JP2002138110A - Polyethylene resin and pipe and joint using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyethylene resin, and pipe and its joint using the resin having excellent rigidity, impact resistance and long-term durability under stress. SOLUTION: This polyethylene resin is produced using Ziegler-Natta catalyst and having characteristics (1) to (6) listed below: (1) melt flow rate of 0.20 to 0.50 g/10 min, (2) density of 0.948 to 0.952 g/cm3, (3) fluidity ratio of 65 to 130, (4) relaxation parameter by stress relaxation measurement of 1.90×10-8 dyn/cm2 or less, (5) ratio of the amount of high polymer component for each of plural fractions by exudation temperature accumulated for total exudation temperature range to the total exudate of 39 to 45 wt.%, (6) peak temperature of the exudation curve obtained by the above amount of high polymer component of 96.5 deg.C or lower, and peak temperature of the exudation curve obtained by the amount of low molecular weight component for each of plural fractions by exudation temperature of 99.2 deg.C or higher both of (5) and (6) based on a specific fractionation procedure. The pipe and the joint are made using the resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a polyethylene resin having excellent rigidity, impact resistance and long-term durability under stress (environmental stress cracking resistance, hot internal pressure creep resistance of pipes, and low-speed crack extension resistance). And a pipe and a joint obtained by using the same.

[0002]

2. Description of the Related Art Polyethylene pipes and their joints are lightweight and easy to construct, do not corrode, have rigidity that can withstand burial in the soil, and have flexibility that can follow ground deformation. In recent years, its usage has rapidly increased due to the characteristics described above. The characteristics required for polyethylene pipes and their joints are (1) In addition to these features, (2) Sufficient impact resistance to withstand the impact given by other works during and after construction, and (3) Gas and water It has good long-term durability under pressure of water or the like (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, and as for the long-term durability of (3), for example, in a gas pipe, the internal pressure of the pipe defined by ISO 12162 is 8 MPa or more and less than 10 MPa in terms of circumferential stress. In this state, a material (PE80) which is said to have a durability of 50 years at room temperature is used. However, these materials still have insufficient long-term durability for use in applications where the internal pressure is high. Therefore, in recent years, the internal pressure of pipes specified by ISO12162 is 10 MPa or more and 11.2 in terms of circumferential stress.
A material (PE100) which is said to have a durability of 50 years at room temperature under the MPa has started to be used. However, even in the case of the PE100 material, brittle cracks may occur due to stress concentration generated in minute structural defects, especially at high temperatures, and when used under a higher pressure for a long period of time, such brittle fracture may occur. Occurrence is undesirable from a reliability standpoint.

[0003] The long-term durability of a polyethylene pipe has a so-called tensile creep characteristic due to the fact that the internal pressure applied to the pipe acts as a circumferential tensile stress and is applied to the material for a long period of time. It is believed to be ESCR characteristics. Therefore, in order to improve the long-term durability of the polyethylene pipe, it is necessary to improve not only the so-called tensile creep property but also the ESCR property under this tensile stress. As a method for improving creep characteristics and ESCR characteristics, it is known to increase the molecular weight of polyethylene. As a method for improving the ESCR characteristics, it is known that lowering the density (ρ) is effective. However, when the molecular weight is increased, there is a problem that the fluidity is reduced and the pipe extrusion characteristics and the injection moldability at the time of manufacturing a joint are significantly deteriorated. Further, when the density (ρ) is decreased, the rigidity is decreased, and it is not preferable that the rigidity cannot withstand a sudden increase in the internal pressure.

In order to solve the above-mentioned problem, Japanese Patent Laid-Open No.
JP-67413 discloses a polyethylene resin for pipes in which a melt flow rate, a flow ratio, a density, and a relaxation parameter H obtained by stress relaxation measurement are defined within a specific range. According to the technical matters described in the above publication, a polyethylene resin for pipes having excellent rigidity, impact resistance, and long-term durability under stress (creep characteristics and ESCR characteristics) is obtained. In addition, when this kind of polyethylene resin pipe is used particularly for an application having a high internal pressure (for example, as a large-diameter pipe such as a main pipe for gas or water supply), rigidity, impact resistance and long-term durability are required. In fact, there is a need for a pipe that satisfies all of the properties at a high level.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to provide a hot creep characteristic and an ES under tensile stress while maintaining good rigidity and impact resistance.
Polyethylene resin having improved CR characteristics and significantly improved long-term durability, and excellent in moldability, productivity, etc., and pipes and joints manufactured therefrom (for example, connecting a long pipe to a pipe) As a means).

[0006]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, it has been found that a polyethylene resin having specific physical properties produced by using a Ziegler-Natta catalyst achieves the above object. And completed the present invention.

That is, the first invention is produced using a Ziegler-Natta catalyst and comprises the following (1) to (6):
A polyethylene resin having the above physical properties. (1) The melt flow rate (MFR5) measured at 190 ° C under a test load of 5.00 kg is 0.20 to 0.5.
0 g / 10 minutes. (2) Density (ρ) of 0.948 to 0.952 g / c
m ³ . (3) The flow ratio (flow ratio FR) is 65 to 130. (4) The relaxation parameter H of the following formula (I) obtained by the stress relaxation measurement is 1.90 × 10 ⁻⁸ dyn / cm ² or less. (5) Cross fractionation (TR) consisting of temperature rising elution fractionation (TREF) and size exclusion chromatography (SEC)
Although the amounts of the high molecular weight components calculated for each of the plurality of elution temperature categories determined by EF-SEC) were integrated for all the elution temperature categories, the ratio (WH) to the total output amount was 39.
~ 45% by weight. (6) Cross fractionation (TR) consisting of temperature-rise elution fractionation (TREF) and size exclusion chromatography (SEC)
EF-SEC), the peak temperature (TH) of the elution curve obtained from the amount of high molecular weight component calculated for each of a plurality of elution temperature categories is 96.5 ° C. or less, and TR
The peak temperature (TL) of the elution curve determined from the amount of low molecular weight components calculated for each of a plurality of elution temperature categories determined by EF-SEC is 99.2 ° C or higher.

[0008]

(Equation 2) (Where E (τ) is the relaxation modulus at time τ)
It is.

A second invention is a pipe and a joint made of the above polyethylene resin. Further, the third invention is an embodiment of 8
Initial tensile load of 6M in a constant stress environment stress crack test at 0 ° C
The pipe and the joint described above, characterized in that the pipe and the joint have a performance in which the fracture time at Pa is 20 hours or more and the fracture time at an initial tensile load of 4 MPa is 80 hours or more.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Polyethylene Resin The above-mentioned polyethylene resin (also referred to as linear polyethylene in the present specification) used in the present invention is produced using a Ziegler-Natta catalyst. For example, a highly active Ziegler catalyst comprising a solid catalyst component containing Mg, Ti, and a halogen and an organoaluminum compound is used as a polymerization catalyst, and ethylene or ethylene and an α-olefin having 3 to 20 carbon atoms having a desired density (ρ ) Can be suitably produced by copolymerizing in such a ratio. 3 to 2 carbon atoms
The α-olefin of 0 is represented by the general formula R—CHＲCH ₂
(Wherein, R represents an alkyl group having 1 to 12 carbon atoms), for example, propylene, 1-butene, 1-
Hexene, 4-methyl-1-pentene, 3-methyl-1
-Butene, 1-pentene, 1-octene and the like.

Examples of the polymerization method for producing the polyethylene resin include slurry polymerization, gas phase polymerization, and solution polymerization.

The polyethylene resin for pipes and joints of the present invention can be used in two or more reactors having different reaction conditions.
It is manufactured by a low pressure multi-stage polymerization method. That is, MFR5 is 0.20 to 0.50 g / 10 min, and density (ρ) is 0.94.
8 to 0.952 g / cm ³ , flow ratio FR is 65 to
By adjusting them as a range of 130, a cross-fractionation (TREF-S) consisting of temperature-rise elution fractionation (TREF) and size exclusion chromatography (SEC)
EC), the amount of the high molecular weight component calculated for each of the plurality of elution temperature categories was integrated for all the elution temperature categories, but the ratio (WH) to the total amount of release was 39 to 45% by weight. The peak temperature (TH) of the elution curve obtained from the amount of the high molecular weight component calculated for each temperature category is 9
The peak temperature (TL) of the elution curve obtained from the low molecular weight components calculated for each of the plurality of elution temperature categories is not more than 6.5 ° C. and not less than 99.2 ° C., and the relaxation parameter H
Of 1.90 × 10 ⁻⁸ dyn / cm ² or less. Pipes and joints can be formed using this polyethylene.

The present inventors have found that it is not sufficient to independently change the density (ρ) and the MFR in order to improve the durability of a pipe as in the prior art.
Find WH, TL and TH, and relaxation parameter H required by EC, and control the durability, MFR5, flow ratio FR, and density (ρ) within the above-mentioned predetermined ranges, and , This W
By putting H, TL, TH, and the parameter H in the target value range, the polyethylene having excellent durability can be obtained.
As a result, a pipe and a joint can be obtained.

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 under a test load of 5.00 kg is 0.20 to 0.5.
0 g / 10 min, preferably 0.22 to 0.45 g / 10
Min, particularly preferably 0.25 to 0.43 g / 10 min. (2) Density (ρ) of 0.948 to 0.952 g / c
m ^3, preferably 0.949~0.951g / cm ^3. (3) The flow ratio (flow ratio FR) is 65 to 130, preferably 70 to 120, particularly preferably 80 to 115. (4) The relaxation parameter H of the following formula (I) obtained by the stress relaxation measurement is 1.90 × 10 ⁻⁸ dyn / cm ² or less, preferably 1.85 × 10 ⁻⁸ dyn / cm ² or less. (5) Cross fractionation (TR) consisting of temperature rising elution fractionation (TREF) and size exclusion chromatography (SEC)
Although the amounts of the high molecular weight components calculated for each of the plurality of elution temperature categories determined by EF-SEC) were integrated for all the elution temperature categories, the ratio (WH) to the total output amount was 39.
~ 45% by weight. (6) Cross fractionation (TR) consisting of temperature-rise elution fractionation (TREF) and size exclusion chromatography (SEC)
EF-SEC), the peak temperature (TH) of the elution curve obtained from the amount of high molecular weight component calculated for each of a plurality of elution temperature categories is 96.5 ° C. or less, and TR
The peak temperature (TL) of the elution curve determined from the amount of low molecular weight components calculated for each of a plurality of elution temperature categories determined by EF-SEC is 99.2 ° C or higher.

[0015] The long-term durability under stress required for polyethylene used for pipes and joints, that is, environmental stress cracking resistance, hot internal pressure creep resistance and low-speed crack extension resistance of polyethylene is determined by the crystal part of polyethylene. It is well known that the more the so-called tie molecules connecting the crystal part and the crystal part, the better. It is also known that polyethylene having a structure with a small number of tie molecules has a high cracking speed, that is, a high breaking speed.

As described by Brown et al. (Y. Hua
ng & N. Brown, J. Poly. Sci .: Part B: Poly. Phys.,
29, 129 (1991)) The distance between the ends of a molecule at the time of melting is
If it is longer than {(thickness of crystal lamella part) × 2 + thickness of amorphous part} (= long period), it can be considered that tie molecules are generated. It is considered that the end-to-end distance becomes longer as the molecular weight becomes larger, that is, as the molecular length becomes longer. Brown et al further state that the rate of slow crack extension slows with increasing average molecular weight (Y. Huang & N. Brown, J. Pol
y. Sci .: Part B: Poly. Phys., 28, 2007 (1990)).
This just suggests that the higher the average molecular weight, the higher the probability of tie molecule formation. The average molecular weight is MF
Expressed as R5, the molecular weight increases when MFR5 is small.

The thickness of the crystal part can be determined as proposed by Illers et al. (VK Illers & H. Hendus, Polymer, 24
1647 (1983)) It is expressed by the melting point, and the higher the thickness of the crystal lamella part, the higher the melting point. The thickness of the amorphous portion can be easily calculated if the thickness and crystallinity of the crystal lamella portion are known. This is because the crystallinity is a ratio of the entire crystal part to the crystal part, and the ratio between the thickness of the crystal lamella part and the thickness of the amorphous part can be defined as the crystallinity in two dimensions. Normal,
Crystallinity is represented by density (ρ). Generally density (ρ)
Is controlled by the molecular weight and the concentration of the α-olefin to be copolymerized. By increasing the molecular weight, the density (ρ) decreases because it becomes difficult to form a folded structure, but the density (ρ) can be further reduced for the same reason by the presence of α-olefin as a comonomer during polymerization. Will be possible.

From the above, it can be seen that it is preferable that the molecular weight be as high as possible, that is, the MFR5 is as low as possible and the density (ρ) is as low as possible in order to produce tie molecules.

However, when the average molecular weight is simply increased, that is, when the MFR5 is set to less than 0.20 g / 10 minutes, the fluidity is remarkably deteriorated, the moldability is insufficient, and the productivity of the pipe is not satisfied. Rather, the skin becomes rough, and as a result, stress concentration occurs at the uneven portion, which adversely affects long-term durability. In addition, when a joint or the like is formed by injection molding, it cannot be formed, or even if it can be formed, the appearance becomes extremely poor. On the other hand, when the MFR5 exceeds 0.50 g / 10 minutes, that is, when the average molecular weight is small, the long-term durability of the pipe and the joint is insufficient from the viewpoint of tie molecule generation. Further, the impact resistance is insufficient, the resin coming out of the die at the time of molding is apt to hang, and the roundness and the uniformity of the wall thickness of the manufactured pipe are poor. Poor roundness causes connection problems, such as the inability to insert a pipe into the joint. If the wall thickness is not uniform, the circumferential stress of the thin portion increases, which is a serious problem in an actual piping system, and undesirably increases the warpage of the pipe.

Further, if the overall density (ρ) is less than the above range, the rigidity of the pipe is remarkably insufficient, so that it is easy to be deformed by earth pressure after burying, and it is not preferable because it cannot withstand a sudden increase in internal pressure. . On the other hand, exceeding the above range is not preferable because the probability of tie molecule formation becomes extremely small and the long-term durability of the pipe is insufficient.

Therefore, it is extremely difficult to simultaneously optimize the durability, moldability, and other properties by simply controlling the MFR5, that is, the average molecular weight and the density (ρ). In order to produce the most suitable polyethylene, the present inventors share the necessary physical properties between a high molecular weight component and a low molecular weight component by a low pressure multistage polymerization method using two or more reactors having different reaction conditions. It is necessary to achieve the required performance, and the content of each component is determined by the ratio of the high molecular weight component by TREF-SEC (WH) and the elution peak temperature of the high molecular weight component (TH). , Low molecular weight component elution peak temperature (T
L), FR and the relaxation parameter H were found to be controllable.

In TREF-SEC, the distribution of crystallinity and molecular weight of polyethylene can be examined by the method described below. First, a TREF column is used to separate steps from low crystallinity to high crystallinity using the difference in dissolution temperature. Continue this SE
By injecting into the C column, the size of the molecule, ie,
Separate by molecular weight. By this operation, the elution amount (% by weight) and the molecular weight distribution (dW / d (log)
M) vs log M).

The ratio (WH) of the high molecular weight component, the elution peak temperature (TH) of the high molecular weight component, and the elution peak temperature (TL) of the low molecular weight component are determined according to the following procedures. In two or more reactors having different reaction conditions, the polyethylene resin produced by the low-pressure multi-stage polymerization method is separated by the above-mentioned method, so that each of the elution temperature sections is divided into a low molecular weight component and a high molecular weight component. A molecular weight distribution consisting of 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 component and the high molecular weight component are each assigned to the low molecular weight component in the elution temperature category.・ High molecular weight components. The value normalized so that the sum of the amounts of the low molecular weight component and the high molecular weight component obtained by peak separation becomes equal to the elution amount (% by weight) of the elution temperature category,
The amounts of the low molecular weight component and the high molecular weight component in the elution temperature category are defined. The sum of the amounts of the high molecular weight components in all elution temperature categories is defined as the ratio of high molecular weight components (WH).

The amount of the high molecular weight component in each elution temperature section is plotted with respect to the elution temperature section, and a curve obtained by fitting a normal distribution in the range of 80 ° C. to 110 ° C. is defined as an elution curve. 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, the amount of the component corresponding to logM = 5 ± 0.1 (M: molecular weight) in the low molecular weight component of each elution temperature section is used instead of the amount of the low molecular weight component of each elution temperature section. This means that the molecular weight is 30,000 or less (lo
For components with gM <4.5, the elution temperature shows a remarkable dependence on molecular weight (for example, Journal of Polymer Science: Po.
lymer Physics Edition, Vol. 20, 441-445 (1982)). For low molecular weight components containing a large amount of components having a molecular weight of 30,000 or less, a method for obtaining an elution curve for a specific molecular weight component having a molecular weight of 30,000 or more. Is to reflect the exact nature.
The peak temperature obtained in this manner is defined as the elution peak temperature (TL) of the low molecular weight component.

TL and TH are indicators of the crystallinity, that is, the degree of crystallinity, as can be seen from the method of obtaining them. A high value indicates that the crystallinity is high, while a low value indicates that the crystallinity is low. The TL is set to 99.2 ° C. or higher, that is, the rigidity is ensured by increasing the crystallinity of a low molecular weight component that hardly contributes to the improvement of creep characteristics and ESCR characteristics under tensile stress. By setting the temperature to 5 ° C. or less, the degree of crystallinity of the high molecular weight component that greatly contributes to the creep characteristics and the ESCR characteristics under tensile stress is reduced, that is, the tie molecules are generated by lowering the density (ρ), and the rigidity and For the first time, it is possible to achieve both long-term durability.

In the case of polyethylene manufactured in the above MFR5 and density (ρ) range, when TL is lower than 99.2 ° C. and TH is higher than 96.5 ° C., apparent rigidity is the same. But the creep properties and the resistance to stress cracking, ie, the E under tensile stress
This means that the crystallinity of the high molecular weight component that expresses the SCR characteristics is low, that is, the probability of forming tie molecules is significantly reduced, and these characteristics are significantly reduced. The occurrence of brittle cracks due to stress concentration is inevitable.

The flow ratio FR is expressed as a numerical value obtained by dividing the amount of extrusion for 10 minutes under a load of 11.6 kg at 190 ° C. by the amount of extrusion for 10 minutes under a load of 1.16 kg using a melt indexer. It is a physical property that indicates a measure of the molecular weight distribution of polyethylene. A smaller flow ratio FR value indicates a narrower molecular weight distribution, and a larger flow ratio indicates a wider molecular weight distribution. In the case of polyethylene produced in the above MFR5 and density (ρ) range, if the flow ratio FR is less than 65, the molecular weight distribution becomes narrow, that is, the molecular weight of the low molecular weight component becomes relatively large. ,
The fluidity is remarkably reduced, resulting in poor moldability. When the flow ratio FR exceeds 130, the molecular weight distribution is widened, that is, the molecular weight of the low molecular weight component is relatively reduced, and although the fluidity is excellent, the impact resistance due to the influence of the low molecular weight component is low. It tends to decrease.

When WH is less than 39% by weight, it means that the amount of the high molecular weight component is small.
In the case of polyethylene produced in the range of FR5 and density (ρ), it means that the molecular weight of the high molecular weight component increases. Higher molecular weight components are preferred from the viewpoint of durability as described above, but the compatibility of the two components is significantly reduced, impact resistance is reduced, and fish eyes are increased, resulting in poor pipe surface. Is not preferred. On the other hand, W
When H is more than 45% by weight, the molecular weight of the high molecular weight component becomes small, and the probability of forming a tie molecule becomes small, so that the long-term durability is remarkably reduced.

The relaxation parameter H is a parameter derived from the following theory, and polyethylene having H in a specific range has good long-term durability. That is, in order to exhibit long-term durability, it is considered that a large proportion of the component that relaxes the stress in a short time is required. In order to evaluate this stress relaxation, when a constant strain is applied to the test piece, the relaxation obtained by measuring the time change of the elastic modulus obtained by dividing the stress generated in the test piece by the strain is measured. It is known that an elastic 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-time conversion rule. A method of obtaining a relaxation distribution function from this relaxation elastic modulus has been proposed by Schwarz-Staverman, Leaderman et al. (Reference: Deformation of objects, published by Seibundo Shinkosha in 1972, pp. 201-204). The relaxation spectrum h (j) at the time j is represented by the following equation (II).

[0031]

(Equation 3) (Where E (k) (kj) = d ^k E / d ^t k and the relaxation modulus is differentiated k times with time t.) When this is approximated by k = 1, the following equation is obtained. III) is obtained.

[0032]

(Equation 4) Relaxation distribution function h (10 ³ ) for a long time (j = 10 ³ seconds)
Is H, H is represented by the following equation (IV).

[0033]

(Equation 5) Here, using the value measured at 10 ⁰ seconds, so the following formula (V) is obtained,

[0034]

(Equation 6) H can be obtained from an experimental value as in the following equation (I).

[0035]

(Equation 7)

As described above, the relaxation parameter H (dyn / cm ² ) in the formula (I) is a parameter corresponding to the relaxation distribution function at a specific time (10 ³ seconds), and can be obtained from an experimental value. . The fact that H is within the above-mentioned 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 preferably small. The relaxation parameter H is a parameter mainly determined by the average molecular weight and the molecular weight distribution, and controls MFR5, FR and density (ρ) within the above-mentioned range, and sets the parameter H to 1.90 × 10 ⁻⁸ dyn / cm ² or less. , Preferably 1.
It is necessary to control it within the range of 85 × 10 ⁻⁸ dyn / cm ² or less.

The polyethylene obtained here is 80
The initial tensile load is 6MP in constant stress environmental stress crack test at ℃
In the case of a, the breaking time is 20 hours or more, and when the initial tensile load is 4 MPa, the breaking time is 80 hours or more.

In a constant stress environmental stress crack test at 80 ° C., the fracture time when the initial tensile load was 6 MPa was 20 hours or less,
Further, a material having a fracture time of 80 hours or less when the initial tensile load is 4 MPa is particularly inferior in low-speed crack extension resistance among long-term durability under stress required for polyethylene used for pipes and joints. . That is, sensitivity to scratches and the like,
In other words, cracks easily occur due to scratches, etc.
In addition, it means that the growth speed of the crack is high. Pipes and fittings made of such materials, especially at high temperatures,
Brittle cracking tends to occur due to stress concentration generated in minute structural defects, and such brittle fracture is undesirable from the viewpoint of reliability.

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. As this optional component, those known or used as ordinary additives and compounding agents for polyolefins, for example, antioxidants, neutralizers, weather resistance improvers, foam inhibitors,
Dispersants, antistatic agents, lubricants, heat stabilizers, light stabilizers, ultraviolet absorbers, lubricants, metal deactivators, bactericides, fungicides,
A coloring agent, a release agent, a processing aid, and the like can be mentioned, and these can be appropriately combined and blended at an arbitrary stage from the production of a molding raw material to the production of a pipe and a joint.

The above polyethylene resin and, if desired, optional components can be directly charged into a molding machine for molding. Generally, these components are melt-kneaded in advance to form a pellet-like molding material. Is desirably molded. Pipe molding is usually performed by an extrusion molding method, but a pipe joint or the like may be molded by an injection molding method. The molding may be performed not only in a single layer but also in a plurality of layers.

[0041]

The present invention will be further described below with reference to specific examples. In the examples, each physical property of the resin was evaluated by the following methods. ○ MFR5: Conforms to JIS K7210. ○ Density (ρ): Based on JIS K7112. ○ Impact resistance: JIS K7110 (23 ° C) compliant
Evaluate the zip impact strength. ○ Olzen bending stiffness: according to ASTM D747. ○ ESCR: Using a JIS K6760 constant stress environment stress crack test apparatus, water temperature was set to 80 ° C, and 1
% Of higher alcohol sodium sulfonate aqueous solution, and the initial tensile load was measured at 6 MPa and 4 MPa. The test piece used was a press plate having a thickness of 1 mm and a width of 6 mm, and a laser notch having a depth of 0.4 mm was provided at the narrowest portion in the center of the tensile portion.

The TREF-SEC measuring device used was CFC T-100 manufactured by Diamond Instruments. The sample to be measured was dissolved using o-dichlorobenzene as a solvent and injected into a TREF column. 40
At T ° C from TREF column to SEC column (Showa Denko A
D806MS (3 pieces). While the molecular size was being fractionated on the SEC column, the temperature of the TREF column was raised. Thereafter, the temperature was repeatedly raised to 140 ° C. every 5 ° C., and injection into the SEC column was repeated. Obtained. The molecular weight distribution of each elution temperature category with two peaks is 2
By fitting two lognormal distributions, peaks were separated into two components, and WH, TL, and TH were calculated by calculation on the low molecular weight side and the high molecular weight side as low molecular weight components and high molecular weight components in the elution temperature section. .

応 力 Stress relaxation: Using an optreometer “HRS-100” manufactured by Oak Manufacturing Co., Ltd., a test piece was formed by press molding and then annealed at 100 ° C. for 10 hours, and the size was 30 mm × 5 mm × 0.3 mm. One used. In the measurement, stress relaxation after pulling 1 mm at a speed of 1 mm / sec was measured by changing the temperature, and evaluated by a master curve at 30 ° C.

○ Hot internal pressure creep, tube appearance, inner surface smoothness: using a 65φ extruder manufactured by Gunze Sangyo Co., Ltd., a spiral die, and a vacuum cooling water bath manufactured by IKG, and a resin temperature of about 210 ° C., in a water bath Cooling water temperature is about 20 ° C, take-off speed is about 65cm / min, outer diameter 60mmφ, wall thickness 5.5mm
Was formed and the internal pressure was adjusted so that the circumferential stress was 5.5 MPa at 80 ° C. in accordance with ISO 1167, and the creep performance was evaluated. The test is based on ISO4427
The durability was confirmed at 80 ° C. and 5.5 MPa for 165 hours or more, and the test was further performed up to 10,000 hours to confirm whether brittle fracture was observed.
Moreover, the external appearance of the tube was visually observed and evaluated by the following A to D. A: Good. B: Slight surface roughness was observed at the time of extrusion, and the surface of the tube was partially roughened. C: Slight surface roughness was observed at the time of extrusion, and the surface of the tube was partially roughened. D: Severe roughening was observed at the time of extrusion, and severe unevenness occurred on the entire surface of the tube. Furthermore, the smoothness of the inner surface of the tube was visually checked, and evaluated by the following A and B. A: Good. B: Point-like irregularities derived from the gel were observed.

Example 1 (A) Preparation of solid catalyst 77.9 kg of Mg (OEt) ₂ and Ti (OBu) ₃ Cl
103.1 kg of n-BuOH and 25.3 kg of n-BuOH
After mixing at 50 ° C. for 6 hours, the mixture was homogenized. After cooling, a predetermined amount of benzene was added to obtain a uniform solution. Next, 51.5 kg of ethyl aluminum sesquichloride was added dropwise at a predetermined temperature, and the mixture was stirred for 1 hour. Further, washing with n-hexane was repeated to obtain 25 kg of a solid catalyst.

(B) Polymerization Using the catalyst component obtained, continuous polymerization was carried out using an apparatus in which two 0.6 m ³ reactors were connected in series. In the first polymerization tank, 70 kg / h of n-hexane, 3.63 g / h of diethylaluminum monochloride, and 1.0 g of the solid catalyst component were used.
88 g / h, 31 kg / h of ethylene and hydrogen were continuously supplied, and the temperature was 90 ° C., and the hydrogen / ethylene molar ratio in the gas phase was kept at 2.8 to carry out continuous polymerization. The polymer slurry of the first polymerization tank is continuously supplied to the second polymerization tank, and 47 kg / hour of n-hexane and 27.0 kg / hour of ethylene are continuously supplied. The hydrogen / ethylene molar ratio is 0.03, and the 1-butene / ethylene molar ratio is 0.03.
08 and continuous polymerization was carried out.

The slurry was continuously withdrawn from the second polymerization tank, solid-liquid separated by a centrifugal separator, and the polymer was dried.
The obtained polymer was kneaded and pelletized under predetermined conditions using a 90 mmφ extruder, and then subjected to pipe molding and physical property measurement. The measurement results are shown in Table 1.

Example 2 In Example 1, triethylaluminum was used as a cocatalyst. In the second polymerization tank, the hydrogen / ethylene molar ratio in the gas phase was 0.003, and the 1-butene / ethylene molar ratio was 0.003. Was adjusted to 0.12, and the ethylene supply ratio of the first stage and the second stage was maintained at 55/45 to carry out continuous polymerization.

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 carried out by setting the hydrogen / ethylene molar ratio in the gas phase of the second polymerization tank to 0.05 and the 1-butene / ethylene molar ratio to 0.05.

Comparative Example 3 In Example 1, the hydrogen / ethylene molar ratio in the gas phase of the first polymerization tank was set to 6, the hydrogen / ethylene molar ratio in the gas phase of the second polymerization tank was set to 0.1, and 1-butene / The ethylene molar ratio is set to 0.
06, and the ethylene supply ratio of the first stage and the second stage is 46
/ 54 to perform continuous polymerization.

Comparative Example 4 In Example 1, the hydrogen / ethylene molar ratio in the gas phase of the second polymerization tank was set to 0.01, the 1-butene / ethylene molar ratio was set to 0.13, and the first and second stages were used. Was carried out at an ethylene supply ratio of 55/45 to carry out continuous polymerization.

Comparative Example 5 In Comparative Example 1, without changing the ethylene supply rate and the ethylene / hydrogen molar ratio in the gas phase of the first polymerization tank,
The 1-butene is supplied so that the 1-butene / ethylene molar ratio is maintained at 0.003, and continuous polymerization is performed. In the second polymerization tank, the hydrogen / ethylene molar ratio in the gas phase is set to 0.05, 1
-Continuous polymerization was carried out with a butene / ethylene molar ratio of 0.065.

Comparative Example 6 In Example 2, without changing the ethylene supply rate and the ethylene / hydrogen molar ratio in the gas phase of the first polymerization tank,
Continuous polymerization is carried out by supplying 1-butene so that the 1-butene / ethylene molar ratio can be maintained at 0.001, and the hydrogen / ethylene molar ratio in the gas phase is 0.012 in the second polymerization tank.
Continuous polymerization was carried out at a 1-butene / ethylene molar ratio of 0.04 and a first and second stage ethylene supply ratio of 54/46.

Comparative Example 7 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 7, and the hydrogen / ethylene molar ratio in the gas phase was reduced to 0 in the second polymerization tank. .01, 1-
Continuous polymerization was performed with a butene / ethylene molar ratio of 0.14.

Comparative Example 8 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 4.5, and in the second polymerization tank, the hydrogen / ethylene molar ratio in the gas phase was maintained. 0.15,
Continuous polymerization was carried out with the 1-butene / ethylene molar ratio being 0.04 and the ethylene supply ratio of the first and second stages being 35/65.

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 maintained. Is 0.00
5, the 1-butene / ethylene molar ratio was 0.15,
Continuous polymerization was performed with the ethylene supply ratio of the stage and the second stage being 25/75.

Comparative Example 10 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 0.015.

Comparative Example 11 In Example 1, without changing the ethylene supply rate and the ethylene / hydrogen molar ratio in the gas phase of the first polymerization tank,
Continuous polymerization is carried out by supplying 1-butene so that the 1-butene / ethylene molar ratio can be maintained at 0.006. In the second polymerization tank, the hydrogen / ethylene molar ratio in the gas phase is 0.06,
The 1-butene / ethylene molar ratio was 0.0047,
Continuous polymerization was performed with the supply ratio of ethylene in the second stage to the second stage being 55/45.

Comparative Example 12 In Example 2, the molar ratio of hydrogen / ethylene in the gas phase of the second polymerization tank was set to 0.012, and the molar ratio of 1-butene / ethylene was set to 0.12. Was carried out at a feed ratio of ethylene of 47/53.

As shown in Example 1 and Example 2 in Table 1, MH5, flow ratio FR, and density (ρ) were controlled to obtain WH, TL, TH, and parameter H.
Is in the range defined in claim 1, the pipe made of the polyethylene has a circumferential stress of 5.5 MPa at 80 ° C.
In the hot internal pressure creep test, not only the performance of not cracking for 165 hours or more shown in ISO4427, but also the test was continued for 10,000 hours, but no brittle fracture was observed until then. . The Olsen bending stiffness was 1,100 MPa and 1,00 MPa, respectively.
It was 0 MPa, and the Izod impact test was performed, but was not broken (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 the brittle fracture occurred in the Izod impact test.
kJ / m ² was insufficient. Further, as shown in Comparative Example 2, even when the density (ρ) exceeded the range of claim 1, brittle fracture occurred in the hot internal pressure creep test. On the other hand, when the density (ρ) is lower than the range of claim 1 as in Comparative Example 4, the 165 hours specified in ISO4427 cannot be satisfied in the hot internal pressure creep test, and further, 12 kJ / m in the Izod impact test. m ² was insufficient. As shown in Comparative Example 8, the flow ratio FR was lower than the range of claim 1, and M
When FR5, WH, parameters H and TH were out of the range defined in claim 1, brittle fracture occurred in the hot internal pressure creep test, and the Izod impact test was insufficient at 13 kJ / m ² . Further, as shown in Comparative Example 9, 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 a remarkably low value of 5 kJ / m ² .

As shown in Comparative Example 3, when WH and parameter H are out of the scope of Claim 1, TL as shown in Comparative Example 5, and TL as shown in Comparative Examples 6 and 11,
As shown in Comparative Example 12, when H was out of the range of claim 1, brittle fracture occurred in the hot internal pressure creep test. Further, in Comparative Example 3, the result of the Izod impact test was insufficient. Further, as shown in Comparative Example 7, when the parameter H exceeds the range described in claim 1,
Brittle fracture occurs in the hot internal pressure creep test, and Izo
d Impact test was insufficient at 15 kJ / m ² .

Comparative Examples 1, 2, 3, 5, 6 and 8
As shown in the figure, in a constant stress environmental stress crack test at 80 ° C., the fracture time when the initial tensile load was 6 MPa was 20 hours or more, and the fracture time when the initial tensile load was 4 MPa was 80 hours or more. Otherwise, brittle fracture was found to occur within 10,000 hours in all hot internal pressure creep tests.

[0065]

[Table 1]

[0066]

According to the present invention, polyethylene having excellent rigidity, impact resistance and long-term durability under stress (environmental stress cracking resistance, hot internal pressure creep resistance of pipes, and low-speed crack extension resistance), It becomes possible to provide a polyethylene pipe and a polyethylene joint. In particular, regarding long-term durability, the initial tensile load was 6M in a constant stress environmental stress crack test using a notched test piece in a surfactant at 80 ° C.
It has a performance in which the fracture time at Pa is 20 hours or more and the fracture time at an initial tensile load of 4 MPa is 80 hours or more. In addition, the circumferential stress was 5.5 in a hot internal pressure creep test.
The fracture time in MPa is 65 hours or more and the brittle fracture is 1
It did not occur within 000 hours.

Continuation of the front page (72) Inventor Tetsuya Yoshikiyo 3-1, Chidori-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Japan Inside the Polychem Co., Ltd. Material Development Center (72) Inventor Kazuya Sakata 3-dori-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa No.1 F-term in Material Development Center of Japan Polychem Co., Ltd. (Reference) 3H111 AA04 BA15 BA34 4J100 AA02P CA01 DA01 DA15 DA42 DA43 DA47 FA09 JA67

Claims (3)

[Claims] 1. A polyethylene resin produced using a Ziegler-Natta catalyst and having the following physical properties (1) to (6). (1) The melt flow rate (MFR5) measured at 190 ° C under a test load of 5.00 kg is 0.20 to 0.5.
0 g / 10 minutes. (2) Density (ρ) of 0.948 to 0.952 g / c
m ³ . (3) The flow ratio (flow ratio FR) is 65 to 130. (4) The relaxation parameter H of the following formula (I) obtained by the stress relaxation measurement is 1.90 × 10 ⁻⁸ dyn / cm ² or less. (5) Cross fractionation (TR) consisting of temperature rising elution fractionation (TREF) and size exclusion chromatography (SEC)
Although the amounts of the high molecular weight components calculated for each of the plurality of elution temperature categories determined by EF-SEC) were integrated for all the elution temperature categories, the ratio (WH) to the total output amount was 39.
~ 45% by weight. (6) Cross fractionation (TR) consisting of temperature-rise elution fractionation (TREF) and size exclusion chromatography (SEC)
EF-SEC), the peak temperature (TH) of the elution curve obtained from the amount of high molecular weight component calculated for each of a plurality of elution temperature categories is 96.5 ° C. or less, and TR
The peak temperature (TL) of the elution curve determined from the amount of low molecular weight components calculated for each of a plurality of elution temperature categories determined by EF-SEC is 99.2 ° C or higher. (Equation 1) (Where E (τ) is the relaxation modulus at time τ) 2. A pipe and a joint made of the polyethylene resin according to claim 1. 3. 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 more, and the fracture time at an initial tensile load of 4 MPa is 80 hours or more. The pipe and the joint according to claim 2, characterized in that: