JP2022142725A - polyethylene resin composition - Google Patents

Abstract

To provide a polyethylene resin composition which has both high melt flowability to facilitate molding treatment, and high abrasion resistance to have abrasion resistance against abrasive wear in a well-balanced manner, and is usable for manufacturing an extrusion molding excellent in surface smoothness.SOLUTION: A polyethylene resin composition contains 5-40 pts.mass of ultrahigh molecular weight polyethylene (A) satisfying (a-1), and 95-60 pts.mass of low molecular weight or high molecular weight polyethylene (B) satisfying (b-1) and (b-2) (the total of (A) and (B) is 100 pts.mass), has intrinsic viscosity [η] in a decalin solvent at 135°C of 2.0-15 dl/g, and forms a uniform phase. (a-1) Intrinsic viscosity [η] measured in a decalin solvent at 135°C of 8-50 dl/g; (b-1) intrinsic viscosity [η] measured in a decalin solvent at 135°C of 0.1-5 dl/g; and (b-2) density of 950-985 kg/m3.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to a polyethylene resin composition, a molded article using the composition, and a method for producing the composition.

Compared to general-purpose resins such as general polyethylene, ultrahigh-molecular-weight polyethylene has weaker intermolecular cohesion, a more symmetrical molecular structure, and a higher degree of crystallinity. It is also excellent in terms of durability, abrasion resistance, tensile strength, etc., and can be suitably used as a sliding material. However, since ultra-high molecular weight polyethylene has a high molecular weight, it is difficult to produce a molded article, and it is often difficult to directly use the methods employed for molding general-purpose polyethylene.

Therefore, as a method of improving the moldability of ultra high molecular weight polyethylene without impairing the excellent properties of ultra high molecular weight polyethylene, various methods such as blending ultra high molecular weight polyethylene and polyethylene with low intrinsic viscosity [η] are available. is proposed.

For example, in Patent Document 1, 15 to 40% by weight of an ultra-high molecular weight polyolefin having an intrinsic viscosity [η] of 10 to 40 dl/g and a low to high molecular weight polyolefin having an intrinsic viscosity [η] of 0.1 to 5 dl/g An injection molding polyolefin composition comprising 85-60% by weight polyolefin is disclosed. Although this composition contains ultra-high molecular weight polyolefin, it has the advantage that it can be injection-molded. It is excellent in that it has wear resistance.

In Patent Document 2, ultra-high molecular weight polyethylene with an intrinsic viscosity [η] of 10 to 40 dl / g exceeding 35% by weight and 90% by weight or less, and a low molecular weight with an intrinsic viscosity [η] of 0.1 to 5 dl / g A composition obtained by blending a polyethylene resin composition containing 10% by weight or more and less than 65% by weight of high molecular weight polyethylene with a specific polyolefin resin composition is disclosed. This composition gives a molded article with a good balance of wear resistance, appearance and moldability.

Further, in Patent Document 3, 5 to 18% by weight of ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of 10 to 40 dl / g and a low to high molecular weight polyethylene having an intrinsic viscosity [η] of 0.1 to 5 dl / g A polyethylene resin composition is disclosed comprising 82-95% by weight of polyethylene and having a density of 955-970 kg/m ³ .

Furthermore, in Patent Document 4, 5 to 25% by mass of ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of 10 to 40 dl / g and a low to high molecular weight polyethylene having an intrinsic viscosity [η] of 0.1 to 5 dl / g A composition is disclosed in which 0.1 to 10 parts by mass of a polyorganosiloxane having an intrinsic viscosity [η] of 0.1 to 10 dl/g is blended with 100 parts by mass of a polyethylene resin containing 75 to 95% by mass of polyethylene. .

JP-A-63-12606 WO 2003/022920 JP 2012-25904 A JP 2016-204405 A

Although the compositions disclosed in Patent Documents 1 to 4 are all excellent in moldability and abrasion resistance, polyethylene resins having even higher abrasion resistance than these compositions have been desired in recent years. In particular, there is a demand for a resin that exhibits wear resistance even in a form of wear called abrasive wear, in which the sliding surface is scraped by hard particles or projections. However, when the wear resistance of a polyethylene resin composition is improved, the melt fluidity tends to be lost and the moldability tends to deteriorate. Not done.
Furthermore, there is an increasing demand for the appearance of moldings obtained from the composition, and in particular, it is also required to improve the smoothness of the surface of moldings obtained by extrusion molding.

The present invention has a high degree of melt fluidity that facilitates molding processing and a high degree of wear resistance that has wear resistance against abrasive wear in a well-balanced manner, and further has excellent surface smoothness. An object of the present invention is to provide a polyethylene resin composition that can be used to produce extrudates.

As a result of the research conducted by the present inventors, it was found that the above problems can be solved by the following configuration example. A configuration example of the present invention is as follows.
In this specification, "A to B" indicating a numerical range indicates A or more and B or less.

[1] 5 to 40 parts by mass of ultra-high molecular weight polyethylene (A) that satisfies the following requirements (a-1) and low or high molecular weight polyethylene (B) that satisfies the following requirements (b-1) and (b-2): 95 to 60 parts by mass (the total amount of polyethylene (A) and polyethylene (B) is 100 parts by mass), and
A polyethylene resin composition having a limiting viscosity [η] of 2.0 to 15 dl/g as measured in a decalin solvent at 135°C and forming a homogeneous phase:
(a-1) the intrinsic viscosity [η] measured in decalin solvent at 135° C. is 8 to 50 dl/g;
(b-1) the intrinsic viscosity [η] measured in decalin solvent at 135° C. is 0.1 to 5 dl/g;
(b-2) It has a density of 950 to 985 kg/m ³ .

[2] The polyethylene resin composition according to [1], wherein the homogeneous phase is a phase in which domains of 1 µm or more are not observed when a thin section of the resin composition is observed with an optical microscope at a magnification of 400.

[3] A molded article of the polyethylene resin composition according to [1] or [2].

[4] Producing a low to high molecular weight polyethylene (B) having an intrinsic viscosity [η] of 0.1 to 5 dl/g and a density of 950 to 985 kg/m ³ measured in decalin solvent at 135°C. The first step of causing
After the first step, a second step of producing an ultra-high molecular weight polyethylene (A) having an intrinsic viscosity [η] measured in a decalin solvent at 135°C in the range of 8 to 50 dl/g,
By a multi-stage polymerization method including at least two steps of
A method for producing a polyethylene resin composition, wherein the intrinsic viscosity [η] measured in a decalin solvent at 135° C. is in the range of 2.0 to 15 dl/g and the polyethylene resin composition forms a homogeneous phase. .

According to the present invention, a high degree of melt fluidity that facilitates molding processing and a high degree of wear resistance that has wear resistance against abrasive wear are combined in a well-balanced manner, and the surface smoothness is improved. A polyethylene resin composition that can be used to produce excellent extrudates can be provided.

1 is an example of an optical micrograph of the polyethylene resin composition obtained in Example 1. FIG. 2 is an example of an optical micrograph of the polyethylene resin composition obtained in Example 2. FIG. 4 is an example of an optical micrograph of the polyethylene resin composition obtained in Example 3. FIG. 1 is an example of an optical micrograph of a polyethylene resin composition obtained in Comparative Example 1. FIG. It is a figure which shows the example of the relationship between the wear amount in a Taber abrasion test, and MFR of a polyethylene resin composition.

<<Polyethylene resin composition>>
The polyethylene resin composition (hereinafter also referred to as "the present composition") according to the present invention comprises a specific ultra-high molecular weight polyethylene (A) and a specific low or high molecular weight polyethylene (B) (hereinafter "polyethylene (B)"). (also referred to as)) and satisfies the following requirements (X) and (Y).

Requirement (X): The limiting viscosity [η] of the present composition measured in decalin solvent at 135° C. is in the range of 2.0 to 15 dl/g, preferably in the range of 2.5 to 10 dl/g, more It is preferably in the range of 3.0 to 8.0 dl/g, more preferably in the range of 3.5 to 7.0 dl/g.
When the intrinsic viscosity [η] of the present composition in a decalin solvent at 135°C satisfies the above range, the present composition has a high melt fluidity that facilitates molding and resistance to abrasive wear. Since it has high abrasion resistance to the extent that it has abrasion resistance, it is possible to achieve both abrasion resistance and moldability.
If the intrinsic viscosity [η] in decalin solvent at 135° C. is less than 2.0 dl/g, the abrasion resistance of the composition is impaired. On the other hand, if the intrinsic viscosity [η] in a decalin solvent at 135° C. exceeds 15 dl/g, the flowability of the composition is lowered, resulting in impaired moldability.

Requirement (Y): The polyethylene resin composition forms a homogeneous phase.
In the present composition, the ultra-high molecular weight polyethylene (A) and polyethylene (B) are compatible with each other to form a uniform phase, and phase separation occurs between the ultra-high molecular weight polyethylene (A) and polyethylene (B). do not have.

Whether or not the present composition has a homogeneous phase is determined by the size of the island phase (domain) observed when a thin section prepared by cutting the present composition with a microtome is observed with an optical microscope, as follows. to judge. Observation conditions with an optical microscope are as described in Examples described later.
Homogeneous phase: The composition does not contain domains of 1 µm or more Phase separation: The composition contains domains of 1 µm or more, that is, the present composition does not form a sea-island structure containing domains of 1 µm or more.

When the ultra-high molecular weight polyethylene (A) and polyethylene (B) are compatible to form a uniform phase, the wear resistance is excellent and the surface smoothness of the molded article obtained by extrusion molding is good. Therefore, it is preferable. The reason why the present composition has excellent abrasion resistance is that the ultrahigh molecular weight polyethylene (A) and polyethylene (B) are compatible with each other so well that they form a uniform phase, and the abrasion resistance derived from the ultrahigh molecular weight polyethylene (A). It is because the nature is exhibited. The reason why the present composition has excellent surface smoothness is that the present composition does not contain domains of 1 μm or more, so that the surface of the molded article does not become rough due to the domains.

In addition, when ultra-high molecular weight polyethylene (A) and polyethylene (B) are phase-separated, the ultra-high molecular weight polyethylene (A) is a domain (island phase), and the polyethylene (B) is a matrix (sea phase). A structure is formed. In this case, since the wear resistance derived from the ultra-high molecular weight polyethylene (A) is not exerted in the entire composition, the polyethylene (B) portion is worn, and then the domain located on the worn surface is dropped off, thereby progressing wear. Therefore, the abrasion resistance of the composition is impaired. Furthermore, when the composition is extrusion-molded, the domains formed of the ultra-high molecular weight polyethylene (A) are located near the surface of the molded article, causing roughness and impairing the surface smoothness of the molded article.

The content of ultra-high molecular weight polyethylene (A) in the present composition is 5 to 40 parts by mass, preferably 8 to 30 parts by mass, more preferably 10 to 25 parts by mass, and still more preferably 12 to 20 parts by mass. (However, the total amount of ultra-high molecular weight polyethylene (A) and polyethylene (B) shall be 100 parts by mass).
The content of polyethylene (B) in the present composition is 60 to 95 parts by mass, preferably 70 to 92 parts by mass, more preferably 75 to 90 parts by mass, and still more preferably 80 to 88 parts by mass (however, , the total amount of ultra-high molecular weight polyethylene (A) and polyethylene (B) being 100 parts by mass).
When the contents of ultra-high molecular weight polyethylene (A) and polyethylene (B) are within the above range, the composition has good moldability and abrasion resistance.

If the content of the ultra-high molecular weight polyethylene (A) in the composition exceeds 40 parts by mass and the content of the polyethylene (B) is less than 60 parts by mass, the melt fluidity of the composition will be low. Poor moldability. On the other hand, when the content of the ultra-high molecular weight polyethylene (A) is less than 5 parts by mass and the content of the polyethylene (B) exceeds 95 parts by mass, the abrasion resistance derived from the ultra-high molecular weight polyethylene (A) is insufficient. Therefore, the wear resistance of the resulting composition is poor.

The present composition has a melt flow rate (hereinafter also referred to as "MFR") measured at 190° C. under a load of 10 kg according to the measurement method of ASTM D-1238E, preferably 0.01 to 500 g/10 minutes. Yes, more preferably 0.1 to 100 g/10 minutes, still more preferably 1.0 to 50 g/10 minutes. When the MFR of the composition is within the above range, the moldability is good, which is preferable.

<Ultra-high molecular weight polyethylene (A)>
The ultra-high molecular weight polyethylene (A) blended in the present composition has an intrinsic viscosity [η] measured in decalin solvent at 135°C of 8 to 50 dl/g, preferably 8 to 45 dl/g, more preferably 10 to 45 dl/g, more preferably 15 to 45 dl/g, particularly preferably 18 to 42 dl/g. When the intrinsic viscosity [η] of the ultra-high molecular weight polyethylene (A) is within the above range, the composition can achieve both wear resistance and moldability, which is preferable.

When an ultra-high molecular weight polyethylene having a limiting viscosity [η] of less than 8 dl/g measured in a decalin solvent at 135°C is used instead of the ultra-high-molecular-weight polyethylene (A), the abrasion resistance of the composition deteriorates, It is not preferable because the wear resistance of the molded article obtained is inferior. On the other hand, when ultra-high molecular weight polyethylene (A) is replaced with ultra-high molecular weight polyethylene having an intrinsic viscosity [η] of more than 50 dl/g measured in a decalin solvent at 135°C, the melt fluidity of the composition is low. Therefore, the moldability of the composition is lowered, which is not preferable.

Ultra high molecular weight polyethylene (A) is an ethylene homopolymer, or ethylene and propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4-methyl-1 - is a copolymer with an α-olefin such as pentene or 3-methyl-1-pentene. The ultra-high molecular weight polyethylene (A) is preferably a homopolymer of ethylene or a copolymer of ethylene and the above α-olefin, which is composed mainly of ethylene, and more Ethylene homopolymers are preferred.

<Low-molecular-weight or high-molecular-weight polyethylene (B)>
The intrinsic viscosity [η] of polyethylene (B) measured in decalin solvent at 135° C. is 0.1 to 5 dl/g, preferably 0.5 to 2 dl/g, more preferably 0.7 to 1.5 dl/g, more preferably 0.8 to 1.2 dl/g. When the intrinsic viscosity [η] of polyethylene (B) measured in a decalin solvent at 135° C. is within the above range, a composition excellent in both abrasion resistance and moldability can be obtained.

When a low-molecular-weight or high-molecular-weight polyethylene having a limiting viscosity [η] of less than 0.1 dl/g measured in a decalin solvent at 135°C is used in place of polyethylene (B), the abrasion resistance of the composition deteriorates. is not preferable because the wear resistance of the resulting molded article is poor. On the other hand, when a low-molecular-weight or high-molecular-weight polyethylene having a limiting viscosity [η] of more than 5 dl/g measured in decalin solvent at 135°C is used instead of polyethylene (B), the melt fluidity of the composition becomes low. Therefore, the moldability of the composition is lowered, which is not preferable.

Polyethylene (B) has a density of 950 to 985 kg/m ³ , preferably 960 to 980 kg/m ³ , more preferably 960 to 975 kg/m ³ , still more preferably 965 to 975 kg/m ³ . be. When the density of polyethylene (B) is within the above range, a composition having both excellent abrasion resistance and moldability can be obtained.

When a low-molecular-weight or high-molecular-weight polyethylene having a density of less than 950 kg/m ³ is used instead of polyethylene (B), the low-molecular-weight or high-molecular-weight polyethylene has a low degree of crystallinity and tends to be scraped off. This is not preferable because the abrasion resistance of the composition deteriorates and the abrasion resistance of the resulting molded article is poor. Also, since the density of low-molecular-weight to high-molecular-weight polyethylene is usually 985 kg/m ³ or less, low-molecular-weight to high-molecular-weight polyethylene having a density of 985 kg/m ³ or less is used in the present composition.

Polyethylene (B) is a homopolymer of ethylene or a copolymer of ethylene and α-olefin. Ethylene homopolymers are preferred.
Examples of the α-olefins constituting the copolymer include linear or branched α-olefins having 3 to 20 carbon atoms, specifically propylene, 1-butene, 1-pentene, 3- methyl-1-butene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-pentene, 3,4-dimethyl-1-pentene, 4-methyl-1-hexene, 3-ethyl-1- Pentene, 3-ethyl-4-methyl-1-pentene, 3,4-dimethyl-1-hexene, 4-methyl-1-heptene, 3,4-dimethyl-1-heptene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, or 1-eicosene. Among these, propylene and 1-butene are preferably used in relation to the density range of polyethylene (B).

The copolymer of ethylene and α-olefin more preferably has an ethylene content of 90 mol % or more, more preferably 95 mol % or more. When polyethylene (B) is a copolymer of ethylene and α-olefin, the higher the ethylene content, the better.

<Other ingredients>
As long as the object of the present invention is not impaired, the composition may contain thermoplastic resins such as other polyolefin resins, resin additives (e.g., heat stabilizers, stabilizers such as weather stabilizers, cross-linking agents, etc.). , crosslinking aids, antistatic agents, slip agents, antiblocking agents, antifog agents, lubricants, dyes, pigments, fillers, mineral oil softeners, petroleum resins, waxes, etc.).
When the above other components are included, the total amount of the above other components in the present composition is usually 5% by mass or less, preferably 2% by mass or less, and more preferably 1% by mass or less. . In other words, the ratio of the sum of the mass of ultra-high molecular weight polyethylene (A) and the mass of polyethylene (B) in the composition to the mass of the composition is usually 95% by mass or more, preferably 98% by mass. % or more, more preferably 99 mass % or more.

<Method for producing polyethylene resin composition>
The present composition comprises at least two steps of producing polyethylene (B) as the first step and producing ultra-high molecular weight polyethylene (A) as the second step in the presence of a known olefin polymerization catalyst. It is manufactured by a multi-stage polymerization method including steps. The second step is performed in the presence of the polyethylene (B) produced in the first step.

It is speculated that when ultra-high molecular weight polyethylene (A) is produced in the presence of polyethylene (B), a granular polyethylene resin composition in which particles of ultra-high molecular weight polyethylene (A) are coated with polyethylene (B) is obtained. be. It is presumed that when the surfaces of the particles of the polyethylene resin composition are coated with polyethylene (B), when the polyethylene resin composition is molded into pellets or the like, a sea-island structure is unlikely to occur, and a uniform phase tends to occur.

On the other hand, even if the multi-stage polymerization method is used, the ultra-high molecular weight polyethylene (A) is produced prior to the polyethylene (B), and the polyethylene (B) is produced in the presence of the ultra-high molecular weight polyethylene (A). The composition does not form a homogeneous phase. This is because in the composition obtained when polyethylene (B) is produced in the presence of ultra-high molecular weight polyethylene (A), polyethylene (B) is coated with ultra-high molecular weight polyethylene (A), so polyethylene resin It is presumed that when the composition is formed into pellets or the like, it tends to form a sea-island structure and hardly forms a homogeneous phase.

As olefins such as ethylene used for polymerization in the production of the present composition, various olefins described in the items of ultrahigh molecular weight polyethylene (A) and polyethylene (B) can be used without limitation.

≪Molded body≫
The present composition can be prepared by a conventionally known method, specifically, for example, an extrusion method, a co-extrusion method, an injection molding method, a profile extrusion method, a pipe molding method, a tube molding method, a heterogeneous molding method, or a coating molding method. , injection blow molding method, direct blow molding method, T-die sheet or film molding method, inflation film molding method, press molding method, container, tray, sheet, rod, film or various molded products. It can be molded into a coating or the like.

The molded article obtained by the above molding method can be widely used for conventionally known polyethylene applications, and is particularly excellent in wear resistance. metal coatings, pressure resistant rubber hoses, automotive door gaskets, clean room door gaskets, automotive glass run channels, automotive weather strips and other rubber reels, various guide rails, elevator rail guides, and sliding materials such as protective liner materials. etc.

When a Taber abrasion test (test temperature 23° C., grinding wheel H22, load 1000 g, rotation speed 60 rpm, test rotation number 10800 times (3 hours)) was performed on the molded body obtained from the composition, the abrasion amount was Preferably it is 100 mg or less. The smaller the amount of wear, the better, but the lower limit is usually 0.1 mg or more. It is preferable that the amount of wear by the Taber abrasion test is within the above range, because the wear resistance of the molded article obtained from the present composition is sufficient under the usage environment. In addition, in the Taber abrasion test, since there are small projections on the surface of the grinding wheel (H22) used, the Taber abrasion test is a test related to abrasive abrasion.

The surface roughness (arithmetic mean roughness (Ra)) of a molded article obtained by extrusion molding the present composition is preferably 3.0 μm or less, more preferably 2.0 μm or less. The smaller the surface roughness, the better, but the lower limit is usually 0.1 μm or more. It is preferable that the surface roughness of the extruded product is within the above range, since the surface smoothness is sufficient.

EXAMPLES Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In some cases, the following polymerization was carried out multiple times in order to obtain the amount of polymer and composition required for evaluation.

[Measurement conditions, etc.]
Measurement conditions and the like for each physical property are as follows.

[Intrinsic viscosity [η]]
The intrinsic viscosities [η] of various polymers and resin compositions obtained in Examples and Comparative Examples were measured at 135° C. in a decalin solvent. In addition, below, the intrinsic viscosity of ultra high molecular weight polyethylene (A) may be described as "intrinsic viscosity [η]u". Similarly, the intrinsic viscosity of polyethylene (B) may be described as "intrinsic viscosity [η]h".

〔density〕
The density of polyethylene (B) was measured according to ASTM D1505.

[Phase structure]
Thin slices of the resin composition were prepared by cutting pellets of the resin composition obtained in Examples and Comparative Examples with a microtome. After that, the thin section was observed with an optical microscope at a magnification of 400 times, and it was judged whether the phase was uniform according to the following criteria.
Homogeneous Phase: No domains larger than 1 μm were observed in thin sections of the composition.
Phase separation: Domains of 1 μm or larger were observed in thin sections of the composition.

[MFR]
The MFR of the compositions obtained in Examples or Comparative Examples was measured under a load of 10 kg according to ASTM D1238E. The measurement temperature was 190°C.

[Abrasion amount of compact]
The compositions obtained in Examples or Comparative Examples were molded into square plates of 10 cm square and 2 mm thick, and the resulting molded bodies were weighed. A Taber abrasion test was performed on the obtained compact according to JIS K7204. The test conditions were as follows.
Polishing whetstone: H22
Load during test: 1000g
Rotation speed: 60rpm
Test rotation speed: 10800 times (3 hours)
Test temperature: 23°C
The molded body after the test was weighed again, and the difference in the mass of the molded body before and after the test was taken as the wear amount of the molded body by the Taber abrasion test.

[Surface roughness of compact]
A ram extrudate and/or a laminate coextruded with an ethylene/propylene/ethylidene norbornene copolymer (hereinafter also referred to as "EPDM") from the composition obtained in Examples or Comparative Examples by the method described later. manufactured. The arithmetic mean roughness (Ra) of the surface of the obtained molded article (the laminate is the side facing the polyethylene resin composition obtained in Examples or Comparative Examples) was determined by a method according to JIS B 0601. .

[Example 1]
[Preparation of solid titanium catalyst component [C1]]
A reactor was charged with 95.2 g of anhydrous magnesium chloride, 398.1 g of decane and 306 g of 2-ethylhexyl alcohol and heated at 140° C. for 6 hours. After cooling the solution in the reaction vessel to 50° C., 17.6 g of ethyl benzoate was added, and the mixture was stirred and mixed at 130° C. for 1 hour to obtain a uniform solution.
After the homogeneous solution thus obtained was cooled to room temperature, the entire amount of 50 ml of the homogeneous solution was added dropwise to 200 ml of titanium tetrachloride kept at 0° C. over 60 minutes with stirring to obtain a mixed solution. After the dropwise addition was completed, the resulting mixture was kept at 0°C for 1 hour, then the temperature of the mixture was raised to 20°C over 1 hour, and then to 80°C over 30 minutes. When the temperature of the mixed liquid reached 78°C, 2.35 g of ethyl benzoate was added to the mixed liquid, and the reaction was carried out for 2 hours while maintaining the temperature at 80°C. After completion of the reaction for 2 hours, the solid portion was collected by hot filtration, resuspended in 200 ml of titanium tetrachloride, and subjected to a heating reaction again at 90° C. for 2 hours. After completion of the heating reaction again, the solid portion was collected again by hot filtration, washed with decane at 90° C. and thoroughly washed with hexane at room temperature until no free titanium compound was detected in the washing liquid.

The solid titanium catalyst component prepared by the above procedure was stored as a decane slurry, and part of it was dried for the purpose of examining the catalyst composition. The composition of the solid titanium catalyst component [C1] after drying is 3.1% by mass of titanium, 18% by mass of magnesium, 60% by mass of chlorine, 15.4% by mass of ethyl benzoate, and 1.5% by mass of 2-ethylhexyl alcohol residue. % by mass.

[Production of polyethylene resin composition]
500 ml of purified decane at room temperature was charged into a 1-liter polymerization vessel that had been sufficiently purged with nitrogen, and 0.5 mmol of triisobutylaluminum and solid titanium catalyst component [C1] (titanium atom equivalent to 0.01 mmol) was added. Next, hydrogen is fed until the pressure in the polymerization vessel reaches 0.406 MPaG in gauge pressure, and then ethylene is fed until the pressure in the polymerization vessel reaches 0.66 MPaG in gauge pressure. A second stage of ethylene polymerization was carried out. When 119 liters of ethylene had been fed, the feed of ethylene was stopped, the temperature was rapidly cooled to 45° C., the pressure was released, and nitrogen purge was performed. In addition, polyethylene (B1) is obtained by performing the first-stage ethylene polymerization under the above conditions.
Subsequently, ethylene was fed into the polymerization vessel until the pressure inside the polymerization vessel reached 0.60 MPaG in gauge pressure, and the second-stage ethylene polymerization was carried out at a temperature of 53°C. When 21 liters of ethylene was fed, the feed of ethylene was stopped, the temperature was rapidly cooled to 40° C., pressure was released, and purging was performed. In addition, ultra high molecular weight polyethylene (A1) is obtained by carrying out the second-stage ethylene polymerization under the above conditions.
The slurry containing the resulting solids was filtered and dried under vacuum overnight at a temperature of 80°C. The resulting ethylene resin composition weighed 190 g and had a limiting viscosity [η] of 3.9 dl/g in decalin solvent at 135°C.

[Analysis of each component in the polyethylene resin composition]
- Content and physical properties of polyethylene (B1) Of the polymerizations carried out when the polyethylene resin composition was produced, only the first-stage polymerization was carried out separately under the same conditions as during the production of the polyethylene resin composition. The yield of the obtained ethylene polymer was 162 g. Since polyethylene (B1) was produced by this polymerization, the content of polyethylene (B1) in the polyethylene resin composition (yield: 190 g) was calculated to be 85% by mass. When the intrinsic viscosity [η] of the obtained polyethylene (B1) was measured in decalin solvent at 135° C., it was 1.0 dl/g. The density of the obtained polyethylene (B1) was 971 kg/m ³ .

・ Content and intrinsic viscosity [η] of ultra-high molecular weight polyethylene (A2)
By omitting the first-stage polymerization of the polymerization performed when manufacturing the polyethylene resin composition, and performing only the second-stage polymerization separately under the same conditions as when manufacturing the polyethylene resin composition, Ultra high molecular weight polyethylene (A2) was produced. The intrinsic viscosity [η] of the ultra-high molecular weight polyethylene (A2) was 30 dl/g.
Next, the molecular weight distribution of the ultra-high molecular weight polyethylene (A2) was measured by gel permeation chromatography (GPC), and compared with the measurement results of the molecular weight distribution of the polyethylene resin composition by GPC, the peak position of the chromatogram The shape was consistent with the high-molecular-weight component (ultra-high-molecular-weight polyethylene (A1)) contained in the polyethylene resin composition. Based on this result, the physical properties of ultra-high molecular weight polyethylene (A1) were considered to be the same as those of ultra-high molecular weight polyethylene (A2). That is, the intrinsic viscosity [η] of the ultra-high molecular weight polyethylene (A1) was set to 30 dl/g.

[Granulation of polyethylene resin composition]
Irganox 1010 (manufactured by BASF), Irgafos 168 (manufactured by BASF), and calcium stearate (manufactured by NOF Corporation) were dry blended with the obtained polyethylene resin composition. The blend amount of each substance was 0.1% by mass of Irganox 1010, 0.2% by mass of Irgafos 168, and 0.12% by mass of calcium stearate, assuming that the composition after dry blending was 100% by mass. . The dry-blended composition was melt-kneaded using a twin-screw extruder (manufactured by Technobel, φ=15 mm, L/D=30, cylinder temperature: 200° C.), and then granulated into pellets.

Using the obtained pellets, each physical property of the polyethylene resin composition was measured. Table 1 shows the results. An optical micrograph of a thin section obtained from the pellet is shown in FIG. From FIG. 1, it can be seen that the polyethylene resin composition forms a homogeneous phase.

[ram extrusion molding]
The furnace (inner diameter 10 mm) of a capillary rheometer (Capilograph 1D manufactured by Toyo Seiki Seisakusho) equipped with a slit die (1 mm × 6 mm) is heated to 230 ° C., and the polyethylene resin composition is extruded at a piston speed of 200 mm / min. The resulting polyethylene resin composition was cooled with water to obtain a molded article. After that, the arithmetic average roughness (Ra) was determined for the surface of the obtained compact. Table 1 shows the results.

[Co-extrusion molding]
An ethylene/propylene/ethylidene norbornene copolymer (EPDM) (Shore A hardness = 75, vulcanizing agent included) was formed into a sheet, and the obtained sheet was cut into square pellets with a sheet cutter. The obtained EPDM pellets were extruded at a temperature of 80° C. and a polyethylene resin composition was co-extruded on the surface thereof at 200° C. to obtain a co-extruded laminate. The thickness of the EPDM layer in the coextruded laminate was 1.0 mm, and the thickness of the polyethylene resin composition layer was 0.1 mm. After that, the coextruded laminate was heated to 230° C. and held for 5 minutes to vulcanize and crosslink the EPDM layer. After that, the arithmetic mean roughness (Ra) was determined for the surface of the coextrusion laminate on the side of the polyethylene resin composition layer. Table 1 shows the results.

[Example 2]
Polymerization, analysis, and granulation were performed in the same manner as in Example 1, except that the ethylene polymerization temperature was changed from 53° C. to 68° C. in the second-stage polymerization during the production of the polyethylene resin composition, and physical properties were measured. did Table 1 shows the analysis results and physical property measurement results. In addition, FIG. 2 shows an optical microscope photograph of a thin section obtained from the pellet. It can be seen from FIG. 2 that the polyethylene resin composition forms a homogeneous phase.

[Example 3]
[Preparation of solid titanium catalyst component [C2]]
75.0 g of anhydrous magnesium chloride, 280.3 g of decane and 308.3 g of 2-ethylhexyl alcohol were charged in a reaction vessel and heated at 130° C. for 3 hours. 9 g was added, and further stirred and mixed at 100° C. for 1 hour.
After the homogeneous solution thus obtained was cooled to room temperature, the entire amount of 30 ml of the homogeneous solution was added dropwise to 80 ml of titanium tetrachloride kept at 0° C. over 45 minutes with stirring to obtain a mixed solution. After the dropwise addition was complete, the resulting mixture was heated to 110° C. over 6 hours, 0.55 g of 2-isobutyl-2-isopropyl-1,3-dimethoxypropane was added, and the mixture was stirred at 110° C. over 2 hours. It was kept under stirring. After completion of the reaction for 2 hours, the solid portion was collected by hot filtration, washed with decane at 90° C. and thoroughly washed with hexane at room temperature until no free titanium compound was detected in the washing liquid.

The solid titanium catalyst component prepared by the above procedure was stored as a decane slurry, and part of it was dried for the purpose of examining the catalyst composition. The composition of the solid titanium catalyst component [C2] after drying is 2.8% by mass of titanium, 18.1% by mass of magnesium, 58.2% by mass of chlorine, and 2-isobutyl-2-isopropyl-1,3-dimethoxypropane. 19.6% by weight and 1.4% by weight of 2-ethylhexyl alcohol residues.

[Production of polyethylene resin composition]
500 ml of purified decane at room temperature was charged into a 1-liter polymerization vessel that had been sufficiently purged with nitrogen, and 0.5 mmol of triisobutylaluminum and solid titanium catalyst component [C2] (titanium atom equivalent to 0.01 mmol) was added. Next, hydrogen is fed until the pressure in the polymerization vessel reaches 0.24 MPaG in gauge pressure, and then ethylene is fed until the pressure in the polymerization vessel reaches 0.44 MPaG in gauge pressure. A second stage of ethylene polymerization was carried out. When 130 liters of ethylene was fed, the feed of ethylene was stopped, the temperature was rapidly cooled to 45° C., the pressure was released, and nitrogen purge was performed.
Next, 0.75 μmole of titanocene dichloride in terms of titanium atom was added to the polymerization vessel, ethylene was fed until the pressure in the polymerization vessel reached 0.66 MPaG in terms of gauge pressure, and the second-stage ethylene polymerization was carried out at a temperature of 70°C. did When 25 liters of ethylene was fed, the feed of ethylene was stopped, the temperature was rapidly cooled to 40° C., the pressure was released, and purging was performed.

Analysis, granulation, and measurement of physical properties of the obtained polyethylene resin composition were carried out in the same manner as in Example 1. Table 1 shows the analysis results and physical property measurement results. In addition, FIG. 3 shows an optical microscope photograph of a thin section obtained from the pellet. It can be seen from FIG. 3 that the polyethylene resin composition forms a homogeneous phase.
The composition of Example 3 was neither co-extruded with EPDM nor measured for arithmetic mean roughness (Ra).

[Comparative Example 1]
The composition was produced by exchanging the polymerization conditions of the first stage and the second stage of the examples. That is, the catalyst component input temperature was changed from 80° C. to 48° C., hydrogen was not fed in the first stage polymerization, the ethylene polymerization temperature was changed from 85° C. to 53° C., and the ethylene feed amount was changed from 119 liters to changed to 21 liters. In addition, in the second-stage polymerization, hydrogen was fed until the pressure in the polymerization vessel reached 0.40 MPaG in gauge pressure, the ethylene polymerization temperature was changed from 53°C to 85°C, and the ethylene feed amount was changed from 21 liters to Changed to 119 liters. Other conditions were the same as in the example. Next, analysis, granulation, and co-extrusion molding with EPDM were conducted in the same manner as in Examples, and each physical property was measured. Table 1 shows the analysis results and physical property measurement results. Also, FIG. 4 shows an optical micrograph of the obtained composition. It can be seen from FIG. 4 that the composition obtained in Comparative Example 1 has a sea-island structure.

[Comparative Example 2]
Comparative Example 1 except that the feed amount of ethylene in the first-stage polymerization was changed from 21 liters to 33.6 liters, and the feed amount of ethylene in the second-stage polymerization was changed from 119 liters to 106.4 liters. Polymerization was carried out in the same manner, followed by analysis, granulation, and measurement of physical properties. Table 1 shows the analysis results and physical property measurement results. For the composition of Comparative Example 2, the arithmetic mean roughness (Ra) of the molded body obtained by ram extrusion molding, co-extrusion molding with EPDM, and these molding treatments was not measured.

The polyethylene resin compositions obtained in Examples 1 to 3 have a high degree of melt fluidity that facilitates molding processing and a high degree of wear resistance that has wear resistance even against abrasive wear. Well put together. Furthermore, the polyethylene resin compositions of Examples 1 to 3 can be used to produce extrudates with excellent surface smoothness because the arithmetic mean roughness of the coextruded surfaces is relatively small. These results show that the polyethylene resin composition of the example contains ultrahigh molecular weight polyethylene (A) and polyethylene (B) in a predetermined ratio, has a predetermined intrinsic viscosity, and forms a homogeneous phase. It is thought that it depends.

FIG. 5 is a diagram showing an example of the relationship between the wear amount in the Taber abrasion test and the MFR of the polyethylene resin composition. In the composition of Comparative Example 1, the content of the ultra-high molecular weight component was reduced in order to improve the moldability, resulting in a decrease in abrasion resistance. In addition, with the composition of Comparative Example 1, the arithmetic mean roughness of the surface of the coextruded product was larger than that of Examples, and the surface smoothness was insufficient. The reason why the composition of Comparative Example 1 is inferior to the polyethylene resin compositions of Examples in abrasion resistance and surface smoothness is considered to be that the composition of Comparative Example 1 has a sea-island structure. In Comparative Example 2, the moldability was lowered by increasing the content of the ultrahigh molecular weight component in order to improve wear resistance.
On the other hand, the plots of Examples 1 to 3 show that the wear amount is smaller than that of Comparative Examples 1 and 2, and the melt fluidity is such that moldability is good. That is, the compositions of the examples have both high melt fluidity to facilitate molding and high abrasion resistance.

Claims (4)

5 to 40 parts by mass of ultra-high molecular weight polyethylene (A) that satisfies the following requirements (a-1), and 95 to 60 parts of low or high molecular weight polyethylene (B) that satisfies the following requirements (b-1) and (b-2): parts by mass (the total amount of polyethylene (A) and polyethylene (B) being 100 parts by mass),
A polyethylene resin composition having a limiting viscosity [η] of 2.0 to 15 dl/g as measured in a decalin solvent at 135°C and forming a homogeneous phase:
(a-1) the intrinsic viscosity [η] measured in decalin solvent at 135° C. is 8 to 50 dl/g;
(b-1) the intrinsic viscosity [η] measured in decalin solvent at 135° C. is 0.1 to 5 dl/g;
(b-2) It has a density of 950 to 985 kg/m ³ . 2. The polyethylene resin composition according to claim 1, wherein the homogeneous phase is a phase in which domains of 1 μm or more are not observed when a thin section of the resin composition is observed with an optical microscope at a magnification of 400. A molded article of the polyethylene resin composition according to claim 1 or 2. The first to produce a low to high molecular weight polyethylene (B) having an intrinsic viscosity [η] of 0.1 to 5 dl/g and a density of 950 to 985 kg/m ³ measured in decalin solvent at 135°C. process,
After the first step, a second step of producing an ultra-high molecular weight polyethylene (A) having an intrinsic viscosity [η] measured in a decalin solvent at 135°C in the range of 8 to 50 dl/g,
By a multi-stage polymerization method including at least two steps of
A method for producing a polyethylene resin composition, wherein the intrinsic viscosity [η] measured in a decalin solvent at 135° C. is in the range of 2.0 to 15 dl/g and the polyethylene resin composition forms a homogeneous phase. .

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