JPS6143377B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing chemical-resistant polyethylene molded articles suitable for use in environments where various chemicals are present. Conventionally, chloroprene, soft vinyl chloride mixtures, or polyethylene resins have been widely used as sheath materials for power cables, communication cables, etc. because of their cost advantages. However, when these cables are used in an atmosphere where chemicals are present, they inevitably suffer from the following drawbacks. That is, chloroprene and soft vinyl chloride, which have polar groups, are susceptible to molecular cleavage by acids or bases, and their sheaths tend to deteriorate. Moreover, polyolefin resins such as nonpolar polyethylene have good resistance to such acids or bases, and are swollen or dissolved by organic solvents. Although high-density polyethylene is known to exhibit relatively good properties against common chemicals, there still remains a problem in the resistance to organic solvents that needs to be improved. High-density polyethylene, which has resistance to organic solvents, is cross-linked to further increase its resistance. Generally speaking, the method for cross-linking high-density polyethylene is to use peroxide. A chemical crosslinking method by irradiation, a crosslinking method by irradiation with radiation, and a condensation crosslinking method using alkoxysilane-grafted polyethylene called the so-called Dow Corning process, that is, a silane crosslinking method are known. However, the first method requires processing under heat and pressure when it is applied to, for example, the sheath layer of the cable, making it difficult to obtain a molded product with a desired size and structure. Next, in the second method, expensive irradiation equipment is required for radiation irradiation, and there are restrictions on the thickness of the irradiated molded product in order to obtain a sufficient degree of crosslinking for polyethylene. In the case of a solid body such as a cable sheath, there are unavoidable operational problems, such as the need to repeat the irradiation from multiple directions in order to uniformize the irradiation dose. The third method is well known, for example, the method shown in Japanese Patent Publication No. 1711/1983. Specifically, (1) polyethylene is treated with the general formula RR'SiY ₂ (in the formula R is a monovalent olefinic unsaturated hydrocarbon group or a hydrocarbonoxy group, Y is a hydrolyzable organic group, R' is a monovalent hydrocarbon group not containing fatty unsaturation, the group Y or hydrogen) (2) The mixture obtained in (1) above is passed through an extrusion pelletizer to obtain pellets of silane-grafted polyethylene. (3) The above pellets are mixed with a desired amount of silanol condensation catalyst and extruded into a molded body using an extruder; (4) this molded body is exposed to an atmosphere containing moisture to cause crosslinking; There is. In the Dow Corning process using silane crosslinking, the above-mentioned silane-grafted polyethylene can be easily molded into a molded product of the desired shape in the same way as ordinary thermoplastic resins, and crosslinking can be achieved by simply contacting it with moisture, etc. This method is attracting particular attention because it can eliminate the drawbacks of the first and second methods. However, the graft reaction product obtained by the third method has a melt index that is approximately 1/10 that of the raw material polyethylene.
It is normal for the value to decrease even further. Generally, in order to extrude molded bodies for a wide range of purposes, it is required that the melt index of the material be at least 0.2 due to processability issues. For this reason, in consideration of the decrease in the melt index mentioned above, it is necessary to meet the above requirements by using a melt index of 3 or more for the raw polyethylene. However, when the melt index of the raw polyethylene is greater than 3, when the reaction product is melt-molded and exposed to a moisture atmosphere for crosslinking, the molded product becomes susceptible to environmental stress cracking before the crosslinking is completed. It was found that cracking occurred when exposed to the environment of solvent crazing. That is, if polyethylene having a melt index of 3 or more is used as the raw material polyethylene, the resulting molded product will not have sufficient environmental stress cracking resistance. As mentioned above, in the Dow Corning process using silane crosslinking, there are conflicting demands regarding the selection of the melt index of the raw polyethylene. The melt index of the reaction product must be small in order to improve the environmental stress cracking resistance of the molded product. Not currently proposed. The inventors conducted intensive studies to solve this problem, and found that the high-density polyethylene used had a density of 0.945 or more and a melt index of 0.6 to 0.6.
By using 3.0 or higher and also using specific compounds detailed below in the formulation,
The inventors completed this invention by discovering that the above-mentioned grafted polyethylene maintains a melt index sufficient for flow processing, and that molded products made of the grafted polyethylene no longer cause environmental stress cracks and become polyethylene with good chemical resistance. . That is, this invention has a melt index of 0.6 to 3.0 and a density of 0.945.
The above polyethylene and the general formula RR′SiY ₂ (in the formula R
is a monovalent olefinic unsaturated hydrocarbon group or a hydrocarbonoxy group, Y is a hydrolyzable organic group, R' is a monovalent hydrocarbon group not containing fatty unsaturation, the group Y or hydrogen) 4.4'-methyllene-bis(2,6-di-tertiary-butyl) -phenol), 2,6-jeter-butyl-alpha-
dimethylamino-p-cresol), hexamethylene glycol bis[β-(3,5
6-(4-hydroxy-3,5-di-ter-shyary-butyl-anilino)-2,4-bis-octyl-thio-1,3 ,5-triazine, N,N'-hexamethylene-bis-(3,5-
tertiary-butyl-4-hydroxy-hydrocinnamide), 3,5-di-tertiary-butyl-4-hydroxy-benzylphosphoric acid diethyl ester, bis(3,5-di-tertiary-butyl-4-hydroxy-benzylphosphoric acid diethyl ester) Shary Butyl-4-
nickel salt of hydroxybenzoylphosphoric acid monoethyl ester), 1,3,5-tri-methyl-2,4,6-tris(3,5-di-tert-shari-butyl-4-hydroxy-benzyl)benzene , tetrakis [methylene-3 (3,5-jeta-
shary-butyl-4-hydroxy-phenyl)
proponate] methane, n-octadecyl-3-(4'-hydroxy-
3′,5′-jeter-shari-butylphenol) propionate, tris(3,5-je-ter-shari-butyl-4)
-Hydroxy-phenyl)isocyanurate, Tris[β-3,5-di-tertiary-butyl-4-hydroxy-phenyl)propionyl-
The graft-modified polyethylene obtained by reacting one or more kinds of [oxyethyl]isocyanurate with one or more kinds is melt-molded in the presence of a silanol condensation catalyst, and the obtained molded product is exposed to an atmosphere containing moisture. This is a method for producing a polyethylene molded product, which is characterized by crosslinking. The polyethylene used in this invention has a melt index in the range of 0.6 to 3.0 and a density of 0.945 or more. And the following compounds, namely 4,4'-methylene-bis(2,6-di-tertiary-butyl-phenol), 2,6-di-tertiary-butyl-alpha-
dimethylamino-p-cresol), hexamethylene glycol bis[β-(3,5
6-(4-hydroxy-3,5-di-ter-shyary-butyl-anilino)-2,4-bis-octyl-thio-1,3 , 5-triazine, N,N'-hexamethylene-bis(3,5-di-tertiary-butyl-4-hydroxy-hydrocinnamide), 3,5-di-tertiary-butyl-4-hydroxy -benzylphosphoric acid diethyl ester, bis(3,5-tertiary-butyl-4-
nickel salt of hydroxybenzoylphosphoric acid monoethyl ester), 1,3,5-tri-methyl-2,4,6-tris(3,5-di-tert-shari-butyl-4-hydroxy-benzyl)benzene , tetrakis [methylene-3 (3,5-jeta-
shary-butyl-4-hydroxy-phenyl)
proponate] methane, n-octadecyl-3-(4'-hydroxy-
3′,5′-jeter-shari-butylphenol) propionate, tris(3,5-je-ter-shari-butyl-4)
-Hydroxy-phenyl) isocyanurate, tris[β-(3,5-di-tert-butyl-4-hydroxy-phenyl)propionyl-oxyethyl] isocyanurate, one or more selected from It is necessary to use this together. The reasons for selectively using the above polyethylene and using the above compounds in combination in this invention are as follows. In order to have good environmental stress cracking resistance, the raw material polyethylene must have a melt index of 3 or less, and from the viewpoint of moldability, in order for the reaction product to have a melt index of 0.2 or more,
The above compounds are used in combination, and the raw material polyethylene is
It is necessary to regulate it to 0.6 or higher. Next, as the silane compound and the compound capable of generating free radical sites in polyethylene used in the present invention, those described in the above-mentioned Japanese Patent Publication No. 1711-1982 are used, respectively.
That is, the former includes vinyltriethoxysilane, vinyltrimethoxysilane, etc., and the latter includes dicumyl peroxide, benzoyl peroxide, dichlorobenzosyl peroxide, etc. And these are 0.5-10 and 0.05-0.2% by weight, respectively, based on the polyethylene resin used.
used. In addition, in this invention, the silanol condensation catalyst is
It is appropriate to use 0.01 to 1.0 parts by weight, and specific examples of the silanol condensation catalyst include dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, and the like. Other auxiliaries which may then be used in the compositions of the invention include fillers such as carbon black, clay, talc and calcium carbonate, blowing agents, foam nucleating agents, lubricants, UV stabilizers, colorants, voltage Stabilizers and the like can be mentioned. These auxiliaries are used in such proportions as to produce the intended effect in the resulting composition. The composition of the present invention may also contain other polymers other than the above-mentioned polyethylene resins which are compatible with the polyethylene, that is, can be physically blended or alloyed with the polyethylene resin. It can also be added as a bulking agent. These auxiliaries may be added at any stage as long as they do not inhibit the graft reaction, have a silanol catalytic effect, or release moisture, but if any of these effects If it has, it is desirable to add it after the grafting reaction is completed. As described above, the present invention is a silane that reduces the decrease in the melt index of raw polyethylene, that is, significantly improves the moldability, and furthermore, the crosslinking operation can be performed by simply exposing the molded product to an atmosphere in which moisture is present. This is a method for producing a crosslinked polyethylene molded body, and furthermore, the environmental stress cracking resistance of the resulting molded body is significantly improved. Therefore, compared to the conventional method using peroxide, the moldability and properties of the molded product are improved, and the crosslinking cost is significantly improved compared to the method using radiation irradiation. Compared to the crosslinking method, this method has the effect of significantly improving the properties such as environmental stress cracking resistance of the molded product, and has extremely high industrial value. The present invention will be specifically explained below by showing Examples and Comparative Examples. Comparative Example 1 A mixture of 100 parts by weight of polyethylene with a density of 0.955 and a melt index of 7.0 (the following parts are the same), 2.0 parts of vinyltrimethoxysilane, and 0.12 parts of 1,3-bis(tert-butylperoxy-isopropyl)benzene. The silane graft was extruded into a strand using an extruder with L/D = 22 and D = 65 mm with the extrusion temperature set at 160 to 220°C in advance at a residence time of approximately 100 seconds (screw rotation speed 45 times/min). The reaction was carried out.
The melt index of the obtained strand-like extrudate was 1.2. To 95 parts of the pelletized product of this strand-like extrudate, 100 parts of the same polyethylene as above, 1 part of dibutyltin dilaurylate, and 2 parts of 4,4'-thiobis(6-t-butyl-hydroxybenzyl) were added.
Mix 5 parts of catalyst masterbatch, which is made by kneading 100 parts of the mixture into pellets using a roll kneader, and
A coated wire was obtained by extrusion coating a 0.8 mm conductor to a film thickness of 0.5 mm using an extruder with L/D = 22 and an extrusion temperature set at ~190°C. The appearance of this covered wire was good. This coated wire was scratched with a maximum depth of 0.25 mm using a sharp blade in the direction normal to the conductor (thickness direction), and then wound around its own diameter so that the scratches appeared on the outside.
Then, this was immersed in JIS No. 2 oil at 50° C. and examined for the occurrence of cracks in the scratches, but cracks were observed in this comparative example product. Next, this coated wire was left in hot water at 80°C for 24 hours, and the gel fraction was measured under xylene (120°C) extraction conditions for 24 hours, and the value was 65%. The sample was examined for cracks after being immersed in xylene at 90°C for 3 months, but no cracks were observed. The above results are shown in the table below. Comparative Example 2 A covered wire was obtained in exactly the same manner as in Comparative Example 1, except that polyethylene having a density of 0.955 and a melt index of 3.0 was used. Similar tests were conducted on this covered wire, and the results are shown in the same table. Although some melt fracture was observed in the molded product of this comparative example, it was acceptable. Comparative Example 3 Using the polyethylene of Comparative Example 2, 100 parts thereof,
2 parts vinyltrimethoxysilane, 1,3-bis(tert-butylperoxy-isopropyl)
A covered wire was obtained in the same manner as in Comparative Example 1, except that the grafting reaction was carried out in the same manner as in Comparative Example 1 using a mixture of 0.12 parts of benzene and 0.1 part of hydroquinone. Similar tests were conducted on this coated wire, and the results are shown in the same table. Comparative Examples 4 to 6 In place of the hydroquinone in Comparative Example 3, methylhydroquinone (Comparative Example 4), 2,5-ditertiabutyl-hydroquinone (comparative example 5), 4,4′-thiobis(6-tertiarybutyl-3) Comparative Example 3 except that methylphenol) (same 6) was used.
The same procedure as above was carried out, and the results are shown in the same table. Example 1 In Comparative Example 3, instead of hydroquinone, mono(α-methylbenzyl)phenol and di(α-
The same procedure as in Comparative Example 3 was carried out except that 0.1 part of a mixture of methylbenzyl)phenol and tri(α-methylbenzyl)phenol was used, and the results are shown in the same table. Examples 2 to 9 In place of hydroquinone in Comparative Example 3, N,
N'-di-2-naphthyl-p-phenylenediamine (Example 2), poly(2,2,4-trimethyl-1,2 dihydroquinoline) (Example 3), nickel dibutyldiocarbamate (Example 4) , pentaerythrityl-tetrakis [3-(3,5-dithyabutyl-4-hydroxyphenol)propionate] (same 5), 2,2'-thiodiethylbis-
[3-(3,5-dithyabutyl-4-hydroxyphenyl)-propionate] (same 6),
Tris(3,5-dithyabutyl-4-hydroxybenzyl)isocyanate (same 7), the following formula, (In the formula, Y is ) are listed as (8), and 1, 3, 5
-trimethyl-2,4,6-tris(3,5-dithyabutyl-4-hydroxybenzyl)benzene was used in the same manner as in Comparative Example 3, and the results are shown in the table. The polyethylene used in Comparative Example 2 was prepared in advance.
A 0.8 mm conductor was extruded and coated with a film thickness of 0.5 mm using an extruder with L/D = 22 set at a temperature of 140 to 190°C, and the obtained covered wire was tested in the same manner as above, and the results are shown in the table. It was shown to.

[Table] According to the results in the above table, Comparative Example 2 has a lower moldability than Comparative Example 1 due to a lower melt index, and this can be improved by adding various anti-aging agents. . However, on the other hand, the environmental stress cracking resistance deteriorates, such as cracks occurring after being immersed in xylene at 90°C for three months. On the other hand, by adding the above-mentioned specific compound that can be used in the present invention according to Examples 1 to 9, that is, the anti-aging agent, the above-mentioned decrease in the melt index was significantly suppressed, and the above-mentioned decrease in the environmental stress cracking resistance was almost completely suppressed. It is clear that this is not acceptable.

Claims (1)

[Claims] 1. Melt index is 0.6 to 3.0, density is 0.945
The above polyethylene and the general formula RR′SiY ₂ (wherein R is a monovalent olefinic unsaturated hydrocarbon group or a hydrocarbonoxy group, Y is a hydrolyzable organic group, and R′ contains aliphatic unsaturation. a silane compound that is released by a monovalent hydrocarbon group, a group Y or hydrogen); a compound that generates free radical sites in the polyethylene resin at a temperature of 140°C or higher; -Methylene-bis(2,6-di-tert-butyl-phenol), 2,6-di-tert-butyl-alpha-
dimethylamino-p-cresol), hexamethylene glycol bis[β-(3,5
6-(4-hydroxy-3,5-jeter-shyary-butyl-anilino)-2,4-bis-octyl-thio 1,3, 5-triazine, N,N'-hexamethylene-bis(3,5-di-tertiary-butyl-4-hydroxy-hydroxy-hydroxy-hydrocinnamide), 3,5-di-tertiary-butyl-4- Hydroxy-benzylphosphoric acid diethyl ester, bis(3,5-di-tertiary-butyl-4-
nickel salt of hydroxybenzoylphosphoric acid monoethyl ester), 1,3,5-tri-methyl-2,4,6-tris(3,5-di-tert-shari-butyl-4-hydroxy-benzyl)benzene , Tetrakis [methylene-3 (3,5-di-tert-butyl-4-hydroxy-phenyl)
proponate] methane, n-octadecyl-3-(4'-hydroxy-
3′,5′-jeter-shari-butylphenol) propionate, tris(3,5-je-ter-shari-butyl-4)
-hydroxy-phenyl) isocyanurate, one or two of tris[β-(3,5-di-tert-butyl-4-hydroxy-phenyl)propionyl-oxyethyl] isocyanurate
A polyethylene characterized in that a graft-modified polyethylene obtained by reacting at least one species with: is melt-molded in the presence of a silanol condensation catalyst, and the resulting molded product is crosslinked by exposing it to an atmosphere containing moisture. Method of manufacturing molded products.