JPS60112842A - Ethylene polymer composition - Google Patents

Abstract

PURPOSE:To obtain titled composition of high impact strength and heat deterioration resistance suitable for rotational molding, by incorporating an ethylene polymer with specific dialkyl peroxide as crosslinking agent, tetraryl silicate as crosslinking promotor, and phenol-based antioxidant. CONSTITUTION:The objective composition can be obtained by incorporating (A) 100pts.wt. of an ethylene polymer with a density >=0.935g/cm<3> and melt flow rate 6-50g/10min with (B) either 0.1-3pts.wt. of (i) 2,5-dimethyl-2,5-di(t-butyl peroxy) hexyn-3 or 0.05-2pts.wt. of (ii) 1,3-bis(t-butyl peroxyisopropyl)benzene puls the component (i) with a weight ratio (i)/(ii) <=1.5 (pref. >=0.01pt.wt. of the component (ii)), (C) 0.1-5pts.wt. of tetraryl silicate as crosslinking promotor and (D) 0.01-1pt.wt. of phenol-based antioxidant (e.g. 4-hydroxymethyl-2,6-t-butylphenol with a boiling point >=200 deg.C).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ethylene polymer composition having improved moldability and product performance, particularly heat aging resistance, suitable for use as a crosslinked polyethylene rotomolding material.

Traditionally, by cross-linking high-rigidity medium-high density polyethylene during rotational molding, large hollow products with significantly improved impact strength, environmental stress cracking resistance, and creep resistance have been easily obtained, making them suitable for industrial parts, It has been used for a wide range of purposes, including leisure goods.

Dialkyl peroxides are generally used for crosslinking polyethylene, but in the case of rotational molding, crosslinking agents with a high scorch temperature are preferred because the fluidity of the melt affects the smoothness of the inner surface of the product. 5-dimethyl-2,5-
Di(t-butylperoxy)hexyne-3 is widely used.

Furthermore, if a crosslinking agent is used alone, volatile low molecules are generated from the crosslinking agent due to the influence of the residual transition metal component, resulting in a product with bubbles and no commercial value. For this reason, crosslinking aids such as triallyl cyanurate and triallyl isocyanurate have been used as bubble suppressants.

However, recently, the development of applications that require heat-resistant life, such as A-radioactive waste storage containers, cargo transportation containers, etc., has become active, and it has become necessary to add antioxidants that meet the required level. .

However, strengthening the antioxidant in combination with dialkyl peroxide or triaryl isocyanurate significantly inhibits crosslinking efficiency, resulting in a decrease in gel fraction and H
This is not preferable because it lowers the lij·li1 strength.

The present invention was developed as a result of intensive studies to solve these drawbacks.
It was discovered that the use of tetraallyl silicate as a crosslinking aid not only suppresses bubbles but also reduces gel fraction fluctuations due to the addition of antioxidants and extends heat aging life.

Furthermore, by using tetraallyl silicate,
Conventionally, the crosslinking agent has been substantially 2,5-dimethyl-2,5-di(t~butylperoxy)hexyne- from the viewpoint of scorch.
3 (on the other hand, the crosslinking efficiency is lower than that of crosslinking agents with a low decomposition temperature).
It has also become possible to use 1,3-bis(t-)-f-ruboxyisopropyl)benzene, which has a low scorch temperature and high crosslinking efficiency. That is, 1,3-bis(1-butylperoxyisopropyl)benzene is mixed with 2.
It was found that when used in combination with 5-dimethyl-2,5-di(7-butylperoxy)hexyne-3 at a weight ratio of 1.5 times or less, other quality requirements could be satisfied even with a small amount of crosslinking agent used. did.

That is, the present invention has a density of 0.935! P/crt
(a) for 100 parts of one or more ethylene polymers
Using either of the following (a) or (b) as a crosslinking agent, (a) 0.1 to 3 times of 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 Part (b) 1,
The heavy sleeve ratio of 3-bis(t-butylperoxyisopropyl)benzene and 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 is 1.5 or less, and the total of both is 0.05 to 2 parts by weight, and (b) 0.1 to 5 parts by weight of tetraallyl silicate as a crosslinking aid, and (C) 01 to 1 part by weight of a phenolic IT-forming inhibitor. An ethylene polymer composition characterized by:

The ethylene copolymer used in the present invention is preferably a medium- to high-density ethylene homopolymer or copolymer, and in the case of a copolymer, α-olefins (propylene, butene-1, Pentene-1,4-methylpentene-11, hexene-1, octene-1, etc. alone or in combination), vinyl esters (vinyl acetate, etc.), unsaturated organic acids or derivatives thereof (acrylic acid or its esters, maleic anhydride, Ethylene copolymers obtained by grafting, block or random copolymerization of unsaturated aromatic monomers (styrene, methylstyrene, etc.), methacrylic acid or its esters, etc.) are suitable for use. Among them, a medium/high density ethylene polymer produced using a low pressure method Ziegler catalyst or a mixed composition of this and a high pressure method low density polyethylene with a density of 0.950 y/ca.
The above materials or low-pressure normal ethylene polymers with a density of 0.950 to 0.970 f/cJ are preferred in terms of rigidity when formed into a molded product. Moreover, the melt flow rate (MFR) of this ethylene polymer is preferably higher in terms of inner surface smoothness, and is preferably 6 to 509710 minutes.

The crosslinking agent used in the present invention is (a) 2,5-dimethyl-2
, s-(t-butylba-ogycinohexine-3 or 0) and 1,3-bis(t-buty/l/peroxyisopropyl)benzene. In the case of (a), the amount added is 0.1 to 3 parts by weight, preferably 3 to 2 parts by weight, per 100 parts by weight of the ethylene polymer; in the case of ←), 1, 3-bis(t-butylperoxyisopropyl)benzene is 2,5-dimethyl-2
, 5-di(t-butylperoxy)hexyne-3 in an amount within 1.5 times that of City 1, and the total amount of both is 0.
0.05 to 2 parts by volume, preferably 0.1 to 1.5 parts by volume.

Here, if the amount added in case (a) is less than 0.1%, or if the amount added in case (b) is less than 0.05 parts by weight, the gel fraction is low. , the impact strength of the product is low, which is not desirable, and the amount added in case (a) is still 3 tons.
If the amount exceeds 1 part by weight, or if the amount added exceeds 2 parts by weight in the case of (b), the fluidity during melting will be impaired and the appearance will be poor, which is not preferable. In addition, in case (b), when the weight ratio of both is more than 1.5 times, it is not preferable for the same reason. Further, in the case of (b), the amount of 1,3-bis(t-butylperoxyisopropyl)benzene is preferably 0.01 parts by weight or more.

The crosslinking aid used in the present invention is tetraallylsilicate (CH2=CHCI(20)4Si),
L'n is used in a range of 0.1 to 5M for the combined ioo heavy section. If it is less than 0.1 part by weight, the cross-linked product will partially decompose into low molecular weight due to long-term heating, resulting in a decrease in impact strength, and if it exceeds 5 parts by weight, the fluidity will be impaired and the appearance will be poor, which is not desirable. .

Furthermore, the phenolic antioxidant used in the present invention preferably has a boiling point of 200°C or higher, such as 4-hydroxymethyl-2,6-t-butylphenol, n-octadecyl-3-(4'-?: )"Roxy 315'
-') -t-butylphenyl)probionate, 2
．． 2'-methylenebis(4-methyl-6-t-butylphenol), 1,3,5-trimethyl-2,4,6-
Tris(3,5-di-t-butyl-4-hydroxybenzyl)benzene, tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, tetrakis[methylene-3(37;5/-di t-phthyl-4'-hydroxyphenyl)glochionate]methane, 4.4'
-Thiobis-(6-t-butyl'-3-methylphenol), dialkylphenol sulfide, 1,3.5-
Tris(4-t-butyl-3-hydroxy-2,6-
dimethylbenzyl)isocyanuric acid, 1,3.5-tris(2-hydroxyethyl)-8-triazine-2,
4,6 (IFI.

3H,5H)-)ion and 3,5-di-t-butyl-4
Triesters with -hydroxyhydrocinnamic acid, etc. may be mentioned. This stabilizer is used in an amount of 0.01 to 1 part by weight per 100 parts by weight of the ethylene polymer. If it is less than 0.01 part by weight, the heat resistance life will be low, and if it exceeds 1 part by weight, the gel fraction will be low, which is not preferable.

In the present invention, in addition to these components, other components such as propylene polymer, nylon, ethylene-glopylene rubber, styrene-based rubber, etc.
Thermoplastic (finishing or rubber) such as butadiene-based combs; various stabilizers such as sulfur-based, phosphorus-based, and amine-based; mold release agents; p
H regulator: pigment; crosslinking agent adsorption inhibitor to pigment: pigment dispersant; weatherability improver, etc. may be added.

Example: High-density polyethylene (Yukalon Hard JX manufactured by Mitsubishi Yuka Co., Ltd.)
IO: MFI 2 o y / 1 o min, density 0.96
2 f/t, rl) powder was mixed with each component shown in Table 1 using a Henschel mixer, and granulated at 140 to 150°C using a 40 m diameter shaft extruder under a nitrogen atmosphere. The pellets were crushed with a crusher in 32 mesh passes, and the powder 5 (I O1i' was put into a cylinder with an inner diameter of 250 mm.
It was sealed with a lid with a hole and heated at 190 to 200°C for about 15 minutes while rotating in the -R1+ direction.

This was air-cooled for 5 minutes, then cooled by showering with cooling water, and the product was taken out. The wall thickness at the center of the product was 2 hus. Product evaluations such as appearance and mechanical strength were as shown in Table 1.

Examples 1 and 2 used tetraallyl as the crosslinking aid.

Compared to Comparative Example 1, which did not use a crosslinking aid, no air bubbles were generated, and the gel fraction was higher than Comparative Example 2, which used triarylisocyanuric acid as a crosslinking aid. It was found that the strength was high and the heat aging resistance was significantly improved.

Moreover, Example 3 is a combination system with a crosslinking agent that has high crosslinking efficiency but low scorch temperature. The concentration of crosslinking agent used is as in Example 1.
Although the gel fraction was high, the inner surface smoothness was also good. However, when using a crosslinking agent in combination, if the ratio of 1,3-bis(t-butylperoxyisopropyl)benzene to 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 increases, As in Comparative Example 3, the inner surface smoothness is impaired.

Regarding the evaluation method, the gel fraction is boiling xylene 1
Extraction for 5 hours, tensile resistance using ASTt-D1822, environmental stress cracking resistance using ASTM-D1693, and heat-resistant aging Katsura using Suga Test Isogya Open aged at 110°C and tensile testing using JIS-6760 (No. 2 dumbbell). The method used was to measure the holding time during opening at which the tensile elongation retention rate reached 50% during the test.

(Margin below)

Claims (1)

[Claims] For 1.00 parts by weight of an ethylene polymer having a density of 0.9359/d or more, (a) the following (a) or ← as a crosslinking agent.
), (<)2. 0.1 to 3 folds of S-dimethyl-2,5-di(t-butylperoxy)hexyne-3 (b) 1,3
- The weight part ratio of bis(t-butylbaroxyisoglobil)benzene and 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 is 1.5 or less, and the total of both is In addition, (b) using 011 to 5 parts by weight of tetraallyl silicate as a crosslinking aid, and (C) adding 0 to 1 part by weight of a phenolic antioxidant. Characteristic ethylene polymer composition.