JPH0721093B2 - Resin composition for polyethylene cross-linking modification - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a resin composition for cross-linking modification of polyethylene used for the structure of cross-linked polyethylene.

(Prior art) Polyethylene having a crosslinked structure (crosslinked polyethylene)
Is transparent and has excellent heat resistance, chemical resistance and mechanical properties, so it is used in various fields such as heat resistant insulating materials, corrosion resistant parts, and various containers.

As a method for cross-linking and modifying linear polyethylene, a method by a chemical operation using an organic peroxide and a method by a radiation treatment are industrially carried out. Since the equipment cost of the radiation treatment is expensive, the chemical treatment is generally used. The chemical method is based on the principle that the peroxide compounded in polyethylene decomposes by heating, abstracts hydrogen from the main chain of polyethylene, and the resulting polymer radicals bond to each other to crosslink the main chains. .

Generally, when manufacturing plastic products, a masterbatch containing a high concentration of a coloring agent or a crosslinking agent is prepared in advance in order to uniformly color the obtained product or to obtain a uniform crosslinking degree. The method of kneading this with resin (masterbatch method) is adopted. It is considered that a homogeneous molded body can be effectively produced by using this masterbatch method even when a molded body made of the crosslinked modified polyethylene is obtained. However, since polyethylene is a compound in which a radical reaction is easily caused by a peroxide, if the peroxide is melt-kneaded with polyethylene at a high concentration, deterioration of the resin due to the radical reaction is severe. Furthermore, the obtained pellets have a crosslinked structure and are difficult to mix with untreated polyethylene, resulting in phase separation. Due to these problems, the masterbatch method has not been used in the production of crosslinked polyethylene.

(Problems to be Solved by the Invention) The present invention is to solve the above-mentioned conventional problems, and an object thereof is to provide a resin composition for polyethylene cross-linking modification suitable for the production of cross-linked polyethylene by a masterbatch method. It is in. Another object of the present invention is to provide a resin composition for polyethylene cross-linking modification, which contains a high concentration of peroxide and does not show deterioration of the resin.

(Means for Solving the Problems) The polyethylene crosslinking-modifying resin composition of the present invention comprises a mixture of polyethylene and a peroxide having a thermal decomposition property with a half-life at 140 ° C. of 20 minutes or more, It is obtained by melt-kneading at a temperature of 170 ° C or lower, which achieves the above object.

The polyethylene cross-linking modification resin composition of the present invention comprises a mixture of polyethylene, a peroxide having a thermal decomposition property with a half-life at 140 ° C. of 20 minutes or more, and a radical scavenger.
Obtained by melt-kneading at a temperature below 70 ℃,
Thereby, the above object is achieved.

The polyethylene used in the resin composition of the present invention includes low density, medium density and high density polyethylene. In addition, copolymers of polyethylene such as ethylene-vinyl acetate copolymer, and chlorinated polyethylene can be used. A small polyethylene of molten clay, preferably a polyethylene having a melt index (MI value) of 10 or more is suitable for easy kneading during melting.

The peroxide used in the resin composition of the present invention is 140
A high temperature decomposable peroxide with a half-life at ℃ of 20 minutes or more is used. For example, dicumyl peroxide which is a dialkyl peroxide, α, α′-bis (tert-butylperoxy-meta-isopropyl) benzene, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di (tertiary Butylperoxy) hexyne-3 and the like can be used. The mixing amount of these peroxides is 0.5 to 10 parts by weight with respect to 100 parts by weight of the resin.

Known radical scavengers can be used as the radical scavenger. Particularly, hydroquinone monomethyl ether, hydroquinone, pt-butylcatechol, chloranil, lauryl mercaptan and the like are preferable. The addition amount is necessary to calculate the amount of peroxide cleavage at the time of production from the temperature at the time of producing the resin composition, the residence time of the resin in the kneading device and the half-life of the peroxide, and to capture the generated radicals. Greater amounts of radical scavenger are included. Usually, 0.1 to 1 part by weight is used for 100 parts by weight of resin.

It is also possible to add 0.5 to 5 parts by weight of maleic anhydride to the composition of the present invention for the purpose of imparting adhesiveness to the resulting crosslinked polyethylene.

In order to obtain the polyethylene crosslinking-modifying resin composition of the present invention, the above-mentioned polyethylene, the above-mentioned peroxide, and optionally the above-mentioned radical scavenger and maleic anhydride are heated to a melting point of polyethylene to 170 ° C and kneaded. It is obtained by For heating and kneading, a usual extruder or kneader can be used. In order to shorten the kneading time, it is preferable to use a twin-screw extruder in which the screws are closely meshed with each other. For example, polyethylene is charged into an extruder, and the inside of the extruder is at the melting point of polyethylene or higher and
Set the temperature below ℃. For example, 120-140 ℃ for low density polyethylene and 135 for high density polyethylene.
It is preferable to set the temperature to ˜155 ° C. Next, the peroxide and, if necessary, the radical scavenger and maleic anhydride are added. The mixture is extruded and pelletized.

The resin composition prepared as described above contains a high concentration of peroxide and has almost no cross-linking structure, and therefore is well melt-dispersed in untreated polyethylene. When 1 to 10 parts by weight of the resin composition of the present invention is added to 100 parts by weight of untreated polyethylene and melt-kneaded at a high temperature (180 ° C. to 200 ° C.), a crosslinking reaction proceeds and crosslinked polyethylene is easily obtained. To be When the resin composition is prepared by adding a radical scavenger, the radical scavenger captures radicals generated during the preparation of the polyethylene crosslinking-modifying resin composition, and therefore has a substantially crosslinked structure. A composition is obtained which has no When this composition is melt-kneaded with untreated polyethylene, a small amount of the remaining radical scavenger suppresses the crosslinking reaction until the resin composition is uniformly melt-dispersed in the untreated polyethylene, and the radical scavenger is consumed. At that point, the crosslinking reaction begins. As a result, polyethylene having a uniformly crosslinked structure is obtained. Such crosslinked polyethylene is used as various molded products such as sheets, containers and various parts.

(Examples) Examples of the present invention will be described below.

Example 1 Commercially available high-density polyethylene pellets (MI value 20; JIS K6760
Using a twin-screw extruder (diameter 44 cm), the temperature is gradually lowered while extruding in a strand at 180 ° C, and the hopper, cylinder and die are all 140-150 ° C.
It was confirmed that the temperature was controlled. Next, α, α'-bis (tertiary butyl peroxy-meta-isopropyl) benzene (Nippon Yushi Co., Ltd. trade name Perbutyl P; half-life at 140 ° C) per 100 parts by weight of polyethylene extrusion 2
4 minutes) 5 parts by weight and 1 part by weight of 4-methoxyphenol were added from the vacuum vent using a volume screw. The molten resin was extruded in a strand shape (first extrusion), and after confirming that the viscosity did not change, the strand was cooled to form pellets. 20 parts by weight of untreated high-density polyethylene pellets (MI value 20) were mixed with 1 part by weight of the obtained pellets, and the mixture was extruded into a film at 200 ° C (second extrusion).

The extrusion conditions during the first extrusion and the second extrusion were observed, and the presence or absence of melt fracture (striped pattern) and fish eyes (lump of resin) was observed. Further, the MI value of the obtained film was measured according to JIS K6760. The results are shown in the table below. The results of Examples 2 to 3 and Comparative Examples 1 to 3 described later are collectively shown in the table below.

Example 2 A commercially available low-density polyethylene pellet (MI value of 30) was extruded in a strand shape at 160 ° C. using a twin-screw extruder (diameter 44 cm) to gradually lower the temperature, and the hopper portion was heated to 100 ° C.
And the cylinder and die were controlled at 125-130 ° C. Next, α, α′-bis (tert-butylperoxy-meta-isopropyl) benzene (Nippon Yushi Co., Ltd. trade name Perbutyl P; half-life at 140 ° C., 24 minutes) was added to 100 parts by weight of the above polyethylene. Parts by weight and 4-
After adding 1 part by weight of methoxyphenol and mixing for 2 minutes with a super mixer, this was introduced from the hopper of the above twin-screw extruder. The molten resin was extruded in a strand shape (first extrusion), and after confirming that the viscosity did not change, the strand was cooled to obtain pellets. 20 parts by weight of untreated low-density polyethylene pellets (MI value of 30) were mixed with 1 part by weight of the obtained pellets and extruded into a film at 180 ° C. (second extrusion). Extrusion conditions and the obtained film were evaluated in the same manner as in Example 1.

Example 3 The same as Example 2 except that 4-methoxyphenol (radical scavenger) was not used. The evaluation results of the obtained resin composition are shown in the table below.

Comparative Example 1 The same as Example 1 except that the extrusion temperature at the time of preparing the resin composition was 180 ° C.

Comparative Example 2 The same as Example 1 except that tertiary butyl peroxyacetate (trade name Perbutyl A manufactured by NOF CORPORATION) (half-life at 140 ° C. of about 8 minutes) was used as the peroxide.

It can be seen that when the resin composition of the present invention is used, the viscosity of the molten resin extruded before and after the addition of the peroxide hardly changes, and the crosslinking reaction hardly progresses in the resin composition. The state of the obtained cross-linked polyethylene film is
No or little melt fracture or fish eyes were observed, and it is clear that a polyethylene film having a uniform crosslinked structure throughout the resin was obtained.

On the other hand, when the melting temperature for obtaining the resin composition is high (Comparative Example 1) and the half-life of the peroxide is short (Comparative Example 2), the crosslinking reaction proceeds considerably during the preparation of the resin composition. Therefore, it is difficult to obtain pellets. Further, since the resin composition has poor compatibility with untreated polyethylene, the surface condition of the obtained film is poor.

(Effect of the Invention) The polyethylene crosslinking-modifying resin composition of the present invention contains a peroxide in a high concentration and has almost no crosslinking structure. When this composition is used as a masterbatch and added to polyethylene and extrusion-molded, crosslinked polyethylene can be easily obtained. The resulting crosslinked polyethylene has a high degree of crosslinking and a uniform crosslinked structure. Such crosslinked polyethylene is used as various molded products such as sheets, containers and various parts.

Claims (2)

[Claims] 1. A mixture containing polyethylene and a peroxide having a thermal decomposition property having a half-life at 140 ° C. of 20 minutes or more, 1
A polyethylene crosslinking-modifying resin composition obtained by melt-kneading at a temperature of 70 ° C. or lower. 2. A melt-kneading mixture containing polyethylene, a peroxide having a thermal decomposition property of which the half-life at 140 ° C. is 20 minutes or more, and a radical scavenger at a temperature of 170 ° C. or less. A resin composition for cross-linking modification of polyethylene obtained by.