JPS6237660B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to an improvement in a method for producing a silane-crosslinked polyolefin molded product. Silane crosslinked polyolefin molded products have attracted particular attention in recent years because they do not require expensive and large-scale crosslinking equipment, unlike crosslinked polyolefin molded products made using organic peroxide crosslinking methods or electron beam irradiation. be. As a method for obtaining such a silane crosslinked polyolefin molded product, for example, the method described in Japanese Patent Publication No. 1711/1982 is well known, but in general, crosslinked molded products are produced industrially as follows. It is being said. (1) For polyolefins, 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' is a group R or a group Y or hydrogen) and free A radical generating substance is mixed and kneaded at a temperature of 180 to 235°C to obtain a silane-grafted polyolefin. (2) A mixture of a separately prepared polyolefin masterbatch containing a silanol condensation catalyst and the silane-grafted polyolefin obtained in (1) is shaped to obtain a desired molded product. (3) The method for producing a crosslinked polyolefin molded product, in which the uncrosslinked silane-grafted polyolefin molded product thus obtained is crosslinked by exposing it to an atmosphere in the presence of moisture, has the following drawbacks: . (i) As mentioned above, there are relatively many processing steps and the work is complicated. (ii) Since the silane-grafted polyolefin described above undergoes crosslinking even in the presence of a trace amount of moisture, its storage period is short and strict moisture control is required. (iii) If the crosslinking proceeds due to the influence of a small amount of moisture during the molding in (2) above, there is a risk that the appearance of the molded product will deteriorate and further the tensile properties will be significantly reduced. Particularly when carbon, clay, flame retardants, etc. are mixed, molding becomes difficult. (iv) When carrying out the step (3) above on an industrial scale, equipment and time are required to expose the molded body to a moisture atmosphere in order to promote crosslinking, which impedes continuous productivity. (v) Silane crosslinking by the catalyst masterbatch mixing method generally tends to locally concentrate the crosslinking points due to disproportionation of the mix, and as a result, it is difficult to obtain a uniform crosslinking density. For this reason, it is difficult to apply it to foam products, films that require a stretching process, and crosslinked products such as tubes. In order to overcome the drawbacks of such a catalyst masterbatch method, for example, the silane-grafted polyolefin obtained as described above is suitably shaped into a molded product, the molded product is directly immersed in a silanol condensation catalyst solution, and then brought into contact with moisture. A method of crosslinking (for example, Japanese Patent Publication No. 51-9283) has also been proposed. However, in this method, the immersion process in the silanol condensation catalyst takes time for the catalyst to permeate, resulting in inconvenience in continuity with the molding process, which is a serious cause of reducing productivity. Ta. The inventors conducted intensive studies to solve these drawbacks, and found that by immersing a molded product made of the silane-grafted polyolefin in a mixture of a silanol condensation catalyst and a solvent, the inside of the catalyst molded body was removed. The small amount of water present in the mixed liquid causes smooth crosslinking, and as a result, as mentioned above, in the conventional method, (1), (2), (3) and 3.
This invention was completed by discovering a method for producing a crosslinked polyolefin molded article, which shortened the manufacturing method that required several steps to one step. That is, this invention provides (a) an olefinic polymer, and (b) a 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′ is a group R or a group Y or hydrogen) a silane compound,
(c) A molded article made of a silane-grafted polyolefin obtained by grafting the olefin-based polymer with a compound that generates a free radical site at a temperature of 140°C or higher is combined with a silanol condensation catalyst and an aromatic hydrocarbon-based polymer. This is a method for producing a crosslinked polyolefin molded product, which is characterized by immersing the molded product in a mixed solution with a solvent. In this invention, the above components (a), (b), and (c) are extruded into a desired shape using an extruder to simultaneously perform silane grafting and molding of the polyolefin. The biggest feature is that a molded product is obtained, and this silane-grafted polyolefin molded product is continuously passed through a mixed solution of a silanol condensation catalyst and a solvent to cause crosslinking at once, thereby obtaining a directly crosslinked molded product in one step. Although it is a traditional method, silane grafted polyolefin is prepared separately using the conventional method.
After obtaining a desired molded article using this graft polymer, the effect of speeding up the crosslinking process can also be obtained by continuously treating this molded article with a pre-catalyst-solvent mixture. In this invention, polyolefin-based polymers are polyolefin-based homopolymers such as polyethylene, polybutene-1, polypropylene, etc., or polyolefin-based polymers such as ethylene propylene copolymer, ethylene vinyl acetate copolymer, and ethylene ethyl acrylate copolymer. Copolymers, chlorinated polyethylene, ionomers such as DuPont's Surlyn (trade name), derivatives of polyolefin polymers such as chlorosulfonated polyethylene, natural rubber, butyl rubber, butadiene rubber, chloroprene rubber, styrene-butadiene rubber, etc. This refers to polymers obtained by hydrogenating hydrocarbon rubber to eliminate double bonds except for aromatic rings. Next, as the silane compound according to the above general formula and the compound capable of generating a free radical site in the polyolefin used in the present invention, those described in the above-mentioned Japanese Patent Publication No. 1711-1982 are used, namely, the former is Vinyltriethoxysilane, vinyltrimethoxysilane, etc., and the latter include dicumyl peroxide, benzoyl peroxide, dichlorobenzoyl peroxide, etc. These are used in an amount of 0.5 to 1% by weight for the former and 0.05 to 0.2% by weight for the latter based on the polyolefin polymer. Next, as the silanol condensation catalyst used in this invention, the well-known dibutyltin dilaurylate, dibutyltin diacetate, stannous acetate, lead naphthenate, tetrabutyl titanate, etc. can be used, but especially Dibutyltin dilaurylate and dibutyltin diacetate are preferred, and it is desirable that they are soluble or uniformly dispersed in the solvent described below. The solvent to be mixed with the silanol condensation catalyst is desirably one that has an affinity for the olefinic polymer used and the catalyst, that is, a good solvent, and is effective if it has appropriate volatility. As the most specific example, when the polyolefin is polyethylene and the catalyst is dibutyltin dilaurylate, aromatic hydrocarbon solvents such as benzene, toluene, xylene, decalin, and tetralin are used. Such a solvent should be appropriately selected depending on the type of polyolefin polymer used, its manufacturing method, the shape of the molded product, etc., but it may be a mixed solvent of two or more of these. The amount of the silanol condensation catalyst to be mixed with the solvent cannot be determined unconditionally depending on the shape, wall thickness, processing speed, etc. of the molded article, but it is preferably in the range of 0.1 to 80% by weight. If the amount is below this lower limit, silane crosslinking may become insufficient, while if the concentration is too high to exceed the upper limit, product characteristics may be adversely affected, both of which are undesirable. The temperature at which the molded product is treated with this mixed solution is preferably as high as the temperature at which the molded product does not melt or undergo thermal deformation. This activates the diffusion of the catalyst and promotes the crosslinking reaction. In fact, the temperature of this mixed solution is preferably below the melting temperature of the silane-grafted polyolefin and at least 20°C higher than the glass transition temperature; for example, in the case of silane-grafted polyethylene, it is 5 to 100°C below the melting temperature.
is suitable. The time for passing through the molded article with this mixed solution varies depending on the thickness of the molded article, the type of solvent, the treatment temperature, etc., but is usually from several seconds to several minutes. Treatment for too short a time will result in insufficient crosslinking, while treatment for too long will result in a loss of industrial benefits. Next, as mentioned above, the crosslinked polyolefin molded product according to the present invention can improve its tensile properties, and this is thought to be due to the crosslinking treatment with the mixture of the silanol condensation catalyst and solvent. That is, in general, in silane crosslinking of such polyolefins, localization of the crosslinking tends to occur. Such localized crosslinking significantly reduces the appearance and elongation properties of the crosslinked product. For example, when using polyethylene, as shown in the formula below,
The alkoxysilane grafted onto polyethylene (in the formula, polyethylene chains are indicated by 〓〓〓) has three crosslinking points (encircled by dotted lines). If the crosslinking catalyst is inappropriately dispersed, the crosslinking points will tend to concentrate near the catalyst, resulting in localized crosslinking. In the method of this invention, since the catalyst is diluted with a solvent, the diffusion of the catalyst is made uniform,
It seems that the localization of the crosslinks is prevented and the properties are improved. Next, in the present invention, other polymers that are compatible with and physically blendable with the olefinic polymer can also be mixed as an extender. Of course, these auxiliaries may be added at any stage as long as they do not inhibit the graft reaction, have silanol catalytic action, or release moisture, but if any of these actions If it has, it is desirable to add it after the grafting reaction is completed. Furthermore, other auxiliaries such as carbon black, talc, calcium carbonate, foaming agents, lubricants, UV stabilizers,
Heavy metal deterioration inhibitors, colorants, voltage stabilizers, etc. may be used. As is clear from the above description, according to the present invention, the silane grafting step, molded article forming step, and silane crosslinking step can be performed as one step, and the work steps can be significantly simplified. As is clear from the above, it is possible to substantially eliminate the above-mentioned problems, such as improving the quality and properties of the resulting crosslinked polyolefin molded product, and its industrial value is extremely large. The present invention will be specifically explained below with reference to Examples. Example 1 Polyethylene (NUC9025, Nippon Unicar Co., Ltd.)
Using a mixture of 100 parts by weight, 2 parts by weight of vinyltrimethoxysilane, and 0.2 parts by weight of dicumyl peroxide, extrusion temperature was adjusted using an extruder for wire coating (L/D = 28, D = 1 inch) connected to a crosshead.
1mm at 210℃ and screw rotation speed 60 times/min
It was extruded and coated onto a copper wire with a thickness of 0.2 mm. This coated wire was immediately kept at 50-60°C. The wire was passed through a 4:6 mixed solution of dibutyltin dilaurylate and xylene for an immersion time of about 5 seconds, and then appropriately cooled and wound into a crosslinked polyethylene insulated wire. The appearance of the coating layer of the obtained insulated wire was observed, and it was peeled off to determine its gel fraction, etc. The results are shown in Table 1. Comparative Example 1 An insulated wire was obtained in exactly the same manner as in Example 1, except that instead of passing it through the dibutyltin dilaurylate-xylene mixture, the coated wire was immersed in dibutyltin dilaurylate kept at 80°C to 90°C for 1 hour. Ta. The obtained insulated wire was investigated in the same manner as in Example 1, and the results are shown in the same table. Comparative Example 2 Using polyethylene, vinyltrimethoxysilane and dicumyl peroxide. Silane-grafted polyethylene pellets were obtained using the same composition and the same extrusion conditions as in Example 1. Separately, 1 part by weight of dibutyltin dilaurylate was mixed with 100 parts by weight of polyethylene (described above) to obtain a pellet-like catalyst masterbatch. Next, using 95 parts by weight of the silane-grafted polyethylene and 5 parts by weight of this catalyst masterbatch,
Using the extruder used in Example 1, the coating was extruded onto a 1 mm diameter copper wire under the same conditions, and then immersed in hot water kept at 100° C. for 4 hours to cause crosslinking. The obtained covered wire was investigated in the same manner as in Example 1, and the results are shown in Table 1.

[Table] According to the results in the above table, the example product achieved the same degree of crosslinking as the comparative example product (1 hour or 4 hours) in an extremely short crosslinking time (5 seconds), and It was clear that the characteristics were superior. Comparative Example 3 In Example 1, the silane-grafted polyethylene insulated wire extruded using an extruder was not passed through the dibutyltin dilaurylate-xylene mixture, but the coated wire was left in the air at room temperature for 7 days, and then the coated wire was removed. When the layer was peeled off and the gel fraction was measured, the value was 0. Example 2 100 parts by weight of polyethylene (NUC-9025), 2 parts by weight of vinyltrimethoxysilane, 0.2 parts by weight of dicumyl peroxide, 4 parts by weight of calcined clay and 1 part by weight of carbon were thoroughly dried and mixed together with the above formulation. Mix and use an extruder for wire coating (L/D: 28D:
21/2 inch), extrusion temperature 210℃, screw rotation speed 45 times/min, 1mm wall thickness on 5.5mm diameter conductor.
The sample was coated by extrusion and immersed in the same catalyst-solvent mixture as in Example 1 for 15 seconds. The obtained insulated wire (OC) had an appearance comparable to that of the OC wire obtained by ordinary chemical crosslinking methods, and the degree of crosslinking was 65%, showing excellent properties. Comparative Example 4 Adding dibutyltin dilaurylate to the composition of Example 2
An attempt was made to produce a coated electric wire in the same manner as in Example 2 by adding 0.05 parts by weight, but the kneaded product had a rubber-like appearance, and proper coating could not be achieved, perhaps because the crosslinking reaction partially progressed in the extruder. Example 3 Polyethylene (YF-30 Mitsubishi Yuka Co., Ltd.) 100 parts by weight Blowing agent (azodicarbonamide) 17 Vinyltriethoxysilane 1.2 Dicumyl peroxide 0.1 The following composition was kneaded in an extruder and heated to 140°C. It was extruded into a sheet-like product under the following extrusion conditions. The sheet was immediately passed through a 1:1 mixture of dibutyltin dilaurylate and benzene (50-60 DEG C.) for a immersion time of 10 seconds, and the sheet was then placed in an infrared heating oven for foaming. The resulting foam sheet has a gel fraction of 56
%, the foam structure was composed of regular closed cells and the surface condition was good. Comparative Example 5 An insulated wire was obtained in exactly the same manner as in Example 2, except that instead of being immersed in the catalyst-solvent mixture for 15 seconds, it was immersed in dibutyltin dilaurylate kept at 80 to 90°C for 1 hour. When the degree of crosslinking was examined, it was found to be at the same level as in Example 2, although the gel fraction was 64% and a long time was required.

Claims (1)

[Claims] 1 (a) Polyolefin polymer and (b) 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′ is a group R or a group Y or hydrogen) a silane compound,
(c) A molded product made of a silane-grafted polyolefin obtained by grafting the above olefin polymer with a compound that generates free radical sites at a temperature of 140°C or higher, and a silanol condensation catalyst and an aromatic hydrocarbon solvent. A method for producing a crosslinked polyolefin molded article, which comprises immersing it in a mixed solution of