JPS6345692B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a crosslinked polyolefin molded article with improved properties. It is well known that crosslinking of polyethylene improves its heat resistance and mechanical properties, and this crosslinked polyethylene is used for a wide variety of purposes. As a method for crosslinking polyethylene, a method using electron beam irradiation and a chemical crosslinking method using a crosslinking agent such as an organic peroxide are well known. However, when the above-mentioned crosslinking technology is applied to resins such as polypropylene, polybutene-1, and poly-4-methylpentene-1, which are polyolefin resins similar to polyethylene, it is not possible to obtain the excellent properties improvement effect seen in polyethylene. For example, when chemical crosslinking technology using organic peroxides such as dicumyl peroxide is applied to polypropylene,
The resin deteriorated significantly and could only be obtained with poor practical use. The inventors focused on this point and conducted intensive research on crosslinking methods for polyolefin resins other than polyethylene, and found that polypropylene has at least two reactive double bonds or triple bonds in the molecule. A compound is blended, this composition is heated and molded at a temperature higher than the melting point of polypropylene,
It was discovered that by irradiating the obtained molded body with ionizing radiation, it was possible to obtain a cross-linked polypropylene molded body with a high degree of crosslinking (commonly known as gelling degree) with little deterioration of the resin, and achieved some results. I was able to do that. However, the crosslinked polypropylene obtained by the above method has a relatively low elongation of 200 to 300%, and its long-term life characteristics are also quite short, so it cannot be used as an electrical insulation material or processed product material that requires a high degree of reliability. It was something I didn't have. From this point of view, the inventors continued their research and found that, per 100 parts by weight of a polyolefin polymer other than polyethylene such as polypropylene, a polymer having at least three acryloyloxy groups or methacryloyloxy groups in the molecule. compound
0.1 to 20.0 parts by weight and 0.55 parts by weight of phenolic derivatives
A large amount of ~5.0 parts by weight is blended, the composition is heated and molded at a temperature higher than the melting point of the polyolefin used, and the resulting molded product is then irradiated with ionizing radiation to achieve a high degree of gelation and 400% by weight. The inventors have discovered that it is possible to obtain a crosslinked polyolefin molded article that has a high elongation property of at least 1.9% and has little resin deterioration, and has established the present invention. The reason why the method of the present invention as described above can impart a high degree of crosslinking effect to polypropylene resin is considered as follows. That is, when a polymer such as polypropylene is irradiated with ionizing radiation in the presence of a phenolic derivative and a compound having at least three acryloyloxy or methacryloyloxy groups in the molecule, acryloyloxy or methacryloyloxy groups are formed in the polymer. Since the group-containing compound reacts and significantly promotes crosslinking, a high degree of crosslinking can be achieved even with a low dose of ionizing radiation. Further, although the mechanism of action of the phenolic derivative blended in a relatively large amount is not clear, it is thought that it has an effect of promoting crosslinking since the degree of gelation increases with addition. In the present invention, a high degree of crosslinking can be achieved with a small irradiation dose due to the synergistic effect of both these compounds, but the reason why the polymer exhibits high elongation properties of over 400% despite being highly crosslinked is the This is thought to be because the phenolic derivative has a large amount of crosslinking, so it hardly gels during molding and can be molded in a stable molecular state, and then crosslinked by ionizing radiation. In addition, since the method of the present invention is a so-called post-crosslinking method in which the composition is crosslinked by irradiation with ionizing radiation after being molded, the composition is heated to a temperature higher than the melting point of the polyolefin.
No crosslinking occurs during molding, and there is no need for seizure in an extruder or poor moldability, which often occur when crosslinking is performed using a crosslinking agent. The polyolefin in this invention refers to polymers such as polypropylene, polybutene-1, poly4-methylpentene, or blends thereof with less than 50% of other resins or rubbers. In addition, examples of compounds having at least three acryloyloxy groups or methacryloyloxy groups in the present invention include trimethylolpropane triacrylate, 1,2,3propanetriol triacrylate, 2,2'bis(4-acryloyloxy-diethoxyphyl) enyl) propane, 1,3,
5 triacryloyloxybenzene, trimethylolpropane trimethacrylate, 2,2'bis(4
-methacryloyloxydiethoxyphenyl)propane, etc. are used. Preferred examples include trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, and tetramethylolmethanetetraacrylate. The above-mentioned compound having at least three acryloyloxy groups or methacryloyloxy groups is mixed in an amount of 0.1 to 20.0 parts by weight per 100 parts by weight of the polyolefin, but if the amount is less than this range, the effect of the present invention will not be achieved, while if the upper limit is exceeded. This is not preferable because it causes brittleness in the crosslinked product. The phenolic derivatives used in this invention include 2,6-dithyabutyl-4-methylphenol, 2,5-dimethylhydroquinone,
2,2-bis(4-hydroxy-3,5-dimethylphenyl)propane, 2,4,6-trimethylphenol, bis(4-hydroxy-3,5-dithyabutylphenyl)sulfide, bis( 2-hydroxy-3,5-dimethylphenyl)
Methane, pentaerythrityl-tetrakis [3-
3,5-ditersiabutyl-4-hydroxyphenyl)propionate], bis(3-hydroxy-2,5-tetramethylphenyl)methane, 2,5-dimethylhydroquinone, 1,3,5
-trimethyl-2,4,6-tris-(3,5-
ditertiarybutyl-4-hydroxybenzyl)benzene, 1,1,3-tris-(5-tertiarybutyl-4-hydroxy-2-methylphenyl)
Butane, octadecyl-3-(3',5'-ditertyabutyl-4'-hydroxyphenyl) propionate, tris-(3,5-ditertyabutyl-4-hydroxybenzyl) isocyanurate, etc. Among these, preferred are pentaerythrityl-tetrakis [3-(3,5-tertsyabutyl-4-hydroxyphenyl)propionate], 1,1,3-tris-(5-tertsyabutyl-4-hydroxy- 2-methylphenyl)butane, octadecyl 3-(3',5'-ditertyabutyl-4'-hydroxyphenyl)propionate, tris-(3,5-ditertyabutyl-4
-hydroxybenzyl) isocyanurate, etc. These phenolic derivatives are polyolefins.
Mix 0.55 to 5.0 parts by weight per 100 parts. If the amount is less than this, a high degree of crosslinking and high elongation cannot be achieved by radiation irradiation, and the polyolefin reacts with a compound having three or more acryloyloxy or methacryloyloxy groups during molding, making it impossible to suppress so-called thermal crosslinking, resulting in poor molding process. This may cause burn-in or burn-in. On the other hand, if the upper limit is exceeded, crosslinking by radiation irradiation will be significantly impaired, which is not preferable. As the molding method of the present invention, all conventional plastic molding methods such as press molding and extrusion molding using an extruder can be used. Next, the ionizing radiation according to the present invention refers to electron beams, neutron beams, α rays, γ rays, X rays, ultraviolet rays, etc., and the absorbed dose thereof is preferably 0.05 to 5 Mrad.
A low dose of about 0.1 to 2 Mrad is sufficient. Irradiation of 5 Mrad or more does not improve the gel fraction, but rather causes deterioration, which is not preferable. As described above, this invention is a polyolefin in which a compound having at least three acryloyloxy groups or methacryloyloxy groups and a phenol derivative are present in the molecule, and the polyolefin is crosslinked by irradiation with ionizing radiation. ,
As is clear from the examples below, the properties of the resulting crosslinked polyolefin molded article were significantly improved, and its industrial value is extremely large. The present invention will be specifically explained below using Examples. [Example 1 and Comparative Example 1] 100 parts by weight of MI1 isotactic polypropylene, 2.0 parts by weight of tetramethylolmethanetetraacrylate, 0.8 parts by weight of enyl) propionate was added, and the mixture was extruded into a 2 mm thick sheet at 220°C using a 40 mmφ extruder. For comparison, a sheet having a thickness of 2 mm was similarly extruded using the composition of Example 1 except that tetramethylolmethanetetraacrylate was removed. Using a linear accelerator on both sheets,
A 1 Mrad electron beam was irradiated. The physical properties of both sheets thus obtained are shown in Table 1.

[Example 2 and Comparative Example 2]

To 100 parts by weight of polybutene-1 of MI1, 2,
2.5 parts by weight of 2'bis(4-methacryloyloxy-ethoxyphenyl)propane, 1,1,3-tris-(5-tertiarybutyl-4-hydroxy-
A sheet was prepared under the same conditions as in Example 1 by adding 1.5 parts of 2-methylphenyl)butane. In addition, with this composition, there is a composition in which only 0.1 parts by weight of 1,1,3-tris-(5-tertiarybutyl-4-hydroxy-2-methylphenyl)butane is used (Comparative Example 2-1), and a composition in which this is added to 7 parts by weight. A sheet was similarly made using the composition (Comparative Example 2-2). 2 Mrad for these three types of sheets as in Example 1.
The material was irradiated with an electron beam and its physical properties were measured. The results obtained are shown in Table 2.

[Example 3 and Comparative Example 3]

MI1 isotactic polypropylene 100 parts by weight trimethylolpropane triacrylate
2.0 parts by weight and 0.8 parts by weight of tris-(3,5-ditertyabutyl-4-hydroxybenzyl)isocyanurate were extruded into a 2 mm thick sheet in the same manner as in Example 1. In addition, a similar sheet was extruded in Example 3 except that 2.5 parts by weight of triallyl cyanurate was used instead of trimethylolpropane triacrylate.
This was designated as Comparative Example 3. Both sheets thus obtained were irradiated with an electron beam of 0.1 Mrad to 20 Mrad using a linear accelerator.
The dose dependence of the physical properties of the sheet was investigated. The results obtained are shown in Table 3.

[Example 4 and Comparative Example 4]

To 100 parts by weight of polypropylene of MI1.5, 2 parts by weight of trimethylolpropane triacrylate, octadecyl 3-(3',5'-ditertyabutyl-
Add 20 parts by weight of 4-hydroxyphenyl) propionate and use a 65 mmφ extruder at 220°C with an outer diameter of 40 mm.
The pipe has a wall thickness of 2 mm. As Comparative Example 4, a pipe was made in the same manner as in Example 4 except that only 0.3 parts by weight of octadecyl 3-(3',5'-dithyabutyl-4-hydroxyphenyl)propionate was used. The pipe of the example had a smooth surface, whereas the pipe of the comparative example had fine wrinkles on its surface. Both of them are 1.0Mrad by linear accelerator.
The physical properties of the pipe obtained after irradiation with an electron beam were measured. The results obtained are shown in Table 4.

[Table] As is clear from the table, in Comparative Example 4, the surface of the pipe was rough due to crosslinking that occurred during molding, and the elongation after electron beam crosslinking was reduced, but in Example 4
In this method, a pipe with a smooth surface was obtained, and by electron beam irradiation, the pipe had excellent physical properties. As is clear from the above Examples, the method of the present invention makes it possible to produce crosslinked polyolefin molded articles with excellent physical properties, and its industrial value is extremely large.

Claims (1)

[Claims] 1 Polypropylene, polybutene-1, poly4-
0.1 to 20.0 parts by weight of a compound having at least three acryloyloxy groups or methacryloyloxy groups in the molecule and phenol to 100 parts by weight of polyolefin containing at least 50% by weight of at least one selected from the group of methylpentene-1. system derivative 0.55
1. A method for producing a crosslinked polyolefin molded article, which comprises heating and molding a composition containing up to 5.0 parts by weight at a temperature equal to or higher than the melting point of the polyolefin used, and then irradiating the molded article with ionizing radiation. 2. A compound having at least three acryloyloxy groups or methacryloyloxy groups in the molecule,
trimethylolpropane trimethacrylate,
Claim 1, which is any compound selected from the group of trimethylolpropane triacrylate, tetramethylolmethane triacrylate, and tetramethylolmethane tetraacrylate.
A method for producing a crosslinked polyolefin molded article as described in 1. 3 The phenolic derivative is 1,1,3-tris-(5-tert-butyl-4-hydroxy-2
-methylphenyl)butane, octadecyl 3-
(3',5'-ditertyabutyl-4'-hydroxyphenyl)propionate, tris-(3,5-ditertyabutyl-4-hydroxybenzyl)isocyanurate, pentaerythrityl-tetrakis [3-( 3,5-Jetashiyabutyl-4-
2. The method for producing a crosslinked polyolefin molded article according to claim 1, wherein the phenol derivative is selected from the group of hydroxyphenyl) propionate.