JP7056304B2 - Polyethylene for high-purity chemical containers and high-purity chemical containers - Google Patents

Description

The present invention relates to polyethylene for high-purity chemical containers, and is particularly suitable for large-sized high-purity chemical containers. The present invention relates to polyethylene for high-purity chemical containers and high-purity chemical containers having excellent environmental stress crack resistance (ESCR).

In recent years, plasticization of various containers has been actively promoted for the purpose of weight reduction and energy saving. As the plastic material, a polyolefin resin is generally used from the viewpoints of high strength, high weather resistance, high chemical resistance, environmental problems and the like. Among the polyolefin resins, polyethylene resin is particularly suitable as various molding resins. However, cleaner polyethylene resins are required for the use of containers filled with high-purity contents. In particular, in polyethylene resins for pharmaceutical containers, reagent containers, and high-purity chemical containers for semiconductors, cleaner polyethylene resins are required from the viewpoint of the purity of the contents to be filled, and the number of additives is reduced. In addition to being required to be additive-free, it is also necessary that the amount of ash derived from the polymerization catalyst and the like is small.
In particular, in the field of semiconductor manufacturing, various cleaning liquids and high-purity chemicals such as hydrofluoric acid and hydrogen peroxide are used in processes such as wafer cleaning and etching. The demand for reduction of impurities and fine particles in chemicals is becoming more stringent, and in order to satisfy this demanding demand, the demand for cleaning the containers filled with these chemicals is increasing year by year. In addition to the above demands, there are increasing demands for larger containers filled with these chemicals and higher durability.

As a method for solving this problem, Patent Document 1 (Japanese Unexamined Patent Publication No. 11-080257) has a density of 0.94 to 0.97 g / cm ³ , a temperature of 190 ° C., and a melt flow rate of a load of 21.6 kg. ~ 50g / 10 minutes, ratio (Mw / Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) determined by gel permeation chromatography (GPC) is 8 to 15, boiling normal hexane extraction amount is 0. A polyethylene resin for high-purity chemical containers having properties of 1% by weight or less and a chlorine content of 15 PPM or less with respect to the polyethylene resin has been proposed, but it is said that the improvement against the influence of the metal component derived from the polymerization catalyst component is sufficient. This does not mean that a satisfactory high-purity chemical container can be obtained.

According to Patent Document 2 (Japanese Unexamined Patent Publication No. 11-08258), the density is 0.935 to 0.97 g / cm ³ , the temperature is 190 ° C., and the melt flow rate under a 21.6 kg load is 2 to 100 g / 10 minutes, from GPC. A high-purity chemical container having the properties that the ratio (Mw / Mn) of the required weight average molecular weight (Mw) to the number average molecular weight (Mn) is 1.5 to 5, the ash content is 50 PPM or less, and the chlorine content is 5 PPM or less. Polyethylene resin for use has been proposed, but the improvement against the influence of the metal component derived from the polymerization catalyst component is not sufficient, and the moldability is not always good due to the small Mw / Mn, and a satisfactory high-purity chemical container is provided. It does not mean that you can get it.

According to Patent Document 3 (Japanese Unexamined Patent Publication No. 11-08449), the density is 0.94 to 0.97 g / cm ³ , the temperature is 190 ° C., and the melt flow rate under a 21.6 kg load is 1 to 15 g / 10 minutes, from GPC. The ratio (Mw / Mn) of the required weight average molecular weight (Mw) to the number average molecular weight (Mn) is 8 to 15, the melt tension at 190 ° C. is 15 to 65 g, and the amount of boiling normal hexane extracted is 0.1% by weight or less. A polyethylene resin for a large high-purity chemical container having a property of having an ash content of 50 PPM or less has been proposed, but the improvement against the influence of the metal component derived from the polymerization catalyst component is not sufficient, and it is manufactured by a two-stage polymerization method. The characteristics of the components are not specific, and it does not necessarily mean that a satisfactory high-purity chemical container can be obtained.

According to Patent Document 4 (Japanese Unexamined Patent Publication No. 2000-129044), the density is 0.945 g / cm ³ or more and 0.975 g / cm ³ or less, and I ₂ is 0.05 g / 10 min or more and 30 g / 10 min or less. A high-purity chemical comprising a polyethylene composition consisting of 99 to 1 wt% polyethylene having specific properties produced by a metallocene catalyst by a slurry polymerization method and 1 to 99 wt% polyethylene having specific properties produced by a chromium catalyst by a slurry polymerization method. Although a container for use has been proposed, improvement in the influence of the metal component derived from the polymerization catalyst component is not sufficient, and it is not always possible to obtain a satisfactory high-purity chemical container.

According to Patent Document 5 (Japanese Unexamined Patent Publication No. 2003-096133), the melt flow rate measured at a density of 0.95 to 0.97 g / cm ³ , a temperature of 190 ° C. and a load of 2.16 kg is 0.1 to 1 g / cm. 10 minutes, ash content is 15 ppm or less, storage elastic modulus G'determined by dynamic viscoelastic measurement (temperature 190 ° C., strain amount 10%) and loss elastic modulus G'are equal. A polyethylene resin for a high-purity chemical container characterized by having a property of G ₀ of 300,000 to 540000 dyn / cm ² has been proposed, but there is room for improvement in the long-term low elution of fine particle components.

Patent Document 6 (Japanese Unexamined Patent Publication No. 2008-179799) describes a polyethylene resin composition produced by a cheegler catalyst by a multi-stage polymerization method consisting of at least a low molecular weight component and a high molecular weight component, wherein the low molecular weight component is used. However, the single weight of polyethylene having a melt flow rate (JIS K7210-1999, code D) of 3 g / 10 minutes or more and 50 g / 10 minutes or less and a density (JIS K7112-1999) of 960 kg / m ³ or more and 974 kg / m ³ or less. A combined or a polymer of ethylene and an α-olefin having 3 or more and 20 or less carbon atoms, wherein the high molecular weight component has a mass fraction of 0.40 or more and 0.46 or less with respect to the polyethylene resin composition. The polyethylene resin composition has a density (JIS K7112-1999) of 955 kg / m ³ or more and 965 kg / m ³ or less, and a melt flow rate (JIS K7210-1999, code T) of 0.40 g / 10 minutes or more and 1.0 g / 10. A polyethylene resin composition for a large high-purity chemical container, which is less than a minute and is substantially free of additives and has excellent rough skin during molding, has been proposed. However, a metal derived from a polymerization catalyst component has been proposed. Improvements to the effects of the ingredients are not sufficient, and verification of rough skin during molding is limited to 2L small containers, and studies on large containers that are prone to sharkskin have not been conducted, so large and satisfactory. It does not mean that you can obtain a high-purity chemical container.

In Patent Document 7 (Japanese Unexamined Patent Publication No. 2010-242077), it is a linear polyethylene and comprises an ethylene homopolymer or an ethylene unit and one or two or more kinds of α-olefin units having 3 to 20 carbon atoms. It is a copolymer, has a density of 940 to 975 kg / m ³ , a melt flow rate of 0.1 to 20 g / 10 minutes at a temperature of 190 ° C. and a load of 2.16 kg, and Mw / Mn obtained by GPC. The occupancy of the components having a molecular weight of 1,000 or less obtained from the molecular weight distribution curve obtained by GPC is 3.0 to 7.0, and the occupancy rate is 1.0% by weight or less, which is obtained from the molecular weight distribution curve obtained by GPC. The occupancy rate of the component having a molecular weight of 1 million or more is 0.5% by weight or less, the melting point peak of the heat absorption curve obtained by the temperature rise measurement by the differential scanning calorimeter is one, and the normal heptane extraction at 80 ° C. Proposed polyethylene for high-purity chemical containers is characterized in that the amount of the fraction is 1.0% by weight or less and the amount of hydrocarbon components having 18 and 20 carbon atoms by extraction with ethanol is 100 ppm or less. The improvement against the influence of the metal component derived from the polymerization catalyst component is not sufficient, and the moldability is not always good because Mw / Mn is small, and it does not mean that a satisfactory high-purity chemical container can be obtained.

Patent Document 8 (Japanese Unexamined Patent Publication No. 2015-183130) describes a high-purity chemical having a density of 0.940 to 0.960 g / cm ³ , an HLMFR of 5 to 15 g / 10 minutes, and a specific molecular weight. Polyethylene for containers has been proposed. However, it does not mean that a satisfactory high-purity chemical container can be obtained.

Patent Document 9 (Japanese Unexamined Patent Publication No. 2004-331706) describes a high-purity chemical having a density of 0.94 to 0.97 g / cm ³ , an HLMFR of 1 to 15 g / 10 minutes, and a specific molecular weight. Polyethylene for containers has been proposed, but it has extremely high melt tension and excellent drawdown resistance, but it has poor fluidity and dischargeability is not always good, and surface smoothness is also subject to certain evaluation conditions. Although the smoothness is excellent, the sharkskin suppressing effect in molding a large molded product is not always good, and it does not mean that a satisfactory high-purity chemical container can be obtained.

Japanese Unexamined Patent Publication No. 11-080257 Japanese Unexamined Patent Publication No. 11-080258 Japanese Unexamined Patent Publication No. 11-080449 Japanese Unexamined Patent Publication No. 2000-129044 Japanese Patent Application Laid-Open No. 2003-096133 Japanese Unexamined Patent Publication No. 2008-179799 Japanese Unexamined Patent Publication No. 2010-242077 JP-A-2015-183130 Japanese Unexamined Patent Publication No. 2004-331706

An object of the present invention is that there are few fine particles derived from polyethylene resin and metal elution components derived from a polymerization catalyst component into the contents stored and stored, and the moldability such as drawdown resistance and ejection property at the time of molding is excellent. Moreover, it is an object of the present invention to provide polyethylene for a high-purity chemical container having an excellent balance of ESCR / cleanliness and a high-purity chemical container formed by molding the polyethylene. In particular, it is an object of the present invention to provide polyethylene for a container, which is less likely to generate sharkskin, which is often a problem in molding a large container, and has a small amount of fine particles eluted over a long period of time with respect to the filled chemical solution.

As a result of diligent research to solve the above problems, the present inventor has found that when polyethylene having a specific polymer physical characteristic is used, the amount of fine particles derived from polyethylene and the metal elution component derived from the polymerization catalyst component is small, and the moldability and ESCR We have found that a large-sized high-purity chemical container excellent in quality can be obtained, and have reached the present invention.

The polyethylene for a high-purity chemical container of the present invention has an ethylene polymer (A) of 25 to 49% by mass having a density (d) of 0.930 to 0.950 g / cm ³ and an HLMFR of 0.1 to 2 g / 10 minutes. And the ethylene polymer (B) having a density (d) of 0.960 to 0.970 g / cm ³ , a temperature of 190 ° C., and a melt flow rate (MFR) of 1 to 50 g / 10 min measured at a load of 2.16 kg. ) 51 to 75% by mass as an essential component, and has the following characteristics (1) to (7).
(1) The density (d) is 0.950 to 0.965 g / cm ³ .
(2) The melt flow rate (HLMFR) measured at a temperature of 190 ° C. and a load of 21.6 kg is 5 to 20 g / 10 minutes.
(3) The Charpy impact strength measured at −20 ° C. is 7 kJ / m ² or more.
(4) The melt tension (MT) measured at 210 ° C. is 80 mN or more.
(5) The constant strain ESCR is 40 hours or more.
(6) The amount of normal hexane extracted is 0.20% by mass or less.
(7) The ash content is 20 mass ppm or less.

It is preferable that the polyethylene of the present invention further satisfies the following property (8).
(8) The tan δ at 190 ° C. and 0.01 rad / sec measured by a rheometer is 1.00 to 1.60.

It is preferable that the polyethylene of the present invention further satisfies the following property (9).
(9) The extensional viscosity (ηe) (unit: Pa · s) and the shear viscosity (ηs) (unit: Pa · s) measured by the rheometer satisfy the following relational expression (A).
ηe ≧ 16.5 × ηs ^0.980 Equation (A)

It is preferable that the polyethylene of the present invention further satisfies the following property (10).
(10) The ratio (ηe / ηs) of the extensional viscosity (ηe) (unit: Pa · s) and the shear viscosity (ηs) (unit: Pa · s) measured by the rheometer is 13.5 to 21.0. be.

It is preferable that the polyethylene of the present invention further satisfies the following property (11).
(11) The extensional viscosity (ηe) (unit: Pa · s) measured by a rheometer is 60,000 to 100,000.

It is preferable that the polyethylene of the present invention further satisfies the following property (12).
(12) The number of fish eyes having a diameter of 0.2 mm or more is 150 / 0.02 m ² or less.

It is preferable that the polyethylene of the present invention further satisfies the following property (13).
(13) 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 more than 7.0 and 15.0 or less.

It is preferable that the polyethylene of the present invention further satisfies the following property (14).
(14) No phosphorus-based antioxidant is added.

The high-purity chemical container of the present invention is characterized by being a polyethylene molded product for the high-purity chemical container.

The high-purity chemical container of the present invention preferably has an internal volume of 5 L to 1000 L.

The polyethylene of the present invention has few fine particles derived from polyethylene resin and metal elution components derived from a polymerization catalyst component, is excellent in moldability such as drawdown resistance and ejection property at the time of molding, and is excellent in ESCR. It can be made of polyethylene for a pure chemical container, and a high-purity chemical container having an excellent balance of ESCR / cleanliness can be molded without adding an additive. Further, the polyethylene of the present invention is particularly suitable for a large container, sharkskin, which is often a problem in molding a large container, is unlikely to occur, and the amount of fine particles eluted from the filled chemical solution over a long period of time. It is possible to provide a large high-purity chemical container with a small size.

It is a graph which shows the relationship between the extensional viscosity (ηe) and the shear viscosity (ηs). The solid line in the graph shows the lower limit of the extensional viscosity (ηe) specified by the relational expression (A) relating to the extensional viscosity (ηe) and the shear viscosity (ηs) of the characteristic (9). It is a graph which shows the relationship between the ratio of extensional viscosity (ηe) and shear viscosity (ηs), and HLMFR.

Hereinafter, the polyethylene of the present invention and its uses will be described in detail for each item. Further, in the present specification, "-" indicating a numerical range is used in the sense that the numerical values described before and after the numerical range are included as the lower limit value and the upper limit value.

1. 1. Characteristics of Polyethylene The polyethylene for high-purity chemical containers of the present invention has an ethylene polymer (A) 25 to a density (d) of 0.930 to 0.950 g / cm ³ and an HLMFR of 0.1 to 2 g / 10 minutes. Ethylene weight with a melt flow rate (MFR) of 1 to 50 g / 10 min, measured at 49% by mass, a density (d) of 0.960 to 0.970 g / cm ³ , a temperature of 190 ° C. and a load of 2.16 kg. It is characterized by containing 51 to 75% by mass of the combined product (B) as an essential component and having the following characteristics (1) to (7).
(1) The density (d) is 0.950 to 0.965 g / cm ³ .
(2) The melt flow rate (HLMFR) measured at a temperature of 190 ° C. and a load of 21.6 kg is 5 to 20 g / 10 minutes.
(3) The Charpy impact strength measured at −20 ° C. is 7 kJ / m ² or more.
(4) The melt tension (MT) measured at 210 ° C. is 80 mN or more.
(5) The constant strain ESCR is 40 hours or more.
(6) The amount of normal hexane extracted is 0.20% by mass or less.
(7) The ash content is 20 mass ppm or less.

The polyethylene of the present invention has a composition having the above-mentioned components and a blending ratio, so that the amount of fine particles derived from the polyethylene resin and the metal elution component derived from the polymerization catalyst component is small, and the draw-down resistance and ejection property at the time of molding are improved. Since it has excellent moldability and ESCR, it can be used as polyethylene for high-purity chemical containers, and it is possible to mold high-purity chemical containers with an excellent balance of ESCR / cleanliness without adding additives. can.
Further, the polyethylene of the present invention is particularly suitable for a large container, sharkskin, which is often a problem in molding a large container, is unlikely to occur, and the amount of fine particles eluted from the filled chemical solution over a long period of time. It is possible to provide a large high-purity chemical container with a small size.
The sharkskin specified here is Rheol. Acta, 2003, 42, p. 544-556, POLYMER ENGINEERING AND SCIENCE, 2012, 52, p. 1968-1977, and POLYMER ENGINEERING AND SCIENCE, MARCH 2002, Vol. 42, No. 3, p. It is a kind of flow instability phenomenon defined in 611-633 and the like, and it tends to occur when the relaxation time distribution is narrow, and it tends to occur when the viscosity is high. It is also known that it depends on the molding conditions, and it tends to occur in high-speed molding, especially in the molding of large containers.
Sharkskin can be suppressed by widening the molecular weight distribution of polyethylene and widening the relaxation time distribution. Further, in molding, which can be suppressed by high-temperature molding and low-speed molding, there are problems that the resin deteriorates and the molding cycle is lowered.
The polyethylene of the present invention has a composition of an ethylene polymer (B) rather than an ethylene polymer (A) in terms of the composition ratio of the ethylene polymer (A) which is a high molecular weight component and the ethylene polymer (B) which is a low molecular weight component. By appropriately increasing the ratio as in the above range, the relaxation time distribution is appropriately widened, and the difference in viscosity between the ethylene polymer (A) and the ethylene polymer (B) becomes too large for the fish eye. The increase can be suppressed, the generation of sharkskin can be suppressed, and the deterioration of the resin and the deterioration of the molding cycle can be suppressed.

The polyethylene of the present invention is a material suitable for a high-purity chemical container, and is suitable for a hollow container having an internal volume of preferably 5 L to 1000 L, more preferably 10 L to 1000 L, and further preferably 20 L to 300 L. The high-purity chemical container is a container for storing chemicals with few impurities used in semiconductor manufacturing processes and the like.
The polyethylene for a high-purity chemical container of the present invention comprises an ethylene homopolymer or a copolymer of ethylene and another α-olefin, and the α-olefin is an α-olefin having 3 to 20 carbon atoms, for example, propylene. , 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, 1-nonen, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene and the like are preferable. 1-butene, 1-hexene, and more preferably 1-butene. These may be used alone or in combination of two or more.

The polyethylene of the present invention is obtained by polymerizing with a highly active catalyst such as a Ziegler-type catalyst or a metallocene catalyst, but polymerization with a highly active Ziegler-type catalyst is preferable. Examples of solid catalyst components in Ziegler-type catalysts include catalyst components in which titanium trichloride, vanadium trichloride, titanium tetrachloride or titanium haloalcolate is carried on a magnesium compound, and co-precipitates or eutectic compounds of magnesium compounds and titanium compounds. Examples thereof include catalyst components composed of the above. Among these, a solid catalyst component containing magnesium and titanium is preferable, and a catalyst system composed of a combination of the solid catalyst component and an organoaluminum compound is preferable.

Further, as the polymerization catalyst of the polyethylene of the present invention, the general formula Mg (OR ² ) _m X ² _2-m (in the formula, R ² represents an alkyl, aryl or cycloalkyl group, and X ² represents a halogen atom. The compound represented by m is 1 or 2) and the general formula Ti (OR ³ ) _n X ³ _4-n (in the formula, R ³ represents an alkyl, aryl or cycloalkyl group, and X ³ represents a halogen atom. A homogeneous hydrocarbon solution containing the compound represented by (where n is 1, 2 or 3) is represented by the general formula AlR ¹ _l X ¹ _3-l (where R ¹ is an alkyl, aryl or cycloalkyl group). , X ¹ represents a halogen atom, and l represents a number of 1 ≦ l ≦ 2), which comprises a hydrocarbon-insoluble solid catalyst obtained by treatment with an organic halogenated aluminum compound and an organic aluminum compound. It is preferably a catalyst, and more preferably m = 2 and n = 3.

Examples of the polymerization method in polyethylene production using the above polymerization catalyst system include a slurry polymerization method, a gas phase polymerization method, and a solution polymerization method. Among them, a slurry polymerization method using a polymerization solvent having 4 to 10 carbon atoms, for example, isobutane, isopentane, normal hexane, normal heptane, etc. is preferable, and it is preferable to adopt a multi-stage polymerization method by this polymerization method.
In the ethylene polymer obtained by the above polymerization method, it is preferable to remove polyethylene (wax) having a low molecular weight dissolved in the solvent. Examples of the method for removing the wax include removal by a centrifuge, removal by washing with a solvent, and the like. By removing the wax, it is possible not only to suppress the stain on the molding machine due to the wax derived from the molding process, but also to suppress the elution of the wax from the molded product.

Hereinafter, the characteristics of the polyethylene of the present invention will be described.

(1) Density (d)
The polyethylene of the present invention has a lower limit of 0.950 g / cm ³ or more, preferably 0.951 g / cm ³ or more, more preferably 0.952 g / cm ³ or more, and an upper limit of 0. .965 g / cm ³ or less, preferably 0.963 g / cm ³ or less, more preferably 0.960 g / cm ³ or less. When the density is 0.950 g / cm ³ or more, the amount of the polymer component eluted from the molded container into the filling internal solution is reduced, and the cleanliness of the internal solution is improved and the rigidity is improved. Further, when the density is 0.965 g / cm ³ or less, the impact resistance of the container is improved and the ESCR is improved.
The density can be measured according to JIS-K6922-1, 2: 1997.
The desired density can be obtained by changing the density depending on the type and amount of the comonomer to be copolymerized with ethylene.

(2) Melt flow rate (HLMFR) measured at a temperature of 190 ° C. and a load of 21.6 kg.
The polyethylene of the present invention has a lower limit of 5 g / 10 minutes or more, preferably 6 g / 10 minutes or more, and more preferably 7 g / 10 minutes or more in terms of melt flow rate (HLMFR) measured at a temperature of 190 ° C. and a load of 21.6 kg. It is even more preferably more than 9 g / 10 minutes, particularly preferably 12 g / 10 minutes or more, and the upper limit is 20 g / 10 minutes or less, preferably 18 g / 10 minutes or less, and more preferably 16 g / 10 minutes or less. ..
When the HLMFR is 5 g / 10 minutes or more, the fluidity is improved, the discharge performance is improved, and the productivity of the container is improved. Further, when it is 20 g / 10 minutes or less, the draw-down resistance is improved, the container moldability is improved, and the ESCR is improved.
HLMFR can be measured in accordance with JIS-K6922-2: 1997. The HLMFR can be adjusted by adjusting the ethylene polymerization temperature, the use of a chain transfer agent, or the like, and a desired one can be obtained. That is, by raising the polymerization temperature of ethylene and α-olefin, the HLMFR can be increased as a result of lowering the molecular weight, and by lowering the polymerization temperature, the HLMFR can be lowered as a result of raising the molecular weight. Can be done. Further, in the copolymerization reaction between ethylene and α-olefin, the HLMFR can be increased as a result of lowering the molecular weight by increasing the amount of hydrogen to coexist (the amount of chain transfer agent), and the amount of hydrogen to coexist (the amount of hydrogen to coexist). By reducing the amount of chain transfer agent), the HLMFR can be reduced as a result of increasing the molecular weight.

(3) Sharpy impact strength measured at -20 ° C The polyethylene of the present invention has a lower limit of the Sharpy impact strength measured at -20 ° C of 7 kJ / m ² or more, preferably 10 kJ / m ² or more, more preferably. It exceeds 13 kJ / m ² , and even more preferably 14 kJ / m ² or more. When the Charpy impact strength is 7 kJ / m ² or more, the impact resistance of the molded product is improved. The upper limit of the Charpy impact strength is not particularly limited, but is usually 30 kJ / m ² or less.
The Charpy impact strength is based on JIS K-7111 (2004), a type 1 test piece is prepared, the striking direction is edgewise, the notch type is type A (0.25 mm), and the test piece is cooled in a constant temperature bath. , Can be measured at −20 ° C.
The value of Charpy impact strength can be controlled by the molecular weight and the molecular weight distribution. That is, the higher the molecular weight, the higher the Charpy impact strength. Further, if the molecular weight distribution is narrowed and the low molecular weight components are reduced, the Charpy impact strength is increased.

(4) Melt tension (MT) measured at 210 ° C.
The polyethylene of the present invention has a melt tension (MT) measured at 210 ° C. of 80 mN or more, preferably 100 mN or more.
When the melt tension (MT) is 80 mN or more, the drawdown during molding becomes small and molding becomes easy.
For the melt tension (MT), a capillograph manufactured by Toyo Seiki Seisakusho Co., Ltd. is used, the nozzle diameter is 2.095 mmφ, the nozzle length is 8.00 mm, the inflow angle is 180 °, the set temperature is 210 ° C, the piston extrusion speed is 10.0 mm / min, and the take-up is performed. It can be measured under the condition of a speed of 4.0 m / min.
The melt tension (MT) can be adjusted by the molecular weight and the molecular weight distribution of polyethylene, and usually, the melt tension can be increased by increasing the molecular weight. Further, if the molecular weight distribution is widened and the number of high molecular weight components is increased, the melt tension increases.

(5) Constant strain ESCR (unit: time)
The polyethylene of the present invention has a constant strain ESCR of 60 hours or more. From the viewpoint of physical balance and required performance of the container lid, the lower limit of the constant strain ESCR is preferably more than 100 hours, more preferably more than 130 hours, still more preferably 140 hours or more, and the upper limit is preferably 400 hours or less. This is environmental stress crack resistance (stress crack) resistance under constant strain. Specifically, from the compression molded sheet prepared according to JIS-K6922-2: 1997, it conforms to ASTM D 1693-01, 38 ×. It is measured in a 10 vol% solution of Igepearl (CO-630) under a temperature condition of 50 ° C. using a sample obtained by punching a plate having a size of 13 × 1.9 mm and notching.
When this constant strain ESCR is 60 hours or more, the container lid is not easily broken by stress, and liquid leakage of the contents can be suppressed. Further, the one having 400 hours or less can improve the stress crack resistance and can achieve both high rigidity and fluidity suitable for container lid molding.

(6) Normal hexane extraction amount (mass%)
The polyethylene of the present invention has a normal hexane extraction amount of 0.20% by mass or less, preferably less than 0.20% by mass, and more preferably 0.10% by mass or less.
When the amount of normal hexane extracted is 0.20% by mass or less, the cleanliness of the molded product is improved. The lower limit of the amount of normal hexane extracted is not particularly limited, but the smaller the amount, the more preferable.
The amount of normal hexane extracted is shown by extracting 2 g of the resin with 400 ml of the normal hexane solvent for 2 hours using a Soxhlet extractor and expressing the amount of the extracted amount with respect to the total resin by mass%.

(7) Ash content (mass ppm)
The polyethylene of the present invention has an ash content of 20 mass ppm or less.
The polyethylene of the present invention has an ash content of preferably 15% by mass or less.
When the ash content is 20 mass ppm or less, it is possible to suppress the elution of ash-derived components from the container of the molded product into the internal solution, improve the cleanliness of the internal solution, and improve the performance as a high-purity chemical container. Tends to improve.
The ash content can be determined in accordance with JIS K2272-1985.
The ash content can be adjusted by the type of catalyst, the type of co-catalyst, and the like. As the catalyst, it is difficult to achieve this requirement unless the activity is high, and a catalyst system consisting of the above-mentioned solid catalyst component containing magnesium and titanium and an organoaluminum compound is preferable.

The polyethylene of the present invention preferably satisfies at least one of the following properties (8) to (16) in addition to the above properties (1) to (7).

(8) tanδ;
The polyethylene of the present invention preferably has a tan δ of 1.00 to 1.60, more preferably 1.36 to 1.59, at 190 ° C. and 0.01 rad / sec measured by a rheometer.
For the measurement of tan δ at 190 ° C. and 0.01 rad / sec measured by a rheometer, a sample prepared by a hot press was used, and a rheometer (Ares manufactured by Rheometerics) was used for storage at 190 ° C. and an angular modulus of 0.01 rad / sec. The elastic modulus G'and the loss elastic modulus G'can be measured and tan δ (= G'/ G') can be calculated.

(9) Extensional viscosity (ηe) and shear viscosity (ηs)
The polyethylene of the present invention preferably has an extensional viscosity (ηe) (unit: Pa · s) and a shear viscosity (ηs) (unit: Pa · s) measured by a rheometer satisfying the following relational expression (A). ..
ηe ≧ 16.5 × ηs ^0.980 Equation (A)
When the elongational viscosity ηe and the shear viscosity ηs of polyethylene satisfy the formula (A), it is shown that the elongational viscosity corresponding to the shear viscosity is high and the relaxation time distribution of the polyethylene is wide. When the relaxation time distribution is wide, the sharkskin on the surface of the molded product is less likely to appear, so that the moldability of a large container is excellent.
The extensional viscosity ηe and shear viscosity ηs of polyethylene are measured under the following conditions using the inflow pressure loss method and based on Cogswell's theory [Polymer Engineering Science, Vol. 12, pp. 64-73 (1972)]. Can be asked.
That is, the extensional viscosity (ηe) and the extension strain rate (dε / dt) are the following equations (B) to (No. 1) proposed by Cogswell (POLYMER ENGINEERING AND SCIENCE, JANUARY, 1972, Vol. 12, No. 1). It can be calculated using D).
ηe = [9 (n + 1) ² P ₀ ² ] / [32ηs (dγ / dt) ² ] Equation (B)
dε / dt = 4σs (dγ / dt) / [3 (n + 1) P ₀ ] Equation (C)
σs = k (dγ / dt) ⁿ equation (D)
Here, ηe is the elongation viscosity, ηs is the shear viscosity, dγ / dt is the shear strain rate, dε / dt is the elongation strain rate, σs is the shear stress, k is a constant, and the exponent n of the equation (D) is a melt fracture or It is obtained by fitting with a quadratic function, assuming that the shear stress and the shear strain rate follow the power law in the shear rate region where the slip stick does not occur. P ₀ is a pressure loss generated by a die having a capillary length of 0, and is obtained by Bagley correction of measurement results using two or more capillaries having different lengths.
The extensional viscosity ηe can be obtained by using the value obtained by interpolation when the extensional strain rate is 10s ^-1 , and the shear viscosity ηs can be obtained by using the value when the shear strain rate is 10s ^-1 .
Measuring device: Rheometer RH2000 manufactured by Bohlin Instruments
Measurement temperature: 190 ° C
Long die: length 16 mm, diameter 1 mm, inflow angle 180 °
Short die: length 0.25 mm, diameter 1 mm, inflow angle 180 °
In order for the polyethylene of the present invention to satisfy the relational expression (A), it can be adjusted by the molecular weight and composition ratio of the ethylene polymer (A) which is a high molecular weight component and the ethylene polymer (B) which is a low molecular weight component. ..

(10) Ratio of extensional viscosity to shear viscosity (ηe / ηs)
The polyethylene of the present invention has an extensional viscosity (ηe) (unit: Pa · s) at an extension strain rate of 10s ^-1 and a shear viscosity (ηs) (unit: Pa · s) at a shear strain rate of 10s ^-1 as measured by a rheometer. ) Satisfy the range of 13.5 to 21.0.
When the ratio (ηe / ηs) of the extensional viscosity and the shear viscosity of polyethylene used in the present invention is within the above range, the generation of sharkskin during molding can be suppressed, and the degree of cleanliness is lowered due to the increase in the specific surface area. Can be prevented.
The ratio of extensional viscosity to shear viscosity (ηe / ηs) is preferably 14.0 to 20.0, more preferably 14.5 to 19.0, and even more preferably 15.0 to 18.0. .. If the ratio of extensional viscosity to shear viscosity (ηe / ηs) is smaller than the above lower limit, sharkskin is likely to occur on the surface of the molded product due to the decrease in extensional viscosity. May increase and the cleanliness may decrease. On the other hand, if the ratio of the extensional viscosity to the shear viscosity (ηe / ηs) is larger than the above upper limit value, the extensional viscosity becomes too high, so that melt fracture and slip are likely to occur, and it becomes difficult to maintain the appearance of the molded product and to mold it. There is a risk of becoming.
The ratio of elongational viscosity to shear viscosity (ηe / ηs) of polyethylene can be adjusted by the molecular weight and composition ratio of the ethylene polymer (A) which is a high molecular weight component and the ethylene polymer (B) which is a low molecular weight component. ..

(11) Extensional viscosity (ηe)
The polyethylene of the present invention preferably has an extensional viscosity (ηe) (unit: Pa · s) at an extension strain rate of 10s ^-1 measured by a rheometer in the range of 60,000 to 100,000 Pa · s.
When the extensional viscosity (ηe) of polyethylene used in the present invention is within the above range, it is possible to achieve both drawdown resistance during molding and suppression of melt fracture.
The extensional viscosity (ηe) is preferably 65,000 to 95,000 Pa · s, more preferably 68,000 to 90,000 Pa · s, and even more preferably 70,000 to 85,000 Pa · s. If this extensional viscosity is smaller than the above lower limit value, drawdown during molding is likely to occur, which may not be suitable for large hollow molding. On the other hand, if the extensional viscosity is larger than the above upper limit value, the extensional viscosity becomes too high, so that melt fracture and slip are likely to occur, and it may be difficult to maintain the appearance of the molded product and to mold it.
The extensional viscosity (ηe) of polyethylene can be adjusted by adjusting the fluidity of polyethylene and the molecular weight and composition ratio of the ethylene polymer (A) which is a high molecular weight component and the ethylene polymer (B) which is a low molecular weight component.

(12) Fisheye (FE);
The polyethylene of the present invention preferably has 150 fish eyes with a diameter of 0.2 mm or more / 0.02 m ² or less.
When the number of fish eyes is 150 / 0.02 m ² or less, the inner surface of the molded product becomes smooth and the specific surface area in contact with the content liquid can be reduced, so that elution of fine particles and metals can be suppressed. Can be done.
The fisheye uses an air-cooled inflation molding machine equipped with a single-screw extruder with a 40 mmφ diameter and an effective screw length (L / D) of 26, with a blow ratio of 3 and a take-up speed of 15 m / min, with a thickness of 25 μm and a folding diameter of 235 mm. Inflation film can be prepared and the number of fish eyes of 0.2 mm or more can be measured using a detector of the CCD detection method.

(13) Ratio (Mw / Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) determined by gel permeation chromatography (GPC):
In the polyethylene of the present invention, the Mw / Mn obtained by GPC is preferably more than 7.0 and 15.0 or less, more preferably 9 to 13, and even more preferably 10 to 12.
The molecular weight distribution (Mw / Mn) measured by GPC is related to the improvement of various physical properties and moldability of the polymer, and is also related to the improvement of the appearance and the like of the molded product.
When the molecular weight distribution (Mw / Mn) of the polyethylene of the present invention is within the above range, more excellent moldability can be exhibited. Further, when the molecular weight distribution (Mw / Mn) exceeds 7.0, the appearance of the product is excellent, the resin pressure at the time of molding becomes appropriate, and the flow unstable phenomenon such as sharkskin is less likely to occur, resulting in poor appearance. It is preferable because it is easy to suppress. On the other hand, when the molecular weight distribution (Mw / Mn) is 15.0 or less, deterioration of the pinch-off shape of the molded product is suppressed, and the impact strength of the molded product is likely to be improved.

The measurement of the molecular weight and the molecular weight distribution by gel permeation chromatography (GPC) can be performed under the following conditions.
[Measurement condition]
Model used: Alliance GPCV2000 type manufactured by Japan Waters Corp. Measurement temperature: 145 ° C
Solvent: Ortodichlorobenzene (ODCB)
Column: Showa Denko's Shodex HT-806M x 2 + HT-G
Flow rate: 1.0 mL / min Injection volume: 0.3 mL

[Sample preparation]
A 4 mL vial was weighed with 3 mg of sample and 3 mL of orthodichlorobenzene (containing 0.1 mg / mL 1,2,4-trimethylphenol) and covered with a resin screw cap and Teflon® septum. After that, melting is carried out for 2 hours using an SSC-9300 type high temperature shaker manufactured by Senshu Kagaku Co., Ltd. set at a temperature of 150 ° C. After the dissolution is completed, visually confirm that there are no insoluble components.
[Creating a calibration curve]
Prepare four 4 mL glass bottles, weigh 0.2 mg each of the monodisperse polystyrene standard sample or n-alkane of the combination of (1) to (4) below, and then weigh orthodichlorobenzene (0.1 mg / mL). Weighed 3 mL (including 1,2,4-trimethylphenol), covered with a resin screw cap and Teflon (registered trademark) septum, and then set the temperature to 150 ° C. SSC-9300 manufactured by Senshu Kagaku Co., Ltd. Melt for 2 hours using a high temperature shaker.
(1) Shodex S-1460, S-66.0, n-eicosane (2) Shodex S-1950, S-152, n-tetracontane (3) Shodex S-3900, S-565, S -5.05
(4) Shodex S-7500, S-1010, S-28.5
A vial containing the sample solution is set in the device, the measurement is performed under the above conditions, and the chromatogram (data set of retention time and response of the differential refractometer detector) is recorded at a sampling interval of 1 second. The retention time (peak apex) of each polystyrene standard sample is read from the obtained chromatogram and plotted against the logarithmic value of the molecular weight. Here, the molecular weights of n-icosane and n-tetracontane are 600 and 1200, respectively. The nonlinear least squares method is applied to this plot, and the obtained quadratic curve is used as the calibration curve.

[Calculation of molecular weight]
The measurement is performed under the above-mentioned conditions, and the chromatogram is recorded at a sampling interval of 1 second.
From this chromatogram, Sadao Mori, "Size Exclusion Chromatography" (Kyoritsu Shuppan), Chapter 4, p. The differential molecular weight distribution curve and the average molecular weight value (Mn, Mw and Mz) are calculated by the method described in 51 to 60. However, in order to correct the molecular weight dependence of dn / dc, the height H from the baseline in the chromatogram is corrected by the following formula. Chromatogram recording (data acquisition) and average molecular weight calculation are performed using an in-house program (created with Microsoft Visual Basic 6.0) on a PC on which Microsoft OS Windows (registered trademark) XP is installed.
H'= H / [1.032 + 189.2 / M (PE)]
The following formula is used for the molecular weight conversion from polystyrene to polyethylene.
M (PE) = 0.468 x M (PS)

Mw / Mn can be adjusted by the type of catalyst, the type of co-catalyst, the polymerization temperature, the residence time in the polymerization reactor, the number of polymerization reactors, etc., and also by the temperature, pressure, shear rate, etc. of the extruder. It is possible, and preferably it can be increased or decreased by adjusting the mixing ratio of the high molecular weight component and the low molecular weight component.
The Mw / Mn of the ethylene polymer is easily affected by the type of catalyst, and generally has a wide molecular weight distribution according to the Phillips catalyst, a narrow molecular weight distribution according to the metallocene catalyst, and an intermediate molecular weight according to the Ziegler catalyst. It becomes a polymer having a distribution.

(14) No phosphorus-based antioxidant is added.
The polyethylene of the present invention preferably contains no phosphorus-based antioxidant. Since no phosphorus-based antioxidant is added, it can be used as a container for high-purity chemicals, and can be used, for example, as a container for chemicals used for manufacturing semiconductors.

(15) Ti content:
The polyethylene of the present invention preferably has a Ti content of 1.5 mass ppm or less, more preferably 1.0 mass ppm or less, and preferably 0.9 mass ppm or less with respect to the entire polyethylene. When the ratio is 1.5 mass ppm or less, the amount of Ti eluted in the molded product tends to be reduced, and the performance as a high-purity chemical container tends to be improved.
As for the Ti content, about 0.5 g of a sample is collected in a quartz beaker, 2 ml of sulfuric acid is added thereto, and the sample is carbonized by heating, and then a transparent solution of colorless to pale yellow is obtained while heating. Repeat "heating, cooling, and adding nitrate" until the temperature is increased, and after cooling, the volume is reduced to 50 ml with pure water and further diluted 10-fold to ICP-MS (Inductively Coupled Plasma-Mass Spectrometry (inductively coupled plasma mass spectrometry)). It can be obtained by measuring the target metal element by method)) and converting it to the concentration in the sample.
The content can be adjusted by the type of catalyst, the type of co-catalyst, and the like. As the catalyst, it is difficult to achieve the requirements of the present invention unless the activity is high, and a catalyst system consisting of the above-mentioned solid catalyst component containing magnesium and titanium and an organoaluminum compound is preferable.

(16) Al content:
The polyethylene of the present invention preferably has an Al content of 3.0 mass ppm or less, more preferably 2.0 mass ppm or less, and preferably 1.6 mass ppm or less with respect to the entire polyethylene. When the ratio is 3.0 mass ppm or less, the amount of Al eluted in the molded product tends to be reduced, and the performance as a high-purity chemical container tends to be improved.
As for the Al content, about 0.5 g of a sample is collected in a quartz beaker, 2 ml of sulfuric acid is added thereto, and the sample is carbonized and then heated to obtain a colorless to pale yellow transparent solution. Repeat "heating, cooling, and adding sulfuric acid" until, after cooling, the volume is reduced to 50 ml with pure water, further diluted 10 times, the target metal element is measured by ICP-MS, and converted to the concentration in the sample. It can be obtained by doing.
The content can be adjusted by the type of catalyst, the type of co-catalyst, and the like. As the catalyst, it is difficult to achieve the requirements of the present invention unless the activity is high, and a catalyst system consisting of the above-mentioned solid catalyst component containing magnesium and titanium and an organoaluminum compound is preferable.

2. 2. Composition of Polyethylene The polyethylene of the present invention has an ethylene polymer (A) having a density (d) of 0.930 to 0.950 g / cm ³ , an HLMFR of 0.1 to 2 g / 10 minutes, and an ethylene polymer (A) of 25 to 49% by mass. Ethylene polymer (B) 51 having a density (d) of 0.960 to 0.970 g / cm ³ , a temperature of 190 ° C., and a melt flow rate (MFR) of 1 to 50 g / 10 minutes measured at a load of 2.16 kg. By using ~ 75% by mass as an essential component, the characteristics (1) to (7) are satisfied at the same time.

The composition ratio of the ethylene polymer (A) may be 25 to 49% by mass, preferably 30 to 47% by mass, and more preferably 35 to 45% by mass.
When the composition ratio of the polyethylene polymer (A) is 25% by mass or more, it is not necessary to make the molecular weight of the polyethylene polymer (A), which is a high molecular weight component, extremely large in order to satisfy the specified HLMFR, and the molecular weight is low. Since the difference in molecular weight from the ethylene polymer (B), which is a component of the above, can be reduced and the difference in viscosity becomes small, the HLMFR of the polyethylene of the present invention is within the specified range, and the ethylene polymer (A) is moderately different. Dispersion can be maintained, fisheye generation can be suppressed, and good moldability and environmental stress crack resistance can be achieved.
On the other hand, when the composition ratio of the ethylene polymer (A) is 49% by mass or less, the molecular weight distribution of the polyethylene of the present invention is appropriately widened, the relaxation time distribution is widened, and the generation of sharkskin can be suppressed.

3. 3. Characteristics of Ethylene Polymer (A) The ethylene polymer (A) used in the present invention is an ethylene homopolymer or a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms. A method for producing an ethylene homopolymer or a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms will be described later.
The density of the ethylene polymer (A) has a lower limit of 0.930 g / cm ³ or more, preferably 0.933 g / cm ³ or more, more preferably 0.935 g / cm ³ or more, and an upper limit of 0. It is 950 g / cm ³ or less, preferably 0.945 g / cm ³ or less, and more preferably 0.940 g / cm ³ or less.
The density of the ethylene polymer (A) can be measured by the same method as the density of the polyethylene characteristic (1) of the present invention described above.
When the density of the ethylene polymer (A) is 0.930 g / cm ³ or more, the desired rigidity of the molded product is obtained, while when it is 0.950 g / cm ³ or less, the durability is improved.
The density of the ethylene polymer (A) can be adjusted, for example, by changing the amount of α-olefin to be copolymerized with ethylene, and can be reduced by increasing the amount of α-olefin.

The ethylene polymer (A) has an HLMFR having a lower limit of 0.1 g / 10 minutes or more, preferably 0.2 g / 10 minutes or more, and an upper limit of 2 g / 10 minutes or less, preferably 1 g / 10 minutes or less. , More preferably 0.8 g / 10 minutes or less. The HLMFR can be measured by the same method as that of the above-mentioned HLMFR of the polyethylene characteristic (2) of the present invention.
When the HLMFR of the ethylene polymer (A) is 0.1 g / 10 minutes or more, the desired fluidity is obtained at the time of molding, and the molding becomes stable. When the HLMFR is 2 g / 10 minutes or less, the impact resistance tends to be improved.
The HLMFR of the ethylene polymer (A) can be adjusted by changing the amount of the chain transfer agent (hydrogen, etc.) coexisting during the ethylene polymerization or by changing the polymerization temperature, and the amount of hydrogen can be adjusted. It can be increased by increasing or increasing the polymerization temperature.

4. Characteristics of Ethylene Polymer (B) The ethylene polymer (B) used in the present invention is an ethylene homopolymer or a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms.
The density of the ethylene polymer (B) has a lower limit of 0.960 g / cm ³ or more, preferably 0.961 g / cm ³ or more, more preferably 0.962 g / cm ³ or more, and an upper limit of 0. It is 970 g / cm ³ or less, preferably 0.969 g / cm ³ or less, and more preferably 0.968 g / cm ³ or less.
The density of the ethylene polymer (B) can be measured by the same method as the density of the polyethylene characteristic (1) of the present invention described above.
When the density of the ethylene polymer (B) is 0.960 g / cm ³ or more, the desired rigidity of the molded product is obtained, while when it is 0.970 g / cm ³ or less, the impact resistance is improved.
The density of the ethylene polymer (B) can be adjusted, for example, by changing the amount of α-olefin to be copolymerized with ethylene, and can be reduced by increasing the amount of α-olefin.

The lower limit of the melt flow rate (MFR) of the ethylene polymer (B) at a temperature of 190 ° C. and a load of 2.16 kg is 1 g / 10 minutes or more, preferably 3 g / 10 minutes or more, and more preferably 5 g / 10 minutes or more. The upper limit is 50 g / 10 minutes or less, preferably 30 g / 10 minutes or less, and more preferably 20 g / 10 minutes or less.
When the MFR of the ethylene polymer (B) is 1 g / 10 minutes or more, the fluidity is improved and the desired extrusion characteristics can be obtained, which is preferable. On the other hand, when the MFR of the ethylene polymer (B) is 50 g / 10 minutes or less, the desired impact resistance can be obtained, which is preferable.
The MFR can be measured in accordance with JIS K6922-2: 1997.
The MFR of the ethylene polymer (B) can be adjusted mainly by the amount of hydrogen at the time of producing the ethylene polymer (B).

The ethylene polymer contained in the polyethylene of the present invention can be produced by homopolymerization of ethylene alone or copolymerization of ethylene and an α-olefin having 3 to 20 carbon atoms.
The ethylene polymer contained in the polyethylene of the present invention can be obtained by polymerizing by ordinary one-stage polymerization, but it can also be produced as a composition by serially multi-stage polymerization or by mixing polymerized components under different conditions. ..

The polyethylene of the present invention can be obtained by mixing the ethylene polymer (A) and the ethylene polymer (B). Further, for reasons such as the uniformity of the resin, those obtained by continuously polymerizing the ethylene polymer (A) and the ethylene polymer (B) (sequential multistage polymerization method) are preferable, and for example, a plurality connected in series. It can be obtained by sequentially and continuously polymerizing ethylene and α-olefin in the reactor of.
In the present invention, the ethylene polymer (A) and the ethylene polymer (B) are subjected to multi-stage polymerization in which at least two polymerization reactors are combined in the presence of a polymerization catalyst, and the weight of ethylene alone in at least one polymerization reactor. It is preferable that the coalescence is polymerized and at least an ethylene copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms is polymerized in another polymerization reactor.

Further, the composition composed of the ethylene polymer (A) and the ethylene polymer (B) of the present invention may be a composition obtained by separately polymerizing the ethylene polymer (A) and the ethylene polymer (B) and then mixing them. Further, the ethylene polymer (A) and the ethylene polymer (B) can each be composed of a plurality of components. The ethylene polymer may be a polymer sequentially and continuously polymerized in a multi-stage polymerization reactor using one type of catalyst, and may be produced in a single-stage or multi-stage polymerization reactor using a plurality of types of catalysts. It may be a polymer, or it may be a mixture of polymers polymerized using one kind or a plurality of kinds of catalysts.

5. High-purity chemical container The polyethylene for high-purity chemical container of the present invention can be made into a high-purity chemical container by molding it into a container shape by a known molding method such as blow molding, injection molding, extrusion molding, or rotary molding. 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 blow air is preferable for producing a clean container.
The shape of the high-purity chemical container is not particularly limited.
The internal volume of the high-purity chemical container is not particularly limited, but is preferably 5L to 1000L, more preferably 10L to 500L, and further preferably 20L to 300L.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples as long as the gist thereof is not exceeded.

[Various evaluation (measurement) methods]
(1) Density (d):
Measured according to JIS-K6922-1, 2: 1997.
(2) Melt flow rate (HLMFR) measured at a temperature of 190 ° C. and a load of 21.6 kg:
Measured according to JIS K6922-2: 1997.
(3) Melt flow rate (MFR) at a temperature of 190 ° C. and a load of 2.16 kg:
Measured according to JIS K6922-2: 1997.

(4) Charpy impact strength measured at -20 ° C:
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), cooled in a constant temperature bath, and cooled at -20 ° C. It was measured.

(5) Melt tension (MT):
Using a capillograph manufactured by Toyo Seiki Seisakusho, a nozzle diameter of 2.095 mmφ, a nozzle length of 8.00 mm, an inflow angle of 180 °, a set temperature of 210 ° C, a piston extrusion speed of 10.0 mm / min, and a take-up speed of 4.0 m / min. Measured under conditions.

(6) Constant strain ESCR (time):
Compliant with JIS-K6922-2: 1997, a compression molded sheet was prepared, and according to ASTM D 1693-01, a 10 vol% solution of Igepearl (CO-630) was used as a test solution, and measurement was performed under a temperature condition of 50 ° C. Then, plotting was performed on logarithmic probability paper to determine the 50% crack occurrence time (F ₅₀ ).

(7) Normal hexane extraction amount (mass%):
Using a Soxhlet extractor, 2 g of the resin was extracted with 400 ml of normal hexane solvent for 2 hours. It is shown by the mass% of the extract with respect to the total resin.

(8) Ash content:
Measured according to JIS K2272-1985.

(9) Pinch-off characteristics; tan δ at 190 ° C. and 0.01 rad / sec measured by a rheometer:
For the measurement of tan δ at 190 ° C. and 0.01 rad / sec measured by a rheometer, a sample prepared by a hot press was used, and a rheometer (Ares manufactured by Rheometerics) was used for storage at 190 ° C. and an angular modulus of 0.01 rad / sec. The elastic modulus G'and the loss elastic modulus G'were measured, and tan δ (= G'/ G') was calculated. The conditions at the time of measurement are described below.
[Measurement condition]
Equipment: Ares manufactured by Rheometrics
Jig: 25 mm diameter parallel plate, plate spacing approx. 1.7 mm
Measurement temperature: 190 ° C
Distortion: 5%

(10) Extensional viscosity (ηe) and shear viscosity (ηs)
The extensional viscosity ηe and shear viscosity ηs of polyethylene are measured under the following conditions using the inflow pressure loss method and based on Cogswell's theory [Polymer Engineering Science, Vol. 12, pp. 64-73 (1972)]. I asked.
That is, the extensional viscosity (ηe) and the extension strain rate (dε / dt) were calculated using the following equations (B) to (D) proposed by Cogswell.
ηe = [9 (n + 1) ² P ₀ ² ] / [32ηs (dγ / dt) ² ] Equation (B)
dε / dt = 4σs (dγ / dt) / [3 (n + 1) P ₀ ] Equation (C)
σs = k (dγ / dt) ⁿ equation (D)
Here, ηe is the elongation viscosity, ηs is the shear viscosity, dγ / dt is the shear strain rate, dε / dt is the elongation strain rate, σs is the shear stress, k is a constant, and the exponent n of the equation (D) is a melt fracture or It was obtained by fitting with a quadratic function, assuming that the shear stress and shear strain rate in the shear rate region where slip sticks do not occur follow the power law. P ₀ is a pressure loss generated by a die having a capillary length of 0, and was obtained by Bagley correction of the measurement results using two or more capillaries having different lengths.
As the extensional viscosity ηe, the value obtained when the elongational strain rate was 10s ^-1 was used, and as the shear viscosity ηs, the value when the shearing strain rate was 10s ^-1 was used.
Measuring device: Rheometer RH2000 manufactured by Bohlin Instruments
Measurement temperature: 190 ° C
Long die: length 16 mm, diameter 1 mm, inflow angle 180 °
Short die: length 0.25 mm, diameter 1 mm, inflow angle 180 °

(11) Fish eyes (pieces / m ² ):
The fisheye uses an air-cooled inflation molding machine equipped with a single-screw extruder with a 40 mmφ diameter and an effective screw length (L / D) of 26, with a blow ratio of 3 and a take-up speed of 15 m / min, with a thickness of 25 μm and a folding diameter of 235 mm. Inflation film was prepared and the number of fish eyes of 0.2 mm or more was measured using a detector of the CCD detection method.

(12) Measurement of molecular weight (weight average molecular weight Mw, number average molecular weight Mn) and molecular weight distribution by gel permeation chromatography (GPC):
It was measured by gel permeation chromatography (GPC) under the following conditions.
[Measurement condition]
Model used: Alliance GPCV2000 type manufactured by Japan Waters Corp. Measurement temperature: 145 ° C
Solvent: Ortodichlorobenzene (ODCB)
Column: Showa Denko's Shodex HT-806M x 2 + HT-G
Flow rate: 1.0 mL / min Injection volume: 0.3 mL

[Sample preparation]
A 4 mL vial was weighed with 3 mg of sample and 3 mL of orthodichlorobenzene (containing 0.1 mg / mL 1,2,4-trimethylphenol) and covered with a resin screw cap and Teflon® septum. After that, melting was carried out for 2 hours using an SSC-9300 type high temperature shaker manufactured by Senshu Kagaku Co., Ltd. set at a temperature of 150 ° C. After the dissolution was completed, it was visually confirmed that there were no insoluble components.
[Creating a calibration curve]
Prepare four 4 mL glass bottles, weigh 0.2 mg each of the monodisperse polystyrene standard sample or n-alkane of the combination of (1) to (4) below, and then weigh orthodichlorobenzene (0.1 mg / mL). Weigh 3 mL (including 1,2,4-trimethylphenol), cover with a resin screw cap and Teflon (registered trademark) septum, and then set the temperature to 150 ° C. SSC-9300 type high temperature manufactured by Senshu Kagaku. Dissolution was performed for 2 hours using a shaker.
(1) Shodex S-1460, S-66.0, n-eicosane (2) Shodex S-1950, S-152, n-tetracontane (3) Shodex S-3900, S-565, S -5.05
(4) Shodex S-7500, S-1010, S-28.5
A vial containing the sample solution was set in the device, measurements were performed under the above conditions, and chromatograms (retention time and response data set of the differential refractometer detector) were recorded at a sampling interval of 1 s. The retention time (peak apex) of each polystyrene standard sample was read from the obtained chromatogram and plotted against the logarithmic value of the molecular weight. Here, the molecular weights of n-icosane and n-tetracontane were set to 600 and 1200, respectively. The nonlinear least squares method was applied to this plot, and the obtained quadratic curve was used as the calibration curve.

[Calculation of molecular weight]
The measurement was performed under the above-mentioned conditions, and the chromatogram was recorded at a sampling interval of 1 s. From this chromatogram, Sadao Mori, "Size Exclusion Chromatography" (Kyoritsu Shuppan), Chapter 4, p. The differential molecular weight distribution curve and the average molecular weight value (Mn, Mw and Mz) were calculated by the method described in 51 to 60. However, in order to correct the molecular weight dependence of dn / dc, the height H from the baseline in the chromatogram was corrected by the following formula. Chromatogram recording (data acquisition) and average molecular weight calculation were performed using an in-house program (created with Microsoft Visual Basic 6.0) on a PC on which Microsoft OS Windows (registered trademark) XP was installed.
H'= H / [1.032 + 189.2 / M (PE)]
The following formula was used for the molecular weight conversion from polystyrene to polyethylene.
M (PE) = 0.468 x M (PS)

(13) Ti content:
Approximately 0.5 g of the sample is collected in a quartz beaker, 2 ml of sulfuric acid is added to the sample, and the sample is carbonized. Cold, addition of nitric acid "was repeated. After cooling, the volume was reduced to 50 ml with pure water, further diluted 10-fold, the target metal element was measured by ICP-MS, and converted to the concentration in the sample.

(14) Al content:
Approximately 0.5 g of the sample is collected in a quartz beaker, 2 ml of sulfuric acid is added to the sample, and the sample is carbonized. Cold, addition of nitric acid "was repeated. After cooling, the volume was reduced to 50 ml with pure water, further diluted 10-fold, the target metal element was measured by ICP-MS, and converted to the concentration in the sample.

(15) Large blow moldability (discharge amount, motor load):
Using a TP-5 manufactured by Tahara Co., Ltd., which is a small multi-layer blow molding machine, the discharge amount per hour and the resin pressure at a temperature of 200 ° C., a screw rotation speed of 40 rpm, a die diameter of 18 mm, and a core diameter of 15 mm were measured. Those having a discharge rate of 15 kg / hr or more and a resin pressure of 25 MPa or less were designated as “◯”, and those other than that were designated as “x”.

(16) Drawdown resistance The time for the parison length to reach 12 cm and 60 cm was measured under the same conditions as the discharge property, and the drawdown rate was calculated by the following formula.
Drawdown rate = (time when parison length reaches 60 cm) / (time when parison length reaches 12 cm)
Those with a drawdown rate of 4.5 or more were rated as "○", and those with a drawdown rate of 4.5 or higher were designated as "x".

(17) Fine particle elution (cleanliness (pieces / ml))
After washing the blow-molded bottle with an internal volume of 500 mL 5 times in a clean room with ammonia water (EL ammonia water for electronic industry manufactured by Mitsubishi Chemical Corporation; 29% ammonia aqueous solution), fill the container with ammonia water and leave it for 3 months. The number of fine particles of 0.2 μm or more was measured with a KL-25 type liquid fine particle counter manufactured by Rion.
Those having 100 or less fine particles were designated as "○", and those having other fine particles were designated as "x".

(18) Metal elution amount (cleanliness)
The blow-molded internal volume 500 mL bottle was washed 5 times with cheap water in a clean room, the container was filled with cheap water, and the bottle was left for 3 months, and then the concentrations of Ti and Al were measured. Those having a metal elution amount of 10 mass ppb or less were designated as "◯", and those other than that were designated as "x".

(19) Surface roughness (Ra) (μm):
<Creation of extruded strands>
Using an Intesco capillary leometer, nozzle diameter 5 mmφ, nozzle length 10 mm, inflow angle 90 °, set temperature 190 ° C, piston extrusion speed 300 mm / min (apparent shear rate: 29 sec ^-1 ) as low speed conditions, high speed conditions After extrusion under the condition of a piston extrusion speed of 1000 mm / min (apparent shear rate: 97 sec ^-1 ), water-cooled strands for evaluation were prepared.
<Surface roughness measurement>
Using an ultra-deep color 3D shape measuring microscope manufactured by KEYENCE, 10 fields of view were continuously captured in the length direction of the strand with a 10x objective lens, and the surface roughness was measured according to JIS B 0601-1994.

(20) Molded product skin (500 mL container)
Judgment was made by visual confirmation of the inner surface and the outer surface of the 500 mL container obtained by the above blow molding. Those in which no sharkskin was found were marked with "○", and those in which sharkskin was found were marked with "x".

(21) Molded product skin (40L container)
<Molding of large containers>
Using the NB150 multi-layer hollow forming machine manufactured by Japan Steel Works, the ratio of inner layer / intermediate layer / outer layer was fixed to 20/40/40% by mass under three-layer conditions, and each extruder was set to 190 ° C, and all the same polyethylene. A single-composition molded product was formed by flowing a resin, and a 40 L container having a product mass of 8.5 kg was molded.
Judgment was made by visually confirming the inner surface of the 40L container obtained by the above blow molding. Those in which no sharkskin was found were marked with "○", and those in which sharkskin was found were marked with "x".

(22) Sharkskin suppressing effect Arithmetic mean roughness obtained by surface roughness measurement: Determined by the magnitude of Ra value. Those having a Ra value smaller than 20 μm were judged to have a high sharkskin inhibitory effect, and were evaluated as “◯”, and those having a Ra value of 20 μm or more were evaluated as “x”.

(23) Comprehensive evaluation “○” indicates that all of the large blow moldability, drawdown resistance, fine particle elution, metal elution amount, molded product skin, surface roughness, and sharkskin suppression effect are good, and others. The thing was set as "x".

[Example 1]
(A) Preparation of solid catalyst 75 g of Mg (OEt) ₂ and 755 g of Ti (OBu) ₃ Cl and 185 g of n- _{C4H 9} OH were mixed at 150 ° C. for 6 hours to homogenize, and after cooling, normal hexane was used. Was added in a predetermined amount to make a uniform solution.
Then, 2285 g of ethylaluminum sesquichloride was added dropwise at a predetermined temperature, and the mixture was stirred for 1 hour.
Further, washing with normal hexane was repeated to obtain 1100 g of a solid catalyst.

(B) Polymerization of ethylene Using the above solid catalyst, continuous polymerization was carried out using an apparatus in which two 0.6 m ³ reactors were connected in series.
Normal hexane 70 kg / hour, triethylaluminum 1.5 g / hour, the solid catalyst component 0.70 g / hour, ethylene 34 kg / hour, and hydrogen are continuously supplied to the first polymerization tank, and the polymerization temperature is 90. Continuous polymerization was carried out while maintaining the hydrogen in the gas phase at a temperature of 1.1 mol / mol with respect to the ethylene concentration ratio.
The polymer slurry of the first polymerization tank is continuously supplied to the second polymerization tank, and 47 kg / hour of normal hexane and 28 kg / hour of ethylene are continuously supplied, the polymerization temperature is 80 ° C., and hydrogen in the gas phase. The second-stage polymerization was carried out while maintaining the concentration of butene at 0.16 mol / mol with respect to ethylene and the concentration of butene at 0.026 mol / mol with respect to ethylene.
The obtained polymerized slurry was subjected to solid-liquid separation with a concentric separator and dried to obtain polyethylene powder.
The obtained polyethylene powder is kneaded using a CIM90 twin-screw kneader manufactured by Japan Steel Works, Ltd. under the conditions of a rotation speed of 300 rpm, a slot width of 25 mm, and a processing amount of 280 kg / hour without using any additives, and then extruded with a 120 mmφ single shaft. It was made into polyethylene under the condition of a resin temperature of 278 ° C. and the physical properties were measured.
The results of physical property measurement are shown in Table 1.

(C) Molding of a container Using the polyethylene obtained above using TP-5 manufactured by Tahara Co., Ltd., which is a small multi-layer blow molding machine, the pinch-off length becomes 95% of the bottom diameter at a temperature of 200 ° C. and a screw rotation speed of 40 rpm. A 500 mL bottle was molded while appropriately selecting a die core. Table 1 shows the evaluation results of blow moldability and the evaluation results of the molded product.
The obtained polyethylene had few fine particles derived from polyethylene resin and metal elution components derived from a polymerization catalyst component, was excellent in moldability such as drawdown resistance and ejection property at the time of molding, and was excellent in ESCR.

[Examples 2 to 3]
The same procedure as in Example 1 was carried out except that the ethylene polymer (A) and the ethylene polymer (B) having the characteristics shown in Table 1 were produced, and then polyethylene having the characteristics shown in Table 1 was produced.
Table 1 shows the physical characteristics and evaluation results of the polyethylene. The obtained polyethylene had few fine particles derived from polyethylene resin and metal elution components derived from a polymerization catalyst component, was excellent in moldability such as drawdown resistance and ejection property at the time of molding, and was excellent in ESCR.

[Comparative Example 1]
Polyethylene powder was obtained according to Example 1 of JP-A-2015-183130, and a polyethylene resin and a blow-molded container thereof were obtained in the same manner as in the pelletization conditions of Example 1 of the present application. Table 1 shows the physical characteristics of polyethylene and the evaluation results of the container.

[Comparative Examples 2 to 3]
A blow-molded container was obtained in the same manner as in Example 1 except that polyethylene having the characteristics shown in Table 1 was produced. Table 1 shows the physical characteristics of polyethylene and the evaluation results of the container.

[Comparative Example 4]
Polyethylene powder was obtained according to Comparative Example 2 of JP-A-2015-183130, and a polyethylene resin and a blow-molded container thereof were obtained in the same manner as in the pelletization conditions of Example 1 of the present application. Table 1 shows the physical characteristics of polyethylene and the evaluation results of the container.

[evaluation]
The experimental results will be described with reference to the experimental results shown in Table 1.
As is clear from Table 1, a container made of polyethylene containing essential components in a predetermined ratio and having characteristics such as density and melt flow rate satisfying the requirements of the present invention has excellent large blow moldability and rigidity of the container. , It was excellent in cleanliness (Examples 1 to 3).
On the other hand, in Comparative Example 1, the ethylene polymer (A) and the ethylene polymer (B) are excellent in formability such as draw-down resistance and ejection property, and are excellent in balance between physical properties such as ESCR and impact resistance and cleanliness. ) Does not satisfy the requirements of the present invention, sharkskin is likely to occur in the molding of a large container, the inner surface surface becomes rough in the molding of a large container, and there is concern about the influence on long-term fine particles and metal elution. It was a result.
In Comparative Example 2, since the composition ratios of the ethylene polymer (A) and the ethylene polymer (B) do not satisfy the requirements of the present invention, the modifying effect of sharkskin is not sufficient, and the inner surface skin is formed in the molding of a large container. The result was that there was concern about the effects on long-term fine particles and metal elution.
In Comparative Example 3, since the molecular weight distribution is wider and the fluidity is higher than that of Comparative Example 1, the improvement effect of sharkskin in a small container of about 500 ml was confirmed, but the sharkskin in large molding was confirmed. The reforming effect was not sufficient, and the inner surface of the large container was roughened, and there was concern about the effect on long-term fine particles and metal elution.
Further, in Comparative Example 4, since the HLMFR deviates from the requirements of the present invention, the melt tension is lowered, the drawdown resistance is lowered, and the result is not suitable for large hollow forming.

FIG. 1 is a graph showing the relationship between extensional viscosity (ηe) and shear viscosity (ηs). The solid line in the graph shows the lower limit of the extensional viscosity (ηe) specified by the relational expression (A) relating to the extensional viscosity (ηe) and the shear viscosity (ηs) of the characteristic (9). In addition, 1.00E + 03, 1.00E + 04, and 1.00E + 05 in FIG. ¹ mean 1.00 × 10 ³ , 1.00 × 10 ⁴ , and 1.00 × 105, respectively.
As shown in FIG. 1, it can be seen that all of Examples 1 to 3 satisfy the condition of the relational expression (A).
On the other hand, it can be seen that none of Comparative Examples 1 to 4 satisfies the condition of the relational expression (A).
As shown in Table 1, in Examples 1 to 3 that satisfy the condition of the relational expression (A), the sharkskin on the surface of the molded product is less likely to appear, the drawdown resistance is good, and the moldability of the large container is excellent. It was proved.
Therefore, satisfying the condition of the relational expression (A) is an index that the sharkskin on the surface of the molded product is less likely to appear, the drawdown resistance is good, and the moldability of the large container is excellent.
FIG. 2 is a graph showing the relationship between the ratio of extensional viscosity (ηe) and shear viscosity (ηs) and HLMFR.
As shown in FIG. 2, it can be seen that Examples 1 to 3 have an excellent balance between the ratio of extensional viscosity (ηe) and shear viscosity (ηs) and HLMFR.
Therefore, in Examples 1 to 3, since the ratio of the extensional viscosity (ηe) to the shear viscosity (ηs) has a desired value, the generation of sharkskin during molding can be suppressed and the specific surface area is increased. It can be seen that it is possible to prevent a decrease in cleanliness due to the above, and further, since it has a desired HLMFR, it is excellent in moldability of a large container.

According to the present invention, since there are few fine particles derived from the polyethylene resin and metal elution components derived from the polymerization catalyst component and the durability is excellent, the polyethylene resin for high-purity chemical containers can be obtained, and the durability / cleanness is high. It is possible to mold a high-purity chemical container with an excellent balance. In addition, it has excellent hollow moldability such as draw-down resistance and is less likely to generate sharkskin on the parison surface during molding, so it is particularly suitable for large containers and the amount of fine particle components eluted in the filled chemical solution. It is very useful industrially because it is possible to provide a large-sized high-purity chemical container having a small size and a small amount of fine particles eluted over a long period of time.

Claims (10)

Ethylene polymer (A) having a density (d) of 0.930 to 0.950 g / cm ³ , an HLMFR of 0.1 to 1 g / 10 minutes, and a density (d) of 0.960 to 49% by mass. Contains 51-75% by mass of ethylene polymer (B) having a melt flow rate (MFR) of 1 to 50 g / 10 minutes measured at 0.970 g / cm ³ , temperature 190 ° C. and load 2.16 kg as an essential component. , Polyethylene for high-purity chemical containers having the following characteristics (1) to (7).
(1) The density (d) is 0.950 to 0.965 g / cm ³ .
(2) The melt flow rate (HLMFR) measured at a temperature of 190 ° C. and a load of 21.6 kg is 5 to 20 g / 10 minutes.
(3) The Charpy impact strength measured at −20 ° C. is 7 kJ / m ² or more.
(4) The melt tension (MT) measured at 210 ° C. is 80 mN or more.
(5) The constant strain ESCR is 40 hours or more.
(6) The amount of normal hexane extracted is 0.20% by mass or less.
(7) The ash content is 20 mass ppm or less. The polyethylene for a high-purity chemical container according to claim 1, further satisfying the following property (8).
(8) The tan δ at 190 ° C. and 0.01 rad / sec measured by a rheometer is 1.00 to 1.60. The polyethylene for a high-purity chemical container according to claim 1 or 2, further satisfying the following property (9).
(9) The extensional viscosity (ηe) (unit: Pa · s) and the shear viscosity (ηs) (unit: Pa · s) measured by the rheometer satisfy the following relational expression (A).
ηe ≧ 16.5 × ηs ^0.980 Equation (A) The polyethylene for a high-purity chemical container according to any one of claims 1 to 3, further satisfying the following characteristic (10).
(10) The ratio (ηe / ηs) of the extensional viscosity (ηe) (unit: Pa · s) and the shear viscosity (ηs) (unit: Pa · s) measured by the rheometer is 13.5 to 21.0. be. The polyethylene for a high-purity chemical container according to any one of claims 1 to 4, further satisfying the following property (11).
(11) The extensional viscosity (ηe) (unit: Pa · s) measured by a rheometer is 60,000 to 100,000. The polyethylene for a high-purity chemical container according to any one of claims 1 to 5, further satisfying the following characteristic (12).
(12) The number of fish eyes having a diameter of 0.2 mm or more is 150 / 0.02 m ² or less. The polyethylene for a high-purity chemical container according to any one of claims 1 to 6, further comprising satisfying the following property (13).
(13) 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 more than 7.0 and 15.0 or less. The polyethylene for a high-purity chemical container according to any one of claims 1 to 7, further satisfying the following property (14).
(14) No phosphorus-based antioxidant is added. A high-purity chemical container, which is a polyethylene molded product for a high-purity chemical container according to any one of claims 1 to 8. The high-purity chemical container according to claim 9, wherein the internal volume is 5 L to 1000 L.

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