Alkali dispersible hot melt pressure sensitive adhesive

Abstract

The present invention aims to provide an alkali-dispersible hot-melt pressure-sensitive adhesive which (i) has high alkali dispersibility, (ii) is excellent in strength of maintaining a label, (iii) hardly causes adhesive residue problems, and (iv) can reduce stringing. The present invention relates to an alkali-dispersible hot-melt pressure-sensitive adhesive comprising: (A) a thermoplastic block copolymer which is a copolymer of a vinyl-based aromatic hydrocarbon and a conjugated diene compound, (B) a tackifying resin, and (C) at least one selected from fatty acids and derivatives thereof, wherein component (C) comprises (C1) a fatty acid derivative having a melting point of 40° C. or higher.

Description

Technical Field

[0001] The present invention relates to an alkali-dispersible hot-melt pressure-sensitive adhesive suitable as a pressure-sensitive adhesive for labels of glass bottles, PET (polyethylene terephthalate) bottles, etc., and particularly to an alkali-dispersible hot-melt pressure-sensitive adhesive effective for bonding PET bottles for carbonated beverages to labels. Background Art

[0002] Generally, aluminum cans, glass bottles, and polyethylene terephthalate (PET) bottles are widely used as containers for medicines and beverages. Labels are attached to the surfaces of these containers with a pressure-sensitive adhesive with such strength that the labels cannot be peeled off by hand. As labels for beverage containers, polyethylene terephthalate (PET) films, biaxially oriented polypropylene films (OPP), and polylactic acid (PLA) films are mostly used as body wrap (roll-on) labels (roll labels).

[0003] When a container with a label is reused, it is necessary to recover the used container at a factory, immerse the container in a heated alkaline aqueous solution, and separate the label from the container. Therefore, the pressure-sensitive adhesive applied to the label of the container is required to have the property of swelling, softening, dispersing or dissolving in an alkaline aqueous solution (alkali dispersibility) so that the label can be peeled off from the container in a short time.

[0004] Patent Documents 1 to 3 disclose alkali-dispersible hot-melt pressure-sensitive adhesives containing a styrene-based block copolymer, a tackifying resin and fats. The hot-melt pressure-sensitive adhesives in these documents contain modified rosin as a tackifying resin, and coconut oil, rice bran oil, sunflower oil, rapeseed oil, etc. as fats.

[0005] In addition to being excellent in alkali dispersibility, alkali-dispersible hot-melt pressure-sensitive adhesives are also required to be excellent in adhesion (holding strength) between labels and containers. In particular, in the beverage field, it is required not only to have "alkali dispersibility" and "holding strength", but also to have no adhesive residue left on the container after the label is peeled off from the container, that is, to have excellent peelability.

[0006] In beverage manufacturers, when producing carbonated beverages, there is a step of filling carbonated beverages into PET bottles with attached labels. When the carbonated beverage is filled and then the PET bottles are left to stand, carbon dioxide may cause the PET bottles to expand slightly, causing problems of the labels warping or peeling off from the bottles in some cases. However, the hot melt pressure-sensitive adhesives described in Patent Documents 1 to 3 are not sufficient to solve the problems of label warping and label peeling. In the beverage industry, an alkali-dispersible hot melt pressure-sensitive adhesive having particularly excellent holding strength is required.

[0007] Alkali-dispersible hot melt pressure-sensitive adhesives also require reduced stringing during application. When applying the hot melt pressure-sensitive adhesive, a special coating device such as a hot melt coater or a labeling machine is generally used. The hot melt pressure-sensitive adhesive is heated to about 120 to 190°C and applied to a label as an adherend from the head of the special coating device. When the hot melt pressure-sensitive adhesive is applied to the label, in some cases, a linear substance (stringing) of the hot melt pressure-sensitive adhesive may be generated between the tip of the head and the label. In addition, stringing may sometimes be generated between the label that has been applied and the label that has not been applied. This stringy substance is due to the stringing of the hot melt pressure-sensitive adhesive and it stains the head or label. Therefore, it is an important responsibility of adhesive manufacturers to develop a hot melt pressure-sensitive adhesive with less stringing.

[0008] Recently, there has been an increasing demand for reducing stringing of hot melt pressure-sensitive adhesives. However, the hot melt pressure-sensitive adhesives described in Patent Documents 1 to 3 do not fully meet the demand for reducing stringing.

[0009] Therefore, it is desired to develop an alkali-dispersible hot-melt pressure-sensitive adhesive that is excellent in all characteristics including alkali dispersibility, holding strength, reduction in adhesive residue, and reduction in stringing.

[0010] Citation List

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent Publication No. 5671846

[0013] Patent Document 2: Japanese Patent Publication No. 6223203

[0014] Patent Document 3: Japanese Patent Publication No. 2016-60847 Summary of the invention

[0015] Technical issues

[0016] An object of the present invention is to provide an alkali-dispersible hot-melt pressure-sensitive adhesive which (i) has high alkali dispersibility, (ii) is excellent in holding strength of holding a label, (iii) hardly causes adhesive residue problems, and (iv) can reduce stringing.

[0017] Solution to the problem

[0018] The present invention and preferred embodiments of the present invention are as follows.

[0019] 1. An alkali-dispersible hot-melt pressure-sensitive adhesive comprising:

[0020] (A) a thermoplastic block copolymer which is a copolymer of a vinyl-based aromatic hydrocarbon and a conjugated diene compound,

[0021] (B) tackifying resin and

[0022] (C) at least one selected from fatty acids and their derivatives,

[0023] The component (C) comprises (C1) a fatty acid derivative having a melting point of 40° C. or higher.

[0024] 2. The alkali-dispersible hot-melt pressure-sensitive adhesive according to item 1 above, wherein the component (C1) includes a hardening oil.

[0025] 3. The alkali-dispersible hot-melt pressure-sensitive adhesive according to item 2 above, wherein the hardening oil includes hydrogenated castor oil.

[0026] 4. The alkali-dispersible hot-melt pressure-sensitive adhesive according to item 3 above, wherein the hydrogenated castor oil has a melting point of 50 to 100°C.

[0027] 5. A label having applied thereon the alkali-dispersible hot-melt pressure-sensitive adhesive described in any one of items 1 to 4 above.

[0028] 6. A container having the label according to item 5 above affixed thereto.

[0029] Advantageous Effects of the Invention

[0030] The alkali-dispersible hot-melt pressure-sensitive adhesive of the present invention can be used to attach labels to containers such as PET bottles or glass bottles, and is excellent in maintaining the strength of the label. For example, when a label is attached to a container such as a PET bottle filled with a carbonated beverage using the alkali-dispersible hot-melt pressure-sensitive adhesive of the present invention, displacement and lifting of the label hardly occur even if the container expands.

[0031] The alkali-dispersible hot-melt pressure-sensitive adhesive of the present invention has high alkali dispersibility, and when a container with a label is immersed in an alkaline aqueous solution, the label can be cleanly peeled off without adhesive residue. Further, the alkali-dispersible hot-melt pressure-sensitive adhesive of the present invention can be removed by hand power, etc., and almost no adhesive residue is left when the label is removed. Therefore, the alkali-dispersible hot-melt pressure-sensitive adhesive of the present invention is suitable for recycling containers, etc.

[0032] The alkali-dispersible hot-melt pressure-sensitive adhesive of the present invention is applied to a label or the like by using a dedicated coater or the like, and the generation of stringing can be suppressed when the adhesive is applied. DETAILED DESCRIPTION

[0033] The alkali-dispersible hot-melt pressure-sensitive adhesive according to the present invention comprises: (A) a thermoplastic block copolymer, which is a copolymer of a vinyl-based aromatic hydrocarbon and a conjugated diene compound, (B) a tackifying resin, and (C) at least one selected from fatty acids and derivatives thereof. In this specification, they may be described as "component (A)", "component (B)", "component (C)", respectively, and the alkali-dispersible hot-melt pressure-sensitive adhesive of the present invention may be referred to as "hot-melt pressure-sensitive adhesive".

[0034] Label retention is a property opposite to label peelability and alkali dispersibility. The hot melt pressure-sensitive adhesive of the present invention comprises the following components (A), (B) and (C), and component (C) comprises (C1) a fatty acid derivative having a melting point of 40° C. or higher, thereby improving the above two opposite properties and reducing stringing when applied to an adherend. Hereinafter, each component will be described.

[0035] <(A) Thermoplastic Block Copolymer>

[0036] In the present invention, "(A) thermoplastic block copolymer" is a copolymer in which a vinyl-based aromatic hydrocarbon and a conjugated diene compound are block-copolymerized, and is generally a resin composition having a vinyl-based aromatic hydrocarbon block and a conjugated diene compound block.

[0037] The “vinyl-based aromatic hydrocarbon” refers to an aromatic hydrocarbon compound having a vinyl group. Specific examples thereof include styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene, and vinylanthracene. In particular, styrene is preferred. These vinyl-based aromatic hydrocarbons may be used alone or in combination.

[0038] "Conjugated diene compound" refers to a diene compound having at least one pair of conjugated double bonds. Specific examples of "conjugated diene compound" may include 1,3-butadiene, 2-methyl-1,3-butadiene (or isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene and 1,3-hexadiene. 1,3-butadiene and 2-methyl-1,3-butadiene are particularly preferred. These conjugated diene compounds may be used alone or in combination.

[0039] The thermoplastic block copolymer (A) used in the present invention may be a non-hydrogenated or hydrogenated thermoplastic block copolymer.

[0040] Specific examples of the "non-hydrogenated thermoplastic block copolymer (A)" may include block copolymers in which one or more blocks based on a conjugated diene compound are not hydrogenated. Specific examples of the "hydrogenated thermoplastic block copolymer (A)" include block copolymers in which all or part of the blocks based on a conjugated diene compound are hydrogenated.

[0041] The ratio of hydrogenated "hydrogenated thermoplastic block copolymer (A)" can be represented by "hydrogenation rate". The "hydrogenation rate" of "hydrogenated thermoplastic block copolymer (A)" refers to the ratio of double bonds converted into saturated hydrocarbon bonds by hydrogenation based on all aliphatic double bonds contained in the block based on conjugated diene compound. The "hydrogenation rate" can be measured by infrared spectrophotometer, nuclear magnetic resonance device, etc.

[0042] As one aspect of the present invention, the thermoplastic block copolymer (A) is preferably a styrene-based block copolymer. A styrene-based block copolymer refers to a polymer having at least one styrene block. A styrene block refers to a segment containing styrene as a main monomer, and preferably the segment is substantially composed of styrene only.

[0043] Specific examples of the "non-hydrogenated thermoplastic block copolymer (A)" include styrene-isoprene-styrene block copolymer (also referred to as "SIS") and styrene-butadiene-styrene block copolymer (also referred to as "SBS"). Specific examples of the "hydrogenated thermoplastic block copolymer (A)" include hydrogenated styrene-isoprene-styrene block copolymer (also referred to as "SEPS"), hydrogenated styrene-butadiene-styrene block copolymer (also referred to as "SEBS") and styrene-butylene / butadiene-styrene block copolymer (also referred to as "SBBS").

[0044] In the present invention, the weight average molecular weight (Mw) of the compound contained as component (A) is not particularly limited, but is preferably 1.0×10 4 Up to 3.0×10 5 , more preferably 5.0×10 4 Up to 2.0×10 5 .

[0045] In this specification, the weight average molecular weight is measured by gel permeation chromatography (GPC) using a calibration curve for converting the molecular weight using monodisperse molecular weight polystyrene as a standard substance.

[0046] In one aspect of the present invention, the thermoplastic block copolymer (A) (component (A)) preferably comprises (A1) a styrene-based block copolymer having a styrene content of less than 40% by mass (also described as "component (A1)"). "Styrene content" refers to the proportion of styrene contained in the thermoplastic block copolymer. The styrene content of component (A1) is preferably less than 40% by mass, more preferably less than 35% by mass, and further preferably 15% by mass or more and less than 35% by mass.

[0047] When the hot-melt pressure-sensitive adhesive of the present invention includes component (A1) having a styrene content within the above range, the label can be stably held on a container such as a PET bottle, and the label is less likely to be lifted, displaced, or the like.

[0048] In the hot melt pressure-sensitive adhesive of the present invention, based on 100 parts by mass of the total amount of component (A), the content of component (A1) is preferably 70 parts by mass or more, more preferably 80 parts by mass or more, and can be 100 parts by mass. When the content of component (A1) in the hot melt pressure-sensitive adhesive of the present invention is within the above range, the retention strength is further improved.

[0049] The thermoplastic block copolymer (A) can be used alone or in combination of two or more. As an embodiment, a styrene-based block copolymer (A1) having a styrene content of less than 40% by mass and a styrene-based block copolymer not included in component (A1) can be blended together. The styrene-based block copolymer not included in component (A1) refers to a styrene-based block copolymer having a styrene content of 40% by mass or more (hereinafter, also described as "(A2) a styrene-based block copolymer having a styrene content of 40% by mass or more" or "component (A2)").

[0050] In the present invention, commercially available products can be used as the (A1) styrene-based block copolymer having a styrene content of less than 40% by mass. Examples thereof include:

[0051] Tufprene T420 (trade name), Tuftec P3000 (trade name), Tuftec H1053 (trade name) manufactured by Asahi Kasei Chemicals Corporation;

[0052] Quintac3460 (trade name), Quintac3433N (trade name), Quintac3520 (trade name), Quintac3270 (trade name) manufactured by ZEON Corporation;

[0053] D1160 (trade name), Kraton G1650 (trade name), Kraton G1652 (trade name), Kraton G1657 (trade name) manufactured by Kraton Corporation.

[0054] Component (A) is preferably a triblock type styrene block copolymer having a diblock content of 0 mass %. In particular, when a triblock type styrene block copolymer having a diblock content of 0 mass % is used as component (A1), the holding strength of the hot melt pressure-sensitive adhesive becomes more excellent.

[0055] In the present specification, "diblock" refers to a block copolymer having two blocks, and generally refers to a block copolymer having one "vinyl-based aromatic hydrocarbon block" (preferably one "styrene block") and one "conjugated diene compound block (which may be hydrogenated), for example, which can be represented by the following formula (1).

[0056] SE (1)

[0057] (In formula (1), S is a styrene block, and E is a conjugated diene compound block.)

[0058] In the present specification, the "diblock content" of component (A) refers to the proportion of the diblock copolymer (preferably a block copolymer represented by formula (1) having one styrene block and one conjugated diene compound block) contained in the thermoplastic copolymer of component (A).

[0059] The triblock type styrene-based block copolymer is preferably a styrene-based block copolymer having a structure represented by the following formula (2) and having no other blocks.

[0060] SES (2)

[0061] (In formula (2), S is a styrene block, and E is a conjugated diene compound block.)

[0062] In the present specification, the triblock type styrene-based block copolymer has a diblock content of 0% by mass, and is different from the diblock type styrene-based block copolymer.

[0063] In the present invention, it is most desirable that component (A1) is a styrene-ethylene / butylene-styrene (SEBS) triblock copolymer. When the hot melt pressure-sensitive adhesive of the present invention contains a styrene-ethylene / butylene-styrene (SEBS) triblock copolymer, the adhesive force is significantly improved. As a result, when a label is attached to a container using the hot melt pressure-sensitive adhesive, the label can remain attached for a long time without lifting from the container and without shifting.

[0064] Examples of commercially available products of the styrene-based block copolymer (A2) having a styrene content of 40% by mass or more include:

[0065] Asaprene T439 (trade name), Tufprene 125 (trade name), Tufprene A (trade name), Tuftec P2000 (trade name), Tuftec H1043 (trade name), and Tuftec H1051 (trade name) manufactured by Asahi Kasei Chemicals Co., Ltd.;

[0066] TR2000 (trade name) and TR2250 (trade name) manufactured by JSR Corporation; and

[0067] SO1T6414 (trade name) manufactured by Enichem. These commercially available products may be used alone or in combination.

[0068] <(B) Tackifying Resin>

[0069] The hot melt pressure-sensitive adhesive of the present invention can be improved in strength to hold the label on the container by containing (B) a tackifying resin (component (B)). The "tackifying resin" may be a resin commonly used in hot melt pressure-sensitive adhesives, and is not particularly limited as long as the hot melt pressure-sensitive adhesive of the present invention can be obtained. In this specification, component (B) does not contain the compound described as the above-mentioned component (A).

[0070] Examples of the tackifying resin may 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 phenol-based 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, alicyclic petroleum hydrocarbon resins, and hydrogenated derivatives of alicyclic petroleum hydrocarbon resins.

[0071] Among these, component (B) preferably contains a tackifying resin having an acid value of 0 to 300 mgKOH / g, more preferably a rosin-based tackifying resin having an acid value of 50 to 300 mgKOH / g, further preferably a rosin-based tackifying resin having an acid value of 150 to 300 mgKOH / g, and still more preferably a rosin-based tackifying resin having an acid value of 150 to 250 mgKOH / g. The acid value within this range improves the alkali dispersibility of the hot-melt pressure-sensitive adhesive of the present invention.

[0072] As one aspect of the present invention, it is preferred that the tackifying resin (B) further comprises an α-methylstyrene-based resin in addition to the rosin-based tackifying resin. The α-methylstyrene-based resin enhances the cohesiveness of the hot-melt pressure-sensitive adhesive and improves its peelability and holding strength. As the α-methylstyrene-based resin, for example, an α-methylstyrene homopolymer or a styrene / α-methylstyrene copolymer may be used.

[0073] As one embodiment of the present invention, the α-methylstyrene-based resin as component (B) is preferably a styrene / α-methylstyrene copolymer. The α-methylstyrene-based resin preferably has a softening point of 65° C. to 160° C. (measured by the ring and ball method specified in JIS K2207), and more preferably a softening point of 85° C. to 160° C. Specifically, examples of commercially available products include Kristalex 3085 (trade name), Kristalex 3100 (trade name), Kristalex 1120 (trade name), Kristalex 5140 (trade name), Endix 155 and Plastrin 290 manufactured by Eastman Chemical Company, FTR-2120 (trade name) manufactured by Mitsui Chemical Company, and the like.

[0074] These tackifying resins may be used alone or in combination. As the tackifying resin, liquid type tackifying resins may also be used as long as they are colorless to pale yellow in color, have substantially no odor, and have good thermal stability.

[0075] <(C) Fatty acids and their derivatives>

[0076] The hot melt pressure-sensitive adhesive of the present invention comprises (C) at least one selected from fatty acids and derivatives thereof (component (C)). When the hot melt pressure-sensitive adhesive comprises component (C), the hot melt pressure-sensitive adhesive of the present invention has excellent alkali dispersibility. Component (C) may comprise one compound alone, or may comprise two or more.

[0077] Here, fatty acid refers to an aliphatic carboxylic acid having at least one carboxyl group, and may have a hydroxyl group. Fatty acids are generally divided into saturated fatty acids and unsaturated fatty acids. Saturated fatty acids are acids that do not have double bonds or triple bonds in the carbon chain. Unsaturated fatty acids are acids that have double bonds or triple bonds in the carbon chain.

[0078] Any saturated fatty acid can be used, as long as it does not have a negative impact on hot-melt pressure-sensitive adhesive of the present invention, and it preferably has 1 to 30 carbon atoms, more preferably 3 to 26 carbon atoms, more preferably 8 to 24 carbon atoms, further preferably 12 to 22 carbon atoms, further preferably 14 to 22 carbon atoms. Saturated fatty acids can be open-chain or cyclic, and are preferably open-chain. Open-chain saturated fatty acids can have straight or branched chains, and are preferably straight-chain saturated fatty acids. The specific examples of saturated fatty acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, lauric acid, tridecanoic acid, myristic acid, palmitic acid, stearic acid, behenic acid and 12-hydroxystearic acid, etc.

[0079] Any unsaturated fatty acid may be used as long as it does not adversely affect the hot-melt pressure-sensitive adhesive of the present invention and has preferably 3 to 26 carbon atoms, more preferably 4 to 22 carbon atoms, still more preferably 14 to 22 carbon atoms.

[0080] The number of carbon-carbon unsaturated bonds of the unsaturated fatty acid is preferably 1-6, more preferably 1-3, most preferably 1-2.

[0081] Examples of unsaturated fatty acids include crotonic acid, oleic acid, linolenic acid, docosahexaenoic acid, linoleic acid, and ricinoleic acid.

[0082] In this specification, the derivative of fatty acid (fatty acid derivative) refers to a compound obtained by substitution or other chemical reactions of fatty acid. Examples of fatty acid derivatives include grease, hardened oil, fatty acid amide, fatty acid alkyl ester, monoglyceride, diglyceride, sorbitan fatty acid ester, diglycerol fatty acid ester, etc., and preferably grease and hardened oil, more preferably hardened oil. "Grease" contains triglyceride (triacylglycerol) which is an ester of fatty acid and glycerol as a main component.

[0083] The hot melt pressure-sensitive adhesive of the present invention can include greases and fats that are commonly used as edible or industrial greases and fats. Greases and fats can be liquid or solid at normal temperatures (about 20 to 26° C.), and are preferably liquid at normal temperatures, and vegetable oils are preferred. Examples of greases and fats include corn oil, soybean oil, epoxidized soybean oil, sesame oil, linseed oil, olive oil, lettuce oil, fish oil, butter, lard, castor oil, rapeseed oil, sunflower oil, rice bran oil and cottonseed oil. One can be used alone, or two or more can be used in combination.

[0084] "Hardened oil" is obtained by hydrogenating fats and oils in liquid form at room temperature and increasing the proportion of saturated fatty acids with a higher melting point to solidify the fats and oils at room temperature. Any "hardened oil" can be used as long as it does not adversely affect the hot-melt pressure-sensitive adhesive of the present invention. Specific examples of hardened oils include castor oil subjected to hydrogenation (i.e., hydrogenated castor oil), hydrogenated soybean oil, and hydrogenated salad oil.

[0085] The hot melt pressure-sensitive adhesive of the present invention comprises (C1) a fatty acid derivative having a melting point of 40° C. or higher (also referred to as “component (C1)” or “fatty acid derivative (C1)”) as a fatty acid or a derivative thereof (C). The melting point of the fatty acid derivative (C1) is preferably 45 to 120° C., more preferably 50 to 100° C., further preferably 50 to 90° C. In one embodiment of the present invention, the hot melt pressure-sensitive adhesive preferably comprises castor oil having a melting point of 50 to 100° C. Component (C1) may comprise one species alone or two or more species.

[0086] When the melting point of the fatty acid derivative (C1) is within the above range, the hot-melt pressure-sensitive adhesive of the present invention is suitable as a hot-melt pressure-sensitive adhesive for labels due to improved holding strength. When a PET bottle for carbonated beverages and a label are attached to each other through the hot-melt pressure-sensitive adhesive of the present invention, the label remains on the PET bottle for a long time without displacement or warping even if the PET bottle expands with carbon dioxide gas.

[0087] Here, the melting point refers to a value measured using differential scanning calorimetry (DSC). Specifically, 10 mg of a sample is weighed in an aluminum container, measured using DSC6220 (trade name) manufactured by Nano Technology Inc. at a temperature increase rate of 5°C / min, and the temperature of the top of the melting peak is referred to as the melting point.

[0088] Based on 100 parts by mass of the total amount of component (C), the content of component (C1) is preferably 40 parts by mass or more, more preferably 50 parts by mass or more, further preferably 60 parts by mass or more, and may be 100 parts by mass. In one embodiment of the present invention, in addition to component (C1), component (C) may further contain (C2) a fatty acid derivative having a melting point lower than 40°C (preferably a fat having a melting point lower than 40°C).

[0089] In the present invention, it is preferred to contain a hardened oil as the fatty acid derivative (C1). The melting point of the hardened oil as component (C1) is 40° C. or higher, preferably 50 to 100° C., more preferably 50 to 90° C. When the hot-melt pressure-sensitive adhesive of the present invention contains a hardened oil having a melting point of 40° C. or higher, it remains solid without melting even at high temperatures, and improves the adhesive force with an adherend such as a label, resulting in high holding strength.

[0090] Examples of hardened oils include castor oil subjected to hydrogenation (ie, hydrogenated castor oil), hydrogenated soybean oil, hydrogenated salad oil, hydrogenated rapeseed oil, hydrogenated palm oil, hydrogenated tallow, etc. In particular, hydrogenated castor oil, hydrogenated soybean oil, and hydrogenated rapeseed oil are preferred, and hydrogenated castor oil is most preferred.

[0091] When the hot melt pressure-sensitive adhesive of the present invention contains hydrogenated castor oil having a melting point of 40°C or higher, its holding strength becomes particularly excellent. In one embodiment of the present invention, it is preferred that the hot melt pressure-sensitive adhesive contains hydrogenated castor oil having a melting point of 50 to 100°C as component (C1).

[0092] In the present invention, commercially available products can be used as the fatty acid or its derivative (C).

[0093] Examples of commercially available products of the fatty acid derivative (C1) include hydrogenated palm oil A (trade name), Technol MH (trade name), Technol ML98 (trade name), 12-hydroxystearic acid (trade name), hydrogenated soybean oil (trade name), hydrogenated rapeseed oil (trade name), hydrogenated palm oil (trade name) and rice bran wax SS-1 (trade name).

[0094] Examples of commercially available fatty acid derivatives other than component (C1) may include:

[0095] FS oil (trade name) and prime taste (trade name) manufactured by Showa Sangyo Co., Ltd.;

[0096] Rice oil (trade name) and rice salad oil (trade name) manufactured by Boso oil and fat Co., Ltd.;

[0097] Cottonseed oil (trade name) manufactured by Okamura oil and fat Co., Ltd;

[0098] Rikemal (trade name) manufactured by Riken Vitamin Co., Ltd.;

[0099] Nonion (trade name) manufactured by NOF Corporation; and the like.

[0100] These commercially available fatty acid derivatives may be used alone or in combination.

[0101] The hot-melt pressure-sensitive adhesive of the present invention may contain wax in addition to components (A) to (C).

[0102] "Wax" is an organic substance that is solid at room temperature and forms a liquid when heated, and is generally used for hot melt pressure-sensitive adhesives, and is not particularly limited as long as the hot melt pressure-sensitive adhesive of the present invention can be obtained. The wax generally has a weight average molecular weight of less than 10,000. Specific examples of waxes may include synthetic waxes such as Fischer Tropschwax, polyolefin waxes (such as polyethylene wax and polypropylene wax); petroleum waxes such as paraffin wax and microcrystalline wax; and natural waxes such as castor wax.

[0103] When the hot melt pressure-sensitive adhesive of the present invention contains wax, the adhesive residue of the hot melt pressure-sensitive adhesive on the container is reduced when the label is peeled off from the container.

[0104] In one embodiment of the present invention, the wax preferably comprises a Fischer-Tropsch wax. The Fischer-Tropsch wax is a wax that is fractionated from a wax that includes component molecules with a wider carbon atom number distribution to include component molecules with a narrow carbon atom number distribution. The Fischer-Tropsch wax reduces the adhesive residue of the hot melt pressure-sensitive adhesive when the label is peeled off from the container.

[0105] The hot melt pressure-sensitive adhesive of the present invention may contain a plasticizer.

[0106] For the purpose of reducing the melt viscosity of the hot melt pressure sensitive adhesive, providing flexibility and improving the wettability of the hot melt pressure sensitive adhesive to the adherend for the hot melt pressure sensitive adhesive, a plasticizer is mixed in. The plasticizer is not particularly limited, as long as it is compatible with other components and the hot melt pressure sensitive adhesive of the present invention can be obtained. The example of the plasticizer includes paraffin base oil, naphthenic oil and aromatic oil. Especially, paraffin base oil and / or naphthenic oil are preferred, and colorless and odorless paraffin base oil is most preferred.

[0107] Examples of commercial products of plasticizers include White Oil Broom 350 (trade name) manufactured by Kukdong Oil & Chem; Diana Fresia S-32 (trade name), Diana Process Oil PW-90 (trade name), and Daphne Oil KP-68 (trade name) manufactured by Idemitsu Kosan Co., Ltd.; Enerper M1930 (trade name) manufactured by BP Chemicals; Kaydol (trade name) manufactured by Crompton; Primol 352 (trade name) manufactured by Exxon Mobil Corporation; NS-100 (trade name) manufactured by Idemitsu Kosan Co., Ltd.; and DN4010 manufactured by PetroChina. These may be used alone or in combination of two or more.

[0108] Mixing of a plasticizer improves the compatibility of components (A) to (C) contained in the hot-melt pressure-sensitive adhesive of the present invention and further improves the compatibility with other components, and thus improves the tack, adhesion and coating suitability of the hot-melt pressure-sensitive adhesive.

[0109] The hot melt pressure-sensitive adhesive according to the present invention may further contain various additives as required. Examples of such various additives include stabilizers and fine particle fillers.

[0110] The "stabilizer" is mixed to prevent the molecular weight reduction, gelation, coloring, odor generation, etc. caused by heating in the hot melt pressure-sensitive adhesive to improve the stability of the hot melt pressure-sensitive adhesive. The "stabilizer" is not particularly limited as long as the hot melt pressure-sensitive adhesive of the present invention can be obtained. Examples of the "stabilizer" include antioxidants and ultraviolet absorbers.

[0111] Examples of "antioxidants" include phenol-based antioxidants, sulfur-based antioxidants, and phosphorus-based antioxidants. Examples of "ultraviolet light absorbers" include benzotriazole-based ultraviolet light absorbers and benzophenone-based ultraviolet light absorbers. In addition, lactone-based stabilizers may also be added. These may be used alone or in combination. As commercial products of antioxidants, the following products may be used.

[0112] Specific examples thereof include SUMILIZER GM (trade name), SUMILIZER TPD (trade name), and SUMILIZER TPS (trade name) manufactured by Sumitomo Chemical Co., Ltd.; IRGANOX 1010 (trade name), IRGANOX HP2225FF (trade name), IRGAFOS 168 (trade name), IRGANOX 1520 (trade name), and TINUVIN P manufactured by Ciba Specialty Chemicals; JF77 (trade name) manufactured by Johoku Chemical Co.; TOMINOX TT (trade name) manufactured by API Corporation; and AO-412S (trade name) manufactured by ADEKA CORPORATION. These stabilizers may be used alone or in combination.

[0113] "Ultraviolet absorbers" are used to improve the light resistance of hot melt pressure sensitive adhesives. "Antioxidants" are used to prevent oxidative degradation of hot melt pressure sensitive adhesives.

[0114] The hot melt pressure-sensitive adhesive of the present invention may further include a fine particle filler. The fine particle filler may be a commonly used filler, and is not particularly limited, as long as the hot melt pressure-sensitive adhesive of the present invention can be obtained. The example of "fine particle filler" includes mica, calcium carbonate, kaolin, talcum, titanium oxide, diatomaceous earth, urea-based resin, styrene beads, fired clay and starch. These shapes are preferably spherical, and their size (diameter in the case of spherical) is not particularly limited.

[0115] The hot melt pressure-sensitive adhesive according to the present invention can be prepared by mixing component (A), component (B) and component (C), and preferably wax and plasticizer and, as required, other various additives, using a generally known method for producing a hot melt pressure-sensitive adhesive. The hot melt pressure-sensitive adhesive according to the present invention can be produced by mixing a predetermined amount of the above components and heating and melting them. The order of adding the components, the heating method, etc. are not particularly limited as long as the target hot melt pressure-sensitive adhesive is obtained.

[0116] In the hot melt pressure-sensitive adhesive of the present invention, the blending amount of component (A) is not particularly limited, but is preferably 10 to 50 parts by mass, more preferably 15 to 40 parts by mass, based on 100 parts by mass of the total mass of component (A), component (B) and component (C). When the blending amount of component (A) is within the above range, the hot melt pressure-sensitive adhesive of the present invention has increased cohesive force (holding strength), so that the label can be easily attached to the container without displacement.

[0117] In the hot melt pressure-sensitive adhesive of the present invention, the blending amount of component (B) is not particularly limited, but is preferably 40 to 80 parts by mass, more preferably 50 to 75 parts by mass, based on 100 parts by mass of the total mass of component (A), component (B) and component (C). When the blending amount of component (B) is within the above range, the hot melt pressure-sensitive adhesive of the present invention becomes stable as a pressure-sensitive adhesive and is excellent in the balance of alkali dispersibility, retention strength, adhesive residue reduction and stringing reduction.

[0118] In the hot melt pressure-sensitive adhesive of the present invention, the blending amount of component (C) is not particularly limited, but is preferably 3 to 40 parts by mass, more preferably 5 to 35 parts by mass, based on 100 parts by mass of the total mass of component (A), component (B) and component (C). When the blending amount of component (C) is within the above range, the alkali dispersibility of the hot melt pressure-sensitive adhesive of the present invention is improved and the holding strength is maintained, and in addition, the adhesive residue on the adherend can be reduced when the label is peeled off.

[0119] In the hot-melt pressure-sensitive adhesive of the present invention, the total content of component (A), component (B) and component (C) based on the total mass of the hot-melt pressure-sensitive adhesive is not particularly limited, but is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, and preferably 90 parts by mass or less, and more preferably 85 parts by mass or less.

[0120] In the hot melt pressure-sensitive adhesive of the present invention, based on 100 parts by mass of the total mass of component (A), component (B) and component (C), the blending amount of the wax is not particularly limited, and may be 0 parts by mass, but is preferably 1 to 30 parts by mass and more preferably 3 to 25 parts by mass. In one embodiment of the present invention, the hot melt pressure-sensitive adhesive preferably contains a Fischer-Tropsch wax, and based on the total amount of the wax, the blending amount of the Fischer-Tropsch wax is not particularly limited, but is preferably 20% by mass or more, more preferably 50% by mass or more, and may be 100% by mass.

[0121] As a preferred embodiment of the present invention, the hot melt pressure-sensitive adhesive has a viscosity (or melt viscosity) at 160° C. of preferably 4000 mPa.s or less, more preferably 3000 mPa.s or less, and particularly preferably 2000 mPa.s or less. With a viscosity at 160° C. within the above range, the hot melt pressure-sensitive adhesive is more suitable for coating. The viscosity (or melt viscosity) at 160° C. herein refers to a value measured by a Brookfield viscometer using a No. 27 rotor.

[0122] The label according to the present invention is coated with a hot melt pressure-sensitive adhesive. Specific examples of the label on which the hot melt pressure-sensitive adhesive is applied include: labels made of paper, such as paper, processed paper (paper that has been subjected to aluminum vapor deposition treatment, aluminum lamination treatment, varnish treatment, resin treatment, etc.), synthetic paper, etc.; and labels made of organic compound films, inorganic compound films, metal films, etc.

[0123] As the label used in the present invention, a film made of an organic compound generally used for alkali washing such as polypropylene, polyethylene terephthalate (PET), polylactic acid (PLA), etc. is particularly preferred. As the polypropylene film, a biaxially oriented polypropylene (OPP) film is particularly preferred.

[0124] The hot melt pressure-sensitive adhesive of the present invention can be applied to the entire back side of the label or a portion of the back side of the label. Examples of coating methods include an open wheel method, a closed gun method, and a direct coating method. As methods in which the adhesive does not remain on the PET bottle when the label is peeled off, the open wheel method and the direct coating method are preferred.

[0125] The container according to the present invention is a container with the above-mentioned label affixed. Specifically, examples thereof include glass containers such as glass bottles for soft drinks, condiments, detergents, shampoos, edible oils, cosmetics, medicines, etc.; plastic containers such as PET (polyethylene terephthalate) bottles; and metal cans such as aluminum cans. Among the above-mentioned containers, PET bottles are particularly preferred in the present invention. In one embodiment of the present invention, examples of PET bottles with the label of the present invention include: a PET bottle with a label attached to a portion of the bottle body and a PET bottle with a "wrap-around label" that is wrapped around the bottle body to cover the circumference of the bottle. Since the hot-melt pressure-sensitive adhesive of the present invention is excellent in holding strength, even if a container such as a PET bottle expands due to, for example, a carbonated beverage being placed in the container, the label can be prevented from shifting or warping.

[0126] The hot melt pressure-sensitive adhesive of the present invention is preferably used for pasting wrap-around labels. As wrap-around labels, biaxially oriented polypropylene (OPP) films are generally used. The labels on which the hot melt pressure-sensitive adhesive of the present invention is applied may be printed or may not be printed. When a printed label is used, the hot melt pressure-sensitive adhesive of the present invention may be applied not only on a non-printing surface but also on a printed surface.

[0127] As an apparatus for attaching a label to a PET bottle using the hot melt pressure-sensitive adhesive of the present invention, an open wheel apparatus can be cited. The hot melt pressure-sensitive adhesive is melted at 120 to 190° C. and applied to the back of the label by an open wheel apparatus. The label is attached to a PET bottle to manufacture the container of the present invention.

[0128] Since the label is easily peeled off from the container when immersed in a hot alkaline solution, the container to which the label is attached by the hot melt pressure-sensitive adhesive of the present invention is suitable for container reuse, etc. The method of peeling the label with a hot alkaline solution is not particularly limited, but examples thereof include a method in which the container with the label attached is cut into small pieces into particles, the particles are put into a hot alkaline aqueous solution (for example, a sodium hydroxide aqueous solution having a concentration of 0.5 to 5.0% by mass at a temperature of 80° C. to 90° C.) and stirring is performed for about 1 minute to 2 hours.

[0129] The container to which the label is attached with the hot melt pressure-sensitive adhesive of the present invention has sufficient adhesiveness so that the label does not peel off under normal use of the container. In addition, when the label is peeled off after using the container, it can be peeled off by hand without adhesive residue, and the peelability is excellent.

[0130] Example

[0131] In order to describe the present invention in more detail and more specifically, the present invention is described below using examples. These examples do not limit the present invention.

[0132] In Examples and Comparative Examples, components to be mixed into the hot-melt pressure-sensitive adhesive are shown below.

[0133] (A) Thermoplastic Block Copolymer

[0134] (A1) a styrene-based block copolymer having a styrene content of less than 40% by mass

[0135] (A1-1) Styrene-ethylene / butylene-styrene triblock copolymer (Kraton G-1652 (trade name) manufactured by Kraton Corporation, styrene content: 30% by mass, diblock content: 0% by mass, weight average molecular weight: 72,000)

[0136] (A1-2) Styrene-ethylene / butylene-styrene triblock copolymer (Kraton G-1650 (trade name) manufactured by Kraton Corporation, styrene content: 30% by mass, diblock content: 0% by mass, weight average molecular weight: 92,000)

[0137] (A1-3) Styrene-ethylene / butylene-styrene block copolymer (Kraton G-1726 (trade name) manufactured by Kraton Corporation, styrene content: 31% by mass, diblock content: 73% by mass, weight average molecular weight: 43,000)

[0138] (A1-4) Styrene-ethylene / butylene-styrene block copolymer (Kraton G-1657 (trade name) manufactured by Kraton Corporation, styrene content: 15 mass %, diblock content: 33 mass %, weight average molecular weight: 106,000)

[0139] (A2) a styrene-based block copolymer having a styrene content of 40% by mass or more

[0140] (A2-1) Styrene-ethylene / butylene-styrene triblock copolymer (Tuftec H1043 (trade name) manufactured by Asahi Kasei Chemicals Corporation, styrene content: 68 mass %, diblock content: 0 mass %, weight average molecular weight: 53,000)

[0141] (A2-2) Styrene-butadiene / butylene-styrene triblock copolymer (Tuftec P2000 (trade name) manufactured by Asahi Kasei Chemicals Corporation, styrene content: 68 mass %, diblock content: 0 mass %, weight average molecular weight: 54,000)

[0142] (A2-3) Styrene-butadiene-styrene triblock copolymer (TR2250 (trade name) manufactured by JSR Corporation, styrene content: 52 mass %, diblock content: 0 mass %, weight average molecular weight: 109,000)

[0143] (A2-4) Styrene-butadiene-styrene triblock copolymer (Tufprene A (trade name) manufactured by Asahi Kasei Chemicals Corporation, styrene content: 41% by mass, diblock content: 0% by mass, weight average molecular weight: 105,000)

[0144] (A2-5) Styrene-butadiene-styrene block copolymer (Asaprene T-439 (trade name) manufactured by Asahi Kasei Chemicals Corporation, styrene content: 46% by mass, diblock content: 69% by mass, weight average molecular weight: 63,000)

[0145] (A2-6) Styrene-isoprene-styrene triblock copolymer (Kraton D-1162 (trade name) manufactured by Kraton Corporation, styrene content: 41% by mass, diblock content: 0% by mass, weight average molecular weight: 82,000)

[0146] (B) Tackifying resin

[0147] (B1) Hydrogenated alicyclic / aromatic copolymer-based hydrocarbon resin (T-REZ HC103 (trade name) manufactured by JXTG Energy Corporation, softening point: 103° C.)

[0148] (B2) Hydrogenated alicyclic hydrocarbon resin (T-REZ HA103 (trade name) manufactured by JXTG Energy Corporation, softening point: 103° C.)

[0149] (B3) Hydrogenated alicyclic hydrocarbon resin (T-REZ HA125 (trade name) manufactured by JXTG Energy Corporation, softening point: 125° C.)

[0150] (B4) Hydrogenated rosin ester (KOMOTAC KHR75 (trade name) manufactured by GUANGDONG KOMO Co., Ltd., acid value: 170 mgKOH / g, softening point: 80° C.)

[0151] (B5) Hydrogenated rosin ester (ForalAX-E (trade name) manufactured by Eastman Chemical Company, acid value: 160 mgKOH / g, softening point: 80°C)

[0152] (B6) Rosin ester (KOMOTAC K107 (trade name) manufactured by GUANGDONG KOMO Co., Ltd., acid value: 155 mgKOH / g, softening point: 80° C.)

[0153] (B7) α-Methylstyrene-based resin (Kristalex 3070 (trade name) manufactured by Eastman Chemical Company, softening point: 70° C.)

[0154] (B8) α-Methylstyrene-based resin (Kristalex 3085 (trade name) manufactured by Eastman Chemical Company, softening point: 85° C.)

[0155] (B9) α-Methylstyrene-based resin (Kristalex 3100 (trade name) manufactured by Eastman Chemical Company, softening point: 100° C.)

[0156] (B10) α-methylstyrene-based resin (Kristalex 5140 (trade name) manufactured by Eastman Chemical Company, softening point: 140° C.)

[0157] (B11) Hydrogenated rosin ester (Foral 85E (trade name) manufactured by Eastman Chemical Company, acid value: 9 mgKOH / g, softening point: 85°C)

[0158] (B12) Rosin ester (KOMOTAC KB90H (trade name) manufactured by GUANGDONG KOMO Co., Ltd., acid value: 15 mgKOH / g, softening point: 90° C.)

[0159] (C) at least one selected from fatty acids and their derivatives

[0160] (C1) fatty acid derivatives having a melting point of 40°C or higher

[0161] (C1-1) Hardened castor oil (Hardened castor oil A (trade name) manufactured by Ito Oil Co., Ltd., melting point: 85.5° C.)

[0162] (C1-2) Monohydroxystearic acid-hardened castor oil (Technol MH (trade name) manufactured by Yokozeki Oil & Fat Industries Co., Ltd., melting point: 58.0° C.)

[0163] (C1-3) Hydrogenated castor oil laurate (Technol ML98 (trade name) manufactured by Yokozeki Oil & Fat Industries Co., Ltd., melting point: 51.0° C.)

[0164] (C1-4) castor oil hardened fatty acid (12-hydroxystearic acid (trade name) manufactured by NOF CORPORATION, melting point: 69.0°C)

[0165] (C1-5) Hydrogenated tallow (beef tallow 51° hydrogenated oil HO (trade name) manufactured by NOF CORPORATION, melting point: 51.0°C)

[0166] (C1-6) Extremely hardened soybean oil (Hydrogenated soybean oil (trade name) manufactured by Yamakei Sangyo Co., Ltd., melting point: 68.2° C.)

[0167] (C1-7) Extremely hardened rapeseed oil (hydrogenated rapeseed oil (trade name) manufactured by Yamakei Sangyo Co., Ltd., melting point: 68.4° C.)

[0168] (C1-8) Extremely hardened palm oil (Hydrogenated palm oil (trade name) manufactured by Yamakei Sangyo Co., Ltd., melting point: 58.6° C.)

[0169] (C1-9) Rice bran wax extremely hardened rapeseed oil (Rice wax SS-1 (trade name) manufactured by Boso Oil & Fat Co., Ltd., melting point: 79.0° C.)

[0170] (C2) Fatty acid derivatives with a melting point below 40°C

[0171] (C2-1) Castor oil (Industrial No. 1 castor oil (trade name) manufactured by Hokoku Corporation, melting point: not observed (freezing point: -22°C))

[0172] (C2-2) Rice bran oil (Rice bran salad oil (trade name) manufactured by Boso Oil & Fat Co., Ltd., melting point: not observed (freezing point: -10 to -5°C))

[0173] (C2-3) Sunflower oil (High oleic sunflower oil (trade name) manufactured by Yamakei Sangyo Co., Ltd., melting point: none (freezing point: -18 to -16°C))

[0174] (C2-4) Coconut oil (coconut oil (trade name) manufactured by Yamakei Sangyo Co., Ltd., melting point: 24.6° C.)

[0175] (C2-5) Diglycerol fatty acid ester (Rikemal L-71-D (trade name) manufactured by RIKEN Vitamin Co., Ltd., melting point: 34° C.)

[0176] (D) Wax

[0177] (D1) Fischer-Tropsch wax (Sasol C80 (trade name) manufactured by Sasol Limited, melting point: 80° C., needle penetration: 7)

[0178] (D2) Fischer-Tropsch wax (Sasol H1 (trade name) manufactured by Sasol Limited, melting point: 108° C., needle penetration: 2)

[0179] (D3) Ethylene-vinyl acetate copolymer wax (AC400 (trade name) manufactured by Honeywell, melting point: 92° C.)

[0180] (D4) Polyethylene wax (High wax 320P (trade name) manufactured by Mitsui Chemicals, Inc., melting point: 109° C., needle penetration: 7)

[0181] (D5) Polypropylene wax (High wax NP105 (trade name) manufactured by Mitsui Chemicals, Inc., melting point 140 / 148° C., needle penetration: 1)

[0182] (D6) Paraffin wax (HNP-9 (trade name) manufactured by Nippon Seiro Co., Ltd., melting point: 75° C., needle penetration: 6)

[0183] (E) Plasticizer (oil)

[0184] (E1) Paraffin oil (Daphne oil KP-68 (trade name) manufactured by Idemitsu Kosan Co., Ltd.)

[0185] (E2) Paraffin oil (Diana process oil PW90 (trade name) manufactured by Idemitsu Kosan Co., Ltd.)

[0186] (E3) Polybutene (Nisseki Polybutene HV-300 (trade name) manufactured by Nippon Oil Corporation)

[0187] (E4) Naphthenic oil (DN4010 (trade name) manufactured by China National Petroleum Corporation)

[0188] (F) Stabilizer (antioxidant)

[0189] (F1) Hindered phenol-based antioxidant (ADK STAB AO-60 (trade name) manufactured by Adeka Corporation)

[0190] (F2) Thioether-based antioxidant (ADK STAB AO-412S (trade name) manufactured by Adeka Corporation)

[0191] Components (A) to (F) were blended at the blending ratios shown in Tables 1 and 2, and melt-mixed at about 145° C. for about 3 hours using a universal stirrer to prepare hot melt pressure-sensitive adhesives of Examples 1 to 16 and Comparative Examples 1 to 4. The numerical values ​​regarding the compositions (blends) of the hot melt pressure-sensitive adhesives shown in Tables 1 and 2 are all parts by weight.

[0192] Alkali dispersibility, retention, adhesive residue, and stringiness were evaluated for each of the hot-melt pressure-sensitive adhesives of Examples and Comparative Examples. Each measuring method and evaluation method will be described below.

[0193] <Alkali dispersibility>

[0194] The hot melt pressure-sensitive adhesive of each embodiment and comparative example was applied to the OPP film to have a thickness of 20 to 25 μm to prepare an OPP film label (25 mm × 50 mm) with a hot melt pressure-sensitive adhesive. The label was attached to an empty PET bottle by pressing at 100°C for 5 seconds to prepare a test sample. After measuring the mass of the test sample (the mass of the test sample before washing), it was placed in a 1.5% by mass sodium hydroxide aqueous solution at 85°C and stirred (washed) for 15 minutes. After 15 minutes, the test sample was taken out and fully air-dried. The mass of the test sample after air drying (the mass of the test sample after washing) was measured, and the alkali dispersion rate was calculated from the mass before and after washing. The alkali dispersion rate is calculated by the following formula, and the alkali dispersibility is evaluated by the calculated value.

[0195] Alkali dispersion rate (%) = {(mass of test sample before washing - mass of test sample after washing) / (mass of hot melt pressure-sensitive adhesive used)} × 100

[0196] The evaluation results are shown in Table 3. The evaluation criteria are as follows.

[0197] ○○: Alkali dispersion rate is more than 90%.

[0198] ○: The alkali dispersion rate is 60% or more and 90% or less.

[0199] ×: The alkali dispersion rate was less than 60%, or could not be measured because the film was not attached and a test sample could not be prepared.

[0200] <Retention (label lift and label shift)>

[0201] The hot melt pressure-sensitive adhesive was applied on the OPP film to have a thickness of 20 to 25 μm to prepare an OPP label (25 mm×50 mm) with the hot melt pressure-sensitive adhesive. The label was attached to an empty PET bottle by pressing at 100° C. for 5 seconds to prepare a test sample.

[0202] Next, the carbonated beverage was filled into a PET bottle, and the test sample containing the carbonated beverage was stored in an atmosphere of 50° C. for one week. Another test sample containing the carbonated beverage was stored in an atmosphere of −10° C. for one day. The presence of label lift and the label shift distance of each test sample were observed.

[0203] The evaluation results are shown in Table 3. The evaluation criteria are as follows.

[0204] ○○: No label lifting was observed, and the label displacement distance was less than 2 mm.

[0205] ○: No label lifting was observed, and the label displacement distance was 2 mm or more and less than 4 mm.

[0206] △: No label lifting was observed, and the label displacement distance was 4 mm or more and less than 7 mm.

[0207] ×: Label lifting was observed, or the label shift distance was 7 mm or more.

[0208] <Adhesive Residue>

[0209] The hot melt pressure-sensitive adhesive was applied to the OPP film to have a thickness of 20 to 25 μm to prepare an OPP label (25 mm×50 mm) with the hot melt pressure-sensitive adhesive. The label was attached to an empty PET bottle by pressing at 100° C. for 5 seconds to prepare a test sample. After the test sample was stored in an atmosphere of 23° C. and 55% humidity for 3 days, the label was peeled off from the PET bottle by hand, and the sticking state of the hot melt pressure-sensitive adhesive to the PET bottle was visually observed.

[0210] The evaluation results are shown in Table 3. The evaluation criteria are as follows.

[0211] ○○: Interfacial failure (peeling at the interface) was observed and no hot-melt pressure-sensitive adhesive remained.

[0212] ○: The hot-melt pressure-sensitive adhesive slightly remains.

[0213] ×: Adhesion failure was observed, and most of the hot-melt pressure-sensitive adhesive remained on the PET bottle.

[0214] <Evaluation of Wire Drawing Properties>

[0215] The hot melt pressure-sensitive adhesive was intermittently applied to an adherend set 20 cm away from the tip of the hot melt gun in the vertical direction. The state of the dropped material between the hot melt gun and the adherend was visually observed to evaluate the stringiness. The measurement conditions were as follows.

[0216] Temperature setting: 160°C for all boxes, hoses and nozzles

[0217] Nozzle diameter: 14 / 1000 inch

[0218] Nozzle: Single nozzle

[0219] Applied pressure: 0.3MPa

[0220] Number of injections: 90 times / 30 seconds

[0221] The evaluation results are shown in Table 3. The evaluation criteria are as follows.

[0222] ○: Drops fell from the nozzle (no stringing).

[0223] ×: Drops adhered around the nozzle (there was stringing).

[0224] Table 1

[0225]

[0226] Table 2

[0227]

[0228] Table 3

[0229]

[0230] As shown in Table 3, the alkali dispersible hot melt pressure-sensitive adhesives of Examples 1 to 16 are excellent in alkali dispersibility and retention strength, can reduce adhesive residue and drawing, and therefore all properties are good. On the other hand, for each of the hot melt pressure-sensitive adhesives of Comparative Examples 1 to 4, all results of adhesive residue are ×, and some other properties are also ×. From these results, it can be seen that when the hot melt pressure-sensitive adhesive comprises components (A), (B) and (C) and component (C) comprises component (C1), it is possible to obtain a hot melt pressure-sensitive adhesive having (i) high alkali dispersibility, (ii) excellent strength for maintaining labels, (iii) hardly causing adhesive residue and (iv) being able to reduce drawing.

[0231] Industrial Applicability

[0232] The present invention can provide an alkali-dispersible hot-melt pressure-sensitive adhesive, a label on which the alkali-dispersible hot-melt pressure-sensitive adhesive is applied, and a container to which the label is attached.

Claims

1. An alkali-dispersible hot-melt pressure-sensitive adhesive comprising: (A) a thermoplastic block copolymer which is a copolymer of a vinyl-based aromatic hydrocarbon and a conjugated diene compound, which includes a styrene-ethylene / butylene-styrene triblock copolymer having a styrene content of less than 40% by mass, (B) a tackifying resin, and (C) at least one selected from fatty acids and their derivatives, The fatty acid and its derivative (C) include (C1) a fatty acid derivative having a melting point of 40°C or higher, wherein the (C1) fatty acid derivative having a melting point of 40°C or higher includes hardened oil. 2 . The alkali-dispersible hot-melt pressure-sensitive adhesive according to claim 1 , wherein the hardening oil comprises hydrogenated castor oil.

3. A label having applied thereon the alkali-dispersible hot-melt pressure-sensitive adhesive according to claim 1 or 2.

4. A container having a label according to claim 3 attached thereto.

Images