JPH0673244A - Ethylene copolymer composition - Google Patents

Abstract

PURPOSE:To provide an ethylene copolymer compsn. giving a thick-walled pipe which rarely has linear wrinkles irregularly occurring on the inside wall surface even when produced by the outside-diameter-sizing molding method. CONSTITUTION:This copolymer compsn. is prepd. by compounding 0.02-1wt.% phosphite and/or phosphonite into a linear ethylene/alpha-olefin copolymer which is obtd. with a chromium oxide-base Phillips catalyst and has an MFR of 0.5-2g/10min and a melt tension at 190 deg.C of 3g or higher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ethylene copolymer composition excellent in smoothness of a pipe, which is particularly suitable as a molding material for a thick pipe by an outer diameter sizing molding method.

[0002]

2. Description of the Related Art Conventionally, in the method of molding a polyethylene pipe, the outer diameter is more important than the inner diameter in the pipe dimension control in the construction of the joint connection. Therefore, the outer diameter sizing molding method is used. In general, from the viewpoint of extrusion moldability, general-purpose high-density polyethylene for extrusion molding and low-density polyethylene having a relatively wide molecular weight distribution are used. Since polyethylene pipes have excellent long-term performance and chemical resistance, are inexpensive, and are easy to process, they have been used mainly for water supply and drainage pipes for a long time due to their characteristics. In particular, low-density ethylene / α-olefin copolymer (linear low-density polyethylene) has excellent characteristics such as flexibility and chlorine water resistance.
In recent years, 62 type 1 pipes (soft pipes) have been used.
Further, in the case of a pipe molded by the outer diameter sizing molding method, the resin is extruded from the extruder die in the molten state and then guided to the external cooling sizing device, so that the shape retention in the molten state, that is, the draw It is required to have excellent down property, and an ethylene homopolymer having a relatively wide molecular weight distribution or ethylene / α-
Olefin copolymers and the like have been used.

[0003]

However, it is attempted to form a thick pipe by the outer diameter sizing molding method using the linear ethylene polymer having a relatively wide molecular weight distribution and good extrudability as described above. Then, it was found that random streaky wrinkles are generated on the inner surface (inner wall) of the pipe, which impairs the commercial value in appearance and at the same time increases the flow resistance in the pipe, which is a serious problem in practical use. Although the detailed mechanism of the occurrence of such wrinkles is unclear, the flow state of the molten resin becomes unstable (a kind of pulsation), the sizing die narrows the outer diameter of the molten resin, and the pipe As the product becomes thicker, it cools from the outer surface first,
As a result, it is considered that the cause is that the inner surface is contracted toward the outer surface. On the other hand, wrinkling does not occur if molding is performed using a resin with a relatively narrow molecular weight distribution, but drawdown is deteriorated due to insufficient melt tension of the resin, and as a result, the molten resin sags and molding becomes difficult. It is known that a skin roughening phenomenon (commonly referred to as sharkskin) occurs on the inner and outer surfaces of a pipe particularly under conditions of low temperature and high speed extrusion molding, and this is also a serious problem.

[0004]

[Means for Solving the Problems]

[Summary of the Invention] In order to solve the above-mentioned problems, the present inventors have earnestly studied to prevent wrinkles on the inner surface of a thick-walled pipe by an outer diameter sizing molding method, and as a result, a specific ethylene-based The present invention has been completed by finding that a pipe in which a drawdown property is excellent and wrinkle does not occur is formed by using a composition in which a resin is mixed with a specific additive. That is, the ethylene copolymer composition of the present invention is obtained by using a chromium oxide-based Phillips type catalyst, MF
0.02 to 1% by weight of phosphite and / or phosphonite in a linear ethylene / α-olefin copolymer having an R of 0.05 to 2 g / 10 minutes and a melt tension at 190 ° C. of 3 g or more. It is characterized by being mixed.

DETAILED DESCRIPTION OF THE INVENTION [I] Constituent Component (1) Ethylene Copolymer The ethylene copolymer used in the ethylene copolymer composition of the present invention uses a chromium oxide-based Phillips type ionic polymerization catalyst. It is a linear polymer produced by, and can be applied by any production method such as a gas phase method, a solution method, a slurry method, a high pressure method, etc., and one or more of ethylene as a main component and a comonomer other than ethylene. It is a copolymer obtained by copolymerizing.

Other than chromium oxide type Phillips type catalyst,
For example, a linear ethylene copolymer produced using a Ziegler type catalyst containing titanium and organoaluminum as a main component has a narrower molecular weight distribution than that produced using the Phillips type catalyst. Therefore, in order to broaden the molecular weight distribution, a method of producing a high molecular weight component and a low molecular weight component under different conditions, that is, a batch polymerization method or a continuous multi-tank polymerization method with two or more tanks can be adopted. However, in both cases, the equipment is complicated and the productivity is inferior as compared with the method of continuously producing in one polymerization tank using the Phillips type catalyst, which is not preferable.

The ethylene copolymer used in the present invention has an MFR (JIS-K6760, load 2.
16 kg) of 0.05 to 2 g / 10 minutes can be applied, and 0.1 to 1 g / 10 minutes is particularly preferable. Among these, the polymer with the lower MFR has a drawdown property,
It is excellent in strength, etc., but is too low, for example, MFR is 0.
If it is less than 05, the moldability such as fluidity at the time of molding becomes poor. If the MFR exceeds 2, drawdown property and strength are poor. The melt tension of this ethylene copolymer is
A cylinder extrusion rod is extruded at a speed of 10 mm / min from a furnace and a nozzle used in the MFR measurement method of JIS-K6760 at a temperature of 190 ° C., and a melt tension when pulled at a speed of 4 m / min is 3 g or more. Those having a weight of 4 g or more are preferable, and those having a weight of 4 g or more are particularly preferable from the viewpoint of drawdown property.

Such an ethylene copolymer has chromium oxide supported on an inorganic carrier such as silica or alumina,
That is, using a chromium oxide type Phillips catalyst, a gas phase method, a solution method, a slurry method, or a pressure of 500 kg / c.
It can be obtained by applying a production process such as a high-pressure ionic polymerization method under the conditions of m ² or more and a temperature of 100 to 350 ° C. to copolymerize ethylene as a main component with α-olefin.
When the α-olefin is copolymerized with ethylene, the α-olefin having about 3 to 12 carbon atoms, for example, propylene, butene-1, pentene-1, hexene-1, 4,
-Methylpentene-1, octene-1 and the like.
Particularly preferred α-olefins have 4 to 8 carbon atoms,
Especially butene-1, hexene-1,4-methylpentene-
1 and octene-1. Two or more kinds of these α-olefins can be used in combination. The content of α-olefin in the copolymer is 0.5 to 20% by weight, preferably 1 to 1
It is 5% by weight.

Above all, the density of the ethylene copolymer (JIS
-According to the test method of K6760) is 0.915 to 0.93
0 g / cm ³ , especially 0.920 to 0.925 g / cm ³
Those having a pressure resistance and long winding are preferable. The density of these copolymers varies depending on the type and / or content of the copolymerized α-olefin. This copolymer is
FR, which is a guide for the molecular weight distribution (M at a load of 10 kg,
The ratio of FR and MFR at a load of 2.16 kg) is 13 to 2
5 and particularly 14 to 20 are preferable. A polymer having a lower FR has excellent impact strength and the like, but the moldability such as fluidity during molding tends to be lowered. Further, the higher the FR, the lower the impact strength and the like. Such an ethylene polymer can be appropriately selected and used from commercially available products.

(B) Phosphite and Phosphonite In the ethylene copolymer composition of the present invention, the compounding agent which is mixed with the ethylene copolymer to form a resin composition is phosphite or phosphonite. These can be used in combination. Specific examples of the phosphite include tris (2,4-di-t-butylphenyl) phosphite, bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol-di-phosphite, Bis (2,4-di-t-butylphenyl) pentaerythritol-di-phosphite, di-stearyl-pentaerythritol-di-phosphite and the like can be mentioned, but when used as a water pipe, hydrolysis Therefore, it is particularly preferable to use tris (2,4-di-t-butylphenyl) phosphite, which is difficult to hydrolyze, since it deteriorates the chlorine resistance of the pipe. Examples of the phosphonite include tetrakis (2,4-di-t-butylphenyl) -4,4 '.
-Biphenylene-di-phosphonite can be mentioned. The blending amount of these phosphite and / or phosphonite is 0.02 with respect to the ethylene copolymer.
~ 1% by weight. Preferably 0.03 to 0.5% by weight
Is. If it is less than this amount, the effect of preventing wrinkles is small,
On the other hand, if the amount is larger than this amount, the effect will be saturated and the cost of the product will increase, and when used as a water pipe, problems such as outflow to tap water due to bleed and chlorine resistance will occur. Is not preferable.

(2) Preparation of composition As a method for preparing a composition by blending the above-mentioned constituents, a method of melt kneading with a kneader such as a direct roll, a Banbury machine, a kneader, an extruder, or a dispersion of a compounding agent is carried out. In order to improve the method, it is mixed with the ethylene copolymer powder in advance with a Henschel type mixer or the like, and then melt-kneaded with the above-mentioned kneader, or an unblended ethylene copolymer after once producing a high-concentration masterbatch. Various known methods such as a method of diluting with can be applied. Further, if necessary, polypropylene, branched polyethylene (high-pressure radical polymerized polyethylene), within a range that does not significantly impair the effects of the present invention,
Other miscible resins such as ethylene / vinyl acetate copolymer, or other antioxidants, neutralizing agents, lubricants, antiblocking agents, antistatic agents, ultraviolet absorbers, light stabilizers,
Additives such as optical brighteners, or colorants such as organic pigments and inorganic pigments and fillers may be added directly or in the form of a masterbatch of resin or the like. However, addition of these may reduce the wrinkle prevention effect, so care must be taken regarding the type and amount of addition.

As a method for molding a pipe using the above-mentioned composition of the present invention, an outer diameter sizing molding method which is versatile and characterized in outer diameter dimension control is suitable. It is not limited to etc. However, the main object of the present invention is that even if the wall thickness is large, the smoothness of the inner surface of the pipe is not impaired. Since a resin composition improved to achieve this is used, the wall thickness of the pipe is preferably 3 mm or more, Is 4 mm or more, and particularly preferably 6 mm or more has a great effect. Further, this pipe does not necessarily have to be circular, and includes pipes classified into irregular-shaped extrusion molding such as rectangular. The wall thickness in this case means the minimum wall thickness portion. Further, as long as the effects of the present invention are exhibited, it is possible to form a multilayer pipe.

[0013]

EXAMPLES Examples 1 to 7 and Comparative Example 1 (a) Preparation of resin composition In the vapor phase process, commonly known as Phillips type ionic polymerization in which chromium oxide and titanium oxide are supported on silicon dioxide in the presence of a trace amount of oxygen. Copolymerization of ethylene and butene-1 using a catalyst, MFR 0.5g / 10min, density 0.922g /
A linear ethylene / butene-1 copolymer having a cm ³ of FR16 was obtained. Commercially available phosphite, phosphonite, and zinc stearate were added to the copolymer in the amounts shown in Table 1, then mixed in a Henschel mixer, and melt-kneaded in a single-screw extruder with a screw diameter of 40 mm to prepare a resin. A pellet of the composition was obtained.

(B) Pipe molding The resin composition pellet obtained in the above (a) was used to obtain an outer diameter of 30 mm,
Vacuum sizing machine using a single screw extruder with a screw diameter of 40 mm and a straight die with an inner diameter of 20 mm to extrude at a resin temperature of 190 ° C. to an outer diameter of 27 mm, an inner diameter of 15 mm and a wall thickness of 6 mm. The outer surface of the pipe was cooled in a water tank while controlling the outer diameter with a single-layer pipe. The degree of wrinkling on the inner surface of the pipe obtained by such molding was visually observed and judged. The results are shown in Table 1. The abbreviations of additives in Table 1 have the following meanings. IR168: Ciba-Geigy tris (2,4-di-
t-Butylphenyl) phosphite PEP36: bis (2,6-di-, manufactured by ADEKA ARGUS CORPORATION
t-Butyl-4-methylphenyl) pentaerythritol-di-phosphite P-EPQ: Tetrakis (2,4-di-t) manufactured by Sand Co.
-Butylphenyl) -4,4'-biphenylene-di-phosphonite UX624: BorgWarner bis (2,4-di-)
t-butylphenyl) pentaerythritol-di-phosphite W618: BorgWarner di-stearyl-pentaerythritol-di-phosphite

Examples 8 to 13 Evaluations were made in the same manner as in Example 4 except that the ethylene polymer shown in Table 2 was used. The results are shown in Table 2.

Comparative Examples 2 to 5 The ethylene polymers were replaced with those shown in Table 3 and the phosphites shown in Table 3 were used. The results are shown in Table 3.

[0017]

[Table 1]

[0018]

[Table 2]

[0019]

[Table 3]

[0020]

EFFECTS OF THE INVENTION According to the ethylene copolymer resin composition of the present invention, when a specific additive is added to a specific ethylene copolymer, wrinkles are formed on the inner surface of the pipe in the above-mentioned prior art. Is solved. Furthermore, it was totally unexpected that the use of a specific phosphorus compound that has been conventionally used as a secondary antioxidant has excellent drawdown properties and solves the problem of wrinkling on the inner surface of the pipe. . Therefore, the ethylene copolymer resin composition of the present invention can be utilized as a highly practical molding material in the field where thick-walled pipes are required.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location B29L 23:22 4F (72) Inventor Kiyo Maru Suto 1 Toho-cho, Yokkaichi-shi, Mie Mitsubishi Petrochemical Incorporated company Yokkaichi Research Institute

Claims (4)

[Claims] 1. A MFR obtained by a chromium oxide type Phillips type catalyst is 0.05 to 2 g / 10 minutes, and 19
Ethylene copolymer, characterized by comprising 0.02 to 1% by weight of phosphite and / or phosphonite in a linear ethylene / α-olefin copolymer having a melt tension of 3 g or more at 0 ° C. Polymer composition. 2. The ethylene copolymer composition according to claim 1, wherein the linear ethylene / α-olefin copolymer is a copolymer having a density of 0.915 to 0.930 g / cm ³ . 3. A linear ethylene / α-olefin copolymer has a FR (MFR at a load of 10 kg and a load of 2.16 kg).
Ethylene copolymer composition according to claim 1 or 2, which is a copolymer having a ratio of MFR to MFR of 13 to 25. 4. Phosphite and / or phosphonite are tris (2,4-di-t-butylphenyl) phosphite, bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol. -Di-phosphite, bis (2,4-di-t-butylphenyl) pentaerythritol-di-phosphite, di-stearyl-
The compound is at least one compound selected from the group consisting of pentaerythritol-di-phosphite and tetrakis (2,4-di-t-butylphenyl) -4,4'-biphenylene-di-phosphonite. The ethylene copolymer composition according to any one of 1 to 3.