JP2995668B2 - Polyethylene resin and pipe and pipe joint using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field to which the Invention Belongs] The present invention is suitable for both extrusion molding and injection molding, and is also suitable for providing a pipe having an excellent long-term life. The present invention relates to a pipe and a pipe joint.

[Conventional technology]

Although pipes formed by molding a polyethylene resin are widely used, in recent years, they have been particularly used for water pipes and gas pipes. Since these pipes buried in the ground are used for an extremely long period after construction, reliability that does not cause deformation or breakage for a long period of time is required. These properties are attributed to the creep life, which is the time to failure of a statically loaded material, and the long-term fatigue strength, which is the time to failure of the material when periodically loaded. Is shown.

Further, since these pipes are constructed while being added at the time of construction, joints are required. Since this joint is formed by injection molding, high fluidity is required, and at the same time, long creep life and fatigue strength are required.

Generally, it is possible to improve the fluidity of a polyethylene resin by lowering its average molecular weight. However, if the average molecular weight is lowered, there is a disadvantage that the long-term life is deteriorated.

For the purpose of resin for pipes, there has been proposed a method of broadening the molecular weight distribution by mixing ethylene-based polymers having different molecular weights by a method such as two-stage polymerization, melt blending, and dry blending. However, for example, the one proposed in Japanese Patent Publication No. 63-67811 has a high density and high rigidity, but has a poor long-term life, and the one proposed in Japanese Patent Application Laid-Open No. 8-134285, for example, has a high viscosity when molten and has a high fluidity. Due to poor moldability, there is a drawback in moldability, and a material that sufficiently satisfies both physical properties and moldability has not been obtained.

[Problems to be solved by the invention]

An object of the present invention is to provide a polyethylene resin having excellent creep life and fatigue strength, and also having excellent fluidity and being injection-moldable, and further having a pipe having the above characteristics and a pipe used in combination with the pipe. To provide a coupling.

[Means for solving the problem]

The present inventors have conducted intensive studies to achieve the above object, and as a result, a polyethylene resin having a melt flow rate with a different load satisfying a predetermined value and a dynamic melt viscosity and a frequency dispersion satisfying a predetermined relationship has been extruded and extruded. It has excellent injection moldability and has excellent creep life and fatigue strength, and it has been found that when used for molding pipes and pipe joints that require long-term physical properties, it shows a remarkably excellent effect, and reached the present invention. did.

The present invention firstly provides a density of 0.915 to 0.955 g · cm ⁻³ at 190 ° C.
The melt flow rate measured using a load of 2.16 kgf at 0.20 dg · min ^-1 or less, and a load 2 at 190 ° C.
Melt flow rate measured using 1.6 kgf is 17.0-7
Obtained when measuring in the frequency (ω) range from 100 to 0.01 rad · s ^-1 with a plate gap of 1.5 mm and a strain of 10 to 15% using a parallel plate at 0.0dg · min ^-1 and a rheometer 190 ° C using a parallel plate. When the dynamic melt viscosity (η ^* : unit Pa · s) is sufficiently approximated by the formula [1], the zero shear viscosity (η ₀ ) is 200,000-
2,000,000Pa · s, the specific time constant (τ ₀ ) is 50-500s,
And (τ ₀ / η ₀ ) is 1.0 × 10 ^{−4 to} 4.0 × 10 ⁻⁴ Pa ^−1. Secondly, the present invention resides in a pipe characterized in that the above-mentioned polyethylene resin is formed by extrusion.

Thirdly, the present invention resides in a pipe joint obtained by molding the above-mentioned polyethylene resin by extrusion.

Fourth, the present invention resides in a connected pipe formed by combining pipes formed by the above-described extrusion molding and pipe joints formed by the above-described injection molding.

[Embodiment of the invention]

The polyethylene resin of the present invention has a density of 0.915 to 0.955 g
m ⁻³ , preferably in the range of 0.935 to 0.955 g · cm ⁻³ . If the density is less than 0.915 g · cm ^-3, it is too soft, which is inconvenient as a pipe. If the density exceeds 0.955 g · cm ^-3 , creep characteristics and fatigue strength become insufficient.

The polyethylene resin of the present invention has a load of 2.16k at 190 ° C.
The melt flow rate measured using gf (hereinafter MFR _2.16
Is abbreviated as 0.20 dg · min ⁻¹ or less, preferably 0.02 to 0.20 d
g · min ^-1 . If it exceeds 0.20 dg · min ^-1 , the creep life will be insufficient.

The polyethylene resin of the present invention has a melt flow rate (hereinafter referred to as M) measured at 190 ° C. using a load of 21.6 kgf.
FR _21.6 ) is 17.0 to 70.0 dg · min ⁻¹ , preferably 17.
It must be 0 to 30.0 dg · min ^-1 . 17.0dg ・ min ^-1
If it is less than 3, there is a possibility that extrusion may be difficult when molding the pipe, productivity may be significantly reduced, and injection molding of the pipe joint may be difficult, or deformation may be caused after molding. If it exceeds 70.0 dg · min ^-1 , the long-term life of the pipe will be reduced.

Furthermore, the polyethylene resin composition of the present invention has a plate gap of 1.5 mm using a parallel plate at 190 ° C.
Dynamic melt viscosity (η ^* ) obtained when measured in a frequency (ω) range from 100 to 0.01 s ⁻¹ at a strain of 10 to 15%.
S) and frequency (ω; unit s ^-1 ) must satisfy a certain relationship.

Specifically, η ₀ when the dynamic melt viscosity and the frequency are sufficiently approximated to the above formula [1] is 200,000 to 2,000,000 Pa ·
s, more preferably in the range of 350,000 to 1,000,000 Pa · s, the specific time constant (τ ₀ ) is in the range of 50 to 500 s, more preferably 100 to 300 s, and (τ ₀ / η ₀ ) is 1.0.
The range is from × 10 ^{−4 to} 4.0 × 10 ⁻⁴ Pa ⁻¹ .

The values of η ₀ and τ ₀ are determined from values measured with a rheometer using a parallel plate. Ie 190 ° C
The dynamic melt viscosity (η ^* ) was measured at a plate interval of 1.5 mm, a strain of 10 to 15%, and a frequency (ω) in the range of 100 to 0.01 (unit: rad. · S ⁻¹ ). [1]
Approximates By this approximation, the zero shear viscosity (η ₀ ), the specific time constant (τ ₀ ), and the parameter (n) are obtained. The approximation of the regression method to the equation [1] can be calculated using an appropriate computer program of a commercially available regression method.

Note that τ ₀ is a parameter representing a relaxation time, and n is a parameter representing a shear rate dependency in a high shear rate region.

Equation [1] is an empirical equation generally called “Cross equation”. For example, Green V. Gordon, Montgomery T. Shaw, “Com
puter Programs for Rheologists ", Hanser Publish
outlined in ers.

The relationship between the dynamic melt viscosity at 190 ° C. and the frequency can be obtained by using a commercially available device, for example, RMS-800 type rheometer manufactured by Rheometrics.

The parameter n in the equation represents the shear rate dependence of the melt viscosity in the high shear rate region.

In the sense that the "when sufficiently fit" in the present invention, the deflection coefficient R ² is a linear correlation coefficient of the square of the approximated regression curve and the data points by the least squares method is approximated as a 0.9992 more is there.

η ₀ represents the melt viscosity in the absence of any shear stress, and is a parameter that is affected by both the weight average molecular weight and the Z average molecular weight. If this value is large, the average molecular weight is generally high, and the creep life and fatigue High strength.

In the polyethylene resin of the present invention, η ₀ is 200,000P
If it is less than a · s, the creep life becomes insufficient and 2,000,000
Exceeding Pa · s results in poor extrusion and injection moldability.

The characteristic time constant (τ ₀ ) is an index of the difficulty of deformation in the molten state, and in the polyethylene resin composition of the present invention, τ ₀ is in the range of 50 to 500 s, preferably 100 to 300 s. If it is less than 50 s, the balance between creep life and fatigue strength and extrudability and injection moldability will be poor, and it will be difficult to produce a material exceeding 500 s on a practical scale.

The ratio of τ ₀ to η ₀ (τ ₀ / η ₀ ) is a parameter serving as an index of the elasticity of the resin at the time of melting. In particular, when there is a long-chain branch in the molecular structure, it shows a remarkably large value. In the polyethylene resin of the present invention, a long-chain branched molecular structure is not desirable because the creep life and fatigue strength may be insufficient and the smoothness of the surface of the molded article may be deteriorated. .
In that sense, in the polyethylene resin of the present invention, τ ₀ / η
₀ is in the range of 1.0 × 10 ^{−4 to} 4.0 × 10 ⁻⁴ Pa ⁻¹ . τ ₀ / η ₀
If it exceeds 4.0 × 10 ⁻⁴ Pa ⁻¹ , it is expected that the molecular structure has long-chain branching, resulting in poor long-term performance,
If it is less than 1.0 × 10 ⁻⁴ Pa ⁻¹ , the moldability is poor.

The polyethylene resin of the present invention is a polyethylene resin that satisfies all the requirements described above, and such a polyethylene resin is a polyethylene resin having a special molecular weight distribution, and without impairing moldability by satisfying these requirements, is excellent. It has creep life and fatigue strength.

Due to such characteristics, the polyethylene resin of the present invention is most preferably used for pipes, particularly water pipes and gas pipes buried in the ground, but can of course be used for purposes other than pipes.

The polyethylene resin of the present invention is a homopolymerization of ethylene or ethylene and propylene, 1-butene, 1-pentene,
It is obtained by copolymerization with an α-olefin such as 1-hexene, 1-octene, 4-methyl-1-pentene and the like. The production method is not particularly limited, such as multi-stage polymerization of more than one kind of components, or a method of mixing these by post-blending, but among others, considering the complexity of time and labor for uniform mixing, the molecular weight is low. The method of producing two or more different components by multistage polymerization is most preferable.

One of the most preferable production methods is described in, for example, JP-A-58-225105.
Patent Publication No.
In this method, a high-molecular-weight component is continuously subjected to suspension polymerization in a pipe-loop reactor using an egler catalyst, and a low-molecular-weight component is used in a subsequent-stage reactor. In this case, the weight average molecular weight of the high molecular weight component is particularly 700,000 to 2,000.
About 000, and the weight average molecular weight of the low molecular weight component is 20,000
The range is about 0 to 100,000, and the ratio of both is 10
When the molecular weight of the high molecular weight component is relatively high and the ratio thereof is low, a polyethylene resin satisfying the above specific conditions can be obtained.

The thermoplastic resin of the present invention may be appropriately blended with other thermoplastic resins, additives, pigments, fillers, etc. within a range that does not impair the properties of the present invention, depending on the purpose of use.

The pipe in the present invention has a particularly long creep life and a small decrease in strength against long-term fatigue, and is formed by extrusion molding, and is particularly suitable for a water supply pipe such as a water supply pipe, a water distribution pipe, or a gas pipe because of its characteristics. It is a pipe used for. When these are used as water pipes or gas pipes,
About 50-500mmφ, about 2-50mm wall thickness, 20 ℃
It can be used for more than 50 years under hoop stress of about 10Mpa.

The pipe joint according to the present invention is formed by injection molding and is used for joining the pipes. A method of welding a joint having a wire heater embedded therein after fitting the pipe, and heating the fusion surface. It is used to connect pipes by a method such as the following.

This joint is required to have a long life equivalent to that of a pipe as well as injection moldability.

〔Example〕

Next, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Example 1: [Sample preparation] A two-stage polymerization reactor in which two pipe loop reactors each having 145 liters in the former stage and 290 liters in the latter stage were connected in series was sufficiently purged with nitrogen. Next, after supplying isobutane and filling the inside of the reactor with isobutane, triisobutylaluminum was added at a concentration of 1.0 mmol.
Was supplied so as to l ^-1, 80 ° C. The preceding reactor while stirring, and heating the subsequent reactor to 90 ° C.. Then, hydrogen was fed into the first-stage reactor at a concentration of 0.1 × 10 ⁻³ wt% and the second-stage reactor at a concentration of 0.027% so that the concentration of ethylene was 1.0 wt% in the first-stage reactor and 2.6 wt% in the second-stage reactor. In addition, 1-hexene was supplied such that the concentration in the first-stage reactor was 6.4 wt%. Example 1 of JP-A-58-225105
The hexane slurry of the solid catalyst component prepared according to the method for producing the solid catalyst component of
The polymerization was started by continuously supplying the ^mixture at h ^-1 . While continuously supplying isobutane to the first reactor at 51.5 kgh ^-1 and further to the second reactor at 34.0 kgh ^-1 , the produced polyethylene is discharged at 20 kgh ^-1 and the triisobutylaluminum concentration at the first stage is The ethylene and hydrogen concentrations in the preceding and following reactors and the temperature were maintained as described above.

The discharged isobutane slurry of polyethylene was returned to normal pressure to evaporate isobutane, and then heated to 80 ° C.
The powder was dried by a conveyor dryer, and pelletized using a meshing twin-screw extruder (L / D = 32) in the same direction of 37 mmφ to obtain a sample.

The weight average molecular weight of the high molecular weight component in the former stage is about 770,000,
The density was 0.917 g · cm ⁻³ , the low molecular weight component in the latter stage had an estimated weight average molecular weight of about 56,000, the estimated density was 0.957 g · cm ⁻³ , and the physical properties of the polymer are shown in Table 1.

(Physical property measurement)

Melt flow rate is 190 according to JIS K 7210
Using a load of 2.16 kgf at 200 ° C (test condition 4 in Table 1 of JIS K7210), a load of 21.6 kgf (JI
The measurement was performed using the test conditions 7) in Table 1 of SK7210.

Using a Rheometrics RMS-800 rheometer, measured at 190 ° C. using a parallel plate with a plate gap of 1.5 mm, a strain of 10 to 15% in a frequency (ω) range from 100 to 0.01 s ⁻¹ , Dynamic melt viscosity (η ^* ; unit Pa)
S) and frequency (ω; unit s ⁻¹ ) were obtained. Data was collected at 5 points per digit of frequency. The obtained data was sufficiently approximated by the equation [1]. Table 1 shows the results.

Using a UH-70-32DN type pipe molding machine (70 mmφ) manufactured by Hitachi Zosen Corporation, a pipe having a nominal diameter of 50 specified in JIS K 6762 was extruded. JIS K 6
After cutting to 5.9 ± 0.2mm width according to 3.1 of Appendix 774,
Using a razor blade, a notch around the entire circumference was formed at a depth of 1 mm to obtain a test piece.

The extrudability was evaluated based on the amount of extrusion at this time and the motor current, and was classified into good (）), slightly good (○), slightly poor (△), and poor (×).

This test piece is immersed in a constant load tensile tester CR
Using a -20-50P type, a creep life was measured by applying a tensile load and cutting from the notch (JIS K677).
Notch type tensile creep test of Annex 1 of 4). Also at 80 ° C, the servo pulsar EH manufactured by Shimadzu Corporation
Using a F-EB08 type, a tensile load was applied with a rectangular wave of 0.5 Hz, and the time until cutting was defined as the fatigue strength (JIS K 6774, Appendix 2, full-circle notch tensile fatigue test). The creep life and the fatigue strength were measured at several points while changing the load, and the load was divided by the cross-sectional area of the cut surface to obtain the stress. The results are shown in Table 1. Those having a long creep life even under high stress are excellent, and those whose stress decreases rapidly with the life time are inferior.

Fatigue strength is excellent even under high stress.

The sample was injection molded using an MIIISycap480 / 150 type injection molding machine manufactured by Sumitomo Heavy Industries, Ltd., and the spiral flow was evaluated. At that time, the nozzle temperature is 230 ℃, mold temperature is 45 ℃, injection pressure is 750
kgf · cm ^-2 .

The various test results are shown in Table 1. In Example 1, the larger the value of the spiral flow is, the better the flowability is, and therefore, the injection molding is easy, and it is particularly suitable for molding a joint. Example 1 has good extrusion moldability, creep life, fatigue strength, and spiral flow.

Example 2: Polymerization was carried out in the same manner as in Example 1 except that the molecular weight, density and formation ratio of the front and rear stages were changed. Table 1 shows the results. The physical property tests were performed in the same manner as in Example 1, and the results are shown in Table 1. The extrudability, creep life, fatigue strength, and spiral flow are all good.

Example 3 Using the same catalyst as in Example 1, a high molecular weight component and a low molecular weight component were separately polymerized and blended. At this time, the following operation was performed to homogenize the blend. That is, first, 60% of high molecular weight component and 40% of low molecular weight component are blended, and 37mm
The pellets were pelletized using a meshing twin screw extruder (L / D = 32) in the same direction of φ to obtain a primary blend. Next, this primary blend was melt-kneaded with the same extruder, and at this time, only a low molecular weight component was side-bed from another feed port and a low molecular weight component was added to obtain a secondary blend. The feed rate ratio at this time was 70.7 for the primary blended product and 29.3 for the low molecular weight component.
And Further, using the same extruder again for the secondary blend, the low molecular weight component was side-fed at exactly the same speed ratio and additionally blended to obtain a final blend. As a result, the blending ratio of the high molecular weight component and the low molecular weight component in the final blend was 30/70% by weight. The physical properties of the final blend were tested in the same manner as in Example 1, and are shown in Table 1. The extrudability, creep life, fatigue strength, and spiral flow are all good.

Comparative Example 1 Multistage polymerization was performed in the same manner as in Example 1 except that the molecular weight, density, and generation ratio of the front and rear stages were changed. Table 2 shows the results. The physical property tests were performed in the same manner as in Example 1, and the results are shown in Table 2. η ₀ and τ ₀ are low and creep life and fatigue strength are inferior.

Comparative Example 2 Multistage polymerization was performed in the same manner as in Example 1 except that the molecular weight, density, and generation ratio of the front and rear stages were changed. Table 2 shows the results. The physical property tests were performed in the same manner as in Example 1, and the results are shown in Table 2. MFR _21.6 , low τ ₀ , poor creep life, fatigue strength, injection moldability and slightly poor extrusion moldability.

Comparative Example 3 Multistage polymerization was performed in the same manner as in Example 1 except that the molecular weight, density, and generation ratio of the front and rear stages were changed. Table 2 shows the results. These physical properties were also tested in the same manner as in Example 1, and the results are shown in Table 2. Low MFR _21.6 , creep life,
Poor fatigue strength, injection moldability and extrusion moldability.

Comparative Example 4 In the same manner as in Example 1, a multistage polymerization was carried out by changing the comonomer / molecular weight, density, and generation ratio of the front and rear stages. Table 2 shows the results. The physical property tests were performed in the same manner as in Example 1, and the results are shown in Table 2. MFR _21.6 , τ ₀
, Creep life, fatigue strength, and extrudability are somewhat poor.

Comparative Examples 5 and 6 The same measurement as in Example 1 was performed using a commercially available pipe resin. Table 2 shows the results. Comparative Example 5 has an MFR of _21.6 ,
η ₀ and τ ₀ are low, and fatigue strength, injection moldability, and extrusion moldability are inferior. Comparative Example 6 has low τ ₀ / η ₀ , inferior creep life, and fatigue strength.

In the data in the table, MFR is an actually measured value. The other data are charts of measured values of the frequency and the dynamic melt viscosity, approximated to the equation [1] by the least squares method, and calculated values obtained from the obtained calculation results. Note that “e-04” in the table is × 10
^It means ^-4 .

From these results, the polyethylene resin of the present invention can be used for water pipes and gas pipes having a longer life than polyethylene resins conventionally used for pipes. Because it can be a joint, it is possible to manufacture a pipe body and a joint to be combined with it using polyethylene resin having the same characteristics, and it is possible to further extend the workability of adding and the life of the entire pipe that is added and buried. Become.

Claims (4)

(57) [Claims] 1. A melt flow rate measured at a density of 0.915 to 0.955 g · cm ^-3 and a load of 2.16 kgf at 190 ° C. of 0.2
0 dgmin- ¹ or less, the melt flow rate measured using a load of 21.6 kgf at 190 ° C. is 17.0 to 70.0 dgmin
^-1 , using a parallel plate at a rheometer 190 ° C, using a parallel plate with a plate gap of 1.5 mm and a strain of 10 to 15%, and 100 to 0.01 ra.
The zero-shear viscosity (η ₀ ) when the dynamic melt viscosity (η ^* : unit Pa · s) obtained when measured in the frequency (ω) range to d · s ⁻¹ is sufficiently approximated by the formula [1]. ) Is 200,000-2,000,000
Pa · s, the specific time constant (τ ₀ ) is 50 to 500 sec, and (τ
₀ / η ₀ ) is 1.0 × 10 ^{−4 to} 4.0 × 10 ⁻⁴ Pa ^−1, which is excellent in moldability and long-term physical properties and is suitable for pipes and pipe joints. 2. A pipe formed by extrusion-molding the polyethylene resin according to claim 1. 3. A joint for a pipe, wherein the polyethylene resin according to claim 1 is formed by injection molding. 4. A combination product of a pipe formed by extrusion molding according to claim 2 and a pipe joint formed by injection molding according to claim 3.