JP7808440B2 - Resin composition, and molded article, electric wire coating material, and coated electric wire using the same - Google Patents

Description

The present invention relates to a resin composition, as well as a molded article, wire coating material, and coated electric wire using the same. More specifically, the present invention relates to a resin composition that is ideal as a coating material for electric wires that require high flame retardancy, as well as a molded article and wire coating material obtained from the resin composition, and a coated electric wire coated with the wire coating material.

Polyolefins have superior electrical properties compared to flexible polyvinyl chloride resins and are also economically advantageous, making them widely used in a variety of molded products, including electrical wire and cable sheathing. However, polyolefin resins are flammable solids, and once a fire breaks out, it is difficult to prevent the fire from spreading. Therefore, in applications requiring high flame retardancy, such as electrical wire sheathing, metal hydroxides, bromine-based flame retardants, and phosphorus-based flame retardants are added to improve flame retardancy. Furthermore, a technique for improving flame retardancy by using metal hydroxides in combination with composite rubber is also known (Patent Documents 1 and 2).
Furthermore, for applications requiring heat resistance, a composition for electric wire coating material is known in which a silane-grafted polyolefin is blended with a silicone/acrylic composite rubber compound, a bromine-based flame retardant which is a halogen-based flame retardant, and antimony trioxide (Patent Document 3).

Japanese Patent Application Laid-Open No. 2000-26664 Japanese Patent Application Laid-Open No. 2002-338755 JP 2016-50287 A

However, the inventors of the present application have conducted research and found that the above-mentioned technique of using a metal hydroxide in combination with a composite rubber does not achieve the flame retardancy required for electric wire products, etc., as shown in Comparative Example 4 below. Furthermore, a composition for electric wire coating material in which a silane-grafted polyolefin is blended with a silicone/acrylic composite rubber compound, a bromine-based flame retardant, which is a halogen-based flame retardant, and antimony trioxide has poor flame retardancy, as shown in Comparative Examples 5 and 6 below.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polyolefin-based flame-retardant compound having high flame retardancy, and a molded article thereof, an electric wire covering material, and an electric wire.

The present inventors have conducted extensive research in light of the above problems and have found that flame retardancy can be significantly improved by using a silane-modified polyolefin, a metal hydroxide, and a rubber containing a siloxane component.
That is, the present invention has the following features.

[1] A flame-retardant polyolefin resin composition comprising (A) a silane-modified polyolefin, (B) a metal hydroxide, and (C) a siloxane component-containing rubber.
[2] The flame-retardant polyolefin resin composition according to [1], wherein the metal hydroxide (B) is synthetic magnesium hydroxide.
[3] A molded article using the flame-retardant polyolefin resin composition according to [1] or [2].
[4] A wire covering material comprising the molded article according to [3].
[5] A coated wire obtained by coating the wire coating material according to [4].

The present invention provides a resin composition that combines the resin properties unique to polyolefin resins with high flame retardancy, as well as molded articles, wire coating materials, and coated wires made from the same.

The following describes in detail the embodiments of the present invention, but the present invention is not limited to the following description and can be modified and implemented as desired within the scope that does not deviate from the gist of the present invention.
In this specification, when "~" is used to express a value with a numerical value or physical property value before and after it, the value before and after it is included in the expression.

The flame-retardant polyolefin resin composition of the present invention (hereinafter, sometimes simply referred to as the "resin composition") is characterized by comprising a silane-modified polyolefin as component (A), a metal hydroxide as component (B), and a siloxane component-containing rubber as component (C).
Each component used in the resin composition of the present invention will be described in detail below.

<Component (A): Silane-modified polyolefin>
In the present invention, the silane-modified polyolefin (sometimes referred to herein as "(A) silane-modified polyolefin" or "component (A)") is believed to finely disperse the metal hydroxide (B) and the siloxane component-containing rubber (C) described below in the resin composition. It is also necessary for the polyolefin to exhibit the mechanical and electrical properties required.

The silane-modified polyolefin (A) in the present invention is distinguished from crosslinked polyolefins obtained by crosslinking silane-modified polyolefins by water crosslinking or the like. In other words, the silane-modified polyolefin refers to a non-crosslinked silane-modified polyolefin resin.

(A) Silane-modified polyolefins can be obtained, for example, by grafting an unsaturated silane compound onto the raw polyolefin resins listed below to modify them.

(A) The polyolefin resin used as a raw material for silane-modified polyolefin (hereinafter sometimes referred to as "raw material polyolefin resin") is not particularly limited, but examples include homopolymers of α-olefins having approximately 2 to 8 carbon atoms, such as ethylene, propylene, and 1-butene, and copolymers of these α-olefins with other α-olefins having approximately 2 to 20 carbon atoms, such as ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, and 1-decene, as well as copolymers of vinyl acetate, (meth)acrylic acid, and (meth)acrylic acid esters. Here, "(meth)acrylic acid" refers to either or both "acrylic acid" and "methacrylic acid." The same applies to "(meth)acryloyl," described below.

Specific examples of the raw material polyolefin resin include ethylene homopolymers such as branched or linear low-density polyethylene, branched or linear medium-density polyethylene, and branched or linear high-density polyethylene; ethylene-based resins such as ethylene-propylene copolymers, ethylene-1-butene copolymers, ethylene-4-methyl-1-pentene copolymers, ethylene-1-hexene copolymers, ethylene-1-octene copolymers, ethylene-vinyl acetate copolymers, ethylene-(meth)acrylic acid copolymers, and ethylene-ethyl (meth)acrylate copolymers; propylene-based resins such as propylene homopolymers, propylene-ethylene copolymers, propylene-1-butene copolymers, propylene-ethylene-1-butene copolymers, and propylene-4-methyl-1-pentene copolymers; and 1-butene-based resins such as 1-butene homopolymers, 1-butene-ethylene copolymers, and 1-butene-propylene copolymers.
These raw material polyolefin resins may be used alone or in combination of two or more.

Here, the ethylene-based resin, propylene-based resin, and 1-butene-based resin refer to resins containing ethylene units, propylene units, and 1-butene units, respectively, in a proportion of 50% by mass or more of all monomer units constituting the resin.
Among these, ethylene-based resins are preferred as the polyolefin resins used as the raw material for the silane-modified polyolefin (A).

The silane-modified polyolefin (A) in the present invention can be obtained by, for example, grafting an unsaturated silane compound onto a raw polyolefin resin by a graft reaction using a free radical generator, as described below, and it is preferable that the raw polyolefin resin is an ethylene-based resin, since grafting can be carried out suitably.Furthermore, it is preferable that the raw polyolefin resin is an ethylene-based resin, since the heat resistance is good when the resin composition of the present invention is used for electric wire coating.
Among the above ethylene-based resins, ethylene-1-butene copolymer, ethylene-1-hexene copolymer, ethylene-1-octene copolymer, ethylene-vinyl acetate copolymer, and ethylene-methyl (meth)acrylate copolymer are particularly preferred.

To obtain the silane-modified polyolefin (A) by graft-modifying a raw polyolefin resin with an unsaturated silane compound, the raw polyolefin resin is usually subjected to a graft reaction step of an ethylenically unsaturated silane compound in the presence of a free radical generator such as an organic peroxide, thereby graft-modifying the raw polyolefin resin by a known method.
For example, a method can be used in which a raw material polyolefin resin is mixed with a predetermined amount of an unsaturated silane compound and a free radical generator, and then melt-kneaded at a temperature of 80 to 250° C. In this case, if water is present, a water crosslinking reaction will proceed, so it is preferable to melt-knead in a water-free state.

The unsaturated silane compound used for the graft modification includes an ethylenically unsaturated silane compound represented by the following general formula (I).
R ¹ SiR ² _n Y _3-n ...(I)

In the above formula (I), R ¹ represents an ethylenically unsaturated hydrocarbon group or a hydrocarbonoxy group, R ² represents a hydrocarbon group, Y represents a hydrolyzable organic group, and n is an integer of 0 to 2.

Here, examples of ^R1 include ethylenically unsaturated hydrocarbon groups or hydrocarbonoxy groups having 2 to 6 carbon atoms, such as vinyl, propenyl, butenyl, cyclohexenyl, and γ-(meth)acryloyloxypropyl groups. Examples of ^R2 include hydrocarbon groups having 1 to 10 carbon atoms, such as methyl, ethyl, propyl, decyl, and phenyl groups. Examples of Y include methoxy, ethoxy, formyloxy, acetoxy, propionyloxy, alkylamino, and arylamino groups.

Specific examples of such ethylenically unsaturated silane compounds include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltriacetoxysilane, and γ-methacryloyloxypropyltrimethoxysilane. Among these, vinyltrimethoxysilane is preferably used from the viewpoint of odor, etc.
The unsaturated silane compounds may be used alone or in combination of two or more.

There are no limitations on the amount of the unsaturated silane compound used; a larger amount is preferable to obtain sufficient dispersion of the flame retardant and obtain flame retardancy for the resin composition of the present invention, but a smaller amount is preferable from the standpoint of processability. Specifically, the amount is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, per 100 parts by mass of the raw material polyolefin resin, while it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

The free radical generator is not limited as long as it is capable of grafting an unsaturated silane compound onto the raw polyolefin resin, but organic peroxides such as dicumyl peroxide and 2,5-(tert-butylperoxy)hexyne-3,1,3-bis(tert-butylperoxyisopropyl)benzene are the most commonly used. These organic peroxides may be used alone or in combination.

There are no restrictions on the amount of the free radical generator used; a larger amount is preferable so that the unsaturated silane compound is sufficiently graft-copolymerized with the raw polyolefin resin to achieve a sufficient crosslinking effect, but a smaller amount is preferable from the standpoint of processability. Specifically, the amount is preferably at least 0.01 part by mass, more preferably at least 0.02 part by mass, per 100 parts by mass of the raw polyolefin resin, and is preferably no more than 0.2 part by mass, more preferably no more than 0.1 part by mass.

The density of the silane-modified polyolefin (A) used in the present invention is preferably 0.850 to 0.960 g/ ^cm3 , more preferably 0.870 to 0.920 g/ ^cm3 . The higher the density, the better the heat resistance, chemical resistance, abrasion resistance, flex resistance, etc. of the resulting covered electric wire, while the lower the density, the better the flexibility. By setting the density within the above range, the heat resistance, chemical resistance, abrasion resistance, and flex resistance of the resulting covered electric wire are sufficiently improved, and sufficient flexibility can be obtained.

The melt flow rate (MFR) of the silane-modified polyolefin (A) measured in accordance with JIS K7210 at 190°C under a load of 2.16 kg is preferably higher in terms of moldability, but lower in terms of mechanical properties. Specifically, the MFR of the silane-modified polyolefin (A) at 190°C under a load of 2.16 kg is preferably 0.1 g/10 min or more, more preferably 1 g/10 min or more, and preferably 20 g/10 min or less, more preferably 10 g/10 min or less. By keeping the MFR within these ranges, a good balance between moldability and mechanical properties can be achieved.

The silane-modified polyolefin (A) may be used alone or in combination of two or more different types having different monomer compositions, physical properties, etc.
As the silane-modified polyolefin (A), commercially available products can be used, and for example, a product under the trade name "Linkron" manufactured by Mitsubishi Chemical Corporation can be suitably used.

In the present invention, the silane-modified polyolefin (A) can be used in any amount, but is preferably 10 wt% or more, more preferably 20 wt% or more, of the total composition. On the other hand, it is preferably 80 wt% or less, more preferably 70 wt% or less. If the blending ratio of the silane-modified polyolefin (A) is above the above-mentioned lower limit, the metal hydroxide (B) and the siloxane component-containing rubber (C) tend to be easily dispersed. On the other hand, if the blending ratio is below the above-mentioned upper limit, the content of the metal hydroxide (B) and the siloxane component-containing rubber (C) increases, which tends to increase flame retardancy.

<Component (B): Metal Hydroxide>
In the present invention, the metal hydroxide (sometimes referred to in this specification as the “(B) metal hydroxide” or the “(B) component”) is a component that mainly imparts flame retardancy to the resin composition, molded article, and wire coating material of the present invention.

The type of (B) metal hydroxide is not limited, but specific examples include magnesium hydroxide, aluminum hydroxide, calcium hydroxide, and hydrotalcite. Of these, magnesium hydroxide is preferred. Among these, synthetic magnesium hydroxide is particularly preferred. Synthetic magnesium hydroxide refers to magnesium hydroxide produced by the hydration reaction of magnesium oxide or by reacting a magnesium-containing aqueous liquid with a strongly basic compound such as magnesium hydroxide. The mechanism by which these hydroxides work effectively in the present invention is unclear, but it is thought that this may be due to factors such as their smaller particle size and fewer impurities compared to natural magnesium hydroxide made by crushing brucite (hydrotalcite). These (B) metal hydroxides may be used alone or in combination of two or more types.

The (B) metal hydroxide may be surface-treated with a surface treatment agent. Examples of surface treatment agents include silane coupling agents, titanate coupling agents, fatty acids, and fatty acid metal salts. Known methods such as wet methods, dry methods, and direct kneading methods can be used to treat the (B) metal hydroxide with these surface treatment agents. Using a surface-treated (B) metal hydroxide may improve dispersibility in the resulting resin composition, thereby improving mechanical properties.

The average particle size of the metal hydroxide (B) is preferably 2 μm or less, for example, 0.5 to 2 μm, from the viewpoints of mechanical properties, dispersibility, and flame retardancy.
Here, the average particle size of the metal hydroxide (B) is the particle size at a volume-based cumulative distribution of 50 vol %.

In the present invention, the blending ratio of (B) metal hydroxide is preferably 30 wt% or more, more preferably 40 wt% or more, based on the total composition, and is preferably 80 wt% or less, more preferably 70 wt% or less. If the blending ratio of (B) metal hydroxide is above the above-mentioned lower limit, sufficient flame retardancy can be obtained. On the other hand, if the blending ratio of (B) metal hydroxide is below the above-mentioned upper limit, it is possible to prevent a decrease in productivity due to an increase in extrusion load and a decrease in mechanical properties.

<Component (C): Siloxane-Containing Rubber>
In the present invention, the siloxane component-containing rubber (sometimes referred to in this specification as "(C) siloxane component-containing rubber" or "component (C)") is added mainly for the purpose of improving the flame retardancy of the metal hydroxide, and is a component that ultimately imparts flame retardancy to the resin composition, molded article, and wire coating material of the present invention.

The (C) siloxane component-containing rubber is not particularly limited as long as it contains a polyorganosiloxane rubber component, but a composite rubber containing a polyorganosiloxane rubber component is preferred.
As a composite rubber containing a polyorganosiloxane rubber component, a composite rubber composed of a polyorganosiloxane rubber component and a polyalkyl (meth)acrylate component, and a copolymer in which one or more vinyl monomers are graft-polymerized as the main component can be suitably used.

The polyorganosiloxane rubber component and polyalkyl (meth)acrylate component constituting the composite rubber are preferably in the range of 1 to 99% by mass of the polyorganosiloxane rubber component and 99 to 1% by mass of the polyalkyl (meth)acrylate component (however, the total of each component is 100% by mass). From the viewpoint of flame retardancy and flexibility, the polyorganosiloxane rubber component is more preferably in the range of 30 to 95% by mass, and even more preferably 50 to 90% by mass.
The composite rubber may be produced by any method, but emulsion polymerization is the most suitable method, in which a polyorganosiloxane latex is first prepared, and then the polyorganosiloxane latex particles are impregnated with a synthesis monomer of alkyl (meth)acrylate, and then the synthesis monomer is polymerized.

The polyorganosiloxane rubber component that makes up the composite rubber can be prepared by emulsion polymerization using the organosiloxane and crosslinking agent (CI) shown below. A grafting agent (GI) can also be used in combination. Organosiloxanes include various cyclic compounds with three or more members, with three- to six-membered rings being preferred. Examples include hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane, trimethyltriphenylcyclotrisiloxane, tetramethyltetraphenylcyclotetrasiloxane, and octaphenylcyclotetrasiloxane. These can be used alone or in combination of two or more. The amount of these compounds used is preferably 50% by weight or more of the polyorganosiloxane component, and more preferably 70% by weight or more.

As the crosslinking agent (CI), trifunctional or tetrafunctional silane-based crosslinking agents such as trimethoxymethylsilane, triethoxyphenylsilane, tetramethoxysilane, tetraethoxysilane, tetra-n-propoxysilane, and tetrabutoxysilane are used. Tetrafunctional crosslinking agents are particularly preferred, with tetraethoxysilane being particularly preferred. The amount of crosslinking agent used is preferably in the range of 0.1 to 30% by weight of the polyorganosiloxane component.

As the grafting agent (GI), compounds capable of forming units represented by the following formulae (GI-1 to GI-4) and the like are used.
In the formula, ^R3 represents a methyl group, an ethyl group, a propyl group, or a phenyl group, ^R4 represents a hydrogen atom or a methyl group, m represents 0, 1, or 2, and p represents 1 to 6.

(Meth)acryloyloxysiloxanes capable of forming the units of formula (GI-1) have high grafting efficiency and are therefore capable of forming effective graft chains, and are advantageous in terms of exhibiting flexibility, with methacryloyloxysiloxane being particularly preferred. Specific examples of methacryloyloxysiloxanes include β-methacryloyloxyethyldimethoxymethylsilane, γ-methacryloyloxypropylmethoxydimethylsilane, γ-methacryloyloxypropyldimethoxymethylsilane, γ-methacryloyloxypropyltrimethoxysilane, γ-methacryloyloxypropylethoxydiethylsilane, γ-methacryloyloxypropyldiethoxymethylsilane, and γ-methacryloyloxybutyldiethoxymethylsilane.
Examples of compounds capable of forming the unit of formula (GI-2) include vinylsiloxanes, and a specific example thereof is tetramethyltetravinylcyclotetrasiloxane.

Examples of compounds capable of forming the unit of formula (GI-3) include p-vinylphenyldimethoxymethylsilane, and examples of compounds capable of forming the unit of formula (GI-4) include γ-mercaptopropyldimethoxymethylsilane, γ-mercaptopropylmethoxydimethylsilane, and γ-mercaptopropyldiethoxymethylsilane.
The amount of the grafting agent used is preferably 0 to 10% by weight, more preferably 0.5 to 5% by weight, of the polyorganosiloxane component.

This polyorganosiloxane component latex can be produced using methods described, for example, in U.S. Pat. Nos. 2,891,920 and 3,294,725. In practicing the present invention, it is preferable to produce the latex by shear mixing a mixed solution of organosiloxane, crosslinking agent (CI), and, optionally, grafting agent (GI) with water in the presence of a sulfonic acid emulsifier, such as alkylbenzenesulfonic acid or alkylsulfonic acid, using, for example, a homogenizer. Alkylbenzenesulfonic acid is preferred because it acts as an emulsifier for organosiloxane and also as a polymerization initiator. In this case, using a metal salt of alkylbenzenesulfonic acid, metal salt of alkylsulfonic acid, or the like in combination is preferable, as it is effective in maintaining polymer stability during graft polymerization.

The polyalkyl(meth)acrylate component that makes up the composite rubber can be synthesized using the alkyl(meth)acrylate, crosslinking agent (CII), and grafting agent (GII) shown below. Examples of alkyl(meth)acrylates include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate, and alkyl methacrylates such as hexyl methacrylate, 2-ethylhexyl methacrylate, and n-lauryl methacrylate. The use of n-butyl acrylate is particularly preferred.

Examples of the crosslinking agent (CII) include ethylene glycol dimethacrylate, propylene glycol dimethacrylate, 1,3-butylene glycol dimethacrylate, and 1,4-butylene glycol dimethacrylate.
Examples of the grafting agent (GII) include allyl methacrylate, triallyl cyanurate, triallyl isocyanurate, etc. Allyl methacrylate can also be used as a crosslinking agent.

These crosslinking agents and graft crosslinking agents may be used alone or in combination of two or more. The total amount of these crosslinking agents and graft crosslinking agents used is preferably 0.1 to 20% by weight of the polyalkyl (meth)acrylate component. Polymerization of the polyalkyl (meth)acrylate component is carried out by adding the alkyl (meth)acrylate, crosslinking agent, and graft crosslinking agent to a latex of the polyorganosiloxane component neutralized with an aqueous alkali solution such as sodium hydroxide, potassium hydroxide, or sodium carbonate, impregnating the polyorganosiloxane particles, and then reacting with a conventional radical polymerization initiator. As the polymerization progresses, a composite rubber latex of the polyorganosiloxane component and polyalkyl (meth)acrylate component is obtained.

When implementing the present invention, the composite rubber preferably used is one in which the main skeleton of the polyorganosiloxane rubber component has repeating units of dimethylsiloxane and the main skeleton of the polyalkyl (meth)acrylate component has repeating units of n-butyl acrylate.

Vinyl monomers to be graft polymerized onto this composite rubber include various vinyl monomers such as aromatic alkenyl compounds such as styrene, α-methylstyrene, and vinyltoluene; methacrylic acid esters such as methyl methacrylate and 2-ethylhexyl methacrylate; acrylic acid esters such as methyl acrylate, ethyl acrylate, and n-butyl acrylate; and vinyl cyanide compounds such as acrylonitrile and methacrylonitrile. These may be used alone or in combination of two or more. Of these vinyl monomers, methacrylic acid esters are preferred, with methyl methacrylate being particularly preferred.

The ratio of composite rubber to vinyl monomer in the (C) siloxane component-containing rubber is preferably 5 to 95% by mass of composite rubber and 5 to 95% by mass of vinyl monomer, and even more preferably 25 to 90% by mass of composite rubber and 10 to 75% by mass of vinyl monomer. If the vinyl monomer content is less than 5% by mass, the dispersibility of the graft copolymer in the resin composition will be poor, and if it exceeds 95% by mass, flexibility will be significantly reduced.

The (C) siloxane component-containing rubber is obtained by adding a vinyl monomer to a composite rubber latex and polymerizing it in one or multiple stages using radical polymerization techniques. The graft copolymer latex can be separated and recovered by pouring it into hot water containing a metal salt, such as calcium chloride, calcium acetate, or magnesium sulfate, followed by salting out and coagulation. The composite rubber graft copolymer, in which one or more vinyl monomers are grafted onto the composite rubber composed of this polyorganosiloxane component and polyalkyl (meth)acrylate rubber component, is blended. This allows for high flame retardancy without sacrificing flexibility and while significantly reducing the amount of metal hydroxide (B) added. If necessary, polyorganosiloxane can be mixed into the resulting composite rubber graft copolymer.

The effect of the (C) siloxane component-containing rubber is presumed to be as follows: (C) siloxane component-containing rubber itself has no flame retardant properties, and mixing it alone with a polyolefin resin does not change the flame retardancy of the resin composition. When a resin composition based on (A) silane-modified polyolefin is placed in a combustion field with (B) metal hydroxide nearby, the high temperature causes the formation of a compound with (B) metal hydroxide, thereby demonstrating high flame retardancy.

It is believed that the (A) silane-modified polyolefin has electrical polarity in the modifying group, which allows the (B) metal hydroxide and (C) siloxane component-containing rubber to be dispersed and positioned in close proximity to each other. On the other hand, when a polyolefin resin with lower polarity than the (A) silane-modified polyolefin is used, the (B) metal hydroxide and (C) siloxane component-containing rubber are both electrically polar compounds, which presumably makes them prone to self-aggregation and makes it difficult to achieve the synergistic flame retardancy effect.

<Flame-retardant polyolefin resin composition>
The flame-retardant polyolefin resin composition of the present invention exhibits excellent flame retardancy by containing (A) a silane-modified polyolefin, (B) a metal hydroxide, and (C) a siloxane component-containing rubber.
The flame-retardant polyolefin resin composition preferably has a ratio of component (A)/component (C) of 10/1 to 2/1. If this ratio is not met, the effect of improving flame retardancy will decrease.

<Other ingredients>
The resin composition of the present invention may contain, as necessary, resins and additives other than the above-mentioned components (A) to (C) as "other components" within the scope of not significantly impairing the effects of the present invention. The other components may be used alone or in any combination and ratio of two or more.
The resin components other than the silane-modified polyolefin (A) are not particularly limited, but unmodified polyolefins such as unmodified polyethylene resins can be used as components for improving the mechanical properties and moldability of the resin composition, as well as the molded articles and wire coating materials using the resin composition.

The unmodified polyolefins refer to polyethylene-based resins such as various polyethylenes and ethylene copolymers into which functional groups have been introduced by copolymerization, and polypropylene-based resins such as polypropylene and propylene copolymers into which functional groups have been introduced by copolymerization, and are resins that have not been modified by a silane coupling agent, functional groups, or the like.
Here, the ethylene-based resin and the propylene-based resin refer to resins containing ethylene units and propylene units, respectively, in a proportion of 50% by mass or more of all monomer units constituting the resin.

Examples of the polyethylene resin include copolymers of ethylene with other α-olefins having approximately 3 to 20 carbon atoms, such as propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-octene, and 1-decene, as well as copolymers of ethylene with vinyl acetate, (meth)acrylic acid, and (meth)acrylic acid esters.

The unmodified polyethylene resin preferably has a density of 0.850 to 0.970 g/cm ^3. If the density is 0.850 g/cm ³ or more, the heat resistance, chemical resistance, abrasion resistance, bending resistance, etc. of the obtained electric wire will be good, and if the density is 0.970 g/cm ³ or less, the flexibility will be good.
The unmodified polyethylene resin preferably has an MFR of 1 to 10 g/10 min at 190°C under a load of 2.16 kg, measured in accordance with JIS K 7210. As with the MFR of (A) silane-modified polyolefin, a larger MFR of the unmodified polyethylene is preferable in terms of moldability, enabling an improvement in production volume per unit time, and a smaller MFR is preferable in terms of mechanical properties and heat resistance.

The unmodified polyethylene resin may be used alone, or two or more types with different monomer compositions, physical properties, etc. may be mixed and used.

(A) Examples of the resins other than silane-modified polyolefins and unmodified polyethylene-based resins include the unmodified polypropylene-based resins mentioned above, as well as thermoplastic resins such as polyphenylene ether-based resins; polycarbonate resins; polyamide-based resins such as nylon 66 and nylon 11; polyester-based resins such as polyethylene terephthalate and polybutylene terephthalate; styrene-based resins such as polystyrene; and (meth)acrylic resins such as polymethyl (meth)acrylate-based resins, as well as various thermoplastic elastomers.

Specific examples of the additives include process oils, processing aids, plasticizers, crystal nucleating agents, impact modifiers, flame retardants other than component (B), flame retardant assistants, crosslinking catalysts, crosslinking assistants, antistatic agents, antioxidants, lubricants, fillers, compatibilizers, heat stabilizers, light stabilizers, ultraviolet absorbers, carbon black, and colorants.

In the present invention, the crosslinking catalyst is a component that can water-crosslink the silane-modified polyolefin (A) contained in the resin composition of the present invention.
Since (A) silane-modified polyolefin is a modified polyolefin graft-modified with an unsaturated silane compound, a compound that can form a crosslinked structure in the polyolefin resin when contacted with moisture in the presence of the crosslinking catalyst, i.e., a silanol condensation catalyst, is preferably used. Specific examples of the silanol condensation catalyst include metal fatty acid salts such as dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dibutyltin dioctaate, stannous acetate, stannous caprylate, zinc caprylate, lead naphthenate, and cobalt naphthenate.
The crosslinking catalyst may be used alone or in any combination and ratio of two or more kinds.

In the present invention, the blending ratio of the crosslinking catalyst is preferably 0.0001 wt% or more, more preferably 0.0002 wt% or more, of the total resin, and is preferably 0.02 wt% or less, more preferably 0.01 wt% or less. If the blending ratio of the crosslinking catalyst is above the above-mentioned lower limit, crosslinking of the silane-modified polyolefin proceeds sufficiently, and sufficient crosslinking properties can be obtained. On the other hand, if the blending ratio of the crosslinking catalyst is below the above-mentioned upper limit, a decrease in moldability due to excessive crosslinking can be prevented.

Flame retardants other than component (B) can be broadly divided into halogen-based and non-halogen-based flame retardants, with non-halogen-based flame retardants being preferred. (B) Non-halogen-based flame retardants other than metal hydroxides include, for example, phosphorus-based flame retardants, nitrogen-containing compound (melamine-based, guanidine-based) flame retardants, and inorganic compound (borate, molybdenum compound) flame retardants.

Examples of the heat stabilizers and antioxidants include hindered phenols, phosphorus compounds, hindered amines, sulfur compounds, copper compounds, and alkali metal halides.

The fillers are broadly divided into organic fillers and inorganic fillers. Examples of organic fillers include naturally occurring polymers such as starch, cellulose particles, wood flour, soybean pulp, rice husks, and bran, as well as modified versions of these. Examples of inorganic fillers include talc, calcium carbonate, zinc carbonate, wollastonite, silica, alumina, magnesium oxide, calcium silicate, sodium aluminate, calcium aluminate, sodium aluminosilicate, magnesium silicate, glass balloons, carbon black, zinc oxide, antimony trioxide, zeolite, hydrotalcite, metal fibers, metal whiskers, ceramic whiskers, potassium titanate, boron nitride, graphite, and carbon fibers.

The resin composition of the present invention may also contain a hydrocarbon-based rubber softener. As the hydrocarbon-based rubber softener, a mineral oil-based or synthetic resin-based softener is preferred, and a mineral oil-based softener is more preferred.
The mineral oil-based softener is generally a mixture of aromatic hydrocarbons, naphthenic hydrocarbons, and paraffinic hydrocarbons, and those in which 50% or more of the total carbon atoms are paraffinic hydrocarbons are called paraffinic oils, those in which approximately 30 to 45% or more of the total carbon atoms are naphthenic hydrocarbons are called naphthenic oils, and those in which 35% or more of the total carbon atoms are aromatic hydrocarbons are called carbon-aromatic oils.

The synthetic resin-based softener is preferably one selected from paraffinic oil, naphthenic oil, and carbon-atom aromatic oil. Of these, paraffinic oil is more preferable because of its good color. Examples of synthetic resin-based softeners include polybutene and low-molecular-weight polybutadiene.

When the resin composition of the present invention contains other components such as these additives and resins, their content is not limited, but it is preferable that the total content of components (A) to (C) be in a range such that it accounts for 50% by mass or more of the resin composition of the present invention, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

<Method of producing resin composition>
There are no particular limitations on the method for producing the resin composition of the present invention, as long as it can be produced so as to contain (A) silane-modified polyolefin, (B) metal hydroxide, and (C) siloxane component-containing rubber. The resin composition of the present invention can be produced, for example, by mixing the respective components simultaneously or in any order. Other components such as antioxidants and colorants may be added at any time as long as they can be uniformly dispersed.

There are no limitations on the equipment used to mix the raw material components, but general-purpose equipment such as a kneader, Banbury mixer, roll, single-screw extruder, or twin-screw extruder can be used. The temperature during melt mixing may be any temperature at which at least one of the raw material components is molten, but a temperature at which all components used are melted is usually selected, and mixing is generally carried out at 150 to 250°C.

Furthermore, by subjecting the resin composition of the present invention to a water crosslinking treatment, it is possible to produce a crosslinked resin composition with excellent heat resistance, mechanical properties, and flame retardancy. When water crosslinking is to be performed, it is preferable to add a crosslinking catalyst, and further, the formation of a crosslinked structure can be promoted by contacting the resin with liquid or vapor water at room temperature to about 200°C, usually room temperature to about 100°C, for about 10 seconds to about 1 week, usually about 1 minute to about 1 day.

<Molded products and applications>
The method for molding the resin composition of the present invention is not particularly limited, and may include extrusion molding, compression molding, injection molding, etc., but extrusion molding is preferred from the perspective of the fluidity of the resin composition in a molten state. The molding temperature is not particularly limited as long as it is higher than the melting temperature of the resin composition, but a temperature of 150 to 200°C is preferred. If the molding temperature is above the lower limit, the fluidity of the molten resin composition is high, making it easy to obtain a molded product with the desired shape. On the other hand, if the molding temperature is below the upper limit, deterioration of the appearance due to foaming caused by decomposition of (B) the metal hydroxide is less likely to occur.

When the resin composition of the present invention is to be converted into a crosslinked structure by water crosslinking, it is preferable to first mold it into the desired shape before performing the water crosslinking treatment, and then perform the water crosslinking treatment. Because the resin composition of the present invention has good moldability, when it is subjected to extrusion molding, for example, it is possible to obtain a molded product with a smooth surface and a good appearance free of scorch (burn marks). Furthermore, by performing water crosslinking on this molded product, it is possible to obtain a molded product of the water crosslinkable resin composition with the same good appearance as before water crosslinking.

The uses of molded articles obtained using the resin composition of the present invention are not particularly limited, but because they combine excellent heat resistance, mechanical properties, and flame retardancy with an excellent appearance, they can be suitably used as insulators or sheaths for electric wires and cables. Furthermore, they can be suitably used for tubes that bundle multiple resin-coated electric wires, as well as various insulating films, insulating pipes, power supply boxes, etc. Among the above, it is particularly preferred to use the resin composition of the present invention as an electric wire coating material, using it on an electric wire and then using the electric wire coating material to produce a coated electric wire.

Specific embodiments of the present invention will be described in more detail below using examples, but the present invention is not limited to these examples as long as they do not depart from the gist of the invention. Note that the various manufacturing conditions and evaluation result values in the following examples represent preferred upper or lower limits for embodiments of the present invention, and preferred ranges may be defined by combining the above-mentioned upper or lower limits with the values in the following examples or values between examples.

[Raw materials]
In the following examples and comparative examples, the following raw materials were used.
<Component (A): Silane-modified polyolefin>
Silane-grafted polyolefin-1: trade name Linkron SH710N (manufactured by Mitsubishi Chemical Corporation, MFR: 2 g/10 min, density: 0.892 g/cm ³ , content of ethylene units in all constituent monomer units: 50 mass% or more, ethylene-1-butene copolymer), hereinafter referred to as “SH710N.”

<Component (B): Metal Hydroxide>
Metal hydroxide-1: Synthetic magnesium hydroxide, trade name Magseeds S-6 (manufactured by Konoshima Chemical Co., Ltd., average particle size: 1.0 μm, silane surface treatment), hereinafter referred to as “S-6”.
Metal hydroxide-2: Synthetic magnesium hydroxide, trade name KISUMA5 (manufactured by Kyowa Chemical Industry Co., Ltd., average particle size: 0.8 μm, no surface treatment), hereinafter referred to as “KISUMA5”.
Metal hydroxide-3: Synthetic magnesium hydroxide, trade name KISUMA5A (manufactured by Kyowa Chemical Industry Co., Ltd., average particle size: 0.8 μm, fatty acid surface treatment), hereinafter referred to as “KISUMA5A”.
Metal hydroxide-4: Synthetic magnesium hydroxide, trade name KISUMA5P (manufactured by Kyowa Chemical Industry Co., Ltd., average particle size: 0.8 μm, silane surface treatment), hereinafter referred to as “KISUMA5P”.

<Component (C): Siloxane-Containing Rubber>
Siloxane component-containing rubber 1: Trade name Metablen SX-005 (manufactured by Mitsubishi Chemical Corporation), alkyl methacrylate/alkyl acrylate/dimethylsiloxane copolymer, hereinafter referred to as "SX-005".
Siloxane component-containing rubber 2: Trade name Chaline R-175S (manufactured by Nissin Chemical Industry Co., Ltd.), silicone-acrylic copolymer, hereinafter referred to as "R-175S".
Siloxane component-containing rubber 3: trade name Kane Ace MR-01 (manufactured by Kaneka Corporation), hereinafter referred to as "MR-01".

<Other ingredients: resins>
Polyethylene resin: ethylene-1-butene copolymer, trade name: ENGAGE 7256 (manufactured by Dow Chemical Japan, MFR: 2.5 g/10 min, density: 0.885 g/cm ³ ), hereinafter referred to as "ENGAGE 7256".
<Other ingredients: additives>
Antioxidant: pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], trade name: Irganox 1010 (manufactured by BASF Japan Ltd.), hereinafter referred to as “Irganox 1010.”

<Other ingredients: Other>
Brominated flame retardant: ethylenebis(pentabromophenyl), trade name: Seitex 8010 (manufactured by Albemarle Japan Co., Ltd.), hereinafter referred to as "Seitex 8010".
Antimony-based flame retardant aid: antimony trioxide, trade name: PATOX-KN (manufactured by Nippon Seiko Co., Ltd.), hereinafter referred to as "PATOX-KN."

[evaluation]
<Flame retardancy>
The oxygen index was measured as an evaluation index of flame retardancy. The obtained flame-retardant polyolefin resin composition pellets were compression molded at 180°C, and then test specimens were punched out with a forging blade to prepare test specimens, and the oxygen index was measured according to the method of JIS K 7201-2.
The higher the oxygen index number, the better the flame retardancy.

<Preparation of Resin Composition>
Example 1
In a pressure kneader with a capacity of 1.0 L, 50 parts by mass of silane graft polyolefin-1 (SH710N) as component (A), 100 parts by mass of metal hydroxide-1 (S-6) as component (B), 5 parts by mass of siloxane component-containing rubber 2 (R-175S) as component (C), 50 parts by mass of polyethylene resin (ENGAGE 7256) as other components, and 0.5 parts by mass of antioxidant (Irganox 1010) were added and kneaded for 15 minutes at a set temperature of 100 ° C. The resulting kneaded product was further sheeted with a roll and then pelletized with a pelletizer to produce a flame-retardant polyolefin resin composition.
The resulting pellets of the flame-retardant polyolefin resin composition were used to evaluate flame retardancy, and the results are shown in Table 1.

<Examples 2 to 11, Comparative Examples 1 to 6, Reference Example 1>
According to the formulations shown in Tables 1 and 2, flame-retardant polyolefin resin compositions were obtained in the same manner as in Example 1.
The flame retardancy was evaluated in the same manner as in Example 1. The results are shown in Tables 1 and 2.
Note that the component (C) was not used in Comparative Example 1, and the component (B) was not used in Comparative Examples 2, 5, and 6. Furthermore, the components (A) and (C) were not used in Comparative Example 3, and the component (A) was not used in Comparative Example 4. Reference Example 1 shows a case where the components (B) and (C) were not used.

(result)
In Examples 1 to 11 in which the components (A), (B) and (C) were blended, a significant improvement in flame retardancy was observed.
In contrast, the comparative examples lacking any of the components (A), (B), and (C) gave the following results.

No improvement in flame retardancy was observed in Comparative Examples 3 and 4, which did not contain component (A). This is presumably because the dispersion of components (B) and (C) in the resin composition was insufficient.
No improvement in flame retardancy was observed in Comparative Examples 2, 5, and 6, which did not contain component (B), or in Comparative Examples 1 and 3, which did not contain component (C). This suggests that the coexistence of components (B) and (C) contributes to a dramatic improvement in flame retardancy. Among these, Comparative Examples 5 and 6 contained a bromine-based flame retardant and an antimony-based flame retardant aid as flame retardants other than component (B), but no synergistic effect with component (C) was observed for these.

Halogen-antimony flame retardants are known to exhibit the same level of flame retardancy as metal hydroxides when added in smaller amounts (Reference: Fundamentals of Flame Retardant Technology and Latest Development Trends (Author: Nishizawa Hitoshi)). In Comparative Examples 5 and 6, an investigation was conducted using an amount of addition that provided the halogen-antimony flame retardant with the same level of flame retardancy as metal hydroxides (same level of flame retardancy as in Comparative Example 1). As a result, it was confirmed that even when the halogen-antimony flame retardant coexists with (A) silane-modified polyolefin and (C) siloxane-modified rubber, no significant improvement in flame retardancy was observed. This behavior is different from that of (B) metal hydroxides.

These results demonstrate that the present invention provides a polyolefin resin composition with extremely high flame retardancy.

Claims (5)

A resin composition comprising (A) a silane-modified polyolefin, (B) a metal hydroxide, and (C) a siloxane component-containing rubber,
The component (C) is a copolymer in which one or more vinyl monomers are graft-polymerized onto a composite rubber composed of a polyorganosiloxane rubber component and a polyalkyl(meth)acrylate component ,
A flame-retardant polyolefin resin composition, wherein the blending ratio of the (A) component to the entire resin composition is 10 wt % or more and 47.5 wt % or less, the blending ratio of the (B) component is 30 wt % or more and 80 wt % or less, and the ratio (mass ratio) of the (A) component to the (C) component is (A)/(C) is 2/1 or more and 10/1 or less . The flame-retardant polyolefin resin composition according to claim 1, characterized in that the (B) metal hydroxide is synthetic magnesium hydroxide. A molded article made using the flame-retardant polyolefin resin composition according to claim 1 or 2. A wire coating material comprising the molded article described in claim 3. A coated electric wire coated with the electric wire coating material according to claim 4.