JP7585902B2 - Thermoplastic elastomer composition and molded article thereof - Google Patents

Description

The present invention relates to a thermoplastic elastomer composition and a molded article thereof.

In recent years, synthetic resins have come to be used as transport materials for pallets, containers, and other items. Because synthetic resin transport materials are more slippery than traditional wooden materials, grommets are attached to prevent slipping.

Pallet grommets are required to have both blocking resistance and slip resistance.
In other words, blocking refers to the phenomenon in which, when pallets are loaded, the grommets fitted into the pallets overlap and are left under vertical pressure for a long time, and then when the pallet is lifted, they stick to the grommets of the pallet below, and if the grommets are so tightly attached to each other when the pallet is lifted that a peeling force greater than the load of the pallet occurs, the problem of the pallet below lifting up occurs. To prevent this type of blocking, blocking resistance is required that allows the pallets to be easily peeled off even when left under vertical pressure for a long time.
Furthermore, if a strong lateral force, such as braking, is applied to stacked pallets during transport, and the grommet surface is slippery, the pallets may slide off, so slip resistance is required to prevent this.

Grommets made of a thermoplastic elastomer composition containing polypropylene, a styrene-based block copolymer elastomer, and mineral oil are known because they provide good mechanical properties.

For example, Patent Document 1 proposes a resin composition containing a specific amount of a block copolymer consisting of a specific propylene-based resin and petroleum resin containing a rubber component, at least two polymer blocks A made mainly of an aromatic vinyl compound and at least one polymer block B made mainly of a conjugated diene compound, and/or a block copolymer obtained by hydrogenating the block copolymer, in order to achieve appropriate anti-slip and lubricity.

Patent Document 2 proposes a thermoplastic elastomer composition that is resistant to bleeding of a hydrocarbon-based rubber softener even at high compression, and that contains: Component (A): a hydrogenated block copolymer having at least two polymer blocks P mainly composed of aromatic vinyl compound units and at least one polymer block Q mainly composed of conjugated diene compound units; Component (B): a hydrocarbon-based rubber softener; Component (C): a polypropylene resin; and Component (E): diallyl orthophthalate and/or diallyl isophthalate.

JP 2004-323659 A JP 2020-152787 A

According to detailed studies by the present inventors, the resin composition described in Patent Document 1 had insufficient blocking resistance. In addition, the thermoplastic elastomer composition described in Patent Document 2 had a poor balance between slip resistance and blocking resistance.

On the other hand, paper packaging materials such as paper bags and cardboard boxes are often loaded onto pallets. When these materials are stored for long periods of time in a warehouse in summer or in a high-temperature region, the oil contained in the thermoplastic elastomer composition from which the grommets are made migrates to the paper packaging material, causing stains and contamination on the surface of the packaging material.
For this reason, pallet grommets must not only be slip-resistant and anti-blocking, but also difficult for oil to transfer to the paper.

The present invention was made in consideration of the above-mentioned conventional situation, and aims to provide a thermoplastic elastomer composition and molded article thereof that has a good balance of excellent slip resistance and blocking resistance and is less susceptible to migration of oil to paper.

As a result of intensive research conducted by the present inventors in order to solve the above-mentioned problems, it has been found that a thermoplastic elastomer composition having an excellent balance between slip resistance and blocking resistance and being less susceptible to migration of oil to paper can be obtained by blending a hydrogenated block copolymer having at least two polymer blocks P mainly composed of aromatic vinyl compound units and at least one polymer block Q mainly composed of conjugated diene compound units, a hydrocarbon-based rubber softener, a specific propylene-based resin, and a rosin ester, thereby completing the present invention.
That is, the present invention relates to the following.

[1] A thermoplastic elastomer composition comprising the following components (A) to (D):
Component (A): A hydrogenated product of a block copolymer having at least two polymer blocks P mainly composed of aromatic vinyl compound units and at least one polymer block Q mainly composed of conjugated diene compound units. Component (B): A softener for hydrocarbon-based rubber. Component (C): A propylene-based resin containing the following components (C1) and (C2): Component (C1): A propylene homopolymer. Component (C2): A propylene-α-olefin block copolymer. Component (D): A rosin ester.

[2] The thermoplastic elastomer composition according to [1], in which the propylene-α-olefin block copolymer of component (C2) is a reactor TPO.

[3] The thermoplastic elastomer composition according to [1] or [2], in which the propylene-based resin of component (C) further contains a propylene-α-olefin random copolymer as component (C3).

[4] The thermoplastic elastomer composition according to [3], in which the content of component (C3) is 70% by mass or less, where the total of components (C1) and (C3) is 100% by mass.

[5] The thermoplastic elastomer composition according to any one of [1] to [4], further comprising diallyl phthalate as component (E).

[6] The thermoplastic elastomer composition according to any one of [1] to [5], wherein the thermoplastic elastomer composition has a Duro A hardness (JIS K6253) of 40 to 95.

[7] A molded article made of a thermoplastic elastomer composition according to any one of [1] to [6].

[8] A composite molded product obtained by fusing the thermoplastic elastomer composition described in any one of [1] to [6] with an olefin-based resin.

[9] A pallet grommet made from the composite molding of [8].

The present invention provides a thermoplastic elastomer composition that has a good balance between slip resistance and blocking resistance and is less susceptible to oil migration to paper.

The present invention will be described in detail below. However, the following description is an example of an embodiment of the present invention, and the present invention is not limited to the contents of the following description as long as it does not go beyond the gist of the present invention. The present invention can be modified and implemented as desired without departing from the gist of the present invention.
In the present invention, when "~" is used to express a value with a numerical value or physical property value before and after it, the values before and after it are included in the expression.

[Thermoplastic elastomer composition]
The thermoplastic elastomer composition of the present invention is characterized by comprising the following components (A) to (D).
Component (A): A hydrogenated product of a block copolymer having at least two polymer blocks P mainly composed of aromatic vinyl compound units and at least one polymer block Q mainly composed of conjugated diene compound units. Component (B): A softener for hydrocarbon-based rubber. Component (C): A propylene-based resin containing the following components (C1) and (C2): Component (C1): A propylene homopolymer. Component (C2): A propylene-α-olefin block copolymer. Component (D): A rosin ester.

Each ingredient is explained in detail below.

<Component (A)>
The component (A) used in the present invention is a hydrogenated product of a block copolymer (hereinafter, sometimes referred to as a “hydrogenated block copolymer (A)”) having at least two polymer blocks P (hereinafter, sometimes referred to simply as “block P”) mainly composed of aromatic vinyl compound units and at least one polymer block Q (hereinafter, sometimes referred to simply as “block Q”) mainly composed of conjugated diene compound units.
Here, the term "mainly composed of" means that the target monomer unit is contained in the target polymer block in an amount of 50 mol % or more.

The aromatic vinyl compound constituting the block P is not particularly limited, and examples thereof include aromatic vinyl compounds such as styrene, α-methylstyrene, p-methylstyrene, divinylbenzene, 1,1-diphenylethylene, N,N-dimethyl-p-aminoethylstyrene, and N,N-diethyl-p-aminoethylstyrene. Among these, from the viewpoints of availability and productivity, styrene, α-methylstyrene, and 4-methylstyrene are preferably used. Styrene is particularly preferred.
Block P may be composed of one type of aromatic vinyl compound unit or two or more types of aromatic vinyl compound units, and may also contain monomer units other than vinyl aromatic compound units.

The conjugated diene compound constituting the block Q is a diolefin having a pair of conjugated double bonds, and examples thereof include, but are not limited to, 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 2-methyl-1,3-pentadiene, and 1,3-hexadiene. Among these, from the viewpoints of availability and productivity, 1,3-butadiene and isoprene are preferably used. 1,3-butadiene is particularly preferred.
The block Q may be composed of one type of conjugated diene compound unit or may be composed of two or more types of conjugated diene compound units. In addition, the block Q may contain a monomer unit other than the conjugated diene compound unit.

The block polymer before hydrogenation having at least two blocks P and at least one block Q may be linear, branched, radial, or the like, but is preferably a block copolymer represented by the following formula (1) or (2):
P-(Q-P)m (1)
(P-Q)n (2)
(In the formula, P represents a block P, Q represents a block Q, m represents an integer of 1 to 5, and n represents an integer of 2 to 5.)

In formula (1) or (2), the larger the m and n, the lower the order-disorder transition temperature of the rubber-like polymer, but the smaller the m and n, the lower the cost and ease of production.

The component (A) used in the present invention is more preferably a hydrogenated product of a block copolymer represented by formula (1) in which m is 3 or less, even more preferably a hydrogenated product of a block copolymer represented by formula (1) in which m is 2 or less, and most preferably a hydrogenated product of a block copolymer represented by formula (1) in which m is 1.

The content of block P in component (A) is preferably 10 to 50% by mass, more preferably 15 to 45% by mass, and even more preferably 20 to 40% by mass. When component (A) contains 10% or more by mass of block P, the mechanical strength and heat resistance of the resulting thermoplastic elastomer composition tends to be good, while when the content of block P is 50% or less by mass, the flexibility and rubber elasticity are excellent, and bleeding of the softener is easily suppressed.

The hydrogenation rate of all conjugated diene compound units contained in the hydrogenated block copolymer (A) (hereinafter, this hydrogenation rate may be simply referred to as "hydrogenation rate"), i.e., the hydrogenation rate of carbon-carbon double bonds of the conjugated diene compound units, is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more.
When the hydrogenation rate is 80% or more, the solubility parameter value approaches that of the propylene-based resin of component (C) described below, and dispersion becomes good, so that oil bleeding tends to be further reduced. This hydrogenation rate can be measured by proton nuclear magnetic resonance ( ^1H -NMR) method.
In this specification, the conjugated diene compound unit is referred to as "conjugated diene compound unit" regardless of whether it is before or after hydrogenation.

The weight-average molecular weight of component (A) used in the present invention is preferably 80,000 to 1,000,000, more preferably 80,000 to 600,000, and even more preferably 80,000 to 400,000, as polystyrene-equivalent molecular weight measured by gel permeation chromatography. If the weight-average molecular weight is 80,000 or more, the rubber elasticity and mechanical strength are good, and bleeding of the hydrocarbon rubber softener of component (B), which will be described later, is less likely to occur. On the other hand, if the weight-average molecular weight is 1,000,000 or less, the fluidity is good and moldability is excellent.

The method for producing component (A) in the present invention is not particularly limited, and may be any method that can obtain the above-mentioned structure and physical properties. The block copolymer before hydrogenation can be obtained, for example, by block polymerization in an inert solvent using a lithium catalyst or the like according to the method described in JP-B-40-23798. The hydrogenation of the block copolymer can be carried out in an inert solvent in the presence of a hydrogenation catalyst according to the methods described, for example, in JP-B-42-8704, JP-B-43-6636, JP-A-59-133203, and JP-A-60-79005.

Examples of commercially available products of such hydrogenated block copolymers (A) include "KRATON (registered trademark)-G" (Kraton Polymers), "Septon (registered trademark)" (Kuraray Co., Ltd.), "Tuftec (registered trademark)" (Asahi Kasei Corporation), and "TAIPOL (registered trademark)" (TSRC Corporation).

The hydrogenated block copolymer (A) may be used alone or in the form of a mixture of two or more types having different block structures, physical properties, etc.

<Component (B)>
The component (B) used in the present invention is a hydrocarbon-based rubber softener.

Hydrocarbon-based rubber softeners are typically made with a weight-average molecular weight of 300 to 2,000, preferably 500 to 1,500, and mineral oil-based or synthetic resin-based hydrocarbons are suitable. The weight-average molecular weight is the polystyrene-equivalent molecular weight measured by gel permeation chromatography.

Mineral oil-based rubber softeners are generally mixtures of aromatic hydrocarbons, naphthenic hydrocarbons, and paraffinic hydrocarbons. Oils in which the proportion of aromatic hydrocarbon carbon relative to the total carbon content is 35% by mass or more are called aromatic oils, those in which the proportion of naphthenic hydrocarbon carbon is 30 to 45% by mass are called naphthenic oils, and those in which the proportion of paraffinic hydrocarbon carbon is 50% by mass or more are called paraffinic oils. In the present invention, paraffinic oils are preferably used.

Paraffin oils are not particularly limited, but the kinematic viscosity at 40°C is usually 20 cSt (centistokes) or more, preferably 50 cSt or more, and usually 800 cSt or less, preferably 600 cSt or less. The pour point is usually -40°C or more, preferably -30°C or more, and preferably 0°C or less. Furthermore, the flash point (COC) is usually 200°C or more, preferably 250°C or more, and usually 400°C or less, preferably 350°C or less.

The hydrocarbon rubber softener of component (B) may be used alone or in combination of two or more.

<Component (C)>
The propylene-based resin of component (C) essentially comprises a propylene homopolymer of component (C1) and a propylene-α-olefin block copolymer of component (C2), and may further comprise a propylene-α-olefin random copolymer as component (C3).

Component (C1): Propylene homopolymer Propylene homopolymer is called homopolypropylene and is a polymer consisting of propylene alone.
The propylene homopolymer that can be used generally has an MFR (melt flow rate, 230° C., 21.2 N load) of 0.1 to 50 g/10 min, preferably 0.1 to 30 g/10 min.

Examples of commercially available propylene homopolymers include "Novatec (registered trademark) PP" (Japan Polypropylene Corporation) and "Prime Polypro (registered trademark)" (Prime Polymer Co., Ltd.).

Component (C2): Propylene-α-olefin block copolymer A general production method for a propylene-α-olefin block copolymer comprises two steps: a step of randomly polymerizing propylene homopolymer or propylene and a small amount of an α-olefin other than propylene, and a step of randomly polymerizing propylene and an α-olefin. The first segment polymerized in the first step is a propylene homopolymer portion or a random copolymer portion of propylene and a small amount of an α-olefin, and the second segment polymerized in the second step is a propylene-α-olefin random copolymer portion, and the propylene-α-olefin random copolymer of the second segment forms a dispersed phase in the propylene homopolymer of the first segment or the random copolymer of propylene and a small amount of an α-olefin, resulting in a structure.

The propylene/α-olefin block copolymer used in the present invention is composed of a first segment which is a crystalline propylene-based polymer portion and a second segment which is a non-crystalline propylene/α-olefin copolymer portion or a low-crystalline propylene/α-olefin copolymer portion.
The crystalline propylene polymer portion which is the first segment is composed of a propylene homopolymer portion or a random copolymer portion of propylene and a small amount of an α-olefin.
In the present invention, the non-crystalline propylene/α-olefin copolymer portion or the low-crystalline propylene/α-olefin copolymer portion which is the second segment is called a propylene/α-olefin random copolymer portion.
In the entire propylene-α-olefin block copolymer (the total of the first segment and the second segment), the content of the second segment is preferably 5 to 90 mass%, more preferably 30 to 90 mass%, and even more preferably 35 to 75 mass%. In this specification, a propylene-α-olefin block copolymer containing 30 mass% or more of a second segment consisting of a propylene-α-olefin random copolymer portion is called a reactor TPO. In other words, among propylene-α-olefin block copolymers, reactor TPO is preferred.

The α-olefin in the propylene-α-olefin block copolymer refers to α-olefins in the broad sense including ethylene, and examples thereof include α-olefins having 2 to 20 carbon atoms (excluding propylene having 3 carbon atoms), such as ethylene, 1-butene, 3-methyl-1-butene, 1-pentene, 4-methyl-1-pentene, 4,4-dimethyl-1-pentene, 1-hexene, 4-methyl-1-hexene, 1-heptene, 1-octene, 1-decene, and 1-octadecene, and more preferably α-olefins having 2 to 8 carbon atoms (excluding propylene having 3 carbon atoms), but are not particularly limited thereto. Among these, ethylene, 1-butene, 1-hexene, and 1-octene are preferred from the viewpoint of easy availability.
The α-olefins may be used alone or in any combination of two or more in any ratio.

Commercially available propylene-α-olefin block copolymers include "Novatec (registered trademark) PP" (Japan Polypropylene Corporation), "Prime Polypro (registered trademark)" (Prime Polymer Co., Ltd.), and "Tefabloc (registered trademark)" (Mitsubishi Chemical Corporation).

Component (C3): Propylene-α-olefin random copolymer The propylene-based resin of component (C) may have a propylene-α-olefin random copolymer as component (C3), but in this case, the mixing ratio of the propylene homopolymer of component (C1) and the propylene-α-olefin random copolymer of component (C3) is preferably 70 mass% or less of component (C3) relative to the total mass of components (C1) and (C3), from the viewpoint of maintaining good slip resistance. When the content ratio of the propylene-α-olefin random copolymer is high, the slip resistance tends to deteriorate.

As the α-olefin in the propylene/α-olefin random copolymer, the α-olefin in the propylene/α-olefin block copolymer described above can be used similarly.
The propylene unit content (content of repeating units derived from propylene) in the propylene-α-olefin random copolymer is desirably 55 mol % or more.
The content of each structural unit in the propylene-based resin of component (C) can be determined by infrared spectroscopy.

Commercially available propylene-α-olefin random copolymers include "Novatec (registered trademark) PP" (Japan Polypropylene Corporation) and "Prime Polypro (registered trademark)" (Prime Polymer Co., Ltd.).
Examples of such products include:

In component (C), it is preferable that components (C1) to (C3) are contained in the following proportions.

Component (C1): Propylene homopolymer is preferably 60 to 95% by mass when the entire component (C) is taken as 100% by mass. By making the content of propylene homopolymer equal to or higher than the lower limit, it becomes easier to control the obtained thermoplastic elastomer composition so that it has an appropriate gripping force. By making the content of propylene homopolymer equal to or lower than the upper limit, it is possible to prevent the material from becoming slippery due to a decrease in frictional force.
Component (C2): The propylene/α-olefin block copolymer is preferably 5 to 40% by mass when the entire component (C) is taken as 100% by mass. By making the content of the propylene/α-olefin block copolymer equal to or higher than the lower limit, it becomes easier to effectively prevent oil from migrating to the paper. By making the content of the propylene/α-olefin block copolymer equal to or lower than the upper limit, the adhesion strength when stacked is suppressed, and deterioration of blocking resistance can be suppressed.
Component (C3): the propylene/α-olefin random copolymer preferably accounts for 0 to 60% by mass when the total amount of component (C) is taken as 100% by mass.

The melt flow rate of the propylene-based resin of component (C) (JIS K7210 (1999), 230°C, 21.2 N load) is usually 0.05 to 200 g/10 min, preferably 0.1 to 100 g/10 min. By using one with a melt flow rate of 0.05 g/10 min or more, the moldability of the resulting thermoplastic elastomer composition can be improved and appearance defects are less likely to occur, and by using one with a melt flow rate of 200 g/10 min or less, the mechanical properties of the resulting thermoplastic elastomer composition, particularly the tensile strength, can be maintained within the desired range.

<Component (D)>
Component (D) in the present invention is a rosin ester represented by the following structural formula (Chemical Formula 1).

Rosin esters are ester resins derived from the natural resin rosin, and typical examples are disproportionated rosin esters and hydrogenated rosin esters.

The raw rosin is not particularly limited, and examples include natural rosins such as gum rosin, tall oil rosin, and wood rosin; refined rosin obtained by refining natural rosin; maleated rosin, fumarated rosin, acrylated rosin, polymerized rosin, polymerized rosin ester, and rosin-modified phenol.

The method for producing purified rosin is not particularly limited, and any known method such as reduced pressure distillation, steam distillation, extraction, or recrystallization can be appropriately selected.

Polymerized rosin is not particularly limited, and can be obtained, for example, by heating natural rosin in the presence of a polymerization catalyst. Polymerization catalysts are not particularly limited, and examples include acids such as sulfuric acid, phosphoric acid, and hydrofluoric acid; and metal halides such as boron fluoride, aluminum chloride, and zinc chloride.

There are no particular limitations on the method for producing rosin esters, and they can be obtained, for example, by reacting natural rosin with alcohol under heating. If necessary, an esterification catalyst may be added to the reaction.

The alcohol is not particularly limited, and examples thereof include aliphatic monohydric or polyhydric alcohols having 1 to 20 carbon atoms. Examples of such alcohols include monohydric alcohols such as methanol, ethanol, isopropyl alcohol, isoamyl alcohol, n-hexyl alcohol, 2-ethylhexyl alcohol, n-octyl alcohol, dodecyl alcohol, lauryl alcohol, stearyl alcohol, and dihydroabietyl alcohol; dihydric alcohols such as ethylene glycol, diethylene glycol, propylene glycol, and neopentyl glycol; trihydric alcohols such as glycerin, trimethylolethane, and trimethylolpropane; and tetrahydric alcohols such as pentaerythritol and diglycerin.

The esterification catalyst is not particularly limited, and examples thereof include acid catalysts such as acetic acid, paratoluenesulfonic acid, and the like; alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and the like; alkaline earth metal hydroxides such as calcium hydroxide, magnesium hydroxide, and the like; and metal oxides such as calcium oxide, magnesium oxide, zinc oxide, lead oxide, tin oxide, and the like.

Hydrogenated rosin may be used as the raw material rosin for disproportionated rosin ester, while disproportionated rosin may be used as the raw material rosin for hydrogenated rosin ester.

(Disproportionated rosin ester)
The disproportionated rosin ester is not particularly limited and can be obtained by various known methods, for example, by subjecting the above-mentioned raw material rosin to a heating reaction in the presence of a disproportionation catalyst.

The disproportionation catalyst is not particularly limited, and various known catalysts can be used, such as supported catalysts such as palladium-carbon, rhodium-carbon, and platinum-carbon; metal powders such as nickel and platinum; and iodides such as iodine and iron iodide. The amount of the catalyst used is usually about 0.01 to 5 parts by mass, and preferably about 0.01 to 1 part by mass, per 100 parts by mass of the raw rosin. The reaction temperature is about 100 to 300°C, and preferably about 150 to 290°C.

(Hydrogenated Rosin Ester)
The hydrogenated rosin ester is not particularly limited and can be obtained by various known methods, for example, by blowing hydrogen into the above-mentioned raw material rosin in the presence of a hydrogenation catalyst at a pressure of about 2 to 20 MPa, preferably about 5 to 20 MPa, and heating the rosin at a temperature of about 100 to 300° C., preferably about 150 to 300° C.

The hydrogenation catalyst is not particularly limited, but examples thereof include supported catalysts, metal powders, iodine, and iodides. The supported catalyst is not particularly limited, but examples thereof include palladium-carbon, rhodium-carbon, ruthenium-carbon, and platinum-carbon. The metal powder is not particularly limited, but examples thereof include nickel and platinum. The iodide is not particularly limited, but examples thereof include iron iodide. Among these, palladium, rhodium, ruthenium, and platinum-based catalysts are preferred in that they can increase the hydrogenation rate while shortening the hydrogenation time. The amount of the hydrogenation catalyst used is not particularly limited, but is usually about 0.01 to 5 parts by mass, and preferably about 0.01 to 2 parts by mass, per 100 parts by mass of the raw rosin.

The rosin ester of component (D) is preferably a hydrogenated rosin ester. That is, since grommets are often attached to pallets and exposed to the outdoors, from the viewpoint of weather resistance, a hydrogenated rosin ester that is as stable as possible is desirable.

Component (D) may be one obtained by the above-mentioned manufacturing method, or a commercially available product may be used. An example of a commercially available product is "PINECRYSTAL" manufactured by Arakawa Chemical Industries, Ltd.

The rosin ester of component (D) may be used alone or in combination of two or more types.

<Component (E)>
The thermoplastic elastomer composition of the present invention may further contain diallyl phthalate as component (E). The diallyl phthalate is diallyl orthophthalate represented by the following structural formula (Chemical Formula 2B) and/or diallyl isophthalate represented by the following structural formula (Chemical Formula 2B).

The two vinyl groups contained in component (E) are components that promote modification by component (F), which will be described later. The details of the mechanism by which the thermoplastic elastomer composition of the present invention contains diallyl orthophthalate and/or diallyl isophthalate as component (E) in addition to the aforementioned components (A) to (D), thereby suppressing oil bleeding in the high hardness region, are not clear, but are presumed to be as follows.

Diallyl phthalate has a double bond in its chemical structure that contributes to the reaction, and the phthalate structure has the property of having high affinity and easy migration in aromatic vinyl compounds such as polystyrene. For example, plasticizers such as DEHP (bis(2-ethylhexyl) phthalate) and DINP (diisononyl phthalate), which are used in polyvinyl chloride resins, are easy to migrate into polystyrene resins, and similarly, hydrogenated block copolymers having polymer block P mainly composed of aromatic vinyl compound units and polymer block Q mainly composed of conjugated diene compound units, which are component (A), are also easy to migrate. The skeleton that is easy to migrate is derived from aromatic vinyl compound units, and since diallyl phthalate has a structure similar to these phthalate plasticizers, it is thought to have a high affinity for polymer block P mainly composed of aromatic vinyl compound units. When polymer block P mainly composed of aromatic vinyl compound units is cut by organic peroxides, diallyl phthalate is thought to react in polymer block P mainly composed of aromatic vinyl compound units.

Diallyl phthalate has three isomers, ortho, iso, and tere, but in the present invention, the ortho and/or iso isomers are used. From the viewpoint of reactivity, the iso isomer is preferred from the viewpoint of steric hindrance.

There are no particular limitations on the method for producing diallyl orthophthalate and diallyl isophthalate, and examples of such methods include a method in which ortho- or iso-phthalic anhydride is directly esterified with allyl alcohol in the presence of an acid catalyst (direct esterification method), and a method in which ortho- or iso-phthalic anhydride is reacted with an aqueous sodium hydroxide solution to produce sodium phthalate, and then allyl chloride is reacted under pressure (allyl chloride method).

Component (E) may be one obtained by the above-mentioned manufacturing method, or a commercially available product may be used. Examples of commercially available products include "Daiso DAP (registered trademark) Monomer" and "Daiso DAP (registered trademark) 100 Monomer" manufactured by Osaka Soda Co., Ltd.

The diallyl phthalate of component (E) may be one of the above structures or two of them may be used in combination.

<Mixing ratio of components (A) to (E)>
The thermoplastic elastomer composition of the present invention preferably contains 20 to 40 mass% of component (A), 20 to 50 mass% of component (B), and 10 to 60 mass% of component (C) relative to 100 mass% in total of components (A), (B), and (C). It is more preferable that the content of component (C) is 10 to 50 mass%.

The rosin ester of component (D) in the thermoplastic elastomer composition of the present invention is often used as a tackifier due to its nature, and is excellent in providing tackiness. As mentioned above, the important performance required for a pallet grommet is particularly three, namely, blocking resistance, slip resistance, and no migration of oil to paper (migration resistance). By blending the rosin ester of component (D) with components (A) to (C), the effect of achieving both blocking resistance and slip resistance is achieved. Blocking refers to a phenomenon in which grommets fitted into a pallet overlap each other when the pallet is loaded, and after being left in a state where pressure is applied vertically for a long time, when the pallet is lifted, the grommets stick to the grommet of the pallet below. When the pallet is lifted, if the adhesion between the grommets is high and a peeling force is generated that is greater than the load of the pallet, the pallet below will lift up. To prevent such blocking, the pallet needs to be easily peeled off even when left in a state where pressure is applied vertically for a long time.
Furthermore, if a strong lateral force, such as braking, is applied to stacked pallets during transport, the pallets may slide off if the grommet surface is slippery, so high slip resistance is required.
With regard to these two performance characteristics, the inventors have discovered that the inclusion of component (D), Longines ester, contributes to reducing adhesion against vertical pressure, which is required for blocking resistance, and has the effect of increasing frictional force against lateral force, which is required for slip resistance, and have arrived at the present invention, which achieves both blocking resistance and slip resistance.
Rosin ester is highly tackifying and generally exhibits high adhesion even when subjected to vertical pressure, and exerts the above-mentioned effects in the composition of the present invention.

In the thermoplastic elastomer composition of the present invention, the content of the rosin ester of component (D) is preferably 0.1 to 20 parts by mass, and more preferably 0.5 to 10 parts by mass, per 100 parts by mass of the total of components (A) to (C). If the content of component (D) is equal to or greater than the lower limit, the effect of improving blocking resistance and slip resistance due to the inclusion of component (D) can be effectively obtained, and if it is equal to or less than the upper limit, the effect commensurate with the amount added can be obtained.

When the thermoplastic elastomer composition of the present invention contains diallyl phthalate as component (E), the content of component (E) is preferably 0.05 to 3 parts by mass, and more preferably 0.1 to 2 parts by mass, per 100 parts by mass of the total of components (A) to (C). If the content of component (E) is 0.05 parts by mass or more, the oil-bleed suppression effect of blending component (E) can be sufficiently obtained, and if it is 3 parts by mass or less, the oil-bleed suppression effect commensurate with the amount added can be obtained.

<Component (F)>
In addition to the above-mentioned components (A) to (E), the thermoplastic elastomer composition of the present invention preferably contains an organic peroxide as component (F). By containing component (F), a part of component (A) is modified, and oil bleeding can be more effectively suppressed. The organic peroxide may be used alone or in any combination and ratio of two or more kinds.

The organic peroxide may be either aromatic or aliphatic, and may be a single peroxide or a mixture of two or more peroxides. Specifically, dialkyl peroxides such as di-t-butyl peroxide, t-butylcumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, 1,3-bis(t-butylperoxyisopropyl)benzene, and 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane; peroxy esters such as t-butylperoxybenzoate, t-butylperoxyisopropyl carbonate, 2,5-dimethyl-2,5-di(benzoylperoxy)hexane, and 2,5-dimethyl-2,5-di(benzoylperoxy)hexyne-3; and hydroperoxides such as acetyl peroxide, lauroyl peroxide, benzoyl peroxide, p-chlorobenzoyl peroxide, and 2,4-dichlorobenzoyl peroxide may be used. Of these, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane is particularly preferred.

When the thermoplastic elastomer composition of the present invention contains an organic peroxide as component (F), the content thereof is preferably 0.05 to 2.0 parts by mass, and more preferably 0.07 to 1.5 parts by mass, per 100 parts by mass of the total amount of components (A), (B), and (C). If the content of component (F) is equal to or greater than the above lower limit, the effect of modification by component (F) can be sufficiently obtained, and if it is equal to or less than the above upper limit, the modification reaction is easily controlled.

<Other ingredients>
The thermoplastic elastomer composition of the present invention may contain various additives such as stabilizers, lubricants, antioxidants, ultraviolet absorbers, foaming agents, flame retardants, colorants, and fillers, as well as thermoplastic resins and rubbers other than the essential components, as necessary, within the scope of the object of the present invention.

In particular, the thermoplastic elastomer composition of the present invention preferably contains an antioxidant as a stabilizer.
Examples of antioxidants include monophenol-based, bisphenol-based, tri- or higher polyphenol-based, thiobisphenol-based, naphthylamine-based, diphenylamine-based, and phenylenediamine-based antioxidants. Among these, monophenol-based, bisphenol-based, tri- or higher polyphenol-based, and thiobisphenol-based antioxidants are preferred. When an antioxidant is contained, the content is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, relative to 100 parts by mass of the total amount of components (A) to (C). If the content of the antioxidant is 0.01 parts by mass or more, the effect of adding the antioxidant can be sufficiently obtained, and if it is 5 parts by mass or less, an improvement effect commensurate with the increase in the amount added can be obtained.

Examples of fillers include glass fiber, hollow glass spheres, carbon fiber, talc, calcium carbonate, mica, potassium titanate fiber, silica, metal soap, titanium dioxide, carbon black, etc. These can be used alone or in any combination and ratio of two or more types.

Examples of thermoplastic resins other than the essential components include polyphenylene ether-based resins, polyamide-based resins such as nylon 6 and nylon 66, polyester-based resins such as polyethylene terephthalate and polybutylene terephthalate, polyoxymethylene-based resins such as polyoxymethylene homopolymers and polyoxymethylene copolymers, polymethyl methacrylate-based resins, polystyrene-based resins, biodegradable resins, and plant-derived raw material resins.
The optional rubber may include, for example, ethylene propylene rubber, polybutadiene rubber.

<Method of producing thermoplastic elastomer composition>
The thermoplastic elastomer composition of the present invention can be produced by mixing, kneading or melt-kneading the above-mentioned components (A), (B), (C) and (D), preferably component (E) and further component (F), other resin components and various additives, etc., in a conventional manner using a conventional extruder, Banbury mixer, mixing roll, roll, Brabender Plastograph, Kneader Brabender, etc. Among these, it is preferable to use an extruder, particularly a twin-screw extruder.

When the thermoplastic elastomer of the present invention is produced by kneading it in an extruder or the like, it is preferable to carry out dynamic heat treatment in which the elastomer is melt-kneaded in a state where it is heated to a temperature of usually 80 to 300°C, preferably 100 to 250°C. The treatment time for dynamic heat treatment is not particularly limited, but is usually 0.1 to 30 minutes, taking into consideration productivity, etc.

This dynamic heat treatment is preferably carried out by melt kneading as described above, and when using a twin-screw extruder, it is more preferable to carry out the dynamic heat treatment by supplying each component to a raw material supply port (hopper) of a twin-screw extruder having multiple raw material supply ports.

<Duro A hardness>
The thermoplastic elastomer composition of the present invention preferably has a Duro A hardness (JIS K6253) of 40 to 95, more preferably 50 to 95, as measured by the method described in the Examples section below.
That is, since the thermoplastic elastomer composition of the present invention has the feature of obtaining high gripping properties, the Duro A hardness of the thermoplastic elastomer composition of the present invention is preferably not less than 40. On the other hand, if the Duro A hardness is greater than 95, the elastomer loses flexibility and its rubber-like properties deteriorate, so from the viewpoint of the practical range of use, the Duro A hardness of the thermoplastic elastomer composition of the present invention is preferably not more than 95.

[Molded body]
The molded article of the present invention can be obtained by molding the thermoplastic elastomer composition of the present invention using a molding machine such as an injection molding machine, a single screw extruder, a twin screw extruder, a compression molding machine or a calendar processing machine.
Examples of composite molded articles in which the thermoplastic elastomer composition of the present invention is fused with other materials include an insert molded article in which a thermoplastic resin is inserted into a molded article made of the thermoplastic elastomer composition of the present invention, and a multicolor molded article obtained by multicolor molding the thermoplastic elastomer composition of the present invention and an olefin-based resin.
The olefin resin is not particularly limited, but polypropylene is preferred.

[Application]
The molded article of the present invention can be applied to many applications, including various automobile components, building components, miscellaneous goods components, and distribution materials, but is particularly suitable as an anti-slip material, and the effects of the present invention are particularly well exhibited in pallet grommets for distribution materials.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not deviate from the gist of the invention. Note that the various manufacturing conditions and evaluation result values in the following examples are meant as preferred upper or lower limit values in the embodiments of the present invention, and the preferred range may be a range defined by a combination of the above-mentioned upper or lower limit values and the values of the following examples or values between the examples.

[raw materials]
In the following examples, the following raw materials were used:

<Component (A): Hydrogenated Block Copolymer>
A: Hydrogenated copolymer of styrene block, butadiene block, and styrene block (TAIPOL (registered trademark) 6151, manufactured by TSRC Corporation)
Styrene unit content: 33% by mass
Hydrogenation rate: 98% or more Weight average molecular weight: approx. 260,000

<Component (B): Hydrocarbon-based rubber softener>
B: Paraffin-based oil (Idemitsu Kosan Co., Ltd. "Diana (registered trademark) Process Oil PW90")
Kinematic viscosity at 40°C: 95.5 cSt
Pour point: -15°C
Flash point: 272°C

<Component (C): Polypropylene-based resin>
C-1: Propylene homopolymer ("Novatec (registered trademark) PP FY6" manufactured by Japan Polypropylene Corporation)
MFR: 2.5/10 min (230°C, 21.2 N load)
C-2: Reactor TPO ("Tefabloc (registered trademark) 5013" manufactured by Mitsubishi Chemical Corporation)
MFR: 0.7g/10min (230℃, 21.2N)
Propylene-ethylene random copolymer content: 55% by mass
C-3: Propylene-ethylene random copolymer (Novatec (registered trademark) PP EG7F, manufactured by Japan Polypropylene Corporation)
MFR: 1.3g/10min (230℃, 21.2N load)
Propylene unit content: 97% by mass

<Component (D): Rosin Ester>
D: Hydrogenated rosin ester ("PINECRYSTAL-311" manufactured by Arakawa Chemical Industries, Ltd.)

<Component (E): Diallyl Phthalate>
E: Diallyl isophthalate ("Daiso DAP (registered trademark) 100 Monomer" manufactured by Osaka Soda Co., Ltd.)

<Component (F): Organic peroxide>
F: A mixture of 40% by mass of 2,5-dimethyl-2,5-di(t-butylperoxy)hexane and 60% by mass of calcium carbonate ("AD40C" manufactured by Nouryon Chemical Industries, Ltd.)

<Component (G): Petroleum resin>
G: Hydrogenated petroleum resin ("Alcon (registered trademark) P-140" manufactured by Arakawa Chemical Industries, Ltd.)

[Evaluation method]
The thermoplastic elastomer compositions in the following Examples and Comparative Examples were evaluated as follows.

(1) Measurement of Melt Flow Rate (MFR) Measurement was performed according to the method of JIS K7210 at a measurement temperature of 230° C. and a measurement load of 21.2 N. MFR is an index of injection moldability, and is preferably in the range of 2 to 50 g/10 min.

(2) Evaluation of Physical Properties In measuring the following physical properties, each thermoplastic elastomer composition was injection molded using an in-line screw type injection molding machine (manufactured by Toshiba Machine Co., Ltd., product number: IS130) under conditions of an injection pressure of 50 MPa, a cylinder temperature of 220°C, and a mold temperature of 40°C to form a sheet with a thickness of 2 mm, a width of 120 mm, and a length of 80 mm.
In the tensile test of (2-2), a dumbbell-shaped test piece was punched out from the obtained sheet (thickness 2 mm × width 120 mm × length 80 mm) using a test piece punching blade (JIS No. 3 dumbbell-shaped) in accordance with JIS K6251, and the measurement was performed using this test piece.
The measuring probe for evaluating slip property (2-4), also called a normal indenter, was prepared by heat-molding a thermoplastic composition made of a styrene-based thermoplastic elastomer having a Duro A hardness of 88 to a thickness of 1 mm onto a molded product previously made of polypropylene, to prepare a circular measuring probe with a contact surface area of 5.6 ^cm2 , and a wire hook pin was inserted into the measuring probe, and measurement was performed using the measuring probe with a total load of 9.2 g.

(2-1-1) Duro A Hardness The hardness (after 15 seconds) was measured in accordance with JIS K6253 (JIS-A).
(2-1-2) Duro D Hardness The hardness (after 15 seconds) was measured in accordance with JIS K6253 (JIS-D).

(2-2) Tensile strength at break/elongation at break (tensile test)
The measurement was performed in accordance with JIS K6251 at a test speed of 500 mm/min.

(2-3) Peel Force To evaluate adhesion as an index of blocking resistance, a test piece having a diameter of 29 mm for compression set was punched out from a sheet having a thickness of 2 mm obtained by injection molding using a compression set tool conforming to JIS K6262, six sheets were stacked, and compressed at 70°C and a compression ratio of 25% for 22 hours. The maximum peel force when peeling the upper sheet from the stacked test pieces was measured using a "Digital Force Gauge AD-4932A-50N" manufactured by A&D Co., Ltd.
The smaller this value, the better the blocking resistance, and it is preferable that this value is 5N or less.

(2-4) Pull-out force In order to evaluate slipperiness as an index of slip resistance, the probe prepared as described above was placed on a sheet having a thickness of 2 mm, a width of 120 mm, and a length of 80 mm obtained by injection molding, and a load of 2.25 kg was placed on the probe. While keeping the sheet and the load placed on the probe stationary, the probe was slowly pulled out sideways, and the maximum pull-out force was measured using a "Digital Force Gauge DST-500N" manufactured by Imada Co., Ltd.
The larger this value, the better the slip resistance, and a value of 12N or more is preferable.

(2-5) Paper migration test A test piece having a diameter of 29 mm for compression set was punched out from a sheet having a thickness of 2 mm obtained by injection molding the obtained thermoplastic elastomer composition, and six of these were stacked together to obtain a sample of the thermoplastic elastomer composition. Using a measuring tool for compression set according to JIS K6262, a piece of paper cut from wrapping paper to a length of 8 cm and a width of 5 cm was set, and a sample of the thermoplastic elastomer composition was set on top of it, and compressed at 70°C and a compression rate of 25% for 68 hours, after which the sample was removed and the traces on the piece of paper were observed, and evaluation was performed according to the following criteria.
<Criteria for determining oil migration (bleed) onto paper>
○: Almost no oil transfer observed ×: Oil transfer clearly observed

[Examples 1 to 6, Comparative Examples 1 to 6]
To the blending amounts shown in Table 1, 0.1 parts by mass of tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane ("Irganox 1010" manufactured by BASF Japan Ltd.) was further added as an antioxidant, and mixed in a Henschel mixer. The mixture was then extruded using a gravimetric feeder in a JSW twin-screw extruder "TEX30" at a cylinder temperature of 200°C and a screw rotation speed of 400 rpm to obtain a thermoplastic elastomer composition.

The thermoplastic elastomer composition obtained was evaluated as described above, and the results are shown in Table 1.

As can be seen from Table 1, in comparison with Examples 1 to 6, Comparative Examples 1 to 3, which are formulations not containing rosin ester, have a maximum peel force of 5 N or less and a maximum pull-out force of 12 N or more, and thus do not achieve a balance between blocking resistance and slip resistance.
Comparative Example 4 is a compounding example that does not contain a propylene homopolymer, and the maximum pull-out force is not 12N or more, and the maximum peel force is not 5N or less.
Comparative Example 5 is a compounding example containing a petroleum resin used as a tackifier as an alternative material to rosin ester, but the maximum peel force did not reach 5N or less.
Comparative Example 6 is a formulation that does not contain Reactor TPO, and oil migration to the paper was observed.

Claims (9)

A thermoplastic elastomer composition comprising the following components (A) to (D):
A thermoplastic elastomer composition comprising 20 to 40 mass% of component (A), 20 to 50 mass% of component (B), and 10 to 60 mass% of component (C) relative to 100 mass% in total of components (A), (B), and (C), and the content of component (D) is 0.1 to 20 parts by mass relative to 100 parts by mass in total of components (A), (B), and (C) .
Component (A): A hydrogenated product of a block copolymer having at least two polymer blocks P mainly composed of aromatic vinyl compound units and at least one polymer block Q mainly composed of conjugated diene compound units. Component (B): A softener for hydrocarbon-based rubber. Component (C): A propylene-based resin containing the following components (C1) and (C2): Component (C1): A propylene homopolymer. Component (C2): A propylene-α-olefin block copolymer. Component (D): A rosin ester. The thermoplastic elastomer composition according to claim 1, wherein the propylene-α-olefin block copolymer of component (C2) is a reactor TPO. The thermoplastic elastomer composition according to claim 1 or 2, wherein the propylene-based resin of component (C) further contains a propylene-α-olefin random copolymer as component (C3). The thermoplastic elastomer composition according to claim 3, wherein the content of component (C3) is 70% by mass or less in a total of 100% by mass of components (C1) and (C3). The thermoplastic elastomer composition according to any one of claims 1 to 4, further comprising diallyl phthalate as component (E). The thermoplastic elastomer composition according to any one of claims 1 to 5, wherein the thermoplastic elastomer composition has a Duro A hardness (JIS K6253) of 40 to 95. A molded article made of the thermoplastic elastomer composition according to any one of claims 1 to 6. A composite molded product obtained by fusing the thermoplastic elastomer composition according to any one of claims 1 to 6 with an olefin-based resin. A pallet grommet made from the composite molding of claim 8.