JP2016148002A - Polyolefin crosslinked foam molded body, polyolefin crosslinking foam molded body and manufacturing method thereof, and polyolefin crosslinked foam product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyolefin crosslinked foam molded body excellent in heat resistance and, if needed, mechanical strength and flame retardancy and excellent in appearance even with highly filling metal hydrate and a manufacturing method capable of manufacturing the molded body by an inexpensive extrusion foaming method, a polyolefin crosslinking foam molded body capable of manufacturing the polyolefin crosslinked foam molded body and a manufacturing method therefor and a polyolefin crosslinked foam product.SOLUTION: There are provided a manufacturing method having a process (i) of melting and mixing a polyolefin resin, organic peroxide, metal hydrate and a silane coupling agent at specific mass ratio to prepare a molten mixture and a process (ii) of foam molding the molten mixture while melting with using an extruder in a presence of a foaming agent, a polyolefin crosslinked foam composition manufactured by the same and a polyolefin crosslinking foam molded body and a polyolefin crosslinked foam product.SELECTED DRAWING: None

Description

  The present invention relates to a polyolefin cross-linked foamed molded product, a polyolefin cross-linkable foamed molded product, a method for producing the same, and a polyolefin cross-linked foamed product.

  Products made of polyolefin cross-linked foam are industrially used in a wide range of applications, including construction and civil engineering materials such as joint materials and roofing materials, heat insulating materials for air conditioners or refrigerators, industrial materials such as pipe covers, and automobile interior materials. ing.

Products used for these applications are required to have characteristics such as heat resistance. For example, in order to obtain a product having excellent heat resistance, a material obtained by crosslinking a polyolefin resin is used.
Conventionally, as a method for crosslinking a polyolefin-based resin, there is a method using chemical crosslinking such as electron beam crosslinking or silane crosslinking. Of these, the silane crosslinking method is preferably used as a method for crosslinking a polyolefin resin because it is a method in which a polyolefin resin is not crosslinked at the time of extrusion foaming but is brought into contact with moisture after extrusion foaming.
For example, in Patent Document 1, a base resin mainly composed of a resin composed of a silyl-modified polypropylene resin and a polypropylene resin is kneaded together with a foaming agent under heating and pressure conditions to obtain a foamable melt, A process for producing a crosslinked polypropylene resin foam is described in which a foam is obtained by extruding the melt into a low pressure region, and then the foam is brought into contact with moisture in the presence of a silanol condensation catalyst to form a crosslinked foam. .
In Patent Document 2, a base resin composed of 60 to 97% by weight of a polyolefin resin and 3 to 40% by weight of a silane crosslinkable polyolefin resin, a crosslinking catalyst, a crosslinking agent, and a foaming agent are melt-kneaded in an extruder. However, a process for producing a polyolefin-based resin foam is described in which a crosslinking reaction is allowed to proceed to a gel fraction of 25% in an extruder to cause extrusion foaming.

In addition to heat resistance, the products used for the above applications are also required to have properties such as mechanical properties (preferably mechanical strength) and flame retardancy. In order to impart heat resistance, mechanical properties and flame retardancy to the product, not only is the polyolefin resin crosslinked, but also an inorganic filler is added to the polyolefin resin at a high content, for example, 50 parts by mass relative to 100 parts by mass of the polyolefin resin. It is effective to fill (highly fill) with ˜150 parts by mass.
However, if the inorganic filler is highly filled in the electron beam crosslinking method or the chemical crosslinking method, it becomes difficult to foam-mold the polyolefin resin itself.
Even if the polyolefin resin can be foam-molded, the inorganic filler may fall off during foam molding or post-processing. Here, dropping off of the inorganic filler means that the inorganic filler that has been in contact with the resin in the foam is not in contact with the foam. When the inorganic filler is removed in this manner, the heat resistance, mechanical strength, or flame retardance expected of the crosslinked foam is not exhibited. In addition, the appearance tends to deteriorate. On the other hand, if the filling amount of the inorganic filler is suppressed, foam molding becomes possible and an excellent appearance can be imparted, but the crosslinked foam is inferior in heat resistance, mechanical strength and flame retardancy.

  In the silane crosslinking methods described in Patent Documents 1 and 2, it is not assumed that the inorganic filler is highly filled, and the polyolefin resin is highly filled with the inorganic filler and the specific method and conditions thereof are described. Absent. That is, Patent Document 1 describes that an inorganic filler can be added up to 40% by mass of the total weight (paragraph [0062] of the same document). However, in the examples, only 1.0% by mass of talc is added as a bubble regulator. In Example 4 of Patent Document 2 (paragraph [0043] of the same document), aluminum hydroxide trihydrate is used as a cross-linking agent. It is only added.

  As described above, in the conventional foam molded body, in order to enable foam molding and to give the foam molded body an excellent appearance, it is necessary to reduce the content of the inorganic filler, sufficient heat resistance, machine Strength and flame retardancy could not be imparted to the foamed molded product.

Japanese Patent No. 38677941 Japanese Patent No. 3520909

The present invention overcomes the problems of conventional silane cross-linking methods, has excellent heat resistance, and if necessary, has excellent mechanical strength and flame retardancy, and has excellent cross-linking properties even when highly filled with metal hydrates It is an object of the present invention to provide a foamed molded article and a production method capable of producing the polyolefin crosslinked foamed molded article by an inexpensive extrusion foaming method.
Moreover, this invention makes it a subject to provide the polyolefin crosslinkable foaming molding which can manufacture the polyolefin crosslinked foaming which has said outstanding characteristic, and its manufacturing method.
Furthermore, this invention makes it a subject to provide the polyolefin crosslinked foamed product containing a polyolefin crosslinked foaming molding.

  As a result of various studies on the above problems, the present inventors previously melt-mixed a metal hydrate, a silane coupling agent, a polyolefin-based resin, and an organic peroxide so that the metal hydrate is a silane coupling agent. When a molten mixture containing a polyolefin resin supported via a metal is prepared, the molten mixture can be foam-molded in the presence of a foaming agent even if a high content of metal hydrate is added to the polyolefin resin. In addition, the present inventors have found that a polyolefin crosslinked foamed article having a crosslinked structure can be formed. Furthermore, it has been found that this polyolefin cross-linked foam molded article has excellent heat resistance and appearance, as well as mechanical strength and flame retardancy. Based on this finding, the present inventors have further studied and have completed the present invention.

The object of the present invention has been achieved by the following means.
(1) 0.01 to 0.6 parts by mass of organic peroxide, 20 to 200 parts by mass of metal hydrate, and 0 to silane coupling agent with respect to 100 parts by mass of polyolefin resin and 100 parts by mass of polyolefin resin (I) a step of melt-mixing 5 to 15.0 parts by mass of the organic peroxide at a decomposition temperature or higher to prepare a molten mixture;
(Ii) a step of foam-molding in the presence of a foaming agent while melting the molten mixture using an extruder to obtain a foam-molded product;
And a step (iii) of bringing the foam-molded article into contact with moisture to cross-link (iii).
(2) The method for producing a polyolefin crosslinked foamed article according to (1), wherein the step (ii) is foam-molded in the presence of a foaming agent while melt-mixing the molten mixture and the silanol condensation catalyst.
(3) The method for producing a polyolefin crosslinked foamed article according to (1) or (2), wherein the foaming agent is a physical foaming agent.
(4) The method for producing a polyolefin crosslinked foamed article according to any one of (1) to (3), wherein the step (iii) is performed at a temperature of 15 to 30 ° C.
(5) A polyolefin crosslinked foamed article produced by the method for producing a polyolefin crosslinked foamed article according to any one of (1) to (4) above,
(I) including a polyolefin resin and 20 to 200 parts by mass of a metal hydrate with respect to 100 parts by mass of the polyolefin resin,
(II) The metal hydrate is supported on the polyolefin resin by a chemical bond via a silane coupling agent,
(III) The polyolefin-based resin has a crosslinked structure, and the gel fraction is 50% or more,
(IV) A polyolefin crosslinked foamed article having an expansion ratio of 1.5 to 10 times.
(6) The polyolefin cross-linked foamed molded article according to (5), wherein the polyolefin resin is a resin of polyethylene or polyethylene copolymer.
(7) The polyolefin crosslinked foamed article according to (5) or (6), wherein the metal hydrate is magnesium hydroxide or aluminum hydroxide.
(8) A polyolefin crosslinked foamed product including the polyolefin crosslinked foamed article according to any one of (5) to (7) above.
(9) 0.01 to 0.6 parts by mass of organic peroxide, 20 to 200 parts by mass of metal hydrate, and 0 to silane coupling agent with respect to 100 parts by mass of the polyolefin resin and 100 parts by mass of the polyolefin resin. (I) a step of melt-mixing 5 to 15.0 parts by mass of the organic peroxide at a decomposition temperature or higher to prepare a molten mixture;
And a step (ii) of obtaining a foamed molded product by foaming in the presence of a foaming agent while melting the molten mixture using an extruder.
(10) A polyolefin crosslinkable foamed molded article produced by the method for producing a polyolefin crosslinkable foamed molded article described in (9) above.

  In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

According to the present invention, a polyolefin cross-linked foamed article having excellent heat resistance and excellent appearance even when highly filled with a metal hydrate can be produced by an inexpensive extrusion foaming method. Furthermore, according to the present invention, a polyolefin crosslinked foamed article having at least one of excellent mechanical strength and flame retardancy can be produced by an extrusion foaming method, if necessary, in addition to heat resistance and appearance.
Therefore, according to the present invention, a polyolefin crosslinked foamed article having excellent heat resistance and appearance, and if necessary, mechanical strength and flame retardancy, and the polyolefin crosslinked foamed article for an inexpensive extrusion foaming method. The manufacturing method which can be manufactured can be provided. In addition, a polyolefin crosslinkable foamed molded article capable of forming a polyolefin crosslinked foamed mold having the above-described excellent characteristics and a method for producing the same can be provided. Furthermore, a polyolefin crosslinked foamed product including the polyolefin crosslinked foamed article having the above-described excellent characteristics can be provided.

Hereinafter, preferred embodiments of the present invention will be described.
Both the “method for producing a polyolefin cross-linked foamed molded product” and the “method for producing a polyolefin cross-linkable foamed molded product” of the present invention perform at least the following steps (i) and (ii). Therefore, the “method for producing a polyolefin cross-linked foamed molded product” of the present invention and the “method for producing a polyolefin cross-linkable foamed molded product” of the present invention will be described together below. May be referred to as a manufacturing method.)

Step (i): 0.01 to 0.6 parts by weight of organic peroxide, 20 to 200 parts by weight of metal hydrate, and silane coupling agent with respect to 100 parts by weight of polyolefin resin and polyolefin resin A step of preparing a molten mixture by melt-mixing 0.5 to 15.0 parts by mass with an organic peroxide decomposition temperature or higher Step (ii): A foaming agent while melting the molten mixture using an extruder Process of foam molding in the presence of

First, each component used for the manufacturing method of this invention is demonstrated.
(A) Polyolefin-based resin The polyolefin-based resin is not particularly limited as long as the silane coupling agent has a site capable of grafting reaction. Preferably, the resin which consists of a polymer obtained by superposing | polymerizing or copolymerizing the compound which has an ethylenically unsaturated bond is mentioned. Examples of such a resin include polyethylene, polypropylene, and polyethylene copolymer resins. Here, the polyethylene copolymer may be a copolymer of ethylene and a compound having an ethylenically unsaturated bond other than ethylene, such as an ethylene-α-olefin copolymer, an ethylene component and an acid copolymer. Examples thereof include a polyethylene copolymer having a component or an acid ester copolymer component.
Of these, polyethylene or a polyethylene copolymer resin is preferred because of its high acceptability for metal hydrates and the ability to maintain mechanical strength even when a large amount of metal hydrates are blended. Polyethylene or ethylene-α-olefins are preferred. A copolymer resin is more preferred.
In the present invention, the content of each polymer and copolymer is determined within the following content range so that the total content is 100% by mass.
In the present invention, the polyolefin resin may be used alone or in combination of two or more.

The polyethylene is not particularly limited as long as it is a polymer containing an ethylene component as a constituent component. For example, high density polyethylene (HDPE), low density polyethylene (LDPE), ultrahigh molecular weight polyethylene (UHMW-PE), linear low Examples thereof include density polyethylene (LLDPE) and very low density polyethylene (VLDPE). Among these, high density polyethylene (HDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE) are preferable.
The content of the resin made of polyethylene in the polyolefin resin is not particularly limited, but is preferably 0 to 100% by mass, more preferably 50 to 100% by mass in 100% by mass of the polyolefin resin. .

Although it does not specifically limit as an ethylene-alpha-olefin copolymer, Preferably, the copolymer of ethylene and C3-C12 alpha-olefin is mentioned. Specific examples of the α-olefin are not particularly limited, and examples thereof include propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-octene, 1-decene, and 1-dodecene. The ethylene-α-olefin copolymer is preferably an ethylene-propylene copolymer.
The content of the resin comprising the ethylene-α-olefin copolymer in the polyolefin resin is not particularly limited, but is preferably 0 to 50% by mass, and 0 to 30% by mass in 100% by mass of the polyolefin resin. % Is more preferable.

The polyolefin copolymer having an ethylene component and an acid copolymerization component or an acid ester copolymerization component is not particularly limited. Examples thereof include an ethylene-vinyl acetate copolymer (EVA), an ethylene- (meth) acrylic acid copolymer, an ethylene- (meth) acrylic acid alkyl copolymer, and the like. Among these, ethylene-vinyl acetate copolymer (EVA), ethylene-methyl acrylate copolymer, ethylene-ethyl acrylate copolymer, ethylene-butyl acrylate copolymer are preferable, and further metal hydrates From the viewpoint of acceptability and flame retardancy, it is particularly preferable to use an ethylene-vinyl acetate copolymer.
The content of the resin composed of the polyolefin copolymer in the polyolefin resin is not particularly limited, but is preferably 0 to 50% by mass, and 0 to 30% by mass in 100% by mass of the polyolefin resin. It is more preferable.

Polypropylene is not particularly limited as long as it is a resin made of a polymer containing a propylene component as a constituent component. Polypropylene resins include propylene homopolymer (h-PP), random polypropylene (r-PP) which is a copolymer with a small amount of ethylene and / or 1-butene, and rubber such as ethylene rubber. Block polypropylene (b-PP) dispersed in PP or r-PP is included. Among these, random polypropylene is preferable.
Examples of the polypropylene resin include Novatec (registered trademark) PP (manufactured by Nippon Polypro Co., Ltd.), PM940M, PM921V (both trade names, manufactured by Sun Allomer Co., Ltd.), Sumitomo Nobrene (registered trademark, manufactured by Sumitomo Chemical Co., Ltd.), and Prime Polypro. (Registered trademark, manufactured by Prime Polymer Co., Ltd.).
The content of the polypropylene resin in the polyolefin resin is not particularly limited, but is preferably 0 to 49% by mass, more preferably 0 to 30% by mass in 100% by mass of the polyolefin resin. -20 mass% is further more preferable.

(B) Organic peroxide An organic peroxide generates radicals by at least thermal decomposition, and a radical reaction between a grafting reaction site of a silane coupling agent described later and a polyolefin resin (hydrogen radicals from the polyolefin resin). It serves to cause a grafting reaction by a pulling reaction).
The organic peroxide is not particularly limited as long as it generates radicals. For example, the general formula: R ¹ —OO—R ² , R ³ —OO—C (═O) R ⁴ , R ⁵ C A compound represented by (═O) —OO (C═O) R ⁶ is preferred. Here, R ^{1 to} R ⁶ each independently represents an alkyl group, an aryl group, or an acyl group. Among R ^{1 to} R ⁶ of each compound, those in which all are alkyl groups or those in which any one is an alkyl group and the remainder is an acyl group are preferable.

  Examples of such organic peroxides include dicumyl peroxide (DCP), di-tert-butyl peroxide, 2,5-dimethyl-2,5-di- (tert-butylperoxy) hexane, , 5-Dimethyl-2,5-di (tert-butylperoxy) hexyne-3, 1,3-bis (tert-butylperoxyisopropyl) benzene, 1,1-bis (tert-butylperoxy) -3, 3,5-trimethylcyclohexane, n-butyl-4,4-bis (tert-butylperoxy) valerate, benzoyl peroxide, p-chlorobenzoyl peroxide, 2,4-dichlorobenzoyl peroxide, tert-butylperoxy Benzoate, tert-butyl peroxyisopropyl carbonate, diace Peroxide, lauroyl peroxide, may be mentioned tert- butyl cumyl peroxide and the like. Of these, dicumyl peroxide, 2,5-dimethyl-2,5-di- (tert-butylperoxy) hexane, 2,5-dimethyl-2,5-di in terms of odor and colorability. -(Tert-Butylperoxy) hexyne-3 is preferred.

The decomposition temperature of the organic peroxide is preferably 80 to 195 ° C, and more preferably 125 to 180 ° C.
In the present invention, the decomposition temperature of an organic peroxide means a temperature at which a decomposition reaction occurs in two or more compounds at a certain temperature or temperature range when an organic peroxide having a single composition is heated. means. Specifically, it refers to the temperature at which heat absorption or heat generation starts when heated from room temperature in a nitrogen gas atmosphere at a rate of temperature increase of 5 ° C./min by thermal analysis such as DSC method.

(C) Metal hydrate The metal hydrate is included in the inorganic filler. Among them, in the present invention, the metal hydrate has at least a site on the surface that can chemically bond with the reaction site of the silane coupling agent. Use. The site where the metal hydrate can be chemically bonded is not particularly limited, and examples thereof include a site where the reactive site of the silane coupling agent can be chemically bonded by hydrogen bonding or the like, or a site where the metal hydrate can be chemically bonded. Specific examples include OH groups (hydroxy groups, water molecules containing water or crystal water, OH groups such as carboxy groups), amino groups, and SH groups.
Examples of such metal hydrates include hydrated water, crystal water, and metal compounds having a hydroxyl group. Examples thereof include aluminum hydroxide, magnesium hydroxide, calcium silicate, magnesium silicate, aluminum borate whisker, hydrated aluminum silicate, hydrated magnesium silicate, basic magnesium carbonate, hydrotalcite and the like.

  As the metal hydrate, a surface-treated metal hydrate that has been surface-treated in advance can also be used. As the surface-treated metal hydrate that has been surface-treated in advance, a metal hydrate that has been surface-treated with a silane coupling agent described later, a metal hydrate that has been surface-treated with something other than a silane coupling agent described later, a fatty acid or Examples thereof include metal hydrates surface-treated with phosphate esters. The surface treatment amount of the surface-treated metal hydrate is not particularly limited, but is preferably 5% by mass or less, and more preferably 2% by mass or less. The lower limit is preferably 0.5% by mass or more.

  The average particle size of the metal hydrate is preferably 0.01 to 10 μm, more preferably 0.1 to 5 μm, and still more preferably 0.5 to 3 μm. If the average particle size of the metal hydrate is less than 0.01 μm, the metal hydrates tend to agglomerate with each other, and the mechanical properties and flame retardancy tend to decrease. There exists a tendency for the reinforcement effect and flame retardance by addition to fall. In addition, an average particle diameter means the average value calculated | required from the particle size of 100 metal hydrates measured by TEM, SEM, etc.

A metal hydrate may be used individually by 1 type and may use 2 or more types together.
Among the above, the metal hydrate is preferably magnesium hydroxide or aluminum hydroxide in terms of flame retardancy.

(D) Silane Coupling Agent In the present invention, the silane coupling agent is a grafting reaction site (group or atom) that can be grafted to the polyolefin resin in the presence of radicals generated by the decomposition of the organic peroxide. And at least a reactive site (including a site generated by hydrolysis, such as a silyl ester group) that reacts with a site where metal hydrate can chemically bond. As such a silane coupling agent, conventionally, a silane coupling agent used in a silane crosslinking method is exemplified, and examples thereof include a silane coupling agent represented by the following general formula (1).

In general formula (1), R _a11 is a group containing an ethylenically unsaturated group, and R _b11 is an aliphatic hydrocarbon group, a hydrogen atom, or Y ¹³ . Y ¹¹ , Y ¹² and Y ¹³ are each an independently hydrolyzable organic group. Y ¹¹ , Y ¹² and Y ¹³ may be the same as or different from each other.

Examples of R _a11 include a vinyl group, an allyl group, a (meth) acryloyloxyalkylene group, and a p-styryl group, and a vinyl group is preferable.

R _b11 is an aliphatic hydrocarbon group, a hydrogen atom or Y ¹³ described later, and the aliphatic hydrocarbon group is an aliphatic hydrocarbon group other than an aliphatic unsaturated hydrocarbon group, and preferably has 1 carbon atom. -8 monovalent aliphatic hydrocarbon groups. R _b11 is preferably Y ¹³ described later.

Y ¹¹ , Y ¹² and Y ¹³ are hydrolyzable organic groups, and examples thereof include an alkoxy group having 1 to 6 carbon atoms, an aryloxy group having 6 to 8 carbon atoms, and an acyloxy group having 1 to 4 carbon atoms. It is done. Of these, an alkoxy group having 1 to 4 carbon atoms and an acyloxy group having 1 carbon atom (OCOCH ₃ )) are preferable, and an alkoxy group having 1 or 2 carbon atoms is more preferable. Specific examples of the hydrolyzable organic group include a methoxy group, an ethoxy group, a butoxy group, an acetyloxy group, and a (meth) acrylooxy group. Among these, a methoxy group or an ethoxy group is preferable from the viewpoint of reactivity.

The silane coupling agent is preferably a silane coupling agent having a high hydrolysis rate, more preferably R _b11 is Y ¹³ and Y ¹¹ , Y ¹² and Y ¹³ are the same as each other. It is. Specific examples of such silane coupling agents include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltributoxysilane, vinyldimethoxyethoxysilane, vinyldimethoxybutoxysilane, vinyldiethoxybutoxysilane, and allyltrimethoxysilane. And vinyl silanes such as allyltriethoxysilane and vinyltriacetoxysilane, and (meth) acryloxysilanes such as methacryloxypropyltrimethoxysilane, methacryloxypropyltriethoxysilane, and methacryloxypropylmethyldimethoxysilane.
Among the silane coupling agents, a silane coupling agent having a vinyl group and an alkoxy group at the terminal is more preferable, and vinyltrimethoxysilane and vinyltriethoxysilane are particularly preferable.
A silane coupling agent may be used individually by 1 type, and may use 2 or more types together. Further, it may be used as it is or diluted with a solvent or the like.

(E) Silanol condensation catalyst In the production method of the present invention, a silanol condensation catalyst is used in step (iii) for the purpose of causing a condensation reaction between the silane coupling agents grafted to the polyolefin resin in the presence of moisture. May be. Based on the action of this silanol condensation catalyst, crosslinking between polyolefin resins is promoted through a silane coupling agent. When the polyolefin-based resins are cross-linked, a foamed molded article having excellent heat resistance, mechanical strength, and flame retardancy can be obtained.

  As the silanol condensation catalyst, an organic tin compound, a metal soap, a platinum compound, or the like is used. Common silanol condensation catalysts include, for example, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin dioctate, dibutyltin diacetate, zinc stearate, lead stearate, barium stearate, calcium stearate, sodium stearate, Lead naphthenate, lead sulfate, zinc sulfate, organic platinum compounds and the like are used. Among these, organic tin compounds such as dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin dioctiate, and dibutyltin diacetate are particularly preferable.

<Carrier resin>
The silanol condensation catalyst can be used alone, but it can also be mixed with a carrier resin and used as a catalyst master batch. Although it does not specifically limit as carrier resin, The thing similar to the said polyolefin-type resin can be used, and a polyethylene resin is preferable at the point which has a good affinity with a silanol catalyst and a flame retardance. Specifically, the polyethylene resin includes linear low density polyethylene, low density polyethylene, ultra low density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, etc., linear low density polyethylene, low density polyethylene, ultra low density, etc. Polyethylene and high density polyethylene are preferred, and linear low density polyethylene is particularly preferred.

(F) Foaming agent In the manufacturing method of this invention, the foaming agent which foams a molten mixture in the case of foam molding is made to exist. The foaming agent may be a chemical foaming agent or a physical foaming agent, or both of them may be used.

  A chemical foaming agent is one that decomposes at a specific temperature or higher to generate gas. Specifically, in addition to organic blowing agents such as azodicarbonamide (ADCA), p, p′-oxybisbenzenesulfonyl hydrazide (OBSH), dinitrosopentamethylenediamine (DPT), sodium bicarbonate (sodium bicarbonate), Inorganic foaming agents such as sodium borohydride can be mentioned. Among these, azodicarbonamide or sodium bicarbonate is preferable from the viewpoints of gas generation amount, foam moldability, decomposition residue, and decomposition temperature.

The physical foaming agent is one that is vaporized by decompression when released from the outlet of the extruder while being pressurized in the extruder and dissolved in a polyolefin resin. Specifically, hydrocarbon blowing agents such as propane, butane and pentane, chlorinated hydrocarbon blowing agents such as dimethyl chloride and methylene chloride, chlorofluorocarbons, carbon dioxide, nitrogen gas, air, etc. An inorganic foaming agent is mentioned. Of these, propane, butane, carbon dioxide gas or nitrogen gas is preferred from the viewpoints of solubility in polyolefin resin, foam moldability, and environmental impact, and carbon dioxide gas is preferred because it can enhance safety during production. Or nitrogen gas is particularly preferable.
In the present invention, a physical foaming agent is preferred from the viewpoint of production cost.

(G) Additives In the production method of the present invention, additives such as antioxidants, lubricants, metal deactivators, flame retardant (auxiliary) agents, and the like can be appropriately blended within a range that does not impair the effects of the present invention. . When these additives are used, it is particularly preferable to add an antioxidant or a metal deactivator to the carrier resin so as not to inhibit the grafting of the silane coupling agent onto the polyolefin resin. The content of these additives is appropriately set as long as the object of the present invention is not impaired.

Flame retardant (auxiliary) and filler include carbon, clay, zinc oxide, tin oxide, titanium oxide, magnesium oxide, molybdenum oxide, antimony trioxide, silicone compound, quartz, talc, calcium carbonate, zinc borate, white carbon Etc.
Examples of the lubricant include hydrocarbons, siloxanes, fatty acids, fatty acid amides, esters, alcohols, metal soaps, and the like.

Next, the manufacturing method of this invention is demonstrated.
In the production method of the present invention, the step (i) of melt-mixing a polyolefin resin, an organic peroxide, a metal hydrate, and a silane coupling agent is performed.

  In the step (i), the content of the organic peroxide is 0.01 to 0.6 parts by mass, preferably 0.1 to 0.5 parts by mass with respect to 100 parts by mass of the polyolefin resin. . When the content of the organic peroxide is less than 0.01 parts by mass, the grafting reaction of the silane coupling agent to the polyolefin resin does not proceed and the silane coupling agent may be polymerized. On the other hand, when it exceeds 0.6 parts by mass, the silane coupling agent is likely to volatilize, or many of the polyolefin-based resin components are directly cross-linked by side reactions to form aggregates, and the appearance is May be inferior. That is, by setting the content of the organic peroxide within the above range, a grafting reaction can be performed within an appropriate range, and a molten mixture excellent in extrudability can be obtained without generating gel-like spots. Can do.

  Content of metal hydrate is 20-200 mass parts with respect to 100 mass parts of polyolefin resin, Preferably it is 50-150 parts. When the content of the metal hydrate is less than 20 parts by mass, the polyolefin cross-linked foamed molded article may not be provided with desired mechanical strength and flame retardancy even if the metal hydrate is supported on the polyolefin resin. . On the other hand, when it exceeds 200 parts by mass, melt mixing becomes difficult and extrusion foaming may become difficult.

  Content of a silane coupling agent is 0.5-15.0 mass parts with respect to 100 mass parts of polyolefin resin, Preferably it is 0.7-10.0 mass parts, More preferably, it is 1.2- 6.0 parts by mass. When the content of the silane coupling agent is less than 0.5 parts by mass, the grafting reaction does not proceed sufficiently, and the polyolefin cross-linked foamed molded article may not have the desired mechanical strength, heat resistance and flame retardancy. is there. On the other hand, if it exceeds 15.0 parts by mass, no more silane coupling agent can be adsorbed on the surface of the metal hydrate, and the silane coupling agent volatilizes during melt mixing, which is not economical. Moreover, the non-adsorbing silane coupling agent may condense, and the polyolefin cross-linked foamed product may be fuzzy or burnt to deteriorate its appearance. In particular, the appearance defect is remarkable when the content exceeds 15.0 parts by mass. In the first place, foam molding itself becomes difficult.

  As a method of melt mixing, for example, a single screw extruder, a twin screw extruder, a roll, a Banbury mixer, or various kneaders can be used. Of these, a closed mixer such as a Banbury mixer or various kneaders is preferable in terms of the dispersibility of the polyolefin resin and the stability of the grafting reaction.

The temperature for melting and mixing is equal to or higher than the decomposition temperature of the organic peroxide, preferably the decomposition temperature of the organic peroxide + (1 to 80) ° C. By melting and mixing the above components at this temperature, a polyolefin resin (silane graft polymer) in which a metal hydrate is supported via a silane coupling agent can be formed as described later. That is, when melt-mixing below the decomposition temperature of the organic peroxide, the silane grafting reaction does not occur and the silane graft polymer is not generated. Therefore, desired heat resistance and mechanical strength cannot be obtained. In addition, the organic peroxide may react (decompose) during extrusion foam molding, and a desired expansion ratio may not be obtained. The decomposition temperature at the time of melt mixing is preferably set after the polyolefin resin is melted.
Other conditions in the melt mixing can be appropriately determined. For example, the mixing time may be a time during which the grafting reaction of the silane coupling agent to the polyolefin resin sufficiently proceeds at the melting temperature, and is preferably, for example, 5 minutes to 1 hour.

  In the step (i), the mixing order of the polyolefin resin, organic peroxide, metal hydrate and silane coupling agent is not particularly limited. For example, these components can be melted and mixed simultaneously (once) in a closed mixer or the like. Also preferred is a method in which a metal hydrate and a silane coupling agent are mixed first, and the resulting mixture is mixed with a polyolefin resin and an organic peroxide. By such a mixing order (mixing method), the silane coupling agent can be efficiently adsorbed or reacted with the metal hydrate, and volatilization of the silane coupling agent during melt mixing can be suppressed. As a result, a silane graft polymer can be formed efficiently. Moreover, it can also prevent that the silane coupling agent which is not adsorb | sucked condenses and a puddle arises.

  On the other hand, as in the production methods described in Patent Documents 1 and 2, using a silyl-modified polypropylene resin or a silane crosslinkable polyolefin resin obtained by reacting a silane coupling agent or the like in advance, these resins and metal water are used. When a hydrate is mixed later, the silyl ester group of the silyl-modified polypropylene resin, etc., is fixed (bonded) at a low density (content) in the resin, so the surface of the metal hydrate It is difficult to contact the silyl ester group at a high density (high probability). As a result, metal hydrate cannot be bonded to almost all of the silyl ester groups.

  In step (i), it is preferable to melt and mix the components without substantially mixing the silanol condensation catalyst. Thereby, the condensation reaction of a silane coupling agent can be suppressed, it is easy to melt and mix, and a desired shape can be obtained during extrusion foaming. Here, “substantially not mixed” does not exclude the unavoidably existing silanol condensation catalyst, and is present to such an extent that the above-mentioned problem due to silanol condensation of the silane coupling agent does not occur. Means good. For example, in the step (i), the silanol condensation catalyst may be present as long as it is 0.01 part by mass or less with respect to 100 parts by mass of the polyolefin resin.

  Thus, when step (i) is performed, a molten mixture is prepared. This molten mixture contains the silane graft polymer described above. This silane graft polymer is an uncrosslinked product in which the silane coupling agent is not silanol condensed. In practice, partial cross-linking (partial cross-linking) is unavoidable, but at least the foam moldability in the foam molding in step (ii) is maintained.

In the production method of the present invention, when a silanol condensation catalyst is used, it is preferable to mix the molten mixture obtained in step (i) and the silanol condensation catalyst before performing foam molding in step (ii) described later.
The mixing of the molten mixture and the silanol condensation catalyst is not particularly limited as long as the silanol condensation catalyst is mixed with the molten mixture during foam molding of the molten mixture. For example, before performing step (ii), the molten mixture and the silanol condensation catalyst can be melt-mixed with an appropriate mixer. Further, the molten mixture and the silanol condensation catalyst can be charged into an extruder and melt-mixed in the extruder. In any case, the molten mixture and the silanol condensation catalyst can be melt-mixed and foam-molded. Mixing of the molten mixture and the silanol condensation catalyst can employ the melt mixing conditions of step (i).

  When the silanol condensation catalyst is used, the content of the silanol condensation catalyst is not particularly limited, and is preferably 0.0001 to 0.5 parts by mass, more preferably 0.001 to 0 parts with respect to 100 parts by mass of the polyolefin resin. .1 part by mass. When the content of the silanol condensation catalyst (E) is within the above range, the condensation reaction of the silane coupling agent can proceed rapidly to form a uniform crosslinked structure. Thereby, mechanical strength and heat resistance are expressed in the polyolefin cross-linked foamed molded article, and productivity is also improved. Furthermore, partial gelation is suppressed and the appearance and resin physical properties of the polyolefin crosslinked foamed article are excellent.

  The silanol condensation catalyst is preferably a mixture with a carrier resin. Although content of carrier resin to be used is not specifically limited, Preferably it is 1-50 mass parts with respect to 100 mass parts of polyolefin resin, More preferably, it is 1-25 mass parts. When the content of the carrier resin is 1 to 50 parts by mass, the dispersibility of the silanol condensation catalyst is improved, and the crosslinking reaction can be rapidly advanced. As a result, the appearance of the polyolefin crosslinked foamed article is excellent, and the mechanical strength and heat resistance are also excellent.

Next, in the production method of the present invention, the step (ii) of foam-molding in the presence of a foaming agent while melting the molten mixture using an extruder is performed.
Although it does not specifically limit as an extruder, A single screw extruder or a twin screw extruder can be used. Further, two extruders may be connected in series as in a tandem system, or a plurality of extruders may be connected in parallel as in multilayer extrusion. For foam molding, a T die, a hanger coat die, a rod die, a circular die, a deformed die, or the like can be used as a molding die.

Extrusion foaming is performed by setting the cylinder temperature (melting temperature) of the extruder to be equal to or higher than the temperature at which the polyolefin resin melts. Further, when a chemical foaming agent is used as the foaming agent, it is set at a temperature higher than the temperature at which the chemical foaming agent decomposes. The preferable cylinder temperature is the melting temperature of the polyolefin-based resin + (5-30) ° C. or the decomposition temperature of the chemical foaming agent + (5-30) ° C. By setting the cylinder temperature to the above temperature, the molten mixture can be melted before foam molding. In particular, when a silanol condensation catalyst or a blowing agent is used, the molten mixture obtained in step (i) and the silanol condensation catalyst or the blowing agent can be mixed.
The die temperature (foaming temperature) of the extruder can be adjusted as appropriate depending on the desired expansion ratio, and is set within the range of the melting temperature of the polyolefin resin −30 ° C. or more and the melting temperature of the polyolefin resin + 20 ° C. or less. be able to.

In the production method of the present invention, the melt mixture obtained in step (i) and the foaming agent are mixed before foam molding in step (ii) described later.
The mixing of the molten mixture and the foaming agent is not particularly limited as long as the foaming agent is mixed in the molten mixture during foam molding of the molten mixture. For example, before performing step (ii), the molten mixture and the foaming agent can be mixed with an appropriate mixer. Moreover, it is also possible to charge the molten mixture and the foaming agent together with the foaming agent or separately into the extruder and melt and mix in the extruder. In any case, the molten mixture can be foam-molded in the presence of a foaming agent.

When using a physical foaming agent, a physical foaming agent can be inject | poured into the cylinder part of an extruder from a gas cylinder. For example, you may inject | pour into a extruder directly from a gas cylinder, and you may inject | pour via a gas flow control apparatus and a pressure | voltage riser. The physical foaming agent can be injected by attaching a gas supply port from the middle part to the downstream part of the extruder cylinder part.
When a chemical foaming agent is used, the chemical foaming agent may be used alone, or when a catalyst masterbatch is used, it may be contained in the carrier resin.

The injection amount of the physical foaming agent and the addition amount of the chemical foaming agent are appropriately determined depending on the desired expansion ratio.
The injection pressure of the physical foaming agent is preferably in the range of 1 to 10 MPa, and the injection amount of the physical foaming agent is preferably in the range of 0.1 to 8% by mass in terms of gas concentration.
The addition amount of the chemical foaming agent can be appropriately determined depending on the desired expansion ratio. For example, it is preferable to set it as the range of 1-30 mL / g in conversion of the gas generation volume with respect to the mass of polyolefin resin.

  Thus, when process (ii) is performed, a polyolefin crosslinkable foaming molding is obtained as a foaming molding by which the melt mixture was foam-molded. This polyolefin crosslinkable foamed molded article contains an uncrosslinked silane graft polymer as in the case of the molten mixture. Therefore, the polyolefin crosslinked foamed molded product of the present invention is formed into a molded product that has been crosslinked or finally crosslinked by performing the step (iii).

In the method for producing a polyolefin cross-linked foam molded article of the present invention, the step (iii) of crosslinking the polyolefin cross-linkable foam molded article obtained by bringing it into contact with moisture is performed.
The process itself of this process (iii) can be performed by a normal method. By bringing the polyolefin crosslinkable foamed article into contact with moisture, a silane coupling agent possessed by the silane graft polymer in the polyolefin crosslinkable foamed molded article, in particular, a silane coupling agent that is not bonded to a metal hydrate described later. The silyl ester group is hydrolyzed and silanol condensed. Thereby, the crosslinked structure of the polyolefin resin through the silane coupling agent is formed, and a polyolefin crosslinked foamed article can be obtained.

In the step (iii), the silanol condensation reaction occurs even when the polyolefin crosslinkable foamed molded product is brought into contact with moisture under the condition of storing at normal temperature (15 to 30 ° C.). In order to further accelerate (accelerate) the silanol condensation reaction, the polyolefin crosslinkable foamed molded article can be positively brought into contact with moisture. For example, it is possible to employ a method of positively contacting water, such as immersion in warm water (40 to 60 ° C.), injection into a wet heat tank, exposure to water vapor, and the like. Moreover, you may apply a pressure in order to permeate | transmit a water | moisture content inside in that case.
The contact time can be appropriately set according to the progress of the silanol condensation reaction.

  Thus, the manufacturing method of the polyolefin crosslinked foaming molding of the present invention is carried out, and the polyolefin crosslinked foaming molding of the present invention is manufactured.

In the polyolefin cross-linked foam molded article of the present invention, the details of the excellent heat resistance and appearance, as well as the mechanism of mechanical strength and flame retardancy, and the influence on foam molding are not clear, but are considered as follows. It is done.
In the step (i), when a polyolefin resin, an organic peroxide, a metal hydrate, and a silane coupling agent are mixed, the reaction site contained in the silane coupling agent is a group that can be hydrolyzed. Part undergoes hydrolysis (when the hydrolyzable group is a silyl ester group or the like, it exists as a silanol group). The reaction site (hydrolyzed group, preferably silanol group) acts or reacts with a chemically bondable site on the surface of the metal hydrate to be physically or chemically adsorbed or bonded.
On the other hand, when polyolefin resin, organic peroxide, metal hydrate, and silane coupling agent are melt-mixed, the grafting reaction contained in the silane coupling agent starts from radicals generated by decomposition of organic peroxide. A site (preferably an ethylenically unsaturated group) undergoes a grafting reaction at a site where a polyolefin resin can be grafted.
Due to the reaction between the silane coupling agent and the metal hydrate and the grafting reaction between the silane coupling agent and the polyolefin resin, the metal hydrate is converted into a polyolefin resin by chemical bonding via the silane coupling agent. It is believed that a supported structure can be taken (a silane graft polymer is formed).

Next, when the molten mixture containing the silane graft polymer is subjected to extrusion foaming in the presence of a blowing agent (step (ii)), when the molten mixture is released from the outlet of the extruder, bubbles grow while spreading outward. . Specifically, when the molten mixture in which the gas generated from the physical blowing agent gas or the gas generated from the chemical blowing agent is released from the outlet of the extruder, the gas is bubbled by the reduced pressure to form the silane graft polymer in the molten mixture. Bubbles grow while spreading.
At this time, if the polyolefin resin and the metal hydrate are only mixed (when no silane coupling agent is used), the metal hydrate exists alone and causes friction at the interface with the polyolefin resin. . Thereby, the melt viscosity and melt tension of the molten mixture (melted in the extruder) before foam molding are increased. For this reason, during bubble growth, the melt tension of the polyolefin resin is superior to the expansion force of the gas, and the gas cannot push the polyolefin resin outward and escapes from the polyolefin resin ( Degassing). As a result, the polyolefin-based resin does not foam sufficiently, and a high expansion ratio cannot be obtained.
However, in the present invention, a silane coupling agent and an organic peroxide are used. Therefore, as described above, the metal hydrate is supported on the polyolefin resin via the silane coupling agent. In this case, the ratio of the interface between the metal hydrate and the polyolefin resin is smaller than when the silane coupling agent is not used. Thereby, the melt viscosity and melt tension of the melt mixture before foam molding are similarly lowered. For this reason, at the time of bubble growth, the melt tension of the silane graft polymer can be balanced to the same extent with respect to the expansion force of the gas, and the gas can appropriately spread the silane graft polymer. As a result, it is considered that the metal hydrate can be highly filled into the polyolefin resin, and the silane graft polymer can be sufficiently foamed to obtain a high expansion ratio.

A part of the silane coupling agent not bonded to the metal hydrate among the silane coupling agents grafted to the polyolefin resin is present in the polyolefin cross-linkable foamed molded article thus foam-molded. The silyl ester groups of the silane coupling agent come into contact with moisture to cause hydrolysis and silanol condensation reaction. Thereby, the crosslinked structure of silane coupling agents is formed, and polyolefin resin is considered to bridge | crosslink.
On the other hand, among the silane coupling agents grafted to the polyolefin resin, a silane coupling agent bonded to a metal hydrate hardly causes a condensation reaction between silyl ester groups. However, it is considered that when a plurality of silane coupling agents are bonded to one metal hydrate, the polyolefin resins are cross-linked through the metal hydroxide and the silane coupling agent.

  Thus, the polyolefin cross-linked foamed molded article is highly filled with metal hydrate and the polyolefin resin has a cross-linked structure. Therefore, it can be excellent in all of heat resistance, mechanical strength, flame retardancy, and appearance.

The polyolefin cross-linked foam molded article of the present invention preferably satisfies the following (I) to (IV) in addition to the above-described excellent characteristics.
(I) The polyolefin cross-linked foamed molded article contains 20 to 200 parts by mass of a polyolefin resin and a metal hydrate with respect to 100 parts by mass of the polyolefin resin.
(II) All or part of the metal hydrate is supported on the polyolefin resin by chemical bonding via a silane coupling agent. That is, it contains a silane graft polymer obtained by grafting a silane coupling agent to which a metal hydrate is bonded to a polyolefin resin.

(III) The polyolefin-based resin has a crosslinked structure, and the polyolefin crosslinked foamed article has a gel fraction of 50% or more.
Examples of the crosslinked structure of the polyolefin resin include a crosslinked structure between silane coupling agents by silanol condensation reaction, a crosslinked structure through a plurality of silane coupling agents bonded to one metal hydrate, and the like. .

In the present invention, the cross-linking of the polyolefin resin can be evaluated and confirmed by the gel fraction of the polyolefin cross-linked foamed molded article. In the present invention, the gel fraction is 50% or more, preferably 60% or more, and more preferably 70% or more. When the gel fraction is in the above range, it can be confirmed that the polyolefin-based resin forms a crosslinked structure. Moreover, the heat resistance of the polyolefin cross-linked foamed molded article is excellent.
The gel fraction is calculated by subtracting the content of inorganic hydrate in mass measurement (the mass ratio of xylene-insoluble matter (impregnated at 120 ° C. for 24 hours)) with respect to the mass of the polyolefin crosslinked foamed product. .) The measurement method and conditions will be described later. The gel fraction can be set within a predetermined range depending on the amount of the crosslinking agent, the crosslinking conditions, and the like.

  (IV) The expansion ratio of the polyolefin cross-linked foamed molded product is 1.5 to 10 times, preferably 2 to 8 times. If the expansion ratio is less than 1.5, the light weight effect as a foam may be reduced. On the other hand, if it exceeds 10 times, the desired mechanical strength may not be obtained. A method for measuring the expansion ratio will be described later. The expansion ratio can be set within a predetermined range depending on the amount of the foaming agent, the temperature at the time of foaming, the pressure, and the like.

The polyolefin crosslinked foamed article has a plurality of bubbles. The bubbles may be continuous bubbles that are continuous with other adjacent bubbles, or may be independent bubbles that are not continuous with other adjacent bubbles.
The cell diameter of the cells possessed by the polyolefin cross-linked foamed molded article is not particularly limited, but is preferably 10 to 2000 μm as the diameter measured by the following measurement method. If the bubble diameter exceeds 2000 μm, the mechanical strength may be insufficient. On the other hand, if it is less than 10 μm, the expansion ratio may be insufficient, or the open cell ratio may be too high.

A preferred form of the polyolefin cross-linked foamed article of the present invention will be described.
The external shape of the polyolefin cross-linked foamed molded product of the present invention is not particularly limited, such as a sheet shape and a rod strip, and can be applied as long as it can be molded with a die attached to an extruder.
Although it does not specifically limit as sheet | seat thickness in the case of a sheet form, or the rod diameter in the case of a rod strip, and a spherical diameter, it can be set to 0.1-100 mm by adjustment of die exit size etc.

The polyolefin crosslinked foamed product of the present invention may be a product containing the polyolefin crosslinked foamed product of the present invention. For example, it may be the polyolefin cross-linked foamed molded product itself of the present invention, or may be composed of the polyolefin cross-linked foamed molded product of the present invention and other members such as a support, a support frame and the like.
The polyolefin cross-linked foam molded product used in the polyolefin cross-linked foam product of the present invention may remain in the shape of the molded product obtained by the above production method, and the molded product obtained by the above production method may be extrusion foam molded. It may be formed into another shape immediately after or in a later step.
Although the use in which the polyolefin crosslinked foamed product of this invention is used is not specifically limited, Each use, such as the said construction civil engineering material, various heat insulating materials, industrial materials, and an automotive interior material, is mentioned suitably. Therefore, the shape and dimension of the polyolefin crosslinked foamed product of the present invention are set according to the application.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

<Example 1>
100 parts by mass of high-density polyethylene: HJ362 (trade name, manufactured by Nippon Polyethylene Co., Ltd.) as the polyolefin resin (A), and dicumyl peroxide: PERKADOX BC-FF (trade name, Kayaku Akzo) as the organic peroxide (B) 0.1 parts by mass (decomposition 179 ° C.) and magnesium hydroxide: Magseeds FK-621 (trade name, manufactured by Kamishima Chemical Co., Ltd., 1.0% by mass of vinyltrimethoxysilane) as metal hydrate (C) Surface treated product, average particle diameter 1.0 μm)) 60 parts by mass, and silane coupling agent (D) vinyltrimethoxysilane: KBM1003 (trade name, manufactured by Shin-Etsu Silicone) 5.5 parts by mass (Nippon Roll Manufacturing Co., Ltd .: 2L Intensive Mixer (Banbury Mixer)), heat-kneaded at 200 ° C. for 10 minutes (melt mixing) To obtain a molten mixture (step (i)).
The resulting molten mixture contained a silane graft polymer.

Next, a rod die (hole diameter 2 mm, land length 2 mm) is attached to the tip of a 40 mm single-screw extruder (FS-40 manufactured by Ikegai Co., Ltd., L / D (ratio of effective screw length L to diameter D) = 34), and the cylinder temperature The head temperature and die temperature were set to 150 ° C. and 128 ° C. Into this single screw extruder, the obtained molten mixture was charged, and carbon dioxide gas having a gas pressure of 5 MPa was injected into the cylinder part, and the molten mixture was injected at an injection amount of 1.6 mass%. It was extruded while being melted in the presence of carbon dioxide gas, and foam-molded. In this way, a rod-shaped polyolefin crosslinkable foamed molded article was obtained (step (ii)).
Subsequently, the polyolefin crosslinkable foamed article was impregnated in warm water in a constant temperature water bath at 60 ° C. for 72 hours to obtain a polyolefin crosslinked foamed body (step (iii)).

<Example 2>
A molten mixture was prepared in the same manner as in Step (i) of Example 1.
Next, the same extruder as that used in Example 1 was prepared, and the cylinder temperature was set to 150 ° C., the head temperature, and the die temperature were set to 132 ° C. Into this single-screw extruder, the obtained molten mixture was charged, and carbon dioxide gas having a gas pressure of 1.5 MPa was injected into the cylinder part, and the molten mixture was injected at a gas concentration of 0.2% by mass. Was extruded while being melted in the presence of carbon dioxide gas and subjected to foam molding. In this way, a rod-shaped polyolefin crosslinkable foamed molded article was obtained (step (ii)).
Subsequently, the polyolefin cross-linkable foamed article was impregnated with warm water under the same conditions as in Example 1 to obtain a polyolefin cross-linked foam (step (iii)).

<Example 3>
A molten mixture was prepared in the same manner as in Step (i) of Example 1.
In addition, 1 part by mass of dioctyltin dilaurate: KS-1200A-1 (trade name, manufactured by Sakai Chemical Industry Co., Ltd.) as the silanol condensation catalyst (E) and linear low density polyethylene: Novatec PE UE-320 (as carrier resin) 100 parts by mass of a product name (manufactured by Mitsubishi Oil Chemical Co., Ltd.) was melt mixed at 160 ° C. for 10 minutes using a 1 L kneader to prepare a catalyst master batch.
Next, the same extruder as that used in Example 1 was prepared, and the cylinder temperature was set to 150 ° C, the head temperature, and the die temperature were set to 135 ° C. Into this single screw extruder, 5 parts by mass of the catalyst masterbatch and 165.6 parts by mass of the above molten mixture (the content of the silanol condensation catalyst is 0.05 parts by mass with respect to 100 parts by mass of the polyolefin resin) In addition, carbon dioxide gas with a gas pressure of 1.5 MPa is injected into the cylinder part, and the molten mixture and the catalyst master batch are extruded while being melt-mixed in the presence of carbon dioxide gas at an injection amount of 0.5 mass%. And foamed. In this way, a rod-shaped polyolefin crosslinkable foamed molded article was obtained (step (ii)).
Subsequently, the polyolefin crosslinkable foamed molded article was impregnated with warm water in a constant temperature bath at 60 ° C. for 48 hours to obtain a polyolefin crosslinked foamed composition (step (iii)).

<Comparative Example 1>
100 parts by mass of high-density polyethylene: HJ362 (trade name, manufactured by Nippon Polyethylene) as the polyolefin resin (A), and magnesium hydroxide: Magseeds FK-621 (trade name, manufactured by Kamishima Chemical Co., Ltd.) as the metal hydrate (C) 60 parts by mass of a surface-treated product with 1.0% by mass of vinyltrimethoxysilane and an average particle diameter of 1.0 μm) was heated and kneaded with a BM mixer under the same conditions as in Example 1, and a magnesium hydroxide master batch Got.
Next, using the same extruder as in Example 1, the cylinder temperature was 150 ° C., the head temperature and the die temperature were 132 ° C., a magnesium hydroxide master batch was introduced, and carbon dioxide gas having a gas pressure of 3.0 MPa was injected into the cylinder part. And it extruded and foam-molded by the injection amount used as the gas concentration of 1.5 mass%. In this way, a rod-like foamed molded product was obtained.

<Comparative example 2>
Using the same extruder as in Example 1, the magnesium hydroxide master batch obtained in Comparative Example 1 was charged at a cylinder temperature of 150 ° C., a head temperature and a die temperature of 130 ° C., and carbon dioxide gas having a gas pressure of 4.0 MPa. Was injected into a cylinder part and extruded at an injection amount of a gas concentration of 1.8% by mass to perform foam molding. In this way, a rod-like foamed molded product was obtained.

  With respect to the polyolefin crosslinked foam and the crosslinked foam obtained in each example, the expansion ratio, the bubble diameter, the gel fraction, and the heat deformation ratio were measured, and the appearance was evaluated. The results are shown in Table 1 together with the content of each component and production conditions.

<Measurement of expansion ratio>
The expansion ratio of the polyolefin cross-linked foam or the cross-linked foam was calculated by the following formula using an underwater substitution method.
(Foaming ratio) = (Density of composition before foaming) / (Density of foaming composition)
Here, the composition before foaming means a composition that is in a molten state in step (ii), specifically, a molten mixture obtained in step (i), a silanol catalyst, a carrier resin, a foaming agent, and It is a mixture (molding material) with additives and the like. The foamed composition means a polyolefin crosslinkable foamed molded article.

<Measurement of bubble diameter>
Each polyolefin cross-linked foam or an arbitrary cross section of the cross-linked foam was cut out by freezing breakage and observed with a scanning electron microscope (SEM) to measure the cell diameter of the polyolefin cross-linked foam or cross-linked foam.
Specifically, in accordance with ASTM D3576-77, an SEM photograph of the cross section of each polyolefin cross-linked foam or cross-linked foam is taken, a straight line is drawn on the SEM photograph in the horizontal direction and the vertical direction, and these two straight lines cross. The length of the string of bubbles was measured and the average value t was determined. Assuming that the magnification of the photograph is M, the average bubble diameter d was determined by substituting it into the following equation.
d = t / (0.616 × M)

<Measurement of gel fraction>
Each polyolefin cross-linked foam or a test piece cut out from the cross-linked foam was put in a metal mesh bag, and the mesh bag was impregnated with xylene heated to 120 ° C. in a test tube for 24 hours. Thereafter, the mesh bag was taken out of the test tube and sufficiently dried. At this time, the mass of the insoluble matter before and after the impregnation and drying treatment was measured, and the value calculated by the following formula was taken as the gel fraction. However, the mass measurement was performed by subtracting the mass of magnesium hydroxide.
(Gel fraction%) = (Mass of insoluble matter after impregnation and drying treatment) / (Mass of test piece before impregnation and drying treatment) × 100
In the present invention, the gel fraction serves as an index of the formation and degree of crosslinking of the polyolefin resin, and is preferably 50% or more.

<Measurement of heating deformation rate>
For the polyolefin cross-linked foam of Example 1 having a high expansion ratio, a 50 mm long rod-shaped test piece was used. Moreover, about the polyolefin crosslinked foam of Example 2 and 3 made into low foaming ratio, and the crosslinked foam of Comparative Example 1 and 2, the 10 mm long rod-shaped test piece was used, respectively.
Each of these test pieces was tested by placing an iron of 1 kg in mass heated to 160 ° C. for 30 seconds. The rate of change of the thickness (diameter) of each test piece before and after this test was calculated from the following formula to obtain the heating deformation rate.
(Heat deformation rate%) = (Thickness after test) / (Thickness before test) × 100
In the measurement of the heat deformation rate of the present invention, 70% of the heat deformation rate in this test is an acceptable level in terms of heat resistance.

<Appearance test>
For the appearance evaluation of each polyolefin crosslinked foam or crosslinked foam, the surface property and shape were observed with the naked eye. Here, the surface property refers to the degree of unevenness on the surface of the polyolefin cross-linked foamed molded article, and the surface property is good (no problem in this test) means that the surface is uneven and smooth. The shape refers to the degree of swell of the shape of the polyolefin cross-linked foamed molded product (which does not deform the polyolefin cross-linkable foamed molded product and the like after step (ii)).
In the appearance test of the present invention, the case where the surface property is good and the shape is not wavy (the case where the polyolefin cross-linked foamed product is obtained as a rod-like product) is an acceptable level.

The following can be seen from the results in Table 1.
That is, in Examples 1 to 3, it was possible to obtain a polyolefin crosslinked foamed article having a good surface property (appearance) when the expansion ratio was 1.6 to 7.5. Moreover, this excellent appearance could be obtained even when as much as 60 parts by mass of magnesium hydroxide was used with respect to 100 parts by mass of the polyolefin resin.
Moreover, since the gel fraction was 50% or more, the above-mentioned crosslinked structure was sufficiently formed in the polyolefin resin contained in the polyolefin crosslinked foamed molded article. Since the polyolefin cross-linked foamed molded article contains a polyolefin cross-linked resin obtained by cross-linking such a polyolefin-based resin, excellent heat resistance with a heat deformation rate of 70% or more was obtained.

  On the other hand, Comparative Examples 1 and 2 did not use an organic peroxide and a silane coupling agent, and the foaming ratio did not increase to 2.4 times at the maximum. Moreover, even if it contained 60 mass parts of magnesium hydroxide, it was able to be extruded and foam-molded, but it was confirmed that the magnesium hydroxide was dropped from the polyolefin resin. Therefore, the polyolefin resin did not have a crosslinked structure, and the gel fraction was as low as 26%. Moreover, the heat deformation rate was 20% or less, which was a result inferior to Examples 1 to 3. In addition, in the crosslinked foams of Comparative Examples 1 and 2, undulation occurred, and it was impossible to obtain a rod-like crosslinked foam having a straight and good appearance.

  As described above, the polyolefin-based resin (molten mixture) highly filled with metal hydrate can be produced in a wide range of expansion ratio by the method for producing a polyolefin cross-linked foamed molded article of the present invention through steps (i) to (iii). It was shown that extrusion foam molding can be performed with good appearance, and finally a polyolefin cross-linked foam molded article having excellent heat resistance can be produced.

Claims (10)

0.01 to 0.6 parts by mass of organic peroxide, 20 to 200 parts by mass of metal hydrate, and 0.5 to 0.5 parts of silane coupling agent with respect to 100 parts by mass of polyolefin resin and 100 parts by mass of polyolefin resin. Step (i) of preparing a molten mixture by melting and mixing 15.0 parts by mass of the organic peroxide at a decomposition temperature or higher;
(Ii) a step of foam-molding in the presence of a foaming agent while melting the molten mixture using an extruder to obtain a foam-molded product;
And a step (iii) of bringing the foam-molded article into contact with moisture to cross-link (iii).   The method for producing a polyolefin crosslinked foamed article according to claim 1, wherein the step (ii) is foam-molded in the presence of a foaming agent while melt-mixing the molten mixture and the silanol condensation catalyst.   The method for producing a polyolefin crosslinked foamed article according to claim 1 or 2, wherein the foaming agent is a physical foaming agent.   The method for producing a polyolefin crosslinked foamed article according to any one of claims 1 to 3, wherein the step (iii) is performed at a temperature of 15 to 30 ° C. A polyolefin cross-linked foam molded article produced by the method for producing a polyolefin cross-linked foam molded article according to any one of claims 1 to 4,
(I) including a polyolefin resin and 20 to 200 parts by mass of a metal hydrate with respect to 100 parts by mass of the polyolefin resin,
(II) The metal hydrate is supported on the polyolefin resin by a chemical bond via a silane coupling agent,
(III) The polyolefin-based resin has a crosslinked structure, and the gel fraction is 50% or more,
(IV) A polyolefin crosslinked foamed article having an expansion ratio of 1.5 to 10 times.   The polyolefin cross-linked foamed molded article according to claim 5, wherein the polyolefin resin is a polyethylene or polyethylene copolymer resin.   The polyolefin crosslinked foamed article according to claim 5 or 6, wherein the metal hydrate is magnesium hydroxide or aluminum hydroxide.   A polyolefin crosslinked foamed product comprising the polyolefin crosslinked foamed article according to any one of claims 5 to 7. 0.01 to 0.6 parts by mass of organic peroxide, 20 to 200 parts by mass of metal hydrate, and 0.5 to 0.5 parts of silane coupling agent with respect to 100 parts by mass of polyolefin resin and 100 parts by mass of polyolefin resin. Step (i) of preparing a molten mixture by melting and mixing 15.0 parts by mass of the organic peroxide at a decomposition temperature or higher;
And a step (ii) of obtaining a foamed molded product by foaming in the presence of a foaming agent while melting the molten mixture using an extruder.   A polyolefin crosslinkable foam molded article produced by the method for producing a polyolefin crosslinkable foam molded article according to claim 9.