Hot melt adhesive

Abstract

To provide a hot-melt adhesive which is excellent in low temperature coating property and creep resistance, has a good balance between tackiness and cohesive force, and can bond and hold a stretchable material to a non-woven fabric and a plastic film.SOLUTION: A hot-melt adhesive contains (A) a thermoplastic block copolymer that is a copolymer of a vinyl-based aromatic hydrocarbon and a conjugated diene compound, (B) a tackifier resin, and (C) a plasticizer, wherein (A) the thermoplastic block copolymer contains the following component (A1) and component (A2): (A1) a styrene isoprene block copolymer having a styrene percentage content higher than 40 mass%; and (A2) a styrene isoprene block copolymer having a styrene percentage content higher than 15 mass% and lower than 30 mass%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a hot-melt adhesive, and more particularly to a hot-melt adhesive used in the field of disposable products typified by paper diapers and napkins.

Background Art

[0002] Hot-melt adhesives are used in disposable products typified by paper diapers and napkins. The hot-melt adhesive is applied to substrates such as non-woven fabrics, tissues, and polyethylene films, and disposable products are manufactured by combining these multiple substrates.

[0003] Examples of hot-melt adhesives mainly include synthetic rubber-based hot-melt adhesives containing a thermoplastic block copolymer as a main component, and olefin-based hot-melt adhesives typified by ethylene / propylene / butene copolymers. Considering coating properties and cohesive strength, etc., synthetic rubber-based hot-melt adhesives may be used rather than olefin-based adhesives.

[0004] Generally, a hot-melt adhesive contains a base polymer and a plasticizer. It has been studied to reduce the viscosity of the hot-melt adhesive and improve coating suitability by reducing the amount of the base polymer and increasing the amount of the plasticizer.

[0005] However, a hot-melt adhesive containing a large amount of a plasticizer has a problem that the balance between cohesive strength and tack is poor, and the adhesiveness to a paper diaper member (for example, a polyethylene film) etc. decreases.

[0006] As a type of paper diaper, there is one incorporating rubber thread. When adhering the stretched rubber thread to the paper diaper body, a hot-melt adhesive is used. Since the paper diaper body is made of a material without elasticity, the paper diaper body with the rubber thread adhered is folded by the contraction force of the rubber thread when the rubber thread contracts. As a result, the stretching and contracting force of the rubber thread is imparted to the paper diaper body, and the paper diaper can fit the body.

[0007] Hot-melt adhesives used to bond elastic materials such as elastic threads to the diaper body must have excellent creep resistance. If a hot-melt adhesive with insufficient creep resistance is used to bond an elastic material to the diaper body, the hot-melt adhesive will stretch due to the contraction force of the elastic material, and will no longer be able to hold the elastic material in place on the diaper body. As a result, only the elastic material will contract without the diaper body, and even if the elastic material contracts, the diaper body will not fold, and the diaper will no longer fit the body. Therefore, excellent creep resistance is required for hot-melt adhesives.

[0008] Patent documents 1 to 3 disclose synthetic rubber-based hot-melt adhesives based on styrene-based block copolymers.

[0009] Patent Document 1 discloses a hot melt adhesive comprising a styrene-based block copolymer and an amorphous wax modified with a carboxylic acid anhydride ([Claim 1]). Patent Document 1 also discloses a hot melt adhesive that has improved wet creep resistance, excellent low-temperature coating properties and adhesion, and reduced odor (

[0012]

[0018] ).

[0010] However, the hot-melt adhesive described in Patent Document 1 does not have sufficient creep resistance to hold the stretched elastic material in place at the bonding position, making it difficult to use for applications where the elastic material is incorporated into disposable products.

[0011] Patent Document 2 describes a hot-melt adhesive containing a radial styrene block copolymer and a linear styrene block copolymer ([Claim 1]). The hot-melt adhesive of Patent Document 2 allows for low-temperature coating and has excellent creep resistance (

[0013]

[0020] ). However, consumers have recently been demanding better performance for low-temperature coating.

[0012] Patent Document 3 discloses a hot melt composition containing a styrene-based block copolymer and a plasticizer, but without a tackifying resin (Table 1,

[0093] ). Patent Document 3 states that the content of the tackifying resin in the hot melt composition is preferably 30% by mass or less. By lowering the content of the tackifying resin, the hot melt composition does not become too hard and the recovery of expansion and contraction after stretching is improved (

[0050] ). However, because the content of the tackifying resin is too low, the hot melt composition of Patent Document 3 has a poor balance between tack and cohesive force, and its melt viscosity is high, making it unsuitable for low-temperature coating. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] Japanese Patent Publication No. 2016-153448 [Patent Document 2] Japanese Patent Publication No. 2016-44289 [Patent Document 3] Republished Gazette No. WO2020 / 110921 [Overview of the project] [Problems that the invention aims to solve]

[0014] Hot-melt adhesives used to fix stretchable materials to disposable product bodies contain a relatively large amount of styrene block copolymer to enhance cohesive force and achieve creep resistance. However, a higher styrene block copolymer content tends to result in hot-melt adhesives with higher melt viscosity and inferior low-temperature coating properties compared to general assembly adhesives.

[0015] In recent years, when manufacturing disposable products, there has been an emphasis on reducing manufacturing costs and environmental impact, as well as maintaining a soft texture. As a result, the materials used in disposable products, such as elastic threads and nonwoven fabrics, have become thinner, and the plastic films have become thinner. Because such delicate materials are susceptible to thermal degradation, hot-melt adhesives require a higher level of low-temperature coating properties.

[0016] Thus, there is a demand for hot-melt adhesives for holding stretchable materials that offer good low-temperature coating properties, creep resistance, and a good balance of tack and cohesive force.

[0017] The present invention has been made to solve the aforementioned problems and aims to provide a hot melt adhesive that has excellent low-temperature coating properties and creep resistance, a good balance of tack and cohesive force, and can adhere and hold stretchable materials to nonwoven fabrics and plastic films, as well as disposable products obtained using the hot melt adhesive. [Means for solving the problem]

[0018] The present invention and preferred embodiments are as follows. 1. A hot melt adhesive comprising (A) a thermoplastic block copolymer which is a copolymer of a vinyl aromatic hydrocarbon and a conjugated diene compound, (B) a tackifying resin, and (C) a plasticizer, (A) Hot melt adhesives in which the thermoplastic block copolymer contains the following components (A1) and (A2): (A1) Styrene isoprene block copolymer having a styrene content higher than 40% by mass; and (A2) A styrene-isoprene block copolymer having a styrene content higher than 15% by mass and lower than 30% by mass.

[0019] 2. The hot melt adhesive according to claim 1, wherein component (A1) contains a linear styrene-isoprene block copolymer and component (A2) contains a linear styrene-isoprene block copolymer.

[0020] 3. The hot melt adhesive according to 1 or 2, wherein component (A1) has a weight-average molecular weight of 50,000 to 150,000.

[0021] 4. A hot melt adhesive according to any one of 1 to 3, wherein component (A1) is contained in an amount of 10 to 25 parts by mass and component (A2) is contained in an amount of 2 to 10 parts by mass per 100 parts by mass of the total amount of components (A) to (C).

[0022] 5. The hot melt adhesive according to any one of 1 to 4, wherein the tackifier resin (B) is contained in an amount of 45 to 70 parts by mass based on 100 parts by mass of the total amount of components (A) to (C).

[0023] 6. The hot melt adhesive according to any one of 1 to 5, which is used for fixing the stretchable material to the disposable product body.

[0024] 7. A disposable product coated with the hot melt adhesive according to any one of 1 to 6.

Advantages of the Invention

[0025] The hot melt adhesive of the present invention is excellent in low-temperature coating property and creep resistance, has a good balance between tack and cohesive force, and can adhere and hold a stretchable material to a non-woven fabric or a plastic film.

[0026] By using the hot melt adhesive of the present invention, a disposable product in which a stretchable material such as rubber thread is firmly held to a substrate can be produced.

Embodiments for Carrying Out the Invention

[0027] The hot melt adhesive of the present invention has a thermoplastic block copolymer (A) which is a copolymer of a vinyl aromatic hydrocarbon and a conjugated diene compound, a tackifier resin (B), and a plasticizer (C).

[0028] <(A) Thermoplastic block copolymer> In the hot melt adhesive of the present invention, the thermoplastic block copolymer (A) is a copolymer in which a vinyl aromatic hydrocarbon and a conjugated diene compound are block copolymerized. The thermoplastic block copolymer (A) is usually a resin composition containing a copolymer having a vinyl aromatic hydrocarbon block and a conjugated diene compound block.

[0029] Here, "vinyl aromatic hydrocarbons" refers to aromatic hydrocarbon compounds having a vinyl group, and specifically, examples include styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene, and vinylanthracene. Among these, styrene is preferred. These vinyl aromatic hydrocarbons can be used individually or in combination.

[0030] A "conjugated diene compound" refers to a diolefin compound having at least one conjugated double bond. Specific examples of "conjugated diene compounds" include, for example, 1,3-butadiene, 2-methyl-1,3-butadiene (or isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene. Among these, 1,3-butadiene and 2-methyl-1,3-butadiene are preferred. These conjugated diene compounds can be used individually or in combination.

[0031] The thermoplastic block copolymer (A) according to the present invention may be unhydrogenated or hydrogenated.

[0032] "(A) Unhydrogenated thermoplastic block copolymers" specifically refers to block copolymers in which the block based on the conjugated diene compound has not been hydrogenated. Furthermore, "(A) Hydrogenated thermoplastic block copolymers" specifically refers to block copolymers in which all or part of the block based on the conjugated diene compound has been hydrogenated.

[0033] The hydrogenation rate of "(A) Hydrogenated Thermoplastic Block Copolymer" can be expressed as the "hydrogenation rate." The "hydrogenation rate" of "(A) Hydrogenated Thermoplastic Block Copolymer" refers to the proportion of double bonds that have been hydrogenated and converted to saturated hydrocarbon bonds, based on the total aliphatic double bonds contained in the block based on the conjugated diene compound. This "hydrogenation rate" can be measured using an infrared spectrophotometer and a nuclear magnetic resonance spectrometer, etc.

[0034] Examples of "(A) Unhydrogenated thermoplastic block copolymers" include, for example, styrene-isoprene block copolymers (also known as "SIS") and styrene-butadiene block copolymers (also known as "SBS"). Examples of "(A) Hydrogenated thermoplastic block copolymers" include, for example, hydrogenated styrene-isoprene block copolymers (also known as "SEPS") and hydrogenated styrene-butadiene block copolymers (also known as "SEBS").

[0035] In the present invention, (A) thermoplastic block copolymers include linear styrene block copolymers or radial styrene block copolymers.

[0036] In this specification, "linear type" refers to a linear structure. A linear styrene block copolymer is a linear copolymer in which a styrene block and a conjugated diene block are bonded together.

[0037] A radial styrene block copolymer is a branched styrene block copolymer having a structure in which multiple linear styrene block copolymers protrude radially from a coupling agent.

[0038] The specific structure of the radial styrene block copolymer is shown below. [C1] (SE) n Y (1)

[0039] In the formula, n is an integer of 2 or more, S is a styrene block, E is a conjugated diene compound block, and Y is a coupling agent. n is preferably 3 or 4, and particularly preferably 3. As the conjugated diene compound, butadiene or isoprene is preferred.

[0040] The styrene block copolymer is a resin composition containing a certain proportion of the styrene-conjugated diene block copolymer represented by formula (2). [C2] SE (2)

[0041] In the formula, S and E have the same meanings as above. The styrene-conjugated diene block copolymer of formula (2) is sometimes called a "diblock".

[0042] The coupling agent is a polyfunctional compound that radially bonds linear styrene block copolymers. The type of coupling agent is not particularly limited.

[0043] Examples of coupling agents include silane compounds such as halogenated silanes and alkoxysilanes, tin compounds such as tin halogenates, epoxy compounds such as polycarboxylic acid esters and epoxidized soybean oil, acrylic esters such as pentaerythritol tetraacrylate, epoxysilanes, and divinyl compounds such as divinylbenzene. Specific examples include trichlorosilane, tribromosilane, tetrachlorosilane, tetrabromosilane, methyltrimethoxysilane, ethyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, tetramethoxysilane, tetraethoxysilane, tetrachlorotin, and diethyl adipate.

[0044] (A) The thermoplastic block copolymer comprises (A1) styrene-isoprene block copolymer. Component (A1) preferably has a styrene content higher than 40% by mass. Component (A1) may have a styrene content of, for example, 41-50% by mass, preferably 43-48% by mass, and more preferably 44-46% by mass.

[0045] In this specification, "styrene content" means the proportion of styrene blocks contained in a certain type of block copolymer.

[0046] By having the styrene content of component (A1) within the above range, the hot melt adhesive gains high cohesive strength, excellent creep resistance, and the ability to adhere and hold highly stretchable materials with a high elongation rate to the disposable product body.

[0047] (A) The thermoplastic block copolymer, in a preferred embodiment, further comprises a different type of (A2) styrene-isoprene block copolymer from component (A1). Component (A2) preferably has a styrene content higher than 15% by mass and lower than 30% by mass. Component (A2) may have a styrene content of, for example, 16-29% by mass, preferably 18-27% by mass, and more preferably 19-25% by mass.

[0048] By having the styrene content of component (A2) within the above range, the hot melt adhesive exhibits superior tack, maintaining a balance between cohesive force and tack while also providing better adhesion.

[0049] The hot melt adhesive of the present invention achieves a good balance between cohesive force and tack, and thus improves adhesion, because the styrene content of component (A1) and component (A2) is within the above range.

[0050] In this specification, the diblock content of component (A1) is preferably 0 to 20% by mass, and preferably 0% by mass. A linear styrene block copolymer with a diblock content of 0% by mass is defined as a triblock styrene block copolymer.

[0051] "Diblock content" refers to the proportion of the styrene-conjugated diene compound block copolymer of formula (2) contained in a certain type of block copolymer.

[0052] The diblock content of component (A2) is preferably 0 to 30% by mass, more preferably 0 to 20% by mass, and most preferably 0% by mass.

[0053] The hot melt adhesive of the present invention exhibits excellent adhesive properties due to a good balance between cohesive force and tack, as the diblock content of component (A1) and component (A2) is within the above range.

[0054] The weight-average molecular weight of component (A1) is preferably 50,000 to 150,000, particularly preferably 50,000 to 120,000, and especially desirable to be 70,000 to 100,000. The hot melt adhesive of the present invention has increased cohesive strength due to the weight-average molecular weight of component (A1) being within the above range, and while maintaining a balance between tack and cohesive strength, creep resistance and adhesiveness are further improved.

[0055] The weight-average molecular weight of component (A2) is preferably 80,000 to 500,000, particularly preferably 100,000 to 300,000, and especially desirable to be 120,000 to 200,000. The hot melt adhesive of the present invention, by having the weight-average molecular weight of component (A2) within the above range, has increased tack, and while maintaining a balance between tack and cohesive force, creep resistance and adhesiveness are further improved.

[0056] The weight-average molecular weight (Mw) refers to the value measured by gel permeation chromatography (GPC). Specifically, the value can be measured using the following apparatus and measurement method. A radioisotope (RI) detector manufactured by Tosoh Corporation is used. A TSK Gel SuperHZ-M column manufactured by Tosoh Corporation is used as the GPC column. The sample is dissolved in tetrahydrofuran and flowed at a flow rate of 0.35 ml / min and a measurement temperature of 40°C. The weight-average molecular weight is determined by converting the molecular weight using a polystyrene calibration curve.

[0057] Furthermore, since the number-average molecular weight (Mn) can also be determined using the same method, the molecular weight distribution will also be calculated using GPC. The Mw, Mn, and molecular weight distribution of other components, not just component (A1), can be determined in the same way.

[0058] Components (A1) and (A2) are preferably linear styrene block copolymers, and more preferably triblock styrene isoprene block copolymers. The hot melt adhesive of the present invention, due to the linear (triblock) structure of components (A1) and (A2), can more strongly adhere and hold elastic materials such as elastic threads to materials such as films and nonwoven fabrics of disposable products.

[0059] For component (A1), commercially available products can be used. Examples of commercially available products include GP5562U (product name) from LCY Chemical Corporation, VECTOR 4411AS (product name) from TSRC Corporation, Kraton D1162PT (product name) from Kraton Corporation, and Quintac 3191 (product name) from Nippon Zeon Corporation.

[0060] Component (A2) may be either a linear styrene-isoprene block copolymer or a radial styrene-isoprene block copolymer. The hot-melt adhesive of the present invention, by containing a linear styrene-isoprene block copolymer as component (A2), improves tack and further enhances adhesion while maintaining a balance between cohesive force and tack.

[0061] For component (A2), commercially available products can be used. Examples include JH8291 (product name) from Jinhai Chemical Corporation, Quintac 3280 (product name) and Quintac 3450 (product name) from Nippon Zeon Co., Ltd., and VECTOR 4111 (product name) from TSRC Corporation.

[0062] In the present invention, component (A) may include (A3) other styrene block copolymers (not corresponding to component (A1) or component (A2)).

[0063] In the hot melt adhesive of the present invention, component (A1) is preferably included in an amount of 5 to 40 parts by mass, more preferably 10 to 25 parts by mass, and even more preferably 13 to 22 parts by mass, based on 100 parts by mass of the total amount of components (A), (B), and (C). By having the above content of component (A1) within the above range, the cohesive strength of the hot melt adhesive is further improved and the creep resistance is improved.

[0064] In the hot melt adhesive of the present invention, component (A2) is preferably included in an amount of 0.5 to 20 parts by mass, more preferably 2 to 10 parts by mass, and even more preferably 3 to 9 parts by mass, based on 100 parts by mass of the total amount of components (A), (B), and (C). By having the above content of component (A2) within the above range, the tack of the hot melt adhesive is further improved and the adhesive strength is enhanced.

[0065] <(B) Tackifying resin> The hot melt adhesive of the present invention comprises (B) a tackifying resin. The tackifying resin (B) is not particularly limited as an additive to the hot melt adhesive, as long as it achieves the objectives of the present invention, but it is preferably a hydrogenated resin.

[0066] (B) Examples of tackifying resins include natural rosin, modified rosin, hydrogenated rosin, glycerol ester of natural rosin, glycerol ester of modified rosin, pentaerythritol ester of natural rosin, pentaerythritol ester of modified rosin, pentaerythritol ester of hydrogenated rosin, copolymers of natural terpenes, three-dimensional polymers of natural terpenes, hydrogenated derivatives of copolymers of hydrogenated terpenes, polyterpene resins, hydrogenated derivatives of phenolic modified terpene resins, aliphatic petroleum hydrocarbon resins, hydrogenated derivatives of aliphatic petroleum hydrocarbon resins, aromatic petroleum hydrocarbon resins, hydrogenated derivatives of aromatic petroleum hydrocarbon resins, cyclic aliphatic petroleum hydrocarbon resins, hydrogenated derivatives of cyclic aliphatic petroleum hydrocarbon resins, and the like.

[0067] These tackifying resins can be used individually or in combination. Liquid tackifying resins can also be used, provided they are colorless to pale yellow, substantially odorless, and have good compatibility with other components. Considering these characteristics comprehensively, hydrogenated derivatives of petroleum hydrocarbon resins are preferred as tackifying resins, and hydrogenated dicyclopentadiene resins are particularly desirable.

[0068] In the present invention, (B) commercially available tackifying resins include T-Rez HA103 (product name), T-Rez HB125 (product name), T-Rez HC103 (product name) from JXTG Corporation, HD1120 (product name), HD1100 (product name) from Zibo Luhua Hongjin New Material Corporation, ECR5600 (product name) from ExxonMobil Corporation, Easttack H130 (product name), Plastolyn 290LV (product name) from Eastman Corporation, SUKOREZ SU420 (product name), SUKOREZ SU400 (product name) from Colon Corporation, iMarb S100 (product name), iMarb P125 (product name) from Idemitsu Kosan Corporation, and Alcon M100 (product name), Alcon P115 (product name) from Arakawa Chemical Industries, Ltd.

[0069] In the hot melt adhesive of the present invention, (B) the tackifying resin is preferably included in an amount of 40 to 70 parts by mass, more preferably 45 to 65 parts by mass, based on 100 parts by mass of the total amount of components (A), (B), and (C).

[0070] The hot melt adhesive of the present invention has a better balance between cohesive force and tack by including (B) a tackifying resin within the above range.

[0071] <(C) Plasticizer> The hot melt adhesive of the present invention preferably contains (C) a plasticizer in addition to components (A) and (B). The plasticizer is added for the purpose of reducing the melt viscosity of the hot melt adhesive, imparting flexibility, and improving wettability to the adherend, thereby improving the coatability of the hot melt adhesive.

[0072] (C) Examples of plasticizers include paraffinic oils, naphthenic oils, and aromatic oils.

[0073] Commercially available plasticizers can be used. Examples include White Oil Broom 350 (product name) from Kukdong Oil & Chem, Diana Fresia S32 (product name), Diana Process Oil PW-90 (product name), DN Oil KP-68 (product name) from Idemitsu Kosan, Enerper M1930 (product name) from BP Chemicals, Kaydol (product name) from Crompton, Primol 352 (product name) from Esso, Process Oil NS100 from Idemitsu Kosan, and KN4010 (product name) from PetroChina Company. These plasticizers can be used individually or in combination.

[0074] In the hot melt adhesive of the present invention, (C) plasticizer is preferably included in an amount of 10 to 30 parts by mass, more preferably 15 to 25 parts by mass, based on 100 parts by mass of the total amount of components (A), (B), and (C).

[0075] The hot melt adhesive of the present invention, by containing (C) a plasticizer within the above range, has a lower melt viscosity and is suitable for low-temperature coating.

[0076] The hot-melt adhesive according to the present invention may further contain various additives as needed. Examples of such additives include stabilizers and particulate fillers.

[0077] A stabilizer is added to a hot-melt adhesive to prevent molecular weight reduction, gelation, discoloration, odor generation, etc., caused by heat, thereby improving the stability of the hot-melt adhesive. The stabilizer is not particularly limited as long as it can produce the hot-melt adhesive intended by the present invention. Examples of stabilizers include antioxidants and ultraviolet absorbers.

[0078] UV absorbers are used to improve the light resistance of hot melt adhesives. Antioxidants are used to prevent oxidative degradation of hot melt adhesives. Antioxidants and UV absorbers are generally used in disposable products and can be used as long as they can produce the disposable products intended for the purposes described below; there are no particular restrictions.

[0079] Examples of antioxidants include phenolic antioxidants, sulfur-based antioxidants, and phosphorus-based antioxidants. Examples of UV absorbers include benzotriazole-based UV absorbers and benzophenone-based UV absorbers. Furthermore, lactone-based stabilizers may also be added. These can be used individually or in combination.

[0080] Commercially available stabilizers can be used. Examples include Sumirizer GM (trade name), Sumirizer TPD (trade name), and Sumirizer TPS (trade name) from Sumitomo Chemical Co., Ltd., Irganox 1010 (trade name), Irganox HP2225FF (trade name), Irgaphos 168 (trade name), and Irganox 1520 (trade name) from Ciba Specialty Chemicals, and JF77 (trade name) from Johoku Chemical Co., Ltd. These stabilizers can be used alone or in combination.

[0081] The hot-melt adhesive of the present invention is manufactured by blending the above components in predetermined proportions, adding various additives as needed, heating, melting, and mixing them. Specifically, it is manufactured by putting the above components into a melting and mixing vessel equipped with a stirrer, and heating and mixing them.

[0082] The resulting hot-melt adhesive has a softening point preferably of 85°C or higher, more preferably of 90°C or higher, and even more preferably of 95°C or higher. The hot-melt adhesive of the present invention exhibits excellent creep resistance because its softening point is within the above range.

[0083] The "softening point" is measured using the ring and ball method (a method described in the Japan Adhesives Industry Association standard JAI-7-1999).

[0084] The obtained hot-melt adhesive has a melt viscosity at 140°C that is preferably less than 7,000 mPa·s, more preferably less than 6,500 mPa·s, and even more preferably less than 6,000 mPa·s. The hot-melt adhesive of the present invention exhibits excellent low-temperature coating properties due to its melt viscosity being within the above range.

[0085] "Melt viscosity" refers to the viscosity of the molten hot-melt adhesive. It is measured using a Brookfield RVT viscometer (spindle No. 27).

[0086] Furthermore, in the creep resistance evaluation method described in the examples, the strain measured by dynamic viscoelasticity measurement of the hot melt adhesive according to the present invention is preferably less than 8%, more preferably less than 5%. When the strain of the hot melt adhesive is less than 8%, it becomes possible to stretch and contract non-elastic materials by bonding and holding a stretched rubber thread, making it suitable for disposable product applications.

[0087] The hot-melt adhesive according to the present invention has a wide range of applications, including paper processing, bookbinding, and disposable products, but is primarily used in disposable products. "Disposable products" are not particularly limited to so-called sanitary materials. Specific examples of sanitary materials include disposable diapers, sanitary napkins, pet sheets, hospital gowns, and surgical scrubs.

[0088] The hot-melt adhesive of the present invention is preferably used to bond stretched stretch material to the product body when manufacturing the above-mentioned disposable product that incorporates a stretchable material.

[0089] In another aspect of the present invention, a disposable product obtained by applying the above-described hot-melt adhesive is provided. The disposable product is constructed by bonding at least one member selected from the group consisting of woven fabrics, nonwoven fabrics, rubber, resins, and paper, and a polyolefin film using the hot-melt adhesive according to the present invention. The polyolefin film is preferably a polyethylene film for reasons such as durability and cost.

[0090] In the manufacturing line for disposable products, a hot melt adhesive is generally applied to at least one of the various components of the disposable product (e.g., nonwoven fabric) or polyolefin film, and the film and component are pressed together to produce the disposable product. During application, the hot melt adhesive may be dispensed from various types of dispensers.

[0091] In the present invention, the coating may be either contact coating or non-contact coating.

[0092] "Contact coating" refers to a method of applying hot melt adhesive in which the sprayer is brought into contact with the material or film. A specific example of this is V-slit coating.

[0093] "Non-contact coating" refers to a method of applying hot melt adhesive without the sprayer coming into contact with the material or film. Specific examples of non-contact coating methods include spiral coating, which allows for spiral application; omega coating and control seam coating, which allow for wave-like application; slot spray coating and curtain spray coating, which allow for surface application; and dot coating, which allows for dot-like application. [Examples]

[0094] The present invention will be described in detail below with reference to examples and comparative examples. However, these examples represent only one aspect of the present invention, and the present invention is not limited in any way by these examples. In the descriptions of the examples, unless otherwise specified, portions that do not consider the solvent are based on parts by mass and mass percent.

[0095] The components used in this example are shown below. (A) Thermoplastic block copolymer (A1) Styrene isoprene block copolymer having a styrene content higher than 40% by mass (A1-1) Linear styrene-isoprene block copolymer (GP5562U (trade name), styrene content 45% by mass, diblock content 0% by mass (triblock content 100% by mass), weight-average molecular weight 94600, manufactured by LCY Chemical Corporation)

[0096] (A1-2) Linear styrene-isoprene block copolymer (Vector4411AS (trade name), styrene content 44% by mass, diblock content 0% by mass (triblock content 100% by mass), weight-average molecular weight 95100, manufactured by TSRC Corporation)

[0097] (A1-3) Linear styrene-butadiene block copolymer (Kraton 1162PT (trade name), styrene content 41% by mass, diblock content 0% by mass, weight-average molecular weight 96100, manufactured by Kraton)

[0098] (A2) Styrene isoprene block copolymer having a styrene content higher than 15% by mass and lower than 30% by mass (A2-1) Linear styrene-isoprene block copolymer (JH8291 (trade name), styrene content 29% by mass, diblock content 0% by mass (triblock content 100% by mass), weight-average molecular weight 134,000, manufactured by Jinhai Chemical Corporation)

[0099] (A2-2) Linear styrene-isoprene block copolymer (Quintac 3280 (trade name), styrene content 25% by mass, diblock content 17% by mass, weight-average molecular weight 125,000, manufactured by Nippon Zeon Co., Ltd.)

[0100] (A2-3) Linear styrene-isoprene block copolymer (Vector4111 (trade name), styrene content 18% by mass, diblock content 0% by mass (triblock content 100% by mass), weight-average molecular weight 175,000, manufactured by TSRC Corporation)

[0101] (A2-4) Radial-type styrene-isoprene block copolymer (Quintac 3450 (trade name), styrene content 19% by mass, diblock content 30% by mass, weight-average molecular weight 194,000, manufactured by Nippon Zeon Co., Ltd.)

[0102] (A3) Styrene block copolymer that does not fall under component (A1) or component (A2). (A3-1) Linear styrene-butadiene block copolymer (Asaprene T439 (trade name), styrene content 43% by mass, diblock content 60% by mass, weight-average molecular weight 71000, manufactured by Asahi Kasei Chemicals)

[0103] (A3-2) Linear styrene-butadiene block copolymer (GP3566 (trade name), styrene content 30% by mass, diblock content 10% by mass, weight-average molecular weight 112,000, manufactured by LCY Chemical Corporation)

[0104] (A3-3) Linear styrene-ethylene-butadiene-styrene block copolymer (Kraton 1726MS (trade name), styrene content 30% by mass, diblock content 70% by mass, weight-average molecular weight 44000, manufactured by Kraton)

[0105] (A3-4) Linear styrene-butadiene block copolymer (GP3566 (trade name), styrene content 23% by mass, diblock content 77% by mass, weight-average molecular weight 106,000, manufactured by LCY Chemical Corporation)

[0106] (B) Tackifying resin (B1) Hydrogenated dicyclopentadiene resin (HD1100 (product name), softening point 100℃, manufactured by Zibo Luhua Hongjin New Material Corporation)

[0107] (B2) Hydrogenated dicyclopentadiene resin (HD1120 (trade name), softening point 120°C, manufactured by Zibo Luhua Hongjin New Material Corporation)

[0108] (B3) Hydrogenated dicyclopentadiene resin (iMarb S100 (product name), softening point 100℃, manufactured by Idemitsu Kosan Co., Ltd.)

[0109] (C) Plasticizer (C1) Naphthenic oil ("KN4010" (product name), manufactured by PetroChina)

[0110] (D) Antioxidant (D1) Phenolic antioxidant (Irganox 1010, manufactured by BASF)

[0111] (D2) Phosphate-based antioxidant (Everfos168GF, manufactured by Everspring Chemical Co., Ltd.)

[0112] [Preparation of hot melt adhesives in examples and comparative examples] The hot melt adhesives for the examples and comparative examples were prepared by mixing components (A) to (D) as shown in Table 1 or 2, and melting and mixing them using a universal stirrer at approximately 150°C for 2 hours. All numerical values ​​regarding the composition (formulation) of the hot melt adhesives shown in the table are in parts by mass.

[0113] [Table 1]

[0114] [Table 2]

[0115] The hot-melt adhesives of the examples and comparative examples obtained in this manner were investigated for their softening point, melt viscosity (low-temperature coating properties), peel strength, loop tack, holding power, and creep resistance. The evaluation results are shown in the table. The above properties were evaluated by the following method.

[0116] <Softening point (heat resistance)> The softening point of the hot melt adhesive was measured using the ring and ball method (the method described in the Japan Adhesive Industry Association standard JAI-7-1999). The evaluation criteria are shown below.

[0117] A (Excellent): Softening point is 95°C or higher B (Good): Softening point 90°C or higher, but less than 95°C. C (Acceptable): Softening point is 85°C or higher, but less than 90°C. D (Not acceptable): Softening point is below 85°C

[0118] <Melting viscosity (low-temperature coating properties)> The hot-melt adhesive was heated and melted at 140°C, and its viscosity was measured using a Brookfield-type RVT viscometer with rotor number 27. The evaluation criteria are shown below.

[0119] A (Excellent): Melt viscosity at 140°C is less than 6000 mPa·s. B (Good): Melt viscosity at 140°C is 6000 mPa·s or higher and less than 6500 mPa·s. C (acceptable): Melt viscosity at 140°C is 6500 mPa·s or higher and less than 7000 mPa·s. D (Not acceptable): Melt viscosity at 140°C is 7000 mPa·s or higher.

[0120] <Peel strength (adhesion)> A 50 μm thick adhesive layer was prepared by applying hot-melt adhesive to a 50 μm thick polyethylene terephthalate (PET) film. This layer was then molded to a width of 25 mm to serve as the test specimen. This test specimen was laminated to a 100 μm thick polyethylene film at room temperature. During lamination, a 2 kg roller was applied to the PET film at a speed of 5 mm / second. After leaving the test specimen at room temperature for 12 hours, it was peeled off in a 180° direction at 25°C and a tensile speed of 300 mm / min, and the strength at which the test specimen peeled off the polyethylene (PE) film was measured. The evaluation criteria are shown below.

[0121] A (Excellent): Peel strength of 1500 (g / 25mm) or higher B (Good): Peel strength of 1200 (g / 25mm) or more, and less than 1500 (g / 25mm). C (Acceptable): Peel strength of 1000 (g / 25mm) or more, and less than 1200 (g / 25mm) D (Not acceptable): Peel strength is less than 1000 (g / 25mm)

[0122] <Loop Tack (Adhesive Strength)> A PET film with a thickness of 50 μm was coated with hot-melt adhesive to a thickness of 50 μm. This PET film was cut to a size of 25 mm x 145 mm to prepare a sample. This sample was wound into a loop with the adhesive side (adhesive-coated side) facing outwards, and brought into contact with a PE board at a speed of 300 mm / min at 30°C. The test specimen was then peeled off the PE board at a speed of 300 mm / min, and the peel strength at that time was measured and defined as the loop tack. The evaluation criteria are shown below.

[0123] A (Excellent): Loop tack is 2500 (g / 25mm) or more. B (Good): Loop tack is 2000 (g / 25mm) or more, and less than 2500 (g / 25mm). C (acceptable): Loop tack is 1500 (g / 25mm) or more, and less than 2000 (g / 25mm). D (Not acceptable): Loop tack is less than 1500 (g / 25mm)

[0124] <Holding force (cohesive force)> A PET film with a thickness of 50 μm was coated with hot-melt adhesive to a thickness of 50 μm. This PET film was then molded into a test specimen (1.0 cm × 5.0 cm).

[0125] The test specimen was bonded to a 100 μm thick polyethylene film so that the bonding area was 1.0 cm × 1.0 cm. It was then pressed at 40°C and 0.2 MPa for 3 seconds, and then left at 20°C for 12 hours. After this period, a 1 kg weight was applied vertically under a 40°C atmosphere, and the time it took for the weight to fall was measured; this was defined as the holding force. The evaluation criteria are shown below.

[0126] A (Excellent): Holding ability for 300 minutes or more B (Good): Holding time is 200 minutes or more, but less than 300 minutes. C (Acceptable): Holding time is 150 minutes or more, but less than 200 minutes. D (Not acceptable): Holding time less than 150 minutes

[0127] <Creep resistance> The dynamic viscoelasticity of hot-melt adhesives was measured using a dynamic viscoelasticity measuring device (Rheometer AR-G2 (product name), manufactured by T.A. Instruments Co., Ltd.) to evaluate their creep resistance. The specific method is as follows.

[0128] A hot-melt adhesive was heated using a measuring device jig to obtain a cylindrical molded body with a diameter of 8 mmφ and a thickness of 2000 μm.

[0129] The test specimen was sandwiched between stainless steel parallel plates, and oscillation measurements were performed by applying a constant frequency of 1.0 Hz at 40°C. Subsequently, a torque of 100 μN·m was applied to the specimen, and the strain (%) after 120 seconds was determined to evaluate creep resistance. The evaluation criteria are shown below.

[0130] A (Excellent): Distortion less than 5% B (Good): Distortion of 5% or more, less than 6%. C (Acceptable): Distortion is 6% or more, but less than 8%. D (Not acceptable): Distortion is 8% or more

[0131] [Table 3]

[0132] [Table 4]

[0133] As shown in the table, the hot melt adhesive of the example exhibits an excellent balance of coatability, peel strength, loop tack, holding power, and creep resistance, and in particular, it has extremely superior creep resistance. As shown in the table, the hot melt adhesive of the comparative example has a rating of D (unacceptable) in one or more of the following: coatability, peel strength, loop tack, holding power, or creep resistance.

[0134] These evaluation results demonstrate that the hot-melt adhesive of the present invention has an excellent balance of coatability, peel strength, loop tack, holding power, and creep resistance, and in particular its creep resistance is remarkably excellent, making it suitable for holding stretchable materials in disposable products. [Industrial applicability]

[0135] The present invention provides a hot-melt adhesive and a disposable product obtained by applying the hot-melt adhesive. The hot-melt adhesive according to the present invention is suitable for manufacturing disposable products, and in particular can hold elastic materials in disposable products.

Claims

1. A hot melt adhesive comprising (A) a thermoplastic block copolymer which is a copolymer of a vinyl aromatic hydrocarbon and a conjugated diene compound, (B) a tackifying resin, and (C) a plasticizer, (A) The thermoplastic block copolymer contains the following components (A1) and (A2): Per 100 parts by mass of the total amount of components (A) to (C), component (A1) is contained in an amount of 10 to 25 parts by mass, and component (A2) is contained in an amount of 2 to 10 parts by mass. (B) Hot melt adhesive containing hydrogenated dicyclopentadiene resin as the tackifying resin: (A1) Styrene isoprene block copolymer having a styrene content higher than 40% by mass; and (A2) A styrene-isoprene block copolymer having a styrene content higher than 15% by mass and lower than 30% by mass.

2. The hot melt adhesive according to claim 1, wherein component (A1) has a weight-average molecular weight of 50,000 to 150,000.

3. The hot melt adhesive according to claim 1 or 2, wherein the tackifying resin (B) is contained in an amount of 45 to 70 parts by mass per 100 parts by mass of the total amount of components (A) to (C).

4. A hot melt adhesive according to any one of claims 1 to 3, used for fixing an elastic material to the body of a disposable product.

5. A disposable product coated with the hot melt adhesive described in any one of claims 1 to 4.

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