in a differential scanning calorimeter (DSC) (DSC50, manufactured by Shimadzu Corporation). First, in a nitrogen atmosphere (flow rate 50 ml / min), the temperature rise rate is 100 ° C./min up to 210 ° C. The temperature was raised, and after reaching 210 ° C., it was kept for 5 minutes and switched to an oxygen atmosphere (flow rate 50 ml / min). After switching, the time until the start of oxidation exotherm was measured.

(Formability)
The resin tank was visually observed and the moldability was evaluated according to the following criteria.
◎… Thickness variation is small and surface condition is good ○… Thickness is slightly uneven and surface is slightly rough △… Thickness unevenness is considerable and melt fracture is generated on the surface The shape of the resin tank is maintained. X: The resin tank cannot be formed.

(durability)
Durability was evaluated according to the following criteria.
◎… All-around notch tensile creep strength is 1000 hours or more ○… All-around notch tensile creep strength is 250 hours or more and less than 1000 hours △… All-around notch type tensile creep strength is 100 hours or more and less than 250 hours ×… All-around notch Type tensile creep strength is less than 100 hours.

(Heat resistance against hot water)
The heat resistance against warm water was evaluated according to the following criteria.
◎… OIT is 100 minutes or more ○… OIT is 50 minutes or more and less than 100 minutes △… OIT is 10 minutes or more and less than 50 minutes ×… OIT is less than 10 minutes

  The results are shown in Table 1. In the table, in Comparative Example 3, the notch tensile creep rupture time of the entire circumference is 10000 hours or longer, but it is not broken even after 10000 hours or longer and the test is continuing.

  As is clear from Table 1, the resin tank of the present invention has at least a resin layer composed of a first polyethylene resin having a high molecular weight and a wide molecular weight and a large amount of high molecular weight antioxidant as compared with the comparative example. Therefore, even if hot water is stored for a long time and stress is applied, it has excellent durability and high moldability. In Comparative Example 1, blow molding is possible, but since the antioxidant content is small, the antioxidant effect cannot be obtained in the long term, and the heat resistance against warm water is not sufficient. Moreover, since the all-around notch type tensile creep rupture time is short, durability and rigidity are low. In Comparative Example 2, blow molding cannot be performed because the polyethylene resin has a low molecular weight and a high melt flow rate. Further, in Comparative Example 2, since the antioxidant is blended, heat resistance against warm water can be secured, but since the molecular weight is small, the all-around notch tensile creep rupture time is short, and durability and rigidity are low. . In Comparative Example 3, since the content of the antioxidant is small, the antioxidant effect cannot be obtained in the long term, and the heat resistance against warm water is insufficient. Furthermore, since the density of the polyethylene resin is small and the melt flow rate is large, blow molding is very difficult.

FIG. 1 is a schematic view of an example of the resin tank of the present invention. FIG. 2 is a cross-sectional view of an example of the resin tank of the present invention provided with a foam layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Resin tank 6 ... Rib 7 ... Foam layer

Claims (20)

A resin tank for storing hot water of a hot water supply system, comprising at least a resin layer composed of a polyethylene-based resin and an antioxidant;
The polyethylene resin is composed of a first polyethylene resin having a weight average molecular weight (Mw) of 300,000 to 1,000,000 and a molecular weight distribution of 10 to 50 and a high molecular weight and a wide molecular weight distribution,
The antioxidant comprises a high molecular weight antioxidant;
The molecular weight of the high molecular weight antioxidant is 600 to 10,000;
The high molecular weight antioxidant, the content of branched C _3-8 comprises a phenolic compound having an alkyl group and a phosphorus-based compound having a branched C _3-8 alkyl group, and the high molecular weight antioxidant, the polyethylene Resin tank that is 3,000 to 10,000 ppm in terms of weight with respect to the resin.   The resin tank according to claim 1, wherein the first polyethylene resin has a number average molecular weight (Mn) of 15,000 to 100,000.   The resin tank according to claim 1 or 2, wherein the intrinsic viscosity of the first polyethylene resin is 2.5 to 5 dl / g. The first polyethylene-based resin is (1) a density of 0.940 to 0.980 g / cm ³ , (2) a melt flow rate of 0.1 to 100 g / 10 min under the conditions of a temperature of 190 ° C. and a load of 212 N, ( 3) The resin tank according to any one of claims 1 to 3, which has an all-around notch tensile creep rupture time of 80 to 5000 hours under conditions of a temperature of 90 ° C and a nominal stress of 4.0 MPa.   The resin tank according to any one of claims 1 to 4, wherein the first polyethylene resin has a long-chain branched chain.   The resin tank according to any one of claims 1 to 5, wherein the polyethylene resin further comprises a second polyethylene resin having a high molecular weight and a narrow molecular weight distribution.   The resin tank according to claim 6, wherein a ratio of the second polyethylene resin is 0.1 to 60% by weight with respect to the whole polyethylene resin. The high molecular weight polyethylene resin content of the antioxidant, the resin tank according to claim 1 which is 3,200~9,000ppm in terms of weight.   The high molecular weight antioxidant is composed of a phenolic compound, a phosphorus compound, and at least one selected from a sulfur compound and an amine compound, a total amount of the phenolic compound and the phosphorus compound, a sulfur compound, and 9. The resin tank according to claim 1, wherein a ratio (weight ratio) with at least one selected from amine compounds is the former / the latter = 30/70 to 90/10.   The resin tank according to claim 1, wherein the resin layer further contains a low molecular weight antioxidant.   The resin tank according to any one of claims 1 to 10, wherein the temperature is 210 ° C and the oxidation induction time in an oxygen atmosphere is 30 to 250 minutes.   The resin tank according to claim 10 or 11, wherein the total content of the high molecular weight antioxidant and the low molecular weight antioxidant is 5,000 to 10,000 ppm in terms of weight with respect to the polyethylene resin.   The resin tank according to any one of claims 10 to 12, wherein a ratio (weight ratio) between the high molecular weight antioxidant and the low molecular weight antioxidant is the former / the latter = 50/50 to 99/1.   The resin tank according to claim 1, wherein the capacity is 50 to 300 L, and the resin layer has ribs.   The resin tank according to any one of claims 1 to 14, wherein the hot water supply system is at least one selected from a hot water supply single-function system, a hot water supply / heating system, and a bath cooking system.   The resin tank according to any one of claims 1 to 15, which has a multilayer laminated structure including a resin layer and a foam layer formed on an outer surface of the resin layer.   The resin tank according to claim 16, wherein the foamed layer is constituted by a recycled product of the resin tank according to claim 1.   The resin tank according to claim 17, wherein the foam layer contains a recycled product of the resin tank in a proportion of 0.01 to 50% by weight with respect to the foam layer. A method for producing a resin tank according to any one of claims 1 to 15, comprising a step of blow-molding a resin composition comprising a polyethylene-based resin and an antioxidant.
The polyethylene resin is composed of a first polyethylene resin having a weight average molecular weight (Mw) of 300,000 to 1,000,000 and a molecular weight distribution of 10 to 50 and a high molecular weight and a wide molecular weight distribution,
The antioxidant comprises a high molecular weight antioxidant;
The molecular weight of the high molecular weight antioxidant is 600 to 10,000;
The high molecular weight antioxidant, the content of branched C _3-8 comprises a phenolic compound having an alkyl group and a phosphorus-based compound having a branched C _3-8 alkyl group, and the high molecular weight antioxidant, the polyethylene The manufacturing method which is 3,000-10,000 ppm by weight conversion with respect to a resin. A cylindrical resin layer obtained by melting a resin composition composed of a polyethylene resin and an antioxidant, and a foam composition formed on the outer periphery of the resin layer and composed of the resin composition and a foaming agent are melted. A method for producing a resin tank according to any one of claims 16 to 18, comprising a step of blow-molding a melt composed of the foamed layer.
The polyethylene resin is composed of a first polyethylene resin having a weight average molecular weight (Mw) of 300,000 to 1,000,000 and a molecular weight distribution of 10 to 50 and a high molecular weight and a wide molecular weight distribution,
The antioxidant comprises a high molecular weight antioxidant;
The molecular weight of the high molecular weight antioxidant is 600 to 10,000;
The high molecular weight antioxidant, the content of branched C _3-8 comprises a phenolic compound having an alkyl group and a phosphorus-based compound having a branched C _3-8 alkyl group, and the high molecular weight antioxidant, the polyethylene The manufacturing method which is 3,000-10,000 ppm by weight conversion with respect to a resin.