JP7610940B2 - Hot Melt Composition - Google Patents

Description

The present invention relates to a hot melt 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.

One type of 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, in order to prevent the absorbent article from slipping off and to suppress a feeling of pressure and rash when worn, a stretchable film containing a thermoplastic elastomer composition is used as a stretchable member of a laminate used in the absorbent article. As the thermoplastic elastomer composition used in the stretchable film, a hot melt stretchable adhesive composition (see Patent Document 1) and a hot melt thermoplastic elastomer composition (see Patent Document 2) have been proposed.

Patent No. 2919385 Special Publication No. 2006-502291

However, in Patent Documents 1 and 2, the improvement of extensibility is not fully considered, 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.

In addition, Patent Documents 1 and 2 do not fully consider the prevention of a decrease in stretch recovery. When a sanitary material such as a disposable diaper is worn, the elastic member used in the sanitary material is stretched. Therefore, it is required that the elastic member has a suppressed decrease in stretch recovery even when it is held in a stretched state. Patent Documents 1 and 2 describe blending a considerable amount of tackifier into the hot melt composition ([0007] of Patent Document 1, Table 2 (hydrogenated petroleum resin), and claim 1 (tackifier) of Patent Document 2), which causes the elastic member to become hard and cannot exhibit sufficient stretch recovery.

Furthermore, 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, so that the elastic members are required to have reduced stress relaxation and excellent stress retention when stretched at high temperatures, even when stretched and held in a heated state. Patent documents 1 and 2 describe the incorporation of a significant amount of tackifier into the hot melt composition as described above, and the stress retention when stretched at high temperatures is insufficient.

Even if the elastic member has the above-mentioned characteristics, the hot melt composition forming the elastic member is required to have excellent applicability. If the hot melt composition forming the elastic member has a high melt viscosity or a high softening point, it is necessary to mold the elastic hot melt composition using an extrusion device, which causes a problem of reduced productivity. Therefore, the elastic hot melt composition is required to have coatability (shape processability) that allows it to be applied using a general-purpose hot melt application device.

In view of the above circumstances, the present invention aims to provide a hot melt composition that can form an elastic member that has excellent extensibility, elastic recovery, and stress maintenance when stretched at high temperatures, and that has excellent coating suitability.

As a result of intensive research by the inventors to achieve the above object, it was discovered that the above object can be achieved by a hot melt composition that contains a styrene block copolymer (A), a polyether resin (B), and a plasticizer (C), has a ring and ball softening point temperature of 100 to 150°C, and when dynamic viscoelasticity is measured under specific conditions, the measured storage modulus G' and loss modulus G'' are equal, and has a temperature in the range of 90 to 120°C in a temperature range above room temperature, and thus the present invention has been completed.

That is, the present invention relates to the following hot melt composition.
1. A composition comprising a styrene-based block copolymer (A), a polyether-based resin (B), and a plasticizer (C),
The ring and ball softening point is 100 to 150°C.
Dynamic viscoelasticity measurement is performed under conditions of a frequency of 1 Hz and a temperature rise rate of 5°C/min, and the temperature in the temperature range above room temperature at which the measured storage modulus G' and loss modulus G'' become equal is within the range of 90 to 120°C.
A hot melt composition comprising:
2. The hot melt composition according to item 1, wherein the content of the styrene-based block copolymer (A) is 40 to 65% by mass, based on 100% by mass of the hot melt composition.
3. The hot melt composition according to item 1 or 2, wherein the content of the polyether resin (B) is 1 to 20 parts by mass per 100 parts by mass of the styrene block copolymer (A).
4. The hot melt composition according to any one of Items 1 to 3, wherein the polyether resin (B) is a polyphenylene ether resin.
5. The hot melt composition according to any one of items 1 to 4, which is for an absorbent article.

The hot melt composition of the present invention can form an elastic member that has excellent extensibility, elastic recovery, and stress retention when stretched at high temperatures, and also has excellent suitability for coating.

FIG. 2 is a schematic diagram showing an example of the measurement results of viscoelasticity of a hot melt composition.

1. Hot melt composition The hot melt composition of the present invention contains a styrene block copolymer (A), a polyether resin (B), and a plasticizer (C), has a ring and ball softening point of 100 to 150°C, and has a temperature in a temperature range above room temperature at which the measured storage modulus G' and loss modulus G'' become equal when dynamic viscoelasticity is measured under conditions of a frequency of 1 Hz and a heating rate of 5°C/min (hereinafter also referred to as the "crossover temperature") within the range of 90 to 120°C. The hot melt composition of the present invention can form an elastic member by containing the above (A) to (C), and in particular contains a polyether resin (B) and has a crossover temperature within the range of 90 to 120°C, so that the formed elastic member has excellent stress retention during elongation at high temperatures. Furthermore, by containing the above (A) to (C), the hot melt composition of the present invention can form an elastic member having excellent extensibility, stretch recovery, and stress retention when stretched at high temperatures, as described above, and can set the Ring and Ball softening point temperature to 100 to 150° C., and by exhibiting a Ring and Ball softening point temperature in this range, the hot melt composition of the present invention has excellent coatability. In other words, by having all of the above configurations, the hot melt composition of the present invention can form an elastic member having excellent extensibility, stretch recovery, and stress retention when stretched at high temperatures, and has excellent coatability, and is able to combine all of these properties.

In this specification, "high temperature" means a temperature about the same as human body temperature, i.e., 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. In addition, "warming" means bringing the temperature to within the above range.

In this specification, "room temperature" means 23°C.

The ring and ball softening point temperature of the hot melt composition of the present invention is 100 to 150°C. If the ring and ball softening point temperature is outside the range of 100 to 150°C, the coating suitability decreases. The ring and ball softening point temperature is preferably 110°C or higher, and more preferably 120°C or higher. The ring and ball softening point temperature is preferably 145°C or lower, and more preferably 140°C or lower. In this specification, the ring and ball softening point temperature is a value measured by a measurement method in accordance with JIS K6863.

The hot melt composition of the present invention is subjected to dynamic viscoelasticity measurement under conditions of a frequency of 1 Hz and a heating rate of 5°C/min, and the temperature (crossover temperature) in the temperature range above room temperature at which the measured storage modulus G' and loss modulus G'' become equal is within the range of 90 to 120°C. If the crossover temperature is less than 90°C, the stress retention during elongation at high temperatures decreases. If the crossover temperature exceeds 120°C, the coating suitability decreases. The crossover temperature is preferably 95°C or higher. Also, the crossover temperature is preferably 115°C or lower.

The crossover temperature is explained using a diagram. FIG. 1 is a schematic diagram showing an example of the measurement results of the viscoelasticity of the hot melt composition of the present invention. In FIG. 1, in the temperature range of 23°C or higher, which is room temperature, the value of G' is higher than G'' and is dominant up to around 100°C, and the graphs of G' and G'' intersect at about 100°C, where the storage modulus G' and the loss modulus G'' are equal. At this time, the loss tangent (tan δ) is calculated as tan δ = G''/G', so tan δ = 1. This temperature is the crossover temperature. That is, in FIG. 1, the temperature in the temperature range above room temperature where the storage modulus G' and the loss modulus G'' become equal is about 100°C, which is within the range of 90 to 120°C. In FIG. 1, the graphs of G' and G'' also intersect in the temperature range of -40 to -10°C, but the intersection in this temperature range is not taken into consideration, and the highest temperature at which they intersect in the temperature range of 23°C or higher, which is room temperature, is the crossover temperature. The hot melt composition of the present invention has a crossover temperature in the range of 90 to 120°C, and therefore has a good balance between the elastic term G' and the viscous term G'', and is able to combine elasticity and viscosity, making it possible to form an elastic member that has excellent extensibility, stretch recovery, and stress retention when stretched at high temperatures.

In the present invention, the crossover temperature of the hot melt composition can be measured by the following measurement method.
(Method of measuring crossover temperature (G'=G''))
The hot melt composition is heated and melted at 180°C, and dropped onto the release layer side of the release-treated PET film. Then, another release-treated PET film is laminated on the hot melt composition so that the release layer side is in contact with the hot melt composition. Then, the hot melt composition is compressed with a heat press heated to 120°C, and the thickness of the hot melt composition is adjusted to about 2 mm. After the hot melt composition is sandwiched between the PET films and left at 23°C for 24 hours, the release film is removed to prepare a sample for dynamic viscoelasticity measurement.

Using this sample, dynamic viscoelasticity measurements are performed in the rotational shear mode of a dynamic viscoelasticity measuring device under measurement conditions of temperatures from -80°C to 140°C, a frequency of 1 Hz, and a heating rate of 5°C/min, to measure the storage modulus G' and loss modulus G''. In the obtained curve of storage modulus G' and loss modulus G'', the highest temperature at which the storage modulus G' and loss modulus G'' intersect above room temperature is determined as the crossover temperature.

In addition, in the above measurement, a rotational rheometer (product name "AR-G2") manufactured by TA Instruments, Inc. can be used as a dynamic viscoelasticity measuring device.

(Styrene-based block copolymer (A))
The styrene-based block copolymer (A) is not particularly limited as long as the hot melt composition can have a ring and ball softening point temperature and crossover temperature in the above-mentioned ranges, and examples thereof include styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-butylene-butadiene-styrene copolymer (SBBS), styrene-ethylene-butylene/styrene-styrene copolymer (SEB/S-S), styrene-ethylene-propylene-styrene copolymer (SEPS), styrene-ethylene-ethylene-propylene-styrene copolymer (SEEPS), styrene-ethylene-butylene-olefin crystalline copolymer (SEBC), and the like. Among these, in terms of being even more excellent in extensibility, stretch recovery property, and stress maintenance property during extension at high temperatures, styrene-ethylene-butylene-styrene copolymer (SEBS), styrene-butylene-butadiene-styrene copolymer (SBBS), styrene-ethylene-butylene/styrene-styrene copolymer (SEB/S-S), and styrene-ethylene-propylene-styrene copolymer (SEPS) are preferred, and styrene-ethylene-butylene-styrene copolymer (SEBS) and styrene-ethylene-butylene/styrene-styrene copolymer (SEB/S-S) are more preferred.

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

The styrene content of the styrene-ethylene-butylene-styrene copolymer is preferably 15 to 45% by mass, and more preferably 20 to 40% by mass, with the styrene-ethylene-butylene-styrene copolymer being 100% by mass. If the lower limit of the styrene content is within the above range, the elastic recovery of the elastic member formed from the hot melt composition is further improved. If the upper limit of the styrene content is within the above range, the hot melt composition becomes softer, and the elastic member can exhibit even better extensibility.

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.

As the styrene-ethylene-butylene-styrene copolymer, commercially available products can be used. Commercially available products include G1650 manufactured by Kraton Polymers, MD1648 manufactured by Kraton Polymers, and Tuftec H1041 manufactured by Asahi Kasei Corporation.

The styrene-ethylene-butylene-styrene copolymer may be used alone or in combination of two or more. For example, a styrene-ethylene-butylene-styrene copolymer having a high styrene content and a styrene-ethylene-butylene-styrene copolymer having a low styrene content may be used in combination. When two or more types are used in combination, the styrene content of the entire styrene-ethylene-butylene-styrene copolymer may be calculated as an average value based on weight.

The 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, and in which styrene is also dispersed in the midblock phase. By using a copolymer in which styrene is dispersed in the midblock phase, even if the total 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 hot melt composition containing a styrene-ethylene-butylene/styrene-styrene copolymer can achieve both good extensibility and good stretch recovery. Furthermore, by using a styrene-ethylene-butylene/styrene-styrene copolymer in which styrene is dispersed in the midblock phase for a hot melt composition, an increase in melt viscosity at low temperatures is suppressed, and the coatability of the hot melt composition can be further improved.

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.

The styrene content of the styrene-ethylene-butylene/styrene-styrene copolymer is preferably 20 to 60% by mass, and more preferably 25 to 55% by mass, with the styrene-ethylene-butylene/styrene-styrene copolymer being 100% by mass. If the lower limit of the styrene content is within the above range, the elastic recovery after stretching of the elastic member formed using the hot melt composition is further improved. If the upper limit of the styrene content is within the above range, the hot melt composition becomes softer, and the elastic member can exhibit even better stretchability.

As the styrene-ethylene-butylene/styrene-styrene copolymer, a commercially available product can be used. Examples of commercially available products include MD6951 manufactured by Kraton Polymers, and A1536 manufactured by Kraton Polymers.

The styrene-ethylene-butylene/styrene-styrene copolymer may be used alone or in combination of two or more. For example, a styrene-ethylene-butylene/styrene-styrene copolymer having a high styrene content and a styrene-ethylene-butylene/styrene-styrene copolymer having a low styrene content may be used in combination. When two or more types are used in combination, the styrene content of the entire styrene-ethylene-butylene/styrene-styrene copolymer may be calculated as an average value based on weight.

The content of the styrene-based block copolymer (A) in the hot melt composition of the present invention is preferably 40 to 65% by mass, more preferably 45 to 65% by mass, and more preferably 45 to 60% by mass, based on 100% by mass of the hot melt composition. By having the content of the styrene-based block copolymer (A) in the above range, the elastic member formed using the hot melt composition of the present invention has even better stress retention during elongation at high temperatures, and the coatability of the hot melt composition is further improved.

The styrene content of the styrene-based block copolymer (A) in the hot melt composition of the present invention is preferably 10 to 35% by mass, and more preferably 12 to 25% by mass, with the styrene-based block copolymer (A) being 100% by mass. When the lower limit of the styrene content is within the above range, the stress retention during stretching at high temperatures of the elastic member formed using the hot melt composition is further improved. When the upper limit of the styrene content is within the above range, the hot melt composition becomes even softer, and the elastic member can exhibit even better stretchability.

The weight average molecular weight (Mw) of the styrene-based block copolymer (A) in the hot melt composition of the present invention is preferably 30,000 to 200,000, more preferably 40,000 to 150,000, and even more preferably 45,000 to 125,000. When the lower limit of the weight average molecular weight is in the above range, the stress retention during stretching at high temperatures of the elastic member formed using the hot melt composition is further improved. When the upper limit of the weight average molecular weight is in the above range, the hot melt composition becomes even softer, and the elastic member can exhibit even better stretchability.

The weight average molecular weight (Mw) of the styrene-based block copolymer (A) is a measurement value obtained by converting it into standard polystyrene using a gel permeation chromatography measuring device.

The weight average molecular weight (Mw) in this specification can be measured, for example, using the following measuring device and measuring conditions.
Measuring device: Waters Corporation, product name "ACQUITY APC"
Measurement conditions: Column: ACQUITY APCXT45 1.7 μm x 1, ACQUITY APCXT125 2.5 μm x 1, ACQUITY APCXT450 2.5 μm x 1 Mobile phase: Tetrahydrofuran 0.8 mL/min Sample concentration: 0.2% by mass
Detector: Differential refractive index (RI) detector Standard material: Polystyrene (Waters, molecular weight: 266 to 1,800,000) Column temperature: 40°C
RI detector temperature: 40°C

(Polyether Resin (B))
The hot melt composition of the present invention contains a polyether-based resin (B). By containing the polyether-based resin (B), the elastic member formed from the hot melt composition of the present invention has excellent stress retention when stretched at high temperatures.

The polyether-based resin (B) is not particularly limited as long as it is a polyether-based resin, and examples thereof include polyphenylene ether resin. By using polyphenylene ether resin as the polyether-based resin (B), the stress retention of the elastic member during extension at high temperatures is further improved.

As the polyphenylene ether resin, commercially available products can be used. Examples of commercially available products include Noryl SA90, Noryl SA120, and Noryl SA9000 manufactured by Savic Corporation. Among these, Noryl SA90 is preferred because it further improves the stress retention of the elastic member when stretched at high temperatures.

The polyether resin (B) may be used alone or in combination of two or more.

The content of the polyether-based resin (B) in the hot melt composition of the present invention is preferably 1 to 20 parts by mass, more preferably 2 to 15 parts by mass, and even more preferably 3 to 13 parts by mass, based on 100 parts by mass of the styrene-based block copolymer (A). By setting the upper limit of the content of the polyether-based resin (B) within the above range, the stretchability and stretch recovery of the elastic member formed using the hot melt composition are further improved. By setting the lower limit of the content of the polyether-based resin (B) within the above range, the stress maintenance during stretching at high temperatures of the elastic member formed using the hot melt composition is further improved.

(Plasticizer (C))
The hot melt composition of the present invention contains a plasticizer (C). The plasticizer (C) 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 (C) 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 (C) is not particularly limited, and examples thereof include paraffinic process oil, naphthenic process oil, aromatic process oil, liquid paraffin oil, and hydrocarbon synthetic oil. Among them, paraffinic process oil, naphthenic process oil, liquid paraffin oil, and hydrocarbon synthetic oil are preferred from the viewpoint of excellent heat stability, and naphthenic process oil is more preferred from the viewpoint of further improving the stress maintenance during stretching at high temperatures of the elastic member formed using the hot melt composition.

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

Commercially available naphthenic process oils can be used. Examples of commercially available products include KN4010 manufactured by PetroChina Co., Ltd., Diana Fresia N28 manufactured by Idemitsu Kosan Co., Ltd., Diana Fresia U46 manufactured by Idemitsu Kosan Co., Ltd., and Nyflex 222B manufactured by Nynas Corporation.

Commercially available liquid paraffin oils can be used. Examples of commercial products include P-100 manufactured by MORESCO and Kaydol manufactured by Sonneborn.

Commercially available synthetic hydrocarbon oils can be used. Examples of commercially available products include LUCANT HC-10 and LUCANT HC-20 manufactured by Mitsui Chemicals, Inc.

The plasticizer (C) may be used alone or in combination of two or more.

The content of the plasticizer (C) in the hot melt composition of the present invention is preferably 70 to 150 parts by mass, more preferably 80 to 140 parts by mass, and even more preferably 85 to 100 parts by mass, based on 100 parts by mass of the styrene-based block copolymer (A). By setting the upper limit of the content of the plasticizer (C) within the above range, the stress retention during stretching at high temperatures of the elastic member formed using the hot melt composition is further improved. By setting the lower limit of the content of the plasticizer (C) within the above range, the melt viscosity of the hot melt composition is further reduced, and the coatability of the hot melt composition is further improved.

(Other Additives)
The hot melt composition of the present invention may contain other additives to the extent that the purpose of the present invention is not essentially hindered. Examples of the other additives include antioxidants, ultraviolet absorbers, tackifier resins, 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)ethyl ester, 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, pentaerythritol tetrakis(3-lauryl thiopropionate); phosphorus-based antioxidants such as tris(nonylphenyl) phosphite, tris(2,4-di-t-butylphenyl) phosphite, etc. The antioxidants may be used alone or in combination of two or more.

The content of the antioxidant in the hot melt 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 hot melt composition. When the content of the antioxidant is 0.01 mass% or more, the thermal stability of the hot melt composition is further improved. When the content of the antioxidant is 2 mass% or less, the odor of the hot melt composition is 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 hot melt 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 hot melt composition. If the content of the ultraviolet absorber is 0.01 mass% or more, the weather resistance of the hot melt composition is improved. If the content of the ultraviolet absorber is 2 mass% or less, the odor of the hot melt composition is reduced.

Examples of 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-based petroleum resin, C9-based petroleum resin, C5C9-based petroleum resin, dicyclopentadiene-based 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 hot melt compositions. These tackifying resins may be used alone or in combination of two or more.

The content of the tackifier resin in the hot melt composition of the present invention is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less, based on 100% by mass of the hot melt composition. When the content of the tackifier resin is 30% by mass or less, the hot melt composition does not become too hard, and the elastic recovery of the elastic member is further improved.

Examples of the photopolymerization initiator include ultraviolet polymerization initiators. When the hot melt composition of the present invention contains a styrene block copolymer having a reactive polystyrene hard block in the molecule as the styrene block copolymer (A), it further contains a photopolymerization initiator, so that the hot melt composition is irradiated with light such as ultraviolet light to react the reactive polystyrene hard block and crosslink the molecules, thereby adjusting the properties such as dynamic viscoelasticity of the hot melt composition. When the hot melt 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.

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

The content of liquid rubber in the hot melt 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 hot melt composition. When the content of liquid rubber is 1% by mass or more, the melt viscosity of the hot melt composition decreases, and the coating suitability is further improved. When the content of liquid rubber is 20% by mass or less, the hot melt composition does not become too soft, and the stretch recovery of the stretch 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.

The hot melt composition of the present invention preferably has a melt viscosity at 180°C of 45,000 mPa·s or less, more preferably 28,000 mPa·s or less, and even more preferably 22,000 mPa·s or less. When the upper limit of the melt viscosity is within the above range, the coatability of the hot melt composition is further improved. In addition, the lower limit of the melt viscosity at 180°C of the hot melt composition is not particularly limited, and may be about 5,000 mPa·s.

In this specification, "melt viscosity" refers to the viscosity of a hot melt composition that has been heated to a molten state at a certain temperature. For example, a method for measuring the melt viscosity at 180°C includes a method in which the hot melt composition is heated to melt, and the viscosity of the molten state at 180°C is measured using a Brookfield RVT viscometer (spindle No. 29).

The hot melt composition of the present invention is produced by a known method. For example, the thermoplastic resin (A), polyether resin (B), plasticizer (C), and various additives as necessary are charged into a twin-arm kneader heated to 150°C, and melt-kneaded while being heated.

The hot melt 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 that elastic members formed using the hot melt composition of the present invention can be used for a variety of purposes.

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

A laminate can be produced by bonding porous substrates with the hot melt composition of the present invention. Such a laminate also constitutes the present invention.

Examples of the porous substrate include nonwoven fabrics and paper. The nonwoven fabric is not particularly limited, and examples include spunbond nonwoven fabrics, spunlace nonwoven fabrics, and needle punch nonwoven fabrics. For example, a stretchable laminate with a good texture can be produced by using the hot melt composition of the present invention and laminating two pieces of fabric in a stretched state. A stretchable nonwoven fabric can also be used as the nonwoven fabric. For example, a stretchable laminate can be produced by applying the hot melt composition of the present invention to a stretchable nonwoven fabric without stretching the stretchable nonwoven fabric, and laminating the stretchable nonwoven fabrics together.

The above-mentioned extensible nonwoven fabric stretches to a certain extent when pulled in a certain direction, but it is difficult to return to its original length when the pulling force is removed. By applying the hot melt composition of the present invention to a porous substrate such as an extensible nonwoven fabric to form a laminate, it functions as an elastic reinforcement material and can impart the laminate with the ability to return to its original length.

The extensible nonwoven fabric is not particularly limited, and examples thereof include spunlace nonwoven fabric and needle punch nonwoven fabric. The coating method for coating the hot melt composition on the porous substrate is not particularly limited, and examples thereof include slot coating, curtain spray coating, spiral spray coating, and film coating. When the hot melt composition is applied by slot coating, the hot melt composition is easily absorbed into the porous substrate, and the stress of the laminate is further improved. When the hot melt composition is applied by spray coating, the penetration of the hot melt composition into the porous substrate is suppressed, and the texture and breathability are further improved.

The amount of the hot melt composition applied to the porous substrate is not particularly limited, and is preferably 1 to 200 g/ ^m2 , more preferably 5 to 150 g/ ^m2 , and even more preferably 10 to 100 g/ ^m2 . When the lower limit of the amount applied is within the above range, the stress and stretch recovery rate of the laminate are further improved. When the upper limit of the amount applied is within the above range, the texture of the laminate is further improved.

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:

Styrene-based block copolymer (A):
Styrene-based block copolymer (A1)
Styrene-ethylene-butylene/styrene-styrene copolymer (SEB/S-S) Kraton Polymers, Inc. MD6951 (styrene content 34% by mass, Mw=100,000)
Styrene-based block copolymer (A2)
Styrene-ethylene-butylene-styrene (SEBS) copolymer: MD1648 (styrene content 20% by mass, Mw = 54,000) manufactured by Kraton Polymers
Styrene-based block copolymer (A3)
Styrene-ethylene-butylene-styrene (SEBS) copolymer: Tuftec H1041 (styrene content 30% by mass, Mw = 61,000), manufactured by Asahi Kasei Corporation
Styrene-based block copolymer (A4)
Styrene-ethylene-ethylene-propylene-styrene copolymer (SEEPS): Septon 4033 (styrene content 30% by mass) manufactured by Kuraray Co., Ltd.

Polyether resin (B):
Polyphenylene ether resin (B1)
Polyphenylene ether resin (PPE) Noryl SA90 (Mn=1,700) manufactured by Savic Corporation

Plasticizer (C) :
・Naphthenic process oil (C1) Nyflex 222B manufactured by Nynas

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

Examples and Comparative Examples
The above-mentioned raw materials were charged into a stirring kneader equipped with a heating device in the amounts shown in Table 1. The mixture was kneaded while heating at 170° C. for 90 minutes to produce a hot melt composition.

The properties of the obtained hot melt composition and the elastic member manufactured using the hot melt composition were measured under the following measurement conditions, and the characteristics were evaluated.

Measurement of properties (ring and ball softening point temperature)
The ring and ball softening point of the hot melt composition was measured by a measurement method in accordance with JIS K6863.

(Crossover temperature (G'=G''))
The hot melt composition was heated and melted at 180 ° C., and dropped onto the release layer side of the release-treated PET film. Then, another release-treated PET film was laminated on the hot melt composition so that the release layer side was in contact with the hot melt composition. Then, it was compressed with a heat press heated to 120 ° C., and the thickness of the hot melt composition was adjusted to about 2 mm. After the hot melt composition was sandwiched between the PET films and left at 23 ° C. for 24 hours, the release film was removed to prepare a sample for dynamic viscoelasticity measurement.

Using this sample, dynamic viscoelasticity measurements were performed in the rotational shear mode of a dynamic viscoelasticity measuring device under the measurement conditions of temperatures from -80°C to 140°C, a frequency of 1 Hz, and a heating rate of 5°C/min, and the storage modulus G' and loss modulus G'' were measured. In the obtained curves of storage modulus G' and loss modulus G'', the highest temperature at which the storage modulus G' and loss modulus G'' intersect above room temperature was determined as the crossover temperature.

In the above measurements, a rotational rheometer (product name "AR-G2") manufactured by TA Instruments was used as the dynamic viscoelasticity measuring device.

(180°C Melt Viscosity)
The hot melt composition was heated to melt, and the viscosity of the molten composition at 180° C. was measured using a Brookfield RVT viscometer (spindle No. 29).

Evaluation (Preparation of test pieces (elastic members))
The hot melt composition was applied at a coating temperature of 160 to 180°C on the release layer side of a release-treated PET film in an amount of 50 g/ ^m2 . The coating width was 100 mm. Next, a laminate was prepared by laminating with a release paper that had been subjected to a release treatment on one side. The obtained laminate was cut to a size of 25 mm in the width direction and 50 mm in the coating direction, or a size of 50 mm in the width direction and 100 mm in the coating direction. The PET film and release paper of the laminate were peeled off to prepare a test piece of the hot melt composition having a width of 25 mm and a length of 50 mm, and a test piece (elastic member) having a width of 50 mm and a length of 100 mm.

(Elongation at break (stretchability))
A test piece (width (MD) 50 mm, length (CD) 100 mm) was fixed at both ends in the coating direction with a jig in a tensile tester set to a distance of 50 mm so that the direction (CD direction) perpendicular to the longitudinal direction (coating direction (MD) of the hot melt composition) was positioned at the top and bottom, and the test piece was pulled in the vertical direction at a pulling speed of 500 mm/min until it 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 to evaluate the extensibility.
[Elongation at break (%)] = (distance traveled by the jig until the test piece breaks (mm) / initial jig distance (mm)) x 100

(Permanent set (stretch recovery))
A test piece (width (MD direction) 50 mm, length (CD direction) 100 mm) 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 the hot melt 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 300%. Then, it was returned to the initial position at a speed of 500 mm / min. The process of pulling to a strain displacement of 300% and then returning to the initial position was defined as one cycle, and two cycles were repeated for the same test piece. From the integral value during the first cycle of tension and the integral value during the second cycle of tension, the permanent strain value was calculated based on the following formula to evaluate the stretch recovery.
[Permanent set (%)] =
[(Integral value (J) at the second cycle)−(Integral value (J) at the first cycle)]×100

(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) 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 of the hot melt composition (MD direction)) was located up and down, and the test piece was pulled in the vertical direction at a tensile speed of 100 mm/min until the displacement of the test piece reached 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 to evaluate the stress retention during elongation at high temperatures.
[Stress retention rate (%)] = (Test force after 1 hour (N) / Initial test force (N)) x 100

(Coating suitability)
The hot melt composition was charged into a melt tank heated to 180° C., and discharged from a slot nozzle heated to 180° C. to contact-coat a release-treated PET film at a coating amount of 50 g/m ² and a coating width of 100 mm. The coating state was visually observed and evaluated according to the following criteria.
A: Coating can be performed without unevenness.
B: Some unevenness in the coating is observed, but not to the extent that it causes any problems in practical use.
C: Significant unevenness in application was observed, or the specified amount of hot melt composition was not discharged.

The results are shown in Table 1.

The hot melt composition of Comparative Example 2 could not be evaluated because its ring and ball softening point temperature was too high to apply.

Claims (5)

The composition comprises a styrene-based block copolymer (A), a polyether-based resin (B), and a plasticizer (C),
The polyether-based resin (B) contains a polyphenylene ether resin,
The ring and ball softening point is 100 to 150°C.
Dynamic viscoelasticity measurement is performed under conditions of a frequency of 1 Hz and a temperature rise rate of 5°C/min, and the temperature in the temperature range above room temperature at which the measured storage modulus G' and loss modulus G'' become equal is within the range of 90 to 120°C.
A hot melt composition comprising: The hot melt composition according to claim 1, wherein the content of the styrene-based block copolymer (A) is 40 to 65 mass % relative to 100 mass % of the hot melt composition. The hot melt composition according to claim 1 or 2, wherein the content of the polyether resin (B) is 1 to 20 parts by mass per 100 parts by mass of the styrene block copolymer (A). The hot melt composition according to any one of claims 1 to 3, wherein the polyether-based resin (B) is a polyphenylene ether resin. The hot melt composition according to any one of claims 1 to 4, which is for use in absorbent articles.

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