JP7749961B2 - Silane-modified polypropylene, silane-crosslinked polypropylene, silane-modified polypropylene composition, and molded article, crosslinked molded article, and three-dimensional network fiber assembly using these - Google Patents

Description

The present invention relates to silane-modified polypropylene, silane-crosslinked polypropylene, silane-modified polypropylene compositions, and molded articles, crosslinked molded articles, and three-dimensional network fiber assemblies using these.

In recent years, three-dimensional network fiber aggregates obtained by extrusion molding thermoplastic resins into loops have become increasingly popular as cushioning materials for furniture, pillows, bed mats, and other bedding.

This three-dimensional reticular fiber assembly is generally manufactured as follows: A thermoplastic resin such as polyethylene is melted in an extruder, and the molten resin is extruded through a die with multiple holes to form strands. A water tank is installed below the die, and the strands naturally flow downward and land in the tank. When the strands remain in the water, the resin solidifies due to cooling by the water, producing a three-dimensional reticular fiber assembly with looped entanglements (Patent Document 1). Examples of thermoplastic resins that are being considered for use in molding include ethylene-α-olefin copolymers, foamed polyurethane, and polyester.

In cushioning materials such as bedding that use three-dimensional network fiber assemblies made of thermoplastic resin, strain occurs in the compression and tension directions of the fibers when a load is applied. If this strain occurs over a long period of time or repeatedly, the cushioning material does not recover to its original thickness and gradually collapses in the compression direction, resulting in a loss of cushioning properties, a phenomenon known as "setting." Setting becomes more pronounced at high temperatures, and it is known that when heated bedding such as electric blankets is used, problems such as partial deformation of the bedding occur. This is caused by the thermoplastic resin that makes up the three-dimensional network fiber assembly flowing or plastically deforming when subjected to a load at high temperatures.

Therefore, in order to improve the heat resistance, a major weakness of polyethylene resins, a polyethylene resin composition for three-dimensional network structures has been proposed, which contains a graft reaction product obtained by grafting an ethylenically unsaturated silane compound onto a specific ethylene-α-olefin copolymer polymerized using a metallocene catalyst, and a silanol condensation catalyst (Patent Document 2).

On the other hand, in order to provide a three-dimensional network fiber structure with better chemical resistance and less odor, it has been proposed to use a specific propylene-α-olefin copolymer instead of foamed polyurethane or polyester (Patent Document 3). Furthermore, in order to provide a three-dimensional network fiber structure with better chemical resistance, high heat resistance, and less odor, it has been proposed to use a polymer alloy containing a specific propylene-based polymer and a propylene homopolymer (Patent Document 4).

International Publication No. 2012/035736 JP 2013-181117 A Patent No. 5873225 Patent No. 5894716

The technology in Patent Document 2 is premised on the use of an ethylene/α-olefin copolymer with a low melting point in order to control the fusion strength of the strands immediately after extrusion so that the extruded strands form a three-dimensional network fiber assembly. Furthermore, a specific ethylene/α-olefin copolymer with a relatively low molecular weight is used to obtain an appropriate strand diameter. As a result, it is difficult to ensure sufficient heat resistance, shape retention at high temperatures is insufficient, and problems such as settling and deformation still occur.

On the other hand, while the technologies in Patent Documents 3 and 4 show some improvement in terms of settling and deformation at high temperatures, they have not yet achieved sufficient performance.

The present invention was made in consideration of the above circumstances, and aims to provide silane-modified polypropylene that enables the production of silane-crosslinked polypropylene with excellent flexibility, heat distortion resistance, and shape recovery, and that exhibits heat resistance and fluidity suitable for molding three-dimensional network fiber assemblies; silane-crosslinked polypropylene obtained by crosslinking the silane-modified polypropylene; a silane-modified polypropylene composition; and molded articles, crosslinked molded articles, and three-dimensional network fiber assemblies using these.

In addition to the objectives stated here, the present invention also aims to achieve effects that cannot be obtained with conventional technology, which are derived from the various components shown in the detailed description of the invention described below.

As a result of extensive research conducted by the present inventors to achieve the above object, they discovered that silane-modified polypropylene, which contains a specific propylene polymer in a specific ratio and is silane-modified, has suitable fluidity and is excellent in heat resistance and shape retention, and that the use of this polypropylene makes it possible to realize a three-dimensional network fiber assembly that has good moldability and is excellent in flexibility, heat distortion resistance, and shape retention, and thus completed the present invention.
That is, the present invention provides various specific embodiments as shown below.

[1] A silane-modified polypropylene obtained by silane-modifying a raw material propylene polymer, wherein the raw material propylene polymer contains the following components (a) and (b): 35 to 95 mass% of component (a) and 5 to 65 mass% of component (b), relative to 100 mass% of the total of components (a) and (b):
Component (a): A propylene polymer having an α-olefin unit content of 10 to 30% by mass. Component (b): A propylene polymer having an α-olefin unit content of less than 10% by mass.

[2] The silane-modified polypropylene according to [1], wherein the melting point of the component (a) measured under the following conditions is 110°C or less.
<Measurement conditions>
Using a differential scanning calorimeter in accordance with JIS K7121 (2010), approximately 5 mg of component (a) is heated from 20°C to 200°C at a heating rate of 100°C/min, held at 200°C for 3 minutes, cooled to -10°C at a cooling rate of 10°C/min, and then heated to 200°C at a heating rate of 10°C/min. The melting point is determined as the temperature at the top of the melting peak.

[3] The silane-modified polypropylene according to [1] or [2], wherein the melting point of the component (b) measured under the following conditions exceeds 110°C.
<Measurement conditions>
Using a differential scanning calorimeter in accordance with JIS K7121 (2010), approximately 5 mg of component (b) is heated from 20°C to 200°C at a heating rate of 100°C/min, held at 200°C for 3 minutes, cooled to -10°C at a cooling rate of 10°C/min, and then heated to 200°C at a heating rate of 10°C/min. The melting point is determined as the temperature at the top of the melting peak.

[4] The silane-modified polypropylene according to any one of [1] to [3], wherein the α-olefins of components (a) and (b) are both α-olefins having 2 to 10 carbon atoms, excluding propylene.

[5] The silane-modified polypropylene according to any one of [1] to [4], wherein the silane-modified moiety of the silane-modified polypropylene is a polymerized residue of an unsaturated silane compound represented by the following formula (1):
R-Si(R') ₃ ...(1)
(In the formula, R is an ethylenically unsaturated hydrocarbon group, and R' are each independently a hydrocarbon group having 1 to 10 carbon atoms or an alkoxy group having 1 to 10 carbon atoms, and at least one of the R' is an alkoxy group having 1 to 10 carbon atoms.)

[6] The silane-modified polypropylene according to any one of [1] to [5], having a density of 0.850 to 0.930 g/cm ³ .

[7] The silane-modified polypropylene according to any one of [1] to [6], having an MFR of 10 to 80 g/10 min measured at 230°C under a load of 2.16 kg in accordance with JIS K7210 (1999).

[8] A silane-modified polypropylene composition comprising the silane-modified polypropylene described in any one of [1] to [7] and a silanol condensation catalyst.

[9] A molded article obtained by molding the silane-modified polypropylene composition described in [8].

[10] A crosslinked molded article obtained by crosslinking the molded article described in [9].

[11] The crosslinked molded article according to [10], having a flexural modulus of 300 MPa or less as measured in accordance with JIS K7171 (2008).

[12] A three-dimensional network fiber assembly obtained by molding the silane-modified polypropylene composition described in [9].

[13] A crosslinked molded article obtained by crosslinking the three-dimensional reticular fiber assembly described in [12].

The present invention makes it possible to produce silane-crosslinked polypropylene with excellent flexibility, heat distortion resistance, and shape recovery, and also provides silane-modified polypropylene that exhibits heat resistance and fluidity suitable for molding three-dimensional network fiber assemblies; silane-crosslinked polypropylene obtained by crosslinking the silane-modified polypropylene; silane-modified polypropylene compositions; and molded articles, crosslinked molded articles, and three-dimensional network fiber assemblies using these.

The following describes in detail the embodiments of the present invention. However, the following embodiments are merely examples (representative examples) of the present invention, and the present invention is not limited to these. The present invention can be implemented in any modified form without departing from the spirit of the invention. In this specification, when "~" is used with a numerical value or physical property value between it and the preceding or following value, this is considered to include the preceding or following values. In this specification, "% by mass" and "% by weight", and "parts by mass" and "parts by weight" are synonymous.

[Silane-modified polypropylene]
The silane-modified polypropylene of the present invention is a silane-modified polypropylene obtained by silane-modifying a raw material propylene polymer, characterized in that the raw material propylene polymer contains the following components (a) and (b), with the component (a) accounting for 35 to 95 mass% and the component (b) accounting for 5 to 65 mass%, relative to 100 mass% of the total of the components (a) and (b), and in which a silane compound is grafted onto the raw material propylene polymer:
Component (a): A propylene polymer having an α-olefin unit content of 10 to 30% by mass. Component (b): A propylene polymer having an α-olefin unit content of less than 10% by mass.

Hereinafter, a propylene polymer having an α-olefin unit content of 10 to 30% by mass of component (a) may be referred to as "propylene polymer (a)," and a propylene polymer having an α-olefin unit content of less than 10% by mass of component (b) may be referred to as "propylene polymer (b)."

<Propylene-based polymer (a)>
The propylene polymer (a) of the component (a) is a propylene polymer having an α-olefin unit content of 10 to 30% by mass.
When the propylene polymer (a) has an α-olefin unit content of 10% by mass or more, the crystallization rate of the strands during production of a three-dimensional reticular fiber assembly is slowed down, thereby improving the fusion strength of the strands and providing suitable flexibility when formed into a three-dimensional reticular fiber assembly. From the above-mentioned viewpoints, the lower limit of the α-olefin unit content of the propylene polymer (a) is preferably 11% by mass or more, more preferably 12% by mass or more.
On the other hand, when the α-olefin unit content of the propylene polymer (a) is 30% by mass or less, an increase in die swelling can be suppressed while maintaining an appropriate crystallization rate of the strands when producing a three-dimensional reticular fiber assembly. From the above viewpoints, the upper limit of the α-olefin unit content of the propylene polymer (a) is preferably 29% by mass or less, more preferably 28% by mass or less.

The propylene polymer (a) is a copolymer of propylene units and α-olefin units other than propylene (however, "α-olefin" here also includes ethylene). The propylene polymer (a) may also be a copolymer of propylene units, α-olefin units other than propylene, and monomer units other than α-olefins.

Examples of α-olefins other than propylene include, but are not limited to, ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, 3-methyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, 2-ethyl-1-hexene, and 2,2,4-trimethyl-1-pentene. Among these, α-olefins having 2 to 10 carbon atoms other than propylene, i.e., ethylene and α-olefins having 4 to 10 carbon atoms, are preferred, with ethylene, 1-butene, 1-hexene, and 1-octene being more preferred. The propylene polymer (a) may contain only one type of α-olefin unit other than propylene, or any two or more types.

Monomers other than α-olefins include one or more vinyl bond-containing monomers such as vinyl acetate, vinyl alcohol, (meth)acrylic acid, (meth)acrylic acid alkyl esters, styrene, and styrene derivatives (here, "(meth)acrylic" refers to either or both of "acrylic" and "methacrylic"). However, from the viewpoint of die swelling when silane-modified polypropylene is obtained, the content of these other monomer units in propylene polymer (a) is preferably 10% by mass or less, particularly 5% by mass or less, and most preferably 0% by mass (not included).

The propylene unit content of propylene polymer (a) is preferably 70% by mass or more, particularly 72 to 88% by mass, even when it contains monomer units other than α-olefins.

Furthermore, the propylene-based polymer (a) may be a random copolymer or a block copolymer.

Specific examples of propylene-based polymer (a) include propylene-ethylene copolymers, propylene-C4-C20 α-olefin copolymers, and propylene-ethylene-C4-C20 α-olefin copolymers.

The melting point of the propylene polymer (a) is preferably 110°C or lower, particularly 109°C or lower, from the viewpoint of improving the fusion strength of the strands by slowing the crystallization rate of the strands when producing a three-dimensional reticular fiber aggregate. On the other hand, from the viewpoint of heat resistance when made into a three-dimensional reticular fiber aggregate, the melting point of the propylene polymer (a) is usually 60°C or higher, preferably 61°C or higher.

In the present invention, the melting points of the propylene polymers such as the propylene polymer (a) and the propylene polymer (b) described below are measured under the following measurement conditions.
<Measurement conditions>
Using a differential scanning calorimeter according to JIS K7121 (2010), about 5 mg of a propylene-based polymer is heated from 20°C to 200°C at a heating rate of 100°C/min, held at 200°C for 3 minutes, cooled to -10°C at a cooling rate of 10°C/min, and then heated to 200°C at a heating rate of 10°C/min. The melting point is determined as the temperature at the apex of the melting peak.

The melt flow rate (MFR) of the propylene polymer (a), measured in accordance with JIS K7210 (1999) at a temperature of 230°C and a load of 2.16 kg, is preferably 0.5 g/10 min or more, more preferably 1 g/10 min or more, and preferably 80 g/10 min or less, more preferably 70 g/10 min or less, from the viewpoint of ease of forming loop coils when molding the three-dimensional network fiber assembly.

From the viewpoint of flexibility of the three-dimensional network fiber assembly, the density of the propylene polymer (a), as measured in accordance with JIS K7112 (1999), is preferably 0.840 g/cm or ^more , more preferably 0.850 g/cm or ^more , and is preferably 0.940 g/cm ^{or less} , more preferably 0.930 g/cm or ^less .

Propylene polymers (a) suitable for use in the present invention can be commercially available products, such as the "Vistamax®" series manufactured by ExxonMobil Corporation, the "Versify®" series manufactured by The Dow Chemical Company, the "Tafmer®" series manufactured by Mitsui Chemicals, Inc., and the "Adflex®" series manufactured by LyondellBasell, Inc., which have the above-described properties and can be appropriately selected and used.

The raw material propylene polymer may contain only one type of propylene polymer (a), or may contain two or more types with different monomer unit compositions, physical properties, etc.

<Propylene-based polymer (b)>
The propylene polymer (b) of the component (b) is a propylene polymer having an α-olefin unit content of less than 10% by mass.
When the α-olefin unit content of the propylene polymer (b) is less than 10% by mass, the heat resistance temperature of the three-dimensional plexiform fiber assembly can be increased. From the above viewpoints, the upper limit of the α-olefin unit content of the propylene polymer (b) is preferably 9% by mass or less, more preferably 8% by mass or less.

Examples of the propylene-based polymer (b) include propylene homopolymers, copolymers of propylene units and α-olefin units other than propylene (however, "α-olefin" here also includes ethylene), and copolymers of propylene units, α-olefin units other than propylene, and monomer units other than α-olefins.

Examples of α-olefins other than propylene include, but are not limited to, ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene, 1-eicosene, 3-methyl-1-butene, 3-methyl-1-pentene, 4-methyl-1-pentene, 2-ethyl-1-hexene, and 2,2,4-trimethyl-1-pentene. Among these, α-olefins having 2 to 10 carbon atoms other than propylene, i.e., ethylene and α-olefins having 4 to 10 carbon atoms, are preferred, with ethylene, 1-butene, 1-hexene, and 1-octene being more preferred. The propylene polymer (b) may contain only one type of α-olefin unit other than propylene, or any two or more types.

Monomers other than α-olefins include one or more vinyl bond-containing monomers such as vinyl acetate, vinyl alcohol, (meth)acrylic acid, (meth)acrylic acid alkyl esters, styrene, and styrene derivatives (here, "(meth)acrylic" refers to either or both of "acrylic" and "methacrylic"). However, from the viewpoint of die swelling when silane-modified polypropylene is obtained, the content of these other monomer units in propylene polymer (b) is preferably 10% by mass or less, particularly 5% by mass or less, and most preferably 0% by mass (not included).

The propylene unit content of propylene polymer (b) is preferably 90% by mass or more, particularly 92 to 100% by mass, even when it contains monomer units other than α-olefins.

Furthermore, the propylene-based polymer (b) may be a random copolymer or a block copolymer.

Specific examples of propylene-based polymer (b) include propylene homopolymer, propylene-ethylene copolymer, propylene-C4-C20 α-olefin copolymer, and propylene-ethylene-C4-C20 α-olefin copolymer.

From the viewpoint of the heat resistance of the three-dimensional reticular fiber assembly, the melting point of the propylene polymer (b) is preferably more than 110° C., more preferably not less than 120° C. On the other hand, since molding at a lower temperature is effective in reducing lumps during molding of the three-dimensional reticular fiber assembly, the melting point of the propylene polymer (b) is usually not more than 170° C., preferably not more than 165° C.
In the present invention, the melting point of the propylene polymer (b) is measured under the same measurement conditions as those for the melting point of the propylene polymer (a).

The melt flow rate (MFR) of the propylene polymer (b), measured in accordance with JIS K7210 (1999) at a temperature of 230°C and a load of 2.16 kg, is preferably 0.5 g/10 min or more, more preferably 1 g/10 min or more, and preferably 80 g/10 min or less, more preferably 70 g/10 min or less, from the viewpoint of ease of forming loop coils when molding the three-dimensional network fiber assembly.

From the viewpoint of flexibility of the three-dimensional network fiber assembly, the density of the propylene polymer (b) measured in accordance with JIS K7112 (1999) is preferably 0.840 g/cm or ^more , more preferably 0.850 g/cm or ^more , and is preferably 0.940 g/cm ^{or less} , more preferably 0.930 g/cm or ^less .

Propylene polymers (b) suitable for use in the present invention can be commercially available products, such as the "Zelas (registered trademark)" series manufactured by Mitsubishi Chemical Corporation, the "Novatec (registered trademark)" series manufactured by Japan Polypropylene Corporation, and the "Prime Polypropylene (registered trademark)" series manufactured by Prime Polymer Co., Ltd., which have the above-mentioned properties and can be appropriately selected and used.

The raw material propylene polymer may contain only one type of propylene polymer (b), or may contain two or more types with different monomer unit compositions, physical properties, etc.

<Raw material propylene polymer>
The raw material propylene polymer according to the present invention contains propylene polymer (a) and propylene polymer (b) in proportions of 35 to 95% by mass of propylene polymer (a) and 5 to 65% by mass of propylene polymer (b), relative to a total of 100% by mass. When the raw material propylene polymer contains propylene polymer (a) in an amount of 35% by mass or more and propylene polymer (b) in an amount of 65% by mass or less, it is easy to control the hardness to a suitable level when forming a three-dimensional network fiber aggregate. From the above viewpoints, the lower limit of the content of propylene polymer (a) in the raw material propylene polymer is preferably 40% by mass or more, more preferably 45% by mass or more, and the upper limit of the content of propylene polymer (b) is preferably 60% by mass or less, more preferably 55% by mass or less.
On the other hand, when the content of the propylene polymer (a) in the raw material propylene polymer is 95% by mass or less and the content of the propylene polymer (b) is 5% by mass or more, when silane-modified polypropylene is obtained, the crystallization rate of the strands can be controlled to a level suitable for forming a three-dimensional network structure, and the three-dimensional network structure can be easily produced. From the above viewpoints, the upper limit of the content of the propylene polymer (a) in the raw material propylene polymer is preferably 65% by mass or less, more preferably 60% by mass or less, and the lower limit of the content of the propylene polymer (b) is preferably 35% by mass or more, more preferably 40% by mass or more.

Generally, in propylene copolymers containing α-olefin units, as the content of α-olefin units increases, the molecular weight of the polymer increases upon crosslinking, resulting in increased die swell and melt tension and improved compression set properties. However, in the production of three-dimensional reticular fiber aggregates, appropriate die swell and melt tension are necessary to obtain good three-dimensional reticular fiber aggregates. Therefore, it is important to select the content ratios of propylene polymer (a) and propylene polymer (b) shown above in the raw propylene polymer used to produce silane-modified polypropylene.

The content of propylene units in the raw propylene polymers, including propylene polymer (a) and propylene polymer (b), is preferably 74 to 99% by mass, more preferably 77 to 97% by mass, even more preferably 80 to 95% by mass, particularly preferably 83 to 993% by mass, and especially preferably 86 to 92% by mass, relative to 100% by mass of the raw propylene polymer, from the viewpoints of cushioning properties, heat resistance, and shape retention of the resulting three-dimensional network fiber aggregate, etc. On the other hand, for the same reasons, the total content of α-olefin units other than propylene units and monomer units other than α-olefins in the raw propylene polymer is preferably 1 to 26% by mass, more preferably 3 to 23% by mass, even more preferably 5 to 20% by mass, particularly preferably 7 to 17% by mass, and especially preferably 8 to 14% by mass, relative to 100% by mass of the raw propylene polymer.

The density of the raw material propylene polymer (measured according to JIS K7112 (1999)) is not particularly limited, but from the viewpoints of cushioning properties, heat resistance, heat deformation resistance, etc., it is preferably 0.850 to 0.930 g/cm ³ , more preferably 0.860 to 0.925 g/cm ³ , and even more preferably 0.870 to 0.920 g/cm ³ .

The melt flow rate (MFR, measured in accordance with JIS K7210 (1999) at a temperature of 230°C and a load of 2.16 kg) of the raw material propylene-based polymer is not particularly limited, but is preferably 1 to 60 g/10 min, more preferably 2 to 59 g/10 min, and even more preferably 3 to 58 g/10 min. If the MFR of the raw material propylene-based polymer is below the above upper limit, the melt tension during molding of the three-dimensional reticular fiber aggregate will not be too low, the strands will not be easily stretched, and a stable molded product will tend to be obtained. If the MFR of the raw material propylene-based polymer is above the above lower limit, when forming the three-dimensional reticular fiber aggregate, the melt tension will not be too high, which will result in an excessive increase in strand diameter, making it difficult for the molten strands to deform and making loop formation difficult, and a stable molded product will tend to be obtained.

<Other propylene polymers>
The raw material propylene polymer according to the present invention may contain a propylene polymer other than the above-mentioned propylene polymer (a) and propylene polymer (b) in a range that satisfies the preferred content of propylene units in the raw material propylene polymer.

Other propylene polymers include propylene polymers having an α-olefin unit content of more than 30% by mass and not more than 50% by mass (here, examples of α-olefin units include those exemplified as α-olefin units contained in propylene polymer (a) and propylene polymer (b)), and copolymers of propylene with a monomer other than an α-olefin (here, examples of monomers other than an α-olefin include those exemplified as monomers other than an α-olefin contained in propylene polymer (a) and propylene polymer (b)).

Other commercially available propylene polymers include the "ELMODU (registered trademark)" series manufactured by Idemitsu Kosan Co., Ltd.

The raw propylene polymer may contain only one type of other propylene polymer, or may contain two or more types with different monomer unit compositions, physical properties, etc.

When the raw material propylene polymer contains other propylene polymers, the content of the other propylene polymers is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of the total of propylene polymer (a) and propylene polymer (b).

<Silane modification>
The silane-modified polypropylene of the present invention is obtained by grafting a silane compound onto the above-mentioned starting propylene polymer. The silane compound to be grafted is not particularly limited as long as it is a silane compound having an alkoxy group, but the silane-modified moiety of the silane-modified polypropylene of the present invention is preferably a polymer residue of an unsaturated silane compound represented by the following formula (1):

R-Si(R') ₃ ...(1)
In the formula (1), R is an ethylenically unsaturated hydrocarbon group, and R' are each independently a hydrocarbon group having 1 to 10 carbon atoms or an alkoxy group having 1 to 10 carbon atoms, and at least one of the R' is an alkoxy group having 1 to 10 carbon atoms. R serves as a bonding site during graft introduction into a propylene-based polymer.

In the above formula (1), R is preferably an ethylenically unsaturated hydrocarbon group having 2 to 10 carbon atoms, and more preferably an ethylenically unsaturated hydrocarbon group having 2 to 6 carbon atoms. Specific examples include alkenyl groups such as vinyl, propenyl, butenyl, and cyclohexenyl.

In the above formula (1), R' is preferably a hydrocarbon group having 1 to 6 carbon atoms or an alkoxy group having 1 to 6 carbon atoms, and more preferably a hydrocarbon group having 1 to 4 carbon atoms or an alkoxy group having 1 to 4 carbon atoms. Furthermore, at least one of the R's is preferably an alkoxy group having 1 to 6 carbon atoms, and more preferably an alkoxy group having 1 to 4 carbon atoms.

In the above formula (1), the hydrocarbon group R' having 1 to 10 carbon atoms may be an aliphatic hydrocarbon group, an alicyclic hydrocarbon group, or an aromatic hydrocarbon group, but is preferably an aliphatic hydrocarbon group. Furthermore, the alkoxy group R' having 1 to 10 carbon atoms may be linear, branched, or cyclic, but is preferably linear or branched. Specific examples of the hydrocarbon group R' include alkyl groups such as methyl, ethyl, isopropyl, t-butyl, n-butyl, i-butyl, and cyclohexyl, and aryl groups such as phenyl, but are not limited to these. Specific examples of the alkoxy group R' include methoxy, ethoxy, isopropoxy, and β-methoxyethoxy.

In the above formula (1), at least one of the three R's is an alkoxy group, but it is preferable that two or more R's are alkoxy groups, and it is more preferable that all three R's are alkoxy groups.

Particularly preferred unsaturated silane compounds are vinyltrialkoxysilanes, such as vinyltrimethoxysilane, vinyltriethoxysilane, and propenyltrimethoxysilane. This is because the ethylenically unsaturated hydrocarbon group facilitates silane modification of the starting propylene polymer, and the three alkoxy groups allow for the crosslinking reaction described below. Specifically, the alkoxy groups of the alkoxysilane grafted onto the starting propylene polymer react with water in the presence of a silanol condensation catalyst to hydrolyze and generate silanol groups. These silanol groups then undergo dehydration condensation, resulting in a crosslinking reaction in which the silane-modified polypropylenes bond together. Note that one unsaturated silane compound may be used alone, or two or more may be used in combination as appropriate.

The content of the silane compound in the silane-modified polypropylene (the amount of the unsaturated silane compound introduced into the raw material propylene polymer) is not particularly limited, but is preferably 0.1 to 5.0% by mass relative to the total amount of silane-modified polypropylene from the viewpoints of viscosity during molding, handleability, heat resistance, heat distortion resistance, shape retention, etc. The content of the silane compound in the silane-modified polypropylene is more preferably 0.2% by mass or more, even more preferably 0.3% by mass or more, and is more preferably 4.0% by mass or less, even more preferably 3.0% by mass or less.
The content of the silane compound is the mass ratio of the silane compound (unsaturated silane compound to be introduced) to the total amount of the raw material propylene-based polymer before modification, and can also be confirmed by heating and burning a sample to incinerate it, fusing the ash with an alkali, dissolving it in pure water, and quantifying it, followed by ICP atomic emission spectrometry using a high-frequency plasma atomic emission spectrometer.

The silane-modified polypropylene of the present invention may be grafted with a compound other than a silane compound (unsaturated silane compound) (hereinafter also referred to as "other graft compound"), as long as the effects of the present invention are not impaired. Examples of other graft compounds include, but are not limited to, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, ethacrylic acid, maleic acid, fumaric acid, tetrahydrophthalic acid, itaconic acid, citraconic acid, crotonic acid, and isocrotonic acid, as well as their acid anhydrides.

As described above, the silane-modified polypropylene of the present invention can be produced by grafting a silane compound onto a raw propylene polymer to silane-modify it. The silane modification method can be performed according to known techniques and is not particularly limited. For example, solution modification, melt modification, solid-phase modification by irradiation with an electron beam or ionizing radiation, and modification in a supercritical fluid are preferably used. Of these, melt modification is more preferred due to its superior equipment and cost competitiveness, and melt-kneading modification using an extruder with excellent continuous productivity is even more preferred. Examples of equipment used for melt-kneading modification include single-screw extruders, twin-screw extruders, Banbury mixers, and roll mixers. Of these, single-screw extruders and twin-screw extruders with excellent continuous productivity are preferred.

Generally, grafting of a silane compound onto a propylene-based polymer can be carried out by a graft polymerization reaction in which the carbon-hydrogen bonds of the propylene-based polymer are cleaved to generate carbon radicals, to which unsaturated functional groups are added. In addition to the electron beams and ionizing radiation mentioned above, carbon radicals can also be generated by high temperature or by using radical generators such as organic or inorganic peroxides. From the standpoints of cost and ease of use, the use of organic peroxides is preferred.

The radical generator used in producing the silane-modified polypropylene of the present invention is not particularly limited, but examples include hydroperoxides, dialkyl peroxides, diacyl peroxides, organic peroxides belonging to the peroxy ester and ketone peroxide groups, and azo compounds.

Specific examples of hydroperoxides include cumene hydroperoxide and tertiary butyl hydroperoxide. Examples of dialkyl peroxides include dicumyl peroxide, ditertiary butyl peroxide, 2,5-dimethyl-2,5-ditertiary butylperoxyhexane, and 2,5-dimethyl-2,5-ditertiary butylperoxyhexyne-3. Examples of diacyl peroxides include lauryl peroxide and benzoyl peroxide. Examples of peroxy esters include tertiary peroxyacetate, tertiary butyl peroxybenzoate, and tertiary butyl peroxyisopropyl carbonate. Examples of ketone peroxides include cyclohexanone peroxide. Examples of azo compounds include azobisisobutyronitrile and methyl azoisobutyrate. These radical generators may be used alone or in combination of two or more.

In a commonly used melt-kneading modification procedure using an extruder, the raw propylene polymer, the precursor compound of the silane compound to be grafted (e.g., an unsaturated silane compound), and, if necessary, a radical generator such as an organic peroxide are mixed and blended together, and the mixture is fed into a kneader or extruder. The mixture is then extruded while being heated, melt-kneaded, and the molten resin emerging from the die is cooled in a water tank or the like to obtain silane-modified polypropylene.

The blending ratio of the starting propylene polymer to the precursor compound of the silane compound to be grafted (e.g., an unsaturated silane compound) is not particularly limited and can be set appropriately depending on the desired introduction ratio of the silane compound. From the standpoint of achieving the desired amount of silane modification and reducing residual unreacted materials, the blending ratio of the precursor compound of the silane compound per 100 parts by mass of the starting propylene polymer is preferably 0.3 to 10 parts by mass, more preferably 0.5 to 5 parts by mass.

The amount of radical generator used, which is added as needed, can be adjusted as needed and is not particularly limited. However, in the case of organic peroxides, from the viewpoints of achieving the desired amount of silane modification and suppressing deterioration of the resulting silane-modified polypropylene, the blending ratio of organic peroxide is preferably 0.001 to 10 parts by mass, and more preferably 0.01 to 5 parts by mass, per 100 parts by mass of the precursor compound of the silane compound (e.g., an unsaturated silane compound).

Furthermore, as for the melt extrusion modification conditions, when using, for example, a single-screw extruder or a twin-screw extruder, it is preferable to extrude at a temperature of approximately 150 to 300°C.

<Combined ingredients>
The silane-modified polypropylene of the present invention may contain additives commonly used in resin compositions, as long as the effects of the present invention are not impaired. Examples of such additives include heat stabilizers, ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, crystal nucleating agents, rust inhibitors, viscosity modifiers, and pigments.

Specific examples of antioxidants include, but are not limited to, phenol-based, sulfur-based, and phosphorus-based antioxidants.
The amount of the antioxidant to be added is not particularly limited, but is preferably 0.01 to 2.0 parts by mass, more preferably 0.1 to 1.0 part by mass, per 100 parts by mass of the silane-modified polypropylene.

Specific examples of the ultraviolet absorber include benzophenone-based ones such as 2-hydroxy-4-normal-octyloxybenzophenone, 2-hydroxy-4-methoxybenzophenone, 2,2-dihydroxy-4-methoxybenzophenone, 2-hydroxy-4-methoxy-4-carboxybenzophenone, and 2-hydroxy-4-N-octoxybenzophenone; benzotriazole-based ones such as 2-(2-hydroxy-3,5-di-t-butylphenyl)benzotriazole and 2-(2-hydroxy-5-methylphenyl)benzotriazole; and salicylate-based ones such as phenyl salicylate and p-octylphenyl salicylate, but are not particularly limited to these.
The amount of the ultraviolet absorber to be added is not particularly limited, but is preferably 0.01 to 1.0 part by mass, more preferably 0.02 to 0.5 part by mass, per 100 parts by mass of the silane-modified polypropylene.

As the viscosity modifier, rubber compounding oil, specifically paraffinic process oil, is preferred.
The amount of the viscosity modifier to be added is preferably 0.5 to 5 parts by mass, more preferably 0.8 to 3 parts by mass, based on 100 parts by mass of the silane-modified polypropylene.

<Physical properties>
The melting point of the silane-modified polypropylene of the present invention is not particularly limited, but is preferably 120°C or higher, more preferably 125°C or higher, and even more preferably 130°C or higher. When the melting point is above the above lower limit, heat resistance is high, and the resulting three-dimensional reticular fiber assembly makes it easier to produce products with good heat resistance. Furthermore, by setting the melting point above the above lower limit, settling tends to be less likely to occur when used at high temperatures. On the other hand, the upper limit of the melting point of the silane-modified polypropylene of the present invention is not particularly limited, but is usually 165°C or lower.
The melting point of the silane-modified polypropylene was measured using a differential scanning calorimeter in accordance with JIS K7121 (2010), by heating approximately 5 mg of a sample from 20°C to 200°C at a heating rate of 100°C/min, holding the sample at 200°C for 3 minutes, then cooling the sample to -10°C at a cooling rate of 10°C/min, and then heating the sample to 200°C at a heating rate of 10°C/min. The extrapolated peak end point (°C) was calculated from the thermogram measured at this time, and this was used as the melting point.

The melt flow rate (MFR, measured in accordance with JIS K7210 (1999) at 230°C and a load of 2.16 kg) of the silane-modified polypropylene of the present invention is not particularly limited, but is preferably 10 g/10 min or more, more preferably 11 g/10 min or more, even more preferably 12 g/10 min or more, and is preferably 80 g/10 min or less, more preferably 79 g/10 min or less, and even more preferably 78 g/10 min or less. When the MFR is above the lower limit, die swelling and melt tension are low, making it difficult for the strand diameter to increase. This makes it easier for loops to form along the sides of the resulting three-dimensional network fiber aggregate, which tends to facilitate the production of products with good resilience. Furthermore, when the MFR is below the upper limit, the extrusion of multiple strands tends to be stable, making it difficult for the multiple strands to curl up and form a solidified resin mass. Furthermore, loop formation and strand fusion are stable, strand diameter tends to be uniform, and the resulting three-dimensional network fiber assembly tends to have good uniformity, which tends to improve the performance and quality of the product.

The die swell ratio of the silane-modified polypropylene of the present invention is not particularly limited, but the lower limit is preferably 0.40 or more, more preferably 0.42 or more, and even more preferably 0.44 or more. On the other hand, the upper limit is preferably 0.70 or less, more preferably 0.68 or less, and even more preferably 0.66 or less. When the die swell ratio of the silane-modified polypropylene is equal to or less than the above upper limit, it is possible to prevent the strands from swelling beyond the desired wire diameter during the formation of a three-dimensional network structure, and it tends to be easier to form a loop coil. On the other hand, when the die swell ratio is equal to or greater than the above lower limit, it is possible to prevent the strand diameter from becoming too thin, and it tends to be easier to maintain durability when formed into a three-dimensional network fiber aggregate.

The die swell ratio of the silane-modified polypropylene is a value measured and calculated in accordance with 4.7.2 of JIS K 7199. Specifically, the silane-modified polypropylene is extruded from a die having a die temperature of 210°C at a rate of 10 mm/min, and the extrudate obtained when passing through a die having a diameter D (mm) (measured at room temperature) has a diameter Da (mm) (measured at room temperature). The die swell ratio Sa is calculated by the following formula (2):
Sa=Da/D...(2)

The density of the silane-modified polypropylene of the present invention is measured using a press-molded sheet-like test piece having a thickness of 2 mm in accordance with JIS K7112 (1999). The density of the silane-modified polypropylene of the present invention is not particularly limited, but from the viewpoint of flexibility when made into a three-dimensional network fiber assembly, it is preferably 0.850 g/cm or ^more , more preferably 0.855 g/cm ^{or more} , and even more preferably 0.860 g/cm ^or more, and is preferably 0.930 g/cm ^{or less} , more preferably 0.925 g/cm ^{or less} , and even more preferably 0.920 g/cm ^or less.

[Silane-modified polypropylene composition]
The silane-modified polypropylene composition of the present invention contains at least the above-mentioned silane-modified polypropylene of the present invention and a silanol condensation catalyst.

<Silanol condensation catalyst>
The silanol condensation catalyst used here includes one or more compounds selected from the group consisting of metal organic acid salts, titanates, borates, organic amines, ammonium salts, phosphonium salts, inorganic and organic acids, and inorganic acid esters.

Examples of metal organic acid salts include, but are not limited to, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, stannous acetate, stannous octoate, cobalt naphthenate, lead octoate, lead naphthenate, zinc octoate, zinc caprylate, iron 2-ethylhexanoate, iron octoate, and iron stearate. Examples of titanates include, but are not limited to, tetrabutyl titanate, tetranonyl titanate, and bis(acetylacetonitrile)diisopropyl titanate. Examples of organic amines include, but are not limited to, ethylamine, dibutylamine, hexylamine, triethanolamine, dimethyl soya amine, tetramethylguanidine, and pyridine. Examples of ammonium salts include, but are not limited to, ammonium carbonate and tetramethylammonium hydroxide. Examples of phosphonium salts include, but are not limited to, tetramethylphosphonium hydroxide. Examples of inorganic and organic acids include, but are not limited to, sulfonic acids such as sulfuric acid, hydrochloric acid, acetic acid, stearic acid, maleic acid, toluenesulfonic acid, and alkylnaphthylsulfonic acid. Examples of inorganic acid esters include, but are not limited to, phosphate esters.

Among these, metal organic acid salts, sulfonic acids, and phosphates are preferred, and metal carboxylates of tin, such as dioctyltin dilaurate, alkylnaphthylsulfonic acids, and ethylhexyl phosphate, are more preferred. The silanol condensation catalysts may be used alone or in combination of two or more.

The content of the silanol condensation catalyst in the silane-modified polypropylene composition of the present invention is not particularly limited, but from the viewpoints of suppressing premature crosslinking during molding of the pre-crosslinked molded article, promoting the crosslinking reaction during production of the silane-crosslinked polypropylene, and improving the heat resistance of the resulting three-dimensional network fiber aggregate, etc., it is preferably 0.01 to 0.5 parts by mass, and more preferably 0.03 to 0.3 parts by mass, per 100 parts by mass of the silane-modified polypropylene.

The silanol condensation catalyst is preferably used as a silanol condensation catalyst-containing masterbatch, which is a blend of polypropylene and the silanol condensation catalyst. Examples of polypropylene that can be used in this silanol condensation catalyst-containing masterbatch include homopolypropylene, which is a polymer of propylene, and copolymers of propylene with ethylene or α-olefins such as butene, hexene, and octene (excluding propylene). Among these, homopolypropylene and propylene-ethylene copolymers are preferred from the standpoints of heat resistance, flexibility, and the like. The propylene-ethylene copolymer is preferably a copolymer of 60 to 98% by mass of propylene and 2 to 40% by mass of ethylene. In the silanol condensation catalyst masterbatch, only one of these polypropylenes may be used alone, or two or more may be used in combination as appropriate.

When the silanol condensation catalyst is used as a silanol condensation catalyst-containing masterbatch, which is a blend of polypropylene and the silanol condensation catalyst, there are no particular restrictions on the silanol condensation catalyst content in the masterbatch, but it is usually preferable to set it at around 0.1 to 5.0 mass%. Commercially available silanol condensation catalyst-containing masterbatch products can be used, such as "PZ010" manufactured by Mitsubishi Chemical Corporation.

<Other ingredients>
In addition to the silane-modified polypropylene and silanol condensation catalyst described above, the silane-modified polypropylene composition of the present invention may contain, as other components, various additives, resins other than the silane-modified polypropylene, and resins other than the polypropylene in the silanol condensation catalyst-containing masterbatch, etc., within a range that does not impair the effects of the present invention. For example, the silane-modified polypropylene composition may contain the above-mentioned compounding agents that can be compounded with the silane-modified polypropylene of the present invention.

Specific examples of other ingredients include thermoplastic solid resins other than polypropylene, solid rubber, liquid resins, softeners, plasticizers, etc. These can also be used as tackifiers to improve adhesion or compatibility. For example, rosin and its derivatives, terpene resins, petroleum resins and their derivatives, alkyd resins, alkylphenol resins, terpene phenol resins, coumarone-indene resins, synthetic terpene resins, alkylene resins, polyisobutylene, polybutadiene, polybutene, copolymers of isobutylene and butadiene, mineral oil, process oil, pine oil, anthracene oil, pine root oil, plasticizers, animal and vegetable oils, polymerized oils, etc. may also be included.

[Silane-crosslinked polypropylene]
The silane-modified polypropylene composition of the present invention can be exposed to a water-containing atmosphere to promote a crosslinking reaction between silanol groups, thereby producing a silane-crosslinked polypropylene (hereinafter, sometimes referred to as the "silane-crosslinked polypropylene of the present invention"). The method for exposing the composition to a water-containing atmosphere can be various, and is not particularly limited. Examples of the method include leaving the composition in moist air, blowing air containing water vapor onto the composition, immersing the composition in a water bath, and spraying warm water in a mist.

More specifically, in the silane-modified polypropylene composition of the present invention, hydrolyzable alkoxy groups derived from a silane compound (e.g., an unsaturated silane compound) grafted onto the silane-modified polypropylene react with water in the presence of a silanol condensation catalyst and hydrolyze to generate silanol groups. The silanol groups then undergo dehydration condensation with each other, causing a crosslinking reaction in which the silane-modified polypropylenes bond together to form silane-crosslinked polypropylene.

The crosslinking conditions are determined by the conditions for exposure to the water-containing atmosphere and are not particularly limited, but typically a temperature range of 20 to 130°C and a time range of 10 minutes to 1 week are preferred, and a temperature range of 20 to 130°C and a time range of 1 hour to 160 hours are more preferred. When using air containing moisture, the relative humidity can be adjusted appropriately within the range of 1 to 100%.

[Molded product/crosslinked molded product]
Before the crosslinking treatment, the silane-modified polypropylene composition of the present invention can be molded into a predetermined shape by various molding methods such as extrusion molding, injection molding, press molding, etc. to obtain a (non-crosslinked) molded article. The obtained (non-crosslinked) molded article can then be exposed to a water-containing atmosphere to promote the crosslinking reaction between silanol groups, thereby obtaining a crosslinked molded article (silane-crosslinked polypropylene molded article).

[Three-dimensional network fiber assembly]
The silane-modified polypropylene composition of the present invention can be extruded to form strands (molded articles), and then these strands can be heat-fused together and then cooled with water to form a three-dimensional reticular fiber assembly.For example, the silane-modified polypropylene composition can be molded into a three-dimensional reticular fiber assembly using a manufacturing apparatus and molding method such as those described in International Publication No. 2012/035736.The three-dimensional reticular fiber assembly thus obtained is preferably exposed to a water atmosphere as described above and used as a silane-crosslinked three-dimensional reticular molded article.

The silane-modified polypropylene composition of the present invention can be molded without crosslinking during molding, making it possible to efficiently mold three-dimensional network fiber assemblies that require special moldability, such as loopability and thermal adhesion immediately after molding. Furthermore, the resulting molded articles have improved heat resistance, a major issue with ethylene-based copolymers such as ethylene-α-olefin copolymers. This significantly reduces the problem of settling even under load at high temperatures, making it possible to provide three-dimensional network fiber assemblies that exhibit excellent cushioning properties.

[Physical properties of silane-crosslinked polypropylene]
The test pieces used to evaluate the physical properties of the silane-crosslinked polypropylene of the present invention are specifically produced by the method described in the Examples section below.

The flexural modulus of the silane-crosslinked polypropylene of the present invention can be measured in accordance with JIS K7171 (2008) using an injection-molded test piece having a thickness of 4 mm, a length of 800 mm, and a width of 10 mm.
The flexural modulus of the silane-crosslinked polypropylene of the present invention is not particularly limited, but is preferably 30 MPa or more, more preferably 40 MPa or more, even more preferably 50 MPa or more, and is preferably 300 MPa or less, more preferably 290 MPa or less, even more preferably 280 MPa or less. When the flexural modulus is equal to or greater than the above-mentioned lower limit, the resulting three-dimensional reticular fiber assembly tends to have sufficient strength to withstand loads and is less likely to become worn. When the flexural modulus is equal to or less than the above-mentioned upper limit, the resulting three-dimensional reticular fiber assembly tends to have sufficient flexibility for use.

The compression set of the silane-crosslinked polypropylene of the present invention was determined by punching out an injection-molded sheet having a thickness of 2 mm into a 30 mm diameter circle, stacking six of these sheets, and heat-treating them at a test temperature of 70°C for 22 hours in a state compressed by 25% using a spacer, according to JIS K6262 (2013). The compression set was then released and left in a thermostatic chamber at 23°C and 50% RH for 30 minutes, after which the thickness was measured and the compression set (CS: unit: %) was calculated. The compression set of the silane-crosslinked polypropylene of the present invention is not particularly limited, but is preferably 60% or less, more preferably 59% or less, and even more preferably 58% or less. Having a compression set below the above upper limit results in excellent heat distortion resistance and shape recovery, and the resulting three-dimensional network fiber assembly tends to be less prone to settling. There is no particular limit on the lower limit of the compression set.

[Application]
The applications of the silane-modified polypropylene, silane-modified polypropylene composition, and silane-crosslinked polypropylene of the present invention are not particularly limited. For example, they can be suitably used as cushioning materials for furniture, bedding such as bed mats and pillows, and seats for vehicles such as cars and ships. When applied to these applications, they are preferably used as the three-dimensional reticular fiber assembly described above. This three-dimensional reticular fiber assembly can also be used as a laminate with other materials as necessary. However, as mentioned above, the shape of the molded product is not limited to the three-dimensional reticular fiber assembly, and it can be molded into a predetermined shape depending on the application.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples as long as it does not depart from the gist of the invention. Furthermore, the various manufacturing conditions and evaluation result values in the following examples represent preferred upper or lower limits for the implementation 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 the examples.

[Raw materials]
The raw materials used in the examples and comparative examples are shown below.
The density and MFR of the raw material propylene polymer to be subjected to silane modification are approximately equal to the values calculated by proportional calculation from the densities and MFRs of the propylene polymer (a) and the propylene polymer (b) to be blended into the raw material propylene polymer and their blending ratios.

<Propylene-based polymer (a)>
PP-a1: Vistamax (registered trademark) 6202 (manufactured by ExxonMobil Corporation, propylene-ethylene copolymer, MFR: 20 g/10 min (230° C., 2.16 kg load), density: 0.86 g/cm ³ , melting point: 102° C., ethylene unit content: 15% by mass)

PP-a2: Tafmer (registered trademark) PN-2060 (manufactured by Mitsui Chemicals, Inc., propylene-ethylene-butene copolymer, MFR: 6.0 g/10 min (230°C, 2.16 kg load), density: 0.87 g/cm ³ , melting point: 160°C, α-olefin unit (ethylene unit + butene unit) content: 16% by mass)

PP-a3: Adflex (registered trademark) V-109F (manufactured by LyondellBasell, propylene-ethylene copolymer, MFR: 12 g/10 min (230°C, 2.16 kg load), density: 0.88 g/cm ³ , melting point: 142°C, ethylene unit content: 14% by mass)

<Propylene-based polymer (b)>
PP-b1: ZELAS (registered trademark) 7055 (manufactured by Mitsubishi Chemical Corporation, propylene-ethylene copolymer, MFR: 7.0 g/10 min (230° C., 2.16 kg load), density: 0.89 g/cm ³ , melting point: 160° C., ethylene unit content: 7% by mass)

PP-b2: Novatec PP (registered trademark) MG03BD (manufactured by Japan Polypropylene Corporation, propylene-ethylene copolymer, MFR: 30 g/10 min (230°C, 2.16 kg load), density: 0.90 g/cm ³ , melting point: 155°C, ethylene unit content: 2% by mass)

PP-b3: Novatec (registered trademark) MA3Q (manufactured by Japan Polypropylene Corporation, propylene homopolymer, MFR: 11 g/10 min (230°C, 2.16 kg load), density: 0.90 g/cm ³ , melting point: 160°C)

<Other olefin polymers>
EP-c1: Tafmer (registered trademark) P-0275 (manufactured by Mitsui Chemicals, Inc., ethylene-propylene copolymer, MFR: 2.9 g/10 min (190°C, 2.16 kg load), density: 0.86 g/cm ³ , ethylene unit content: 71 mass %, melting point: 24°C)

<Catalyst Masterbatch (MB)>
Catalyst MB: PZ010 (manufactured by Mitsubishi Chemical Corporation, tin catalyst (dioctyltin dilaurate)-containing homopolypropylene (MFR: 16 g/10 min (230° C., 2.16 kg load), density: 0.90 g/cm ³ ), dioctyltin dilaurate content: 1% by mass)
was used.

[Measurement and evaluation method]
The methods for measuring and evaluating various physical properties and characteristics are as follows:

[Measurement of silane-modified polypropylene]
<Melting point>
Using a differential scanning calorimeter manufactured by Hitachi High-Tech Science Corporation, product name "DSC6220," approximately 5 mg of a sample was heated from 20°C to 200°C at a heating rate of 100°C/min in accordance with JIS K7121 (2010), and then the sample was cooled to -10°C at a cooling rate of 10°C/min and heated to 200°C at a heating rate of 10°C/min. The extrapolated peak end point (°C) was calculated from the thermogram measured when the sample was heated to 200°C at a heating rate of 10°C/min, and the melting point was determined.

<Melt flow rate (MFR)>
Measurement was carried out in accordance with JIS K7210 (1999) at 230°C under a load of 2.16 kg.

<Die swell ratio>
The values used were measured and calculated in accordance with 4.7.2 of JIS K7199. Specifically, the silane-modified polypropylene was extruded at a rate of 10 mm/min from a die having a die temperature of 210°C, and the extrudate was passed through a die having a diameter D (mm) (measured at room temperature). From the diameter Da (mm) (measured at room temperature) of the extrudate obtained, the die swell ratio Sa was calculated using the following formula (2):
Sa=Da/D...(2)

<Density>
The measurement was carried out in accordance with JIS K7112 (1999) using a sheet-like test piece having a thickness of 2 mm obtained by press-molding the silane-modified polypropylene.

[Evaluation of silane-crosslinked polypropylene]
<Flexural modulus>
Measurement was carried out in accordance with JIS K7171 (2008) using an injection-molded silane-crosslinked test piece having a thickness of 4 mm, a length of 800 mm, and a width of 10 mm.

<Compression set>
An injection-molded silane-crosslinked sheet-like molded article having a thickness of 2 mm was punched out into a circle having a diameter of 30 mm, and six of these were stacked. In accordance with JIS K6262 (2013), the sheet was compressed 25% with a spacer and heat-treated at a test temperature of 70°C for 22 hours. After releasing the compression, the sheet was left in a thermostatic chamber at 23°C and 50% RH for 30 minutes, after which the thickness was measured and the compression set (CS: unit: %) was calculated. The lower the compression set value, the better.

[Examples and Comparative Examples]
[Example 1]
60 parts by mass of PP-a1, 40 parts by mass of PP-b1, 1.0 part by mass of vinyltrimethoxysilane (VTMOS), an unsaturated silane compound as a silane compound precursor, and 0.01 parts of di-tertiary butyl peroxide, an organic peroxide as a radical generator, were stirred in a blender. The mixture was then charged into a single-screw extruder (IKG Corporation, PMS50) set at a temperature of 200 ° C., and the strand emerging from the nozzle was cooled and solidified in a water bath and then cut into pellets to obtain silane-modified polypropylene A. The melting point, MFR, die swell ratio, and density of the obtained silane-modified polypropylene A were measured according to the measurement and evaluation methods described above. The results are shown in Table 1.
The density of the raw material propylene polymer for silane-modified polypropylene A was 0.87 (= 0.86 × 0.6 + 0.89 × 0.4) g/cm ³ , and the MFR was calculated to be 14.8 (= 20 × 0.6 + 7.0 × 0.4) g/10 min.

5 parts by mass of PZ010 as catalyst MB was added to 100 parts by mass of the silane-modified polypropylene A obtained above to obtain silane-modified polypropylene composition A. This was placed in an injection molding machine and molded into a 4 mm or 2 mm thick sheet at 200°C. This sheet was left in a thermo-hygrostat at 85°C and 85% RH for 16 hours to obtain a sheet containing silane-crosslinked polypropylene A. The flexural modulus and compression set of the resulting sheet were measured according to the measurement and evaluation methods described above. The results are shown in Table 1.

[Examples 2 to 6, Comparative Examples 1 to 5]
Sheet-like molded articles containing silane-modified polypropylenes B to K and silane-crosslinked polypropylenes B to K were produced and evaluated in the same manner as in Example 1, except that the raw material compositions were as shown in Table 1. The results are shown in Table 1.

The above results reveal the following:

The silane-modified polypropylenes A to F of Examples 1 to 6 have appropriate MFR and density and small die swell ratios, and therefore are easily moldable into three-dimensional network fiber aggregates, and are expected to have excellent cushioning properties.
The silane-crosslinked polypropylenes A to F of Examples 1 to 6 had small compression set at 70°C, which is an index of heat distortion resistance and shape recovery. In addition, the flexural modulus, which is an index of flexibility, was a value indicating sufficient flexibility for use as a three-dimensional network fiber assembly.

The silane-crosslinked polypropylene G of Comparative Example 1, in which the propylene-based polymer (a) was not used as the raw material propylene-based polymer, had a good compression set at 70°C. However, since the silane-modified polypropylene G had a low MFR and a large die swelling ratio, it is presumed that the moldability into a three-dimensional reticular fiber aggregate was poor.
The silane-crosslinked polypropylene H of Comparative Example 2, which used only the propylene polymer (a) as the raw material propylene polymer, had a large compression set and was poor in heat distortion resistance and shape recovery. Therefore, it is thought that distortion tends to remain, and settling occurs when the polypropylene is made into a three-dimensional network fiber assembly.
The silane-crosslinked polypropylenes I to K of Comparative Examples 3 to 6, in which the content of propylene polymer (a) in the raw material propylene polymer was low or in which only propylene polymer (b) was used, showed large compression set and poor heat distortion resistance and shape recovery. This likely resulted in residual distortion, which is thought to cause settling when formed into a three-dimensional reticular fiber assembly. Furthermore, the flexural modulus, which is an index of flexibility, was too hard for use as a three-dimensional reticular fiber assembly.

From the above, it has been shown that the silane-modified polypropylene of the present invention has favorable MFR, melting point, die swell ratio, and density, making it excellent in moldability into three-dimensional network fiber assemblies, and that the silane-crosslinked polypropylene obtained by crosslinking this silane-modified polypropylene also has excellent flexibility, heat distortion resistance, and shape recovery.

The silane-modified polypropylene of the present invention has excellent heat resistance and fluidity suitable for molding three-dimensional network fiber assemblies. Therefore, by using this silane-modified polypropylene to produce three-dimensional network fiber assemblies, it is possible to obtain three-dimensional network fiber assemblies that have low compression set even under heated conditions, are resistant to sagging or deformation due to use with electric bedding such as electric blankets, and have excellent heat distortion resistance and shape recovery. Therefore, the silane-modified polypropylene and silane-modified polypropylene composition of the present invention, as well as molded articles, crosslinked molded articles, and three-dimensional network fiber assemblies made therefrom, can be widely and effectively used as constituent materials for, for example, furniture, bedding such as bed mats and pillows, and cushioning materials for vehicle and marine seats, etc.

Claims (13)

A silane-modified polypropylene obtained by silane-modifying a raw material propylene-based polymer, wherein the raw material propylene-based polymer contains the following components (a) and (b), with the component (a) being 35 to 65% by mass and the component (b) being 35 to 65% by mass, relative to 100% by mass of the total of the components (a) and (b):
Component (a): A propylene polymer having an α-olefin unit content of 10 to 30% by mass. Component (b): A propylene polymer having an α-olefin unit content of less than 10% by mass (wherein the “α-olefin” in the above components (a) and (b) refers to “ethylene or an α-olefin having 4 or more carbon atoms .”). The silane-modified polypropylene according to claim 1, wherein the melting point of the component (a) measured under the following conditions is 110°C or lower.
<Measurement conditions>
Using a differential scanning calorimeter in accordance with JIS K7121 (2010), approximately 5 mg of component (a) is heated from 20°C to 200°C at a heating rate of 100°C/min, held at 200°C for 3 minutes, cooled to -10°C at a cooling rate of 10°C/min, and then heated to 200°C at a heating rate of 10°C/min. The melting point is determined as the temperature at the top of the melting peak. The silane-modified polypropylene according to claim 1 or 2, wherein the melting point of the component (b) measured under the following conditions exceeds 110°C.
<Measurement conditions>
Using a differential scanning calorimeter in accordance with JIS K7121 (2010), approximately 5 mg of component (b) is heated from 20°C to 200°C at a heating rate of 100°C/min, held at 200°C for 3 minutes, cooled to -10°C at a cooling rate of 10°C/min, and then heated to 200°C at a heating rate of 10°C/min. The melting point is determined as the temperature at the top of the melting peak. The silane-modified polypropylene according to any one of claims 1 to 3, wherein the α-olefins of components (a) and (b) are both α-olefins having 2 to 10 carbon atoms, excluding propylene. The silane-modified polypropylene according to any one of claims 1 to 4, wherein the silane-modified moiety of the silane-modified polypropylene is a polymerized residue of an unsaturated silane compound represented by the following formula (1):
R-Si(R') ₃ ...(1)
(In the formula, R is an ethylenically unsaturated hydrocarbon group, and R's are each independently a hydrocarbon group having 1 to 10 carbon atoms or an alkoxy group having 1 to 10 carbon atoms, and at least one of the R's is an alkoxy group having 1 to 10 carbon atoms.) The silane-modified polypropylene according to any one of claims 1 to 5, having a density of 0.850 to 0.930 g/cm3 ^. The silane-modified polypropylene according to any one of claims 1 to 6, having an MFR of 10 to 80 g/10 min, measured at 230°C under a load of 2.16 kg in accordance with JIS K7210 (1999). A silane-modified polypropylene composition comprising the silane-modified polypropylene according to any one of claims 1 to 7 and a silanol condensation catalyst. A molded article obtained by molding the silane-modified polypropylene composition described in claim 8. A crosslinked molded article obtained by crosslinking the molded article according to claim 9. The crosslinked molded article according to claim 10, having a flexural modulus of 300 MPa or less as measured in accordance with JIS K7171 (2008). A three-dimensional network fiber assembly formed by molding the silane-modified polypropylene composition described in claim 8. A crosslinked molded article obtained by crosslinking the three-dimensional network fiber assembly described in claim 12.