JP2004331706A - High-density polyethylene resin and container using the same resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-density polyethylene resin having excellent moldability, high impact resistance and excellent smoothness of the surface of a molded product and a container composed of the resin and having surface smoothness of ≤10 μm average surface roughness and suitable as a large-sized high-purity medicine container having ≥50 L inner volume. <P>SOLUTION: The high-density polyethylene resin having characteristics of (a) 0.94-0.97 g/cm<SP>3</SP>density, (b) 1-15 g/10 min melt flow rate, (c) ≥160 mN melt tension, (d) ≤0.30 MPa shear stress and (e) ≥30 kJ/m<SP>2</SP>Charpy impact strength is used. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-density polyethylene resin having excellent moldability and high impact resistance. The invention further relates to a container suitable for use in high purity chemicals.
[0002]
[Prior art]
When a high-density polyethylene resin becomes a high molecular weight grade having a weight average molecular weight of about 200,000, it has a large melt tension, and also has excellent impact strength and environmental stress cracking time (ESCR). Is used for manufacturing industrial parts such as gasoline tanks and large hollow molded products such as industrial chemical cans and container containers.
[0003]
In recent years, with the remarkable development of the electronics industry, for example, with the large-scale integration of electronic circuits such as LSIs, the demand for high-purity chemicals has increased. Conventionally, polyethylene resin has been used as a material for these high-purity chemical containers from the viewpoint of chemical resistance, impact resistance, price, and the like.
[0004]
However, the conventional high-density polyethylene resin container has a problem in that the content of the chemical is contaminated due to the generation of contaminants such as elutes and degraded substances from the container resin, and is used as a high-purity chemical container. There was trouble on the above. Therefore, the development of a high-density polyethylene resin for a large container that can be used repeatedly without contaminating the filled high-purity chemical is awaited.
[0005]
In high-density polyethylene resins for large containers, it is required to simultaneously satisfy the problem of suppressing the generation of contaminants as well as the balance of flowability, moldability such as melt tension, and impact resistance. As an attempt to solve such a problem, for example, (1) a method of producing a polyethylene having a long chain branch using a Cr-based catalyst or a method of cross-linking a resin using an organic peroxide is used as a method for improving the melt tension. Although proposed, there arise problems such as Cr flowing out into the internal solution (for example, see Patent Literature 1) and insufficient impact strength (for example, see Patent Literature 2). (2) A method for improving mechanical properties using a metallocene catalyst developed in recent years has also been proposed. However, a large blow container is used because it contains a large amount of low molecular weight components in order to achieve both mechanical properties and molding characteristics. (For example, see Patent Document 3). (3) A composition composed of polyethylene having a narrow molecular weight distribution and polyethylene obtained by a high-pressure radical polymerization method (for example, see Patent Document 4), a composition of polyethylene obtained with a metallocene catalyst and polyethylene obtained with a Cr-based catalyst (for example, A method of combining two types of polyethylene has been proposed, such as a polyethylene composition obtained with a Ziegler-based catalyst and a polyethylene composition obtained with a Cr-based catalyst (for example, see Patent Document 6). The cleanliness tends to decrease due to the generation of contaminants from the container, such as an increase in metal species contained in the container.
[0006]
[Patent Document 1]
JP-A-11-80257 (page 2)
[Patent Document 2]
Japanese Patent Publication No. 2-52654 (page 2)
[Patent Document 3]
JP-A-2002-249518 (page 2)
[Patent Document 4]
JP-A-10-7848 (page 3)
[Patent Document 5]
Japanese Patent Application Laid-Open No. 2000-129045 (page 3)
[Patent Document 6]
JP-A-6-299909 (page 3)
[0007]
[Problems to be solved by the invention]
An object of the present invention is to provide a high-density polyethylene resin having excellent moldability, high impact resistance, and excellent surface smoothness of a molded article, and a container made of the resin.
[0008]
[Means for Solving the Problems]
The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by using a high-density polyethylene resin having specific properties, and have reached the present invention.
[0009]
That is, the present invention relates to a high-density polyethylene resin which satisfies the following requirements (a) to (e) and a container made of the resin.
(A) a density (JIS K6760-1981) of 0.94 to 0.97 g / cm ³ ,
(B) a melt flow rate at 190 ° C. under a load of 21.6 kg (JIS K7210-1976, condition 7) is 1 to 15 g / 10 min,
(C) Using a die having a length of 8 mm and a diameter of 2.095 mm, the melt tension at a stretching ratio of 2.4 to 24 at 190 ° C. of 160 mN or more,
(D) using a dice having a length of 20 mm and a diameter of 2 mm, the shear stress at 190 ° C. at a shear rate of 30.4 S ⁻¹ is not more than 0.30 MPa;
(E) The high-density polyethylene resin of the present invention will be described in more detail with a Charpy impact strength (JIS K7111) of 30 kJ / m ² or more.
[0010]
The high-density polyethylene resin of the present invention has a density (JIS K6760-1981) of 0.94 to 0.97 g / cm ³ . If the density is less than 0.94 g / cm ³ , the amount of the polymer component eluted into the drug solution in the container increases, causing the generation of fine particles, and is not suitable for high-purity chemical applications. On the other hand, when the density exceeds 0.97 g / cm ³ , the chemical resistance of the resin decreases, and the strength of the container decreases.
[0011]
The melt flow rate at 190 ° C. under a load of 21.6 kg (JIS K7210-1976, condition 7) (hereinafter referred to as “HLMFR”) is 1 to 15 g / 10 min. If the HLMFR is less than 1 g / 10 minutes, the fluidity of the resin at the time of molding decreases. If the HLMFR exceeds 15 g / 10 minutes, the drop strength of the resin molded article decreases.
[0012]
Using a die having a length of 8 mm and a diameter of 2.095 mm, the melt tension (hereinafter, referred to as “MT”) at a draw ratio of 2.4 to 24 at 190 ° C. is 160 mN or more. If the MT is less than 160 mN, the melt tension for supporting the weight of the parison during resin molding is low, and large blow molding is difficult. In addition, uneven thickness occurs in the molded body during molding, and the drop strength of the resin molded body is reduced.
[0013]
Using a die having a length of 20 mm and a diameter of 2 mm, a shear stress at 190 ° C. at a shear rate of 30.4 S ⁻¹ (hereinafter referred to as “σ _30.4 ”) is 0.30 MPa or less. I do. If σ _30.4 is higher than 0.30 MPa, the smoothness of the surface of the molded body is impaired.
[0014]
The Charpy impact strength (JIS K7111) is characterized by being 30 kJ / m ² or more. If the Charpy impact strength is less than 30 kJ / m ² , the impact resistance will be insufficient. Increasing the wall thickness of the container in order to improve impact resistance impairs economic efficiency.
[0015]
In order for the container using the resin according to the present invention to be suitably used as a large container for high-purity chemicals, it is desirable that the average surface roughness (Ra) of the resin molded product is 10 μm or less.
[0016]
The high-density polyethylene resin of the present invention is not particularly limited, and includes, for example, an ethylene homopolymer resin or an ethylene / α-olefin copolymer resin. Preferably, it is a copolymer resin of ethylene and an α-olefin having 3 to 20 carbon atoms, which satisfies the requirements (a) to (e) described above. Here, the α-olefin includes propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene and the like, and these may be used alone or in combination of two or more. be able to. Among these α-olefins, 1-butene, 1-pentene, 1-hexene, and 1-octene are particularly preferable in satisfying the above-mentioned requirements.
[0017]
The method for polymerizing the high-density polyethylene resin of the present invention is not particularly limited, and a method using a highly active Ziegler-based catalyst composed of a transition metal compound such as titanium or zirconium, a magnesium compound, and an organoaluminum compound, or a Cr-based polymerization catalyst The method used is mentioned. Among them, a method using a highly active Ziegler-based catalyst, in which the catalyst is highly active and the amount of the catalyst residue in the resin is small, that is, the amount of the elution to the chemical solution in the resin container is small, is desirable. The reaction method is not particularly limited, and examples thereof include a slurry polymerization method, a gas phase polymerization method, and a solution polymerization method. Among them, a saturated hydrocarbon-based polymerization medium having 6 to 10 carbon atoms can be used because the concentration of metal impurities eluted in the chemical solution can be suppressed low and the incorporation of a low-molecular polymer that causes fine particles into the resin can be restricted. For example, a slurry polymerization method using normal hexane, normal heptane, or the like is desirable. Furthermore, the high-density polyethylene resin of the present invention has a good balance of fluidity, melt tension, moldability, impact resistance, and the like of the resin, and in order to make the surface of the molded body excellent in smoothness. It is desirable to use a two-stage polymerization method which does not give a heat history and is economical in resin production. The reaction conditions when using the two-stage polymerization method are such that the first-stage polymerization temperature is 78 to 85 ° C., and the hydrogen / ethylene ratio in the solvent is in the range of 0.03 to 0.15 in molar ratio. It is preferable that the polymerization temperature in the second stage is 50 to 80 ° C., the hydrogen / ethylene ratio in the solvent is in the range of 0 to 0.01 in molar ratio, and the polymerization time in the first stage is The ratio of the second polymerization time (second polymerization time (min) / first polymerization time (min)) is preferably 0.05 to 0.5.
[0018]
When the high-density polyethylene resin of the present invention is used for a high-purity chemical container, additives and additives such as an antioxidant, a neutralizing agent, and a light-resistant stabilizer are preferably free of additives. May be added as long as it is within the allowable range of the molding conditions and the purity of the chemical solution to be filled.
[0019]
The antioxidant is desirably 800 ppm or less in order to prevent the antioxidant from being eluted into the chemical solution and causing the generation of fine particles. There is no particular limitation on the antioxidant used, and examples thereof include a phenolic antioxidant.
[0020]
The neutralizing agent is desirably 150 ppm or less in order to avoid elution into the chemical solution and causing the generation of fine particles. The neutralizing agent used is not particularly limited, and examples thereof include fatty acid metal salts and / or hydrotalcites.
[0021]
The method for molding a container using the high-density polyethylene resin of the present invention is not particularly limited, and examples thereof include known molding methods such as a blow molding method and a rotational molding method. Above all, a blow molding method is preferred from the viewpoint of ease of molding, and particularly, an accumulation molding method or a direct molding method is desirable.
[0022]
The molding temperature of the container is not lower than the melting temperature of the high-density polyethylene resin of the present invention and is preferably not higher than 250 ° C. Above all, the temperature is preferably from 180 to 200 ° C. in order to prevent the deterioration of the resin and keep the container clean. In addition, the clean room is molded under a nitrogen atmosphere in order to suppress the oxidation of the resin and maintain the skin condition of the molded product in good condition, and the air from which fine particles have been removed by a filter is used as blow air to prevent contamination by dust. It is preferable to perform molding or the like in the inside.
[0023]
Although the capacity and shape of the container using the high-density polyethylene resin of the present invention are not particularly limited, the container is preferably used for a container having an inner volume of 50 liters or more, and even 100 liters or more from its excellent moldability and impact resistance. desirable. The shape can be used not only as a normal drum type container, but also as an inner container of a 1 to 4 ton container container whose outside is surrounded by FRP, metal, or the like.
[0024]
Also, depending on the type of chemicals, it is necessary to make the container a light-shielding container. Is also good.
[0025]
【Example】
Hereinafter, the present invention will be described with reference to examples. However, these are merely examples, and the present invention is not limited to these examples.
[0026]
[A] the melt tension (MT), method of measuring shear stress (sigma _30.4) [melt tension (MT), the preparation of the shear stress (sigma _30.4) measurement sample]
To a high-density polyethylene resin, 6000 ppm of an antioxidant (trade name: Irganox B225, manufactured by Ciba Specialty Chemicals Co., Ltd.) was mixed with a batch mixer (trade name: Labo Plastomill 60 cc mixer, manufactured by Toyo Seiki Seisaku-sho, Ltd.) The mixture was kneaded for 5 minutes at a temperature of 180 ° C. and a mixer rotation speed of 20 rpm for 5 minutes.
[0027]
[Measurement of melt tension (MT)]
The prepared sample was evaluated using a capillary rheometer (manufactured by Toyo Seiki Seisaku-sho, Ltd., (trade name) Capillograph) (hereinafter referred to as “capillary rheometer”). The cylinder inner diameter was 9.55 mm, the die L / D was 8 / 2.095 (mm), the cylinder temperature was 190 ° C., the piston descending speed was 10 mm / min, and the stretching ratio was 2.4 to 24 when stretched. The tension was measured.
[0028]
[Measurement of shear stress (σ _30.4 )]
The prepared sample was evaluated with a capillary rheometer. When the inner diameter of the cylinder is 9.55 mm, the L / D of the die is 20/2 (mm), the cylinder temperature is 190 ° C., the apparent shear rate is 30.4 S- ¹ , and the tip of the piston is 20 cm from the die inlet. Was measured.
[0029]
[B] Measurement of Surface Smoothness of Molded Product A high-density polyethylene resin was subjected to the same heat treatment as in an actual molding machine using a batch mixer without adding an antioxidant (temperature: 180 ° C., mixer rotation speed: 1 rpm, time: 30 minutes).
[0030]
Immediately after the heat treatment, 6000 ppm of an antioxidant (Irganox B225, trade name, manufactured by Ciba Specialty Chemicals) was added, and the mixture was further kneaded at 20 rpm for 5 minutes. The resin prepared by this method was used as a sample for measuring surface smoothness.
[0031]
The surface smoothness was evaluated by "low speed extrusion" and "high speed extrusion". The low-speed extrusion was carried out using a capillary rheometer, the inner diameter of the cylinder was 9.55 mm, the L / D of the die was 20/2 (mm), the apparent shear rate was 30.4 S ⁻¹ , and the cylinder temperature was 190 ° C. High-speed extrusion uses a capillary rheometer, the cylinder inner diameter is 9.55 mm, the die L / D is 20/2 (mm), the apparent shear rate is 300 to 760 S ^-1 , and the cylinder temperature is 190 ° C. did.
[0032]
After the extruded molten resin was gradually cooled at room temperature, the unevenness of the resin surface was measured by Surftest-402 manufactured by Mitutoyo, and the average value was defined as the average surface roughness (Ra).
[0033]
In high-speed extrusion, those having an average surface roughness (Ra) of 10 μm or less were regarded as having good smoothness, and those having a mean roughness of more than 10 μm were regarded as having poor smoothness.
[0034]
Example 1
(1) Preparation of solid catalyst component (A) In a 10-liter stainless steel autoclave equipped with a stirring device, 108.2 g (1.80 mol) of i-propanol and 134.6 g (1.82 mol) of n-butanol were added. 2.0 g of iodine, 40 g (1.65 mol) of metal magnesium powder and 224.1 g (0.66 mol) of titanium tetrabutoxide were added thereto, and 2.1 liter of hexane was further added, followed by heating to 80 ° C. Then, the mixture was stirred for 1 hour under a nitrogen seal while removing generated hydrogen gas. Subsequently, the temperature was raised to 120 ° C., and the reaction was carried out for 1 hour to obtain a homogeneous solution containing Mg and Ti. While maintaining the internal temperature of the autoclave at 45 ° C., 1.32 kg (3.3 mol) of a 30% hexane solution of diethylaluminum chloride was added over 1 hour. After adding all, the mixture was stirred at 60 ° C. for 1 hour. Next, 197.0 g of methylhydropolysiloxane (viscosity of about 30 centistokes at 25 ° C., containing 3.3 g atom of silicon) was added, and the mixture was reacted under reflux for 1 hour. After cooling to 45 ° C., 2.81 kg (9.1 mol) of a 50% hexane solution of i-butylaluminum dichloride was added over 2 hours. After adding all, the mixture was stirred at 70 ° C. for 1 hour to obtain a solid catalyst component (A). The obtained solid catalyst component (A) was used as a normal hexane slurry in the next polymerization step after removing remaining unreacted substances and by-products using normal hexane.
[0035]
(2) The inside of a stainless steel electromagnetic stirring type autoclave having a polymerization inner volume of 10 liters was sufficiently replaced with nitrogen, 6 liters of normal hexane was charged, and the internal temperature was adjusted to 80 ° C. Thereafter, a slurry containing 160 mg of triisobutylaluminum as the catalyst component (B) and 17.9 mg of the solid catalyst component (A) obtained above was sequentially added. After adjusting the internal pressure of the autoclave to 0.1 MPa, hydrogen was added by a pressure of 0.6 MPa, and then the reaction was carried out for 1 hour while continuously adding ethylene so that the total pressure in the autoclave became 1.3 MPa. Was polymerized. At this time, the hydrogen / ethylene ratio in the first-stage solvent was 0.12 in molar ratio. After the completion of the first-stage polymerization, the system was cooled to 60 ° C. and sufficiently purged with nitrogen gas to drive off unreacted gas. Next, after adjusting the internal temperature to 65 ° C. and the internal pressure of the autoclave to 0.1 MPa, hydrogen was added by a pressure of 0.005 MPa, and then ethylene was continuously added so that the total pressure in the autoclave became 0.705 MPa. The mixture was reacted for 9 minutes to perform the second polymerization. At this time, the hydrogen / ethylene ratio in the solvent in the second stage was 0.001 in molar ratio. After the completion of the polymerization, the system was cooled, unreacted gas was expelled, polyethylene was taken out, separated from the solvent by filtration and dried.
[0036]
The resin obtained by the above method had a density of 0.960 g / cm ³ , an HLMFR of 4.2 g / 10 min, an MT of 490 mN, a σ _30.4 of 0.29 MPa, and a Charpy impact strength of 67 kJ / m ^2. Was.
[0037]
When the surface smoothness of the molded article was measured using the obtained resin, the appearance of high-speed extrusion was good, and the average surface roughness (Ra) of low-speed extrusion was 2.6 μm.
[0038]
Comparative Example 1
Using the same solid catalyst component (A) as in Example 1, polymerization was carried out by the following method. The inside of a stainless steel electromagnetic stirring type autoclave having an internal volume of 10 liters was sufficiently replaced with nitrogen, 6 liters of hexane was charged, and the internal temperature was adjusted to 80 ° C. Thereafter, a slurry containing 160 mg of triisobutylaluminum as the catalyst component (B) and 24 mg of the solid catalyst component (A) obtained above was sequentially added. After adjusting the internal pressure of the autoclave to 0.1 MPa, hydrogen was added by a pressure of 0.6 MPa, and then the reaction was carried out for 50 minutes while continuously adding ethylene so that the total pressure in the autoclave became 1.3 MPa. Was polymerized. At this time, the hydrogen / ethylene ratio in the first-stage solvent was 0.12 in molar ratio. After the completion of the first-stage polymerization, the system was cooled to 60 ° C. and sufficiently purged with nitrogen gas to drive off unreacted gas. Next, after adjusting the internal temperature to 80 ° C. and the internal pressure of the autoclave to 0.1 MPa, hydrogen was added at a pressure of 0.01 MPa, and then ethylene was continuously added so that the total pressure in the autoclave became 0.71 MPa. The reaction was allowed to proceed for 30 minutes to perform the second stage polymerization. At this time, the hydrogen / ethylene ratio in the solvent in the second stage was 0.002 in molar ratio. After the completion of the polymerization, the system was cooled, unreacted gas was expelled, polyethylene was taken out, separated from the solvent by filtration and dried.
[0039]
The resin obtained by the above method had a density of 0.960 g / cm ³ , an HLMFR of 1.5 g / 10 min, an MT of 490 mN, a σ _30.4 of 0.40 MPa, and a Charpy impact strength of 78 kJ / m ^2. Was.
[0040]
When the surface smoothness of the molded article was measured using the obtained resin, the appearance of high-speed extrusion was poor, the average surface roughness (Ra) of low-speed extrusion was 22 μm, and the surface smoothness of the molded article was poor. I was
[0041]
【The invention's effect】
According to the present invention, a high-density polyethylene resin having excellent moldability, high impact resistance, and excellent surface smoothness of a molded article required for a container for high-purity chemicals, and a high-purity chemical resin comprising the resin Is obtained.

Claims (3)

A high-density polyethylene resin that satisfies the following requirements (a) to (e).
(A) a density (JIS K6760-1981) of 0.94 to 0.97 g / cm ³ ,
(B) a melt flow rate at 190 ° C. under a load of 21.6 kg (JIS K7210-1976, condition 7) is 1 to 15 g / 10 min,
(C) Using a die having a length of 8 mm and a diameter of 2.095 mm, the melt tension at a draw ratio of 2.4 to 24 at 190 ° C. of 160 mN or more,
(D) Using a die having a length of 20 mm and a diameter of 2 mm, the shear stress at 190 ° C. at a shear rate of 30.4 S ⁻¹ is 0.30 MPa or less;
(E) Charpy impact strength (JIS K7111) of 30 kJ / m ² or more A high-density polyethylene resin composition comprising the high-density polyethylene resin according to claim 1 and 800 ppm or less of an antioxidant. A container comprising the high-density polyethylene resin or the resin composition according to claim 1.