JP7279455B2 - Polyethylene resin and hollow molded products - Google Patents

Description

The present invention provides a polyethylene-based resin that has an excellent balance between rigidity and durability and is also excellent in moldability, and a polyethylene-based resin that is useful as a material for hollow plastic moldings such as containers, bottles, and tanks, especially automobile fuel tanks. Regarding resin.

Hollow plastic molded articles used for storing or transporting liquid substances are widely used in daily life and industrial fields. It is most commonly used as a material for forming containers such as cans and bottles. Compared to metal materials, plastic materials have a smaller weight/volume ratio, making it possible to reduce weight. Used as fuel tanks in auto parts, it is replacing traditional metal materials.

Plastic fuel tanks for automobiles are important safety parts for ensuring the safety of automobiles, and are required to have various high-level performances. is desired.
In fact, commercially available polyethylenes used in plastic fuel tanks for automobiles include, for example, "HB111R" manufactured by Nippon Polyethylene Co., Ltd., and "4261AG" manufactured by Basell. These materials have met the strict requirements of automobile manufacturers and have been well received in the market, but further improvements in performance are desired.

Under such circumstances, attempts have been made to provide polyethylene resins with improved various performances.
Patent Literature 1 discloses an ethylene-based resin composition for hollow molded articles, which simultaneously satisfies the following requirements [a], [b], [c], and [d].
[a] The melt flow rate (MFR) under a load of 21.6 kg at a temperature of 190° C. is in the range of 1.0 to 15 g/10 minutes.
[b] The density is in the range of 955-970 kg/m ³ .
[c] Less than 0.1 methyl branches per 1,000 carbon atoms as determined by ¹³ C-NMR.
[d] The tensile impact strength at -40°C measured in accordance with JIS K7160 is 270 kJ/ ^m2 or more.
A hollow molded article obtained from the resin composition described in Cited Document 1 and a fuel tank, which is a preferred use thereof, maintains the rigidity of the molded article even when the thickness is reduced, while maintaining high impact resistance and creep resistance for a long period of time. It is said that performance is exhibited (paragraph 0027).
However, it cannot be said that the composition described in Patent Document 1 is necessarily suitable as a resin for plastic fuel tanks for automobiles in terms of moldability.

Patent Document 2 discloses an ethylene-based polymer produced by homopolymerizing ethylene or copolymerizing ethylene and an α-olefin using a chromium catalyst and having the following properties (1) to (8). ing.
(1) High load melt flow rate (HLMFR) is 1 to 10 g/10 minutes.
(2) Density is 0.940 to 0.960 g/cm ³ .
(3) The molecular weight distribution (Mw/Mn) is 25 or more.
(4) The strain hardening parameter (λmax) of elongational viscosity is 1.05 to 1.50.
(5) The Charpy impact strength is 7 kJ/m ² or more.
(6) Tensile impact strength is 130 kJ/m ² or more.
(7) Swell ratio (SR) is 50-65%.
(8) The time to rupture in a full-circumference notch type tensile creep test is 40 hours or more.
The ethylene-based polymer disclosed in Patent Document 2 is said to have excellent moldability and durability (FNCT, etc.) and to have an excellent balance between impact resistance and rigidity. The resulting hollow plastic molded product is said to have excellent moldability, impact resistance, and a good balance of durability and rigidity, and the preferred application is fuel tanks for automobiles. (Paragraph 0033).
However, it cannot be said that the composition described in Patent Document 2 is necessarily suitable as a resin for plastic fuel tanks for automobiles in terms of the balance between long-term performance and rigidity.

In Patent Document 3, one or more ethylene polymers selected from the group consisting of homopolymers of ethylene and copolymers of ethylene and α-olefins having 3 to 12 carbon atoms are included as essential components, A polyethylene is disclosed having the following properties [a], [b], [c], [d] and [e].
[a] Melt flow rate (HLMFR) measured at a temperature of 190° C. and a load of 21.6 kg is 1 to 15 g/10 minutes.
[b] Density (d) is 0.950 to 0.965 g/cm ³ .
[c] Melt tension (MT) measured at 210°C is 147 mN or more.
[d] Using a capillary having a diameter (D) of 5 mm and a ratio of length (L) to diameter (L/D) of 2, the critical shear rate measured at 190° C. is 10 sec ⁻¹ or more.
[e] The Charpy impact strength measured at -40°C is 9 kJ/m2 or ^more .
The polyethylene disclosed in Patent Document 3 is said to have an excellent balance of rigidity and durability, and to be excellent in moldability and impact resistance. It is said to be useful as a material for hollow plastic products such as automobile fuel tanks (Paragraph 0217).
However, it cannot be said that the composition described in Patent Document 3 is necessarily suitable as a resin for plastic fuel tanks for automobiles in terms of moldability.

Patent Document 4 discloses (i) a linear polymer prepared using a first high molecular weight metallocene having a density of 0.920-0.940 g/cm ³ and an HLMI of 0.01-2 g/10 min. A low density polyethylene (mLLDPE) resin was provided and (ii) produced using a Ziegler-Natta or chromium-based catalyst with a density in the range of 0.950-0.970 g/cm ³ and 5-100 g/10 min. providing a second high density polyethylene (HDPE) having an HLMI of; (iii) physically blending the first and second polyethylenes together to provide a sub-high molecular weight broad or multimodal molecular weight distribution; A process for producing a polyethylene resin having a multimodal molecular weight distribution is disclosed comprising the steps of producing a polyethylene resin having a density in the range of 0.948-0.958 g/cm ³ and an HLMI of less than 20 g/10 min. there is
The resins described in US Pat. No. 4,500,500 are purportedly usable for fuel tanks, pipes, and allow for reduced wall thickness due to substantial improvements in environmental stress crack resistance, impact strength, and drop testing. It is said that there are advantages especially in the automobile industry (paragraph 0094).
However, it cannot be said that the composition described in Patent Document 4 is necessarily suitable as a resin for plastic fuel tanks for automobiles in terms of moldability.

Patent Document 5 describes a polyethylene resin comprising 35-49% by weight of a high molecular weight first polyethylene fraction and 51-65% by weight of a low molecular weight second polyethylene fraction, wherein the first polyethylene fraction comprises linear low density polyethylene having a density of at most 0.930 g/cm ³ and an HLMI of less than 0.6 g/10 min, and a second polyethylene fraction having a density of at least 0.969 g/cm ³ and 10 g and a polyethylene resin having a density higher than 0.946 g/cm ₃ ^, HLMI from 1 to 100 g/10 min, 200 measured at 0.01 rad/sec. ,000 Pa.s. Said polyethylene resin is disclosed having a dynamic viscosity η _0.01 higher than s and a ratio of dynamic viscosities η _0.01 /η ₁ higher than 8 measured at 0.01 and 1 rad/s respectively .
The polyethylene resin disclosed in Patent Document 5 is said to be particularly suitable for manufacturing pipes or pipe fittings (paragraphs 0001, 0012 and 0014).
However, it cannot be said that the composition described in Patent Document 5 is necessarily suitable as a resin for plastic fuel tanks for automobiles in terms of moldability.

US Pat. No. 6,200,003 discloses a polyethylene resin having a polymodal molecular weight distribution, which has (a) a density in the range of about 0.925 g/ccm to about 0.950 g/ccm;
(b) has a melt index (I ₂ ) in the range of about 0.05 g/10 min to about 5 g/10 min; and (c) at least one high molecular weight (HMW) ethylene interpolymer and at least one low molecular weight (LMW) an ethylene polymer, wherein (d) at least said HMW component has a density in the range of about 0.910 g/ccm to about 0.935 g/ccm and a melt index of about 1.0 g/10 min or less; (e) said LMW component has a density in the range of about 0.945 g/ccm to about 0.965 g/ccm and a melt index of at least about 2.0 g/10 min or more; Disclosed is a polyethylene resin characterized by comprising at least one or more ethylene polymers having a
The polyethylene resin disclosed in Patent Document 6 is said to be suitable for high durability applications such as pipes (paragraphs 0001 and 0010).
However, it cannot be said that the composition described in Patent Document 6 is necessarily suitable as a resin for plastic fuel tanks for automobiles in terms of moldability.

US Pat. No. 5,931,003 discloses a composition comprising a high density ethylene polymer and a high molecular weight ethylene polymer, wherein the high density ethylene polymer has a density exceeding that of the high molecular weight ethylene polymer, and the high molecular weight ethylene polymer has a high density. having a weight average molecular weight exceeding the weight average molecular weight of the ethylene polymer;
the high density ethylene polymer has (i) a density of 0.94 g/cm ³ to 0.98 g/cm ³ and (ii) a molecular weight distribution, Mw/Mn, of greater than 10 to 50;
The high molecular weight ethylene polymer has (i) a weight average molecular weight of greater than 200,000 g/mole, (ii) a molecular weight distribution, Mw/Mn, of 1.2 to less than 3.5, and (iii) a molecular weight ratio of less than 5, Mz /Mw,
Said composition is disclosed in which the high molecular weight ethylene polymer is present in an amount of 2-20% by weight relative to the total weight of the composition.
The compositions disclosed in US Pat. No. 6,200,408 are used to make single and multi-layer blow molded bottles and containers, etc., and provide improved bottle weight reduction, etc., while maintaining high bottle top load support. It is said to provide processing properties (as this relates to reduced extrudate or die swell) and improved physical properties such as improved resistance to environmental stress cracking (paragraphs 0002, 0030).
However, it cannot be said that the composition described in Patent Document 7 is necessarily suitable as a resin for plastic fuel tanks for automobiles in terms of moldability.

Patent Document 8 discloses: a) Mw/Mn no greater than 3.5 and a deviation in the range of short chain branches (SCB) per 1000 backbone carbon atoms across the molecular weight distribution of ±0.5 SCB/1000C from the average SCB content; a high molecular weight component comprising an ethylene copolymer characterized by a short chain branching (SCB) profile and from 4 to 8 short chain branches (SCB) per 1000 backbone carbon atoms; and b) from 15 to 75 kg/ Compositions containing low molecular weight components comprising ethylene homopolymers or copolymers characterized by Mw in moles are disclosed.
The compositions disclosed in US Pat. No. 6,200,400 can allegedly be formed into a variety of articles, including household containers, household items, film products, drums, fuel tanks, pipes, geomembranes, and liners. It is used in particular for the production of PE-100 classified polyethylene pipes (paragraphs 0005, 0059, 0060).
However, it cannot be said that the composition described in Patent Document 8 is necessarily suitable as a resin for plastic fuel tanks for automobiles in terms of moldability.

International Publication No. 2008/087945 International Publication No. 2012/133713 JP 2017-179015 A Japanese Patent Publication No. 2005-511868 Japanese Patent Publication No. 2004-513202 Japanese translation of PCT publication No. 2005-501951 Japanese Patent No. 5551362 Japanese Patent No. 4995716

A hollow molded article using polyethylene is produced by blow molding in many cases. Generally, in blow molding, molten polyethylene is formed into a tubular shape from an extruder and is continuously extruded so that it hangs down. At this time, this cylindrical continuous body is sandwiched between a pair of blow molding dies, the dies are closed to close the open ends existing at the top and bottom of the cylinder (that is, the mold is clamped), and air is blown into the mold. The basic shape of the hollow molded product is completed by forming the shape of a container from the cylindrical body and cooling it.
Since it takes a certain amount of time to extrude the tubular continuous body of molten polyethylene until it reaches the length of a single hollow molded product, the tubular continuous body of molten polyethylene is pushed out by gravity due to its own weight while being extruded. It tends to grow under action. In addition, as the extrusion time elapses, the tubular continuous body of molten polyethylene becomes longer and its own weight increases. tends to be easy.
As described above, the tubular continuous body of molten polyethylene tends to elongate during the extrusion process, and the ease of elongation varies depending on the timing of extrusion from the extruder, so that the thickness may become uneven. As a result, the wall thickness of the hollow molded product, which is the final product, may also be uneven.
In particular, in the molding of fuel tanks for automobiles, in order to incorporate parts inside the tank, such as struts to withstand increases in tank internal pressure and parts to suppress the flow of fuel inside the tank and reduce noise, a tubular continuous body of molten polyethylene is used. A part may be inserted into the inside of the and welded to the inner surface. If such a process is added, the time required from the start of extrusion of the continuous tubular body of molten polyethylene to the clamping of the mold becomes longer, so that the tendency to stretch becomes stronger and the thickness tends to become non-uniform. As a result, the thickness of the hollow molded product, which is the final product, tends to be more uneven.

Conventionally, the moldability of polyethylene-based resin, which is the material for hollow molded products such as fuel tanks for automobiles, has been studied, but it cannot be said that the problem of uniform thickness of hollow molded products has been completely resolved. .
The present invention has been made in view of the above circumstances, and provides a polyethylene resin that has an excellent balance between rigidity and durability and is also excellent in moldability, and hollow plastic molded articles such as containers, bottles, and tanks. It is an object of the present invention to provide a polyethylene-based resin that is particularly useful as a material for fuel tanks for automobiles, and a hollow molded article containing the polyethylene-based resin.

The polyethylene-based resin of the present invention comprises, as an essential component, one or more ethylene-based polymers selected from the group consisting of ethylene homopolymers and copolymers of ethylene and α-olefins having 3 to 12 carbon atoms. and characterized by having the following properties [a], [b], [c] and [d].
[a] Melt flow rate (HLMFR) measured at a temperature of 190° C. and a load of 21.6 kg is 1 to 15 g/10 minutes.
[b] Density (d) is 0.950 to 0.965 g/cm ³ .
[c] Zero-shear viscosity when dynamic melt viscosity η ^* (unit: Pa·sec) measured at a temperature of 210° C. and frequency ω in the range of 100 to 0.01 rad/sec is approximated by the following formula (1) (η ₀ ) is 300,000 Pa·sec or more.
η ^* /η ₀ =1/{1+(τ ₀ ω) ⁿ } (1)
(In the formula (1), _τ0 is a parameter representing the relaxation time, and n is a parameter representing the shear rate dependence of the melt viscosity in the high shear rate region.)
[d] The swell ratio is 1.33 or more.

In the polyethylene resin of the present invention, it is preferable to further have the following property [e] from the viewpoint of further improving the balance between rigidity and durability.
[e] The rupture time (T) (unit: hour) and the density (d) (unit: g/cm ³ ) in the full circumference notch type creep test satisfy the relationship represented by the following formula (A).
log ₁₀ T≧−348.6×d+333.0 Formula (A)

In the polyethylene resin of the present invention, an ethylene polymer (A) having a density (d) of 0.910 to 0.945 g/cm ³ and an HLMFR of 0.01 to 10 g/10 min; and a density (d) of 0.945 to 0.975 g/cm ³ , a temperature of 190° C., a melt flow rate (MFR) measured at a load of 2.16 kg of 0.5 to 1,000 g/10 minutes, and an HLMFR is higher than the HLMFR of the ethylene polymer (A), and the properties [a], [b], [c] and [d ] is preferable from the point that it is easy to satisfy.

In the polyethylene resin of the present invention, the ethylene polymer (A) has an elongational viscosity (η (t)) (unit : Pa sec) and elongation time (t) (unit: sec). It is preferable because it satisfies [c] and [d] and tends to improve moldability.

In the polyethylene-based resin of the present invention, the ethylene-based polymer (A) has a ratio (Mw /Mn) is preferably 10 to 50 from the viewpoint of moldability and long-term durability.

In the polyethylene-based resin of the present invention, the ethylene-based polymer (A) is
From the viewpoint of long-term durability, it is preferable that HLMFR (unit: g/10 minutes) and density (d) (unit: g/cm ³ ) satisfy the relationship represented by the following formula (B).
d≦−0.0061× log ₁₀ (HLMFR)+0.9358 Formula (B)

The hollow molded article of the present invention has a layer containing the polyethylene-based resin of the present invention.

The blow molded article of the present invention may be at least one selected from the group consisting of fuel tanks, kerosene cans, drum cans, chemical containers, agricultural chemical containers, solvent containers and plastic bottles.

The present invention provides a polyethylene-based resin that has an excellent balance between rigidity and durability and is also excellent in moldability, and a polyethylene-based resin that is useful as a material for hollow plastic moldings such as containers, bottles, and tanks, especially automobile fuel tanks. A resin can be provided, and a hollow molded article containing the polyethylene-based resin can be provided.

FIG. 1 is a plot diagram of typical elongational viscosity, and is a diagram for explaining a case where an inflection point of elongational viscosity is observed. FIG. 2 is a plot diagram of a typical elongational viscosity, and is a diagram for explaining a case where no inflection point of the elongational viscosity is observed.

Hereinafter, the polyethylene-based resin of the present invention and its uses will be described in detail for each item. Further, in this specification, the term "to" indicating a numerical range is used to include the numerical values before and after it as lower and upper limits.

1. Characteristics of polyethylene resin The polyethylene resin of the present invention is one or more selected from the group consisting of ethylene homopolymers and copolymers of ethylene and α-olefins having 3 to 12 carbon atoms. It is characterized by containing a polymer as an essential component and having the following properties [a], [b], [c] and [d].
The polyethylene-based resin of the present invention simultaneously satisfies the following characteristics [a], [b], [c] and [d], so it has an excellent balance between rigidity and durability, and is also excellent in moldability. be.
The polyethylene-based resin of the present invention has HLMFR and density within specific ranges, and the zero shear viscosity and swell ratio are specified as in the following properties [a], [b], [c] and [d]. By making it equal to or more than the value, it is possible to balance the excellent moldability with rigidity and durability while improving moldability such as drawdown resistance and extrusion characteristics.
The polyethylene resin of the present invention has an excellent balance between rigidity and durability while ensuring the performance required for fuel tanks, for example, and has moldability such as improved drawdown resistance. It is suitable for manufacturing hollow molded products such as fuel tanks with improved

Characteristic [a]
The polyethylene-based resin of the present invention has a melt flow rate (HLMFR) of 1 to 15 g/10 minutes measured at a temperature of 190° C. and a load of 21.6 kg, from the viewpoint of exhibiting the effects of the present invention. The HLMFR is preferably 2 to 12 g/10 minutes, more preferably 3 to 10 g/10 minutes, from the viewpoint of the effects of the present invention.
If the HLMFR is less than 1 g/10 minutes, the extrusion rate of the parison will be insufficient in blow molding, resulting in unstable molding and melt fracture, which is not practical. If the HLMFR exceeds 15 g/10 minutes, the drawdown resistance deteriorates and is not practical.
HLMFR can be adjusted by controlling the polymerization temperature and hydrogen concentration during the polymerization of the ethylene-based polymer. For example, the HLMFR can be increased by increasing the polymerization temperature or increasing the hydrogen concentration. Also, it can be prepared by appropriately mixing two or more kinds of ethylene-based polymers.
Here, HLMFR can be measured in accordance with JIS K6922-2:1997 under conditions of a temperature of 190° C. and a load of 21.6 kg.

Characteristic [b]
The polyethylene-based resin of the present invention has a density of 0.950 to 0.965 g/cm ³ from the viewpoint of exhibiting the effects of the present invention. The density is preferably 0.950 to 0.960 g/cm ³ and more preferably 0.950 to 0.955 g/cm ³ from the viewpoint of the effects of the present invention.
If the density is less than 0.950 g/cm ³ , the hollow plastic molded article lacks rigidity and durability, and if it exceeds 0.965 g/cm ³ , the hollow plastic molded article lacks durability.
The density can be adjusted by controlling the type and content of the α-olefin during the polymerization of the ethylene polymer. For example, by reducing the α-olefin content in the ethylene polymer (reducing the amount of α-olefin added during polymerization), or by using an α-olefin with a small carbon number if the content is the same , can be densified. Also, it can be prepared by appropriately mixing two or more kinds of ethylene-based polymers.
The density conforms to JIS K-7112: 2004. After melting the pellets with a thermal compression molding machine at a temperature of 160 ° C., the temperature is lowered at a rate of 25 ° C./min to form a sheet with a thickness of 2 mmt. After conditioning for 48 hours in a room at 23° C., it can be placed in a density gradient tube and measured.

Characteristic [c]
In view of the effect of the present invention, the polyethylene resin of the present invention has a dynamic melt viscosity η ^* (unit: Pa sec) measured at a temperature of 210 ° C. and a frequency ω in the range of 100 to 0.01 rad / sec. The zero-shear viscosity (η ₀ ) as approximated by the following formula (1) is 300,000 Pa·sec or more.
η ^* /η ₀ =1/{1+(τ ₀ ω) ⁿ } (1)
(In the formula (1), _τ0 is a parameter representing the relaxation time, and n is a parameter representing the shear rate dependence of the melt viscosity in the high shear rate region.)
The polyethylene-based resin of the present invention has a zero-shear viscosity (η ₀ ) of 300,000 Pa·s or more and a characteristic [d] swell ratio described later of 1.33 or more, so that moldability is improved. Become.
When the zero-shear viscosity (η ₀ ) is 300,000 Pa·sec or more, the initial strain amount is small, the parison is less likely to sag, and drawdown resistance is improved. Good drawdown resistance results in improved wall thickness uniformity of the blow-molded product. If the zero shear viscosity (η ₀ ) is less than 300,000 Pa, moldability tends to deteriorate.

The zero-shear viscosity (η ₀ ) is preferably 800,000 Pa·sec or more, more preferably 820,000 Pa·sec or more, from the viewpoint of the effects of the present invention. On the other hand, although the upper limit of the zero-shear viscosity (η ₀ ) is not particularly limited, it can be set to 10,000,000 Pa·sec or less from the viewpoint of extrudability, for example.
Zero shear viscosity (η ₀ ) (unit: Pa·sec) is defined as the shear viscosity at zero shear flow and is used herein together with the relaxation time τ ₀ (sec) according to ANTEC '94 (The Society of Plastics Engineers , 1994), page 1814 (authored by S. Lai et al.), dynamic melt viscosity η ^* (unit: Pa·sec) is approximated by the Cross viscosity formula (formula (1) below). Here, the dynamic melt viscosity η ^* is measured at 210° C. using parallel plates with a plate spacing of 1.7 mm and a strain of 5%, with a frequency ω in the range of 100 to 0.01 (unit: rad/sec). can be obtained with a rheometer (Rheometrics Ares) and the approximation of the result to equation (1) below can be calculated using a commercially available computer program by regression methods. can.
η ^* /η ₀ =1/{1+(τ ₀ ω) ⁿ } (1)
In the above formula (1), n is a parameter indicating shear rate dependence of melt viscosity in a high shear rate region, and _τ0 is a parameter indicating relaxation time.
The zero-shear viscosity (η ₀ ) can be adjusted by adjusting the content of time relaxation components such as high molecular weight components and long chain branches in the ethylene polymer.
In addition, the content of the high molecular weight component can be adjusted by adjusting the hydrogen concentration or ethylene pressure during polymerization. When the polymerization is performed under conditions where the hydrogen concentration or ethylene pressure is low, the content of the high molecular weight component can be increased, and the content of the high molecular weight component can be increased. Shear viscosity (η ₀ ) can be increased. Furthermore, as the time relaxation component such as long chain branching, high pressure low density polyethylene (HPLDPE) can be used, but a polymer obtained by polymerization using a polymerization catalyst that easily generates long chain branching is used. can do. In the present invention, the zero-shear viscosity (η ₀ ) can be set to a desired value by appropriately combining the aforementioned control factors.

Characteristic [d]
From the viewpoint of the effect of the present invention, the swell ratio is 1.33 or more, preferably 1.35 or more. Although the upper limit of the swell ratio is not particularly limited, it can be set to 2.0 or less, more preferably less than 1.5, from the viewpoint of thickness uniformity.
The polyethylene resin of the present invention has good moldability when the swell ratio is 1.33 or more. Here, the swell is a phenomenon in which the resin melt extruded from the die head becomes larger than the slit width and clearance at the exit of the die head. When the swell ratio is 1.33 or more, for example, during blow molding, the load applied per unit area of the parison cross section is reduced, the stress is reduced, the strain rate is reduced, and as a result, the drawdown resistance is improved. . Good drawdown resistance results in improved wall thickness uniformity of the blow-molded product. When the swell ratio is less than 1.33, moldability tends to deteriorate even when the zero shear viscosity (η ₀ ) is 300,000 Pa·sec or more.
When both the zero-shear viscosity (η ₀ ) and the swell ratio satisfy the specific values of the present invention, the drawdown resistance can be improved and the moldability can be improved.
Here, the swell ratio tends to increase as the molecular weight of the polymer increases (when the HLMFR decreases), and the swell ratio tends to increase as the molecular weight distribution increases due to the high molecular weight component of the resin. In the present invention, the swell ratio can be set to a desired value by appropriately combining the aforementioned control factors.

The swell ratio is a strand extruded at a nozzle diameter of 1.0 mmφ, a nozzle length of 40.0 mm, an inflow angle of 90 °, a set temperature of 210 ° C., and a piston extrusion speed of 0.5 mm / min. The diameter (D) is measured using a laser measuring machine. Using the nozzle diameter (D ₀ ), the swell ratio is defined as D/D ₀ .

Characteristic [e]
In addition to the properties [a], [b], [c] and [d], the polyethylene resin of the present invention has the following property [e], which further improves the balance between rigidity and durability. preferred from
[e] The rupture time (T) (unit: hour) and the density (d) (unit: g/cm ³ ) in the full circumference notch type creep test satisfy the relationship represented by the following formula (A).
log ₁₀ T≧−348.6×d+333.0 Formula (A)
The rupture time by the full circumference notch type tensile creep test can be measured by the method described in the Examples.
Formula (A) shows the relationship between the rupture time (T) (unit: hour) and the density (d) (unit: g/cm ³ ) in the all-around notch type creep test, and the polyethylene resin of the present application is a conventional This shows that the durability in relation to the density is superior (the breaking time is long) compared to polyethylene resins. That is, in order to distinguish the polyethylene resin of the present application from the conventional polyethylene resin, the rupture time is considered to be a function that has a negative correlation with the increase in density, and the parameters of the function are set, and the polyethylene of the present application It indicates that the breaking time of the system resin is longer than the breaking time defined by the function in proportion to the density. Specifically, based on the data of Examples and Comparative Examples, values of density and rupture time that distinguish Examples and Comparative Examples with insufficient rupture time in proportion to density are assumed, and between the density and rupture time is determined by the method of least squares.

Those having a density (d) of 0.950 to 0.965 g/cm ³ and outside the range represented by the formula (A) have insufficient durability as a hollow plastic molded product, whereas the density (d) is 0. 0.950 to 0.965 g/cm ³ and included in the region represented by formula (A) have excellent durability.
When producing a polymer having the same HLMFR and the same density, the breaking time can be adjusted by controlling the hydrogen concentration during polymerization. For example, the wider the molecular weight distribution of polyethylene and the smaller the amount of long chain branching, the longer the breaking time. Therefore, the breaking time can be increased by increasing the hydrogen concentration.

The polyethylene resin of the present invention preferably has a rupture time (T) (unit: hours) of 40 hours or longer in a full circumference notch type creep test from the viewpoint of achieving the effects of the present invention. The longer the full circumference notch creep test (FNCT) time, the better the long term durability, such as environmental stress crack resistance.

Moreover, the polyethylene-based resin of the present invention preferably has the following property [f] in addition to the properties [a], [b], [c] and [d].
Characteristic [f]
The polyethylene resin of the present invention preferably has a flexural modulus of 1,100 to 1,700 MPa, more preferably 1,100 to 1,600 MPa, measured according to JIS K7171. More preferably 200 to 1,400 MPa, even more preferably 1,200 to 1,300 MPa.
When the flexural modulus is within the above range, the obtained hollow molded article is particularly excellent in rigidity at room temperature. That is, since it is hard and strong, it is possible to make the molded product thinner than before.
The flexural modulus can be adjusted by increasing or decreasing the density of the ethylene-based polymer, and increasing the density can increase the flexural modulus.

2. Composition and Manufacturing Method of Polyethylene-Based Resin The polyethylene-based resin of the present invention is one or more selected from the group consisting of homopolymers of ethylene and copolymers of ethylene and α-olefins having 3 to 12 carbon atoms. By using the ethylene polymer as an essential component, the above properties [a] to [d] are satisfied at the same time. The polyethylene-based resin of the present invention may further contain optional components described later in addition to the ethylene-based polymer, as long as the properties [a] to [d] are satisfied at the same time.
The copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms of the present invention contains 0.001 to 40 mol%, preferably 0.001 to 0.001 to It is an ethylene polymer containing 30 mol %, usually 2.0 mol % or less, preferably 0.02 to 1.5 mol %, more preferably 0.02 to 1.3 mol %.
Here, α-olefins having 3 to 12 carbon atoms (hereinafter also simply referred to as “α-olefins”) include propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 3 -methyl-1-pentene, 1-octene, 1-decene and the like. In the present invention, among these α-olefins, it is preferable to use at least one selected from 1-hexene, 4-methyl-1-pentene and 1-octene.
The ethylene polymer satisfying the properties [a] to [d] at the same time considers the polymerization temperature and hydrogen concentration during polymerization for controlling HLMFR, and the type and content of α-olefin for controlling density. Considering the amount, considering the content of the high molecular weight component and the polymerization catalyst for controlling the zero shear viscosity, considering the amount of the high molecular weight component and the molecular weight distribution for controlling the swell ratio, if necessary, all Considering the hydrogen concentration during polymerization, the type and content of α-olefin, the molecular weight distribution and the amount of long chain branching for controlling the rupture time of the peripheral notch type tensile creep test, one or two or more ethylene-based Manufactured as a polymer. In the case of two or more ethylene-based polymers, the two or more ethylene-based polymers may be continuously polymerized, or the two or more ethylene-based polymers are separately produced, and then the polymers are may be melted and mixed.

The polyethylene-based resin of the present invention is not particularly limited in its polymerization catalyst, production method, etc., as long as it satisfies the above properties [a] to [d] at the same time.
Among them, the polyethylene resin of the present invention contains 5 to 95% by mass of the following ethylene polymer (A) and 5 to 95% by mass of the following ethylene polymer (B) as the essential components. ] to [d] at the same time, and the characteristics [e] and [f] are easily satisfied.
Ethylene-based polymer (A): An ethylene-based polymer having a density (d) of 0.910 to 0.945 g/cm ³ and an HLMFR of 0.01 to 10 g/10 minutes.
Ethylene-based polymer (B): Density (d) of 0.945 to 0.975 g/cm ³ , melt flow rate (MFR) of 0.5 to 1,000 g measured at a temperature of 190°C and a load of 2.16 kg /10 minutes, and an ethylene polymer having a HLMFR higher than that of the ethylene polymer (A).

In the polyethylene-based resin of the present invention, the composition ratio of the ethylene-based polymer (A) and the ethylene-based polymer (B) simultaneously satisfies the above properties [a] to [d], and has an excellent balance between rigidity and durability. And, from the viewpoint of excellent moldability, the ethylene polymer (B) is preferably 10 to 90% by mass with respect to the ethylene polymer (A) 10 to 90% by mass, and the ethylene polymer (A ) 20 to 80% by mass of the ethylene polymer (B) is more preferably 20 to 80% by mass, and the ethylene polymer (B) is 30 to 70% by mass of 30 to 70% by mass of the ethylene polymer (A). % by mass is even more preferred.

(1) Ethylene polymer (A)
The ethylene-based polymer (A) is an ethylene homopolymer or a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms. A method for producing an ethylene homopolymer or a copolymer of ethylene and an α-olefin having 3 to 12 carbon atoms will be described later.
The ethylene polymer (A) has a density of 0.910 to 0.945 g/cm ³ , preferably 0.915 to 0.945 g/cm ³ , more preferably 0.920 to 0.940 g/cm 3 . ^cm3 . Density can be measured in a manner similar to the density of property [b] above.
If the density of the ethylene-based polymer (A) is less than 0.910 g/cm ³ , there is a risk that the molded article will lack rigidity, while if it exceeds 0.945 g/cm ³ , the durability will be insufficient. there is a risk of
Density adjustment can be made, for example, by changing the amount of α-olefin copolymerized with ethylene, and can be decreased by increasing the amount of α-olefin.

The ethylene polymer (A) has an HLMFR of 0.01 to 10 g/10 minutes, preferably 0.05 to 5 g/10 minutes, more preferably 0.1 to 1 g/10 minutes. The HLMFR can be measured in the same manner as the HLMFR of property [a] above.
If the HLMFR of the ethylene-based polymer (A) is less than 0.01 g/10 min, the fluidity during molding may be insufficient, and the molding may become unstable and impractical. When it exceeds, the durability tends to decrease.
HLMFR can be adjusted by changing the amount of chain transfer agent (such as hydrogen) coexisting during ethylene polymerization or by changing the polymerization temperature. You can make it bigger by doing

The ethylene polymer (A) has a molecular weight distribution represented by the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured by a gel permeation chromatography (GPC) method. It is preferably 10-50. When the molecular weight distribution (Mw/Mn) of the ethylene-based polymer (A) is 10 or more, moldability and long-term durability are likely to be improved. When the molecular weight distribution (Mw/Mn) of the ethylene polymer (A) is 50 or less, the impact resistance is easily improved.
Mw/Mn of the ethylene-based polymer (A) is preferably 11 or more, more preferably 15 or more, and preferably 50 or less, further preferably 40 or less.
The molecular weight distribution (Mw/Mn) can be set within a predetermined range mainly by selecting a polymerization catalyst and polymerization conditions, and can be set within a predetermined range by mixing multiple components with different molecular weights. be able to.
The molecular weight distribution (Mw/Mn) of the ethylene polymer (A) can be adjusted mainly by the type of polymerization catalyst used in the polymerization reaction of the ethylene polymer (A), preferably chromium such as Phillips catalyst. system catalysts.
GPC measurement can be performed by the method described in Examples.

In the ethylene polymer (A), HLMFR (unit: g/10 min) and density (d) (unit: g/cm ³ ) satisfy the relationship represented by the following formula (B). It is preferable from the viewpoint of durability.
d≦−0.0061× log ₁₀ (HLMFR)+0.9358 Formula (B)
If the ethylene polymer (A) does not satisfy the formula (B), the polyethylene-based resin of the present invention may lack long-term durability.
In order for the ethylene polymer (A) to satisfy the formula (B), a predetermined range can be obtained mainly by selecting a polymerization catalyst and polymerization conditions. Preferred catalysts include chromium-based catalysts such as Phillips catalysts.
Formula (B) shows the relationship between HLMFR (unit: g/10 min) and density (d) (unit: g/cm ³ ) of ethylene polymer (A). This indicates that the polymer has excellent long-term durability (lower density) than conventional ethylene polymers. That is, in order to distinguish the ethylene polymer (A) of the present application from the conventional ethylene polymer, the density for obtaining the necessary long-term durability is considered to be a function that has a negative correlation with the increase in HLMFR. is set, and the density of the ethylene polymer (A) of the present application is smaller than the density defined by the function in terms of HLMFR. Specifically, based on the data of Examples and Comparative Examples, assuming HLMFR and density values that distinguish between Examples with low density corresponding to HLMFR and Comparative Examples with high density corresponding to HLMFR, The parameters of the relational expression between them are determined by the method of least squares.

The ethylene-based polymer (A) further has an elongational viscosity (η(t)) (unit: Pa sec) measured at a temperature of 170°C and an elongation strain rate of 0.1 (unit: 1/sec) and elongation In the log-log plot of the time (t) (unit: seconds), it is preferable to observe the inflection point of the elongational viscosity due to strain hardening from the viewpoint of improving moldability. Since the ethylene-based polymer (A), which is a relatively high-molecular-weight component, has a molecular structure having a long-chain branched structure, the long-time relaxation component is increased, and moldability is improved.
In the present specification, the presence or absence of an inflection point of extensional viscosity due to strain hardening can be observed in the measurement of the degree of strain hardening.
Regarding the method for measuring the degree of strain hardening, as long as the uniaxial elongational viscosity can be measured, in principle the same value can be obtained by any method. Details are provided.
The presence or absence of an inflection point of extensional viscosity due to strain hardening of the ethylene polymer (A) according to the present invention can be confirmed by measuring the degree of strain hardening by the method described in Examples.
The inflection point of elongational viscosity caused by strain hardening is related to the number of long chain branches contained in the polymer. The number of long chain branches can be controlled by polymerizing using a polymerization catalyst that tends to generate long chain branches.

The ethylene-based polymer (A) used in the present invention can be polymerized using various polymerization catalysts as long as it satisfies the above properties. The ethylene-based polymer (A) used in the present invention is produced by polymerization using a conventionally known catalyst such as a chromium-based catalyst such as a Phillips catalyst, a Ziegler-Natta-based catalyst (ZN catalyst) or a metallocene-based catalyst. be able to. Polymerization catalysts that tend to form long-chain branches include, for example, chromium-based catalysts, specific metallocene-based catalysts, and polymerization catalysts such as those described in Japanese Patent Publication No. 2003-510204. Polyethylene derived from a chromium-based catalyst has a relatively wide molecular weight distribution and a molecular structure with a long-chain branched structure. Therefore, the ethylene-based polymer (A) used in the present invention can preferably be polymerized using a chromium-based catalyst.

A preferred example of the chromium-based catalyst is a chromium-based catalyst in which at least a portion of the chromium atoms become hexavalent by supporting a chromium compound on an inorganic oxide carrier and firing and activating it in a non-reducing atmosphere. It is known and publicly known as a catalyst. A review of this catalyst can be found in M.W. P. McDaniel, Advances in Catalysis, Volume 33, 47, 1985, Academic Press Inc. , M. P. McDaniel, Handbook of Heterogeneous Catalysis, page 2400, 1997, VCH, M.; B. Welch et al., Handbook of Polyolefins: Synthesis and Properties, p. 21, 1993, Marcel Dekker et al.

As the inorganic oxide support, metal oxides of Groups 2, 4, 13 or 14 of the periodic table are preferred. Specific examples include magnesia, titania, zirconia, alumina, silica, thoria, silica-titania, silica-zirconia, silica-alumina, or mixtures thereof. Among them, silica, silica-titania, silica-zirconia and silica-alumina are preferred. In the case of silica-titania, silica-zirconia, silica-alumina, titanium, zirconium or aluminum atoms are 0.2 to 10% by mass, preferably 0.5 to 7% by mass, more preferably 1 to 10% by mass as metal components other than silica. One containing 5% by mass is used.
Preparation, physical properties and characteristics of supports suitable for these chromium-based catalysts are described in C.I. E. Marsden, Preparation of Catalysts, Volume V, p.215, 1991, Elsevier Science Publishers, C.I. E. Marsden, Plastics, Rubber and Composites Processing and Applications, Volume 21, p.193, 1994.

The specific surface area of the chromium-based catalyst support before firing activation is 250 to 1,000 m ² /g, preferably 300 to 900 m ² /g, more preferably 400 to 800 m ² /g. It is preferred to choose an oxide support. When the specific surface area is less than 250 m ² /g, both the durability and the impact resistance may decrease, which is thought to be related to the narrow molecular weight distribution and increased long-chain branching. Further, a carrier with a specific surface area exceeding 1,000 m ² /g may be difficult to manufacture.

The pore volume of the inorganic oxide support is 0.5 to 3.0 cm ³ /g, preferably 1.0 to 2.0 cm ³ /g, as in the case of supports used for general chromium-based catalysts. and more preferably in the range of 1.2 to 1.8 cm ³ /g. If the pore volume is less than 0.5, the pores become smaller due to the polymerization polymer during polymerization, and the monomer cannot diffuse, which may lower the activity. Carriers with pore volumes greater than 3.0 cm ³ /g may be difficult to manufacture.
The average particle diameter of the inorganic oxide carrier is 10 to 200 μm, preferably 20 to 150 μm, more preferably 30 to 100 μm, as with carriers used for general chromium-based catalysts.

A chromium compound is supported on the inorganic oxide support. The chromium compound may be a compound in which at least a portion of the chromium atoms become hexavalent by firing activation in a non-reducing atmosphere after being supported, such as chromium oxide, chromium halide, oxyhalide, and chromate. , dichromates, nitrates, carboxylates, sulfates, chromium-1,3-diketo compounds, chromate esters, and the like. Specifically, chromium trioxide, chromium trichloride, chromyl chloride, potassium chromate, ammonium chromate, potassium dichromate, chromium nitrate, chromium sulfate, chromium acetate, chromium tris(2-ethylhexanoate), chromium acetyl Acetonate, bis(tert-butyl)chromate, and the like can be mentioned. Among them, chromium trioxide, chromium acetate, and chromium acetylacetonate are preferred. Even when a chromium compound having an organic group such as chromium acetate or chromium acetylacetonate is used, the organic group portion is burned by firing activation in a non-reducing atmosphere, which will be described later, and finally chromium trioxide is used. It is known that at least some of the chromium atoms become hexavalent and are immobilized in a chromate ester structure (VJ Ruddick Chem., Volume 100, 11062, 1996, SM Augustine et al., J. Catal., Volume 161, 641, 1996).

The loading of the chromium compound on the inorganic oxide carrier can be carried out by known methods such as impregnation, solvent distillation, sublimation, etc. A suitable method may be used depending on the type of chromium compound used. The amount of the chromium compound to be supported is 0.2 to 2.0% by mass, preferably 0.3 to 1.7% by mass, more preferably 0.5 to 1.5% by mass as chromium atoms relative to the carrier. be.

After supporting the chromium compound, it is fired to perform an activation treatment. The calcination activation can be carried out in a non-reducing atmosphere substantially free of moisture, such as oxygen or air. At this time, an inert gas may coexist. Preferably, it is carried out in a fluid state using air sufficiently dried by circulating molecular sieves or the like. Firing activation is carried out at 350 to 900° C., preferably 420 to 850° C., more preferably 450 to 800° C., for 30 minutes to 48 hours, preferably 1 hour to 36 hours, more preferably 2 hours to 24 hours. By this firing activation, at least a portion of the chromium atoms of the chromium compound supported on the inorganic oxide support are oxidized to hexavalent and chemically fixed on the support. If the temperature is less than 350°C, the polymerization activity may be lost. On the other hand, if the firing activation is performed at a temperature exceeding 900° C., sintering may occur and the activity may decrease.
By using the chromium-based catalyst thus obtained, an ethylene-based polymer suitable for the ethylene-based polymer (A) can be produced.

The ethylene-based polymer (A) is an ethylene homopolymer or ethylene and an α-olefin having 3 to 12 carbon atoms, such as propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene. , 1-octene and the like. Copolymerization with a diene is also possible for the purpose of modification. Examples of diene compounds used at this time include butadiene, 1,4-hexadiene, ethylidenenorbornene, dicyclopentadiene and the like. The comonomer content during polymerization can be arbitrarily selected. The α-olefin content in the is 0.001 to 40 mol%, preferably 0.001 to 30 mol%, usually 2.0 mol% or less, preferably 0.02 to 1.5 mol%, more preferably 0.02 to 1.5 mol%. 02 to 1.3 mol %.

The molecular weight of the produced polymer can be adjusted to some extent by changing the polymerization conditions such as the polymerization temperature and the molar ratio of the catalyst, but the molecular weight can be more effectively adjusted by adding hydrogen to the polymerization reaction system. can be done.
Also, a component for removing moisture, a so-called scavenger, may be added to the polymerization system without any problem.
Such scavengers include organoaluminum compounds such as trimethylaluminum, triethylaluminum and triisobutylaluminum, the above organoaluminumoxy compounds, modified organoaluminum compounds containing branched alkyl, organozinc compounds such as diethyl zinc and dibutyl zinc, diethyl Magnesium, organomagnesium compounds such as dibutylmagnesium and ethylbutylmagnesium, Grignard compounds such as ethylmagnesium chloride and butylmagnesium chloride, and the like are used. Among these, triethylaluminum, triisobutylaluminum and ethylbutylmagnesium are preferred, and triethylaluminum is particularly preferred.
It can also be applied to a multi-stage polymerization system having two or more stages in which polymerization conditions such as hydrogen concentration, amount of monomers, polymerization pressure and polymerization temperature are different from each other.

Conventionally known methods can be used as appropriate for the polymerization method of the ethylene-based polymer (A). For example, slurry polymerization, a liquid phase polymerization method such as solution polymerization, or a gas phase polymerization method can be employed, but the slurry polymerization method is particularly preferable, and the slurry polymerization method using a pipe loop type reactor, Any slurry polymerization method using an autoclave reactor can be used. Among them, a slurry polymerization method using a pipe loop type reactor is preferable (for details of a pipe loop type reactor and slurry polymerization using the same, see Kazuo Matsuura and Naotaka Mikami, "Polyethylene Technical Readers", pp. 148, 2001, listed in the Industrial Research Institute).

A liquid phase polymerization method is usually carried out in a hydrocarbon solvent. As the hydrocarbon solvent, inert hydrocarbons such as propane, n-butane, isobutane, n-pentane, isopentane, hexane, heptane, octane, decane, cyclohexane, benzene, toluene, and xylene are used singly or as a mixture. As the gas phase polymerization method, a commonly known polymerization method such as a fluidized bed, agitated bed, etc., can be employed in the presence of an inert gas, and a so-called condensing mode in which a medium for removing the heat of polymerization is allowed to coexist can also be employed. .
The polymerization temperature in the liquid phase polymerization method is generally 0 to 300°C, practically 20 to 200°C, preferably 40 to 180°C, more preferably 50 to 150°C, particularly preferably 70 to 110°C. °C. The catalyst concentration and ethylene concentration in the reactor can be any concentration sufficient to allow polymerization to proceed. For example, the catalyst concentration can range from about 0.0001 to about 5 weight percent based on the weight of the reactor contents for liquid phase polymerization. Similarly, the ethylene concentration can range from about 1% to about 10% based on the weight of the reactor contents for liquid phase polymerizations. Similarly, the ethylene concentration can be in the range of 0.1 to 10 MPa as total pressure in the case of gas phase polymerization. In addition, it is possible to carry out polymerization in the presence of hydrogen. In order to produce an ethylene-based polymer with an excellent balance of durability, impact resistance, and rigidity, it is necessary to set hydrogen and ethylene in a specific ratio. It is better to polymerize in the bottom. Hydrogen generally functions as a so-called chain transfer agent for adjusting molecular weight.

As a polymerization method, in addition to single-stage polymerization in which an ethylene-based polymer is produced using one reactor, at least two or more reactions are used in order to improve the production amount or to widen the molecular weight distribution or comonomer composition distribution. Multistage polymerization can also be carried out by connecting the reactors in series and/or in parallel. In the case of multi-stage polymerization, serial multi-stage polymerization is preferred in which a plurality of reactors are connected and the reaction mixture obtained by polymerization in the first reactor is continuously supplied to the second and subsequent reactors. In the series multi-stage polymerization method, the polymerization reaction mixture in the reactor of the former stage is transferred to the reactor of the subsequent stage through a connecting pipe by continuous discharge.

A specific embodiment of the above multi-stage polymerization will be described by taking a two-stage polymerization using two reactors as an example.
In the case of two-stage polymerization, ethylene with the same MFR and density may be produced in the first-stage reactor and the second-stage reactor under the same polymerization conditions, or the same MFR and density in the first-stage reactor and the second-stage reactor. However, in order to widen the molecular weight distribution, it is preferable to differentiate the molecular weights of the ethylene polymers produced in both reactors. Any production method in which the high molecular weight component is produced in the first stage reactor and the low molecular weight component in the second stage reactor, or the low molecular weight component is produced in the first stage reactor and the high molecular weight component is produced in the second stage reactor. However, the method of producing the high molecular weight component in the first stage reactor and the low molecular weight component in the second stage reactor requires an intermediate hydrogen flash tank for the transition from the first stage to the second stage. It is more preferable in terms of productivity because it does not

In the first stage, copolymerization using ethylene alone or, if necessary, other α-olefins as comonomers is performed while adjusting the molecular weight by adjusting the ratio of hydrogen concentration to ethylene concentration, the polymerization temperature, or both, and the comonomer concentration of ethylene. A polymerization reaction is carried out while adjusting the density by the weight ratio to the concentration.
In the second stage, there is hydrogen in the reaction mixture flowing in from the first stage and ethylene also flowing in, but if necessary, fresh hydrogen and ethylene, respectively, can be added. Therefore, in the second stage, the polymerization reaction can be carried out while adjusting the molecular weight by adjusting the ratio of hydrogen concentration to ethylene concentration, the polymerization temperature, or both, and adjusting the density by adjusting the ratio of comonomer concentration to ethylene concentration. With respect to catalysts and organometallic compounds such as organoaluminum compounds, not only does the polymerization reaction continue in the second stage with the catalyst that flows in from the first stage, but the catalyst and organometallic compounds such as organoaluminum compounds are newly added in the second stage. Either compound or both may be supplied.

The ethylene polymer (A) used in the present invention can be polymerized sequentially and continuously in a single polymerization vessel, a plurality of reactors connected in series or in parallel, and a plurality of The ethylene polymer may be polymerized separately and then mixed.

(2) Ethylene polymer (B)
The ethylene polymer (B) has a density (d) of 0.945 to 0.975 g/cm ³ and a melt flow rate (MFR) of 0.5 to 1, measured at a temperature of 190° C. and a load of 2.16 kg. 000 g/10 min, and an ethylene polymer having a higher HLMFR than that of the ethylene polymer (A).

The ethylene polymer (B) has a density of 0.945 to 0.975 g/cm ³ , preferably 0.950 to 0.972 g/cm ³ , more preferably 0.955 to 0.970 g/cm 3 . ^cm3 . Density can be measured in a manner similar to the density of property [b] above.
If the density of the ethylene-based polymer (B) is less than 0.945 g/cm ³ , there is a risk that the molded article will lack rigidity ^. There is a risk of shortage.
Density adjustment can be made, for example, by changing the amount of α-olefin copolymerized with ethylene, and can be decreased by increasing the amount of α-olefin.

The ethylene polymer (B) has a melt flow rate (MFR) of 0.5 to 1,000 g/10 minutes, preferably 1 to 500 g/10 minutes, measured at a temperature of 190° C. and a load of 2.16 kg. Yes, more preferably 2 to 300 g/10 minutes. The MFR can be measured in a manner similar to the HLMFR of property [a] above.
If the MFR of the ethylene-based polymer (B) is less than 0.5 g/10 minutes, the fluidity during molding may be insufficient, and the molding may become unstable and impractical. minutes, the long-term durability tends to decrease.
The MFR can be adjusted by changing the amount of a chain transfer agent (such as hydrogen) coexisting during ethylene polymerization or by changing the polymerization temperature. You can make it bigger by doing

The ethylene-based polymer (B) is selected so that the HLMFR of the ethylene-based polymer (B) is higher than the HLMFR of the ethylene-based polymer (A). By selecting an ethylene-based polymer (B) having a higher HLMFR than the ethylene-based polymer (A), a polyethylene having excellent long-term durability can be obtained.
The HLMFR of the ethylene polymer (B) is preferably 10 to 5,000 g/10 minutes, more preferably 50 to 2,000 g/10 minutes, from the viewpoint of the effect of the present invention.

The ethylene polymer (B) has a molecular weight distribution represented by the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured by gel permeation chromatography (GPC). 8 to 100 is preferable in terms of swell.
The lower limit of Mw/Mn of the ethylene polymer (B) is preferably 10 or more, more preferably 12 or more, and the upper limit is preferably 50 or less, more preferably 30 or less.
The molecular weight distribution (Mw/Mn) of the ethylene polymer (B) can be adjusted mainly by the type of polymerization catalyst used in the polymerization reaction of the ethylene polymer (B), preferably chromium such as Phillips catalyst. system catalysts and Ziegler-Natta system catalysts.

The ethylene-based polymer (B) is not particularly limited in terms of polymerization catalyst, production method, etc., as long as it satisfies the above constituent requirements. The ethylene-based polymer (B) used in the present invention can be produced by polymerization using conventionally known catalysts such as chromium-based catalysts such as Phillips catalysts, Ziegler-Natta-based catalysts and metallocene-based catalysts. Polymerization is preferably carried out using a chromium-based catalyst and/or a Ziegler-Natta-based catalyst. Polyethylene derived from a chromium-based catalyst has a relatively wide molecular weight distribution and a molecular structure with a long-chain branched structure, which makes it easy to blow mold, specifically, it has characteristics such as a large swell ratio and melt tension. is. This is also because the polyethylene derived from the Ziegler-Natta catalyst has a moderately wide molecular weight distribution and excellent melt molding properties and mechanical strength.

As the chromium-based catalyst used for producing the ethylene-based polymer (B), the same chromium-based catalyst as described for the ethylene-based polymer (A) can be used.

On the other hand, the Ziegler-Natta catalyst is a polymerization catalyst that uses titanium as an active species, and can be appropriately selected and used from conventionally known catalysts. As the Ziegner-Ratta catalyst, a magnesium-titanium composite Ziegler-Natta catalyst is particularly preferable. The magnesium-titanium composite Ziegler-Natta catalyst has excellent particle shape and excellent polymerization activity.
The magnesium-titanium composite Ziegler-Natta catalyst is preferably modified with an organoaluminum compound. By using such a modified Ziegler-Natta catalyst, it is possible to produce polyethylene with few short chain branches. A magnesium-titanium composite Ziegler-Natta catalyst modified with an organoaluminum compound can be produced with reference to JP-A-2012-72229.

The ethylene polymer (B) is an ethylene homopolymer or ethylene and an α-olefin having 3 to 12 carbon atoms, such as propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene. , 1-octene and the like. Copolymerization with a diene is also possible for the purpose of modification. Examples of diene compounds used at this time include butadiene, 1,4-hexadiene, ethylidenenorbornene, dicyclopentadiene and the like. The comonomer content during polymerization can be arbitrarily selected. The α-olefin content in the is 0.001 to 40 mol%, preferably 0.001 to 30 mol%, usually 2.0 mol% or less, preferably 0.02 to 1.5 mol%, more preferably 0.02 to 1.5 mol%. 02 to 1.3 mol %.

As for the polymerization method of the ethylene-based polymer (B), conventionally known methods can be appropriately used. The ethylene-based polymer (B) can be produced in the same manner as described for the ethylene-based polymer (A).

The polyethylene-based resin of the present invention may be obtained by multi-stage polymerization of the ethylene-based polymer (A) and the ethylene-based polymer (B), or may be a blended composition.
A suitable method for producing a polyethylene resin by multi-stage polymerization is to use the above-mentioned catalyst in a polymerization apparatus in which two or more reactors are connected in series, in which the ethylene polymer (A) is produced in the former reactor, or the ethylene polymer (B) in the former stage reactor and the ethylene polymer (A) in the latter stage reactor are continuously polymerized. .
As a method for blending the ethylene polymer (A) and the ethylene polymer (B), a method in which the degree of kneading is increased is preferable. A blending method using a machine, a brabender, a kneader brabender, or the like can be mentioned.

(3) Other additives The polyethylene resin of the present invention, in addition to the ethylene polymer (A) and the ethylene polymer (B), has the following properties within a range that simultaneously satisfies the properties [a] to [d]. can be blended as optional ingredients.
For example, various ethylene-based polymers such as high-density polyethylene, low-density polyethylene, high-pressure polyethylene, polar monomer-graft-modified polyethylene, ethylene-based wax, ultra-high-molecular-weight polyethylene, ethylene-based elastomer, and modified products thereof can be used. Addition of high-density polyethylene is preferable for improving rigidity, heat resistance, impact strength, and the like. Addition of low-density polyethylene is preferable for improving flexibility, impact strength, easy adhesion, transparency, low-temperature strength, and the like. Addition of high-pressure polyethylene is preferable for improving flexibility, easy adhesion, transparency, low-temperature strength, moldability and the like. Addition of polar monomer-graft-modified polyethylene such as maleic acid-modified polyethylene, ethylene/acrylic acid derivative copolymer, and ethylene/vinyl acetate copolymer improves flexibility, easy adhesion, colorability, compatibility with various materials, gas barrier properties, etc. is preferable for improving Addition of ethylene wax is preferable in order to improve colorability, compatibility with various materials, moldability, and the like. Addition of ultra-high molecular weight polyethylene is preferable in order to improve mechanical strength, wear resistance, and the like. Addition of an ethylene-based elastomer is preferable in order to improve flexibility, mechanical strength, impact strength, and the like.
In addition to the above polymers, various resins can be used. Specifically, various nylon resins, various polyamides, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), various polyesters, polycarbonate resins, EVOH, EVA, PMMA, PMA, various engineering plastics, polylactic acid, celluloses, They include natural rubbers, polyurethane, vinyl chloride, fluorine-based resins such as Teflon (registered trademark), inorganic polymers such as silicone resins, and the like.

The polyethylene-based resin of the present invention can be pelletized by mechanical melt-mixing using a pelletizer, homogenizer, or the like according to a conventional method, and then molded using various molding machines to obtain a desired molded product.
In addition to other olefin polymers and rubbers, antioxidants, ultraviolet absorbers, light stabilizers, lubricants, antistatic agents, antistatic agents, etc., may be added to the ethylene polymer obtained by the above method in accordance with conventional methods. Known additives such as clouding agents, antiblocking agents, processing aids, coloring pigments, cross-linking agents, foaming agents, inorganic or organic fillers, and flame retardants can be added.
As additives, for example, antioxidants (phenol-based, phosphorus-based, sulfur-based), lubricants, antistatic agents, light stabilizers, ultraviolet absorbers, etc. can be used singly or in combination of two or more. Fillers that can be used include calcium carbonate, talc, metal powder (aluminum, copper, iron, lead, etc.), silica stone, diatomaceous earth, alumina, gypsum, mica, clay, asbestos, graphite, carbon black, and titanium oxide. Among them, it is preferable to use calcium carbonate, talc and mica. In any case, the above polyethylene may be mixed with various additives as necessary, and kneaded with a kneading extruder, Banbury mixer, or the like to obtain a molding material.

Examples of antioxidants include 2,4-dimethyl-6-t-butylphenol, 2,6-di-t-butylphenol, 2,6-di-t-butyl-p-cresol, 2,6-di-t -Butyl-4-ethylphenol, 2,4,6-tri-t-butylphenol, 2,5-di-t-butylhydroquinone, butylated hydroxyanisole, n-octadecyl-3-(3',5'-di -t-butyl-4'-hydroxyphenyl)propionate, monophenols such as stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 4,4'-dihydroxydiphenyl, 2, 2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 4,4'-methylenebis(2,6-di-t-butylphenol ), 4,4′-butylidenebis(3-methyl-6-t-butylphenol), 2,6-bis(2′-hydroxy-3′-t-butyl-5′-methylbenzyl)-4-methylphenol, etc. bisphenol, 1,1,3-tris(2′-methyl-4′-hydroxy-5′-t-butylphenyl)butane, 1,3,5-trimethyl-2,4,6-tris(3′ ,5′-di-t-butyl-4′-hydroxybenzyl)benzene, tris(3,5-di-t-butyl-4-hydroxyphenyl)isocyanurate, tris[β-(3,5-di-t -Butyl-4-hydroxyphenyl)propionyloxyethyl]isocyanurate, tri- or higher polyphenols such as tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane , 2,2′-thiobis(4-methyl-6-t-butylphenol), 4,4′-thiobis(2-methyl-6-t-butylphenol), 4,4′-thiobis(3-methyl-6- t-butylphenol), naphthylamines such as aldol-α-naphthylamine, phenyl-α-naphthylamine, phenyl-β-naphthylamine, diphenylamines such as p-isopropoxydiphenylamine, N,N'-diphenyl-p -phenylenes such as phenylenediamine, N,N'-di-β-naphthyl-p-phenylenediamine, N-cyclohexyl-N'-phenyl-p-phenylenediamine, N-isopropyl-N'-phenyl-p-phenylenediamine A diamine-based one and the like are included. Among these, monophenols, bisphenols, tri- or higher polyphenols, thiobisphenols and the like are preferred.

Specific examples of light stabilizers and UV absorbers include 4-t-butylphenyl salicylate, 2,4-dihydroxybenzophenone, 2,2′-dihydroxy-4-methoxybenzophenone, ethyl-2-cyano-3,3′. -diphenyl acrylate, 2-ethylhexyl-2-diano-3,3'-diphenyl acrylate, 2(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole, 2(2 '-hydroxy-3,5'-di-t-butylphenyl)benzotriazole, 2(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-hydroxy-5-chlorobenzophenone, 2-hydroxy-4- Methoxybenzophenone-2-hydroxy-4-octoxybenzophenone, 2(2'-hydroxy-4-octoxyphenyl)benzotriazole, monoglycol salicylate, oxalic acid amide, phenyl salicylate, 2,2',4 , 4′-tetrahydroxybenzophenone, and the like.

Metal damage inhibitors include hydrazide derivatives, oxalic acid derivatives, salicylic acid derivatives and the like.
Hydrazide derivatives as anti-metal damage agents include N,N'-diacetyladipate hydrazide, bis(α-phenoxypropionyl hydrazide) adipate, bis(α-phenoxypropionyl hydrazide) terephthalate, bis(α-phenoxypropionyl hydrazide) sebate. ), isophthalic acid bis (β-phenoxypropionyl hydrazide) and the like, and oxalic acid derivative metal inhibitors include N,N'-dibenzal (oxalyl dihydrazide), N-benzal-(oxalyl dihydrazide), oxalyl bis -4-methylbenzylidene hydrazide, oxalylbis-3-ethoxybenzylidene hydrazide and the like, and salicylic acid derivative metal inhibitors such as 3-(N-salicyloyl)amino-1,2,4-triazole, decamethylene dicarboxylic acid, and acid disalicyloyl hydrazides.
A preferred metal inhibitor in the present invention is a salicylic acid derivative metal inhibitor.

The amount of stabilizers such as antioxidants, light stabilizers, ultraviolet absorbers, and metal damage inhibitors added is not particularly limited, but is preferably 0.001 per 100 parts by mass of the ethylene polymer. to 5 parts by mass, more preferably 0.001 to 3 parts by mass. If the amount is less than 0.001 parts by mass, a sufficient stabilizing effect cannot be obtained, and if the amount exceeds 5 parts by mass, effects such as coloring will occur and molding defects will tend to occur. not economically viable.
The stabilizer in the ethylene-based polymer can be measured using fluorescent X-ray analysis, gas chromatography, and liquid chromatography.

3. Molding of polyethylene-based resin The polyethylene-based resin of the present invention has excellent balance between rigidity and durability, and is excellent in moldability. Therefore, various moldings can be produced by various molding methods. Since it is excellent in drawdown resistance, it is preferably molded mainly by a blow molding method or the like, and various molded articles such as hollow containers are preferably obtained.
The blow-molded article of the polyethylene-based resin of the present invention is not particularly limited, but can be produced by an extrusion blow molding method using a conventionally known multilayer blow-molding machine. For example, after heating and melting the constituent resin of each layer with a plurality of extruders, the molten parison is extruded with a multi-layer die, then this parison is sandwiched between molds, and air is blown into the interior of the parison to produce a multi-layer hollow plastic. A molded article is produced.

In addition, the polyethylene-based resin of the present invention has an excellent balance between rigidity and durability, and is excellent in moldability and appearance of molded products. It is offered as products such as containers for liquids, containers for solvents, and various plastic bottles. Other uses include various pipes for gas and water supply, films, laminates, coatings, fibers, injection moldings for food and daily miscellaneous goods, compression injection moldings, rotational moldings, extrusion moldings, etc. mentioned.
In addition, the polyethylene resin obtained in the present invention has the characteristic of having a wide molecular weight distribution and is excellent in compatibility with other ethylene polymers, so it can be used not only as a single material but also with other polyethylenes to improve tension. It can also be used as a blend material for the product applications listed above.
Since the polyethylene-based resin of the present invention satisfies the above properties, a molded article using it has excellent environmental stress crack resistance, impact resistance, rigidity, heat resistance, and thickness. uniformity is improved.
Therefore, it is suitable for applications such as containers that require such properties. For example, it can be suitably used for applications such as fuel tanks for automobiles, containers for other cosmetics, containers for detergents, shampoos and conditioners, and containers for foods such as edible oils.
The polyethylene resin of the present invention has an excellent balance between rigidity and durability, has moldability such as improved drawdown resistance, and improves the thickness uniformity of the product. , fuel tanks for automobiles, etc.

4. Hollow molded article The hollow molded article of the present invention includes a structure having at least one layer containing the polyethylene-based resin of the present invention, preferably a structure having multiple layers. Further, the hollow molded article of the present invention may have a single-layer structure containing the polyethylene-based resin of the present invention. When the hollow molded article has a multilayer structure, it preferably has a permeation reduction blocking layer, and a barrier layer is usually used for the permeation reduction blocking layer.

When the layer structure of the hollow molded article (hollow plastic molded article) of the present invention is two or more layers, it is preferable that the innermost layer and the outermost layer contain the polyethylene-based resin of the present invention.
The hollow molded article is preferably a multi-layer structure in which at least one barrier layer is present to reduce the permeation of volatile substances and the barrier layer comprises a permeation-reducing barrier layer composed of a polar barrier polymer. For example, in the case of plastic fuel tanks, if the walls of the tank are multi-layered, a barrier layer (which alone has insufficient moldability and mechanical strength) can be fixed between two layers comprising the polyethylene of the present invention. There are advantages. As a result, the moldability of materials having two or more layers containing the polyethylene-based resin of the present invention, particularly during co-extrusion blow molding, is improved primarily due to the improved moldability of the polyethylene-based resin of the present invention. be done. Furthermore, the improved performance of the polyethylene-based resin of the present invention has a very important effect on the mechanical strength of the material, so that the strength of the hollow molded article of the present invention can be significantly increased.
In the case of hollow molded products, the surface of the polyethylene-based resin layer of the present invention may be coated with a base layer by treatment such as fluorination, surface coating or plasma polymerization.

The hollow molded product is preferably a hollow molded product with 6 layers of 4 types, in which the innermost layer, the adhesive layer, the barrier layer, the adhesive layer, the recycled material layer, and the outermost layer are laminated in this order from the inside. By sandwiching the barrier layer between the adhesive layers, a high level of barrier properties can be exhibited. By having the recycled material layer between the outermost layer and the adhesive layer, the effect of reducing the cost of raw materials and maintaining the rigidity of the hollow molded product is exhibited.

The structure of each layer and the layer composition ratio in the Noh are described in detail below.

(1) Outermost Layer The resin constituting the outermost layer of the hollow molded product is preferably the polyethylene-based resin of the present invention.

(2) Innermost layer The resin constituting the innermost layer of the hollow molded article is preferably the polyethylene-based resin of the present invention, and may be the same as or different from the resin constituting the outermost layer. There may be.

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

(4) Adhesive layer The resin forming the adhesive layer of the hollow molded product is selected from high-density polyethylene, low-density polyethylene, linear low-density polyethylene, etc. graft-modified with unsaturated carboxylic acid or its derivative. In particular, it is preferably made of high-density polyethylene graft-modified with an unsaturated carboxylic acid or a derivative thereof.
The content of the unsaturated carboxylic acid or derivative thereof is preferably 0.01 to 5% by mass, more preferably 0.01 to 3% by mass, and still more preferably 0.01 to 1% by mass in the resin constituting the adhesive layer. %. If the content of the unsaturated carboxylic acid or derivative thereof is less than 0.01% by mass, sufficient adhesion performance is not exhibited, and if it exceeds 5% by mass, the unsaturated carboxylic acid that does not contribute to adhesion adversely affects adhesion. give.

(5) Recycled material layer The resins that form the recycled material layer of the hollow molded product include the polyethylene resin that forms the outermost layer, the polyethylene resin that forms the innermost layer, the resin that forms the barrier layer, and the adhesive layer. A composition containing a resin.
Each component of the resin that forms the recycled material layer can be used as a new product, or scraps, burrs, and other unnecessary parts of the multilayer laminate containing each layer made of each resin can be collected and reused for such recycling. The product can also be used as a component raw material for each component. For example, there is a regrind resin obtained by pulverizing a once-molded, used and used hollow molded article (an automotive fuel tank product, etc.). When using molding burrs and unused parisons generated when manufacturing multi-layer laminates as recycled materials, the compatibility of various components may decrease. You may

(6) Layer composition ratio of hollow molded product The hollow molded product is not limited by the thickness structure of each layer, but for example, the thickness ratio is 10 to 30% for the outermost layer, 20 to 50% for the innermost layer, and 1 to 15% for the barrier layer. %, 1-15% for the adhesive layer, and 30-60% for the recycled material layer (where the sum of all layer thickness composition ratios is 100%).
The layer composition ratio of the outermost layer is preferably 10 to 30%, more preferably 10 to 25%, still more preferably 10 to 20%, relative to the layer thickness of the hollow molded product. If the layer composition ratio of the outermost layer is less than 10%, the impact resistance is insufficient, and if it exceeds 30%, the molding stability of the hollow molded article tends to be impaired.
The layer composition ratio of the innermost layer is preferably 20 to 50%, more preferably 35 to 50%, still more preferably 40 to 50% of the layer thickness of the hollow molded product. If the layer composition ratio of the innermost layer is less than 20%, the rigidity of the hollow plastic molded product becomes apparent, and if it exceeds 50%, the molding stability of the hollow plastic molded product tends to be impaired.
The layer composition ratio of the barrier layer is preferably 1 to 15%, more preferably 1 to 10%, and still more preferably 1 to 5% of the layer thickness of the hollow molded article. When the layer composition ratio of the barrier layer is less than 1%, the barrier performance tends to be unsatisfactory, and when it exceeds 15%, the impact performance tends to be insufficient.
The layer composition ratio of the adhesive layer is preferably 1 to 15%, more preferably 1 to 10%, and still more preferably 1 to 5% of the layer thickness of the hollow molded product. If the layer composition ratio of the adhesive layer is less than 1%, the adhesion performance is unsatisfactory, and if it exceeds 15%, the rigidity of the hollow molded product tends to be insufficient.
The composition ratio of the recycled material layer is preferably 30 to 60%, more preferably 35 to 50%, still more preferably 35 to 45% of the layer thickness of the hollow molded product. When the layer composition ratio of the recycled material layer is less than 30%, the molding stability of the hollow plastic molded article is impaired, and when it exceeds 60%, the impact resistance tends to be insufficient.

5. Applications of the hollow molded article The applications of the hollow molded article of the present invention include, for example, fuel tanks for automobiles, various fuel tanks, kerosene cans, drums, containers for chemicals, containers for agricultural chemicals, containers for solvents, and various plastic bottles. mentioned.
As described above, the polyethylene-based resin of the present invention has excellent moldability and an excellent balance between rigidity and durability. Therefore, even if the polyethylene layer is molded as a material for a hollow molded article, particularly as a multi-layered structure including a barrier layer, the polyethylene layer is not adversely affected by the barrier layer, such as deterioration in strength and poor molding, and the barrier property is also excellent. Furthermore, the polyethylene-based resin of the present invention is also excellent in swelling resistance when immersed in a liquid fuel such as gasoline. Therefore, the hollow molded article using the polyethylene-based resin of the present invention is suitable for fuel containers, particularly automobile fuel tanks, etc., which are required to be lightweight and highly durable.

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

1. Various evaluation (measurement) methods (1) Melt flow rate (HLMFR) measured at a temperature of 190°C and a load of 21.6 kg, and melt flow rate (MFR) at a temperature of 190°C and a load of 2.16 kg
Measured according to JIS K6922-2:1997.
(2) Density Measured according to JIS K7112:2004.

(3) Measurement of molecular weight 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 Co., Ltd. Measurement temperature: 145°C
Solvent: ortho-dichlorobenzene (ODCB)
Column: Showa Denko Shodex HT-806M × 2 + same HT-G
Flow rate: 1.0 mL/min Injection volume: 0.3 mL
[Sample preparation]
3 mg of sample and 3 mL of ortho-dichlorobenzene (containing 0.1 mg/mL of 1,2,4-trimethylphenol) were weighed into a 4-mL vial bottle and capped with a resin screw cap and a Teflon (registered trademark) septum. After that, using a Senshu Scientific SSC-9300 high-temperature shaker set at a temperature of 150° C., melting was performed for 2 hours. After the dissolution was completed, it was visually confirmed that there was no insoluble component.
[Create a calibration curve]
Four 4 mL glass bottles were prepared, and 0.2 mg each of monodisperse polystyrene standard samples or n-alkanes in the following combinations (i) to (iv) were weighed out, followed by orthodichlorobenzene (0.1 mg/mL of 1,2,4-trimethylphenol) was weighed out, covered with a resin screw cap and a Teflon (registered trademark) septum, and then set to a temperature of 150 ° C. Senshu Scientific SSC-9300 model high temperature Dissolution was performed for 2 hours using a shaker.
(i) Shodex S-1460, S-66.0, n-eicosane (ii) Shodex S-1950, S-152, n-tetracontane (iii) Shodex S-3900, S-565, S -5.05
(iv) Shodex S-7500, S-1010, S-28.5
A vial bottle containing the sample solution was set in the apparatus, measurement was performed under the conditions described above, and a chromatogram (retention time and response data set of the differential refractometer detector) was recorded at a sampling interval of 1 second. The retention time (peak apex) of each polystyrene standard sample was read from the resulting chromatogram and plotted against the logarithmic value of the molecular weight. Here, the molecular weights of n-eicosane and n-tetracontane were set to 600 and 1200, respectively. A nonlinear least squares method was applied to this plot, and the resulting quartic curve was used as a calibration curve.
[Calculation of molecular weight]
Measurement was performed under the conditions described above, and a chromatogram was recorded at a sampling interval of 1 s. This chromatogram is written by Sadao Mori, "Size Exclusion Chromatography" (Kyoritsu Shuppan), Chapter 4, p. A differential molecular weight distribution curve and average molecular weight values (Mn, Mw and Mz) were calculated by the methods described in 51-60. 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 installed with Microsoft OS Windows (registered trademark) XP.
H′=H/[1.032+189.2/M(PE)]
The following formula was used for molecular weight conversion from polystyrene to polyethylene.
M(PE) = 0.468 x M(PS)

(4) Presence or absence of inflection point of extensional viscosity Using a test piece press-molded into a sheet of 18 mm × 10 mm and a thickness of 0.7 mm, using a rheometer (Ares manufactured by Rheometrics), 170 ° C., strain rate The elongational viscosity was measured at 0.1/sec, and the presence or absence of the long chain branched structure was confirmed by the presence or absence of the inflection point of the elongational viscosity due to strain hardening (whether or not the elongational viscosity rises).
[Measurement condition]
Apparatus: Ares manufactured by Rheometrics
Jig: Extensional Viscosity Fixture manufactured by TA Instruments
Measurement temperature: 170°C
Strain rate: 0.1/sec Preparation of test piece: A sheet of 18 mm x 10 mm and a thickness of 0.7 mm was prepared by press molding.
[Calculation method]
The elongational viscosity at 170° C. and a strain rate of 0.1/sec was plotted on a log-log graph with time t (unit: seconds) on the horizontal axis and elongational viscosity η (t) (unit: Pa·seconds) on the vertical axis. On the log-log graph, the maximum elongational viscosity after strain hardening until the strain amount reaches 4.0 is η _Max (t1) (t1 is the time when the maximum elongational viscosity is shown), and the elongational viscosity before strain hardening where η _Linear (t) is the approximation straight line of , the value calculated as η _Max (t1)/η _Linear (t1) was defined as the strain hardening degree (λmax). Whether or not there is an inflection point in the elongational viscosity due to strain hardening is determined by whether or not the elongational viscosity has an inflection point where the curve changes from an upwardly convex curve to a downwardly convex curve over time. bottom.
1 and 2 are typical extensional viscosity plots. FIG. 1 shows the case where the inflection point of extensional viscosity is observed, and η _Max (t1) and η _Linear (t1) are shown in the figure. FIG. 2 shows the case where no inflection point of elongational viscosity is observed.

(5) Zero shear viscosity (η ₀ )
A melt-kneaded polyethylene resin is formed into a sheet with a thickness of 2.0 mm by a hot press, and a rheometer (ARES manufactured by Reometrics) is used. The stress was relaxed at 210° C., and the sample was cooled to 190° C. while adjusting the plate spacing so as not to create a gap between the plates. The dynamic melt viscosity (unit: Pa sec) when measured at a frequency ω of 0.01 rad/sec is defined as the melt viscosity at a low strain rate (η _{H 0.01} ), and the frequency ω is from 100 to 0.01 rad. / seconds, using the relaxation time τ ₀ (seconds) and the dynamic melt viscosity η ^* (unit: Pa seconds), the zero shear viscosity (η ₀ ) was calculated. The approximation to the Cross viscosity equation was calculated using a commercially available computer program by a regression method.
η ^* /η ₀ =1/{1+(τ ₀ ω) ⁿ } (1)
In formula (1), n is a parameter indicating shear rate dependence of melt viscosity in a high shear rate region, and τ ₀ is a parameter indicating relaxation time.
[Measurement condition]
・ Apparatus: Ares manufactured by Rheometrics
・Jig: Parallel plate with a diameter of 25 mm, plate interval of about 1.7 mm
・Measurement temperature: 210°C
・Frequency range: 0.01 to 100 (unit: rad/sec)
・Strain range: 5%

(6) Swell ratio A strand extruded at a piston extrusion speed of 0.5 mm/min at a nozzle diameter of 1.0 mmφ, a nozzle length of 40.0 mm, an inflow angle of 90°, a set temperature of 210°C, and a capilograph manufactured by Toyo Seiki Seisakusho Co., Ltd. For, the strand diameter (D) at a position of 20 mm from the nozzle exit was measured using a laser measuring machine. Using the nozzle diameter (D ₀ ), the swell ratio was determined as D/D ₀ .

(7) Breaking time (T) by all-round notch type tensile creep test
In accordance with JIS K-6992-2 (2004 edition), after compression molding a sheet with a thickness of 5.9 mm, it is classified into JIS K-6774 (2004 edition) Annex 5 (normative) 50″ shape and size specimens were prepared and subjected to full circumference notched tensile creep testing (FNCT) in pure water at 80°C. The tensile loads were 88N, 98N and 108N, and the test score was 2 points for each load. From the obtained 6-point plot of rupture time and nominal stress on a logarithmic scale, the rupture time at a nominal stress of 6 MPa was used as an index of creep resistance by the least squares method.

(8) Compatibility of formula (A) The rupture time (T) (unit: hours) and the density (d) (unit: g/cm ³ ) in the all-around notch creep test are expressed by the following formula (A). It was determined whether or not the relationship shown was satisfied.
log ₁₀ T≧−348.6×d+333.0 Formula (A)

(9) Flexural Modulus Measured according to JIS K7171:2008.

(10) Moldability (drawdown resistance)
Fuel tanks for automobiles were blow-molded with a molding machine NB150 manufactured by Japan Steel Works, Ltd., and the drawdown of the parison was evaluated at an extrusion speed of 600 kg/h. That is, "○" indicates that the arrival time from the die to 1500 mm is 90 seconds or more (those with good thickness uniformity), and "○" indicates that it is less than 90 seconds (those with poor thickness uniformity). ×”.

(11) Heat/Pressure Resistance An automotive fuel tank was hollow-molded, and the tank was subjected to internal pressure and heat resistance tests at an internal pressure of 0.05 MPa and 60°C. After the passage of 1000 hours, the case where no holes, cracks, etc. occurred was evaluated as "○", and the case where holes, cracks, etc. occurred was evaluated as "x".

(12) Internal Pressure Deformation Resistance An automobile fuel tank was blow-molded, and an internal pressure deformation test was performed on the tank at an internal pressure of 0.05 MPa and 60°C. After 500 hours, the pressure was released and the temperature was returned to room temperature.

(13) Comprehensive Evaluation In the above evaluations, good drawdown resistance, heat/pressure resistance, and internal pressure deformation resistance were evaluated as "◯", and other evaluations were evaluated as "x".

2. Preparation of materials used [Example 1]
[Preparation of chromium-based catalyst (C-1)]
15 g of "Catalyst-1" (manufactured by W.R. Grace) having a chromium atom supported amount of 1.1% by mass, a specific surface area of 500 m ² /g, and a pore volume of 1.5 cm ³ /g was subjected to a porous plate. Put in a quartz glass tube with a dish and a tube diameter of 5 cm, set in a cylindrical electric furnace for firing, fluidize with air passed through a molecular sieve, and activate firing at 500 ° C. for 18 hours at a linear velocity of 6 cm / s. did An orange colored chromium catalyst component was obtained indicating that it contained hexavalent chromium atoms.
2 g of the above chromium catalyst component was placed in a 100 ml flask previously purged with nitrogen, and 30 ml of distilled and purified hexane was added to prepare a slurry. 2.1 ml of a 1.0 mol/L-hexane solution of diethylaluminum ethoxide manufactured by Tosoh Finechem (Al/Cr molar ratio=5) was added and stirred at 40° C. for 1 hour. Immediately after the stirring was completed, the solvent was removed under reduced pressure over 30 minutes to obtain a chromium-based catalyst (C-1).
[Production of ethylene polymer (A1)]
100 mg of the chromium-based catalyst (C-1) and 0.8 L of isobutane were charged into a 2.0 L autoclave sufficiently purged with nitrogen, and the internal temperature was raised to 110°C. 15 g of 1-hexene was charged, and while maintaining the ethylene partial pressure at 1.4 MPa, the hydrogen partial pressure, etc., were adjusted to carry out polymerization so that the catalyst productivity was 1,500 g-polymer/g-catalyst. rice field. Then, the polymerization was terminated by releasing the content gas out of the system. The obtained ethylene polymer had an HLMFR of 0.1 g/10 min and a density of 0.9350 g/cm ³ as a result of physical property evaluation.
[Production of ethylene polymer (B1)]
100 mg of the chromium-based catalyst (C-1) and 0.8 L of isobutane were charged into a 2.0 L autoclave sufficiently purged with nitrogen, and the internal temperature was raised to 110°C. While maintaining the ethylene partial pressure at 1.0 MPa, the hydrogen partial pressure and the like were adjusted to carry out polymerization so that the catalyst productivity was 3,000 g-polymer/g-catalyst. Then, the polymerization was terminated by releasing the content gas out of the system. The obtained ethylene polymer had an MFR of 2.0 g/10 min and a density of 0.9600 g/cm ³ as a result of physical property evaluation.
[Production of polyethylene resin]
The ethylene-based polymer (A1) and the ethylene-based polymer (B1) were melt-mixed at the composition ratio shown in Table 1 to produce a polyethylene-based resin.
[Physical properties and evaluation of polyethylene resin]
Table 2 shows the physical properties and performance evaluation of the above polyethylene resin.

[Example 2]
[Manufacture of polyethylene resin]
Ethylene-based polymer (A2) and ethylene-based polymer (B2) were produced according to Example 1 by adjusting the amount of 1-hexene, the hydrogen partial pressure, and the like. Example 1 except that the ethylene-based polymer (A2) was used instead of the ethylene-based polymer (A1) in Example 1, and the ethylene-based polymer (B2) was used instead of the ethylene-based polymer (B1). A polyethylene resin was obtained in the same manner.
Table 1 shows the physical properties and composition ratios of the ethylene polymer (A) and the ethylene polymer (B) used in the polyethylene resin.
[Physical properties and evaluation of polyethylene resin]
Table 2 shows the physical properties and performance evaluation of the above polyethylene resin.

[Example 3]
[Production of polyethylene resin]
Ethylene-based polymer (A3) and ethylene-based polymer (B3) were produced according to Example 1 by adjusting the amount of 1-hexene, the hydrogen partial pressure, and the like. The ethylene polymer (A3) was used instead of the ethylene polymer (A1) of Example 1, and the ethylene polymer (B3) was used instead of the ethylene polymer (B1) of Example 1. A polyethylene resin was obtained in the same manner as in Example 1.
Table 1 shows the physical properties and composition ratios of the ethylene polymer (A) and the ethylene polymer (B) used in the polyethylene resin.
[Physical properties and evaluation of polyethylene resin]
Table 2 shows the physical properties and performance evaluation of the above polyethylene resin.

[Example 4]
[Production of polyethylene resin]
A Ziegler-Natta catalyst was used instead of the chromium catalyst, and an ethylene polymer (B4) was produced according to Example 1 by adjusting the amount of 1-hexene, the hydrogen partial pressure, and the like. A polyethylene-based resin was obtained in the same manner as in Example 1, except that the ethylene-based polymer (B4) was used instead of the ethylene-based polymer (B1) of Example 1.
Table 1 shows the physical properties and composition ratios of the ethylene polymer (A) and the ethylene polymer (B) used in the polyethylene resin.
[Physical properties and evaluation of polyethylene resin]
Table 2 shows the physical properties and performance evaluation of the above polyethylene resin.

[Example 5]
[Manufacture of polyethylene resin]
An ethylene polymer (A4) was produced according to Example 1 by adjusting the amount of 1-hexene, the hydrogen partial pressure and the like. A polyethylene resin was obtained in the same manner as in Example 1, except that the ethylene polymer (A4) was used instead of the ethylene polymer (A1).
Table 1 shows the physical properties and composition ratios of the ethylene polymer (A) and the ethylene polymer (B) used in the polyethylene resin.
[Physical properties and evaluation of polyethylene resin]
Table 2 shows the physical properties and performance evaluation of the above polyethylene resin.

[Example 6]
[Production of polyethylene resin]
Ethylene-based polymer (A5) and ethylene-based polymer (B2) were produced according to Example 1 by adjusting the amount of 1-hexene, the hydrogen partial pressure, and the like. Example 1 except that the ethylene-based polymer (A5) was used instead of the ethylene-based polymer (A1) in Example 1, and the ethylene-based polymer (B2) was used instead of the ethylene-based polymer (B1). A polyethylene resin was obtained in the same manner.
Table 1 shows the physical properties and composition ratios of the ethylene polymer (A) and the ethylene polymer (B) used in the polyethylene resin.
[Physical properties and evaluation of polyethylene resin]
Table 2 shows the physical properties and performance evaluation of the above polyethylene resin.

[Comparative Example 1]
[Production of polyethylene resin]
A polyethylene-based resin was produced using a chromium-based catalyst. Table 1 shows the physical properties and composition ratio of the ethylene-based polymer used in the polyethylene-based resin.
[Physical properties and evaluation of polyethylene resin]
Table 2 shows the physical properties and performance evaluation of the above polyethylene resin.

[Comparative Example 2]
[Production of polyethylene resin]
A polyethylene-based resin was produced using a chromium-based catalyst containing an organoaluminum compound. Table 1 shows the physical properties and composition ratio of the ethylene-based polymer used in the polyethylene-based resin.
[Physical properties and evaluation of polyethylene resin]
Table 2 shows the physical properties and performance evaluation of the above polyethylene resin.

[Comparative Example 3]
[Production of polyethylene resin]
Using a Ziegler-Natta catalyst, ethylene and 1-hexene were polymerized by multi-stage polymerization in two reactors to produce a polyethylene resin having the properties shown in Table 1.
[Physical properties and evaluation of polyethylene resin]
Table 2 shows the physical properties and performance evaluation of the above polyethylene resin.

[Comparative Example 4]
[Production of polyethylene resin]
Using a Ziegler-Natta catalyst, ethylene and 1-hexene were polymerized by multi-stage polymerization in two reactors to produce a polyethylene resin having the characteristics shown in Table 1.
[Physical properties and evaluation of polyethylene resin]
Table 2 shows the physical properties and performance evaluation of the above polyethylene resin.

[Comparative Example 5]
[Production of polyethylene resin]
A polyethylene resin was produced by multistage polymerization using a metallocene catalyst. Table 1 shows the physical properties and composition ratio of the ethylene-based polymer used in the polyethylene-based resin.
[Physical properties and evaluation of polyethylene resin]
Table 2 shows the physical properties and performance evaluation of the above polyethylene resin.

[Comparative Example 6]
[Production of polyethylene resin]
A metallocene-based catalyst was used to prepare a high molecular weight component, a chromium-based catalyst was used to prepare a low molecular weight component, and the high and low molecular weight components were melt-mixed to prepare a polyethylene resin. Table 1 shows the physical properties and composition ratio of the ethylene-based polymer used in the polyethylene-based resin.
[Physical properties and evaluation of polyethylene resin]
Table 2 shows the physical properties and performance evaluation of the above polyethylene resin.

[Comparative Example 7]
[Production of polyethylene resin]
A metallocene-based catalyst was used to prepare a high molecular weight component, a chromium-based catalyst was used to prepare a low molecular weight component, and the high and low molecular weight components were melt-mixed to prepare a polyethylene resin. Table 1 shows the physical properties and composition ratio of the ethylene-based polymer used in the polyethylene-based resin.
[Physical properties and evaluation of polyethylene resin]
Table 2 shows the physical properties and performance evaluation of the above polyethylene resin.

3. Evaluation The experimental results will be described with reference to the experimental results shown in Table 2.
The polyethylene resins of Examples 1 to 4 have an HLMFR of 1 to 15 g/10 min, a density (d) of 0.950 to 0.965 g/cm ³ , and a zero shear viscosity (η ₀ ) of 300, Since it is 000 Pa·s or more and the swell ratio is 1.33 or more, it is excellent in heat/pressure resistance and internal pressure deformation resistance, and also has improved thickness uniformity as drawdown resistance. It had an excellent balance between rigidity and durability, and was also excellent in moldability.
In the polyethylene-based resins of Examples 5 and 6, although the ethylene-based polymer (A) of the high-molecular-weight component does not satisfy the formula (B), it has excellent heat/pressure resistance and internal pressure deformation resistance, and further has drawdown resistance. As a result, the thickness uniformity is improved, the rigidity and durability are well balanced, and the moldability is also excellent.
On the other hand, the polyethylene resins of Comparative Examples 1 and 2 had a low density (d), were inferior in heat/pressure resistance and internal pressure deformation resistance, and were inferior in rigidity and durability.
The polyethylene resins of Comparative Examples 3 and 5 had high zero shear viscosities (η ₀ ), but had small swell ratios, poor uniformity of thickness as drawdown resistance, and poor moldability.
The polyethylene-based resins of Comparative Examples 4 and 7 had a small zero-shear viscosity (η ₀ ), a small swell ratio, poor drawdown resistance, poor thickness uniformity, and poor moldability.
The polyethylene-based resin of Comparative Example 6 had a large swell ratio but a small zero shear viscosity (η ₀ ), was inferior in thickness uniformity as drawdown resistance, and was inferior in moldability.

The polyethylene-based resin of the present invention has an excellent balance between rigidity and durability, and can provide a material with excellent moldability. , bottles, cans, tanks, etc., and particularly useful as a material for hollow plastic products such as automobile fuel tanks.

Claims (6)

Two or more ethylene-based polymers selected from the group consisting of ethylene homopolymers and copolymers of ethylene and α-olefins having 3 to 12 carbon atoms as essential components,
5 to 95% by mass of an ethylene polymer (A) having a density (d) of 0.910 to 0.945 g/cm ³ and an HLMFR of 0.01 to 10 g/10 min, and a density (d) of 0.945 ~0.975 g/cm ³ , a temperature of 190 ° C., a melt flow rate (MFR) measured at a load of 2.16 kg is 0.5 to 1,000 g / 10 minutes, and the HLMFR of the ethylene polymer (A) 5 to 95% by mass of an ethylene-based polymer (B) having a larger HLMFR is included as the essential component,
The ethylene polymer (A) has an elongational viscosity (η (t)) (unit: Pa·sec) measured at a temperature of 170° C. and an elongation strain rate of 0.1 (unit: 1/sec) and an elongation time ( t) In a log-log plot of (unit: seconds), an inflection point of elongational viscosity due to strain hardening is observed,
The ethylene polymer (A) is a copolymer of ethylene and 1-hexene,
The ethylene-based polymer (B) is an ethylene homopolymer,
A polyethylene resin having the following characteristics [a], [b], [c] and [d].
[a] Melt flow rate (HLMFR) measured at a temperature of 190° C. and a load of 21.6 kg is 1 to 15 g/10 minutes.
[b] Density (d) is 0.950 to 0.965 g/cm ³ .
[c] Dynamic melt viscosity η ^* (unit: Pa·sec) measured at a temperature of 210°C at a frequency ω in the range of 100 to 0.01 rad/sec is approximated by the following formula (1): zero shear viscosity (η ₀ ) is 300,000 Pa·sec or more.
η ^* /η ₀ =1/{1+(τ ₀ ω) ⁿ } (1)
(In the formula (1), _τ0 is a parameter representing the relaxation time, and n is a parameter representing the shear rate dependence of the melt viscosity in the high shear rate region.)
[d] The swell ratio is 1.33 or more. 2. The polyethylene resin according to claim 1, which further has the following property [e].
[e] The rupture time (T) (unit: hour) and the density (d) (unit: g/cm ³ ) in the full circumference notch type creep test satisfy the relationship represented by the following formula (A).
log ₁₀ T≧−348.6×d+333.0 Formula (A) The ethylene polymer (A) has a molecular weight distribution represented by the ratio (Mw/Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured by a gel permeation chromatography (GPC) method. The polyethylene resin according to claim 1 or 2, which is 10 to 50. In the ethylene polymer (A), HLMFR (unit: g/10 min) and density (d) (unit: g/cm ³ ) satisfy the relationship represented by the following formula (B). 4. The polyethylene resin according to any one of 3.
d≦−0.0061× log ₁₀ (HLMFR)+0.9358 Formula (B) A hollow molded article having a layer containing the polyethylene resin according to any one of claims 1 to 4. 6. The hollow molded article according to claim 5, which is at least one selected from the group consisting of fuel tanks, kerosene cans, drum cans, chemical containers, agricultural chemical containers, solvent containers and plastic bottles.

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