High-purity polyethylene resin for chemical use and containers made thereof

Abstract

To provide a polyethylene resin for a high purity chemical container which suppresses elusion of a contaminant such as an eluted matter and a deteriorating matter of a polyethylene resin as much as possible, when the resin is used as a high purity chemical container, and is excellent in chemical resistance, and a container made of the same.SOLUTION: A polyethylene resin for a high purity chemical container contains two components of an ethylene-based polymer having an MFR of 10-40 g / 10 min and density of 0.960-0.970 g / cm3 and an ethylene-based polymer having an HLMFR of 0.01-3 g / 10 min and density of 0.920-0.940 g / cm3, has a weight ratio of the two components of 40:60 to 60:40, and has specific properties.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to polyethylene resin for high-purity chemical containers and containers made therefrom. [Background technology]

[0002] In recent years, with the remarkable development of the electronics industry, the demand for high-purity chemicals has been increasing. High-purity chemicals are used as essential chemicals in the manufacture of electronic circuits such as large-scale, integrated LSIs. Specifically, sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, ammonium fluoride, hydrogen peroxide, isopropyl alcohol, xylene, TMAH (tetramethylammonium hydroxide), methanol, acetic acid, phosphoric acid, ammonia water, PGMEA (propylene glycol acetate methyl ether), DMSO (dimethyl sulfoxide), and NMP (N-methyl-2-pyrrolidone) are used for applications such as wafer cleaning and etching, wiring and insulating film etching, jig cleaning, developing solutions, resist diluents, resist stripping solutions, and drying. Polyethylene resin is used as the container material for these high-purity chemicals. As the integration density of semiconductor circuits improves, the demand for reducing impurities and fine particles in these chemicals has become increasingly stringent, and in order to satisfy these stringent requirements, the demand for cleanliness of the containers that fill these chemicals is also increasing year by year. In addition to the above requirements, there is also a growing demand for larger containers and greater chemical resistance for the containers used to fill these chemicals.

[0003] One proposed solution to this problem is a container that minimizes the amount of hydrocarbon solvents extracted from polyethylene resin, reduces the content of low-molecular-weight components, and limits the amount of antioxidants, neutralizing agents, and lightfasteners added. However, improvements to address the effects of ash content due to residual catalytic components in the polyethylene resin are insufficient, and measures to address the concentration of metal impurities leaching into chemicals remain incomplete. Furthermore, the particle size is not sufficient at 0.2 μm or larger (see Patent Documents 1 and 2).

[0004] Furthermore, the density is 0.950~0.965 g / cm³ 3High-purity polyethylene and high-purity chemical containers have been proposed that exhibit excellent moldability and ESCR, with properties such as a melt flow rate of 5-20 g / 10 min at a temperature of 190°C and a load of 21.6 kg, a constant strain ESCR of 40 hours or more, and an ash content of 20 mass PPM or less. However, the ESCR, which is an indicator of chemical resistance, is insufficient for large 1000L containers (Intermediate Bulk Containers: IBCs), and the level of fine particles is also insufficient, being 0.2 μm or larger (see Patent Document 3).

[0005] Furthermore, the density is 0.940~0.970 g / cm³ 3 Although ultra-high purity polyethylene resins and high-purity chemical containers have been proposed that have properties such as a melt flow rate of 2 to 8.5 g / 10 min at a temperature of 190°C and a load of 21.6 kg, a ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) (Mw / Mn) of 8 to 15 determined by gel permeation chromatography (GPC), a molecular weight distribution curve obtained using GPC showing that components with a molecular weight of 1000 or less are 0.30% by weight or less, and an ESCR of 130 hours or more, the ESCR was insufficient for IBC containers (see Patent Document 4). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 7-62161 [Patent Document 2] Japanese Patent Application Publication No. 7-257540 [Patent Document 3] Japanese Patent Publication No. 2018-172177 [Patent Document 4] Patent No. 6705157 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a polyethylene resin for high-purity chemical containers that minimizes the leaching of contaminants such as leached substances and degraded substances from the resin when used as a high-purity chemical container, and to provide a polyethylene resin for high-purity chemical containers and a container made therefrom that has excellent chemical resistance. [Means for solving the problem]

[0008] As a result of diligent research to solve the above problems, the present inventors have discovered that by using polyethylene having specific properties such as density, melt flow rate, molecular weight determined by gel permeation chromatography (GPC), ESCR, and metal content, a high-purity chemical container with fewer polyethylene-derived fine particles and metal impurities derived from polymerization catalyst components, and excellent chemical resistance, can be obtained, leading to the development of the present invention.

[0009] In other words, the various embodiments of the present invention are as follows [1] to [4]. [1] Melt flow rate (MFR) at 190℃ and 2.16kg load is 10-40g / 10min, density (JIS K6922-1) is 0.960-0.970g / cm³ 3 The ethylene-based polymer has a melt flow rate (HLMFR) of 0.01-3 g / 10 min and a density of 0.920-0.940 g / cm³ at 190°C and a 21.6 kg load. 3 A high-purity polyethylene resin for chemical containers comprising two ethylene-based polymer components, wherein the weight ratio of the two components is 40:60 to 60:40, and having the following properties (1) to (9). (1) Density of 0.940~0.955 g / cm³ 3 (2) HLMFR 1-15g / 10 min (3) The ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) (Mw / Mn) determined by gel permeation chromatography (GPC) is between 8 and 15. (4) In the molecular weight distribution curve obtained using GPC, the component with a molecular weight of 1000 or less is 0.30% by weight or less. (5) In the molecular weight distribution curve obtained using GPC, the component with a molecular weight of 100,000 or more is 35% by weight or more (6) The environmental stress crack resistance (ESCR) is 1000 hours or more (7) 13 The number of short-chain branches with 4 or less carbon atoms per 1000 carbon atoms determined from the measurement of C-NMR is 3 or more (8) The metal content is 20 PPM or less based on the polyethylene resin (9) The Charpy impact strength retention rate after immersion in 70% nitric acid at 40 °C for 35 days is 50% or more [2] The polyethylene resin for high-purity chemical containers according to [1] above, which does not contain additives. [3] A high-purity chemical container made of the polyethylene resin according to [1] or [2] above. [4] The container for high-purity chemicals according to [3] above, in which ultrapure water is filled in an unwashed container, and the number of particles of 0.1 μm or more eluted from the content liquid after standing storage at 40 °C for 35 days is 20 or less per mL.

Advantages of the Invention

[0010] When using the polyethylene resin for high-purity chemical containers, which is one aspect of the present invention, it is possible to mold a high-purity chemical container with few fine particles derived from the polyethylene resin and metal impurities derived from the polymerization catalyst component and excellent chemical resistance. In addition, it is particularly suitable for large containers of 200 L or more, and it is possible to provide a high-purity chemical container with a small elution amount of fine particle components with respect to the filled chemical and a small elution amount of fine particles even after long-term storage.

Embodiments for Carrying Out the Invention

[0011] The polyethylene resin for high-purity chemicals, which is one aspect of the present invention, has a melt flow rate (MFR) of 10 to 40 g / 10 minutes at 190 °C under a load of 2.16 kg, and a density (JIS K6922-1) of 0.960 to 0.970 g / cm 3 of an ethylene polymer, and a melt flow rate (HLMFR) of 0.01 to 3 g / 10 minutes at 190 °C under a load of 21.6 kg, and a density of 0.920 to 0.940 g / cm 3It contains two components of an ethylene polymer, the weight ratio of the two components is 40:60 to 60:40, and it has the following properties (1) to (9). (1) The density is 0.940 to 0.955 g / cm 3 (2) The HLMFR is 1 to 15 g / 10 min (3) The ratio (Mw / Mn) of the weight-average molecular weight (Mw) to the number-average molecular weight (Mn) determined by gel permeation chromatography (GPC) is 8 to 15 (4) In the molecular weight distribution curve obtained using GPC, the component with a molecular weight of 1000 or less is 0.30% by weight or less (5) In the molecular weight distribution curve obtained using GPC, the component with a molecular weight of 100,000 or more is 35% by weight or more [[ID=!3) The environmental stress crack resistance (ESCR) is 1000 hours or more (7) 13 The number of short-chain branches with 4 or fewer carbon atoms per 1000 carbon atoms determined from the measurement of C-NMR is 3 or more (8) The content of the contained metal is 20 PPM or less with respect to the polyethylene resin (9) The Charpy impact strength retention rate after immersion in 70% nitric acid at 40 °C for 35 days is 50% or more The polyethylene resin for high-purity chemicals can be produced by a highly active catalyst such as a Ziegler catalyst or a metallocene catalyst. For example, a highly active Ziegler catalyst composed of a transition metal compound such as titanium or zirconium, a magnesium compound, and an organoaluminum compound is used as the polymerization catalyst, and ethylene or ethylene and an α-olefin having 3 to 20 carbon atoms are copolymerized at a ratio to achieve a desired density, whereby it can be preferably produced. The catalyst can be the catalyst described in Patent No. 3319051.

[0012] Examples of α-olefins having 3 to 20 carbon atoms include propylene, 1-butene, 4-methyl-1-pentene, 3-methyl-1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, and 1-eicosene.

[0013] The polymerization method used in the production of the polyethylene resin is slurry polymerization using a polymerization solvent with 6 to 10 carbon atoms, such as n-hexane or n-heptane, in order to keep the concentration of metal impurities eluted into the chemical low and to limit the incorporation of low-molecular-weight polymers into the resin, which can cause the generation of fine particles. The MFR is 10 to 40 g / 10 min and the density is 0.960 to 0.970 g / cm³. 3 This is a low molecular weight ethylene-based polymer with an HLMFR of 0.01-3 g / 10 min and a density of 0.920-0.940 g / cm³. 3 It consists of two components of a high molecular weight ethylene polymer, with a weight ratio of 40:60 to 60:40. The two components, a low molecular weight component and a high molecular weight component, can be produced, for example, by a two-stage polymerization method.

[0014] Furthermore, the polyethylene resin is specified as follows: density, HLMFR, molecular weight distribution (Mw / Mn), components with a molecular weight of 1000 or less, number of short-chain branches per 1000 carbon atoms, ESCR, and amount of contained metal.

[0015] In other words, the density of the polyethylene resin (JIS K6922-1) is 0.940 to 0.955 g / cm³. 3 The concentration is preferably 0.945 to 0.949 g / cm³. 3 It is 0.940 g / cm³. 3 Below this level, the amount of polymer components leaching into the chemicals in the container increases, leading to the generation of fine particles. Also, a density of 0.955 g / cm³ is considered excessive. 3 If it exceeds a certain level, the container's ESCR will decrease.

[0016] The HLMFR (JIS K6922-1) of the polyethylene resin is 1 to 15 g / 10 min, preferably 5 to 10 g / 10 min. Below 1 g / 10 min, the surface texture of the container deteriorates. Above 15 g / 10 min, the ESCR of the container decreases.

[0017] The Mw / Mn ratio of the polyethylene resin, determined by GPC, is between 8 and 15. If the Mw / Mn ratio is less than 8, the molecular weight distribution is narrow, the surface texture of the container deteriorates, and the ESCR of the container also decreases. If the Mw / Mn ratio exceeds 15, the molecular weight distribution expands, the low molecular weight components increase, and the amount of fine particles in the container increases. In addition, the shape of the pinch-off portion, which is the parison bond, deteriorates, and the drop strength of the container decreases.

[0018] In the molecular weight distribution curve obtained using GPC of the polyethylene resin, the component with a molecular weight of 1000 or less is 0.30% by weight or less. If the component with a molecular weight of 1000 or less exceeds 0.30% by weight, the low molecular weight component increases, and the number of fine particles leached from the container increases.

[0019] In the molecular weight distribution curve obtained using GPC of the polyethylene resin, the component with a molecular weight of 100,000 or more accounts for 35% by weight or more. When the component with a molecular weight of 100,000 or more accounts for 35% by weight or more, the chemical resistance is excellent. If the component with a molecular weight of 100,000 or more accounts for less than 35% by weight, the drop strength of the container decreases, and the probability of forming molecular chains (tie molecules) spanning two or more crystals of the polyethylene resin also decreases, resulting in a decrease in ESCR.

[0020] The ESCR of the polyethylene resin is 1000 hours or more. If the ESCR is less than 1000 hours, when a container with a capacity larger than 200L is filled with chemicals, such as surfactants, and left for more than 6 months, the container may break due to environmental stress cracking.

[0021] The polyethylene has three or more single-chain branches with four or fewer carbon atoms per 1000 carbon atoms. Having three or more single-chain branches provides excellent chemical resistance. If the number of short-chain branches is less than three, the probability of tie molecule formation and ESCR decrease. Furthermore, it is preferable that the short-chain branches are included in high molecular weight ethylene polymers with a molecular weight of 100,000 or more. If short-chain branches are included in low molecular weight ethylene polymers, they leach into chemicals, increasing the number of fine particles leached from the container.

[0022] The amount of metal contained in the polyethylene resin is 20 PPM or less relative to the polyethylene resin. If the amount of metal contained is 20 PPM or less, the amount of metal leaching into high-purity chemicals is small, thus suppressing the concentration of metal impurities in the chemicals. The amount of metal contained is expressed as the percentage of metal content relative to the total resin, expressed in weight PPM. The amount of metal contained is obtained by alkali dissolution after ashing the resin, and consists of residual substances such as Mg, Al, and Ti.

[0023] The Charpy impact strength retention rate of the polyethylene after immersion in 70% nitric acid at 40°C for 35 days is 50% or more compared to before immersion. Generally, polyethylene resin is susceptible to nitric acid, so degradation progresses quickly and its strength tends to decrease. If the Charpy impact strength retention rate after immersion at 40°C for 35 days is 50% or more, it can be used as a container without being damaged even when subjected to impact during transportation, etc.

[0024] Furthermore, it is preferable that the polyethylene resin contains no additives such as antioxidants, light stabilizers, and neutralizing agents. Here, neutralizing agents are fatty acid metal salts such as calcium stearate and zinc stearate, and hydrotalcites, all of which dissolve into the chemical and become metal contaminants, so it is preferable that they are not added.

[0025] The polyethylene resin can be molded into a container shape by blow molding to produce high-purity chemical containers. In particular, a blow molding method using a blow molding machine installed in a clean room and using air from which fine particles have been removed by a filter as the blow air is preferable for producing clean containers. The container shape and capacity are not specified, but in order to reinforce the barrier properties of the contents and the strength of the container, the resin may be used as the inner layer, and ethylene-vinyl alcohol copolymer, polyvinyl alcohol resin, and polyamide resin may be used as the intermediate layer, or FRP may be used as the outer layer for reinforcement.

[0026] When an unwashed container molded using the polyethylene resin is filled with ultrapure water, the number of fine particles 0.1 μm or larger that elute the contents is preferably 20 particles / mL or less after storage at 40°C for 35 days. If the number of fine particles 0.1 μm or larger is 20 particles / mL or less, it can accommodate the miniaturization of LSIs.

[0027] Examples of containers molded using this polyethylene resin include 1000L containers (Intermediate Bulk Containers: IBCs). Smaller containers include, for example, 200L drums and 20L industrial chemical cans. [Examples]

[0028] The present invention will be described below with reference to examples, but is not limited to these examples. The test methods used in the examples and comparative examples are as follows.

[0029] (1) Density The density was measured using the density gradient pipe method in accordance with JIS K6922-1.

[0030] (2) HLMFR Measurements were taken in accordance with JIS K6922-1, at 190°C and under a load of 21.6 kg.

[0031] (3) Mw / Mn Tosoh HLC-8321GPC / HT (Column: Tosoh TSKgel guardcolumnH)HR and TSKgelGMH HR The molecular weight was measured by GPC using -H) and 1,2,4-trichlorobenzene as the eluent. The molecular weight calibration curve was calibrated using polystyrene samples with known molecular weights.

[0032] (4) Components with a molecular weight of 1000 or less and 100000 or more The proportion of integrated amounts for components with molecular weights below 1000 and components with molecular weights above 100000 was calculated from the molecular weight distribution curve obtained by GPC measurement.

[0033] (5) Environmental stress crack resistance (ESCR) In accordance with JIS K6922-2, test specimens were immersed in a nonionic surfactant (10 wt% aqueous solution) at a temperature of 50°C, and the time at which the test specimen fractured with a 50% probability (F50 value) was measured.

[0034] (6) Number of short chain branches per 1000 carbon atoms Using the Bruker AVANCE600, 13 In the NMR spectrum obtained by 13C NMR measurement, the number of short-chain branches was calculated from the peak areas originating from methine carbons with 2-carbon branching groups and methine carbons with 4-carbon branching groups, with the sum of all peak areas having peak tops between 5 and 50 ppm set to 1000.

[0035] (7)Contained metal content The sample was ashed and then subjected to alkaline fusion to obtain a solution, which was used as the measurement solution. The amount of metal contained in the sample was measured by ICP-AES measurement using an Optima 8300.

[0036] (8) Charpy impact strength Test specimens were prepared in accordance with JIS K7111, and the specimens were immersed in 70% nitric acid at 40°C for 35 days. The impact strength of the test specimens after immersion was measured at an ambient temperature of 23°C, and the strength retention rate was determined by comparing it with the impact strength value before immersion. Specimens with a strength retention rate of 50% or more were marked with "○", and those with a strength retention rate of 50% or less were marked with "×".

[0037] (9) Blow molding Using a blow molding machine MSE-50E / 54M-A (manufactured by Tahara Corporation) with a 50mmΦ extrusion screw, parisons were continuously extruded from the die tip at a cylinder temperature of 180-190°C and a screw rotation speed of 16-18 revolutions per minute to form containers with an average wall thickness of 1 mm and an internal volume of 800 mL.

[0038] (10) Number of fine particles An 800 mL container with an internal volume obtained by blow molding a polyethylene resin composition was used. 600 mL of ultrapure water was filled into the unwashed container in a cleanroom at 23°C, the lid was closed, and the container was shaken 15 times. After 35 days of standing storage in a clean oven (Yamato Scientific Co., Ltd., DE411) at a set temperature of 40°C, the number of particles larger than 0.1 μm in the filled water was measured using a particle counter (Rion Co., Ltd., controller: KE-40B1, particle sensor: KS-42A). The number of particles in the water is expressed as particles / mL.

[0039] Example 1 <Manufacturing of Polyethylene A> In the first stage of a 370L continuous polymerizer, 110L / hour of dehydrated and purified hexane, 110 mmol / hour of triisobutylaluminum as an organoaluminum compound, 0.70 g / hour of a Ziegler-type solid catalyst component mainly composed of Mg, Al, Ti, and Cl prepared according to Japanese Patent Publication No. 7-41513, 24.0 kg / hour of ethylene, and hydrogen were supplied at a concentration ratio of 0.50 mol / mol to ethylene, while maintaining a temperature of 85°C and a total pressure of 30 kg / cm². 2 Under conditions of an average residence time of 3.4 hours, the first stage of ethylene polymerization (low molecular weight component) was carried out continuously. The MFR of the low molecular weight component was 20 g / 10 min, and the density was 0.970 g / cm³. 3 That was the case.

[0040] The hexane slurry containing the first-stage polymer was introduced into a 545L second-stage polymerizer after removing unreacted hydrogen and ethylene in a flash tank. While supplying an additional 45L / hour of hexane to this polymerizer, ethylene was supplied at 24.0 kg / hour, 1-butene at 8.1 kg / hour, and hydrogen at a concentration ratio of 0.020 mol / mol to ethylene, at a temperature of 80°C and a total pressure of 20 kPa / cm². 2 Ethylene polymerization (high molecular weight component) was carried out under conditions of an average residence time of 3.3 hours. The HLMFR of the high molecular weight component was 0.10 g / 10 min, and the density was 0.925 g / cm³. 3 The waste from the second polymerizer was flushed in a flash tank to remove unreacted hydrogen, ethylene, and 1-butene, then washed with hexane at 50 L / hour, followed by a drying process to obtain a mixture powder of ethylene copolymers. The proportion of low molecular weight components was 49% by weight, and the proportion of high molecular weight components was 51% by weight. The powder polymerized in the above two-stage process was pelletized without the addition of any additives to obtain polyethylene A. The results of the physical property measurements are shown in Table 1.

[0041] Polyethylene A was blow-molded, and the fine particle measurements described above were performed using the resulting container. The results are shown in Table 1.

[0042] Example 2 <Manufacturing of Polyethylene B> Polymerized powder was obtained by copolymerizing ethylene and butene-1 in hexane in the same manner as in Example 1, except that 1-butene was supplied to the second polymerizer at a rate of 8.5 kg / hour and hydrogen at a concentration ratio of 0.025 mol / mol to ethylene. The HLMFR of the high molecular weight component in the second polymerizer was 0.05 g / 10 min, and the density was 0.922 g / cm³. 3 The two-stage polymerized powder was pelletized without the addition of any additives to obtain polyethylene B. The results of the physical property measurements are shown in Table 1.

[0043] Polyethylene B was blow-molded, and the fine particle measurements described above were performed using the resulting container. The results are shown in Table 1.

[0044] Comparative Example 1 As polyethylene C, the following commercially available high-density polyethylene was used.

[0045] Tosoh Corporation, (product name) Nipolon Hard 8900 (HLMFR = 2.5g / 10 min, density = 0.954g / cm³) 3 ) Polyethylene C was blow-molded in the same manner as in the examples, and the number of particulate matter was measured. The physical properties of the resin and the evaluation results of the container are shown in Table 1.

[0046] Comparative Example 2 As polyethylene D, the following commercially available high-density polyethylene was used.

[0047] Tosoh Corporation, (product name) Nipolon Hard 8D01A (HLMFR = 8.0g / 10 min, density = 0.957g / cm³) 3 ) Polyethylene D was blow-molded, and the number of particulate matter particles was measured. The physical properties of the resin and the evaluation results of the container are shown in Table 1.

[0048] Comparative Example 3 As polyethylene E, the following commercially available high-density polyethylene was used.

[0049] Tosoh Corporation, (product name) Nipolon Hard 8022 (HLMFR = 25g / 10 min, density = 0.958g / cm³) 3 ) Polyethylene E was blow-molded, and the number of particulate matter particles was measured. The physical properties of the resin and the evaluation results of the container are shown in Table 1.

[0050] Comparative Example 4 <Preparation of Solid Catalyst Components> In a 3-liter glass flask equipped with a stirring device, 30.0 g (1.23 mol) of metallic magnesium powder and 168.0 g (0.494 mol) of titanium tetrabutoxide were placed. 192 g (2.59 mol) of n-butanol in which 1.5 g of iodine was dissolved was added over 2 hours at 90°C, and the mixture was stirred at 140°C for 2 hours under a nitrogen seal while removing the generated hydrogen gas. After reducing the temperature to 110°C, 26 g (0.125 mol) of tetraethoxysilane and 19 g (0.125 mol) of tetramethoxysilane were added, and the mixture was stirred at 140°C for another 2 hours. Then, 2.1 liters of hexane were added to obtain a homogeneous solution. This homogeneous solution was placed in a 10-liter stainless steel autoclave equipped with a stirring device. Maintaining the autoclave's internal temperature at 45°C, 800 ml of hexane solution containing 1.0 mole of diethylaluminum chloride and 0.5 moles of i-butylaluminum dichloride was added over 1 hour, and the mixture was stirred at 60°C for another hour to generate particles. After returning the temperature to 45°C, 1.04 kg (3.35 moles) of 50% hexane solution was added over 2 hours. After all components had been added, the mixture was stirred at 60°C for 1 hour to obtain a solid catalyst component. The obtained solid catalyst component was used as a hexane slurry to produce polyethylene F after removing any remaining unreacted materials and by-products using hexane.

[0051] <Production of Polyethylene F> In the first stage of a continuous polymerizer with an internal volume of 370 L, 110 L / hour of dehydrated and purified hexane, 110 mmol / hour of triisobutylaluminum as an organoaluminum compound, 0.4 g / hour of the above solid catalyst component, 25.4 kg / hour of ethylene, and hydrogen are supplied at a concentration ratio of 0.28 mol / mol to ethylene, while maintaining a temperature of 85°C and a total pressure of 30 kg / cm². 2 Under conditions of an average residence time of 3.4 hours, the polymerization of the first stage (low molecular weight component) was carried out continuously. The MFR of the low molecular weight component was 16 g / 10 min, and the density was 0.974 g / cm³. 3 That was the case.

[0052] The hexane slurry containing the first stage polymer was introduced into another continuous polymerizer with a volume of 545 liters after removing unreacted hydrogen and ethylene in a flash tank. Ethylene was added at a rate of 21.5 kg / hour, 1-butene at a rate of 0.8 kg / hour, hydrogen at a concentration ratio of 0.12 mol / mol / ethylene, at a temperature of 80°C, and a total pressure of 20 kg / cm², while an additional hexane of 45 L / hour was supplied to this polymerizer. 2 The second stage (high molecular weight component) polymerization was carried out under conditions of an average residence time of 3.3 hours. The density of the high molecular weight component was 0.940 g / cm³. 3 The waste from the second-stage polymerizer was removed in a flash tank to remove unreacted hydrogen, ethylene, and 1-butene, then washed with hexane at 50 L / hour, and subsequently dried to obtain an ethylene-based copolymer. The proportion of low molecular weight components was 50% by weight, and the proportion of high molecular weight components was 50% by weight. The powder polymerized in the above two-stage process was pelletized without the addition of any additives to obtain polyethylene F. The results of the physical property measurements are shown in Table 1.

[0053] Polyethylene F was blow-molded, and the number of particulate matter particles was measured. The physical properties of the resin and the evaluation results of the container are shown in Table 1.

[0054] [Table 1]

Claims

1. At 190°C and a 2.16 kg load, the melt flow rate (MFR) is 10–40 g / 10 min, and the density (JIS K6922-1) is 0.960–0.970 g / cm³. ３ The ethylene-based polymer and the melt flow rate (HLMFR) at 190°C and a 21.6 kg load are 0.01 to 3 g / 10 min, with a density of 0.920 to 0.940 g / cm³. ３ A high-purity polyethylene resin for chemical containers comprising two ethylene-based polymer components, wherein the weight ratio of the two components is 40:60 to 60:40, and having the following properties (1) to (9). (1) Density of 0.940–0.955 g / cm³ ３ (2) HLMFR 1-15 g / 10 min (3) The ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) (Mw / Mn) determined by gel permeation chromatography (GPC) is between 8 and 15. (4) In the molecular weight distribution curve obtained using GPC, the component with a molecular weight of 1000 or less is 0.30% by weight or less. (5) In the molecular weight distribution curve obtained using GPC, components with a molecular weight of 100,000 or more constitute 35% by weight or more. (6) Environmental stress crack resistance (ESCR) of 1000 hours or more (7) １３ The number of short-chain branches with 4 or fewer carbon atoms per 1000C of carbon atoms, as determined by C-NMR measurements, is 3 or more. (8) The amount of metal contained is 20 PPM or less relative to the polyethylene resin. (9) The Charpy impact strength retention rate after immersion in 70% nitric acid at 40°C for 35 days is 50% or more.

2. A polyethylene resin for high-purity chemical containers according to claim 1, which does not contain additives.

3. A high-purity chemical container made of polyethylene resin according to claim 1 or 2.

4. A container for high-purity chemicals according to claim 3, wherein the number of fine particles 0.1 μm or larger that leach from the contents of an unwashed container filled with ultrapure water after standing storage at 40°C for 35 days is 20 particles / mL or less.

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