JP5175540B2 - Polyethylene resin, hollow molded article using the same, and use thereof - Google Patents

Description

  The present invention relates to a polyethylene-based resin, a hollow molded article using the same, and uses thereof. More specifically, the present invention is obtained using a specific polymerization catalyst, has predetermined characteristics, excellent moldability, durability, and resistance. Excellent balance between impact and rigidity, especially high-rigidity polyethylene-based resin, and hollow molded products using the above-mentioned resin, fuel tanks, cans, containers, bottles, especially automobile fuel tanks, etc. As its use.

  Hollow molded articles used for storage or transportation of liquid substances are widely used in daily life and industrial fields. Particularly in automobile parts, hollow molded articles used as fuel tanks are replacing conventional fuel tanks made of metal materials. Molded products such as plastic containers and tanks have a lower mass / volume ratio than those made of metal materials, so they can be reduced in weight, are less susceptible to corrosion such as rust, and have good impact resistance. It has characteristics and is gaining wider use.

  Hollow molded articles are often obtained by blow molding mainly from high density polyethylene (HDPE). Plastic fuel tanks obtained from polyethylene are classified as important safety parts for ensuring the safety of automobiles, and require particularly high levels of mechanical strength, durability, and impact resistance. Satisfactory materials are desired.

As for polyethylene resins for blow molded products, those having excellent creep resistance and ESCR, a melt flow rate of 1 to 100 g / 10 min, and a density of 0.935 to 0.955 g / cm ³ have been proposed. A solid chromium catalyst component in which a chromium compound in which at least some of the chromium atoms become hexavalent is supported on an inorganic oxide support by calcination activation in a neutral atmosphere, an alkoxide containing a dialkylaluminum functional group, and ethylene comprising a trialkylaluminum A catalyst for system polymerization is also disclosed (see Patent Document 1).
However, the document 1 does not disclose any hollow molded article, particularly polyethylene suitable for an automobile fuel tank excellent in impact resistance.

In addition, a method for producing polyethylene suitable for blow molded products, particularly large blow products, has been proposed by conducting polymerization in the presence of hydrogen using a trialkylaluminum compound-supported chromium catalyst (Patent Literature). 2).
However, the document 2 does not disclose a hollow molded article, particularly polyethylene suitable for an automobile fuel tank, and it is difficult to say that an automobile fuel tank having a sufficient level of durability can be manufactured.

  As for the hollow molded article, for example, a hollow molded article having one or more layers made of polyethylene obtained using a fluorine-modified chromium catalyst has been proposed and used for a plastic fuel tank of an automobile with improved strength. A method is also disclosed (see Patent Document 3). However, when a fluorine-modified chromium catalyst is used, the molecular weight distribution of the resulting polyethylene is narrower than when not fluorine-modified, and therefore, it does not satisfy a sufficient level of durability for hollow molded products, particularly for automobile fuel tanks. Result.

In addition, a chromium catalyst in which at least some of the chromium atoms are hexavalent is supported by supporting the chromium compound on an inorganic oxide support and activated by calcination in a non-reducing atmosphere, and continuously by a plurality of polymerization reactors connected in series. In particular, when carrying out copolymerization of ethylene alone or ethylene and α-olefin having 3 to 8 carbon atoms in multiple stages, a specific organoaluminum compound (alkoxide, siloxide, etc.) is introduced into any one or all of the polymerization reactors. A polyethylene resin production method characterized by this is proposed (see Patent Document 4), and a polyethylene resin excellent in environmental stress crack resistance (ESCR) and creep resistance is disclosed. However, although the above publication discloses a polyethylene resin having a molecular weight distribution (Mw / Mn) of 20.9 (Example), it has excellent impact resistance suitable for a hollow molded product, particularly an automobile fuel tank. Polyethylene is not disclosed.
In addition to the above, for example, HB111R made by Nippon Polyethylene, 4261AG made by Basell, etc. are known as commercially available polyethylene used for fuel tanks for automobiles. These are materials that have been evaluated in the market in response to the strict demands of automobile manufacturers, but the balance of durability and rigidity, impact resistance, and formability are not necessarily high enough.

  Under such circumstances, polyethylene and hollow molded products that solve the problems of conventional polyethylene, have excellent moldability and durability, and have a good balance of impact resistance and rigidity, and can achieve particularly high rigidity, In particular, a polyethylene suitable for a high-performance fuel tank is desired.

JP 2002-020212 A JP 2002-080521 A JP-T-2004-504416 JP 2003-313225 A

  In view of the above-mentioned problems of the prior art, an object of the present invention is a polyethylene resin and a fuel tank such as a fuel tank that are excellent in moldability, durability, and in balance between impact resistance and rigidity, particularly high rigidity. The object of the present invention is to provide a hollow molded article using the above-mentioned resin suitable for use as a can, container, bottle, etc., particularly as a fuel tank of an automobile.

  As a result of intensive studies to solve the above problems, the present inventors have obtained a polyethylene-based resin having specific physical properties obtained by using a chromium-containing catalyst, and has excellent moldability and durability, and has an impact resistance. Excellent balance of property and rigidity, especially improved durability, high rigidity without lowering impact resistance, and such good characteristics are exhibited in hollow molded products using this polyethylene resin And the present invention has been made based on these findings.

That is, according to 1st invention of this invention, it is the polyethylene-type resin manufactured by polymerizing using a chromium containing catalyst, Comprising: It has the following (1)-(5) characteristics , and is bending A polyethylene resin having an elastic modulus of 1000 MPa or more is provided.
(1) Density: 0.945 to 0.950 g / cm ³
(2) Melt flow rate (temperature 190 ° C., load 21.6 kg): 3.5 to 5.0 g / 10 minutes (3) Molecular weight distribution measured by GPC (Mw / Mn): 25 or more (4) Whole circumference Break time (T) of notch type tensile creep test: 30 hours or more (5) Charpy impact strength: 9 KJ / m ² or more

  According to a second invention of the present invention, in the first invention, the polyethylene exhibits a strain hardening behavior in the measurement of elongational viscosity and has an elongational viscosity ratio (λmax) of 1.05-1.50. A system resin is provided.

  According to the third invention of the present invention, in the first or second invention, the polyethylene resin is a homopolymer of ethylene, a copolymer of ethylene and an α-olefin or diene compound having 3 to 12 carbon atoms. Alternatively, there is provided a polyethylene resin, which is a copolymer of ethylene, an α-olefin having 3 to 12 carbon atoms, and a diene compound.

  According to a fourth aspect of the present invention, there is provided a hollow molded article having one or more layers made of the polyethylene resin according to any one of the first to third aspects.

  According to the fifth invention of the present invention, in the fourth invention, when the layer structure of the hollow molded article is two or more, the innermost layer and the outermost layer are the polyethylene of any one of the first to third inventions. There is provided a hollow molded article comprising a resin.

  According to a sixth invention of the present invention, in the fifth invention, the layer structure of two or more layers has the polyethylene resin, adhesive layer, barrier of any one of the first to third inventions from the inside to the outside. A hollow molded article comprising: a layer, an adhesive layer, a recycled material layer, and the polyethylene resin of any one of the first to third inventions in this order is provided.

  According to the seventh invention of the present invention, in any one of the fourth to sixth inventions, the hollow molded article is a fuel tank, kerosene can, drum can, chemical container, agricultural chemical container, solvent container, or A hollow molded article characterized by being a plastic bottle is provided.

  According to an eighth aspect of the present invention, there is provided a hollow molded product according to the seventh aspect, wherein the fuel tank is an automobile fuel tank.

The polyethylene-based resin of the present invention is excellent in moldability and durability, and has an excellent balance between impact resistance and rigidity, particularly, the rigidity is remarkably improved, and the durability is remarkably good.
In addition, the hollow molded article of the present invention is excellent in moldability and durability, excellent in impact resistance and rigidity balance, particularly remarkably improved in rigidity, and remarkably good in durability, etc. Even as a multilayer structure using a barrier layer, it does not have adverse effects such as strength deterioration due to the barrier layer and molding defects, and has excellent barrier properties. Therefore, tanks such as fuel tanks, cans, containers, bottles, etc., especially automobiles It is suitable for use in a fuel tank or the like.

  The present invention is obtained by polymerization using a specific polyethylene-based resin, that is, a chromium-containing catalyst, and has a specific density, melt flow rate, molecular weight distribution (Mw / Mn), all-around notch tensile creep test. A polyethylene resin characterized by having a fracture time (T) and a Charpy impact strength (hereinafter sometimes referred to as the present polyethylene resin), and further, a hollow molded article obtained by using the resin, particularly a fuel tank, In particular, it relates to an automobile fuel tank. Hereinafter, the present invention will be described in detail for each item.

[1] Polyethylene resin Characteristics The polyethylene-based resin of the present invention needs to have the following characteristics (1) to (5) and have a flexural modulus of 1000 MPa or more .
(1) Density: 0.945 to 0.950 g / cm ³
(2) Melt flow rate (temperature 190 ° C., load 21.6 kg): 3.5 to 5.0 g / 10 minutes (3) Molecular weight distribution measured by GPC (Mw / Mn): 25 or more (4) Whole circumference Break time (T) of notch type tensile creep test: 30 hours or more (5) Charpy impact strength: 9 KJ / m ² or more

(I) Density The polyethylene resin of the present invention has a density in the range of 0.945 to 0.950 g / cm ³ , preferably 0.946 to 0.948 g / cm ³ . When the density is less than 0.945 g / cm ³ , the rigidity of the hollow molded product is insufficient and the mechanical strength may be lowered. When the density exceeds 0.950 g / cm ³ , the durability of the hollow molded product is insufficient.
The density is measured according to JIS K6922-1 (1997). The desired density can be obtained by changing the density of the polyethylene resin of the present invention depending on the type and amount of the comonomer copolymerized with ethylene.

(II) Melt Flow Rate The polyethylene resin of the present invention has a melt flow rate in the range of 3.0 to 7.0 g / 10 minutes, preferably 3.5 to 5.0 g / 10 minutes. When the melt flow rate is less than 3.0 g / 10 min, the amount of extrusion is insufficient when extruding the molten resin during molding, and the molding becomes unstable and impractical, exceeding 7.0 g / 10 min. Further, since the melt viscosity and melt tension are insufficient, the molding becomes unstable and impractical, and the mechanical strength may be lowered.
The melt flow rate is measured in accordance with JIS K6922-2 (1997) under conditions of a temperature of 190 ° C. and a load of 21.6 kg.
The melt flow rate of the polyethylene resin of the present invention can be adjusted by the polymerization temperature, the use of a chain transfer agent, etc., and a desired product can be obtained. That is, by increasing the polymerization temperature of ethylene and α-olefin, the molecular weight can be decreased, and as a result, the melt flow rate can be increased. By decreasing the polymerization temperature, the molecular weight can be increased, and as a result, the melt flow rate can be decreased. can do. Also, by increasing the amount of chain transfer agent coexisting during polymerization (for example, the amount of hydrogen), the molecular weight can be lowered, resulting in an increase in the melt flow rate and a decrease in the amount of coexisting chain transfer agent (for example, the amount of hydrogen). By increasing the molecular weight, the melt flow rate can be decreased as a result.

(III) Molecular weight distribution measured by GPC (Mw / Mn)
The polyethylene resin of the present invention has a molecular weight distribution (Mw / Mn) measured by gel permeation chromatograph (GPC) of 25 or more, more preferably 27 or more.
The molecular weight distribution (Mw / Mn) is obtained by performing the following GPC measurement, obtaining the number average molecular weight (Mn) and the mass average molecular weight (Mw), and calculating the molecular weight distribution (Mw / Mn).
[Gel permeation chromatograph (GPC) measurement conditions]
Apparatus: Waters 150C model,
Column: Shodex-HT806M,
Solvent: 1,2,4-trichlorobenzene,
Temperature: 135 ° C
Universal rating using monodisperse polystyrene fraction.
Regarding the molecular weight distribution indicated by the ratio of Mw to Mn (Mw / Mn) (the larger the Mw / Mn, the wider the molecular weight distribution), “size exclusion chromatography (high-performance liquid chromatography of polymers)” (written by Sadao Mori, The molecular weight and detector sensitivity formula described in Kyoritsu Shuppan, page 96) is applied to the data of fractionated linear polyethylene resin with n-alkane and Mw / Mn ≦ 1.2, and the molecular weight M shown by the following formula: The actual sample values were corrected.
Sensitivity of molecular weight M = a + b / M
(A and b are constants, a = 1.32, b = 189.2)
The molecular weight distribution can be adjusted by a method such as control of the catalyst activation temperature and polymerization temperature, particularly control of the activation temperature. That is, if the activation temperature is raised, the molecular weight distribution becomes narrower. Conversely, if the activation temperature is lowered, the molecular weight distribution becomes wider. The effect is smaller than that at the activation temperature, but it can also be adjusted by controlling the polymerization temperature. That is, if the polymerization temperature is raised, the molecular weight distribution becomes slightly narrower. Conversely, if the polymerization temperature is lowered, the molecular weight distribution becomes somewhat wider.

(IV) Rupture time of all-around notch tensile creep test (T)
The polyethylene-based resin of the present invention has a rupture time (T) in the all-around notch tensile creep test of 30 hours or longer, preferably 50 hours or longer. If the breaking time (T) is less than this lower limit, the durability of the hollow molded article is insufficient. The upper limit value of the breaking time (T) is not necessarily limited, but those exceeding 300 hours are usually difficult to manufacture.
The rupture time (T) of the all-around notch tensile creep test is measured in accordance with JIS K-692-2 (2004), and after compression molding a 5.9 mm thick sheet, K-6774 (2004) Annex 5 (normative) A test piece having the shape and size of the section “nominal 50” shown in FIG. 1 was prepared, and an all-around notch tensile creep test in pure water at 80 ° C. ( FNCT). The tensile load is 88 N, 98 N, and 108 N, the number of test points is 2 for each load, and the rupture time (T) at a stress of 6 MPa is obtained from the rupture time and stress 6 point plots on a logarithmic scale by the least square method.
The rupture time (T) of the all-around notch tensile creep test of the polyethylene resin of the present invention can be controlled by the melt flow rate (molecular weight), molecular weight distribution, and density. That is, if the melt flow rate is lowered (the molecular weight is increased), the breaking time becomes longer. Moreover, if the molecular weight distribution is widened, the breaking time becomes longer. If the density is further reduced, the breaking time becomes longer.

(V) Charpy impact strength The polyethylene resin of the present invention has a Charpy impact strength of 9 KJ / m ² or more, preferably 10 KJ / m ² or more. When the Charpy impact strength is less than 9 KJ / m ² , the impact resistance of the hollow molded product is insufficient. The upper limit of the Charpy impact strength is not particularly limited, but is usually 30 KJ / m ² or less.
Charpy impact strength conforms to JIS K-7111 (2004), type 1 test piece is produced, edge direction is edgewise, notch type is type A (0.25mm), in dry ice / alcohol At -40 ° C.
The value of the Charpy impact strength of the polyethylene resin of the present invention can be controlled by density and molecular weight distribution. That is, if the density is increased, the Charpy impact strength is increased. Further, if the molecular weight distribution is narrowed, the Charpy impact strength is increased.

  The polyethylene resin of the present invention preferably further has the following properties (VI) to (VII).

(VI) Strain hardening behavior and elongational viscosity ratio (λmax) in elongational viscosity measurement
The polyethylene-based resin of the present invention preferably exhibits a strain hardening behavior in the measurement of elongational viscosity from the viewpoint of moldability. The elongational viscosity measurement is a method in which the elongational viscosity η (Pa · s) is measured with respect to the time t (s) at a temperature of 170 ° C. and a strain rate of 0.1 / s. A phenomenon in which the extensional viscosity rises on the long side.
The strain hardening behavior in the extensional viscosity measurement can be evaluated by the extensional viscosity ratio (λmax) obtained in the extensional viscosity measurement.
The elongational viscosity ratio (λmax) can be determined as follows. That is, a graph of logarithmic axes of time t (s) on the horizontal axis and elongational viscosity η (Pa · s) on the vertical axis is created, and the maximum elongational viscosity ηEmax of the nonlinear part of the viscosity increasing curve is obtained. Is extrapolated to obtain an extrapolated viscosity ηLmax at time t (s) at which ηEmax is given, and the ratio of ηEmax to ηLmax (ηEmax / ηLmax) is defined as the elongational viscosity ratio (λmax).
This elongational viscosity ratio (λmax) has a correlation with the number of long chain branches, and when the elongational viscosity ratio (λmax) is large, the number of long chain branches increases and the moldability is improved. Further, the elongational viscosity ratio (λmax) and the number of long chain branches have a correlation with the creep resistance, which is one index of durability, and the creep resistance tends to be inferior when the number of long chain branches increases.
The polyethylene resin of the present invention has an elongational viscosity ratio (λmax) of preferably 1.05 to 1.50, more preferably 1.10 to 1.40.
If the elongational viscosity ratio (λmax) is less than 1.05, the durability is improved, but the moldability is inferior and molding defects occur, making it difficult to mold a hollow molded product. Although the moldability of the hollow molded product is good, the durability is lowered.
The elongational viscosity ratio (λmax) can be adjusted by techniques such as the activation temperature of the chromium catalyst and the control of the hydrogen concentration during polymerization. That is, if the activation temperature is increased, λmax is increased, and if the hydrogen concentration during polymerization is increased, λmax is decreased.
Specifically, the elongational viscosity is measured by using a capillary rheometer manufactured by Intesco, using a capillary of 3 mmφ × 15 mmL at a temperature of 190 ° C., and preparing a test piece at a piston speed of 20 mm / min. Then, using a Merten rheometer manufactured by Toyo Seiki Seisakusho, the preheating time is 15 minutes, the elongation viscosity is measured at a temperature of 170 ° C. and a strain rate of 0.1 / s. FIG. 1 schematically shows a viscosity increase curve of a logarithmic axis graph of time t (s) on the horizontal axis and elongational viscosity η (Pa · s) on the vertical axis.

(VII) Flexural rigidity The polyethylene resin of the present invention has a flexural modulus (flexural rigidity) of 1000 MPa or more. If the flexural modulus is less than 1000 MPa, the rigidity of the hollow molded product is insufficient. The upper limit value of the flexural modulus is not particularly limited, but usually it is difficult to produce those exceeding 1500 MPa.
The flexural modulus is measured according to JIS K-7106 (2004). That is, with a stiffness meter manufactured by Toyo Seiki Seisakusho, the cantilever bending stress is measured at 60 ° C./min under the conditions of a span interval of 30 mm, a gripping portion of 30 mm, and a total bending moment of 6 kgf · cm. The test piece was melted by a hot compression molding machine having a temperature of 160 ° C. and then cooled down at a rate of 25 ° C./minute, and formed into a sheet having a thickness of 2 mm. After adjustment, a test piece is used by punching with a dumbbell blade mold so that the length is 85 mm and the width is 15 mm.
The value of the flexural modulus of the polyethylene resin of the present invention can be controlled by the density. That is, if the density is increased, the flexural modulus is increased.

The polyethylene resin of the present invention is further required to be obtained by polymerization using a chromium catalyst.
2. Production method of polyethylene resin The polyethylene resin of the present invention is produced by polymerization using a chromium catalyst.
Hereinafter, the chromium catalyst of the polymerization catalyst and the polymerization method will be described in detail.

(2-1) Polymerization catalyst As the polymerization catalyst for the polyethylene resin of the present invention, a chromium-containing catalyst such as a Philips catalyst is used.
Specifically, any catalyst suitable for slurry olefin polymerization can be used, but a heterogeneous catalyst in which polymerization active sites are localized is preferable.
The solid catalyst component is not particularly limited as long as it is used as a solid catalyst for olefin polymerization containing a transition metal compound. As the transition metal compound, compounds of elements of Group 4 to Group 10 of the periodic table, preferably Group 4 to Group 6, can be used, and specific examples include Ti, Zr, Hf, V, Cr. And compounds such as Mo.

  As the polymerization catalyst for the polyethylene resin of the present invention, a catalyst in which at least a part of chromium atoms are hexavalent by supporting a chromium compound on an inorganic oxide carrier and activating in a non-reducing atmosphere, generally What is known as a Phillips catalyst is preferred.

  As the inorganic oxide carrier, a metal oxide of Group 2, 4, 13 or 14 of the periodic table is preferable. Specific examples include magnesia, titania, zirconia, alumina, silica, tria, silica-titania, silica-zirconia, silica-alumina, or a mixture thereof. Of these, silica, silica-titania, silica-zirconia, and silica-alumina are preferable. In the case of silica-titania, silica-zirconia, silica-alumina, titanium, zirconium or aluminum atoms as metal components other than silica are 0.2 to 10% by mass, preferably 0.5 to 7% by mass, more preferably 1 to Those containing 5% by mass are used. The preparation, physical properties and characteristics of supports suitable for these chromium catalysts are described in C.I. E. Marsden, Preparation of Catalysts, Vol. 5, 215, 1991, Elsevier Science Publishers, C.I. E. Marsden, Plastics, Rubber and Composites Processing and Applications, Vol. 21, 193, 1994, and the like.

As the chromium-containing catalyst of the present invention, a Philips catalyst having an average particle size of 10 to 200 μm, preferably 20 to 150 μm, more preferably 30 to 100 μm is used. The average particle size is measured by a method such as a standard sieving method or a laser diffraction method.
The chromium-containing catalyst of the present invention preferably has a specific surface area of 200 to 600 m ² / g as a Philips catalyst. The specific surface area is measured by a BET method using adsorption of nitrogen gas. For the measurement by the BET method, see A. P. Legland, The Surface Properties of Silicones, Wiley, 1998, and the like.
Chromium-containing catalyst of the present invention, the pore volume, 0.5~3.0cm ³ / g, preferably 0.7~2.7cm ³ / g, more preferably 1.0~2.5cm ³ / Those in the g range are used. The pore volume is measured by the BJH method using desorption of nitrogen gas. For the measurement by the BJH method, see A. P. Legland, The Surface Properties of Silicones, Wiley, 1998, and the like.

  In the chromium-containing catalyst of the present invention, a chromium compound is supported on the inorganic oxide support. The chromium compound may be any compound in which at least a part of chromium atoms becomes hexavalent by being activated in a non-reducing atmosphere after being supported, such as chromium oxide, chromium halide, oxyhalide, chromate, heavy salt, Examples thereof include chromate, nitrate, carboxylate, sulfate, chromium-1,3-diketo compound, chromate ester and the like. Specifically, chromium trioxide, chromium trichloride, chromyl chloride, potassium chromate, ammonium chromate, potassium dichromate, chromium nitrate, chromium sulfate, chromium acetate, tris (2-ethylhexanoate) chromium, chromium acetyl Examples include acetonate and bis (tert-butyl) chromate. Of these, chromium trioxide, chromium acetate, and chromium acetylacetonate are preferable. Even when a chromium compound having an organic group such as chromium acetate or chromium acetylacetonate is used, the organic group part burns by activation in a non-reducing atmosphere described later, and finally chromium trioxide is used. It is known that it reacts with the hydroxyl group on the surface of the inorganic oxide support in the same manner, and at least some of the chromium atoms become hexavalent and are immobilized in the structure of chromate (VJ Ruddick et al. J. Phys. Chem. 100, 11062, 1996, SM Augustine et al., J. Catal. 161, 641 (1996)).

  The chromium compound can be supported on the inorganic oxide support by a known method such as impregnation, solvent distillation, sublimation, etc., and an appropriate method may be used depending on the kind of the chromium compound to be used. The amount of the chromium compound to be supported is 0.2 to 2.0% by mass, preferably 0.3 to 1.7% by mass, more preferably 0.5 to 1.5% by mass with respect to the carrier as chromium atoms. is there.

  After the chromium compound is supported, it is fired and activated. Activation can be performed in a non-reducing atmosphere substantially free of moisture, such as oxygen or air. At this time, an inert gas may coexist. Preferably, it is performed in a fluidized state using sufficiently dried air through which molecular sieves or the like are circulated. In general, the activation of the Philips catalyst is carried out at 400 to 900 ° C., but the activation of the present invention is carried out at a temperature of 400 to 540 ° C., preferably 430 to 530 ° C., more preferably 450 to 500 ° C., for 30 minutes to 48 hours. The reaction time is preferably 1 hour to 24 hours, more preferably 2 hours to 12 hours. As a result of this activation, at least a part of the chromium atom of the chromium compound supported on the inorganic oxide carrier is oxidized to be hexavalent and chemically fixed on the carrier. When the activation is carried out at less than 400 ° C., the polymerization activity is lowered and the molecular weight distribution becomes too wide and the durability is improved, but the impact resistance is lowered. When activation is performed at a temperature exceeding 540 ° C., the molecular weight distribution is narrowed and impact resistance is improved, but durability is lowered.

  In the present invention, before activation after supporting the chromium compound or after supporting the chromium compound, titanium alkoxides such as titanium tetraisopropoxide, zirconium alkoxides such as zirconium tetrabutoxide, aluminum alkoxides such as aluminum tributoxide, Addition of metal alkoxides typified by organoaluminums such as trialkylaluminum, organomagnesiums such as dialkylmagnesium or fluorine-containing salts such as organometallic compounds and ammonium silicofluoride, ethylene polymerization activity, α -You may use together the well-known method of adjusting the copolymerization property with an olefin, the molecular weight of the obtained polyethylene-type resin, and molecular weight distribution. In these metal alkoxides or organometallic compounds, the organic group portion is combusted by activation in a non-reducing atmosphere, and is oxidized into a metal oxide such as titania, zirconia, alumina, or magnesia and contained in the catalyst. In the case of fluorine-containing salts, the inorganic oxide carrier is fluorinated. These methods are described in C.I. E. Marsden, Plastics, Rubber and Composites Processing and Applications, Vol. 21, 193, 1994, T. Pulukat et al. Polym. Sci. , Polym. Chem. Ed. 18, p. 2857, 1980, M.M. P. McDaniel et al. Catal. 82, 118, 1983, and the like.

(2-2) Polymerization method The polyethylene resin of the present invention is obtained by homopolymerization of ethylene or ethylene and an α-olefin having 3 to 12 carbon atoms such as propylene, 1-butene, 1-pentene, 1-hexene, 4 -Obtained by copolymerization with methyl-1-pentene, 1-octene or the like. Also, copolymerization with a diene for the purpose of modification is possible. Examples of the diene compound used at this time include butadiene, 1,4-hexadiene, ethylidene norbornene, dicyclopentadiene, and the like. The comonomer content during the polymerization can be arbitrarily selected. For example, in the case of copolymerization of ethylene and an α-olefin having 3 to 12 carbon atoms, an ethylene / α-olefin copolymer is used. The α-olefin content therein is 0 to 40 mol%, preferably 0 to 30 mol%.
When a polyethylene resin is produced using the above chromium catalyst, any method such as slurry polymerization, liquid phase polymerization method such as solution polymerization, or gas phase polymerization method can be employed. A polymerization method is preferred, and any of a slurry polymerization method using a pipe loop reactor and a slurry polymerization method using an autoclave reactor can be used. Among these, a slurry polymerization method using a pipe loop reactor is preferable (details of a pipe loop reactor and slurry polymerization using the reactor are described in Kazuo Matsuura and Naotaka Mikami, “Polyethylene Technology Reader”, page 148, 2001. (See Industrial Research Committee).

Liquid phase polymerization is usually carried out in a hydrocarbon solvent. As the hydrocarbon solvent, inert hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, hexane, heptane, octane, decane, cyclohexane, benzene, toluene, and xylene are used alone or as a mixture. As the gas phase polymerization method, a commonly known polymerization method such as a fluidized bed or a stirring bed can be employed in the presence of an inert gas, and a so-called condensing mode in which a medium for removing heat of polymerization coexists may be employed. .
The polymerization temperature in the liquid phase polymerization method is generally 0 to 300 ° C., practically 20 to 200 ° C., preferably 50 to 180 ° C., more preferably 70 to 150 ° C. The catalyst concentration and ethylene concentration in the reactor may be any concentration sufficient to allow the polymerization to proceed. For example, the catalyst concentration can range from about 0.0001 to about 5 weight percent based on the weight of the reactor contents in the case of liquid phase polymerization. Similarly, the ethylene concentration can range from about 1% to about 10% based on the mass of the reactor contents in the case of liquid phase polymerization.

In the method of the present invention, when ethylene polymerization is performed using a chromium catalyst, it is preferable to copolymerize an α-olefin as a comonomer. As the α-olefin, propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, or the like is introduced alone or in two or more kinds into the reactor for copolymerization. Preferably 1-butene, 1-hexene, more preferably 1-hexene is suitably used as a comonomer. The α-olefin content in the obtained polyethylene resin is 15 mol% or less, preferably 10 mol% or less.
Further, a chain transfer agent such as hydrogen may be introduced during the polymerization. The concentration ratio of hydrogen and ethylene coexisting with ethylene can be easily adjusted by changing the concentration of hydrogen and ethylene. When ethylene polymerization is a liquid phase polymerization method, the ratio between the hydrogen concentration (mass%) in the liquid phase (abbreviated as Hc) and the ethylene concentration in the liquid phase (abbreviated as ETc) is 1. 0.0 × 10 ⁻⁴ ≦ Hc / ETc ≦ 1.0 × 10 ⁻² , preferably 2.0 × 10 ⁻⁴ ≦ Hc / ETc ≦ 8.0 × 10 ⁻³ , more preferably 3.0 × 10 ^{−. The} polymerization is preferably performed under conditions satisfying the relationship of ⁴ ≦ Hc / ETc ≦ 6.0 × 10 ⁻³ . The hydrogen pressure is not particularly limited. Usually, in the case of the liquid phase polymerization method, the hydrogen concentration in the liquid phase is 1.0 × 10 ^{−4 to} 1.0 × 10 ⁻¹ mass%, preferably 1. It is in the range of 0 × 10 ^{−3 to} 5.0 × 10 ⁻² mass%, more preferably 2.0 × 10 ^{−3 to} 4.0 × 10 ⁻² mass%. The pressure of ethylene is not particularly limited, but usually in the case of liquid phase polymerization, the ethylene concentration in the liquid phase is 1.0 to 10.0% by mass, preferably 3.0 to 8.0% by mass. It is a range.

As a polymerization method, not only single-stage polymerization in which a single reactor is used to produce a polyethylene resin, but also multistage polymerization by connecting at least two reactors in order to improve the production amount or broaden the molecular weight distribution. Can also be done. In the case of multi-stage polymerization, two-stage polymerization is preferred in which two reactors are connected and the reaction mixture obtained by polymerization in the first-stage reactor is continuously fed to the second-stage reactor. The transfer from the first stage reactor to the second stage reactor is effected by continuous discharge of the polymerization reaction mixture from the second stage reactor through a connecting tube.
The first stage reactor and the second stage reactor may be produced under the same polymerization conditions, or the first stage reactor and the second stage reactor produce the same melt flow rate and density polyethylene-based resin. However, when broadening the molecular weight distribution, it is preferable to make a difference in the molecular weight of the polyethylene resin produced in both reactors. In any production method of producing a high molecular weight component in the first stage reactor, a low molecular weight component in the second stage reactor, or a low molecular weight component in the first stage reactor, and a high molecular weight component in the second stage reactor, respectively. Although the method of producing high molecular weight components in the first stage reactor and low molecular weight components in the second stage reactor requires an intermediate hydrogen flash tank for the transition from the first stage to the second stage. Therefore, it is more preferable in terms of productivity.

In the first stage, ethylene is copolymerized alone or optionally with α-olefin, while the molecular weight is adjusted by the mass ratio of hydrogen concentration to ethylene concentration (Hc / ETc), polymerization temperature or both, and α- The polymerization reaction is carried out while adjusting the density by the mass ratio of the olefin concentration to the ethylene concentration.
In the second stage, there are hydrogen in the reaction mixture that flows from the first stage and α-olefin that also flows in, but if necessary, new hydrogen and α-olefin can be added respectively. Therefore, also in the second stage, while adjusting the molecular weight by the mass ratio of hydrogen concentration to ethylene concentration (Hc / ETc), polymerization temperature or both, and by adjusting the density by the mass ratio of α-olefin concentration to ethylene concentration, A polymerization reaction can be performed. For organometallic compounds such as catalysts and organoaluminum compounds, not only does the polymerization reaction continue in the second stage with the catalyst flowing in from the first stage, but also a new catalyst, organometallic compounds such as organoaluminum compounds in the second stage. Compounds or both may be supplied.

  As a ratio of the high molecular weight component and the low molecular weight component in the case of producing by two-stage polymerization, the high molecular weight component is 10 to 90 parts by weight, the low molecular weight component is 90 to 10 parts by weight, and preferably the high molecular weight component is 20 to 80 parts by weight. Parts, low molecular weight components are 80 to 20 parts by mass, more preferably high molecular weight components are 30 to 70 parts by mass, and low molecular weight components are 70 to 30 parts by mass. The high molecular weight component has a melt flow rate of 0.01 to 100 g / 10 minutes, preferably 0.01 to 50 g / 10 minutes, and the low molecular weight component has a melt flow rate of 10 to 1000 g / 10 minutes, preferably 10 ~ 500 g / 10 min.

  The obtained polyethylene resin is then preferably kneaded. It is carried out using a single or twin screw extruder or a continuous kneader. The polyethylene-based resin produced by the above method may be used alone or as a mixture of a plurality of types. After being pelletized by mechanical melt mixing with a pelletizer or homogenizer, etc. according to a conventional method, various molding machines By molding, a desired molded product can be obtained.

In addition to other olefin polymers and rubbers, etc., the polyethylene resin of the present invention, if necessary, in addition to antioxidants, ultraviolet absorbers, light stabilizers, lubricants, antistatic agents, antifogging, etc. Agents, anti-blocking agents, processing aids, coloring pigments, pearl pigments, polarizing pearl pigments, crosslinking agents, foaming agents, neutralizing agents, thermal stabilizers, crystal nucleating agents, inorganic or organic fillers, flame retardants, etc. Additives can be blended.
As additives, for example, antioxidants (phenolic, phosphorus-based, sulfur-based), lubricants, antistatic agents, light stabilizers, ultraviolet absorbers, and the like can be appropriately used in combination of one or more. As the filler, calcium carbonate, talc, metal powder (aluminum, copper, iron, lead, etc.), silica, diatomaceous earth, alumina, gypsum, mica, clay, asbestos, graphite, carbon black, titanium oxide, etc. can be used. . In any case, various additives may be blended with the polyethylene resin as necessary, and the mixture may be kneaded with a kneading extruder, a Banbury mixer, or the like to obtain a molding material.

[II] Hollow molded article The hollow molded article of the present invention has a structure having at least one layer of the present polyethylene resin, preferably a multilayer structure, but may have a single layer structure made of a polyethylene resin. .
When the hollow molded article has a multilayer structure, it is preferable to have a permeation reduction barrier layer, and a barrier layer is usually used as the permeation reduction barrier layer.

When the layer structure of the hollow molded article of the present invention is two or more layers, the innermost layer and the outermost layer are preferably made of the present polyethylene resin.
The hollow molded article of the present invention preferably has a multilayer structure including a permeation-reducing barrier layer in which at least one barrier layer is present to reduce penetration of volatile substances and the barrier layer is composed of a polar barrier polymer. . For example, when the wall of the plastic fuel tank has a multi-layer structure, there is an advantage that a barrier layer (in itself, moldability and mechanical strength are not sufficient) can be fixed between two layers made of the present polyethylene resin. As a result, particularly during coextrusion blow molding, the moldability of a material having two or more layers of the present polyethylene resin is improved primarily due to the improved moldability of the present polyethylene resin. Furthermore, since the improved performance of the present polyethylene-based resin has a very important influence on the mechanical strength of the material, the strength of the hollow molded article of the present invention can be remarkably increased.
In the hollow molded article of the present invention, the base layer may be coated on the surface of the polyethylene resin layer by a treatment such as fluorination, surface coating or plasma polymerization.

A preferred embodiment of the hollow molded article according to the present invention has a four-kind six-layer structure including the following layers from the inside to the outside.
That is, the present polyethylene-based resin layer, adhesive layer, barrier layer, adhesive layer, recycled material layer, and present polyethylene-based resin layer.
Below, the structure of each layer in the said aspect and a layer structure ratio are demonstrated in detail.

(1) Layer structure of hollow molded product Outermost layer The resin (A) constituting the outermost layer of the hollow molded article of the present invention is the polyethylene resin of the present invention produced by polymerization using a chromium catalyst.

2. Innermost layer The resin (B) constituting the innermost layer of the hollow molded article of the present invention is the polyethylene resin of the present invention produced by polymerization using a chromium catalyst, and is the same as the above resin (A). There may be different or different ones.

3. Barrier layer The resin (C) that forms the barrier layer of the hollow molded article of the present invention is selected from ethylene vinyl alcohol resin, polyamide resin, polyethylene terephthalate resin, polybutylene terephthalate resin, etc., and particularly ethylene vinyl alcohol resin. Preferably it consists of. More preferably, the ethylene vinyl alcohol resin has a saponification degree of 93% or more, desirably 96% or more, and an ethylene content of 25 to 50 mol%.

4). Adhesive layer The resin (D) forming the adhesive layer of the hollow molded article of the present invention is selected from high-density polyethylene, low-density polyethylene, linear low-density polyethylene and the like graft-modified with unsaturated carboxylic acid or its derivative However, it is preferably made of high-density polyethylene graft-modified with an unsaturated carboxylic acid or derivative thereof.
Content of unsaturated carboxylic acid or its derivative (s) is 0.01-5 mass%, Preferably it is 0.01-3 mass%, More preferably, it is 0.01-1 mass%. When the graft modification amount is less than 0.01% by mass, sufficient adhesion performance is not exhibited, and when it exceeds 5% by mass, an unsaturated carboxylic acid that does not contribute to adhesion adversely affects the adhesion.

5. Recycled material layer The resin that forms the recycled material layer of the hollow molded article of the present invention includes a polyethylene resin (A) that forms the outermost layer, a polyethylene resin (B) that forms the innermost layer, and a resin that forms the barrier layer ( C) and a resin (D) that forms an adhesive layer.
(A)-(D) each component can use a new article, and collect and reuse unnecessary parts such as scraps, burrs, etc. of the multilayer laminate including each layer composed of the components (A)-(D). Such a recycled product can also be used as a component raw material for each component. For example, a regrind resin obtained by pulverizing a hollow plastic molded product (such as an automobile fuel tank product) once molded, used, and used is used. When using a recycled product, all the components (A) to (D) can be supplied from the recycled product, or can be mixed with a new product.
When using molding burrs or unused parisons that are generated during the production of multilayer laminates as recycled materials, the compatibility of various components may decrease, so further mixing the compatibilizer and the resin that constitutes the adhesive layer May be.

6). Layer composition ratio of hollow molded article The thickness composition of each layer of the hollow molded article of the present invention is 10 to 30% for the outermost layer, 20 to 50% for the innermost layer, 1 to 15% for the barrier layer, and 1 to 15% for the barrier layer. 1 to 15%, and the recycled material layer is 30 to 60% (however, the sum of all layer thickness components is 100%).
The layer composition ratio of the outermost layer is 10 to 30%, preferably 10 to 25%, more preferably 10 to 20%. When the layer composition ratio of the outermost layer is less than 10%, the impact performance is insufficient, and when it exceeds 30%, the molding stability of the hollow molded product is impaired.
The layer composition ratio of the innermost layer is 20 to 50%, preferably 35 to 50%, more preferably 40 to 50%. If the layer composition ratio of the outermost layer is less than 20%, the lack of rigidity of the hollow molded product becomes obvious, and if it exceeds 50%, the molding stability of the hollow molded product is impaired.
The layer composition ratio of the barrier layer is 1 to 15%, preferably 1 to 10%, more preferably 1 to 5%. When the layer composition ratio of the barrier layer is less than 1%, the barrier performance is unsatisfactory, and when it exceeds 15%, the impact performance is insufficient.
The layer composition ratio of the adhesive layer is 1 to 15%, preferably 1 to 10%, more preferably 1 to 5%. When the layer composition ratio of the adhesive layer is less than 1%, the adhesive performance is unsatisfactory, and when it exceeds 15%, the lack of rigidity of the hollow molded article becomes obvious.
The composition ratio of the recycled material layer is 30 to 60%, preferably 35 to 50%, more preferably 35 to 45%. When the layer composition ratio of the recycled material layer is less than 30%, the molding stability of the hollow molded product is impaired, and when it exceeds 60%, the impact performance is insufficient.

  The hollow molded article of the present invention is preferably a four-type six-layer hollow molded article laminated in this order from the outermost layer, the recycled material layer, the adhesive layer, the barrier layer, the adhesive layer, and the innermost layer. By sandwiching the barrier layer with an adhesive layer, a high level of barrier properties is exhibited. By having the recycled material layer between the outermost layer and the adhesive layer, the effects of cost reduction by reducing raw material costs and maintaining the rigidity of the hollow molded product are exhibited.

(2) Production of hollow molded article, and product or application The production method of the hollow molded article of the present invention is not particularly limited, and usually an extrusion blow molding method using a conventionally known multilayer hollow molding machine is used. It is done. For example, after the constituent resin of each layer is heated and melted with a plurality of extruders, the molten parison is extruded with a multilayer die, then the parison is sandwiched between molds, and air is blown into the interior of the parison to form a multilayer hollow molding The product is manufactured.
Furthermore, the hollow molded article of the present invention includes an antistatic agent, an antioxidant, a neutralizing agent, a lubricant, an antiblocking agent, an antifogging agent, an organic or inorganic pigment, as long as the purpose is not impaired as necessary. Known additives such as fillers, inorganic fillers, UV inhibitors, dispersants, weathering agents, crosslinking agents, foaming agents, flame retardants, and the like can be added.
The use of the hollow molded article of the present invention includes automobile fuel tanks, various fuel tanks, kerosene cans, drum cans, chemical containers, agricultural chemical containers, solvent containers, various plastic bottles, etc. Most preferably, it is used as a fuel tank.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples.

(1) Various measurement methods Measurement and evaluation methods in Examples and Comparative Examples are as follows.

1. Determination of hydrogen concentration and ethylene concentration in the liquid phase in the autoclave According to JIS K-2301 (2004 edition), the polymerization temperature, hydrogen partial pressure, and ethylene partial pressure of each example and comparative example conditions were previously measured without introducing the catalyst. The hydrogen concentration and ethylene concentration of each were analyzed and quantitatively analyzed by gas chromatography. A small amount of the solution in the autoclave was withdrawn and vaporized. Using a gas chromatograph GC-14A manufactured by Shimadzu Corporation, the hydrogen concentration and ethylene were analyzed by a thermal conductivity detector under the analysis conditions of page 10 of Table JIS and column combination B. The concentration was quantified.

2. Measurement of physical properties of polyethylene resin, evaluation method (i) Density: Measured in accordance with JIS K6922-1 (1997).

(Ii) Melt flow rate: Measured as a high load melt flow rate (melt flow rate) at a temperature of 190 ° C. and a load of 21.6 kg in accordance with JIS K6922-2 (1997).

(Iii) Molecular weight distribution (Mw / Mn) measured by GPC: The following GPC measurement is performed, the number average molecular weight (Mn) and the mass average molecular weight (Mw) are obtained, and the molecular weight distribution (Mw / Mn) is calculated. It was.
[Gel permeation chromatograph (GPC) measurement conditions]
Apparatus: Waters 150C model,
Column: Shodex-HT806M,
Solvent: 1,2,4-trichlorobenzene,
Temperature: 135 ° C
Universal rating using monodisperse polystyrene fraction.
Regarding the molecular weight distribution indicated by the ratio of Mw to Mn (Mw / Mn) (the larger the Mw / Mn, the wider the molecular weight distribution), “size exclusion chromatography (high-performance liquid chromatography of polymers)” (written by Sadao Mori, The molecular weight and detector sensitivity formula described in Kyoritsu Shuppan, page 96) is applied to the data of fractionated linear polyethylene resin with n-alkane and Mw / Mn ≦ 1.2, and the molecular weight M shown by the following formula: The actual sample values were corrected.
Sensitivity of molecular weight M = a + b / M
(A and b are constants, a = 1.32, b = 189.2)

(Iv) Fracture time (T) of all-around notch tensile creep test: Measured according to JIS K-692-2 (2004). After compression-molding a sheet having a thickness of 5.9 mm, a test piece having the shape and size of the classification “nominal 50” shown in FIG. 1 is prepared according to JIS K-6774 (2004) Annex 5 (normative). The measurement was performed by purely notched tensile creep test (FNCT) in pure water at ° C. The tensile load was 88N, 98N, and 108N, the number of test points was 2 for each load, and the rupture time (T) at a stress of 6 MPa was obtained from the rupture time and 6-point plot of stress on a log-log scale by the least square method. .

(V) Charpy impact strength: In accordance with JIS K-7111 (2004), a type 1 test piece was prepared, the striking direction was edgewise, the notch type was type A (0.25 mm), dry ice / Measurements were made at −40 ° C. in alcohol.

(Vi) Measurement of elongational viscosity and elongational viscosity ratio (λmax): Using a capillary rheometer manufactured by Intesco, using a capillary of 3 mmφ × 15 mmL at a temperature of 190 ° C., producing a test piece at a piston speed of 20 mm / min, Using a Merten rheometer manufactured by Toyo Seiki Seisakusho, the preheating time was 15 minutes, and the elongational viscosity was measured at a temperature of 170 ° C. and a strain rate of 0.1 / s.

(Vii) Flexural rigidity (flexural modulus): In accordance with JIS K-7106 (2004), with a stiffness meter manufactured by Toyo Seiki Seisakusho Co., Ltd., the span is 30 mm, the grip part is 30 mm, and the total bending moment is 6 kgf · cm. The cantilever bending stress was measured at 60 ° C./min under the conditions. The test piece was prepared by melting a resin sample with a hot compression molding machine having a temperature of 160 ° C., then lowering the temperature at a rate of 25 ° C./minute, and forming the sheet into a sheet having a thickness of 2 mm. After adjusting the state, the test piece was punched out with a dumbbell blade so that the length was 85 mm and the width was 15 mm.

3. Measurement and evaluation method of physical properties of hollow molded products (i) Formability Using a Japanese steel mill NB150 hollow molding machine, molding plastic tanks, and evaluating the extrusion characteristics of the parison during hollow molding, ○, where the molding failure occurred was marked as x.

(Ii) Drop impact property: A container filled with antifreeze in half a full capacity in a 60 liter plastic tank is cooled to -40 ° C, and three tanks are dropped vertically from a height of 6 m from the concrete surface. Those that did not leak were marked with ◯, and those that did not leak were marked with ×.

(Iii) Internal pressure deformation test An internal pressure deformation test was performed on a plastic tank at an internal pressure of 0.05 MPa and 60 ° C. After 500 hours had elapsed, the pressure was released and the temperature was returned to room temperature.

(Iv) Heat / Pressure Resistance Test Internal pressure and heat resistance tests were performed on plastic tanks at an internal pressure of 0.05 MPa and 60 ° C. After 1000 hours, the case where no holes or cracks were generated was marked with ◯, and the case where holes or cracks were generated was marked with x.

Example 1
(1) Activation of chromium catalyst 5 kg of catalyst (Phillips catalyst) having a supported chromium atom content of 1.1 mass% (support: silica), a specific surface area of 500 m ² / g, and a pore volume of 1.5 cm ³ / g. Was put into a utilization electric furnace having an inner diameter of 25 cm, fluidized with dry air, and activated at an activation temperature of 450 ° C. for 20 hours. The catalyst was extracted in dry nitrogen and set in a catalyst feeder.

(2) Polymerization A 200 L internal pipe loop reactor is continuously supplied with isobutane at 120 L / h and the chromium catalyst obtained in (1) above at a rate of 7.5 g / h. While discharging at the required speed, the mass ratio of the hydrogen concentration in the liquid phase to the ethylene concentration at 101 ° C. is 2.6 × 10 ⁻³ , and the mass ratio of the 1-hexene concentration in the liquid phase to the ethylene concentration is 0.12. Ethylene, hydrogen, and 1-hexene were supplied so as to keep the polymerization, and polymerization was continuously performed in a liquid-filled state under the conditions of a total pressure of 4.1 MPa and an average residence time of 1.5 h. Catalyst productivity was 2700 g-polymer / g-catalyst, and the average polymerization activity was 1800 g-polymer / g-catalyst / h. Polymerization was continued for 60 hours to obtain 1.2 tons of a polyethylene resin. Table 1 shows the measurement results of physical properties (melt flow rate, density, molecular weight (Mn, Mw), molecular weight distribution (Mw / Mn), rigidity, breaking time, Charpy impact strength, elongational viscosity, melt tension).

(3) Molding of automobile fuel tank ~ 4. Using the above resin, an automobile fuel tank was obtained by molding under the following conditions with a coextrusion blow molding apparatus (NB150 manufactured by Nippon Steel Works) so as to have the following layer structure.

(Used resin)
1. Polyethylene resin The present polyethylene resin produced by polymerization using a chromium catalyst was used.

2. Adhesive resin (MAPE)
Maleic anhydride-modified polyethylene manufactured by Nippon Polyethylene Co., Ltd. grafted with 0.1% by mass of maleic anhydride was used.

3. Barrier resin (EVOH)
Kuraray Co., Ltd. ethylene vinyl alcohol resin Eval was used.

4). Recycled material In the above layer structure, the same resin as that constituting the innermost layer is used as the resin for the recycled material layer at the start of the experiment, and an automobile fuel tank is blow-molded and the automobile fuel tank is pulverized. Grind resin was used as a recycled material. Specifically, a recycled material obtained by molding and pulverizing an automobile fuel tank having the following layer structure was used for the recycled material layer.

(Layer structure)
Outermost layer: This polyethylene resin (layer composition ratio 11%)
Recycled material layer: This polyethylene resin (layer composition ratio 40%)
Adhesive outer layer: MAPE (layer composition ratio 3%)
Barrier layer: EVOH (layer composition ratio 3%)
Adhesive inner layer: MAPE (layer composition ratio 3%)
Innermost layer: This polyethylene resin (layer composition ratio 40%)

(Molding condition)
Under the following co-extrusion multilayer conditions, a fuel tank for automobiles having a multilayer structure of four types and six layers having a molding temperature of 210 ° C., a blow mold cooling temperature of 20 ° C., a cooling time of 180 seconds and a tank mass of 8 kg and a capacity of 60 L was molded. The tank shape was a saddle type. The layer ratio is 11% for the outermost layer, 40% for the second layer, 3% for the third layer, 3% for the fourth layer, while adjusting the screw speed of the extruder while observing the thickness ratio of the tank. The fifth layer was 3% and the innermost layer was 40%.

Outermost layer (first layer from outside) diameter 90mmφ, L / D = 22
Second layer (second layer from the outside) diameter 120 mmφ, L / D = 28
Third layer (third layer from the outside) diameter 50 mmφ, L / D = 22
Fourth layer (fourth layer from the outside) diameter 50 mmφ, L / D = 28
5th layer (5th layer from the outside) diameter 50 mmφ, L / D = 22
Innermost layer (sixth layer from the outside) diameter 120 mmφ, L / D = 241

The drop impact resistance, heat / pressure resistance test, internal pressure deformation test, and extrusion characteristics of an automobile fuel tank were evaluated. The results are shown in Table 1.
This shows that both the physical properties of the polyethylene resin and the evaluation of the fuel tank for automobiles are good.

Example 2
Polymerization and molding were carried out in the same manner as in Example 1 except that the polymerization temperature was changed to 102 ° C. and the mass ratio of 1-hexene concentration to ethylene concentration in the liquid phase was changed to 0.11. The catalyst productivity was 2900 g-polymer / g-catalyst, and the average polymerization activity was 1900 g-polymer / g-catalyst / h. Table 1 shows the physical properties of the polyethylene resin and the evaluation results of the fuel tank for automobiles. This shows that both the physical properties of the polyethylene resin and the evaluation of the fuel tank for automobiles are good.

Comparative Example 1
(1) Activation of chromium catalyst Except that the activation temperature was changed to 550 ° C, activation was performed in the same manner as in Example 1 (1).
(2) Polymerization The polymerization temperature is changed to 100 ° C., the mass ratio of the hydrogen concentration in the liquid phase to the ethylene concentration is changed to 8.1 × 10 ⁻⁴ , and the mass ratio of the 1-hexene concentration in the liquid phase to the ethylene concentration is changed. Polymerization was conducted in the same manner as in Example 1 (2) except that the ratio was changed to 0.10. Catalyst productivity = 4300 g-polymer / g-catalyst, and the average polymerization activity was 2900 g-polymer / g-catalyst / h. Table 1 shows the physical properties of the obtained polyethylene resin.
Table 1 also shows the evaluation results of the automobile fuel tank molded in the same manner as in Example 1.
From this, it can be seen that the molecular weight distribution becomes narrow, and the results of the FNCT and the heat / pressure resistance test are poor.

Comparative Example 2
Polymerization and molding were performed in the same manner as in Example 1 except that the polymerization temperature was changed to 99 ° C. and the mass ratio of the 1-hexene concentration in the liquid phase to the ethylene concentration was changed to 0.13. Catalyst productivity was 2500 g-polymer / g-catalyst, and the average polymerization activity was 1700 g-polymer / g-catalyst / h. Table 1 shows the physical properties of the polyethylene resin and the evaluation results of the fuel tank for automobiles.
As a result, in the extrusion characteristics, the resin pressure was high and molding was difficult.

Comparative Example 3
Polymerization and molding were carried out in the same manner as in Example 1 except that the polymerization temperature was changed to 103.5 ° C. and the mass ratio of 1-hexene concentration to ethylene concentration in the liquid phase was changed to 0.10. The catalyst productivity was 3000 g-polymer / g-catalyst, and the average polymerization activity was 2000 g-polymer / g-catalyst / h. Table 1 shows the physical properties of the polyethylene resin and the evaluation results of the fuel tank for automobiles.
This shows that the impact resistance is inferior.

Comparative Example 4
Polymerization was conducted in the same manner as in Example 1 (2) except that the polymerization temperature was changed to 100 ° C. and the mass ratio of the 1-hexene concentration in the liquid phase to the ethylene concentration was changed to 0.14. The catalyst productivity was 2900 g-polymer / g-catalyst, and the average polymerization activity was 1900 g-polymer / g-catalyst / h. Table 1 shows the physical properties of the polyethylene resin and the evaluation results of the fuel tank for automobiles.
This shows that the rigidity is low and the pressure deformation test is inferior.

Comparative Example 5
Polymerization was conducted in the same manner as in Example 1 (2) except that the polymerization temperature was changed to 102 ° C. and the mass ratio of the 1-hexene concentration in the liquid phase to the ethylene concentration was changed to 0.10. Catalyst productivity was 2700 g-polymer / g-catalyst, and the average polymerization activity was 1800 g-polymer / g-catalyst / h. Table 1 shows the physical properties of the polyethylene resin and the evaluation results of the fuel tank for automobiles.
This shows that the results of the FNCT and the heat / pressure resistance test are inferior.

  From Table 1, the polyethylene resin of the example is excellent in moldability and durability, and is excellent in the balance of impact resistance and rigidity and high in rigidity, whereas the polyethylene resin of the comparative example has these characteristics. At least one of them is inferior, and the hollow molded products of the examples are excellent in moldability and durability, and excellent in the balance between impact resistance and rigidity, whereas the polyethylene resins in the comparative examples are It can be seen that at least one of the characteristics is inferior.

  The polyethylene-based resin of the present invention is excellent in moldability and durability, and has an excellent balance between impact resistance and rigidity, and is particularly high in rigidity. Hollow molded products using the same have the same good characteristics. However, since it is suitable for use as a tank such as a fuel tank, a can, a container, a bottle, etc., particularly as a fuel tank of an automobile, the industrial utility is very high.

It is explanatory drawing which shows the measuring method of elongational viscosity ratio ((lambda) max).

Claims (8)

A polyethylene-based resin produced by polymerization using a chromium-containing catalyst, characterized by having the following properties (1) to (5) and a flexural modulus of 1000 MPa or more: Polyethylene resin.
(1) Density: 0.945 to 0.950 g / cm ³
(2) Melt flow rate (temperature 190 ° C., load 21.6 kg): 3.5 to 5.0 g / 10 minutes (3) Molecular weight distribution measured by GPC (Mw / Mn): 25 or more (4) Whole circumference Break time (T) of notch type tensile creep test: 30 hours or more (5) Charpy impact strength: 9 KJ / m ² or more   2. The polyethylene resin according to claim 1, which exhibits strain hardening behavior in the measurement of elongational viscosity and has an elongational viscosity ratio (λmax) of 1.05 to 1.50.   Polyethylene resin is a homopolymer of ethylene, a copolymer of ethylene and a C 3-12 α-olefin or diene compound, or a copolymer of ethylene, a C 3-12 α-olefin and a diene compound. The polyethylene resin according to claim 1 or 2, which is a coalescence.   A hollow molded article comprising one or more layers made of the polyethylene-based resin according to claim 1.   The hollow molded article according to claim 4, wherein when the layer structure of the hollow molded article is two or more, the innermost layer and the outermost layer are made of the polyethylene resin according to any one of claims 1 to 3. .   The layer structure of the two or more layers has a polyethylene resin according to any one of claims 1 to 3, an adhesive layer, a barrier layer, an adhesive layer, a recycled material layer, and any one of claims 1 to 3 from the inside to the outside. The hollow molded article according to claim 5, comprising the polyethylene-based resin according to the order.   The hollow molded article according to any one of claims 4 to 6, wherein the hollow molded article is a fuel tank, kerosene can, drum can, chemical container, agricultural chemical container, solvent container, or plastic bottle.   The hollow molded article according to claim 7, wherein the fuel tank is an automobile fuel tank.

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