Silane-modified polymer composition and method for producing the same, crosslinked molded article, and automotive cooling pipe

Abstract

This invention provides a silane-modified polymer composition that exhibits excellent creep resistance under high pressure when formed into a cross-linked molded article and is suitable as a substitute for nylon. [Solution] A silane-modified polymer composition comprising a silane-modified propylene polymer (As) obtained by modifying a propylene polymer (A) with silane, and a silane-modified propylene-ethylene copolymer (Bs) obtained by modifying a propylene-ethylene copolymer (B), wherein the propylene polymer (A) has a propylene unit content of more than 95% by mass, the propylene-ethylene copolymer (B) has an ethylene unit content of 5 to 30% by mass, and the content of the silane-modified propylene polymer (As) relative to the total amount of the silane-modified propylene polymer (As) and the silane-modified propylene-ethylene copolymer (Bs) is 75 to 95% by mass.

Description

[Technical Field]

[0001] The present invention relates to a silane-modified polymer composition, a method for producing the same, a crosslinked molded article, and automotive cooling piping. [Background technology]

[0002] Cylindrical molded bodies such as water pipes and heating pipes used for water supply and hot water supply, underfloor heating, and road heating, as well as industrial cylindrical molded bodies such as beverage tubes, liquid food transfer tubes, and compressed air delivery tubes, require durability with a long pipe creep rupture time from the viewpoint of preventing leakage of contents.

[0003] Conventionally, for cylindrical molded products used in applications requiring long pipe creep failure times from a durability standpoint, cross-linked polyethylene pipes, which are made by cross-linking high-density polyethylene and linear low-density polyethylene, have been used.

[0004] Patent Document 1 proposes a cylindrical molded body that is excellent in appearance, film thickness uniformity, heat resistance, and internal pressure creep resistance, and is also flexible and easy to work with during construction, such as bending and stretching. This cylindrical molded body is made by molding a polyolefin composition containing an ethylene-α-olefin copolymer whose melting end peak temperature measured by a differential scanning calorimeter (DSC) is 115°C or higher, and a polyolefin different from the ethylene-α-olefin copolymer whose melting end peak temperature measured by a differential scanning calorimeter (DSC) is 125°C or higher. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-81016 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Among the applications of cylindrical molded bodies that require high pipe creep performance, coolant tubes, in particular, require high pressure resistance, and nylon tubes, which have high mechanical strength and good pressure resistance, have been used. However, nylon has a high density, and when mounted on a vehicle, it increases the overall weight, raising concerns about reduced fuel efficiency. In addition, nylon is more expensive than polyolefin. For this reason, in recent years, there has been a demand for polyolefin, which has a lower density and is cheaper than nylon, to be used as a substitute for nylon in such applications. However, polyolefin generally has lower pressure resistance and inferior creep durability compared to nylon.

[0007] In the cylindrical molded article made of polyolefin composition described in Patent Document 1, different olefin polymers are mixed. Therefore, in creep tests conducted at higher pressures than those described in Patent Document 1, fracture is more likely to occur starting at the interfaces between the different olefin polymers, indicating that there is room to improve creep durability under high pressure.

[0008] This invention has been made in view of the above circumstances, and aims to provide a silane-modified polymer composition that has a lower density compared to nylon, enables weight reduction and cost reduction as a molded article, and possesses creep resistance under high pressure when used as a crosslinked molded article. [Means for solving the problem]

[0009] The inventors of the present invention have conducted extensive research to achieve the above objectives and have found that the above problems can be solved by using a silane-modified polymer composition of a specific composition, thereby completing the present invention.

[0010] In other words, the gist of this invention is as follows: [Aspect 1] A silane-modified propylene polymer (As) is obtained by modifying a propylene polymer (A) with silane, and a silane-modified propylene-ethylene copolymer (Bs) is obtained by modifying a propylene-ethylene copolymer (B). The propylene polymer (A) has a propylene unit content of more than 95% by mass, The propylene-ethylene copolymer (B) has an ethylene unit content of 5 to 30% by mass. A silane-modified polymer composition in which the content of the silane-modified propylene polymer (As) is 75 to 95% by mass relative to the total amount of the silane-modified propylene polymer (As) and the silane-modified propylene-ethylene copolymer (Bs). [Aspect 2] The silane-modified polymer composition according to [Aspect 1], wherein the melt flow rate (measurement temperature 230°C, 2.16 kg load) measured in accordance with JIS K7210 (1999) is 0.1 to 15 g / 10 min. A molded article comprising the silane-modified polymer composition described in [Aspect 3], [Aspect 1], or [Aspect 2]. [Aspect 4] The molded article according to [Aspect 3], which is a crosslinked molded article. [Aspect 5] The molded article according to [Aspect 4], wherein the gel fraction is 30% or more. [Aspect 6] A molded article according to any one of [Aspect 3] to [Aspect 5], wherein the flexural modulus at 23°C is 800 to 2000 MPa. Automotive cooling piping comprising a molded body according to any one of [Aspect 7], [Aspect 3] to [Aspect 6]. [Aspect 8] A method for producing a silane-modified polymer composition, A propylene polymer composition is prepared by mixing a propylene polymer (A), a propylene-ethylene copolymer (B), an unsaturated silane compound, a peroxide, and optionally other components. This includes modifying the propylene polymer composition with silane, The propylene polymer (A) has a propylene unit content of more than 95% by mass, The propylene-ethylene copolymer (B) has an ethylene unit content of 5 to 30% by mass. A method for producing a silane-modified polymer composition, wherein the content of the propylene polymer (A) relative to the total amount of the propylene polymer (A) and the propylene-ethylene copolymer (B) is 75 to 95% by mass. [Effects of the Invention]

[0011] According to the present invention, there is provided a silane-modified polymer composition which is excellent in creep durability under high pressure when formed into a crosslinked molded body and is suitable for replacing nylon.

[0012] The crosslinked molded body made of the silane-modified polymer composition of the present invention is excellent in creep durability under high pressure, and thus can be suitably used for automotive cooling pipes that require high pressure resistance performance, particularly automotive cooling pipes for electric vehicles.

Embodiments for Carrying Out the Invention

[0013] The embodiments of the present invention will be described in detail below. However, the following description is only an example of the embodiments of the present invention, and the present invention is not limited to the following description as long as it does not exceed the gist of the invention.

[0014] The silane-modified polymer composition of the present embodiment is a composition containing a silane-modified propylene-based polymer (A-s) obtained by silane-modifying the following component (A) and a silane-modified propylene-ethylene copolymer (B-s) obtained by silane-modifying the following component (B), and the content of the component (A-s) with respect to the total amount of the component (A-s) and the component (B-s) is 75 to 95% by mass. Component (A): A propylene-based polymer having a propylene unit content of more than 95% by mass Component (B): A propylene-ethylene copolymer having an ethylene unit content of 5 to 30% by mass

[0015] The inventors have found that the above-mentioned silane-modified polymer composition exhibits excellent creep resistance under high pressure when used as a crosslinked molded article, making it suitable as a substitute for nylon. The following points are presumed to be the factors that result in the above-mentioned effects. Firstly, component (As) has a high elastic modulus and therefore high pressure resistance. Secondly, by using component (Bs), the ethylene component, which has a high efficiency in the silane graft reaction, is dispersed in the composition, improving the degree of crosslinking of the crosslinked molded article, thereby improving shape retention and increasing creep resistance. In the silane-modified polymer composition of this embodiment, component (Bs), which provides creep resistance through the above mechanism, is finely dispersed in an appropriate ratio with component (As), which has high pressure resistance. As a result, a silane-modified polymer composition is obtained that provides a crosslinked molded article that has pressure resistance equivalent to nylon, while also having sufficient creep resistance under high pressure for practical use. Thirdly, this is also due to the high compatibility between component (As) and component (Bs), which are both polypropylene polymers. As a result, the ethylene component is dispersed in the composition, improving creep resistance, and the interfacial strength between the two components is high, making cracking at the interface less likely.

[0016] Method for producing silane-modified polymer compositions Examples of methods for producing the silane-modified polymer composition of this embodiment include the following first and second embodiments.

[0017] <First Embodiment> The silane-modified polymer composition can be obtained by mixing component (As) and component (Bs). That is, the method for producing the silane-modified polymer composition according to the first embodiment includes: modifying a propylene polymer (A) with silane to obtain a silane-modified propylene polymer (As); modifying a propylene-ethylene copolymer (B) with silane to obtain a silane-modified propylene-ethylene copolymer (Bs); and mixing the silane-modified propylene polymer (As) and the silane-modified propylene-ethylene copolymer (Bs). In the silane-modified polymer composition, the content of the silane-modified propylene polymer (As) relative to the total amount of the silane-modified propylene polymer (As) and the silane-modified propylene-ethylene copolymer (Bs) is 75 to 95% by mass.

[0018] <Second Embodiment> Industrially, however, it is preferable to produce a silane-modified polymer composition by preparing a propylene-based polymer composition before silane modification by mixing component (A) and component (B) with an unsaturated silane compound and peroxide for silane modification, and other components as needed, and then modifying this propylene-based polymer composition with silane. That is, the method for producing a silane-modified polymer composition according to the second embodiment includes preparing a propylene-based polymer composition by mixing a propylene-based polymer (A), a propylene-ethylene copolymer (B), an unsaturated silane compound, a peroxide, and optionally other components, and then modifying the above propylene-based polymer composition with silane. In the above propylene-based polymer composition, the content of the propylene-based polymer (A) relative to the total amount of the propylene-based polymer (A) and the propylene-ethylene copolymer (B) is 75 to 95% by mass.

[0019] In the following, this embodiment will be described in detail according to a method for producing the silane-modified polymer composition of this embodiment in accordance with the second embodiment described above, and further producing the crosslinked molded article of this embodiment by crosslinking this silane-modified polymer composition with silane.

[0020] However, the silane-modified polymer composition of this embodiment can also be produced according to the first embodiment described above. In this case, the alkoxysilane modification method can be carried out in the same manner as described below, except that instead of using a propylene-based polymer composition containing components (A) and (B), components (A) and (B) are used, respectively.

[0021] Propylene-based polymer composition First, we will describe a propylene polymer composition before silane modification, which includes a propylene polymer having a propylene unit content of more than 95% by mass (component (A)), a propylene-ethylene copolymer having an ethylene unit content of 5 to 30% by mass (component (B)), an unsaturated silane compound, a peroxide, etc.

[0022] <Component (A) (Propylene polymer with a propylene unit content exceeding 95% by mass)> The propylene polymer (A) used in this embodiment must contain propylene units, and the content of said propylene units is greater than 95% by mass. In component (A), the content of monomer units other than propylene units is 0% by mass or more and less than 5% by mass. The type of component (A) is not particularly limited as long as it meets these criteria, and known propylene polymers can be used as appropriate.

[0023] Specific examples of component (A) include copolymers of propylene and one or more monomers other than propylene, such as propylene homopolymer, propylene-ethylene copolymer, propylene-1-butene copolymer, propylene-ethylene-1-butene copolymer, and propylene-1-hexene copolymer. From the viewpoint of pressure resistance, component (A) is preferably a propylene homopolymer.

[0024] In component (A) used in this embodiment, the propylene unit content is greater than 95% by mass. From the viewpoint of pressure resistance, this content is greater than 95% by mass, preferably 98% by mass or more, and may be 100% by mass. That is, as described above, component (A) is preferably a propylene homopolymer. The propylene unit content in component (A) can be measured, for example, by NMR.

[0025] In component (A) used in this embodiment, alkene units having 2 or 4 to 10 carbon atoms are preferred as monomer units other than propylene units. However, component (A) may also contain other monomer units to the extent that they do not impair the effects of the present invention.

[0026] The content of monomer units other than propylene units is 0% by mass or more and less than 5% by mass. From the viewpoint of pressure resistance, this content is less than 5% by mass, preferably 2% by mass or less, and may be 0% by mass.

[0027] The type of catalyst used in producing component (A) is not particularly limited, but examples include Ziegler-Natta catalysts and metallocene catalysts.

[0028] The melting peak temperature of component (A) used in this embodiment is preferably 140°C or higher, and more preferably 150°C or higher. When the melting peak temperature is above the lower limit, the crystals can maintain their shape even at high temperatures, and tend to exhibit excellent creep characteristics at high temperatures. The upper limit of the melting peak temperature is not particularly limited, but is usually 170°C or lower. The melting peak temperature can be measured by the method described in the Examples section below.

[0029] The density of component (A) used in this embodiment (measured according to JIS K7112:2023) is preferably 0.930 g / cm³ from the viewpoint of reducing the weight of the molded article. 3 The following, and more preferably 0.920 g / cm³ 3 The following, and more preferably 0.910 g / cm³ 3 The following applies. While there is no particular limit to the density mentioned above, it is 0.88 g / cm³.3 That's fine too.

[0030] The melt flow rate (MFR) of component (A) used in this embodiment is 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, and is preferably 0.1 to 20 g / 10 min. The MFR of component (A) is preferably 0.1 g / 10 min or more, and more preferably 0.4 g / 10 min or more, from the viewpoint of suppressing the dripping of molten resin during molding and improving yield and ease of molding. On the other hand, the above MFR is preferably 20 g / 10 min or less, and more preferably 10 g / 10 min or less, from the viewpoint of the impact on productivity due to motor load and resin pressure during modified extrusion, and surface quality after molding.

[0031] The flexural modulus of component (A) used in this embodiment is preferably 1500 MPa or higher from the viewpoint of obtaining good pressure resistance.

[0032] From these viewpoints, the flexural modulus of component (A) is preferably 1500 MPa or higher, and more preferably 1800 MPa or higher. The upper limit of the flexural modulus is not particularly limited, but it is usually 2500 MPa or lower. The flexural modulus can be measured by the method described in the Examples section below.

[0033] The component (A) used in this embodiment can be obtained as a commercially available product. For example, the relevant product can be selected and used from the "Novatec®" series manufactured by Nippon Polypropylene Co., Ltd., the "Prime Polypropylene®" series manufactured by Prime Polymer Co., Ltd., etc.

[0034] These components (A) may be used individually, or two or more components with different monomer types, copolymerization compositions, physical properties, etc., may be mixed and used.

[0035] <Component (B) (Propylene-ethylene copolymer with an ethylene unit content of 5-30% by mass)> The propylene-ethylene copolymer (B) used in this embodiment, having an ethylene unit content of 5 to 30% by mass, only needs to have an ethylene unit content of 5% to 30% by mass and a propylene unit content of 70% to 95% by mass, and may also contain monomer units other than ethylene units and propylene units.

[0036] In this embodiment, the monomer units other than ethylene units and propylene units included in component (B) include one or more alkene units having 4 to 10 carbon atoms, but preferably one. However, component (B) may also contain other monomer units to the extent that it does not impair the effects of the present invention.

[0037] The ethylene unit content in component (B) used in this embodiment is 5% by mass or more and 30% by mass or less. When the ethylene unit content is 5% by mass or more, the ethylene component, which readily undergoes graft modification reactions of unsaturated silane compounds and has a high degree of crosslinking, tends to crosslink with silane, resulting in superior creep resistance. On the other hand, when the ethylene unit content is 30% by mass or less, the mechanical strength improves and pressure resistance tends to be superior. The ethylene unit content is preferably 7% by mass or more, more preferably 9% by mass or more, preferably 25% by mass or less, and more preferably 20% by mass or less.

[0038] The propylene unit content in component (B) used in this embodiment is 70% by mass or more and 95% by mass or less. From the viewpoint of compatibility with component A, the content is preferably 75% by mass or more, and more preferably 80% by mass or more. Furthermore, from the viewpoint of creep resistance, the content is preferably 93% by mass or less, and more preferably 91% by mass or less. The ethylene unit and propylene unit content in component (B) can be measured, for example, by NMR.

[0039] The melt flow rate (MFR) of component (B) used in this embodiment is 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, and is preferably 1 to 20 g / 10 min. The MFR of component (B) is preferably 1 g / 10 min or more, and more preferably 2 g / 10 min or more, from the viewpoint of suppressing the dripping of molten resin during molding and improving yield and ease of molding. On the other hand, the above MFR is preferably 20 g / 10 min or less, and more preferably 10 g / 10 min or less, from the viewpoint of the impact on productivity due to motor load and resin pressure during modified extrusion, and surface quality after molding.

[0040] The density of component (B) used in this embodiment (measured according to JIS K6922-1,2:1997) is preferably 0.885 g / cm³ from the viewpoint of reducing the weight of the molded article. 3 The following, and more preferably 0.880 g / cm³ 3 The following, and more preferably 0.875 g / cm³ 3 The following applies. While there is no particular limit to the density mentioned above, it is 0.860 g / cm³. 3 That's fine too.

[0041] The A hardness of component (B) used in this embodiment is measured according to JIS K7215 (1986) under conditions of 23°C, 50% humidity, and after 15 seconds, and is preferably 60 or higher. From the viewpoint of pressure resistance as a molded article, the A hardness of component (B) is preferably 60 or higher, and more preferably 65 or higher. The upper limit of the above A hardness is not particularly limited, but it is usually 95 or lower.

[0042] Component (B) used in this embodiment can be obtained as a commercially available product. For example, a suitable product can be selected and used from the following: the "Vistamax®" series from ExxonMobil, the "Versify®" series from Dow Chemical Japan, the "Tafmer®" series from Mitsui Chemicals, and the "Adflex®" series from LyondellBasell.

[0043] These components (B) may be used individually, or two or more components with different monomer types, copolymer compositions, and physical properties may be mixed and used.

[0044] <Unsaturated silane compounds> The unsaturated silane compound contained in the above propylene polymer composition is not particularly limited, but an unsaturated silane compound represented by the following formula (1) is preferably used. RSi(R')3···(1)

[0045] In formula (1) above, R is an ethylenically unsaturated hydrocarbon group, the three 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 three R' is an alkoxy group having 1 to 10 carbon atoms.

[0046] In 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. Specifically, examples include alkenyl groups such as vinyl groups, propenyl groups, butenyl groups, and cyclohexenyl groups.

[0047] In 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 three R' is preferably an alkoxy group having 1 to 6 carbon atoms, and more preferably an alkoxy group having 1 to 4 carbon atoms.

[0048] The hydrocarbon group having 1 to 10 carbon atoms used as R' may be an aliphatic group, an alicyclic group, or an aromatic group, but it is preferably an aliphatic group. The alkoxy group having 1 to 10 carbon atoms used as R' may be linear, branched, or cyclic, but it is preferably linear or branched.

[0049] When R' is a hydrocarbon group, specific examples include alkyl groups such as methyl, ethyl, isopropyl, t-butyl, n-butyl, i-butyl, and cyclohexyl groups; and aryl groups such as phenyl groups. When R' is an alkoxy group, specific examples include methoxy, ethoxy, isopropoxy, and β-methoxyethoxy groups.

[0050] When an unsaturated silane compound is represented by formula (1), at least one of the three R' groups is an alkoxy group, but it is preferable that two of the R' groups are alkoxy groups, and it is more preferable that all of the R' groups are alkoxy groups.

[0051] Among the unsaturated silane compounds, vinyltrialkoxysilanes, such as vinyltrimethoxysilane, vinyltriethoxysilane, and propenyltrimethoxysilane, represented by formula (1), are preferred. This is because the vinyl group allows for the modification of components (A) and (B), and the alkoxy group facilitates the crosslinking reaction described later.

[0052] Specifically, alkoxy groups introduced by graft modification of propylene polymer (A) and propylene-ethylene copolymer (B) with an unsaturated silane compound react with water in the presence of a silanol condensation catalyst to hydrolyze and generate silanol groups. These silanol groups then undergo dehydration condensation, causing crosslinking reactions to occur as components (A) bond to each other, components (B) to each other, and components (A) to each other.

[0053] These unsaturated silane compounds may be used individually or in combination of two or more.

[0054] <Peroxides> The peroxide contained in the above propylene polymer composition can generate carbon radicals and graft-modify the unsaturated silane compound into components (A) and (B). Furthermore, the peroxide can abstract hydrogen from components (A) and (B), promoting the crosslinking reaction between components (A) and (B). The peroxide is used for at least one of these two reactions.

[0055] From the viewpoint of compatibility with the resin, organic peroxides are preferred as peroxides. Examples of organic peroxides include hydroperoxides such as cumene hydroperoxide and t-butyl hydroperoxide; dialkyl peroxides such as dicumyl peroxide, di-t-butyl peroxide, t-butyl peroxy-2-ethylhexanoate, 2,5-dimethyl-2,5-di-t-butyl peroxyhexane, 2,5-dimethyl-2,5-di-t-butyl peroxyhexine-3, and di(2-t-butylperoxyisopropyl)benzene; diacyl peroxides such as lauryl peroxide and benzoyl peroxide; peroxyesters such as t-butyl peroxyacetate, t-butyl peroxybenzoate, and t-butyl peroxyisopropyl carbonate; and ketone peroxides such as cyclohexanone peroxide.

[0056] These organic peroxides may be used individually or in combination of two or more.

[0057] From the viewpoint of graft efficiency, chain transfer efficiency, and hygiene such as odor, t-butylperoxy-2-ethylhexanoate, di(2-t-butylperoxyisopropyl)benzene, and di-t-butylperoxide are preferred as organic peroxides.

[0058] <Percentage of each component> In the above propylene polymer composition, the proportion of component (B) in the total 100% by mass of the propylene polymer (A) and propylene-ethylene copolymer (B) is 5 to 25% by mass, preferably 5 to 20% by mass, and more preferably 5 to 15% by mass. Furthermore, the proportion of component (A) in the total 100% by mass of the components (A) and (B) is 75 to 95% by mass, preferably 80 to 95% by mass, and more preferably 85 to 95% by mass.

[0059] If the content of component (B) relative to the total amount of component (A) and component (B) is within the above range, it is preferable in terms of pressure resistance and creep durability. If the content of component (B) is below the above upper limit, the mechanical strength is high and pressure resistance is good, and if it is above the above lower limit, the silane graft ratio is improved and the gel fraction of the crosslinked composition is improved, resulting in good creep durability.

[0060] The content of component (A) relative to 100% by mass of the propylene polymer composition is preferably 75 to 95% by mass, and more preferably 80 to 95% by mass. From the viewpoint of creep durability under high pressure, the above content is preferably 75% by mass or more, preferably 80% by mass or more, more preferably 83% by mass or more, even more preferably 85% by mass or more, and also preferably 95% by mass or less, and more preferably 93% by mass or less.

[0061] The content of component (B) relative to 100% by mass of the propylene polymer composition is preferably 3 to 25% by mass, and more preferably 4 to 25% by mass. From the viewpoint of creep durability under high pressure, the above content is preferably 3% by mass or more, more preferably 4% by mass or more, even more preferably 5% by mass or more, and preferably 25% by mass or less, and more preferably 15% by mass or less.

[0062] In the above propylene polymer composition, the ethylene unit content relative to the total amount of component (A) and component (B) is preferably 0.5 to 5.0% by mass. From the viewpoint that the ethylene component facilitates graft modification reactions of unsaturated silane compounds and increases the degree of crosslinking, the above ethylene unit content is preferably 0.5% by mass or more, and more preferably 0.8% by mass or more. Furthermore, from the viewpoint of pressure resistance, the above ethylene unit content is preferably 5.0% by mass or less, and more preferably 2.0% by mass or less.

[0063] The content of the unsaturated silane compound is preferably 0.10 to 5.00 parts by mass, and more preferably 1.00 to 3.00 parts by mass, per 100 parts by mass of the propylene polymer composition. The content of the peroxide is preferably 0.10 to 2.00 parts by mass, and more preferably 0.30 to 1.00 parts by mass, per 100 parts by mass of the propylene polymer composition.

[0064] When the content of unsaturated silane compounds and peroxides is above the lower limit mentioned above, the predetermined amount of modification necessary to achieve the effects of the present invention can be obtained. On the other hand, when the content of these compounds is below the upper limit mentioned above, there is no risk of unreacted substances remaining and adversely affecting the performance.

[0065] The ratio of the unsaturated silane compound to the peroxide is not particularly limited, but a preferred ratio is 5 to 100 parts by mass of peroxide per 100 parts by mass of unsaturated silane compound, and a more preferred ratio is 10 to 50 parts by mass of peroxide per 100 parts by mass of unsaturated silane compound. When the amount of peroxide relative to the unsaturated silane compound is above the lower limit, a sufficient amount of radicals is generated, making it easier to obtain the required predetermined amount of modification, and when it is below the upper limit, it tends to suppress the degradation of components (A) and (B).

[0066] <Other ingredients> In addition to the above-mentioned components, the propylene polymer composition may contain various additives and resins other than components (A) and (B) as other components, to the extent that they do not impair the effects of the present invention.

[0067] Examples of additives include crosslinking aids, heat stabilizers, ultraviolet absorbers, light stabilizers, antioxidants, antistatic agents, crystal nucleating agents, rust inhibitors, viscosity modifiers, and pigments. Of these, it is preferable to include antioxidants, particularly phenolic antioxidants, sulfuric antioxidants, or phosphorus-based antioxidants.

[0068] It is preferable that the antioxidant be included in an amount of 0.1 to 1 part by mass per 100 parts by mass of the above propylene polymer composition.

[0069] Examples of crosslinking aids include unsaturated cyanurate compounds. Among the unsaturated cyanurate compounds, triallyl cyanurates, such as trialyloxytriazine and triallyl isocyanurate, are preferred. This is because the allyl group enables the modification of components (A) and (B), and a dynamic crosslinking reaction between the vinyl groups contained in them and the allyl group proceeds. Specifically, the allyl groups introduced by graft modification to components (As) and (Bs) using the unsaturated cyanurate compound undergo addition reactions via radical chain transfer with the vinyl groups of components (A) and (B), as well as their alkoxysilane modified forms, components (As) and (Bs), in the presence of a peroxide that generates radicals. This results in crosslinking reactions where components (As) bond to each other, components (Bs) to each other, and components (As) to each other. These unsaturated cyanurate compounds may be used individually or in combination of two or more.

[0070] If the above propylene polymer composition contains an unsaturated cyanurate compound, the content of the unsaturated cyanurate compound is preferably 0.01 to 5 parts by mass per 100 parts by mass of the above propylene polymer composition.

[0071] Other resins include, for example, polyolefin resins other than components (A) and (B), polyester resins, polycarbonate resins, polymethyl methacrylate resins, rosin and its derivatives, terpene resins and petroleum resins and their derivatives, alkyd resins, alkylphenol resins, terpene phenol resins, coumarone indene resins, synthetic terpene resins, and alkylene resins.

[0072] Silane-modified polymer composition The silane-modified polymer composition of this embodiment can be obtained by graft modification and / or chemical crosslinking a propylene polymer composition comprising the above-mentioned propylene polymer (A), propylene-ethylene copolymer (B), unsaturated silane compound and peroxide, and other components as optional.

[0073] The method of graft modification and / or chemical crosslinking is not particularly limited and can be carried out according to known methods. For example, solution modification, melt modification, solid-phase modification by irradiation with electron beams or ionizing radiation, and modification in a supercritical fluid are suitably used. Among these, melt modification is preferred due to its superior equipment and cost competitiveness, and melt-kneading modification using an extruder, which offers superior continuous productivity, is more preferred.

[0074] Examples of equipment used for melt-mixing and modification include single-screw extruders, twin-screw extruders, Banbury mixers, and roll mixers. Among these, single-screw extruders and twin-screw extruders, which offer superior continuous productivity, are preferred.

[0075] Generally, graft modification of components (A) and (B) with unsaturated silane compounds and / or peroxides is carried out by a graft reaction in which the carbon-hydrogen bonds of components (A) and (B) are cleaved to generate carbon radicals, to which unsaturated functional groups are added.

[0076] Methods for generating carbon radicals include irradiation with electron beams or ionizing radiation as described above, as well as methods using high temperatures and methods using radical generating agents such as organic or inorganic peroxides. From the viewpoint of cost and ease of operation, the use of organic peroxides is preferable.

[0077] The radical generator used in producing the silane-modified polymer composition of this embodiment is not limited, but examples include organic peroxides belonging to the groups hydroperoxides, dialkyl peroxides, diacyl peroxides, peroxyesters, and ketone peroxides, as well as azo compounds.

[0078] A commonly used melt extrusion modification (melt kneading modification) procedure involves blending and combining the above-mentioned components (A), (B), unsaturated silane compounds, and peroxides, as well as other components as needed, to obtain a propylene polymer composition. This composition is then fed into a kneader or extruder, where it is extruded while being heated, melt-kneaded, and the molten resin coming out of the end die is cooled in a water tank or the like to obtain a modified polyolefin composition.

[0079] When the silane-modified polymer composition of this embodiment is manufactured by kneading in a single-screw extruder or a twin-screw extruder, melt kneading can usually be performed at a temperature of 140 to 240°C, preferably 160 to 220°C.

[0080] The blending ratios of component (A), component (B), unsaturated silane compound, and peroxide in the above-mentioned propylene polymer composition are as described above.

[0081] In the silane-modified polymer composition of this embodiment, the content ratio of component (As) and component (Bs) is based on the content ratio of component (A) and component (B) in the aforementioned propylene-based polymer composition. That is, in the silane-modified polymer composition of this embodiment, the proportion of component (Bs) in the total 100% by mass of component (As) and component (Bs) is 5 to 25% by mass, preferably 5 to 20% by mass, and more preferably 5 to 15% by mass. Also, the proportion of component (As) in the total 100% by mass of component (As) and component (Bs) is 75 to 95% by mass, preferably 80 to 95% by mass, and more preferably 85 to 95% by mass.

[0082] If the content of component (Bs) in the silane-modified polymer composition of this embodiment is within the above range, it is preferable from the viewpoint of creep durability under high pressure. If the content of component (Bs) is below the above upper limit, the mechanical strength is high and the pressure resistance is good, and if it is above the above lower limit, the silane graft ratio is improved and the gel fraction of the crosslinked composition is improved, resulting in good creep durability.

[0083] The content of component (As) in 100% by mass of the silane-modified polymer composition of this embodiment is preferably 75 to 95% by mass, and more preferably 80 to 95% by mass. From the viewpoint of creep durability under high pressure, the above content is preferably 75% by mass or more, preferably 80% by mass or more, more preferably 83% by mass or more, even more preferably 85% by mass or more, and preferably 95% by mass or less, and more preferably 93% by mass or less.

[0084] The content of component (Bs) in this embodiment, relative to 100% by mass of the silane-modified polymer composition, is preferably 3 to 25% by mass. From the viewpoint of creep durability under high pressure, the above content is preferably 3% by mass or more, more preferably 4% by mass or more, even more preferably 5% by mass or more, and preferably 25% by mass or less, and more preferably 15% by mass or less.

[0085] The silane-modified polymer composition of this embodiment may contain only one type of component (As), or it may contain two or more different types of component (A) or unsaturated silane compounds used in the alkoxysilane modified product. Similarly, the component (Bs) may contain only one type, or it may contain two or more different types of component (B) or unsaturated silane compounds used in the alkoxysilane modified product.

[0086] Furthermore, the silane-modified polymer composition of this embodiment may contain components other than components (As) and (Bs).

[0087] The melt flow rate (MFR) of the silane-modified polymer composition in this embodiment is the melt flow rate measured under conditions of 230°C and 2.16 kg load, according to JIS K7210 (1999), and is preferably 0.1 to 15 g / 10 min. If the MFR is too high, the molten resin is likely to drip during molding, which may reduce the yield or make molding difficult. On the other hand, if the MFR is too low, the motor load during modification extrusion will be high, the resin pressure will increase, productivity will deteriorate, and the surface after molding may become rough.

[0088] From these viewpoints, the MFR of the silane-modified polymer composition of this embodiment is preferably 0.1 g / 10 min or more, more preferably 1.0 g / 10 min or more. On the other hand, it is preferably 15 g / 10 min or less, more preferably 10 g / 10 min or less. The MFR of the silane-modified polymer composition can be adjusted, for example, by the MFR of component (A), the MFR of component (B), the content of component (As), and component (Bs).

[0089] Molded body The molded article of this embodiment is made of the silane-modified polymer composition described above. A crosslinked molded article is an example of the molded article.

[0090] In the above-mentioned propylene-based polymer composition, when an unsaturated silane compound is used, one method for obtaining the above-mentioned crosslinked molded article is to blend a silanol condensation catalyst into the above-mentioned propylene-based polymer composition or the silane-modified polymer composition of this embodiment. Specifically, after molding the silane-modified polymer composition by various molding methods such as extrusion molding, injection molding, and press molding, the crosslinking reaction between silanol groups is promoted by exposing it to an aqueous atmosphere, and the above-mentioned crosslinked molded article can be obtained by causing an intermolecular crosslinking reaction between the alkoxysilane-modified material in the silane-modified polymer composition.

[0091] Methods for exposing the product to a watery atmosphere can employ various conditions, including leaving it in air containing moisture, blowing in air containing water vapor, immersing it in a water bath, and spraying it with warm water in a mist.

[0092] Examples of silanol condensation catalysts that can be used in this embodiment include one or more compounds selected from the group consisting of metal organic acid salts, titanates, borates, organic amines, ammonium salts, phosphonium salts, inorganic acids and organic acids, and inorganic acid esters.

[0093] Examples of metal organic salts include dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, stannous acetate, stannous octanoate, cobalt naphthenate, lead octoate, lead naphthenate, zinc octoate, zinc caprylate, iron 2-ethylhexanoate, iron octoate, and iron stearate. Examples of titanates include tetrabutyl titanate, tetranonyl titanate, and bis(acetylacetonitrile)di-isopropyl titanate. Examples of organic amines include ethylamine, dibutylamine, hexylamine, triethanolamine, dimethyl soyamine, tetramethylguanidine, and pyridine. Examples of ammonium salts include ammonium carbonate and tetramethylammonium hydroxide. An example of a phosphonium salt is tetramethylphosphonium hydroxide. Examples of inorganic and organic acids include 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 phosphate esters such as ethylhexyl phosphate.

[0094] Among these, preferred examples include metal organic salts, sulfonic acids, and phosphate esters, and more preferably tin metal carboxylates, such as dioctyl tin dilaurate, alkyl naphthyl sulfonic acid, and ethylhexyl phosphate ester.

[0095] The silanol condensation catalyst may be used alone or in combination of two or more types.

[0096] The amount of silanol condensation catalyst is not particularly limited, but is preferably 0.0001 to 0.01 parts by mass, and more preferably 0.0001 to 0.005 parts by mass, per 100 parts by mass of the silane-modified polymer composition. An amount of silanol condensation catalyst above the lower limit is preferable because the crosslinking reaction proceeds sufficiently and the heat resistance tends to be good. An amount below the upper limit is preferable because premature crosslinking is less likely to occur in the extruder, and roughness of the strand surface and product appearance tends to be less likely to occur.

[0097] The silanol condensation catalyst is preferably used as a masterbatch containing a polyolefin and the silanol condensation catalyst. Examples of polyolefins that can be used in this masterbatch include polyethylene, polypropylene, and propylene-ethylene copolymer.

[0098] When using a silanol condensation catalyst as a masterbatch containing a polyolefin and the silanol condensation catalyst, the content of the silanol condensation catalyst in the masterbatch is not particularly limited, but is preferably 0.1 to 5.0% by mass.

[0099] A commercially available product can be used as the silanol condensation catalyst-containing masterbatch; for example, Mitsubishi Chemical's "LZ082" can be used.

[0100] In the above-mentioned propylene polymer composition or the silane-modified polymer composition of this embodiment, when an unsaturated silane compound and a silanol condensation catalyst are used, hydrolyzable alkoxy groups derived from the unsaturated silane compound used for graft modification of component (A) and component (B) react with water in the presence of the silanol condensation catalyst to hydrolyze and generate silanol groups. Furthermore, the silanol groups undergo dehydration condensation, which promotes a crosslinking reaction, causing components (As) to bond with each other, components (Bs) to each other, and components (As) to bond with each other to form a crosslinked molded article.

[0101] The rate of the crosslinking reaction depends on the conditions under which the material is exposed to a water atmosphere, but typically, exposure within a temperature range of 20-130°C and for a period of 1 hour to 1 month is sufficient. Preferred conditions are a temperature range of 60-100°C and an exposure period of 5-24 hours. When using air containing moisture, the relative humidity should be selected from a range of 1-100%.

[0102] <Suitable physical properties of cross-linked molded articles> The above-mentioned cross-linked molded article preferably has the following physical properties, in order to solve the problem of the present invention, which is to provide a cross-linked molded article with creep resistance under high pressure.

[0103] In order for the crosslinked molded article to exhibit creep resistance under high pressure, the gel fraction (degree of crosslinking) of the crosslinked molded article is preferably 30% or more, and more preferably 33% or more. In the silane-modified polymer composition of this embodiment, by using 5 to 25 parts by mass of component (Bs), the ethylene component is uniformly finely dispersed in 75 to 95 parts by mass of component (As), which is also a propylene-based polymer, thereby improving the gel fraction (degree of crosslinking) of the crosslinked molded article.

[0104] Furthermore, the gel fraction can be adjusted by changing the amount of unsaturated silane compound and / or peroxide added to the propylene polymer composition, the type and amount of silanol condensation catalyst, and the conditions (temperature, time) during crosslinking. While there is no particular upper limit to the gel fraction, it is typically 99%. The gel fraction can be measured by the method described in the Examples section below.

[0105] In order for the crosslinked molded article of this embodiment to exhibit high pressure resistance, the flexural modulus of the crosslinked molded article is preferably 800 MPa or higher, and more preferably 1000 MPa or higher. In this embodiment, by using 75 to 95% by mass of component (As), the mechanical strength and flexural modulus can be improved.

[0106] In addition, in order to ensure the workability of the crosslinked molded body of the present embodiment as a molded body, the flexural modulus of elasticity of the crosslinked molded body is preferably 2000 MPa or less, and more preferably 1500 MPa or less. In the present embodiment, by using 5 to 25 parts by mass of component (B-s), flexibility can be imparted and the flexural modulus of elasticity can be decreased.

[0107] The flexural modulus of elasticity of the crosslinked molded body is preferably 800 to 2000 MPa. The flexural modulus of elasticity of the crosslinked molded body can be measured by the method described in the Examples section below.

[0108] The density of the crosslinked molded body of the present embodiment (measured according to JIS K7112: 2023) is preferably 0.940 g / cm 3 or less, more preferably 0.930 g / cm 3 or less, and even more preferably 0.920 g / cm 3 or less. The lower limit value of the above density is not particularly limited, but may be 0.880 g / cm 3 or more. The density of the molded body can be adjusted by the density of component (A) and component (B), etc.

[0109] As an index of high creep durability, the crosslinked molded body of the present embodiment preferably has a creep rupture time measured according to JIS K7115: 1999 of 10 hours or more, more preferably 20 hours or more, and the longer the better.

[0110] The creep rupture time of the crosslinked molded body can be measured by the method described in the Examples section below.

[0111] 《Applications》 Since the crosslinked molded body of the present embodiment is excellent in creep durability under high pressure, it can be suitably used for automotive cooling pipes that require high pressure resistance performance, particularly automotive cooling pipes for electric vehicles. In addition, it can also be used for water pipes, liquid transfer tubes, air delivery tubes, etc. The automotive cooling pipe of the present embodiment is composed of the above crosslinked molded body.

Examples

[0112] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. Furthermore, the various manufacturing conditions and evaluation result values ​​in the following examples have meaning as preferred upper or lower limits in embodiments of the present invention, and the preferred range may be defined by a combination of the aforementioned upper or lower limits and the values ​​of the following examples or the values ​​of the examples themselves.

[0113] In the following description, "parts" refers to "parts by mass," and "%" refers to "percentage by mass."

[0114] 《Raw materials》 The following raw materials were used in the following examples and comparative examples.

[0115] <Component (A) (Propylene polymer with a propylene unit content exceeding 95% by mass)> • PP-a1: Novatec (trademark registered) PP EA9, manufactured by Nippon Polypropylene Co., Ltd. Homopropylene polymer Propylene unit content: 100% by mass MFR: 0.5g / 10min (230℃, 2.16kg load) Density: 0.90g / cm 3 Melting peak temperature: 165℃ Flexural modulus: 1850 MPa • PP-a2: Novatec (Registered Trademark) PP EA9FTD, manufactured by Nippon Polypropylene Co., Ltd. Homopropylene polymer Propylene unit content: 100% by mass MFR: 0.4g / 10min (230℃, 2.16kg load) Density: 0.90g / cm 3 Melting peak temperature: 167℃ Flexural modulus: 2300 MPa

[0116] <Component (B) (Propylene-ethylene copolymer with an ethylene unit content of 5-30% by mass)> • PP-b1: VistaMax (registered trademark) 6102, manufactured by ExxonMobil Corporation. Propylene ethylene copolymer Ethylene unit content: 16% by mass Propylene unit content: 84% by mass MFR: 3.0g / 10min (230℃, 2.16kg load) Density: 0.862g / cm 3 A hardness: 67 • PP-b2: VistaMax (registered trademark) 3020FL, manufactured by ExxonMobil. Propylene ethylene copolymer Ethylene unit content: 11% by mass Propylene unit content: 89% by mass MFR: 3.0g / 10min (230℃, 2.16kg load) Density: 0.874g / cm 3 A hardness: 85

[0117] <Component (B') (For comparison, a propylene-based or ethylene-based copolymer with an ethylene unit content that is not 5-30% by mass)> • PP-b3: Engage (registered trademark) 8480, manufactured by Dow Chemical Japan Co., Ltd. Metallocene linear low-density polyethylene (ethylene-1-octene copolymer) Ethylene unit content: 80% by mass Propylene unit content: 0% by mass MFR: 1.0g / 10min (190℃, 2.16kg load) Density: 0.902g / cm 3 Melting peak temperature: 38℃ A hardness: 99 • PP-b4: Toughmer (registered trademark) P0680, manufactured by Mitsui Chemicals, Inc. Ethylene-propylene copolymer Ethylene unit content: 75% by mass Propylene unit content: 25% by mass MFR: 0.8g / 10min (230℃, 2.16kg load) Density: 0.869g / cm 3 A hardness: 56 • PP-b5: Toughmer (registered trademark) XM7090, manufactured by Mitsui Chemicals, Inc. Propylene-1-butene copolymer Ethylene unit content: 0% by mass Propylene unit content: 85% by mass MFR: 7.0g / 10min (230℃, 2.16kg load) Density: 0.890g / cm 3 D hardness: 58

[0118] <Unsaturated silane compounds> • Vinyltrimethoxysilane: KBM-1003 (manufactured by Shin-Etsu Chemical Co., Ltd.)

[0119] <Peroxides> • POX: t-butylperoxy-2-ethylhexanoate, perbutyl® (registered trademark) O (manufactured by NOF Corporation)

[0120] <Catalyst Masterbatch (MB)> • Silanol condensation catalyst MB:LZ082, manufactured by Mitsubishi Chemical Corporation. 1% tin catalyst-containing low-density polyethylene MFR: 4g / 10min (190℃, 2.16kg load) Density: 0.91g / cm 3 Melting point: 90℃

[0121] Measurement and evaluation methods for raw material polymers, silane-modified polymer compositions, and crosslinked molded articles. The methods for measuring and evaluating various physical properties and characteristics of raw material polymers, silane-modified polymer compositions, and crosslinked molded articles are as follows.

[0122] <Melting peak temperature> Using a differential scanning calorimeter (DSC6220) manufactured by Hitachi High-Tech Science Corporation, 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 (2012). After holding at 200°C for 3 minutes, the temperature was cooled to -10°C at a cooling rate of 10°C / min, and then heated back up to 200°C at a heating rate of 10°C / min. The melting peak temperature was measured from the thermogram obtained during this process.

[0123] <Melt Flow Rate (MFR)> The MFRs of components (A), (B), and the silane-modified polymer composition were measured in accordance with JIS K7210 (1999) under conditions of a measurement temperature of 190°C or 230°C and a load of 2.16 kg.

[0124] <density> The densities of components (A) and (B), as well as the density of the sheet-like molded articles obtained by molding and crosslinking the silane-modified polymer compositions, were measured in accordance with JIS K7112 (2023).

[0125] <hardness> The durohardness A (after 15 seconds) or durohardness D (after 15 seconds) of components (B) and (B') was measured according to JIS K7215:1986.

[0126] <Flexural modulus> Measurements were taken using sheet-like molded articles obtained by molding and crosslinking a silane-modified polymer composition, in accordance with JIS K7171:2008.

[0127] <Gel fraction> A sheet-like molded body (1 mm thick) formed by molding and crosslinking a silane-modified polymer composition was subjected to Soxhlet extraction in boiling xylene at 144°C for 10 hours. The undissolved resin was dried, its mass was measured, and the percentage (%) of the sample mass before Soxhlet extraction was calculated.

[0128] <Creep destruction time> A JIS No. 2 dumbbell-shaped test specimen was prepared using a sheet-like molded body (2 mm thick) formed by molding and crosslinking a silane-modified polymer composition. A creep test was performed by applying a constant load to the dumbbell test specimen. The creep failure time was measured under conditions of 80°C and 10 MPa pressure, in accordance with JIS K7115:1999.

[0129] [Example Test] <Example 1> 95 parts of PP-a1, 5 parts of PP-b1, 2.0 parts of vinyltrimethoxysilane, and 0.8 parts of POX were mixed and stirred in a blender. Then, the mixture was fed into a twin-screw extruder (manufactured by Japan Steel Works, TEX30αIII) set to a temperature of 220°C. The strands extruded from the nozzle were cooled and solidified in a water bath, and then cut into pellets to obtain a silane-modified polymer composition. The MFR of the obtained silane-modified polymer composition was measured.

[0130] To 100 parts of the silane-modified polymer composition obtained above, 5 parts of LZ082 as a silanol condensation catalyst MB were added and blended. The mixture was then molded using an injection molding machine under conditions of 220°C, and the resulting molded body was left at 85°C and 85% RH for 18 hours to produce a sheet-like molded body made of the crosslinked composition. The density, flexural modulus, gel fraction, and creep fracture time of the obtained crosslinked molded body were measured. The results of the various measurements are shown in Table 1.

[0131] <Examples 2-5, Comparative Examples 1-6> Silane-modified polymer compositions and crosslinked molded articles were obtained in the same manner as in Example 1, except that the types and compositions of raw materials used were changed as shown in Table 1. Various measurements were then performed in the same manner as in Example 1. The results are shown in Table 1.

[0132] Table 1 also shows the ethylene unit content (unit: mass%) relative to the total amount of component (A) and component (B) in the modified propylene polymer composition. This ethylene unit content was calculated from the ethylene unit content of each component and its blending ratio. A blank space in Table 1 indicates that the corresponding component is not present in the propylene polymer composition.

[0133] [Table 1]

[0134] From the results above, we can conclude the following:

[0135] As shown in Examples 1 to 5, silane-modified polymer compositions containing 75-95% by mass of component (As) and 5-25% by mass of component (Bs) showed longer creep failure times in creep tests under high pressure conditions of 10 MPa compared to Comparative Examples 1 to 6. This is presumed to be due to the high elastic modulus and pressure resistance of component (As), which leads to higher pressure resistance and deformation resistance during creep tests. In addition, it is presumed that the use of component (Bs) allows the ethylene component, which has high efficiency in silane graft reactions, to be dispersed throughout the composition, improving the degree of crosslinking of the crosslinked molded article, thereby improving shape retention and creep resistance. Furthermore, it is presumed that the high compatibility of component (As) and component (Bs), both polypropylene polymers, facilitates graft modification reactions of unsaturated silane compounds, leading to increased crosslinking of the ethylene component, which is finely dispersed in the composition, improving creep resistance by increasing the degree of crosslinking of the crosslinked molded article. In addition, the high interfacial strength between the two components makes it difficult for cracks to occur at the interface.

[0136] Comparative Examples 1 and 4 do not contain modified propylene-ethylene copolymers (Bs) with an ethylene unit content of 5-30% by mass, and have an ethylene unit content of 0% by mass, which facilitates graft modification reactions of unsaturated silane compounds and increases the degree of crosslinking. Therefore, it is presumed that the creep failure time was shortened in Comparative Examples 1 and 4 because the degree of crosslinking of the crosslinked molded articles was low and the non-crosslinked portions were easily deformed under high pressure.

[0137] Comparative Examples 2 and 3 do not contain a modified propylene-ethylene copolymer (Bs) with an ethylene unit content of 5-30% by mass, and instead use an ethylene polymer with an ethylene unit content of more than 30% by mass. Therefore, the compatibility with component (As) is low, and the strength of the interface between component (As) and component (Bs) is weak. Furthermore, due to the low compatibility, the dispersion of component (Bs) in component (As) is poor, and the ethylene component is not uniformly dispersed in the composition, resulting in a low degree of crosslinking of the crosslinked molded article. As a result, it is presumed that the creep rupture time was shortened in Comparative Examples 2 and 3 because the interface was more susceptible to deformation under high pressure during the creep test, and the non-crosslinked portion was also more susceptible to deformation under high pressure.

[0138] In Comparative Example 5, the content of component (As) relative to the total amount of component (As) and component (Bs) is less than 75% by mass. Therefore, the elastic modulus is low, resulting in low pressure resistance and deformation resistance during the creep test, and it is presumed that the creep failure time was shorter in Comparative Example 5.

[0139] In Comparative Example 6, since no unsaturated silane compound was added, components (A) and (B) were not modified with silane. As a result, the degree of crosslinking was 0%, and the non-crosslinked portion was more susceptible to deformation under high pressure. Therefore, it is presumed that the creep failure time was shorter in Comparative Example 6.

[0140] From the above, it can be seen that the crosslinked composition of this embodiment, obtained by crosslinking the silane-modified polymer composition of this embodiment, which contains 75-95% by mass of component (As) and 5-25% by mass of component (Bs), exhibits excellent creep durability in creep tests under high-pressure conditions.

Claims

1. The propylene polymer (A) is modified into a silane-modified propylene polymer (A-s), and the propylene-ethylene copolymer (B) is modified into a silane-modified propylene-ethylene copolymer (B-s). The propylene polymer (A) has a propylene unit content of more than 95% by mass, The propylene-ethylene copolymer (B) has an ethylene unit content of 5 to 30% by mass. A silane-modified polymer composition in which the content of the silane-modified propylene polymer (A-s) relative to the total amount of the silane-modified propylene polymer (A-s) and the silane-modified propylene-ethylene copolymer (B-s) is 75 to 95% by mass.

2. The silane-modified polymer composition according to claim 1, wherein the melt flow rate (measurement temperature 230°C, 2.16 kg load) measured according to JIS K7210 (1999) is 0.1 to 15 g / 10 min.

3. A molded article comprising the silane-modified polymer composition described in claim 1.

4. The molded article according to claim 3, which is a crosslinked molded article.

5. The molded article according to claim 4, wherein the gel fraction is 30% or more.

6. The molded article according to claim 4, wherein the flexural modulus at 23°C is 800 to 2000 MPa.

7. Automotive cooling piping comprising the molded body described in claim 4.

8. A method for producing a silane-modified polymer composition, A propylene polymer composition is prepared by mixing a propylene polymer (A), a propylene-ethylene copolymer (B), an unsaturated silane compound, a peroxide, and optionally other components. This includes modifying the propylene polymer composition with silane, The propylene polymer (A) has a propylene unit content of more than 95% by mass, The propylene-ethylene copolymer (B) has an ethylene unit content of 5 to 30% by mass. A method for producing a silane-modified polymer composition, wherein the content of the propylene polymer (A) relative to the total amount of the propylene polymer (A) and the propylene-ethylene copolymer (B) is 75 to 95% by mass.

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