HOT MELT ADHESIVE

Cross-Reference to Related Application

[0001]

This application claims benefit under Paris Convention of Japanese Patent ApplicationNo.2011-203071 filedon September 16, 2011, incorporated herein by reference in its entity. Technical Field

[0002]

The present invention relates to a hot melt adhesive, and more particularly to a hot melt adhesive which is used in the field of disposable products typified by a diaper and a napkin.

Background Art

[0003]

A synthetic rubber-based hot melt adhesive containing a thermoplastic block copolymer as a main component has widely been used as a hot melt adhesive which is used in disposable products such as a diaper and a napkin and is applied to a base material thereof, for example, a nonwoven fabric, a tissue, a polyethylene film and the like.

[0004]

Patent Literature 1 discloses that a synthetic rubber-based hot melt adhesive containing a

styrene-butadiene-styrene block copolymer as a main component can be employed in disposable products (see [Claim 8] of Patent Literature 1) . In case of producing disposable products, a film or a nonwoven fabric is coated with a hot melt adhesive and high-speed coating is sometimes used so as to enhance production efficiency of the disposable products. In particular, it is necessary to increase a discharge amount of the hot melt adhesive so as to coat at a high speed in case of performing spiral coating . Therefore, it is necessary to set the pressure of hot air to be blown to a high value. However, in case of the synthetic rubber-based hot melt adhesive of Patent Literature 1, the hot melt adhesive may be sometimes scattered under the high hot air pressure.

[0005]

One of means for enhancing production efficiency of the disposable products includes a method in which an olefin-based hot melt adhesive typified by an ethylene-propylene copolymer is applied at a high speed.

Patent Literature 2 discloses that a propylene polymer can be used as a raw material for a hot melt adhesive (see [Claim 1] and [Technical Field] of Patent Literature 2) . An olefin-based hot melt adhesive of Patent Literature 2 develops high adhesive strength in case of bonding a nonwoven fabric and a nonwoven fabric together. However, the adhesive is insufficient for the disposable products because of insufficient adhesion of the adhesive to a polyethylene film.

[0006]

The disposable products such as a diaper and a sanitary napkin often have a structure in which an absorber constituted by a pulp, an absorbent polymer and the like is wrapped in a tissue and the outside of the tissue is covered with a nonwoven fabric, a polyethylene film and the like. Therefore, it is required for the hot melt adhesive for disposable products to have a strong adhesive strength to the nonwoven fabric and the polyethylene film.

[0007]

Patent Literature 3 discloses a hot melt adhesive containing a hydrogenated styrene-isoprene block copolymer (SEPS) and polyolefin (see [Claim 1] of Patent Literature 3) . The hot melt adhesive of Patent Literature 3 shows satisfactory adhesion to a nonwoven fabric, but shows poor adhesion to a polyethylene film because of rigid design containing no oil component in principle, and thus it is hard to use in disposable products . Furthermore, since the adhesive of Patent Literature 3 contains an amorphous polyolefin including a high-molecular weight component, it cannot obtain a sufficient width in spiral coating and has high viscosity. Therefore, it was not suited for spiral coating to a polyethylene film at low temperature. In order to cope with a complicated coating pattern, it is necessary to decrease the viscosity by increasing a coating temperature. However, when the coating temperature is increased, the filmmay be melted and the coated hot melt adhesive may shrink due to cooling, resulting in the formation of wrinkles in the film.

[0008]

Patent Literature 1: JP 2004-137297 A

Patent Literature 2: WO 2001-096490 A

Patent Literature 3: JP 2009-242533 A

Disclosure of the Invention

Problems to be Solved by the Invention

[0009]

An object of the present invention is to provide a hot melt adhesive which is excellent in high-speed coating and spiral coating at low temperature, and is also excellent in adhesion to a polyolefin film (preferably a polyethylene film) and a nonwoven fabric; and disposable products obtainable by using the hot melt adhesive.

Means for Solving the Problems

[0010]

The present inventors have intensively studied and found that it ispossible toobtainahotmelt adhesivewhich is excellent in high-speed coating and is excellent in spiral coating at low temperature, and is also excellent in adhesion to a polyolefin film (preferably a polyethylene film) and a nonwoven fabric, when a propylene homopolymer having narrow molecular weight distribution and also having a low melting point is blended with a thermoplastic block copolymer, and that such a hot melt adhesive is suitable for use in disposable products. Thus, the present invention has been completed.

[0011]

That is, the present invention provides, as an aspect, a hot melt adhesive including: (A) a thermoplastic block copolymer which is a copolymer of a vinyl-based aromatic hydrocarbon with a conjugated diene compound; and (B) apropylene homopolymer having a melting point of 100°C or lower which is obtainable by polymerizing propylene using a metallocene catalyst.

[0012]

The present invention provides , as an embodiment, the hot melt adhesive, wherein the thermoplastic block copolymer (A) contains at least one selected from: (Al) a hydrogenated styrene-butadiene block copolymer (SEBS) ; and (A2) a hydrogenated styrene- isoprene block copolymer (SEPS) .

The present invention provides, as another embodiment, the hot melt adhesive, wherein the propylene homopolymer (B) includes at least one selected from: (Bl) apropylene homopolymer having a weight average molecular weight of 60, 000 or less; and (B2) a propylene homopolymer having a weight average molecular weight of more than 60,000.

[0013]

The present inventionprovides, as apreferred embodiment , the hot melt adhesive , further including: (C) a tackifier resin; and (D) a plasticizer, wherein

the plasticizer (D) contains at least one selected from: (Dl) a naphthene oil; and (D2) a paraffin oil.

The present invention provides, as a second aspect, disposable products obtainable by using the above hot melt adhesive.

Effects of the Invention

[0014]

Since the hot melt adhesive of the present invention includes: (A) a thermoplastic block copolymer which is a copolymerof avinyl-basedaromatic hydrocarbonwitha conjugated diene compound; and (B) a propylene homopolymer having a melting point of 100°C or lower which is obtainable by polymerizing propylene using a metallocene catalyst,

the hot melt adhesive is excellent in high-speed coating and is excellent in spiral coating at low temperature, and is also excellent in adhesion to a polyolefin film (preferably a polyethylene film) and adhesion to a nonwoven fabric.

[0015] In the hot melt adhesive of the present invention, when the thermoplastic block copolymer (A) contains at least one selected from: (Al) a hydrogenated styrene-butadiene block copolymer (SEBS) ; and (A2) a hydrogenated styrene-isoprene block copolymer (SEPS) ,

compatibility with the component (B) is improved, and because of improvement of the compatibility, anadhesive strength to a nonwoven fabric and a polyolefin film is improved.

[0016]

In the hot melt adhesive of the present invention, when the propylene homopolymer (B) includes at least one selected from: (Bl) a propylene homopolymer having a weight average molecular weight of 60,000 or less; and (B2) a propylene homopolymer having a weight average molecular weight of more than 60, 000,

the hot melt adhesive is more excellent in spiral coating at low temperature , and more excellent in balance of the adhesion to a polyolefin film and a nonwoven fabric.

[0017]

When the hot melt adhesive of the present invention further includes: (C) a tackifier resin; and (D) a plasticizer, and the plasticizer (D) contains at least one selected from: (Dl) a naphthene oil; and (D2) a paraffin oil,

the adhesion to a polyolefin film and a nonwoven fabric is further improved, and the viscosity further decreases, and thus the hot melt adhesive is more excellent in coating at low temperature (especially, spiral coating) and is more suitable for use in disposable products.

[0018]

Since disposable products of the present invention are obtainable by using the above hot melt adhesive, the disposable products can be efficiently produced using a high-speed coating line and coating can be performed at low temperature of about 140°C, which causes higher safety . The disposable products are excellent in adhesion to a nonwoven fabric and a polyolefin film, and are less likely to cause peeling.

Mode for Carrying Out the Invention

[0019]

The hot melt adhesive according to the present invention includes :

(A) a thermoplastic block copolymer which is a copolymer of a vinyl-based aromatic hydrocarbon with a conjugated diene compound; and

(B) a propylene homopolymer having a melting point of 100 °C or lower which is obtainable by polymerizing propylene using a metallocene catalyst.

[0020]

In the present invention, the " (A) thermoplastic block copolymer" is a copolymer in which a vinyl-based aromatic hydrocarbon and a conjugated diene compound undergo block copolymerization, and is commonly comprised of a vinyl-based aromatic hydrocarbonblockanda conjugateddiene compoundblock . There is no particular limitation as long as the objective hot melt adhesive of the present invention can be obtained.

[0021]

As used herein, the "vinyl-based aromatic hydrocarbon" means an aromatic hydrocarbon compound having a vinyl group, and specific examples thereof include styrene, o-methylstyrene, -methylstyrene, p-tert-butylstyrene, 1 , 3 -dimethylstyrene , a-methylstyrene, vinylnaphthalene , vinylanthracene and the like. Styrene is particularly preferable . These vinyl-based aromatic hydrocarbons can be used alone, or in combination.

[0022]

The "conjugated diene compound" means a diolefin compound having at least a pair of conjugated double bonds. Specific examples of the "conjugated diene compound" include

1, 3 -butadiene, 2 -methyl-1, 3 -butadiene (or isoprene) ,

2 , 3-dimethyl-l , 3 -butadiene, 1 , 3-pentadiene and 1, 3-hexadiene . Among these conjugated diene compounds, 1, 3 -butadiene and 2-methyl-1,3 -butadiene are particularly preferable. These conjugated diene compound can be used alone, or in combination.

[0023]

The thermoplastic block copolymer (A) according to the present inventionmaybe eitheranunhydrogenatedorhydrogenated thermoplastic block copolymer.

Specific examples of the "unhydrogenated thermoplastic block copolymer (A) " include block copolymers in which blocks based on the conjugated diene compound are not hydrogenated. Specific examples of the "hydrogenated thermoplastic block copolymer (A) " include block copolymers in which blocks based on the conjugated diene compound are entirely or partially hydrogenated.

[0024]

A proportion that the "hydrogenated thermoplastic block copolymer (A) " is hydrogenated can be indicated by a

"hydrogenation ratio" . The "hydrogenation ratio" of the "hydrogenated thermoplastic block copolymer (A) " refers to a proportion of double bonds converted into saturated hydrocarbon bonds by hydrogenation of all aliphatic double bonds included in the blocks based on the conjugated diene compound. The "hydrogenation ratio" can be measured by an infrared spectrophotometer, a nuclear magnetic resonance spectrometer and the like.

[0025]

Specific examples of the "unhydrogenated thermoplastic block copolymer (A) " include a styrene-isoprene block copolymer (also referred to as "SIS") and a styrene-butadiene block copolymer (also referred to as "SBS"). Specific examples of the "hydrogenated thermoplastic block copolymer (A)" include a hydrogenated styrene-isoprene block copolymer (also referred to as "SEPS") and a hydrogenated styrene-butadiene block copolymer (also referred to as "SEBS") .

These thermoplastic block copolymers (A) canbe used alone, or in combination.

[0026]

It is possible to use, as the thermoplastic block copolymer (A), commercially available products.

Examples thereof include Asaprene T 39 (trade name) , Asaprene T436 (tradename) , Asaprene T438 (tradename) , Asaprene N505 (tradename) , TAFTEC HI121 (tradename) , TAFTECH1062 (trade name), TAFTEC HI052X (tradename) and TUFPREN T125 (tradename) manufactured by Asahi Kasei Chemicals Corporation;

TR2003 (tradename) , TR2500 (tradename) andTR2600 (trade name) manufactured by JSR Corporation;

Stereon 857 (trade name) and Stereon 841A (trade name) manufactured by Firestone;

Kraton D1118 (trade name) , Kraton G1654 (trade name) and Kraton G1726 (trade name) manufactured by Kraton Polymers; Sol T166 (trade name) manufactured by Enichem;

Quintac 3433N (trade name) and Quintac 3421 (trade name) manufactured by Zeon Corporation; and

SEPTON 2002 and SEPTON 2063 (trade name) manufactured by Kuraray Co . , Ltd .

[0027] These commercially available products of the thermoplastic block copolymer (A) canbe respectivelyusedalone, or in combination.

The styrene content of the thermoplastic block copolymer (A) is preferably 20% by weight or less, and particularly preferably from 10 to 15% by weight. The styrene content refers to the proportion of styrene blocks included in (A) . When the styrene content is 20% by weight or less, compatibility of the component (A) with the component (B) is improved, and thus the adhesive strength to a nonwoven fabric and a polyolefin film (preferably a polyethylene film) of the obtained hot melt adhesive is more improved.

[0028]

In the present invention, the propylene homopolymer (B) refers to a homopolymer of propylene, which is produced by using a metallocene catalyst as a polymerization catalyst. The melting point of the propylene homopolymer (B) is 100°C or lower, more preferably from 60 to 90°C, and most preferably from 65 to 85°C.

[0029]

The melting point refers to a value measured by differential scanning calorimetry (DSC) . Specifically, after weighing 10 mg of a sample in an aluminum container, the measurement is carriedout at temperature rise rate of 5°C/minute using DSC6220 (trade name) manufactured by SII NanoTechnology Inc, and the temperature of a top of a fusion peak refers to the melting point.

[0030]

Whenpropylene is polymerized using ametallocene catalyst , a propylene homopolymer having (i) crystallinity and (ii) very narrow molecular weight distribution is synthesized.

[0031]

(i) means that complete isotacticity and syndiotacticity can be optionally controlled. Therefore, a polymer, in which arrangement, ratio and the like of methyl groups is uniform, is obtained without causing deviation of crystallinity, and a low crystalline site that can cause decrease in adhesive force is less likely to be formed.

[0032]

With respect to (ii) , when molecular weight distribution of the propylene homopolymer (B) is indicated by polydispersity

(Mw/Mn) , it is from 1 to 3. The propylene homopolymer having polydispersity of from 1 to 3 is excellent in spiral coatability . The molecular weight distribution is a concept which indicates distribution of a molecular weight of a synthetic polymer, and a ratio (Mw/Mn) of a weight average molecular weight (Mw) to a number average molecular weight (Mn) serves as an indicator. In the present invention, the molecular weight distribution is measured by gel permeation chromatography (GPC) .

[0033] Examples of the propylene homopolymer (B) include: (Bl) a propylene homopolymer having a weight average molecular weight of 60,000 or less; and (B2) a propylene homopolymer having a weight average molecular weight of more than 60,000.

[0034]

The weight average molecular weight of the propylene homopolymer (Bl) is preferably 60 , 000 or less, particularly preferably from 30 , 000 to 60 , 000 , andmore preferably from 35 , 000 to 55,000.

The weight average molecula weight of the propylene homopolymer (B2) is more than 60 , 000 , preferablymore than 60 , 000 and 90,000 or less, and more preferably more than 60,000 and 80 , 000 or less .

[0035]

The weight average molecular weight (Mw) means a value measuredbygel permeationchromatography (GPC) . Specifically, the value can be measured by using the following apparatus and measuringmethod. RI manufactured byWators Corporation is used as a detector. TSKGEL GMHHR-H (S) HT manufactured by TOSOH CORPORATION is used as a GPC column. A sample is dissolved in 1, 2 , 4-trichlorobenzene and allowed to flow at a flow rate of 1.0 ml/min and a measuring temperature of 145°C, and then the weight average molecular weight is determined by conversion of a molecular weight using a calibration curve derived based on polypropylene. Since the number average molecular weight (Mn) is also determined by the same method, the molecular weight distribution is also calculated by GPC.

[0036]

Examples of a commercially available product of the propylene homopolymer (Bl) include L-MODU X400S (trade name) manufactured by Idemitsu Kosan Co., Ltd., and examples of a. commercially availableproduct of the propylene homopolymer (B2) include L-MODU X600S (tradename) manufactured by Idemitsu Kosan Co., Ltd.

[0037]

When the hot melt adhesive of the present invention contains the thermoplastic block copolymer (A) and the propylene homopolymer (B) , the spiral coatability at low temperature is excellent while maintaining the adhesion to a polyolefin film (preferably a polyethylene film) and a nonwoven fabric.

[0038]

It is preferred that the hot melt adhesive of the present invention further includes: (C) a tackifier resin.

Examples of the tackifier resin (C) include a natural rosin, a modified rosin, a hydrogenated rosin, a glycerol ester of a natural rosin, a glycerol ester of a modified rosin, a pentaerythritol esterof anatural rosin, apentaerythritol ester of a modified rosin, a pentaerythritol ester of a hydrogenated rosin, a copolymer of a natural terpene , a terpolymer of a natural terpene, hydrogenated derivatives of a copolymer of a hydrogenated terpene, a polyterpene resin, hydrogenated derivatives of a phenol-based modified terpene resin, an aliphatic petroleum hydrocarbon resin, hydrogenated

derivatives of an aliphatic petroleum hydrocarbon resin, an aromatic petroleum hydrocarbon resin, hydrogenated derivatives of an aromatic petroleum hydrocarbon resin, a cyclic aliphatic petroleum hydrocarbon resin, and hydrogenated derivatives of a cyclic aliphatic petroleum hydrocarbon resin. These tackifier resins can be used alone, or in combination.

[0039]

It is also possible to use, as the tackifier resin, a liquid type tackifier resin as long as it has a colorless to pale yellow color tone and has substantially no odor, and also has satisfactory thermal stability. Taking these characteristics into consideration comprehensively, the tackifier resin is preferably hydrogenated derivatives of resins, andparticularly preferably a hydrogenated dicyclopentadiene-based resin.

[0040]

It is possible to use, as the tackifier resin (C) , commercially available products. Examples of these

commercially available products include Alcon P100 (trade name) and Alcon Ml00 (trade name) manufactured by Arakawa Chemical Industries, Ltd. ; Clearon M105 (trade name) manufactured by YASUHARA CHEMICAL CO. , LTD.; ECR5400 (tradename) and ECR179EX (tradename) manufacturedbyExxonCorporation; andQuintonDX395 (trade name) and Quinton DX390N (trade name) manufactured by Zeon Corporation. These commercially available tackifier resins can be used alone, or in combination.

[0041]

The hot melt adhesive of the present invention can further include: (D) a plasticizer . The plasticizer (D) is blended for thepurpose of decrease inmelt viscosityof the hot melt adhesive , imparting flexibility to the hot melt adhesive and an improvement in wettability of the hot melt adhesive to an adherend. There is no particular limitation as long as the objective hot melt adhesive of the present invention can be obtained. Examples of the plasticizer (D) include paraffin oil, naphthene oil and aromatic oil, and colorless and odorless oils such as naphthene oil and paraffin oil are particularly preferable.

[0042]

It is possible to use, as the plasticizer (D) , commercially available products. Examples thereof include White Oil Broom 350 (trade name) manufactured by Kukdong Oil & Chemical Co., Ltd. ; Diana Fresia S32 (trade name) , Diana Process Oil PW-90 (trade name) , DN oil KP-68 (trade name) and Process Oil NS100 (trade name) which are manufactured by Idemitsu osan Co. , Ltd. ; KN4010 (tradename) manufactured by PetroChina Company; Enerper 1930 (trade name) manufactured by BP Chemicals Ltd. ; Kaydol (trade name) manufactured by Cromp on Corporation; and Primol 352 (trade name) manufactured by Esso Cor . These plasticizers

(D) can be used alone, or in combination.

[0043]

In the hot melt adhesive of the present invention, the blending amount of the thermoplastic block copolymer (A) is preferably from 3 to 30 parts by weight, and more preferably from 5 to 20 parts by weight, based on 100 parts by weight of the total weight of the components (A) to (D) . When the blending amount of the thermoplastic block copolymer (A) is from 3 to 30 parts by weight, the hot melt adhesive is more excellent in high-speed coating and spiral coating at low temperature, and balance of adhesion to a polyolefin film (preferably a polyethylene film) and a nonwoven fabric.

[0044]

The blending amount of the propylene homopolymer (B) is preferably from 5 to 35 parts by weight, more preferably from 10 to 35 parts by weight, and particularly preferably from 20 to 30 parts by weight, based on 100 parts by weight of the total weight of the components (A) to (D) . When the blending amount of the propylene homopolymer (B) is from 5 to 35 parts by weight, the hot melt adhesive is more excellent in the spiral coatability at low temperature while maintaining the adhesion to a polyolefin film (preferably a polyethylene film) and a nonwoven fabric.

[0045]

The hot melt adhesive of the present inventionmay contain: (E) a wax. As used herein, the "wax" refers to an organic substance having a weight average molecular weight of less than 10, 000, which is solid at normal temperature and becomes liquid when heated, and is commonly considered as a "wax". There is no particularly limitation on the wax as long as the hot melt adhesive according to the present invention can be obtained, if it has wax- like properties.

[0046]

The wax (E) preferably contains: (El) an olefin wax modified with carboxylic acid or carboxylic anhydride.

In the present invention, " (El) olefin wax modified with carboxylic acid or carboxylic anhydride" refers to an olefin wax which is chemically or physically processed with carboxylic acid or carboxylic anhydride, and there is no particular limitation as long as the objective hot melt adhesive of the present invention is obtainable. Examples of chemical or physical processing include oxidation, polymerization, blending, synthesis and the like.

[0047]

Examples of the wax (El) include a wax which is obtainable by graft polymerization of carboxylic acid or carboxylic anhydride with an olefin wax; and a wax which is obtainable by copolymerization of carboxylic acid or carboxylic anhydride on synthesizing an olefin wax by polymerization.

[0048] Therefore, the wax may be an olefin wax which is modified as a result of introduction of carboxylic acid or carboxylic anhydride into the "olefin wax" using various reactions.

There is no particular limitation on "carboxylic acid" and/or "carboxylic anhydride" to be used to modify the olefin wax as long as the objective hot melt adhesive of the present invention is obtainable.

[0049]

Specific examples of the carboxylic acid or carboxylic anhydride include maleic acid, maleic anhydride, fumaric acid, fumaric anhydride , itaconic acid, acrylic acid, methacrylic acid and the like. These carboxylic acids and/or carboxylic anhydrides may be used alone, or in combination. Maleic acid and maleic anhydride are preferable, and maleic anhydride is particularly preferable.

[0050]

If necessary, the hot melt adhesive according to the present invention may further contain various additives. Examples of the various additives include a stabilizing agent and a fine particle filler.

The "stabilizing agent" is blended so as to prevent decrease inmolecular weight , occurrence of gelation, coloration, odor and the like of the hot melt adhesive due to heat, thereby improving stability of the hot melt adhesive, and there is no particular limitation as long as the obj ective hot melt adhesive of the present invention is obtainable. Examples of the "stabilizing agent" include an antioxidant and an ultraviolet absorber.

[0051]

The "ultraviolet absorber" is used so as to improve light resistance of the hot melt adhesive. The "antioxidant" is used so as to prevent oxidative degradation of the hot melt adhesive. There is no particular limitation on the antioxidant and the ultraviolet absorber, as long as they are commonly used in disposable products and the below-mentioned objective disposable products are obtainable.

[0052]

Examples of the antioxidant include a phenol -based antioxidant, a sulfur-based antioxidant and a phosphorus -based antioxidant. Examples of the ultraviolet absorber include a benzotriazole-based ultraviolet absorber and a

benzophenone-based ultraviolet absorber. It is also possible to add a lactone-based stabilizer. These additives can be used alone, or in combination.

[0053]

It is possible to use, as the stabilizer, commercially available products. Examples thereof include SUMILIZER GM (tradename) , SUMILIZER TPD (tradename) and SUMILIZER TPS (trade name) manufactured by Sumitomo Chemical Co. Ltd. ; IRGANOX 1010 (tradename), IRGANOX HP2225FF (tradename), IRGAFOS 168 (trade name) and IRGANOX 1520 (trade name) manufactured by Ciba Specialty Chemicals Inc.; and JF77 (trade name) manufactured byJohoku Chemical Co. , Ltd. These stabilizers canbeusedalone, or in combination.

[0054]

The hot melt adhesive for disposable products of the present invention can further include a fine particle filler. The fine particle fillermaybe commonly used fine particle filler, and there is no particular limitation as long as the objective hot melt adhesive of the present invention can be obtained. Examples of the " fine particle fi l ler" include mica , cal cium carbonate, kaolin, talc, titanium oxide, diatomaceous earth, urea-based resin, styrene beads, calcined clay, starch and the like. These particles preferably have a spherical shape, and there is no particular limitation on the size (diameter in case of a spherical shape) .

[0055]

The hot melt adhesive for disposable products of the present invention can be produced by blending the components (A) and (B) , optionally bleinding the components (C) - (E) , if necessaryblending the various additives, andmelting the mixture with heating, followed by mixing. Specifically, the hot melt adhesive can be produced by charging the above components in a melt-mixing vessel equipped with a stirrer, followed by heating and mixing. [0056]

With regard to the hot melt adhesive for disposable products according to the present invention, a melt viscosity at 140 °C is preferably 8,000 mPa- s or less , more preferably from 2,000 to 7,000 mPa-s, and particularly preferably from 2,000 to 6, 000 mPa*s. The "melt viscosity" is a viscosity of a melt of the hot melt adhesive and is measured by a Brookfield RVT-type viscometer (spindle No. 27) .

[0057]

By controlling the melt viscosity within the above range, the hot melt adhesive is suitable for low-temperature coating. Furthermore, the hot melt adhesive is uniformly applied to a nonwoven fabric and is likely to penetrate, and thus the adhesive is more suitably for use in disposable products .

[0058]

As mentioned above, the hot melt adhesive according to the present invention can also be employed in paper processing, bookbinding, disposable products and the like , and it is suitably used in disposable products since it is excellent in adhesion to a nonwoven fabric and a polyolefin film (preferably a polyethylene film) .

[0059]

The disposable products can be constituted by coating at least one kind of a member selected from a group consisting of a woven fabric, a nonwoven fabric, a rubber, a resin, papers and a polyolefin film with the hot melt adhesive according to the present invention. The polyolefin film is preferably a polyethylene film for the reason of durability, costs and the like.

There is no particular limitation on the disposable products as long as they are so-called sanitary materials. Specific examples thereof include a paper diaper, a sanitary napkin, a pet sheet, a hospital gown, a surgical white garment and the like.

[0060]

In the production line of the disposable products , various members (for example, tissue, cotton, nonwoven fabric, polyolefin film, etc.) of the disposable products are commonly coated with the hot melt adhesive. In case of coating, the hot melt adhesive may be discharged (or ejected) from various dischergers (or ejectors) .

[0061]

There is no particular limitation on the method of coating with the hot melt adhesive as long as the objective disposable products can be obtained. Such a coating method is roughly classified into a contact coating method and a non-contact coatingmethod . The "contact coating" method refers to a coating method in which a discharger is brought into contact with a member or a film in case of coating with the hot melt adhesive, while the "non-contact coating" method refers to a coating method in which a discharger is not brought into contact with a member or a film in case of coating with the hot melt adhesive . Examples of the contact coatingmethod include a slot coater coatingmethod, a roll coater coating method and the like, and examples of the non-contact coating method include a spiral coating capable of coating in a spiral form, an omega coating or control seam coating method capable of coating in a wavy form, a slot spray coating or curtain spray coating method capable of coating in a plane form, and dot coating capable of coating in a dot form.

[0062]

The hot melt adhesive of the present invention is suitable for spiral coating. The spiral coating method is a method in which an adhesive is applied by intermittent or continuous application, wherein the adhesive is applied in a spiral form using air without contact.

It is extremely useful for the production of the disposable products that the hot melt adhesive can be applied in a wide width by the spray coating. The hot melt adhesive capable of being applied in a wide width is capable of decreasing the coating width by adjusting the pressure of the hot air.

[0063]

When it is difficult to apply the hot melt adhesive in a wide width, a lot of spray nozzles for obtaining sufficient bonding area are required, and thus it is unsuitable for the production of comparatively small disposable products such as a urine collection liner, and disposable products having a complicated shape.

Therefore, the hot melt adhesive of the present invention is suitable for the disposable products since the spiral coating can be performed in a wide width.

[0064]

The hot melt adhesive of the present invention is useful for theproductionof disposableproducts because of satisfactory coatability at about 140°C. In case of coating with the hot melt adhesive at a high temperature, since a polyolefin film (preferably a polyethylene film) as a base material of the disposable products is melted and thermally shrinks, appearance of the disposable products is drastically impaired. In case of applying the hot melt adhesive at about 140°C, appearance of a nonwoven fabric and a polyolefin film (preferably a polyethylene film) as a base material of the disposable products scarcely changes and thus the appearance of the product is not impaired.

[0065]

The hot melt adhesive of the present invention is suitable for the production of the disposable products within a short time since it is excellent in high-speed coatability. When the base material to be transported at a high speed is coated with the hot melt adhesive, breakage of the base material due to friction may arise in the contact type coating method. The hot melt adhesive of the present invention is suitable for the spiral coating as a kind of non-contact coating and is therefore suited for high-speed coating, and thus it is possible to improve the productionefficiencyof the disposable products . Furthermore, the hot melt adhesive of the present invention suited for high-speed coating hardly cause disorder of the coating pattern.

[0066]

The hot melt adhesive of the present invention has satisfactory thermal stability and is uniformly melted in a high-temperature tank at 100 to 200°C and does not cause phase separation. A hot melt adhesive having poor thermal stability easily cause phase separation of components in the

high-temperature tank. The phase separation can cause clogging of a tank filter and a transfer piping.

[0067]

Main embodiments of the present invention are shown below.

1. A hot melt adhesive including: (A) a thermoplastic block copolymer which is a copolymer of a vinyl-based aromatic hydrocarbonwith a conjugated diene compound; and (B) a propylene homopolymer having a melting point of 100°C or lower which is obtainable by polymerizing propylene using a metallocene catalyst.

2. The hot melt adhesive according to the above 1, wherein the thermoplastic block copolymer (A) contains at least one selected from: (Al) a hydrogenated styrene-butadiene block copolymer (SEBS) ; and (A2) ahydrogenated styrene-isoprene block copolymer (SEPS) .

3. The hot melt adhesive according to the above 1 or 2 , wherein the propylene homopolymer (B) includes at least one selected from: (Bl) a propylene homopolymer having a weight average molecular weight of 60,000 or less; and (B2) a propylene homopolymer having a weight average molecular weight of more than 60, 000.

4. The hot melt adhesive according to any one of the above 1 to 3 , further including: (C) a tackifying resin; and (D) a plasticizer, wherein the plasticizer (D) contains at least one selected from: (Dl) a naphthene oil; and (D2) a paraffin oil. 5. Disposable products obtainable by using the hot melt adhesive according to any one of the above 1 to 4.

Examples

[0068]

The present invention will be descried for the purpose of describing the present invention inmore detailed and specific manner by way of Examples. These are exemplary of the present invention and are not to be considered as limiting.

Components for blending a hot melt adhesive are shown below.

[0069]

(A) Thermoplastic block copolymer (Al) SEBS (having a styrene content of 12% by weight, manufacturedbyAsahi Kasei Chemicals Corporationunder the trade name of TAFTEC H1221)

(A2) SEPS (having a styrene content of 13% by weight, manufactured by Kuraray Co. , Ltd. under the trade name of SEPTON 2603)

(A3) SIS (having a styrene content of 16% by weight, manufactured by Zeon Corporation under the trade name of Quintac 3433N)

(A4) SBS (having a styrene content of 40% by weight, manufacturedbyAsahi Kasei Chemicals Corporationunder the trade name of Asaprene T439)

[0070]

(B) Propylene homopolymer having a melting point 100°C or lower which is obtained by polymerization using a metallocene catalyst

(Bl) Crystalline propylene homopolymer having a melting point of 75°C and a weight average molecular weight of 45,000, manufactured by Idemitsu Kosan Co., Ltd. under the trade name of "L-MODU X400S"

(B2) Crystalline propylene homopolymer having a melting point of 80°C and a weight average molecular weight of 70,000, manufactured by Idemitsu Kosan Co. , Ltd. under the trade name of "L-MODU X600S"

(Β' 3) Crystalline propylene homopolymer having a melting point of 145°C, manufactured by Clariant K.K. under the trade name of Licocene PP6102

(B'4) Crystalline ethylene/octene copolymer having a melting point 100°C, manufactured by Dow Chemical Company under the trade name of AFFINITY GA1950

(B' 5) Crystalline ethylene/propylene copolymer having a melting point of 145°C, manufactured by Clariant K.K. under the trade name of Licocene PP2602

(B' 6) Amorphous ethylene/propylene copolymer,

manufactured by Huntsman Corp. under the trade name of REXtac 2304

[0071]

(C) Tackifier resin

(CI) Hydrogenated tackifier resin, manufactured by Exxon Mobil Corporation under the trade name of ECR5400

(C2) Hydrogenated tackifier resin, manufactured by Exxon

Mobil Corporation under the trade name of ECR179X

(C3) Unhydrogenated tackifier resin, manufactured by Zeon Corporation under the trade name of Quintone DX395

(C4) Hydrogenated tackifier resin, manufactured by Arakawa Chemical Industries, Ltd. under the trade name of AlconMlOO

(C5) Liquid tackifier resin, manufactured by Maruzen Chemicals Co., Ltd. under the trade name of Maruca Clear-H

[0072]

(D) Plasticizer (Dl) Naphthene oil, manufactured by Idemitsu Kosan Co. , Ltd. under the trade name of Process oil NS100

(D2) Naphthene oil, manufactured by PetroChina Company under the trade name of KN4010

(D3) Paraffin oil, manufactured by Idemitsu Kosan Co.,

Ltd. under the trade name of Diana Process Oil PW90

[0073]

(E) Wax

(El) Maleic acid-modified wax, manufactured by Clariant K.K. under the trade name of Licocene PP MA6252

(F) Additive

(Fl) Antioxidant, manufactured byADEKA Corporation under the trade name of Adekastab AO60

[0074]

These components were blended according to the formulations shown in Tables 1 and 2, and then melt-mixed at about 150 °C over 3 hours using a universal stirrer to prepare hot melt adhesives of Examples 1 to 7 and Comparative Examples 1 to 7.

With respect to the above respective hot melt adhesives, melt viscosity, peel strength and coatability were evaluated. Summary of the respective evaluations is shown below.

[0075]

<Melt Viscosity (mPa-s)>

A hot melt adhesive was melted at 140°C and 160°C and, after 20 minutes, viscosity was measured by a No. 27 rotor using a Brookfield viscometer. The evaluation criteria are as follows.

Melt Viscosity at 140°C

A: 2,000 mPa · s to 6,000 mPa-s

B: 1,000 mPa-s or more and less than 2,000 mPa-s, or more than 6,000 mPa-s and less than 10,000 mPa-s

C: less than 1,000 mPa-s or 10,000 mPa-s or more

Melt Viscosity at 160°C

A: 500 mPa-s to 3,000 mPa · s

B: more than 3,000 mPa-s and 7,000 mPa-s or less

C: less than 500 mPa-s or more than 7,000 mPa-s

[0076]

<Peel Strength Test>

(Production of Samples)

A nonwoven fabric was coated with a hot melt adhesive in a coating amount of 5 g/m ² . Using a slot coater, coating was carriedout at a temperature of 140 °C . The nonwoven fabric coated with the hot melt adhesive was laied on another nonwoven fabric through the hot melt adhesive, followed by pressing under a pressure of 0.5 kgf/cm to obtain a sample (nonwoven

fabric/nonwoven fabric) .

Furthermore, a nonwoven fabric coated with a hot melt adhesive was laid on a polyethylene (PE) film through the hot melt adhesive, followedbypressingunder apressure of 0.5 kgf/cm to obtain another sample (nonwoven fabric/PE film) .

[0077]

(Test Procedure)

Both the nonwoven fabric/nonwoven fabric sample and the nonwoven fabric/PE film sample were cut into a width of 25 mm in a direction (CD direction) vertical to the direction of movement of the base material , and thenpeel strengthwas measured by T type peeling using a universal tensile testing machine

(manufactured by JT Toshi Inc . ) . The measurement was performed by a universal tensile testing machine under an environment of 20°C, 65% Rh and a peeling rate of 300 mm/minute.

Peel Strength between Nonwoven Fabric and PE Film

A: Average peel strength was more than 200 (g/25 mm) .

B: Average peel strength was from 150 to 200 (g/25 mm). C: Average peel strength between PE film and nonwoven fabric was less than 150 (g/25 mm) .

Peel Strength between Nonwoven Fabric and Nonwoven Fabric A: Material fracture (or base material failure)

B: Average peel strength is from 150 to 200 (g/25 mm) .

C: Average peel strength is less than 150 (g/25 mm) .

[0078]

<Coatability>

Using a spiral spray manufactured by Nordson Corporation, a coating base material was coated with a hot melt adhesive to produce a laminate of the coated coating base material and an affixing (or laminating) base material, and coatability was evaluated. Both the coating base material and affixing base material are polyethylene terephthalate (PET) films.

More specifically, after setting at a temperature (i.e. coating temperature) at which melt viscosity of the hot melt adhesive becomes 5,000 mPa · s , the spiral spray (manufactured by Nordson Corporation) was mounted at a position (height of 30 mm from a PET film) and then the PET film as a coating base material was coated with the hot melt adhesive at an open time of 0.5 seconds in a coating weight of 15 g/m ² while appropriately adjusting an air pressure, and the coated PET film was laid on a PET film as an affixing base material to produce a laminate (PET film/PET film) , and then coatability was evaluated.

Spiral coatability was evaluated by confirming a coating width of the hot melt adhesive applied by the spiral coating. High-speed line coatability was evaluated by confirming a situation of scattering of the hot melt adhesive applied by the spiral coating.

[0079]

Evaluation criteria are shown below.

Spiral Coatability

The coatability on the spiral coating (or spiral coatability) was evaluated by a balance between the air pressure of the spiral spray and the spiral width of the applied hot melt adhesive. A: Spiral width of 15 mm was possible under the air pressure of 0.35 kgf/cm ² or less.

B: Spiral width of 15 mm was possible under the air pressure of more than 0.35 kgf/cm ² and 0.40 kgf/cm ² or less.

C: Spiral width of 15 mm was impossible even by controlling the air pressure.

High-Speed Line Coatability

Furthermore, the high-speed line coatability was evaluatedby the airpressure of thespiral sprayand the situation of scattering of the applied hot melt adhesive.

A: Hot melt adhesive did not cause scattering under the air pressure of 0.55 kgf/cm ² .

B: Hot melt adhesive did not cause scattering under the air pressure of 0.50 kgf/cm ² .

C: Hot melt adhesive caused scattering under the air pressure of 0.40 kgf/cm ² or less.

[0080]

[Table 1]

[0081]

[Table 2]

[0082]

As shown in Table 1, the hot melt adhesives of Examples 1 to 7 is suited for spiral coating because of low melt viscosity at 140°C, andtheycanbe used inahigh-speed line since scattering is less likely to arise under high hot air pressure, and is also excellent in peel strength to a nonwoven fabric (nonwoven fabric/nonwoven fabric, nonwoven fabric/PE film) . Therefore, the hot melt adhesives of Examples 1 to 7 are suitable for disposable products such as a diaper and sanitaryproducts , which are typical nonwoven fabric products .

As shown in Table 2, the hot melt adhesives of Comparative Examples 1 to 7 are inferior in any one of melt viscosity, coatability and peel strength as compared with the adhesives of Examples 1 to 5. The hot melt adhesives of Examples 1 to 7 are more suitable for disposable products as compared with the hot melt adhesives of Comparative Examples 1 to 7.

Industrial Applicability

[0083]

The present invention provides a hot melt adhesive. The hot melt adhesive according to the present invention is suited for disposable products.