JPS6058251B2 - Method for producing silane crosslinked polyolefin molded product - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved method for producing a silane-crosslinked polyolefin molded product, and more particularly, to an improved method for producing a silane-crosslinked polyolefin molded product without impairing the extrusion processability of the silane-grafted polyolefin. The present invention relates to a method for quickly crosslinking in the presence of moisture.

Recently, silane-grafted polyolefins have been developed to have heat resistance,
It is being applied to the production of pipes, foams, films, etc. that have excellent physical and mechanical properties such as stress crack resistance.

Its industrial manufacturing method involves adding a silane coupling agent and a free radical generator to a polyolefin resin, mixing the mixture at high temperature in an extruder to produce a silane graft polyolefin, and then separately adding a master material containing a silanol condensation catalyst. By manufacturing a batch, then extruding the mixture of pellets of the silane-grafted polyolefin and catalyst masterbatch, and then immersing the molded product in water or exposing it to an atmosphere in the presence of water vapor. A crosslinked polyolefin molded article is obtained. It is also being considered to directly mix the silanol condensation catalyst into a silane-grafted polyolefin without making it into a masterbatch, extrude it, and then crosslink it in the same manner as the above method. However, in the above production method, when the silane graft olefin and the silanol condensation catalyst are mixed and extruded, the crosslinking reaction proceeds in the extruder even if there is only a small amount of water in the mixture. Due to the increase in the molecular weight of the silane-grafted polyolefin and the accompanying decrease in the melt index value, extrusion moldability is extremely deteriorated.

That is, melt fracture occurs and the surface smoothness of the molded product is impaired.

Furthermore, the resin may gel in the extruder and partially stagnate, eventually making extrusion impossible. In addition, in order to avoid the deterioration of extrusion moldability as described above, if a silanol condensation catalyst with weak catalytic ability is used or the amount of catalyst added is reduced, the crosslinking reaction rate of the molded product after extrusion molding will be reduced. , industrial practicality will be impaired.

The present invention was achieved as a result of intensive studies aimed at solving the above-mentioned problems, achieving good extrusion moldability, and quickly completing the crosslinking reaction of the molded product after extrusion. It is something.

That is, the gist of the present invention is to add an organotin compound and acetylacetone to a silane grafted polyolefin and mold it.
The present invention relates to a method for producing a silane-crosslinked polyolefin molded article, which is characterized in that crosslinking is then carried out in the presence of moisture.
The silane-grafted polyolefin used in the present invention can be obtained by melt-kneading a resin composition in which an alkoxysilane compound having an unsaturated group in an olefin resin and a free radical generator is blended at a temperature higher than the decomposition temperature of the free radical generator. obtained by.

The above-mentioned alkoxysilane compounds having an unsaturated group include those having at least one unsaturated hydrocarbon group, such as a vinyl group or an allyl group, or having at least one hydrocarbonoxy group, such as an acrylic group or a methacrylic group. It is a general term for organosilicon compounds having at least two alkoxy groups such as methoxy, ethoxy, or butoxy groups.

Particularly suitable are silane compounds in which the unsaturated group is a vinyl group and the alkoxy group is a methoxy group or an ethoxy group,
Specifically, vinyltrimethoxysilane or vinyltriethoxysilane is preferred. Examples of free radical generators include organic peroxides such as benzoyl peroxide, dicumyl peroxide, and lauroyl peroxide, and t-butylperoxy-2.
Examples include organic peresters such as ethylhexylhexanoate and t-butylbaroxyisobutyrate.

In addition, the above-mentioned polyolefin resin includes polyethylene,
Ethylene-propylene copolymer, ethylene-propylene-diene terpolymer, ethylene-vinyl acetate copolymer, chlorinated polyethylene, etc. are used.

Further, as the organotin compound in the present invention, one having high catalytic activity is preferable, and for example, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin dioctate, etc. are used.

The method of adding an organotin compound and acetylacetone to a silane-grafted polyolefin involves mixing the organotin compound and acetylacetone with the polyolefin resin used to produce the silane-grafted polyolefin to form a masterbatch. Although it is preferable for manufacturing purposes, the additive may be added directly to the grafted polyolefin.

However, in the latter case, it is necessary to thoroughly mix the organotin compound and acetylacetone in advance, and if necessary, add the heated mixture to the silane-grafted polyolefin. This is because if the organotin compound and acetylacetone are separated, the crosslinking reaction of the silane grafted polyolefin by the condensation catalyst will proceed during extrusion molding, and the advantage of good extrusion moldability in the present invention will be lost. The organic tin compound is preferably added in an amount of 0.01 parts by weight or more per 10 parts of silane-grafted polyethylene. If the amount of the organotin compound added is too small, the condensation crosslinking reaction of the molded product will not be sufficiently promoted, making it industrially unusable. When using an organotin-based compound as the organotin-based compound, since the organotin-based compound has extremely high catalytic activity, 0.0 parts by weight per 10 parts by weight of the silane-grafted polyolefin.
1 part by weight - 2. It is preferable to add it within the rutting area.
Even if more than 2.0 parts by weight is added, there is little practical advantage and it is economically disadvantageous.

Particularly preferably, the amount is in the range of 0.01 part by weight to 0.5 part by weight. It is preferable to add acetylacetone in an amount equal to or more than the same molar ratio as the organotin compound.

Although it varies depending on the type of organotin compound used, it is necessary to add 0.1 part by weight or more in order to obtain an equimolar amount. Further, the amount of acetylacetone added is preferably 10 parts by weight or less. If too much acetylacetone is added,
Resin slips in the extruder during molding. In this way, the method of the present invention improves the extrusion processability of the resin composition by adding a mixture of an organotin compound and acetylacetone mixed in advance to the silane-grafted polyolefin, and at the same time improves the extrusion processability of the resin composition, and at the same time, the molded product is freed from moisture. This makes it possible to have no adverse effect on the reaction rate when crosslinking is carried out in the presence of the compound.

This is because the catalytic activity of the organotin compound is suppressed in the extruder, where the amount of water present in the resin composition is very small, due to the interaction between the acetylacetone added and the organotin compound. Crosslinking does not proceed and the molded product is exposed to water or a steam atmosphere in the next step, and the presence of sufficient water in the surrounding area releases the affinity between the organotin compound and acetylacetone, resulting in the formation of an organotin compound. It is thought that this occurs as a result of the activation of the catalytic activity. The silanol condensation reaction is promoted by either acidic or basic catalysts, and organotin-based compounds as Lewis acids have a particularly remarkable effect, but when the molded product is exposed to a moisture atmosphere, organotin-based compounds Even if the acetylacetone acting on the compound dissociates, acetylacetone, which is a neutral compound, does not change the acidity of the organotin compound, and therefore crosslinking is thought to proceed rapidly.

In the present invention, crosslinking of the extruded product can be easily achieved by simply leaving it in a hot water or steam atmosphere, but preferably at a temperature of 80°C or higher.

In addition, it is not a problem to add other additives such as a stabilizer, a lubricant, a foaming agent, etc. as necessary in carrying out the present invention. The method for producing a silane-crosslinked polyolefin molded product of the present invention involves adding an organotin compound and acetylacetone to a silane-grafted polyolefin, and then crosslinking it in the presence of moisture, so it has good moldability and moldability. The subsequent crosslinking reaction is completed quickly, resulting in a molded product with excellent appearance and physical properties.

The method of the present invention includes heat-resistant vibrators, wire sheathing materials, heat-resistant films,
It is useful for manufacturing foams etc. by mixing blowing agents.

The present invention will be explained below with reference to Examples.

Example: 10 parts of high-pressure polyethylene with a density of 0.924 and a melt index of 2.0, and 1 part of vinyltrimethoxysilane.
．． A mixture of 5 parts by weight and 0.15 parts by weight of dicumyl peroxide was extruded at a set temperature of 160 to 220°C to obtain silane grafted polyethylene.

Separately, for 100 parts by weight of the same polyethylene as above, 2 parts by weight of dibutyltin dilaurate and 2 parts by weight of acetylacetone.
．． The blend to which the heel portion was added was melt-kneaded using an extruder to obtain masterbatch pellets. Thereafter, 95 parts by weight of silane grafted polyethylene and 5 parts by weight of catalyst masterbatch were mixed and extrusion molded at a set temperature of 120 to 150°C to obtain a sheet-like molded product.

Furthermore, the sheet was immersed in warm water at 80° C. for two spacings to obtain a silane crosslinked polyethylene sheet.

The appearance, state during extrusion molding, and progress of crosslinking of the silane crosslinked polyethylene sheet were as shown in Table 1.

Comparative Example 1 A sheet was molded using only the same silane grafted polyethylene as obtained in the example, and the sheet-like molded product was immersed in hot water in the same manner as in the example.

The appearance of the sheet, its condition during extrusion molding, and the progress of crosslinking were as shown in Table 1. Comparative Example 2 A mixture of 10 parts of the same polyethylene used in Example and 2 parts by weight of dibutyltin dilaurate was melt-kneaded in an extruder to obtain catalyst masterbatch pellets.

Claims (1)

[Claims] 1. A method for producing a silane-crosslinked polyolefin molded product, which comprises adding an organotin compound and acetylacetone to a silane-grafted polyolefin, molding the product, and then crosslinking it in the presence of moisture. 2. Production of a silane-crosslinked polyolefin molded product according to claim 1, in which 0.01 parts by weight or more of an organotin compound and 0.1 parts by weight or more of acetylacetone are added to 100 parts by weight of the silane-grafted polyolefin. Method.