WO2002036644A1 - Polyethylene resin and pipe and joint using the same - Google Patents

Abstract

A linear polyethylene which is produced by the use of a Ziegler-Natta catalyst and satisfies the requirements described in the following (1) to (6): 0.20 to 0.50 g/10 minutes in terms of a melt flow rate (190 °C, load: 5.00 kg), 0.948 to 0.952 g/cm3 in terms of a density, 65 to 130 in terms of a flow ratio (FR), 1.90 x 10?-8dyn/cm2¿ or less in terms of a relaxation parameter H as determined by the stress relaxation measurement, 39 to 45 wt % in terms of the proportion (WH) of the amount of high molecular weight components integrated over all the elution temperature divisions to the total amount of the polyethylene eluted, as determined by the cross fractionation method (TREF-SEC), and 96.5 °C or lower in terms of a peak temperature (TH) of the elution curve for the high molecular weight component of the polyethylene and 99.2 °C or lower in terms of peak temperature (TL) of the elution curve for the low molecular weight component thereof, both being determined by the cross fractionation method; and a pipe and a joint using the polyethylene.

Description

 Description Polyethylene resin and pipes and joints using the same <Technical field>

 The present invention provides polyethylene having excellent rigidity, impact resistance and long-term durability under stress (environmental stress crack resistance, hot internal pressure cleave property and low-speed crack extension property of a pipe) and a polyethylene obtained using the same. The present invention relates to a pipe and its joint.

<Background technology>

 Polyethylene pipes and their joints are lightweight and easy to construct, do not corrode, have the rigidity to withstand burial in the soil, and the flexibility to follow the ground deformation. Its usage is increasing rapidly. The characteristics required for polyethylene pipes and their joints are (1) In addition to these characteristics, (2) Sufficient impact resistance to withstand the impact given by other works during and after construction, and (3) Gas and gas It must have good long-term durability under pressures such as tap water (specifically, environmental stress cracking resistance, hot internal pressure creep resistance, and low-speed crack extension resistance). At present, the practicability of (1) and (2) is satisfied. For the long-term durability of (3), for example, for gas pipes, the internal pressure of the pipe specified in ISO 12162 is 8MPa or more in terms of circumferential stress. A material (PE 80), which is said to have a durability of 50 years at room temperature under OMPa, is used. However, these materials are still lacking long-term durability for use in applications with high internal pressures, so in recent years ISO 1

A material that is said to have a durability of 50 years at room temperature when the internal pressure of the pipe specified in 2162 is 1 OMPa or more and less than 11.2 MPa in terms of circumferential stress (PE 10

0) began to be used. However, even with PE 100 material, brittle cracking may occur due to stress concentration generated at minute structural defects, especially at high temperatures. Destruction is undesirable from a reliability standpoint.

The long-term durability of polyethylene pipes is that the internal pressure applied to the pipes is It is considered to be the so-called tensile cleave property by acting as a force and acting on the material for a long period of time, as well as the durability against stress cracks, that is, the ESCR property under tensile stress. Therefore, in order to improve the long-term durability of polyethylene pipes, it is necessary to improve the so-called tensile cleave property and the ESCR property under this tensile stress. As a method for improving the cleave characteristics and ESCR characteristics, it is known to increase the molecular weight of polyethylene. It is also known that lowering the density (p) is an effective way to improve the ESCR characteristics. However, when the molecular weight is increased, fluidity is reduced, and there is a problem that pipe extrusion characteristics and injection moldability at the time of manufacturing a joint are significantly deteriorated. Also, when the density (p) is decreased, the rigidity is decreased, and it is not preferable that the internal pressure cannot withstand a sudden increase in the internal pressure.

 An object of the present invention is to solve the above-mentioned drawbacks of the prior art and improve the hot cleave property and the ESCR property under tensile stress while maintaining good rigidity and impact resistance, thereby significantly improving long-term durability. To provide a polyethylene resin which is improved and which is excellent in formability, productivity, etc., and a pipe and a joint produced therefrom (for example, a joint as a connecting means for connecting a long pipe to a pipe). It is in.

<Disclosure of Invention>

 The present inventors have conducted intensive studies in order to solve the above problems, and as a result, have found that a linear polyethylene having specific physical properties manufactured using a Ziegler-Natu catalyst achieves the above objects, and completed the present invention. did.

 That is, the first present invention is a polyethylene resin which is a linear polyethylene which is produced using a zigzag catalyst and has the following physical properties (1) to (6).

 (1) The melt flow rate (MFR5) measured at 190 ° C with a test load of 5.0 Okg is 0.20 to 0.50 g / 10 minutes

 (2) Fluid ratio (flow ratio FR) is 65 to 130

(3) Density (p) is 0.948 to 0.952 g / cm ³

(4) The relaxation parameter H of the following equation (II) obtained by the stress relaxation measurement is 1.9. 0 x 10- ⁸ dyn / cm ² or less

 (5) The amount of high molecular weight components calculated for each of multiple elution temperature categories determined by cross-fractionation (TREF-SEC) consisting of temperature-elution elution fractionation (TREF) and size exclusion chromatography (SEC) is calculated as the total elution temperature. The ratio (WH) to total output is 39 to 45% by weight

 (6) Elution determined from the amount of high molecular weight components calculated for each of the multiple elution temperatures determined by cross-fractionation (TREF-SEC) consisting of temperature increase elution fractionation (TREF) and size exclusion chromatography (SEC) Peak temperature (TL) of the elution curve obtained from the amount of low molecular weight components calculated for each of multiple elution temperature categories, with a peak temperature (TH) of 96.5 ° C or less and a TREF-SEC Is over 99.2 ° C

Log E (10 ³ ) -Log EC10 ⁰ )

H = -E (10 ³ ) (I)

Log 10 ^s -Log 10 °

 (However, E (te) is the relaxation modulus at time.) A second invention is a pipe and a joint made of the above polyethylene.

Furthermore, the third invention is a constant stress environmental stress crack test at 80 ° C. The fracture time when the initial tensile load is 6 MPa is 20 hours or more and the fracture time when the initial tensile load is 4 MPa is Has a performance of 80 hours or more. BEST MODE FOR CARRYING OUT THE INVENTION>

 Hereinafter, the present invention will be described in more detail with reference to examples. Polyethylene resin

 The above-mentioned polyethylene resin (also referred to as a linear polyethylene in the present specification) used in the present invention is produced using a Ziegler-Natucata catalyst. For example, Mg, Ti

-Active Zigra composed of a solid catalyst component containing sulfur and an organoaluminum compound —A suitable catalyst can be produced by using a system catalyst as a polymerization catalyst and copolymerizing ethylene or ethylene and a one-year-old olefin having 3 to 20 carbon atoms in a ratio to obtain a desired density (p). it can. Examples of the monoolefin having 3 to 20 carbon atoms include compounds represented by the general formula R—CH = CH ₂ (where R represents an alkyl group having 1 to 12 carbon atoms), for example, propylene, 1— Butene, 4-methyl-1-pentene, 3-methyl-1-butene, 1-pentene, 1-octene and the like. Examples of the polymerization method in the production of the polyethylene resin include slurry polymerization, gas phase polymerization, and solution polymerization.

The polyethylene resin for pipes and joints of the present invention is produced by a low-pressure multistage polymerization method in two or more reactors having different reaction conditions. That is,] \ 1 1¾5 is 0.20 to 0.50 gZl 0 min, density (/ o) is 0.948 to 0.952 g / cm ³ , and flow ratio FR is 65 to 130. The amount of high molecular weight components calculated for each of multiple elution temperature categories determined by cross-fractionation (TREF-SEC) consisting of temperature-rise elution fractionation (TREF) and size exclusion chromatography (SEC) The peak temperature of the elution curve calculated from the amount of high molecular weight components calculated for each of the multiple elution temperature categories is 39 to 45% by weight, based on the total elution temperature category. (TH) is 96.5 ° C or less, and the peak temperature (TL) of the elution curve obtained from the amount of low molecular weight components calculated for each of the plurality of elution temperature categories is 99.2 ° C or more, and relaxation parameter Isseki H it is possible to obtain ones ^{1. 90 X 10- 8 d yn} / cm 2 or less, the polyethylene Can be used to form pipes and joints.

 In order to improve the durability as a conventional pipe, the present inventors

It is not enough to fluctuate (p) and MFR independently, and find WH, TL and TH, and relaxation parameter H required by TREF-SEC, and that they govern durability, MFR5 By controlling the flow ratio FR, density, and density (p) within the above-mentioned predetermined ranges, and by setting the WH, TL, TH, and parameter H to the target value range, It has become possible to obtain polyethylene with excellent durability and eventually pipes and joints. That is, the WH, TL, TH and parameter overnight H are MFR5, flow ratio FR, density A method such as a method of adjusting the three factors (p) within a predetermined range, or a method of setting any two factors within a predetermined range and adjusting the remaining one factor within the predetermined range as described above. Can be adjusted by

 The polyethylene resin obtained by the above method is a linear polyethylene having the following physical properties (1) to (6).

 (1) The melt flow rate (MFR5) measured at 190 ° C with a test load of 5.00 kg is 0.20 to 0.50 g / 10 min, preferably 0.22 to 0.45 g / 10 min, especially Preferably 0.25 to 0.43 gZlO min.

 (2) The flow ratio (flow ratio FR) is 65 to 130, preferably 70 to 120, particularly preferably 80 to L15.

(3) The density (P) is 0.948 to 0.952 g / cm ³ , preferably 0.949 to 0.951 z / cm ³ .

(4) relieving parameter Isseki H of the formula obtained by the stress relaxation measurements (II) is ^{1. 9 Ox l 0_ 8 dy n} / cm 2 or less, preferably ^{1. 85 x 10 _ 8 dyn /} cm 2 hereinafter .

 (5) The amount of high molecular weight components calculated for each of multiple elution temperature categories determined by cross-fractionation (TREF-SEC) consisting of temperature increase elution fractionation (TREF) and size exclusion chromatography (SEC) is the total elution temperature The ratio (WH) to total output is 39 to 45% by weight

 (6) Elution determined from the amount of high molecular weight components calculated for each of the multiple elution temperatures determined by cross-fractionation (TREF-SEC) consisting of temperature increase elution fractionation (TREF) and size exclusion chromatography (SEC) Peak temperature (TL) of the elution curve obtained from the amount of low molecular weight components calculated for each of multiple elution temperature categories, with a peak temperature (TH) of 96.5 ° C or less and a TREF-SEC Is over 99.2 ° C

If the MFR 5 of this linear polyethylene is less than 0.20 g / 10 min, the flowability will be remarkably poor, the moldability will be insufficient, and the productivity of the pipe will not be satisfied.In addition, when molding joints etc. by injection molding, Molding cannot be performed, or even if molding can be performed, the appearance becomes extremely poor.On the other hand, if it exceeds 0.50 g / 10 minutes, it will come out of the die during molding. Not only is it difficult for the resin to hang down and good molding cannot be performed, but also the long-term durability and impact resistance of pipes and joints are insufficient.

 In addition, the flow ratio FR was calculated using a melt indexer at 190 ° C for 10 minutes at a load of 11.6 kg divided by the amount of extrusion at 1.16 kg for 10 minutes. It is a physical property that indicates the standard of the molecular weight distribution. The smaller the flow ratio FR value, the narrower the molecular weight distribution, and the larger the FR ratio, the wider the molecular weight distribution. If the flow ratio FR is less than 65, the moldability will be poor. If the flow ratio FR exceeds 130, the impact resistance tends to decrease due to the influence of low molecular weight components. Further, when the density () is less than 0.948, the rigidity of the pipe is remarkably insufficient, so that the pipe tends to be deformed by earth pressure after burial, and it is not preferable because it cannot withstand a sudden increase in internal pressure. Exceeding 952 is not preferable because the long-term durability of the pipe is insufficient.

 TREF-SEC can examine the crystallinity and molecular weight distribution of polyethylene by the method described below. First, using a difference in dissolution temperature, a TREF column is used to gradually separate the components from those with low crystallinity to those with high crystallinity. By continuously injecting the separated components into the SEC column, the components are separated based on the molecular size, that is, the molecular weight. By this operation, the elution amount (% by weight) and molecular weight distribution (dW / d (1 ogM) vs l ogM) of each elution temperature category can be obtained.

 The ratio of high molecular weight component (WH), peak elution temperature of high molecular weight component (TH), and peak elution temperature of low molecular weight component (TL) are determined according to the following procedure. In two or more reactors with different reaction conditions, the polyethylene resin produced by the low-pressure multi-stage polymerization method is fractionated by the above-mentioned method to separate low molecular weight components and high molecular weight components for each elution temperature category. A molecular weight distribution consisting of two peaks is obtained. By fitting the two peaks of the molecular weight distribution for each elution temperature category to two lognormal distributions, the peaks are separated into two components, and the low molecular weight side and high molecular weight side are converted to the low molecular weight in the elution temperature category. Components · High molecular weight components. The sum of the amounts of the low molecular weight component and the high molecular weight component obtained by peak separation is the elution amount (weight%

) Is defined as the amount of low molecular weight component and high molecular weight component in the elution temperature category. The sum of the high molecular weight components of all elution temperature categories The ratio of high molecular weight components (WH). When WH is less than 39% by weight, it means that the amount of the high molecular weight component is small, and in the case of polyethylene manufactured in the above MFR 5 and density (p) range, the molecular weight of the high molecular weight component is high. Means larger. As a result, the compatibility of the two components is significantly reduced, impact resistance is reduced, and fisheye is increased, resulting in a poor pipe surface. On the other hand, when ¾ [is more than 45% by weight, the molecular weight of the high molecular weight component is reduced, and the long-term durability is significantly reduced. In addition, it also means that the molecular weight of the low molecular weight component becomes relatively large, the fluidity is remarkably reduced, and the extrudability is not satisfactory.

 The amount of the high molecular weight component in each elution temperature category is plotted against the elution temperature category, and a curve obtained by fitting a normal distribution in the range of 80 ° C to 110 ° C is used as an elution curve, and the temperature of the peak is raised. The elution peak temperature (TH) of the molecular weight component is used.

The elution peak temperature is similarly determined for the low molecular weight components. However, in that case, instead of the amount of the low molecular weight component in each elution temperature category, the component corresponding to ₁₀ ^ [= 5 ± 0.1 (M: molecular weight) in the low molecular weight component in each elution temperature category is used. Use the amount. This is because the elution temperature of a component with a molecular weight of 30,000 or less (logM <4.5) is significantly dependent on the molecular weight (eg, Journal of Polymer Science: Polymer Physics Editon, Vol. 20, 441-445 (1982) )), For low-molecular-weight components containing a large amount of components with a molecular weight of 30,000 or less, obtaining an elution curve for a component with a specific molecular weight of 30,000 or more reflects more accurate properties. The peak temperature obtained in this way is defined as the elution peak temperature (TL) of the low molecular weight component.

 TL and TH are indicators of crystallinity, as can be seen from the calculation. A high value indicates that the crystallinity is high, while a low value indicates that the crystallinity is low. TL below 99.2 ° C and TH is 9

6. If the temperature is higher than 5 ° C, the creep characteristics and the durability against stress cracks, that is, the ESCR characteristics under tensile stress are significantly reduced, and the brittleness due to the stress concentration generated at the minute structural defects especially at high temperatures Cracking is inevitable. As a method of improving the ESCR characteristics under tensile stress as well as the tensile strength of the bow I tension cleaving, it is effective to increase the molecular weight of polyethylene and reduce the density (p). Is as described above, but simply increasing the molecular weight and decreasing the density (P) are also undesirable because they also cause a significant decrease in formability and a decrease in rigidity as described above. Therefore, the rigidity is secured by setting the temperature to 99.2 ° C or higher, that is, by increasing the crystallinity of components that do not contribute to the improvement in cleave characteristics and ESCR characteristics under tensile stress due to the low molecular weight. In addition, by setting the temperature of D11 to 96.5 ° C or less, the crystallinity of a high molecular weight component that greatly contributes to the creep characteristics and the ESCR characteristics under tensile stress is reduced, that is, the density (/ 0) By lowering this, it is possible for the first time to achieve both rigidity and long-term durability.

 The relaxation parameter H is a parameter derived from the following theory, and polyethylene with H in a specific range has good long-term durability. In other words, in order to achieve long-term durability, it is considered that a large proportion of components that alleviate stress in a short time is required. This stress relaxation can be evaluated by measuring the time change of the elastic modulus obtained by dividing the stress generated in a test piece by the strain when a constant strain is applied to the test piece. It is known that the relaxation modulus curve may be evaluated. In practice, by measuring the temperature while changing it, the relaxation modulus over a long time range is obtained using the temperature temporary conversion rule. A method of calculating the number of relaxations from this relaxation modulus has been proposed by Schwarz-Staverman and Leaderman et al. (Reference: Deformation of objects published by Seibundo Shinkosha in 1972, pp. 201-204) ), The relaxation spectrum h (j) at time j is expressed by the following equation (II).

(― L) ^.k

h (j) = lim ― ~~ (kj) ^k B ^ik) (kj) (ID k → ∞ (kD!

(Where E ^(k) (kj) = d ^k E / dt ^k , and the relaxation modulus is differentiated k times at time t.)

When this is approximated by k = 1, the following equation (III) is obtained. dBCj) dB (i) d (ln B)

h (j) knee j = -E (j) (III) dt dCln j) d (in j) Let H be the relaxation distribution function h (10) for a long time (j = 1 O ³ seconds). It is expressed by the following equation (IV).

d Log B (j)

H = ~ E (1 ひ³ ) (IV) d Log j lO Here, using the measured value at 10 ^Qs , the following equation (V) can be obtained, so-d Log B Log B (10 ³ ) -Log BC10 ⁰ )

(V) d Log j Log 10 ³ — Log 10 ^c

H can be obtained from the experimental value as shown in the following equation (I),

Log B (10 ³ ) -Log E (10 °)

H = -E (10 ³ ) (I)

Log 10 ^s — Log 10 ° As described above, the relaxation parameter H (dyn / cm ² ) of the formula (I) is a parameter corresponding to the relaxation distribution function at a specific time (10 ³ seconds). Can be determined from experimental values. The fact that H is within the above range means that the relaxation distribution function over a sufficiently long time is small, which means that the proportion of the component in which the stress is relaxed over a long time is small, which is preferable. .

The polyethylene obtained here was subjected to a constant stress environmental stress crack test at 80 ° C, and the fracture time was 20 hours or more when the initial tensile load was 6 MPa and the initial tensile load was 4 M. Destruction time at Pa is 8 ◦ hours or more.

 In a constant stress environmental stress crack test at 80 ° C, the fracture time at an initial tensile load of 6 MPa is 20 hours or less, and the fracture time at an initial tensile load of 4 MPa is 80 hours. The following materials are inferior in stress resistance to stress cracking, i.e., ESCR characteristics under tensile stress, as well as bow I tension creep characteristics.Pipes and fittings made of such materials are particularly hot at high temperatures. Brittle cracks tend to occur due to the concentration of stress generated in minute structural defects, and such brittle fractures are not desirable from the viewpoint of reliability.o Optional components

 In the polyethylene resin of the present invention, optional components can be blended as long as the effects of the present invention are not significantly impaired. The optional components include those known or used as ordinary polyolefin additives and compounding agents, such as antioxidants, neutralizers, weather resistance improvers, antifoaming agents, dispersants, antistatic agents, Lubricants, heat stabilizers, light stabilizers, ultraviolet absorbers, lubricants, metal deactivators, bactericides, fungicides, coloring agents, release agents, processing aids, etc. They can be appropriately combined and blended at any stage from the forming raw materials to the production of pipes and joints.

 The above-mentioned polyethylene resin and, if desired, optional components can be directly fed into a molding machine for molding. In general, these components are melt-kneaded in advance to form a pellet-like molding material, which is then molded. It is desirable to do. Pipe molding is usually performed by extrusion molding, but pipe joints and the like are sometimes formed by injection molding. Molding may be performed not only in a single layer but also in multiple layers.

<Example>

 Hereinafter, the present invention will be further described with reference to specific examples. In the examples, each physical property of the resin was evaluated by the following methods.

 〇 MFR5: Conforms to JISK72010.

密度 Density (P): Conforms to JISK7112. 衝 撃 Impact resistance: Izod impact strength is evaluated according to JIS K7110 (23 ° C).オ ル Olzen bending stiffness: ASTM D747 compliant.

 〇 ESCR: Use JISK 6760 constant stress environmental stress crack test equipment, water temperature is 80 ° C, test solution is 1% higher alcohol sodium sulfonate aqueous solution, initial tensile load is 6MPa and It was measured as 4 MPa. The test piece used was a press plate having a thickness of lmm and a width of 6 mm, and a 0.4 mm-depth leather notch was inserted in the narrowest portion at the center of the tensile portion.

OT EF-SEC

The measuring device used was CFC T-100 manufactured by Dia Instruments Co., Ltd.

The sample to be measured was dissolved using 0-dichlorobenzene as a solvent and injected into a TREF column. At 40 ° C., the mixture was injected from a TREF column into an SEC column (AD 806 MS, 3 by Showa Denko). The temperature of the TREF column was raised while the molecular size was being fractionated on the SEC column.Then, the temperature was repeatedly increased every 5 ° C up to 140 ° C and injection into the SEC column. Grams were obtained. By fitting the molecular weight distribution of each elution temperature segment that has two peaks to two lognormal distributions, the peak is separated into two components, and the low molecular weight component and the high polymer component are separated into low molecular weight components in the elution temperature segment. · WH, TL, and TH as high molecular weight components were calculated.

緩和 Stress relaxation: Using Optoleome “HRS-100” manufactured by Oak Manufacturing Co., Ltd., the test specimens were pressed and then annealed at 100 ° C for 10 hours, and the size was 30 mm x 5 mm x 0.3 mm Was used. In the measurement, the stress relaxation after pulling lmm at a speed of 1 mm / sec was measured by changing the temperature, and the mass relaxation curve at 30 ° C was evaluated.

内 Hot internal pressure creep: Gunze Sangyo 650 extruder, spiral die, I

Using a vacuum cooling water tank manufactured by KG, resin temperature is about 210 ° C, cooling water in the water tank is about 20 ° C, take-off speed is about 65 cm / min, outer diameter is 60 mm, wall thickness is 5 A 5 mm pipe is formed and this has a circumferential stress of 5.5 at 80 ° C according to ISO 1167. The internal pressure was adjusted to be MPa, and the creep performance was evaluated. The test was conducted at 80 ° C and 5.5MPa as shown in IS044427 for durability of 165 hours or more, and the test was continued for up to 10,000 hours to determine whether brittle fracture was observed. p / L o Example 1

 (A) Preparation of solid catalyst

And a 25.3kg of Mg (0Et) ₂ of 77.9kg and Ti (0Bu) ₃ Cl of 103.1kg and n-BuOH was mixed for 6 hours at 0.99 ° C and homogenized, after cooling synth ,, emissions in addition a predetermined amount A homogeneous solution was obtained. Then, at a predetermined temperature, 51.5 kg of ethyl aluminate sesquik Drain was dropped and stirred for 1 hour. Further, washing with η-xane was repeated to obtain 25 kg of a solid catalyst.

 (B) Polymerization

Using the obtained catalyst component was carried out continuous polymerization by using a device connected reactors 0. 6 m ³ to 2 group series. In the first polymerization tank, 70 kg / h of n-hexane, 3.63 g / h of getyl aluminum monochloride, 1.88 g / h of the solid catalyst component, 3 lkg / h of ethylene, and hydrogen were continuously fed. The polymerization was performed while maintaining the temperature at 90 ° C and the molar ratio of hydrogen and ethylene in the gas phase at 2.8. The polymer slurry of the first polymerization tank is continuously supplied to the second polymerization tank, and 47 kg of n-hexane and 27.0 kg of ethylene are continuously supplied at a temperature of 65 ° C and a gas phase. The continuous polymerization was carried out with the molar ratio of hydrogen ethylene in the solution maintained at 0.03 and the molar ratio of 1-butene / ethylene kept at 0.08. The slurry was continuously withdrawn from the second polymerization tank. The coalescence was dried. The obtained polymer was kneaded and pelletized under predetermined conditions using a 9 Omm0 extruder, and then subjected to pipe molding and physical property measurement. Table 1 shows the measurement results. Example 2

In Example 1, triethyl aluminum was used as a cocatalyst. Continuous polymerization was carried out while maintaining the hydrogen / ethylene molar ratio in the gas phase of the first polymerization tank at 2.0, and In this case, the propylene / ethylene molar ratio in the gas phase was 0.003, the 1-butene / ethylene molar ratio was 0.12, and the ethylene supply ratio in the first and second stages was maintained at 55/45 for continuous polymerization. Was done. Comparative Example 1

 In Example 1, continuous polymerization was carried out while maintaining the hydrogen / ethylene molar ratio in the gas phase of the second polymerization tank at 0.08. Comparative Example 2

 In Example 1, continuous polymerization was performed with the hydrogen / ethylene molar ratio in the gas phase of the second polymerization tank being 0.05 and the 1-butene Z ethylene molar ratio being 0.05. Comparative Example 3

 In Example 1, the hydrogen / ethylene molar ratio in the gas phase of the first polymerization tank was 6, the hydrogen / ethylene molar ratio in the gas phase of the second polymerization tank was 0.1, and the 1-butene / ethylene molar ratio was 0.06. Then, continuous polymerization was performed with the ethylene supply ratio of the first stage and the second stage being 46/54. Comparative Example 4

 In Example 1, the hydrogen / ethylene molar ratio in the gas phase of the second polymerization tank was 0.01, the 1-butene Z ethylene molar ratio was 0.13, and the ethylene supply ratio of the first and second stages was 55. / 45 to perform continuous polymerization. Comparative Example 5

In Comparative Example 1, continuous polymerization was carried out while maintaining the 1-butene / ethylene molar ratio in the gas phase of the first polymerization tank at 0.003, and the hydrogen / ethylene molar ratio in the gas phase was 0.05 in the second polymerization tank. The continuous polymerization was carried out at a molar ratio of 1-butene / ethylene of 0.065. Comparative Example 6

 In Example 2, continuous polymerization was carried out while maintaining the 1-butene Z ethylene molar ratio in the gas phase of the first polymerization tank at 0.01, and the hydrogen / ethylene mole ratio in the gas phase was 0.1 in the second polymerization tank. 012, 1-Butene The continuous polymerization was carried out with the ethylene molar ratio being 0.04 and the ethylene supply ratio of the first stage and the second stage being 54/46. Comparative Example 7

 In Example 1, continuous polymerization was performed while maintaining the hydrogen Z-ethylene molar ratio in the gas phase of the first dosing tank at 7 and the hydrogen / ethylene molar ratio in the gas phase of the second polymerization tank was 0.01, 1. Continuous polymerization was carried out with a butene Z ethylene molar ratio of 0.14. Comparative Example 8

 In Example 1, continuous polymerization was carried out while maintaining the hydrogen-Z ethylene molar ratio in the gas phase of the first polymerization tank at 4.5, and the hydrogen / ethylene molar ratio in the gas phase was 0.15, 1 in the second polymerization tank. Continuous polymerization was performed with a butene / ethylene molar ratio of 0.04 and a first and second stage ethylene feed ratio of 35Z65. Comparative Example 9

 In Example 1, continuous polymerization was carried out while maintaining the hydrogen / ethylene molar ratio in the gas phase of the first polymerization tank at 5.5, and in the second polymerization tank, the hydrogen / ethylene molar ratio in the gas phase was 0 • 005, 1 —Continuous polymerization was carried out with a butene / ethylene molar ratio of 0.15 and a first and second stage ethylene supply ratio of 25/75. As shown in Example 1 and Example 2 in Table 1, MFR5, flow ratio F

Controlling the R density (P), when WH, TL, TH and parameter H are within the range shown in claim 1, the pipe made of the polyethylene has a circumferential stress of 5 at 80 ° C. In addition to satisfying the performance of no cracking for more than 165 hours shown in IS04427 in the hot internal pressure creep test of 5 MPa,

The test was continued for 00 hours, but no brittle fracture was observed by then. Also The Olzen bending stiffness was 1,10 OMPa, and the Iz 0d impact test was performed, but was not destroyed (NB). As described above, it has become possible to manufacture a pipe that satisfies all of the rigidity, impact resistance and long-term durability.

On the other hand, as shown in Comparative Example 1, when MFR5 was larger than the range of claim 1, brittle fracture occurred in the hot internal pressure creep test, and 15 kJ / m ² in the Iz 0 d impact test. And was insufficient.

Also, as shown in Comparative Example 2, when the density (p) exceeded the range of claim 1, brittle fracture occurred in the hot internal pressure creep test. On the other hand, when the density) is lower than the range of claim 1 as in Comparative Example 4, the 165 hours specified in ISO 4427 cannot be satisfied in the hot internal pressure creep test, and the k J / m ² was insufficient.

As shown in Comparative Example 8, when the flow ratio was below the range of claim 1, and the WH, parameters, and H and TH were out of the range of claim 1, brittle fracture occurred in a hot internal pressure creep test. In addition, the Izod impact test was also insufficient at 13 kJ / m ² . When the flow ratio FR exceeded the range of claim 1 and the WH deviated from the range of claim 1, the Izod impact strength was remarkably low at 5 kJZm ² . As shown in Comparative Example 3, when WH and parameter overnight H were out of the scope of Claim 1, TL as shown in Comparative Example 5, and TH was out of the scope of Claim 1 as shown in Comparative Example 6. In this case also, brittle fracture occurred in the hot internal pressure creep test. Furthermore, in Comparative Example 3, the results of the Iz0d impact test were also insufficient.

Further, as shown in Comparative Example 7, when the parameter H exceeded the range described in Claim 1, brittle fracture occurred in a hot internal pressure creep test, and 15 k in an Iz 0 d impact test. JZm ² was not enough.

In addition, as shown in Comparative Examples 1, 2, 3, 5, 6, and 8, in the constant stress environment stress crack test at 80 ° C, the fracture time when the initial tensile load was 6 MPa was 20 hours or more and When the initial tensile load was 4MPa and the fracture time was not more than 80 hours, brittle fracture was confirmed within 10,000 hours in all hot internal pressure creep tests. . FR5 FR Density WH H TL TH ESC6 ESC4 Creep 1 Creep 2

 X 10 "*

s ίθ min g cm "% dyn / cm" ° C. C kJ / m ^J MPa Time Time

Example 1 0.26 100 0.951 42 1.79 99.7 96.0 NB 1.100 100> 300 O None Example 2 0.36 120 0.950 40 1, 81 99.4 94.9 NB 1.000 200> 300 な し None Comparative Example 1 0.52 80 0.951 42 1.90 99.6 95.9 15 1,100 12 40 O Oh y Comparative example 2 0.28 95 0.955 42 1.88 99.7 96.4 NB 1,200 20 40 Pia y Comparative example 3 0.34 81 0.951 50 2.04 99.5 96.4 1 7 1.100 25 60 O Oh y Comparative example 4 0.22 1 10 0.945 40 1.87 99.5 96.4 12 900 130 300 X No Comparative example 5 0.23 100 0.952 42 1.83 98.7 95.8 NB 1,100 17 35 〇 Yes Comparative example 6 0.27 91 0.952 41 1.84 99.4 96.7 NB 1.100 14 30 o Oh y Comparative example 7 0.42 126 0.949 42 2.10 99.2 94.5 15 1,000 90> 300 o Comparative example 8 0.75 62 0.952 60 2.27 99.4 96.7 13 1.100 5 30 o oh y Comparative example 9 0.48 210 0.952 30 1.85 99.4 94.7 5 1.100 70 250 o Yes

ESC6: ESCR when initial tensile load is 6MPa

ESC4: ESCR when initial tensile load is 4MPa

Creep: In the creep test at 80 ° C and 5.5MPa, those with _a durability of more than 165 hours are rated "0", and those without are rated "x".

Creep 2: 80 ° C. 5.5MPa creep test, if there is a life-time failure within 10,000 hours, it is “Yes”, and if there is no brittle fracture, it is “No”.

<Industrial applicability>

 As described above, according to the present invention, polyethylene is excellent in rigidity, impact resistance, and long-term durability under stress (environmental stress crack resistance, hot internal pressure cleave property, and low-speed crack extension property). It becomes possible to provide a pipe and its joint. In particular, regarding long-term durability, in a constant stress environmental stress crack test using a notched specimen in a surfactant at 80 ° C, the fracture time at an initial tensile load of 6 MPa was 20 hours or more. With an initial tensile load of 4 MPa and a fracture time of 80 hours or more, and in a creep test under a hot internal pressure, the fracture time at a circumferential stress of 5.5 MPa was 65 hours or more. In addition, no brittle fracture occurred within 10,000 hours.

Claims

The scope of the claims

1. A polyethylene resin which is produced using a Ziegler catalyst and has the following properties (1) to (6).

 (1) The melt flow rate (MFR5) measured at 190 ° C with a test load of 5 kg is 0.20 to 0.50 g / 10 min.

(2) Density (p) is 0.948 to 0.952 g / cm ³

 (3) Flow ratio (flow ratio FR) is 65 ~: L 30

(4) The relaxation parameter H of the following equation (I) obtained by the stress relaxation measurement is less than 1.90 x 10—sdyn / cm ²

 (5) Total elution of high molecular weight components calculated for each of multiple elution temperature categories determined by cross-fractionation (TREF-SEC) composed of temperature rise elution fractionation (TREF) and size exclusion chromatography (SEC) The ratio (WH) to the total output is 39 to 45% by weight

 (6) Calculated from the amount of high molecular weight components calculated for each of multiple elution temperature categories obtained by cross-fractionation (TREF-SEC) consisting of temperature-elevated elution fractionation (TREF) and size exclusion chromatography (SEC) The peak temperature (TH) of the elution curve obtained is 96.5 ° C or less, and the peak temperature of the elution curve obtained from the amount of low molecular weight components calculated for each of a plurality of elution temperature categories determined by TREF-SEC Degree (TL) is 99.2 ° C or more

Log BOO ³ ) -Log B (10 °)

H = -E (10 ³ ) (I)

Log 10 ³ -Log 10 °

 (However, E (r) is the relaxation modulus at time.) 2. Pipes and joints made of the polyethylene resin described in claim 1.

3. In a constant stress environmental stress crack test at 80 ° C, the fracture time is 20 hours or more when the initial tensile load is 6 MPa and the fracture time is 80 hours or more when the initial tensile load is 4 MPa. The pipe and the joint _{c according} to claim 2, wherein the pipe and the joint _c have a performance of