JPH04153235A - Production of silane-grafted polyethylene foam - Google Patents

Abstract

PURPOSE:To obtain the title foam of excellent heat resistance by rapid crosslinking, by molding a composition comprising a silane-grafted PE, a thermally decomposable blowing agent, an organic peroxide and a specified compound into a sheet, crosslinking and expanding the sheet by heating, and post- crosslinking it. CONSTITUTION:A composition comprising a silane-grafted PE (e.g. vinyltrimethoxysilane-grafted PE), a thermally decomposable blowing agent (e.g. azodicarbonamide), an organic peroxide (e.g. dicumyl peroxide) and a compound having at least one C-C unsaturated bond (e.g. trimethylol-propane trimethacrylate) is molded into a sheet, crosslinked, expanded by heating, and post-crosslinked.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a silane-grafted polyethylene foam that quickly undergoes the crosslinking necessary for foaming and has excellent heat resistance.

[Prior Art] As a method for producing a polyolefin crosslinked foam such as polyethylene, a vinyltrialkoxy resin having a functional group that can be graft copolymerized with a polyolefin and that can react and bond with each other through hydrolysis and dehydration condensation is used. Using a silane compound such as silane, a thermally decomposable blowing agent is kneaded into a reactive resin into which a functional group is introduced by graft copolymerizing the silane compound to obtain a foamable resin composition, and the composition is formed into a sheet. Methods for crosslinking and foaming after molding are known.

Foams made from such silane-grafted polyethylene are widely used in a variety of fields due to their excellent heat resistance, surface smoothness, and whiteness, and the ability to manufacture thick products. . However, when producing silane-grafted polyethylene foam, in order to obtain the degree of crosslinking that provides the viscoelasticity necessary for foaming, it is necessary to press it into a sheet and then expose it to a water environment for a long time, which is not efficient. do not have. Although the crosslinking time can be shortened by adding a silanol condensation catalyst such as an organotin compound, it is not sufficient. The crosslinking rate can be increased by further increasing the amount of catalyst or using a catalyst with higher catalytic activity, but in this case, a partial crosslinking reaction proceeds in the extruder, resulting in poor surface properties, which is not preferable. .

In order to solve these problems, Japanese Patent Application Laid-Open No. 63-207
No. 833 contains a specified amount of silane-grafted polyethylene,
A foam product with excellent heat resistance is produced by extruding a composition consisting of a specific amount of low-density polyethylene, an organic peroxide, and a silanol condensation catalyst into a sheet, heating and foaming it, and then treating it with water and crosslinking it again. It is disclosed that the following can be obtained. According to this method, the degree of crosslinking necessary for foaming is obtained using the organic peroxide, so the process from extrusion to foaming takes a short time, and a high degree of crosslinking is obtained by water treatment after foaming, which shows good heat resistance. However, since the content of silane-grafted polyethylene is limited, it is difficult to say that sufficient heat resistance is obtained.

[Problem to be solved by the invention]

An object of the present invention is to provide a method for producing a silane-grafted polyethylene foam that quickly performs the crosslinking necessary for foaming and has excellent heat resistance.

As a result of intensive research to solve the problems of the prior art, the present inventors have discovered that a polyethylene containing silane-grafted polyethylene, a pyrolytic blowing agent, an organic peroxide, and one or more carbon-carbon unsaturated bonds. After forming a composition containing the compound into a sheet shape, crosslinking and foaming is performed by heating,
Subsequently, the inventors discovered that the above object could be achieved by post-crosslinking with water, and based on this knowledge, the present invention was completed.

[Means for Solving the Problems] Thus, according to the present invention, a composition containing a silane-grafted polyethylene, a pyrolytic blowing agent, an organic peroxide, and a compound having one or more carbon-carbon unsaturated bonds is provided. Provided is a method for producing a silane-grafted polyethylene foam, which comprises forming the foam into a sheet, crosslinking and foaming it by heating, and then post-crosslinking.

The present invention will be explained in detail below.

(Silane-grafted polyethylene) The silane-grafted polyethylene used in the present invention includes polyethylene, a vinyl group, and -3i (OR).

Bond [where R is a hydrogen atom or an alkyl group,
n represents an integer of 2 to 3] in the presence of a free radical generator.

Examples of free radical generators used here include organic peroxides such as benzoyl peroxide, dicumyl peroxide, and lauroyl peroxide, t-butylperoxy-2ethylhexylhexanoate, and t-butylperoxyisomer. Examples include organic peresters such as butyrate.

Examples of the silane compound include vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, and vinyltris(2-methoxyethoxy)silane.

(Pyrolytic foaming agent) The pyrolytic foaming agent used in the present invention includes azodicarbonamide, which is commonly used in the production of polyethylene foam,
Compounds such as N,N'-dinitrosopentamethylenetetramine, benzenesulfonylhydrazide, toluenesulfonylhydrazide, azobisisobutyronitrile, N,N'-dimethyl N,N'-dinitroterephthalamide and the like are used.

The amount of the pyrolytic blowing agent used is usually in the range of 2 to 40 parts by weight, preferably 5 to 40 parts by weight, per 100 parts by weight of the resin.
It is 30 parts by weight.

(Organic peroxide) The organic peroxide used in the present invention preferably has a half-life decomposition temperature (1 minute) in the range of 140 to 200°C, more preferably in the range of 150 to 180°C. be. Specifically, dicumyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di(t-butyloxy)
Hexane and the like are preferably used.

In addition, the blending amount is 0.1 parts by weight per 100 parts by weight of the resin.
A range of 5 parts by weight is preferred.

(Compound Having a Carbon-Carbon Unsaturated Bond) In the present invention, a compound having one or more carbon-carbon unsaturated bonds is added to promote crosslinking of polyethylene by the organic peroxide.

As such compounds, (meth)acrylic acid derivatives are mainly used. Specifically, monofunctional (meth)acrylic acid derivatives have the general formula % (where R1 is a hydrogen atom or a methyl group, and R3
is a hydrogen atom or an alkyl group), or cyclohexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, glycidyl (meth)acrylate, 2 -Ethoxyethyl (meth)acrylate, 2-phenoxyethyl (meth)acrylate, etc., and polyfunctional (meth)acrylate, etc.
As acrylic acid derivatives, ethylene glycol (meth)acrylate, diethylene glycol (meth)acrylate, triethylene glycol (meth)acrylate, tetraethylene glycol (meth)acrylate, 1
．． 3-butylene glycol (meth)acrylate, 1.4
Butanediol di(meth)acrylate, 1,6-hexanethiol di(meth)acrylate, neobentyl glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, zinc(meth)acrylate, pentaerythritol tetra(meth)acrylate, ) acrylate, trimethylolpropane tri(meth)acrylate, and the like.

Among the above, polyfunctional (meth)acrylic acid derivatives are more preferable because they have higher reactivity.

The compounding amount of these compounds having carbon-carbon unsaturated bonds is usually 0.1 to 10 parts by weight per 100 parts by weight of the resin.
Preferably it is 0.5 to 5 parts by weight. If the amount is less than 0.1 parts by weight, crosslinking with the organic peroxide will not proceed sufficiently, making it difficult to generate uniform cells during foaming, while if it exceeds 10 parts by weight, the polyethylene itself will It is not preferable because the properties are not easily reflected in the properties of the foam and the physical properties such as chemical resistance and alkali resistance deteriorate.

(Optional Components) The composition of the present invention may contain a silanol condensation catalyst, if necessary. Any commonly used silanol condensation catalyst may be used; however, when using the silanol condensation catalyst, the amount of catalyst, Care must be taken when adding the catalyst.

The composition of the present invention may contain, if necessary, a foaming aid such as an aliphatic metal salt or zinc white that improves the decomposition properties of the foaming agent, an antioxidant, a coloring agent, a flame retardant, a filler, etc. You can.

(Method for producing foam) To obtain a crosslinked polyethylene foam using the above composition, first, the composition is heated at a temperature above the melting temperature of the resin and below the half-life decomposition temperature (1 minute) of the organic peroxide. Extrude into a sheet. Then, heating to a temperature above the half-life decomposition temperature of the organic peroxide, and then heating above the decomposition temperature of the blowing agent, or
Alternatively, a foam can be obtained by heating the foam all at once to a temperature higher than the decomposition temperature of the foaming agent. The foam is further heated with steam, hot water, moisture in the air, etc. to promote the silanol condensation reaction, and the degree of gelation (degree of crosslinking) is usually 70 to 9.
It is approximately 0%, and has extremely excellent heat resistance.

〔Example〕

The present invention will be explained in more detail below by giving Examples and Comparative Examples. The methods for measuring physical properties in Examples and Comparative Examples are as follows.

<Crosslinking degree> Cut a small amount of the foam, immerse it in xycin at 120°C for 24 hours, leave it for 24 hours, take out the undissolved part, and
After vacuum drying at ℃ for 2 hours, the weight was measured, and the ratio (%) to the initial foam weight was calculated and shown.

<Status of foam> The surface of the obtained foam and the uniformity of the cells were visually observed and evaluated on the following three scales.

○: Clear and beautiful with uniform bubbles.

Δ: Smooth and beautiful with uniform bubbles, but there are some fine irregularities due to broken bubbles.

×: The surface was rough due to broken bubbles, and the bubbles were not uniform.

Heating dimensional stability> The dimensional change rate after being left in an oven at 120°C for 22 hours was measured.

[Example 1] Low density polyethylene (MI
: 4.5, density: 0.923), 2.0 parts by weight of vinyltrimethoxysilane and 0.15 parts by weight of dicumyl peroxide were mixed in a mixer, and the raw material input temperature of the extruder was 140°C. From the middle to the mold side 200~22
The product was extruded at 0° C., pelletized, and vinyltrimethoxysilane was grafted to produce the desired silane-grafted polyethylene.

Silane-grafted polyethylene 100 parts by weight Azodicarbonamide 15 parts by weight Dicumyl peroxide 0.6 parts by weight Trimethylol bripant trimethacrylate 2 parts by weight Antioxidant 0.4 parts by weight Pigment:
T i Oa 1 part by weight The above composition was put into a 65 mmφ single screw extruder, extruded through a T die at a relatively low temperature so as not to decompose the blowing agent, and then extruded into a 2.5 m diameter
A foamable resin composition sheet having a thickness of m was prepared. The extrusion rate at this time was 25 kg/h, and the temperature conditions were set at 120°C, 140'C, and 135°C from the raw material input side toward the tip. Then, the obtained foamable resin composition sheet was
The foam was cross-linked and foamed by heating at 30° C. for 3 minutes, and then post-crosslinked by immersing it in hot water at 90° C. for 2 hours to obtain the desired foam.

[Example 2] 2 parts by weight of zinc stearate and 0.2 parts by weight of dibutyltin dilaurate were further added and extruded into a sheet at 180°C.
A foam was obtained in the same manner as in Example 1, except that it was heated for 2 minutes at 230 °C, then heated at 230 °C for 1 minute to crosslink and foam, and then immersed in hot water at 90 °C for 20 minutes to perform post-crosslinking. Ta.

[Comparative Example 1] Same as Example 1 except that low density polyethylene (MI: 4.5, density 0.923) was used instead of silane grafted polyethylene.

[Comparative Example 2] A foam was obtained in the same manner as in Example 1 except that trimethylolpropane triacrylate was not added.

[Comparative Example 3] A foam was obtained in the same manner as in Example 1 except that dicumyl peroxide and trimethylolpropane triacrylate were not added.

The results of measuring the physical properties of the foams obtained in the above Examples and Comparative Examples are summarized in Table 1.

[Effects of the Invention] Since the foam made from the composition of the present invention contains a compound having a carbon-carbon unsaturated bond, crosslinking with an organic peroxide is efficiently performed and the crosslinking necessary for foaming is achieved. degree is achieved quickly. Further, by water treatment after heating and foaming, crosslinking of the silane-grafted polyethylene by silanol condensation progresses, resulting in a highly crosslinked foam, which has excellent heat resistance. Therefore, the foam according to the present invention is extremely useful as a heat insulating material used in high-temperature environments such as hot water pipe covers and cooler piping.

Claims (1)

[Claims] 1. Silane grafted polyethylene, pyrolytic foaming agent,
A composition containing an organic peroxide and a compound having one or more carbon-carbon unsaturated bonds is formed into a sheet shape, and then crosslinked and foamed by heating, followed by post-crosslinking. A method for producing a silane-grafted polyethylene foam.