WO2024181438A1 - Laminate - Google Patents

Abstract

This laminate is characterized by including, in the given order, the following: a nonwoven fabric layer (I) constituted by a nonwoven fabric α containing a cellulosic fiber; and a nonwoven fabric layer (II) constituted by an optional nonwoven fabric. The laminate is also characterized in that: the nonwoven fabric layer (I) and the nonwoven fabric layer (II) are bonded together with a hot-melt adhesive β therebetween; the standardized mean deviation (SMD) of the surface roughness of a surface of the nonwoven fabric α on a side contacting the nonwoven fabric layer (II) via the hot-melt adhesive β is 2.3 or less or 3.0 or more; the hot-melt adhesive β contains a component (A) thermoplastic elastomer and a component (B) tackifier; and the hot-melt adhesive β has a loss modulus of 200,000 Pa or more at a temperature of 23°C, a frequency of 1.00 Hz, and a strain of 0.05%, and has a loss tangent of 1.40 or more at a temperature of 23°C, a frequency of 1.00 Hz, and a strain of 0.05%.

Description

Laminate

The present invention relates to a laminate.

Currently, single-use plastics are the main material used for sanitary products such as diapers and napkins. However, in the future, it is expected that these materials will be increasingly replaced by more environmentally friendly materials.

Currently, petroleum-based nonwoven fabrics are the main material used for these hygiene products, but in the future, this is expected to be replaced by nonwoven fabrics made from natural materials.

The surface condition of nonwoven fabrics made from petroleum-based materials is different from that of nonwoven fabrics made from natural materials. For this reason, if adhesives used in the manufacture of conventional sanitary products are used in the process of bonding nonwoven fabrics made from natural materials, appropriate adhesion cannot be obtained.

When laminating nonwoven fabrics used in such sanitary products with adhesives, it is necessary that the nonwoven fabrics not only adhere well to each other in situ, but also that the adhesiveness be maintained over a long period of time (hereinafter, in this specification, this property will be referred to as "strength over time"). To achieve this, in addition to the surface characteristics of the nonwoven fabric, the selection of the adhesive to be combined with it is also important.

Patent Document 1 discloses a hot melt adhesive that is said to have good adhesion even to uneven surfaces such as those used in sanitary products.

Patent Document 2 also discloses a hot melt adhesive that is said to have good adhesion to hydrophilic substrates such as cellulose-based substrates and cotton-based substrates.

International Publication No. WO 2021/039118 Japanese Patent Application Publication No. 2007-169531

However, it is unclear whether the hot melt adhesive disclosed in Patent Document 1 is a good adhesive for nonwoven fabrics made from natural base materials, and it is also unclear whether consideration has been given to the strength over time when nonwoven fabrics made from natural base materials are bonded.

Furthermore, although the hot melt adhesive disclosed in Patent Document 2 has been confirmed in the examples for its adhesiveness between PET film and cotton cloth, it is unclear as to its adhesiveness between nonwoven fabrics made from natural substrates, or between nonwoven fabrics made from natural substrates and other nonwoven fabrics, and it is also unclear whether the adhesive has been designed with consideration given to strength over time.

In view of the above circumstances, the object of the present invention is to find a laminate of a hot melt adhesive and a nonwoven fabric containing specific cellulose fibers, which has excellent adhesive properties and strength over time and can be used to bond nonwoven fabrics containing cellulose fibers to each other, or to bond a nonwoven fabric containing cellulose fibers to another nonwoven fabric.

As a result of extensive research conducted by the inventors to solve the above problems, they discovered that excellent adhesion and strength over time can be achieved by combining a nonwoven fabric containing cellulose fibers and having a specified surface roughness with a hot melt adhesive having a specified composition. Based on this knowledge, the inventors conducted further research and have completed the present invention.

That is, the present invention provides the following laminate.
Item 1.
The nonwoven fabric layer (I) is made of a nonwoven fabric α containing cellulosic fibers, and the nonwoven fabric layer (II) is made of any nonwoven fabric, in this order. The nonwoven fabric layer (I) and the nonwoven fabric layer (II) are bonded to each other via a hot melt adhesive β.
The surface roughness mean deviation (SMD) of the surface of the nonwoven fabric α that contacts the nonwoven fabric layer (II) via the hot melt adhesive β is 2.3 or less or 3.0 or more,
The hot melt adhesive β contains a component (A) a thermoplastic elastomer and a component (B) a tackifier,
The hot melt adhesive β has a loss modulus of 200,000 Pa or more at a temperature of 23° C., a frequency of 1.00 Hz, and a strain of 0.05%, and a loss tangent of 1.40 or more at a temperature of 23° C., a frequency of 1.00 Hz, and a strain of 0.05%.
Item 2.
Item 2. The laminate according to item 1, wherein the hot melt adhesive β has a loss modulus of 10,000 Pa or more at a temperature of 50° C., a frequency of 1.00 Hz, and a strain of 0.05%.
Item 3.
Item 3. The hot melt adhesive β has a loss tangent of 0.21 or more at a temperature of 50 ° C., a frequency of 0.05 Hz, and a strain of 0.05%, and a loss tangent of 0.35 or more at a temperature of 50 ° C., a frequency of 1.00 Hz, and a strain of 0.05%.
Item 4.
Item 4. The laminate according to any one of items 1 to 3, wherein the nonwoven fabric α has a basis weight of 15 to 40 g / m ² .
Item 5.
Item 5. The laminate according to any one of Items 1 to 4, wherein the cellulosic fiber contained in the nonwoven fabric α is cotton or rayon.
Item 6.
Item 6. The laminate according to any one of items 1 to 5, wherein the hot melt adhesive β is a hot melt adhesive for absorbent articles.

The laminate according to the present invention thus obtained also has excellent adhesion and strength over time.

FIG. 2 is an explanatory diagram of the production of laminates in Examples and Comparative Examples.

In this specification, "containing" is a concept that encompasses all of "comprise," "consist essentially of," and "consist of." Furthermore, in this specification, when a numerical range is indicated as "A to B," it means greater than or equal to A and less than or equal to B.

(1. Laminate)
The laminate of the present invention comprises a nonwoven fabric layer (I) made of a nonwoven fabric α containing cellulosic fibers and a nonwoven fabric layer (II) made of an arbitrary nonwoven fabric, in this order, the nonwoven fabric layer (I) and the nonwoven fabric layer (II) are bonded via a hot melt adhesive β, the surface of the nonwoven fabric α that contacts the nonwoven fabric layer (II) via the hot melt adhesive β has a surface roughness mean deviation (SMD) of 2.3 or less or 3.0 or more, the hot melt adhesive β contains a thermoplastic elastomer (A) and a tackifier (B), and the hot melt adhesive β has a loss modulus of 200,000 Pa or more at a temperature of 23° C., a frequency of 1.00 Hz, and a strain of 0.05%, and a loss tangent of 1.40 or more at a temperature of 23° C., a frequency of 1.00 Hz, and a strain of 0.05%.

It is also a preferred embodiment to laminate the laminate of the present invention by further adhering one or more additional sheets of nonwoven fabric (which may be a nonwoven fabric similar to nonwoven fabric α) to the laminate using a separate hot melt adhesive (which may be a hot melt adhesive similar to hot melt adhesive β).

A preferred embodiment is a method in which the nonwoven fabric constituting the laminate of the present invention is processed, such as embossed or perforated, before or after the process of bonding the nonwoven fabric or laminate with a hot melt adhesive.

(2. Nonwoven fabric layer (I))
The nonwoven fabric layer (I) is composed of a nonwoven fabric α containing cellulosic fibers. The content of cellulosic fibers in the nonwoven fabric α is preferably 5% by mass or more, and more preferably 20% by mass or more, based on 100% by mass of the nonwoven fabric α. It is more preferable that the content of the cellulose-based fiber is 100% by mass or less in 100% by mass of the nonwoven fabric α. It may be an embodiment constituted only by fibers.

A wide variety of known cellulose-based fibers can be used. Specific examples include, but are not limited to, cotton, rayon, and lyocell.

The basis weight of the nonwoven fabric α is preferably 15 g/m ² or more, and more preferably 25 g/m ² or more. By having the basis weight of the nonwoven fabric α be 15 g/m ² or more, it is possible to impart a good water retention effect. In addition, the basis weight of the nonwoven fabric α is preferably 40 g/m ² or less, and more preferably 35 g/m ² or less. By having the basis weight of the nonwoven fabric α be 40 g/m ² or less, it is possible to impart good breathability.

The surface roughness mean deviation (SMD) of the surface of the nonwoven fabric α constituting the nonwoven fabric layer (I) that contacts the nonwoven fabric layer (II) via the hot melt adhesive β is 2.3 or less or 3.0 or more. If this value is greater than 2.3, the anchoring effect of the adhesive on the nonwoven fabric substrate cannot be expected, resulting in a decrease in adhesive strength. Also, if this value is less than 3.0, the contact area between the nonwoven fabric substrate and the adhesive decreases, resulting in a decrease in adhesive strength.

In this specification, the mean deviation of the surface roughness (SMD) of the nonwoven fabric surface is specifically defined as something that is measured and calculated as follows:

The measuring device used is a surface testing machine (for example, Kato Tech's KES-FB4-A), and the measurement conditions are an environment with a temperature of 23°C and humidity of 50%, a 0.5 mm roughness sensor as the thickness change sensor, a test piece of the nonwoven fabric to be tested (20 cm x 20 cm), a speed of 1.0 mm/sec, a static roughness load of 10.0 gf, and a 100 g paperweight is used to apply tension to the nonwoven fabric, and measurements are taken in the MD direction of the nonwoven fabric.

The test procedure is to set the test piece so that the MD direction of the nonwoven fabric is the same as the movement direction of the sensor, and to measure the surface roughness by applying a tension of 100g in the MD direction of the nonwoven fabric. Measurements are performed at 12 randomly selected points on the nonwoven fabric, and the average value is obtained as the SMD.

The surface roughness mean deviation (SMD) of the surface of the nonwoven fabric α constituting the nonwoven fabric layer (I) that contacts the nonwoven fabric layer (II) via the hot melt adhesive β is preferably 2.3 or less, more preferably 2.0 or less, and even more preferably 1.8 or less. In addition, the SMD is preferably 0 or more, and more preferably 1.0 or more.

On the other hand, the surface roughness mean deviation (SMD) of the surface of the nonwoven fabric α constituting the nonwoven fabric layer (I) that contacts the nonwoven fabric layer (II) via the hot melt adhesive β is preferably 3.0 or more, more preferably 3.2 or more, and even more preferably 3.5 or more. In addition, the SMD is preferably 7.0 or less, and more preferably 6.5 or less.

(3. Nonwoven fabric layer (II))
The nonwoven fabric layer (II) is composed of any nonwoven fabric. As such a nonwoven fabric, a wide variety of known nonwoven fabrics can be used, including nonwoven fabrics containing cellulosic fibers or nonwoven fabrics composed only of cellulosic fibers. Of course, the nonwoven fabric may be the same as the nonwoven fabric α described above.

　Other than that, nonwoven fabrics made from petroleum-based materials, such as those traditionally used in sanitary products, may also be used.

(4. Hot melt adhesive β)
The hot melt adhesive β contains a component (A) a thermoplastic elastomer and a component (B) a tackifier.

(4.1. Component (A) Thermoplastic Elastomer)
The thermoplastic elastomer of component (A) is not particularly limited, and examples thereof include styrene-based block copolymers, olefin-based block copolymers, polyurethane-based block copolymers, polyester-based block copolymers, etc. Among these, styrene-based block copolymers are preferred from the viewpoint of further improving the peel strength of the hot melt adhesive.

Styrene-based block copolymers are block copolymers obtained by block copolymerization of vinyl aromatic hydrocarbons and conjugated diene compounds.

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, vinylanthracene, etc., and among these, styrene is preferred. The vinyl aromatic hydrocarbons can be used alone or in combination of two or more types.

The conjugated diene compound is a diolefin compound having at least one pair of conjugated double bonds. Specific examples of the conjugated diene compound include 1,3-butadiene, 2-methyl-1,3-butadiene (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 (isoprene) are preferred. The conjugated diene compounds can be used alone or in combination of two or more kinds.

The styrene-based block copolymer is preferably an unhydrogenated styrene-based block copolymer, since it can exhibit better peel strength. Examples of the unhydrogenated styrene-based block copolymer include styrene-butadiene block copolymer (SB), styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), and styrene-butadiene-styrene-butadiene block copolymer (SBSB). These styrene-based block copolymers can be used alone or in combination of two or more kinds. Among these styrene-based block copolymers, styrene-butadiene-styrene block copolymer (SBS) is preferred, since it can exhibit even better peel strength.

The styrene skeleton content in the styrene block copolymer is preferably 10 to 70 mass% and more preferably 30 to 60 mass% in 100 mass% of the styrene block copolymer, in order to achieve better peel strength.

In this specification, the styrene skeleton content in a styrene block copolymer refers to the content (mass%) of styrene blocks in the styrene block copolymer. Methods for calculating the styrene skeleton content in a styrene block copolymer include, for example, methods using proton nuclear magnetic resonance spectroscopy and infrared spectroscopy in accordance with JIS K6239.

In the present invention, it is preferable that the thermoplastic elastomer (A) is a styrene-based block copolymer, and that the styrene-based block copolymer contains a styrene-butadiene-styrene block copolymer (SBS), in order to achieve better peel strength.

In the present invention, it is preferable that the styrene-based block copolymer does not contain an asymmetric styrene-isoprene-styrene block copolymer in order to further improve the heat stability when heated at high temperatures for a long period of time (for example, heating at 160°C for 72 hours).

In the present invention, it is preferable that the thermoplastic elastomer (A) is a styrene-based block copolymer, and that the styrene-based block copolymer does not contain an asymmetric styrene-isoprene-styrene block copolymer.

In the present invention, it is more preferable that the styrene-based block copolymer contains a styrene-butadiene-styrene block copolymer (SBS) and does not contain an asymmetric styrene-isoprene-styrene block copolymer.

In this specification, the term "asymmetric" in asymmetric styrene-isoprene-styrene block copolymer means that the styrene skeleton content is different in the styrene phases at both ends.

As the styrene-based block copolymer, a wide variety of known commercially available products can be used. Examples of commercially available products include Asahi Kasei Corporation's product name "Asaprene T-439" (styrene skeleton content: 45% by mass), Asahi Kasei Corporation's product name "Asaprene T-438" (styrene skeleton content: 35% by mass), Asahi Kasei Corporation's product name "Asaprene T-436" (styrene skeleton content: 30% by mass), Kraton Polymers' product name "DX-405" (styrene skeleton content: 24% by mass), Kraton Polymers' product name "D-1155" (styrene skeleton content: 40% by mass), Kraton Polymers' product name "D-1118" (styrene skeleton content: 30% by mass), and CHIMEI's product name "PB5502" (styrene skeleton content: 32% by mass). These commercially available products can be used alone or in combination of two or more.

The content of thermoplastic elastomer (A) in 100% by mass of the hot melt adhesive of the present invention is preferably 10 to 35% by mass, more preferably 15 to 30% by mass, and even more preferably 18 to 25% by mass, in order to achieve better peel strength.

The content of the styrene block copolymer in 100% by mass of the hot melt adhesive of the present invention is preferably 10 to 35% by mass, more preferably 15 to 30% by mass, and even more preferably 18 to 25% by mass, in order to achieve even better peel strength.

(4.2. Component (B) Tackifier)
The tackifier component (B) preferably contains the components (B1) and (B2). The tackifier component (B) may be composed of only the components (B1) and (B2).

Component (B1) is a terpene-based tackifier, a rosin-based tackifier, or a fully hydrogenated hydrocarbon-based tackifier.

The above-mentioned terpene-based tackifiers include terpene resins (monoterpene, diterpene, triterpene, polyperene, etc.), terpene phenol resins, aromatic modified terpene resins, etc. These terpene-based tackifiers can be used alone or in combination of two or more kinds.

A wide variety of known commercially available products with an acid value of 15 mgKOH/g or less can be used as the terpene tackifier. Examples of such commercially available products include "YS Resin TO-105" (acid value: 0 mgKOH/g) manufactured by Yasuhara Chemical Co., Ltd. and "SYLVARES TRM1115" (acid value: 0 mgKOH/g) manufactured by Kraton Corporation.

As the rosin-based tackifier, it is preferable to use at least one of natural rosin and an esterified product of the natural rosin (rosin ester resin), and it is more preferable to use rosin ester resin, in order to achieve better adhesion (tack).

Examples of the above-mentioned natural rosins include tall rosin, gum rosin, wood rosin, etc. These natural rosins can be used alone or in combination of two or more types.

Examples of the rosin ester resin include rosin glycerin ester, rosin pentaerythritol ester, rosin methyl ester, rosin ethyl ester, rosin butyl ester, rosin ethylene glycol ester, etc. These rosin ester resins can be used alone or in combination of two or more.

As the rosin-based tackifier, a wide variety of known commercially available products having an acid value of 15 mgKOH/g or less can be used. Examples of such commercially available products include Arakawa Chemical Industries Co., Ltd.'s product name "Super Ester A100" (acid value: 5 mgKOH/g), Arakawa Chemical Industries Co., Ltd.'s product name "Pine Crystal KE-100" (acid value: 6 mgKOH/g), Kraton Corporation's product name "SYLVALITE 9100" (acid value: 7 mgKOH/g), and Arakawa Chemical Industries Co., Ltd.'s product name "Super Ester A75" (acid value: 5 mgKOH/g). These commercially available products can be used alone or in combination of two or more types.

The fully hydrogenated hydrocarbon tackifier can be, for example, a fully hydrogenated petroleum resin obtained by adding hydrogen to petroleum resins such as C5 petroleum resin, C9 petroleum resin, C5C9 petroleum resin, and dicyclopentadiene petroleum resin. Note that C5 petroleum resin is a petroleum resin made from the C5 fraction of petroleum, C9 petroleum resin is a petroleum resin made from the C9 fraction of petroleum, and C5C9 petroleum resin is a petroleum resin made from the C5 and C9 fractions of petroleum. Examples of C5 fractions include cyclopentadiene, isoprene, and pentane. Examples of C9 fractions include styrene, vinyltoluene, and indene.

Component (B2) is an unhydrogenated hydrocarbon-based tackifier or a partially hydrogenated hydrocarbon-based tackifier.

Specific examples of the tackifier of component (B2) include unhydrogenated or partially hydrogenated hydrocarbon-based tackifiers of petroleum resins such as the above-mentioned C5 petroleum resins, C9 petroleum resins, C5C9 petroleum resins, and dicyclopentadiene petroleum resins.

In this specification, the ring and ball softening point of component (B) the tackifier means the temperature measured in accordance with JIS K 6863.

The content of component (B) tackifier in 100% by mass of the hot melt adhesive β is preferably 30 to 65% by mass, more preferably 35 to 60% by mass, and even more preferably 40 to 55% by mass, in order to further improve the peel strength.

The content of component (B) tackifier is preferably 150 to 350 parts by mass, and more preferably 200 to 300 parts by mass, per 100 parts by mass of component (A) thermoplastic elastomer, in order to further improve peel strength.

In the present invention, when the parts by mass of component (A) thermoplastic elastomer are A and the parts by mass of component (B) tackifier are B, the ratio B/A is preferably 1.5 to 3.5, and more preferably 2.0 to 3.0.

In addition, in order to obtain good adhesion, the amount of component (B1) in a total of 100% by mass of components (B1) and (B2) is preferably 50% by mass or less, and more preferably 40% by mass or less.

On the other hand, the amount of component (B1) in a total of 100% by mass of components (B1) and (B2) is preferably 5% by mass or more, and more preferably 10% by mass or more. By having the amount of component (B1) in a range of 5% by mass or more, excellent strength over time can be obtained.

(4.3. Various Additives)
The hot melt adhesive β may contain various additives as necessary, as long as the additives do not substantially impede the object of the present invention. Examples of the additives include plasticizers, antioxidants, ultraviolet absorbers, liquid rubbers, waxes, and particulate fillers.

Examples of plasticizers include naphthenic process oil and paraffinic process oil, with naphthenic process oil being preferred in terms of further improving heat stability and peel strength. These plasticizers can be used alone or in combination of two or more.

A wide range of commercially available plasticizers can be used.

Commercially available naphthenic process oils include, for example, PetroChina's product name "KN4010", Idemitsu Kosan's product name "Diana Fresia N28", Idemitsu Kosan's product name "Diana Fresia U46", and Nynas' product name "Nyflex 222B".

Commercially available paraffin-based process oils include, for example, Idemitsu Kosan's products under the names "Diana Process Oil PW32," "Diana Process Oil PW90," "Diana Process Oil PS32," and "Diana Process Oil PS90"; and Witco's product under the name "Kaydol."

If the hot melt adhesive β contains a plasticizer, the upper limit of the plasticizer content in 100% by mass of the hot melt adhesive is preferably 40% by mass, more preferably 30% by mass, and even more preferably 25% by mass.

If the hot melt adhesive β contains a plasticizer, the lower limit of the content of the plasticizer (C) in 100% by mass of the hot melt adhesive is preferably 1% by mass, and more preferably 5% by mass.

A wide variety of known antioxidants can be used as the antioxidant, including, for example, 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 Examples of the antioxidants include phenolic 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. These antioxidants may be used alone or in combination of two or more. Among these antioxidants, phenolic antioxidants are preferred from the viewpoint of further improving heat stability.

A wide variety of known commercially available antioxidants can be used. An example of a commercially available phenolic antioxidant is "Evernox 10" manufactured by EVERSPRING CHEMICAL.

If the hot melt adhesive β contains an antioxidant, the upper limit of the antioxidant content in 100% by mass of the hot melt adhesive is preferably 5% by mass, more preferably 4% by mass, and even more preferably 3% by mass.

If the hot melt adhesive β contains an antioxidant, the lower limit of the antioxidant content in 100% by mass of the hot melt adhesive is preferably 0.1% by mass, more preferably 0.5% by mass, and even more preferably 1% by mass.

A wide variety of known ultraviolet absorbents can be used as the ultraviolet absorbent, including, for example, benzotriazole-based ultraviolet absorbents 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 absorbents such as 2-hydroxy-4-methoxybenzophenone; salicylic acid ester-based ultraviolet absorbents; cyanoacrylate-based ultraviolet absorbents; and hindered amine-based light stabilizers. These ultraviolet absorbents can be used alone or in combination of two or more.

A wide variety of known liquid rubbers can be used as the liquid rubber, including, for example, liquid polybutene, liquid polybutadiene, liquid polyisoprene, and hydrogenated resins thereof. These liquid rubbers can be used alone or in combination of two or more kinds.

A wide variety of well-known particulate fillers can be used as particulate fillers, including, for example, calcium carbonate, kaolin, talc, titanium oxide, mica, and styrene beads. These particulate fillers can be used alone or in combination of two or more.

If the hot melt adhesive β contains the various additives described above, the content of the various additives in 100% by mass of the hot melt adhesive is preferably 5% by mass or less.

The nonwoven fabric used in the laminate of the present invention can be manufactured by standard methods.

Hot melt adhesive β may also be manufactured by a standard method, and there are no particular limitations on the manufacturing method. For example, components (A) and (B), and, if necessary, the various additives described above, may be placed in a stirring and kneading machine equipped with a heating device and kneaded while heating.

The heating temperature during kneading is not particularly limited, but is preferably 100 to 200°C, more preferably 120 to 180°C. The kneading time is not particularly limited, but is preferably 40 to 140 minutes, more preferably 60 to 120 minutes.

When obtaining a laminate, a wide variety of known coating methods can be used to apply the hot melt adhesive β, such as spiral spray coating, slot coater coating, curtain spray coating, roll coater coating, omega coating, dot coating, and bead coating.

When applying the hot melt adhesive β to the bonded portion, a wide variety of known application devices can be used, such as a hot melt applicator. An example of a hot melt applicator is the "REKA Handgun TR80LCD (Spray)" manufactured by Suntool Co., Ltd.

The hot melt adhesive β is capable of exhibiting excellent adhesive properties to porous substrates made of natural materials such as cellulose-based materials and cotton-based materials; hydrophilic nonwoven fabrics, etc., and is therefore suitable for use in bonding adherends together in the manufacture of absorbent articles. It is preferable that the absorbent article is constructed using the hot melt adhesive β.

Absorbent articles are intended to absorb bodily fluids such as blood, urine, sweat, pus, gastric juices, saliva, and nasal mucus. Examples of absorbent articles include disposable diapers, sanitary napkins, panty liners, incontinence pads, portable toilets, portable waste disposal bags, animal waste disposal sheets, hospital gowns, surgical gowns, wound dressings, first aid bandages, and materials for preserving the freshness of meat and fish. Of these, the hot melt adhesive of the present invention is suitable for use in disposable diapers, sanitary napkins, panty liners, etc.

　Disposable diapers are basically composed of a liquid-impermeable back sheet made of a polyolefin resin film or the like, a liquid-permeable top sheet made of a nonwoven fabric or the like, a liquid-diffusion sheet that diffuses the liquid that has permeated through the top sheet, and an absorbent body placed between the liquid-diffusion sheet and the liquid-impermeable back sheet. In order to prevent the absorbent body from becoming sticky after absorbing urine or the like, the absorbent body is used with its surface covered with absorbent paper such as tissue. Absorbent articles also employ a structure in which elastic members such as rubber are attached in a stretchable manner to fit around the wearer's legs and waist and prevent excrement from leaking out.

Hot melt adhesive β is preferably used in the manufacture of such paper diapers, for example, to bond and integrate cellulose-based porous substrates together, and to bond and integrate cellulose-based porous substrates with other porous substrates such as nonwoven fabrics.

The method of bonding the nonwoven fabric layers (I) and (II) to form a laminate using the hot melt adhesive β is not particularly limited, and any known method can be used. For example, a method is used in which the hot melt adhesive β that has been heated and melted is applied to the nonwoven fabric layer (I) or (II), the other nonwoven fabric layer is then superimposed on the applied hot melt adhesive, and the two are then pressed together.

(4.4. Dynamic viscoelasticity of hot melt adhesive β)
The dynamic viscoelasticity of the hot melt adhesive β used in the present invention is such that the loss tangent calculated when viscoelasticity measurements are performed under conditions of a specified temperature and a specified strain and the frequency (frequency at which strain is applied) applied to the hot melt adhesive β is changed falls within a specified range.

The hot melt adhesive β preferably has a predetermined measured value in a dynamic viscoelasticity measurement test carried out at a temperature of 50°C. Specifically, it is preferable that the loss tangent at a temperature of 50°C, a frequency of 0.05 Hz, and a strain of 0.05% is 0.21 or more, and the loss tangent at a temperature of 50°C, a frequency of 1.00 Hz, and a strain of 0.05% is 0.35 or more.

The dynamic viscoelasticity measurement test carried out at the above temperature of 50°C is carried out as follows. The hot melt adhesive β is heated and melted at 150°C and dripped onto the release layer side of a release-treated polyethylene terephthalate film, taking care not to introduce air bubbles. Next, another release-treated polyethylene terephthalate film is laminated onto the hot melt adhesive, with the release layer side in contact with the hot melt adhesive. The resulting laminate is then compressed with a heat press to obtain a laminate with substantially no air bubbles, with the hot melt adhesive adjusted to a thickness of 3 mm. The laminate is sandwiched between polyethylene terephthalate films and left to stand at 23°C for 24 hours, after which a test piece with a length of 10 mm and a width of 10 mm is cut to prepare a sample for dynamic viscoelasticity measurement.

The prepared sample is attached to a dynamic viscoelasticity measuring device (a rotational rheometer manufactured by TA Instruments, product name "DHR-10"), and dynamic viscoelasticity measurement is performed under the following measurement conditions to obtain the loss tangent tan δ at a temperature of 50°C, the storage modulus G' (Pa) at a temperature of 50°C, and the loss modulus G'' (Pa) at a temperature of 50°C.
<Measurement conditions for dynamic viscoelasticity measurement at 50°C>
・Frequency range: 0.01Hz to 10.00Hz
Measurement temperature: 50°C
Strain: 0.05%
Lower plate: 25mm diameter parallel plate Upper plate: 8mm diameter crosshatch plate

The loss tangent of the hot melt adhesive β at a temperature of 50°C, a frequency of 0.05 Hz, and a strain of 0.05% is preferably 0.21 or more, more preferably 0.22 or more, and even more preferably 0.23 or more. When this value is 0.21 or more, sufficient adhesion over time of the laminate can be obtained. In addition, the loss tangent of the hot melt adhesive β at a temperature of 50°C, a frequency of 0.05 Hz, and a strain of 0.05% is preferably 0.60 or less, and more preferably 0.48 or less.

The loss tangent of the hot melt adhesive β at a temperature of 50°C, a frequency of 1.00 Hz, and a strain of 0.05% is preferably 0.35 or more, more preferably 0.40 or more, and even more preferably 0.50 or more. A value of 0.35 or more allows the laminate to have sufficient adhesion over time. The loss tangent of the hot melt adhesive β at a temperature of 50°C, a frequency of 1.00 Hz, and a strain of 0.05% is preferably 2.50 or less, and more preferably 0.65 or less.

The loss modulus of the hot melt adhesive β at a temperature of 50°C, a frequency of 1.00 Hz, and a strain of 0.05% is preferably 10,000 Pa or more, more preferably 12,000 Pa or more, and even more preferably 15,000 Pa or more. By having this value of 10,000 Pa or more, it is possible to obtain sufficient adhesion over time for the laminate.

Hot melt adhesive β has a specified measured value in a dynamic viscoelasticity measurement test carried out at a temperature of 23°C. Hot melt adhesive β is heated and melted at 150°C and dripped onto the release layer side of a release-treated polyethylene terephthalate film. Next, another release-treated polyethylene terephthalate film is laminated onto the hot melt adhesive so that the release layer side is in contact with the hot melt adhesive. The resulting laminate is then compressed with a heat press to obtain a laminate in which the thickness of the hot melt adhesive is adjusted to 3 mm. The laminate is sandwiched between polyethylene terephthalate films and left to stand at 23°C for 24 hours, after which a test piece with a length of 10 mm and a width of 10 mm is cut to prepare a sample for dynamic viscoelasticity measurement.

The prepared sample is attached to a dynamic viscoelasticity measuring device (a rotational rheometer manufactured by TA Instruments, product name "DHR-10"), and dynamic viscoelasticity measurement is performed under the following measurement conditions to obtain the loss tangent tan δ at a temperature of 23°C, the storage modulus G' (Pa) at a temperature of 23°C, and the loss modulus G'' (Pa) at a temperature of 23°C.
<Measurement conditions for dynamic viscoelasticity measurement at 23°C>
- Measurement temperature range: -20℃ to 130℃
Frequency: 1.00Hz
Heating rate: 5°C/min. Strain: 0.05%
Lower plate: 25mm diameter parallel plate Upper plate: 8mm diameter crosshatch plate

The loss modulus of the hot melt adhesive β at a temperature of 23°C, a frequency of 1.00 Hz, and a strain of 0.05% is 200,000 Pa or more, preferably 300,000 Pa or more, and more preferably 400,000 Pa or more. If this value is less than 200,000 Pa, the laminate will not have sufficient adhesion over time.

The loss tangent of the hot melt adhesive β at a temperature of 23°C, a frequency of 1.00 Hz, and a strain of 0.05% is 1.40 or more, preferably 1.50 or more, and more preferably 2.00 or more. If this value is less than 1.40, the laminate will not have sufficient adhesion over time. In addition, the loss tangent of the hot melt adhesive β at a temperature of 23°C, a frequency of 1.00 Hz, and a strain of 0.05% is preferably 6.00 or less, and more preferably 4.50 or less.

The above describes embodiments of the present invention, but the present invention is not limited to these examples, and can of course be embodied in various forms without departing from the spirit of the present invention.

The following provides a more detailed explanation of the embodiments of the present invention based on examples, but the present invention is not limited to these.

Preparation of Hot Melt Adhesive β Thermoplastic elastomer, tackifier, plasticizer, antioxidant and various additives as shown in Tables 1 and 2 below were charged into a stirring kneader equipped with a heating device, heated to 145°C, and kneaded for 90 minutes to obtain Hot Melt Adhesive Preparation Examples 1 to 10.

Preparation of nonwoven fabrics Cotton nonwoven fabrics I to III, rayon nonwoven fabric, and air-through nonwoven fabric composed of polyethylene and polypropylene fibers were prepared. The mean deviation (SMD) of the surface roughness of each nonwoven fabric was measured using a surface tester (e.g., KES-FB4-A manufactured by Kato Tech Co., Ltd.), and the results were 1.623 for cotton nonwoven fabric I, 3.179 for cotton nonwoven fabric II, 6.931 for cotton nonwoven fabric III, 4.857 for rayon nonwoven fabric, and 2.676 for air-through nonwoven fabric.

Preparation of Laminates As shown in FIG. 1, the above nonwoven fabrics I to III and rayon nonwoven fabric were cut out to a size of 70 mm in the MD direction and 50 mm in the CD direction (substrate A), the release paper of each of the above adhesive sheets was peeled off, and the nonwoven fabric was attached to the surface on which the SMD measurement was performed, and a 500 g roll was placed on top of it and rolled back and forth at a speed of 5 mm/sec. Furthermore, the release film of the adhesive sheet was peeled off, and another nonwoven fabric (substrate B) prepared was attached to the exposed adhesive surface on the surface on which the SMD measurement was performed. In both Examples and Comparative Examples, the two nonwoven fabrics sandwiching the adhesive sheet were a combination of nonwoven fabrics of the same material. A 100 g roll was placed on the obtained laminate, and rolled back and forth at a speed of 5 mm/sec.

Dynamic Viscoelasticity Measurement Test Based on the above-mentioned method, the dynamic viscoelasticity was measured for the hot melt adhesives of Production Examples 1 to 11. The obtained values are shown in Table 3 below.

As shown in FIG. 1, a tensile tester (Shimadzu Corporation AGS-X) was used to fix the nonwoven fabric in the laminate of each Example and Comparative Example to the substrate B, and a T-peel test was performed on the substrate A in the MD direction at a tensile strength of 100 mm/min to measure the maximum convex test force. The measurement was performed three times, and the average value was adopted as the test result of the maximum convex test force. The measurement was performed at two points after each Example and Comparative Example was produced, after leaving it for 24 hours in an environment with a temperature of 23° C. and a humidity of 50%, and after leaving it for 2 weeks in an environment of 50° C. Note that, in the present specification, the measurement result after leaving it for 24 hours will be referred to as "initial strength", and the measurement result after leaving it for 2 weeks will be referred to as "2W strength". In addition, the evaluation criteria were evaluated according to the following criteria for the average value obtained by performing the maximum convex test force measurement three times. It was determined that sufficient adhesion was obtained when the following evaluation criteria were ◯ or ◎.
<Evaluation criteria>
Less than 2.00N ×
2.00N or more and less than 2.50N △
2.50N or more but less than 3.00N 〇 3.00N or more ◎

As shown in the following Tables 4 to 18, the laminates of Examples 1 to 40 were confirmed to have excellent adhesion even after two weeks, whereas the laminates of Comparative Examples 1 to 15 were not confirmed to have such excellent adhesion.

Claims (6)

The nonwoven fabric layer (I) is made of a nonwoven fabric α containing cellulosic fibers, and the nonwoven fabric layer (II) is made of any nonwoven fabric, in this order. The nonwoven fabric layer (I) and the nonwoven fabric layer (II) are bonded to each other via a hot melt adhesive β.
The surface roughness mean deviation (SMD) of the surface of the nonwoven fabric α that contacts the nonwoven fabric layer (II) via the hot melt adhesive β is 2.3 or less or 3.0 or more,
The hot melt adhesive β contains a component (A) a thermoplastic elastomer and a component (B) a tackifier,
The hot melt adhesive β has a loss modulus of 200,000 Pa or more at a temperature of 23° C., a frequency of 1.00 Hz, and a strain of 0.05%, and a loss tangent of 1.40 or more at a temperature of 23° C., a frequency of 1.00 Hz, and a strain of 0.05%. The laminate according to claim 1, wherein the hot melt adhesive β has a loss modulus of 10,000 Pa or more at a temperature of 50°C, a frequency of 1.00 Hz, and a strain of 0.05%. The laminate according to claim 1 or 2, wherein the hot melt adhesive β has a loss tangent of 0.21 or more at a temperature of 50°C, a frequency of 0.05 Hz, and a strain of 0.05%, and a loss tangent of 0.35 or more at a temperature of 50°C, a frequency of 1.00 Hz, and a strain of 0.05%. The laminate according to any one of claims 1 to 3, wherein the nonwoven fabric α has a basis weight of 15 to 40 g / ^m2 . The laminate according to any one of claims 1 to 4, wherein the cellulosic fibers contained in the nonwoven fabric α are cotton or rayon. The laminate according to any one of claims 1 to 5, wherein the hot melt adhesive β is a hot melt adhesive for absorbent articles.

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