WO2025023152A1 - Thermoplastic resin composition - Google Patents

Abstract

The present invention provides a thermoplastic resin composition from which it is possible to form a stretch elastic member that has excellent extensibility and expansion/contraction recovery, and excellent in stress maintainability at the time of extension at a high temperature.　The present invention provides a thermoplastic resin composition that contains a thermoplastic elastomer (A) and a plasticizing agent (B), and that is characterized in that the thermoplastic elastomer (A): includes a styrene-based block copolymer; has a melt index of 0.1-100 g/10 min as measured by method-A in compliance with JIS K7210 under a condition of 190°C and 2.16 kg or under a condition of 230°C and 2.16 kg; has a storage modulus G' of 2.5×10⁵ Pa to 1.0×10⁷ Pa at 25°C as measured by the following measuring condition; has at least one peak, of loss tangent tanδ (loss modulus/storage modulus) obtained through measurement of the storage modulus G', in each of a low temperature range of -50°C to 0°C and a high temperature range of 60-120°C; and results in D1, which is the tanδ peak value in the low temperature range, greater than D2, which is the tanδ peak value in the high temperature range. (Storage modulus G' measuring condition) Starting temperature: -60°C, ending temperature: 190°C, temperature elevation rate: 5°C/min., measurement frequency: 1 Hz, distortion: 0.05%

Description

Thermoplastic resin composition

The present invention relates to a thermoplastic resin composition.

In recent years, absorbent articles, including sanitary materials such as disposable diapers and sanitary napkins, have come into widespread use. These absorbent articles use laminates made of stretchable materials to prevent them from slipping off when worn.

A well-known elastic material used in laminates is rubber thread, which is made from natural rubber or synthetic polymers in the form of threads. Rubber thread exhibits good stress when stretched, making it effective in preventing absorbent articles from slipping off when worn.

In addition, a stretch film containing an olefin-based elastomer and an inorganic filler has been proposed as a stretchable film that is used in sanitary products, sporting goods, medical products, etc. and exhibits stretchability and breathability (see Patent Document 1).

JP 2022-108630 A

However, Patent Document 1 does not fully consider how to improve extensibility, and there is room for improvement. When sanitary materials such as disposable diapers are worn, the elastic members used in the sanitary materials are required to have sufficient extensibility.

Furthermore, Patent Document 1 does not fully consider the prevention of deterioration in elastic recovery. When sanitary materials such as disposable diapers are worn, the elastic members used in the sanitary materials are stretched. Therefore, it is required that the elastic members are prevented from decreasing in elastic recovery even when held in a stretched state.

In addition, when sanitary materials such as disposable diapers are worn, they are kept at a temperature close to body temperature for a long period of time. Therefore, even if the elastic material is stretched and held in a heated state, stress relaxation is reduced, and it is required that the material has excellent stress retention when stretched at high temperatures. Patent Document 1 has the problem that the stress retention when stretched at high temperatures is insufficient.

In view of the above circumstances, the present invention aims to provide a thermoplastic resin composition capable of forming an elastic member having excellent extensibility and elastic recovery, and excellent stress maintenance when stretched at high temperatures.

As a result of extensive research conducted by the inventors to achieve the above object, it was discovered that the above object can be achieved by configuring a thermoplastic resin composition containing a thermoplastic resin (A) and a plasticizer (B) in which the thermoplastic elastomer (A) contains a styrene-based block copolymer, the melt index and storage modulus G' are within a specific range, the loss tangent tan δ (loss modulus/storage modulus) has at least one peak each in the low temperature range of -50 to 0°C and the high temperature range of 60 to 120°C, and D1, which is the tan δ peak value in the low temperature range, is greater than D2, which is the tan δ peak value in the high temperature range, thereby completing the present invention.

That is, the present invention relates to the following thermoplastic resin composition.
1. A thermoplastic resin composition comprising a thermoplastic elastomer (A) and a plasticizer (B),
The thermoplastic elastomer (A) contains a styrene-based block copolymer,
The melt index measured by Method A in accordance with JIS K7210 under conditions of 190°C and 2.16 kg or 230°C and 2.16 kg is 0.1 to 100 g/10 min;
The storage modulus G' at 25°C measured under the following measurement conditions is 2.5 x ¹⁰⁵ to 1.0 x ¹⁰⁷ Pa;
The loss tangent tan δ (loss modulus/storage modulus) obtained by measuring the storage modulus G' has at least one peak each in a low temperature range of -50 to 0°C and a high temperature range of 60 to 120°C,
D1, which is a tan δ peak value in the low temperature region, is greater than D2, which is a tan δ peak value in the high temperature region;
A thermoplastic resin composition comprising:
(Measurement conditions for storage modulus G')
Starting temperature -60°C, ending temperature 190°C, heating rate 5°C/min, measuring frequency 1Hz, strain 0.05%
2. The thermoplastic resin composition according to Item 1, wherein the styrene-based block copolymer is a hydrogenated styrene-based block copolymer.
3. The thermoplastic resin composition according to item 1 or 2, wherein the amount of styrene derived from the styrene-based block copolymer contained in the thermoplastic resin composition is 30 to 50 mass% based on 100 mass% of the thermoplastic resin composition.
4. The thermoplastic resin composition according to any one of Items 1 to 3, wherein the content of the thermoplastic elastomer (A) is 50 to 85% by mass, based on 100% by mass of the thermoplastic resin composition.
5. The thermoplastic resin composition according to any one of items 1 to 4, wherein the ratio (D1/D2) of D1 to D2 is greater than 1 and less than or equal to 15.
6. The thermoplastic resin composition according to any one of Items 1 to 5, further comprising a hydrocarbon resin (C), the content of which is 0.5 to 30 mass% relative to 100% of the thermoplastic resin composition.
7. An elastic member made of the thermoplastic resin composition according to any one of items 1 to 6.

The thermoplastic resin composition of the present invention can be used to form elastic members that have excellent stretchability and elastic recovery, and that are excellent in maintaining stress when stretched at high temperatures.

The thermoplastic resin composition of the present invention comprises a thermoplastic elastomer (A) and a plasticizer (B), the thermoplastic elastomer (A) comprising a styrene-based block copolymer, a melt index of 0.1 to 100 g/10 min measured by method A under conditions of 190° C. and 2.16 kg or method A under conditions of 230° C. and 2.16 kg, a storage modulus G' at 25° C. measured under specific measurement conditions of 2.5×10 ⁵ to 1.0×10 ⁷ Pa, and a loss tangent tan δ (loss modulus/storage modulus) obtained by measuring the storage modulus G' has at least one peak each in a low temperature region of -50 to 0° C. and a high temperature region of 60 to 120° C., and D1, which is a peak value of tan δ in the low temperature region, is greater than D2, which is a peak value of tan δ in the high temperature region. By virtue of having the above-described configuration, the thermoplastic resin composition of the present invention has excellent extensibility and stretch recovery properties, and is excellent in stress maintenance when stretched at high temperatures, making it possible to combine all of these properties.

Furthermore, in light of recent environmental considerations, emphasis has been placed on reducing resource consumption, and the above-mentioned elastic members also need to be made thinner. Elastic members are required to have excellent stress retention during stretching, with reduced stress relaxation even when stretched and held in a thin film of about 50 μm. The thermoplastic resin composition of the present invention makes it possible to form an elastic member that has excellent stress retention during stretching in the above-mentioned thin film state.

The thermoplastic resin composition of the present invention will be described below.

In this specification, "high temperature" means a temperature about the same as human body temperature, that is, about 35 to 42°C, preferably about 35.5 to 41.5°C, more preferably about 36 to 41°C, and particularly preferably 40°C. "Heating" also means bringing the temperature to within the above range.

In this specification, "room temperature" and "normal temperature" refer to 23°C.

The thermoplastic resin composition of the present invention has a melt index of 0.1 to 100 g/10 min, measured by Method A in accordance with JIS K7210 under conditions of 190°C and 2.16 kg or 230°C and 2.16 kg. If the melt index is less than 0.1 g/10 min, the stress during extension or the stress maintenance during extension at high temperatures is insufficient. If the melt index exceeds 100 g/10 min, the extensibility and stretch recovery are insufficient. The melt index is preferably 1 to 95 g/10 min, and more preferably 5 to 90 g/10 min.

The melt index of the thermoplastic resin composition is measured by the method described in the Examples below. The melt index is measured under conditions of (1) 190°C and 2.16 kg, or (2) 230°C and 2.16 kg, and either of the conditions that allows measurement is adopted.

The thermoplastic resin composition of the present invention has a storage modulus G' of 2.5 x 10 ⁵ to 1.0 x 10 ⁷ Pa at 25°C measured under the following measurement conditions. If the storage modulus G' is less than 2.5 x 10 ⁵ Pa, the stress during elongation is insufficient. If the storage modulus G' exceeds 1.0 x 10 ⁷ Pa, the stretch recovery is insufficient. The storage modulus G' is preferably 3.0 x 10 ⁵ to 9.5 x 10 ⁶ Pa, and more preferably 4.0 x 10 ⁵ to 9.0 x 10 ⁶ Pa.

(Measurement conditions for storage modulus G')
Starting temperature -60°C, ending temperature 190°C, heating rate 5°C/min, measuring frequency 1Hz, strain 0.05%

The storage modulus G' of the thermoplastic resin composition is measured in detail by the method described in the Examples below.

The thermoplastic resin composition of the present invention has at least one peak in the loss tangent tan δ (loss modulus/storage modulus) obtained by measuring the storage modulus G' in the low temperature range of -50 to 0°C and in the high temperature range of 60 to 120°C, and the tan δ peak value D1 in the low temperature range is greater than the tan δ peak value D2 in the high temperature range. If the thermoplastic resin composition of the present invention does not have at least one peak in the high temperature range and in the low temperature range, or if D1 is equal to or less than D2, the stress retention during elongation at high temperatures or the stretch recovery is poor.

The ratio of D1 to D2 (D1/D2) is preferably greater than 1 and equal to or less than 15, and more preferably 1.5 to 10. By having D1/D2 in the above range, the thermoplastic resin composition of the present invention is further improved in stress retention during elongation at high temperatures and in stretch recovery.

The tan δ, D1, and D2 of the thermoplastic resin composition are measured by the method described in the examples below.

(Thermoplastic elastomer (A))
The thermoplastic elastomer (A) includes a styrene-based block copolymer. The styrene-based block copolymer is not particularly limited as long as it is a styrene-based block copolymer used in a thermoplastic resin composition, and examples thereof include styrene-ethylene-butylene/styrene-styrene copolymer (SEB/S-S), styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-butylene-butadiene-styrene copolymer (SBBS), styrene-ethylene-propylene-styrene copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene copolymer (SEEPS), and styrene-ethylene-butylene-olefin crystalline copolymer (SEBC). Among these, in terms of being even more excellent in extensibility and elasticity recovery, and even more excellent in stress maintenance during extension at high temperatures, styrene-ethylene-butylene/styrene-styrene copolymer (SEB/S-S), styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-butylene-butadiene-styrene copolymer (SBBS), and styrene-ethylene-propylene-styrene copolymer (SEPS) are preferred, styrene-ethylene-butylene/styrene-styrene copolymer (SEB/S-S) and styrene-ethylene-butylene-styrene copolymer (SEBS) are more preferred, and styrene-ethylene-butylene/styrene-styrene copolymer (SEB/S-S) is even more preferred.

The above styrene-based block copolymers may be used alone or in combination of two or more.

The above-mentioned styrene-ethylene-butylene/styrene-styrene copolymer (SEB/S-S) is a styrene-ethylene-butylene-styrene copolymer in which the terminal styrene units form the end block phase and the ethylene-butylene units form the midblock phase, with styrene also dispersed in the midblock phase. By using a copolymer in which styrene is dispersed in the midblock phase, even if the overall styrene content of the styrene-based block copolymer is high, the styrene-based block copolymer does not become too hard and exhibits good extensibility, so that a thermoplastic resin composition containing a styrene-ethylene-butylene/styrene-styrene copolymer can achieve both good extensibility and good stretch recovery.

The method for preparing the styrene-ethylene-butylene/styrene-styrene copolymer is not particularly limited, and examples thereof include the method described in U.S. Patent No. 7,169,848.

As the styrene-ethylene-butylene/styrene-styrene copolymer, commercially available products can be used. Examples of commercially available products include A1537, A1536, and A1535 manufactured by Kraton Polymers.

The above-mentioned styrene-ethylene-butylene-styrene copolymer (SEBS) is a copolymer in which the terminal styrene units form the endblock phase and the ethylene-butylene units form the midblock phase. Furthermore, when a copolymer in which the midblock phase is hydrogenated ethylene-butylene units is used, the polarity difference with the styrene units in the endblock phase becomes more pronounced, and the styrene units in the endblock phase become stronger compared to a copolymer in which the midblock phase is not hydrogenated. As a result, the stretch recovery of the thermoplastic resin composition can be further improved. Furthermore, when the midblock phase is hydrogenated, a thermoplastic resin composition with even better heat stability can be provided.

As the styrene-ethylene-butylene-styrene copolymer, commercially available products can be used. Examples of commercially available products include G1653 manufactured by Kraton Polymers and Tuftec H1043 manufactured by Asahi Kasei Corporation.

The styrene content of the styrene-based block copolymer is preferably 30 to 75 mass%, more preferably 35 to 70 mass%, and even more preferably 40 to 65 mass%, assuming the styrene-based block copolymer to be 100 mass%. By setting the lower limit of the styrene content within the above range, the stress retention rate during extension at high temperatures of the elastic member formed using the thermoplastic resin composition is further improved. By setting the upper limit of the styrene content within the above range, hardening of the thermoplastic resin composition is further suppressed, and the extensibility of the elastic member is further improved.

In this specification, the "styrene content" of a styrene-based block copolymer refers to the content (mass%) of styrene blocks in the styrene-based block copolymer.

In addition, the method for calculating the styrene content in the styrene-based block copolymer in this specification is not particularly limited, and examples include methods using proton nuclear magnetic resonance spectroscopy or infrared spectroscopy in accordance with JIS K6239.

The amount of styrene derived from the styrene-based block copolymer contained in the thermoplastic resin composition of the present invention is preferably 25 to 60 mass%, more preferably 30 to 50 mass%, and more preferably 35 to 45 mass%, based on 100 mass% of the thermoplastic resin composition. By setting the lower limit of the styrene amount within the above range, the stress retention rate during extension at high temperatures of the elastic member formed using the thermoplastic resin composition is further improved. By setting the upper limit of the styrene amount within the above range, hardening of the thermoplastic resin composition is further suppressed, and the extensibility of the elastic member is further improved.

The styrene-based block copolymer may be used alone or in a mixture of two or more types. For example, a styrene-based block copolymer having a high styrene content and a styrene-based block copolymer having a low styrene content may be used in a mixture.

The styrene-based block copolymer is preferably a hydrogenated styrene-based block copolymer. In other words, the styrene-based block copolymer is preferably a hydrogenated product of a styrene-based block copolymer, and such a hydrogenated product of a styrene-based block copolymer is also called a hydrogenated styrene-based block copolymer. More specifically, a hydrogenated styrene-based block copolymer is a block copolymer obtained by block copolymerizing a vinyl aromatic hydrocarbon with a conjugated diene compound, and hydrogenating all or a part of the blocks based on the conjugated diene compound in the resulting block copolymer.

The vinyl aromatic hydrocarbons are aromatic hydrocarbon compounds having a vinyl group. Specific examples of vinyl aromatic hydrocarbons include styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene, and vinylanthracene, with styrene being preferred among these. The vinyl aromatic hydrocarbons may be used alone or in combination of two or more.

The above-mentioned conjugated diene compound is a diolefin compound having at least one pair of conjugated double bonds. Specific examples of conjugated diene compounds include 1,3-butadiene, 2-methyl-1,3-butadiene (or isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene, and among these, 1,3-butadiene and 2-methyl-1,3-butadiene are preferred. The conjugated diene compounds may be used alone or in combination of two or more.

In this specification, the hydrogenation ratio in a hydrogenated styrene-based block copolymer is indicated by the "hydrogenation ratio." The "hydrogenation ratio" of a styrene-based block copolymer refers to the ratio of ethylenically unsaturated double bonds that have been hydrogenated and converted to saturated hydrocarbon bonds, based on the total number of ethylenically unsaturated double bonds contained in the block based on the conjugated diene compound. The hydrogenation ratio can be measured by an infrared spectrophotometer, a nuclear magnetic resonance apparatus, or the like.

The hydrogenated styrene-based block copolymer may be a partially hydrogenated or fully hydrogenated product. Of these, a fully hydrogenated product is preferred. By using a fully hydrogenated styrene-based block copolymer, the heat stability of the thermoplastic resin composition is further improved. The hydrogenation rate of the styrene-based block copolymer is preferably about 100%.

The content of the styrene-based block copolymer in the thermoplastic resin composition of the present invention is preferably 45 to 85 mass%, more preferably 50 to 85 mass%, and even more preferably 55 to 80 mass%, based on 100 mass% of the thermoplastic resin composition. By having the content of the styrene-based block copolymer in the above range, the stress retention during extension at high temperatures of the elastic member formed using the thermoplastic resin composition of the present invention is further improved.

(Plasticizer (B))
The thermoplastic resin composition of the present invention contains a plasticizer (B). The plasticizer (B) is preferably liquid at 23° C. In this specification, the term "liquid" refers to a state exhibiting fluidity. The pour point of such a plasticizer (B) is preferably 23° C. or lower, more preferably 10° C. or lower.

In this specification, pour point is a value measured using a method conforming to JIS K2269.

The plasticizer (B) is not particularly limited, and examples thereof include paraffin-based process oil, naphthene-based process oil, aromatic process oil, liquid paraffin oil, etc. Among them, from the viewpoint of excellent heat stability, paraffin-based process oil, naphthene-based process oil, and liquid paraffin oil are preferred, and paraffin-based process oil and naphthene-based process oil are more preferred. Furthermore, from the viewpoint of further improving the stress maintenance during extension at high temperatures of the elastic member formed using the thermoplastic resin composition, paraffin process oil is more preferred.

Commercially available paraffin-based process oils can be used. Examples of commercially available products include PS-32 and PW-32 manufactured by Idemitsu Kosan Co., Ltd.

Commercially available naphthenic process oils can be used. Examples of commercially available products include KN-4010 manufactured by Petro China, CALSOL 550 manufactured by Calumet Specialty Products Partners, Diana Fresia N28 manufactured by Idemitsu Kosan, Diana Fresia U46 manufactured by Idemitsu Kosan, and Nyflex 222B manufactured by Nynas.

As liquid paraffin oil, commercially available products can be used. Examples of commercially available products include P-100 manufactured by MORESCO and Kaydol manufactured by Sonneborn.

The above plasticizer (B) may be used alone or in a mixture of two or more types.

The content of plasticizer (B) in the thermoplastic resin composition of the present invention is preferably 10 to 55 mass%, and more preferably 15 to 45 mass%, based on 100 mass% of the thermoplastic resin composition. By setting the upper limit of the content of plasticizer (B) within the above range, the stress maintenance during extension at high temperatures of the elastic member formed using the thermoplastic resin composition is further improved. By setting the lower limit of the content of plasticizer (B) within the above range, the thermoplastic resin composition becomes even more flexible, and the extensibility of the thermoplastic resin composition is further improved.

(Hydrocarbon Resin (C))
The thermoplastic resin composition of the present invention preferably further contains a hydrocarbon resin (C). The hydrocarbon resin (C) is a component that acts as a tackifier or an endblock resin. By containing the hydrocarbon resin (C), the stress during extension of the thermoplastic resin composition of the present invention and the stress maintenance during extension at high temperatures are further improved.

The above-mentioned hydrocarbon resin (C) is a hydrocarbon resin other than the thermoplastic elastomer (A) and the plasticizer (B). The hydrocarbon resin (C) preferably does not contain the styrene-based block copolymer described in the above-mentioned thermoplastic elastomer (A), and further preferably does not contain a polyolefin-based copolymer, a polyacrylic-based copolymer, a polyamide-based copolymer, a polyester-based copolymer, or a polyurethane-based copolymer. More specifically, examples of the hydrocarbon resin (C) include tackifier resins, aromatic hydrocarbon resins, etc.

Tackifying resins include natural rosin, modified rosin, glycerol ester of natural rosin, glycerol ester of modified rosin, pentaerythritol ester of natural rosin, pentaerythritol ester of modified rosin, copolymer of natural terpene, three-dimensional polymer of natural terpene, hydrogenated derivative of copolymer of natural terpene, terpene resin, hydrogenated derivative of phenol-based modified terpene resin, petroleum resin such as C5 petroleum resin, C9 petroleum resin, C5C9 petroleum resin, dicyclopentadiene petroleum resin, and partially hydrogenated petroleum resin and fully hydrogenated petroleum resin obtained by adding hydrogen to these petroleum resins. As tackifying resins, petroleum resin, partially hydrogenated petroleum resin, and fully hydrogenated petroleum resin are preferred, and partially hydrogenated petroleum resin and fully hydrogenated petroleum resin are more preferred, in terms of excellent odor and thermal stability of the thermoplastic resin composition. These tackifying resins may be used alone or in combination of two or more.

Aromatic hydrocarbon resins are resins that act as endblock resins for the resin components that form the thermoplastic resin composition. There are no particular limitations on the aromatic hydrocarbon resin, and for example, an oligomer of a vinyl aromatic hydrocarbon can be used. Examples of vinyl aromatic hydrocarbons that form the oligomer include aromatic hydrocarbon compounds having a vinyl group. Specific examples of vinyl aromatic hydrocarbons that form oligomers include styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene, and vinylanthracene, and among these, styrene and α-methylstyrene are preferred.

The content of the hydrocarbon resin (C) is preferably 0.1 to 35 mass%, more preferably 0.5 to 30 mass%, and even more preferably 5 to 30 mass%, based on 100% of the thermoplastic resin composition.

(Other Additives)
The thermoplastic resin composition of the present invention may contain other additives to the extent that the object of the present invention is not essentially hindered. Examples of the other additives include antioxidants, ultraviolet absorbers, photopolymerization initiators, liquid rubbers, and fine particle fillers.

Antioxidants include 2,6-di-t-butyl-4-methylphenol, n-octadecyl-3-(4'-hydroxy-3',5'-di-t-butylphenyl)propionate, 2,2'-methylenebis(4-methyl-6-t-butylphenol), 2,2'-methylenebis(4-ethyl-6-t-butylphenol), 2,4-bis(octylthiomethyl)-o-cresol, 2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate, 2,4-di-t-amyl-6-[1-(3,5-di-t-amyl-2-hydroxyphenyl) Examples of the antioxidant include hindered phenol-based antioxidants such as 2-[1-(2-hydroxy-3,5-di-tert-pentylphenyl)]acrylate, tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane; sulfur-based antioxidants such as dilauryl thiodipropionate, lauryl stearyl thiodipropionate, and pentaerythritol tetrakis(3-lauryl thiopropionate); and phosphorus-based antioxidants such as tris(nonylphenyl)phosphite and tris(2,4-di-t-butylphenyl)phosphite. The antioxidants may be used alone or in combination of two or more.

The content of the antioxidant in the thermoplastic resin composition of the present invention is preferably 0.01 to 2 mass%, more preferably 0.05 to 1.5 mass%, and even more preferably 0.1 to 1 mass%, based on 100 mass% of the thermoplastic resin composition. If the content of the antioxidant is 0.01 mass% or more, the thermal stability of the thermoplastic resin composition is further improved. If the content of the antioxidant is 2 mass% or less, the odor of the thermoplastic resin composition is further reduced.

Examples of ultraviolet absorbers include benzotriazole-based ultraviolet absorbers such as 2-(2'-hydroxy-5'-methylphenyl)benzotriazole, 2-(2'-hydroxy-3',5'-t-butylphenyl)benzotriazole, and 2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotriazole; benzophenone-based ultraviolet absorbers such as 2-hydroxy-4-methoxybenzophenone; salicylic acid ester-based ultraviolet absorbers; cyanoacrylate-based ultraviolet absorbers; and hindered amine-based light stabilizers. The ultraviolet absorbers may be used alone or in combination of two or more.

The content of the ultraviolet absorber in the thermoplastic resin composition of the present invention is preferably 0.01 to 2 mass%, more preferably 0.05 to 1.5 mass%, and even more preferably 0.1 to 1 mass%, based on 100 mass% of the thermoplastic resin composition. If the content of the ultraviolet absorber is 0.01 mass% or more, the weather resistance of the thermoplastic resin composition is improved. If the content of the ultraviolet absorber is 2 mass% or less, the odor of the thermoplastic resin composition is further reduced.

Examples of the photopolymerization initiator include ultraviolet polymerization initiators. When the thermoplastic resin composition of the present invention contains a styrene-based block copolymer having a reactive polystyrene-based hard block in the molecule as the styrene-based block copolymer (A), the thermoplastic resin composition can be further irradiated with light such as ultraviolet light to react the reactive polystyrene-based hard block and crosslink the molecules, thereby adjusting the properties such as dynamic viscoelasticity of the thermoplastic resin composition. When the thermoplastic resin composition is irradiated with ultraviolet light, the irradiation intensity of the ultraviolet light is preferably about 50 to 1,000 mW/cm ² , and the integrated light amount is preferably about 1,000 to 15,000 mJ/cm ² , and may be appropriately adjusted to obtain the desired properties. The photopolymerization initiator may be used alone or in combination of two or more types.

Liquid rubbers include liquid polybutene, liquid polybutadiene, liquid polyisoprene, and hydrogenated resins thereof. Liquid rubbers may be used alone or in combination of two or more types.

The content of liquid rubber in the thermoplastic resin composition of the present invention is preferably 1 to 20% by mass, more preferably 2 to 15% by mass, and even more preferably 3 to 10% by mass, based on 100% by mass of the thermoplastic resin composition. When the content of liquid rubber is 1% by mass or more, the thermoplastic resin composition becomes flexible and the extensibility is further improved. When the content of liquid rubber is 20% by mass or less, the thermoplastic resin composition does not become too soft, and the elastic recovery of the elastic member is further improved.

The particulate filler is not particularly limited, and examples thereof include calcium carbonate, kaolin, talc, titanium oxide, mica, and styrene beads. The particulate filler may be used alone or in combination of two or more types.

2. Method for Producing Thermoplastic Resin Composition The thermoplastic resin composition of the present invention can be produced by a known method, for example, by feeding the thermoplastic elastomer (A), the plasticizer (B), and various additives such as the hydrocarbon resin (C) as required, into a kneader heated to a temperature of 160 to 260°C, preferably 180 to 230°C, and melt-kneading them while heating.

The above-mentioned kneading machine is not particularly limited, and examples thereof include a single-screw extruder, a twin-screw extruder, a Banbury mixer, a Brabender, a kneader, etc.

The above melt kneading may be performed, for example, by (1) dry-blending all of the components constituting the thermoplastic resin composition in advance using a mixer such as a Dalton mixer, a tumbler, or a V-blender, and then kneading them all at once; or (2) kneading the other components except for the plasticizer (B) in advance, and then adding a predetermined amount of the plasticizer (B) to the kneader using a side feeder or the like. Either method may be used.

The thermoplastic resin composition of the present invention is generally solid in the temperature range of 0 to 60°C, particularly at room temperature of 23°C, and exhibits elasticity, so elastic members formed using the thermoplastic resin composition of the present invention can be used for a variety of purposes.

The uses of the thermoplastic resin composition of the present invention are not particularly limited, and examples thereof include absorbent articles including sanitary materials, hospital gowns, masks, etc. Specific examples of the sanitary materials include disposable diapers, sanitary napkins, etc.

3. Elastic member The elastic member of the present invention is an elastic member made of the above-mentioned thermoplastic resin composition. By configuring the elastic member of the present invention to be made of the above-mentioned thermoplastic resin composition of the present invention, the elastic member formed using the thermoplastic resin composition of the present invention becomes an elastic member that is excellent in stretchability and stretch recovery, and excellent in stress maintenance when stretched at high temperatures.

The stress of the elastic member at double extension is preferably 0.4 N/mm2 ^or more, more preferably 0.8 N/mm2 or ^more . When the lower limit of the stress of the elastic member at double extension is within the above range, the sanitary material is further prevented from slipping off when worn. There is no particular limit to the upper limit of the stress of the elastic member at double extension, and it may be, for example, 3.0 N/mm2 ^or less, or 2.0 N/mm2 or ^less .

The stress of the elastic member when extended twice may be less than 0.4 N/ ^mm2 . When the stress of the elastic member when extended twice is less than 0.4 N/ ^mm2 , it can be suitably used for applications other than sanitary materials and the like described below. In this case, the stress of the elastic member when extended twice is preferably less than 0.4 N/ ^mm2 , more preferably 0.3 N/mm2 or ^less , and even more preferably 0.2 N/mm2 or ^less . In this case, the lower limit of the stress of the elastic member when extended twice is not particularly limited, and is ^about 1.0× ^10-3 N/mm2.

The stress of the elastic member when stretched twice is measured using the method described in the examples below.

The permanent set (stretch recovery) of the elastic member is preferably 55% or more, more preferably 70% or more, and even more preferably 80% or more. If the lower limit of the permanent set of the elastic member is within the above range, the elastic recovery after stretching of the elastic member is further improved. In addition, the upper limit of the permanent set of the elastic member is not particularly limited, and may be 99%, 98%, etc.

The permanent strain of the elastic member is measured using the method described in the Examples below.

The thickness of the elastic member is not particularly limited, and is preferably 1 to 100 μm, more preferably 10 to 80 μm, and even more preferably 30 to 70 μm. If the lower limit of the thickness of the elastic member is within the above range, the stress and elastic recovery rate of the elastic member will be further improved. If the upper limit of the thickness of the elastic member is within the above range, the texture of the elastic member will be further improved.

The elastic member of the present invention can be manufactured from the thermoplastic resin composition of the present invention described above. The elastic member of the present invention can be made into a suitable form depending on the application, for example, a film, a strand, a nonwoven fabric, a strip, a fiber, etc.

There are no particular limitations on the method for producing an elastic member from a thermoplastic polymer composition, and general molding and processing methods suitable for various shapes can be used.

When the elastic member of the present invention is, for example, a film, strand or strip, it can be molded using a single screw extruder or a twin screw extruder.

The temperature of the thermoplastic resin composition when producing the elastic member of the present invention is not particularly limited, but is generally preferably 160 to 300°C, more preferably 170 to 290°C.

The uses of the elastic member of the present invention are not particularly limited, and can be used, for example, in absorbent articles including sanitary materials, hospital gowns, masks, etc. Specific examples of the sanitary materials include disposable diapers and sanitary napkins.

The following describes examples of the present invention. The present invention is not limited to the following examples.

The raw materials used in the examples and comparative examples are as follows:

Thermoplastic resin (A)
[Hydrogenated styrene block copolymer]
・A1537
Styrene-ethylene-butylene/styrene-styrene copolymer (SEB/S-S) A1537 (styrene content 60% by mass) manufactured by Kraton Polymers
・A1535
Styrene-ethylene-butylene/styrene-styrene copolymer (SEB/S-S) A1535 (styrene content 57% by mass) manufactured by Kraton Polymers
A1536
Styrene-ethylene-butylene/styrene-styrene copolymer (SEB/S-S) A1536 (styrene content 41% by mass) manufactured by Kraton Polymers
・G1653
Styrene-ethylene-butylene-styrene (SEBS) G1653 (styrene content 30% by mass) manufactured by Kraton Polymers
MD6951
Styrene-ethylene-butylene/styrene-styrene copolymer (SEB/S-S) Kraton Polymers MD6951 (styrene content 34% by mass)
・H1043
Styrene-ethylene-butylene-styrene (SEBS) copolymer: Tuftec H1043 (styrene content 67% by mass), manufactured by Asahi Kasei Corporation

Plasticizer (B)
・PS-32
Paraffin oil Idemitsu Kosan PS-32

Hydrocarbon resin (C)
・C-100L
C5 Hydrocarbon Resin: Synthomer's Eastotac C-100L
・SA120
α-Methylstyrene resin Kraton SYLVARES SA120

Additives [Antioxidants]
-Phenol-based antioxidant: Evernox 10, manufactured by Japan Specialty Chemicals

Examples and Comparative Examples
The above-mentioned raw materials were charged into a Dalton mixer in the amounts shown in Table 1 and dry-blended. Then, the mixture was melt-kneaded at 190° C. in a twin-screw extruder to prepare a strand-shaped thermoplastic resin composition.

(Preparation of test specimen (elastic member))
5 g of the thermoplastic resin composition was dissolved in 15 g of methylcyclohexane to prepare a methylcyclohexane solution containing 25% by mass of the thermoplastic resin composition. Next, the methylcyclohexane solution was applied onto a release-treated PET film using an applicator with a width of 70 mm and a gap of 400 μm, and the film was left to stand in an explosion-proof oven at 80 ° C for 2 minutes to thoroughly dry the methylcyclohexane. Next, the film thickness of the test piece (film) was confirmed after being removed from the oven and thoroughly cooled to room temperature. If the predetermined film thickness was not achieved, the film thickness was adjusted to 50 μm by appropriately adjusting the solution concentration and / or the applicator gap. Next, a laminate was prepared by laminating a PET film that had been subjected to a release treatment, and pressing the film at room temperature. The obtained laminate was stored for 24 hours at 23 ° C and a relative humidity of 50% to prepare a test piece.

The properties and characteristics of the prepared thermoplastic resin composition and test pieces were evaluated using the following methods.

Properties (Melt Index (MI))
The melt index was measured by Method A in accordance with JIS K7210. The measurement was performed under conditions of (1) 190°C and 2.16 kg, or (2) 230°C and 2.16 kg, and either one of the conditions that allowed measurement was adopted.

(Storage modulus G' and tan δ peak value at 25°C)
1 g of the thermoplastic resin composition was dissolved in 20 to 30 g of methylcyclohexane to prepare a methylcyclohexane solution of the thermoplastic resin composition having a fluidity sufficient to be handled with a dropper or the like. The methylcyclohexane solution was then poured into a shallow polyethylene cup and dried in a vacuum drying oven set at 50°C to obtain a sheet-like solid of the thermoplastic resin composition having a thickness of about 1 to 2 mm. The obtained thermoplastic resin composition was removed from the polyethylene cup and allowed to stand at 23°C for 24 hours to prepare a sample for dynamic viscoelasticity measurement. The sample was heated from -60 to 190°C at 5°C/min in a rotational shear mode at a frequency of 1 Hz, and dynamic viscoelasticity measurement (heating process) was performed under the condition of a strain of 0.05% using a dynamic viscoelasticity measuring device. The measured value of the storage modulus G' at 25°C was taken as the storage modulus G' at 25°C. Further, the loss tangent tan δ (loss modulus G"/storage modulus G') was calculated from the measured storage modulus G' and loss modulus G". The value of tan δ at a temperature where tan δ was maximum between the low temperature range of -50 to 0°C and the high temperature range of 60 to 120°C was recorded and taken as the maximum value of tan δ. Note that, as an example of a dynamic viscoelasticity measuring device, a rotational rheometer (product name "DHR10") manufactured by TA Instruments Co., Ltd. can be mentioned.

Evaluation (Elongation at break (stretchability))
The test piece (width (MD) 50 mm, length (CD) 70 mm, thickness 50 μm) was fixed at both ends in the coating direction with a jig so that the direction (CD direction) perpendicular to the longitudinal direction (coating direction (MD) of the thermoplastic resin composition) was located at the top and bottom of a tensile tester with a jig distance of 50 mm, and pulled in the vertical direction at a tensile speed of 500 mm/min until the test piece broke. The travel distance of the jig until the test piece broke was measured, and the value of the breaking elongation was calculated based on the following formula, and the extensibility was evaluated according to the following evaluation criteria. If the evaluation was △ or higher, it was evaluated as having no problem in practical use.
[Elongation at break (%)] = (distance traveled by the jig until the test piece breaks (mm) / initial jig distance (mm)) x 100
◯: The breaking elongation is 600% or more. △: The breaking elongation is 500% or more and less than 600%. ×: The breaking elongation is less than 500%.

(Permanent strain (stretch recovery))
The test piece (width (MD direction)) was placed on a tensile tester with a jig distance of 50 mm, so that the direction perpendicular to the longitudinal direction (coating direction of the thermoplastic resin composition (MD direction)) and the direction perpendicular to the CD direction were positioned at the top and bottom. The test piece (50 mm in length (CD direction), 70 mm in length, and 50 μm in thickness) was fixed with a jig and pulled in the vertical direction at a tensile speed of 500 mm/min until the strain displacement of the test piece reached 200%. The test piece was stretched to a strain displacement of 200% and then returned to the initial position in 1 minute. This process constitutes one cycle, and two cycles were repeated for the same test piece. The integral value during the first cycle and the second cycle were The permanent set was calculated from the integral value of the tension according to the following formula, and the stretch recovery was evaluated according to the following evaluation criteria. do.
[Permanent set (%)] =
[(Integral value of the second cycle (J))/(Integral value of the first cycle (J))]×100
◎: Permanent distortion is 90% or more. ◯: Permanent distortion is 80% or more and less than 90%. △: Permanent distortion is 70% or more and less than 80%. ×: Permanent distortion is less than 70%.

(Stress retention rate (stress retention during elongation at high temperatures))
In an environment of 40 ° C., a test piece (width (MD direction) 25 mm, length (CD direction) 50 mm, thickness 50 μm) was fixed with a jig to a tensile tester with a jig distance set to 25 mm so that the direction (CD direction) perpendicular to the longitudinal direction (coating direction (MD direction) of the thermoplastic resin composition) was located up and down, and the test piece was pulled in the vertical direction at a tensile speed of 100 mm / min to a point where the displacement of the test piece was 100%. This state was maintained for 1 hour, and the change in test force was measured. The maximum value of the test force was taken as the initial test force, and the stress retention rate was calculated based on the following formula from the measured value of the test force after 1 hour, and the stress retention during elongation at high temperatures was evaluated according to the following evaluation criteria. In addition, if the evaluation is △ or higher, it is evaluated that there is no problem in practical use.
[Stress retention rate (%)] = (Test force after 1 hour (N) / Initial test force (N)) x 100
⊚: Stress retention rate is 80% or more. ◯: Stress retention rate is 60% or more and less than 80%. △: Stress retention rate is 50% or more and less than 60%. ×: Stress retention rate is less than 50%.

(Stress at 2x elongation)
A test piece (width (MD direction) 50 mm, length (CD direction) 70 mm, thickness 50 μm) was fixed with a jig to a tensile tester with a jig distance set to 50 mm so that the direction (CD direction) perpendicular to the longitudinal direction (coating direction of thermoplastic resin composition (MD direction)) was located up and down, and the test piece was pulled in the vertical direction at a tensile speed of 500 mm / min to a point where the strain displacement of the test piece was 200%. Then, it was returned to the initial position at a speed of 500 mm / min. The process of pulling to a point where the strain displacement was 200% and returning to the initial position was defined as one cycle, and two cycles were repeated for the same test piece. The stress value at the point where the strain displacement was 100% during the first cycle of tension was recorded and was taken as the stress at 2 times elongation (N / mm ² ). In addition, if the evaluation is △ or higher, it is evaluated that there is no problem in practical use.
◯: The stress at 2-fold extension is 0.8 N/mm2 or ^more . △: The stress at 2-fold extension is 0.4 N/mm2 ^{or more} and less than 0.8 N/mm2. ×: The stress at ² -fold extension is less than 0.4 N/ ^mm2.

The results are shown in Table 1.

Claims (7)

A thermoplastic resin composition comprising a thermoplastic elastomer (A) and a plasticizer (B), wherein the thermoplastic elastomer (A) comprises a styrene-based block copolymer,
The melt index measured by Method A in accordance with JIS K7210 under conditions of 190°C and 2.16 kg or 230°C and 2.16 kg is 0.1 to 100 g/10 min;
The storage modulus G' at 25°C measured under the following measurement conditions is 2.5 x ¹⁰⁵ to 1.0 x ¹⁰⁷ Pa;
The loss tangent tan δ (loss modulus/storage modulus) obtained by measuring the storage modulus G' has at least one peak each in a low temperature range of -50 to 0°C and a high temperature range of 60 to 120°C,
D1, which is a tan δ peak value in the low temperature region, is greater than D2, which is a tan δ peak value in the high temperature region;
A thermoplastic resin composition comprising:
(Measurement conditions for storage modulus G')
Starting temperature -60°C, ending temperature 190°C, heating rate 5°C/min, measuring frequency 1Hz, strain 0.05% The thermoplastic resin composition according to claim 1, wherein the styrene-based block copolymer is a hydrogenated styrene-based block copolymer. The thermoplastic resin composition according to claim 1, wherein the amount of styrene derived from the styrene-based block copolymer contained in the thermoplastic resin composition is 30 to 50 mass % relative to 100 mass % of the thermoplastic resin composition. The thermoplastic resin composition according to claim 1, wherein the content of the thermoplastic elastomer (A) is 50 to 85 mass % relative to 100 mass % of the thermoplastic resin composition. The thermoplastic resin composition according to claim 1, wherein the ratio of D1 to D2 (D1/D2) is greater than 1 and less than or equal to 15. The thermoplastic resin composition according to claim 1, further comprising a hydrocarbon resin (C), the content of which is 0.5 to 30 mass % relative to the thermoplastic resin composition being 100%. An elastic member made of a thermoplastic resin composition according to any one of claims 1 to 6.