KR20240072052A - Hot-melt adhesive having alkali peeling property and container - Google Patents

Abstract

Even when a thin film of hot melt adhesive is applied, the adhesive strength and the ability to follow the label against misalignment due to expansion of the bottle (true adhesiveness) of the hot melt are high, making it difficult for the label to peel off during long-term storage. An alkali-removable hot melt adhesive is provided that can be easily peeled off from a container without leaving adhesive residue.
Styrene-based elastomer (A) containing styrene-butadiene-styrene block copolymer (a1) and styrene-ethylene-butylene-styrene block copolymer (a2), rosin-based adhesive with a specific content having an acid value of 100-300 mgKOH/g An alkali-releasable hot melt adhesive comprising an imparting agent (B), a process oil (C), and a specific content of polypropylene wax (D) with a softening point of 100°C or higher.

Description

Alkali peelable hot melt adhesive, and container {HOT-MELT ADHESIVE HAVING ALKALI PEELING PROPERTY AND CONTAINER}

This application claims priority based on Japanese Patent Application No. 2022-183155 filed on November 16, 2022, the entire disclosure of which is incorporated herein.

The present invention relates to an alkali-releasable hot melt adhesive and a container with a label attached using the adhesive.

Recently, along with the production of polyethylene terephthalate (hereinafter referred to as PET) bottles, the amount of PET bottles used for beverages is also increasing. It is common for a plastic label to indicate the product name, etc. to be attached to the outer circumference of the body of a PET bottle. Methods for attaching a plastic label to the outer periphery of the body of a PET bottle include the “body wrapping label method,” the “stretch label method,” and the “shrink label method.”

In either case, it is required that the used PET bottles be recovered and recycled as raw materials. For example, the “Guidelines for the Self-Regulation of Designated PET Bottles” proposed by the PET Bottle Recycling Promotion Council sets out the following indicators. That is, when pellets made by cutting a bottle with a label are immersed in a 1.5% sodium hydroxide aqueous solution at 90°C at a pellet concentration of 10% (weight ratio) and stirred for 15 minutes, the label is peeled off from the PET pellet, and the printing This is an indicator that ink, adhesive, etc. do not remain in PET pellets. In order to peel (alkali peel) labels in the recycling process, alkali peelable hot melt adhesives have been developed and used as adhesives for labels on containers such as PET bottles.

International Publication No. 1997/08261 Japanese Patent Publication No. 2010-90185 Japanese Patent Publication No. 2010-280878 Japanese Patent Publication No. 2012-1624

On the other hand, if the contents contain carbonic acid, the PET bottle may expand if left under high temperature (40 to 50°C), such as during transportation in the summer. Due to the expansion of the PET bottle, a load is applied to the label wrapped around the body, and the plastic film at the end of the roll of the body-wrapped label may become misaligned from the plastic film located on the inside. In this case, the winding end of the body wrapping label is required to have the property of not peeling off even if it is misaligned (also called thread adhesiveness). Therefore, the adhesive strength (peel strength) between the plastic films that constitute the label is high, and the hot melt adhesive is required to be able to follow the misalignment of the label due to bottle expansion.

Additionally, in recent years, plastic films and adhesives used in labels have been made thinner due to environmental concerns. The thickness of the adhesive layer is usually 30 to 50 μm and thin film: 5 to 15 μm, for example. Therefore, even if the adhesive layer is applied as a thin film, the hot melt adhesive is required to have high adhesive strength (peel strength) between the plastic films, which are the base material of the label, and high followability to label misalignment.

International Publication No. 1997/08261 discloses a water-dispersible hot melt adhesive composition containing copolyester. However, since the copolyester described in this document has poor heat resistance, there is a problem in that the adhesive strength of the adhesive composition is not stable due to partial thermal decomposition.

Japanese Patent Laid-Open No. 2010-90185 discloses a thermoplastic elastomer (A), a rosin-based tackifier with an acid value of 100 mgKOH/g or more and 300 mgKOH/g or less (B), a terpene phenol resin (C), a synthetic oil (D), and A hot melt adhesive comprising polypropylene wax (E) obtained by graft polymerization of maleic anhydride is disclosed.

Japanese Patent Laid-Open No. 2010-280878 discloses a thermoplastic elastomer (A), a rosin-based tackifier with an acid value of 100 mgKOH/g or more and 300 mgKOH/g or less (B), a synthetic oil (C), and a penetration degree of 25°C. A hot melt adhesive containing wax (D) having a strength of 10 dmm or less and polyethylene glycol (E) having a number average molecular weight of 1000 or more is disclosed.

Japanese Patent Laid-Open No. 2012-1624 discloses a thermoplastic elastomer (A), a solid tackifier (B) having an acid value of 100 mgKOH/g or more and 300 mgKOH/g or less, a liquid tackifier (C), a wax (D), and a specific A hot melt adhesive containing a nonionic surfactant (E) is disclosed.

Labels using hot melt adhesives disclosed in Japanese Patent Laid-Open No. 2010-90185, Japanese Patent Laid-Open No. 2010-280878, and Japanese Patent Laid-Open No. 2012-1624 have alkali peelability, adhesive strength between plastic films, and the holding power is sufficiently large. However, when the hot melt adhesive is made thinner, the adhesive strength is significantly lowered, the hot melt adhesive's ability to follow label misalignment due to bottle expansion is lost, and the label peels off.

The purpose of the present disclosure is to ensure that even when a thin film of hot melt adhesive is applied, the adhesive strength and followability (actual adhesiveness) of the hot melt against label misalignment due to expansion of the bottle are high, and the label is difficult to peel when stored for a long period of time. The aim is to provide an alkali-removable hot melt adhesive that can be easily peeled off from a container using a thermal aqueous alkali solution without leaving any adhesive paste.

The present disclosure relates to the following alkali-releasable hot melt adhesive and container.

[1] It is an alkali peelable hot melt adhesive containing styrene-based elastomer (A), rosin-based tackifier (B), process oil (C), and polypropylene wax (D),

The styrene-based elastomer (A) includes styrene-butadiene-styrene block copolymer (a1) and styrene-ethylene-butylene-styrene block copolymer (a2),

The acid value of the rosin-based tackifier (B) is 100 to 300 mgKOH/g, and the content of the rosin-based tackifier (B) is 30 to 65% by mass based on 100% by mass of the hot melt adhesive,

The softening point of the polypropylene wax (D) is 100°C or higher, and the content of the polypropylene wax (D) is 0.1 to 5% by mass based on 100% by mass of the hot melt adhesive,

Alkali release hot melt adhesive.

[2] The alkali-releasable hot melt adhesive according to [1] above, wherein the process oil (C) contains a naphthenic process oil.

[3] A container in which a label is attached to the container body using the alkali-removable hot melt adhesive described in [1] or [2] above.

[4] The container described in [3] above, where the label is a body wrap label.

[5] The container according to [3] or [4] above, wherein the label is made of polypropylene.

In the present disclosure, even when a thin film of hot melt adhesive is applied, the adhesive strength and the hot melt's ability to follow label misalignment due to expansion of the bottle (true adhesiveness) are high, and the label is difficult to peel when stored for a long period of time, and at the same time, it is heat resistant. It is possible to provide an alkali-removable hot melt adhesive that can easily peel off the adhesive from the container using an aqueous alkali solution without leaving any adhesive paste. The present disclosure can also provide a container using this alkali-removable hot melt adhesive.

Hereinafter, the alkali-removable hot melt adhesive and container of the present disclosure will be described in detail, but the present invention is not limited thereto.

In this specification, the numerical range specified using “~” includes the numerical values written before and after “~” as the range of the lower limit and upper limit.

(Styrene-based elastomer (A))

The styrene-based elastomer (A) becomes the base polymer of the alkali-removable hot melt adhesive of the present disclosure. Styrene-based elastomer is a type of thermoplastic elastomer. Thermoplastic elastomer is a polymer material that has properties similar to vulcanized rubber at room temperature and has elasticity, and at high temperatures, like ordinary thermoplastic resins, it can be used with existing molding machines. Thermoplastic elastomers have properties intermediate between rubber and plastic because they contain both a rubber component (soft segment: soft phase) that has elasticity in the molecule and a molecular restraint component (hard segment: hard phase) that prevents plastic deformation.

Styrene-based elastomers generally have a polystyrene block and a rubber middle block. The polystyrene portion (domain) forms a physical crosslink and becomes a crosslinking point, and the middle rubber block provides rubber elasticity to the product. Examples of the intermediate soft segment include polybutadiene (B), polyisoprene (I), polyolefin elastomer (ethylene propylene, EP), and combinations thereof.

Styrene-based elastomer (A) is classified into straight chain (linear type) and branched (radial type) depending on the arrangement of the soft and hard segments with the polystyrene (S).

Styrene-based elastomers include styrene-butadiene-styrene block copolymer (also known as SBS), styrene-ethylene/butylene-styrene block copolymer (also known as SEBS), and styrene-ethylene/propylene-styrene block copolymer (also known as SEPS). ), styrene-isoprene-styrene block copolymer (hereinafter abbreviated as SIS), and styrene-butylene/butadiene-styrene block copolymer (also referred to as SBBS).

The styrene-based elastomer (A) in the present disclosure contains both styrene-butadiene-styrene block copolymer (a1) and styrene-ethylene/butylene-styrene block copolymer (a2). By containing both SBS (a1) and SEBS (a2), it becomes possible to moderately reduce the compatibility of the hot melt adhesive. Decreased compatibility promotes cohesive failure. This allows the hot melt adhesive to follow the bottle when the bottle expands, and peeling of the adhesive material can be suppressed.

In addition, the styrene-based elastomer (A) may contain both SBS (a1) and SEBS (a2), and styrene-based elastomers other than these may be used in combination.

The content of the styrene-based elastomer (A) is preferably 1 to 35% by mass, more preferably 5 to 30% by mass, and particularly preferably 10 to 25% by mass, based on 100% by mass of the hot melt adhesive.

The alkali-removable hot-melt adhesive of the present disclosure is preferable because it can achieve both alkali-removability and adhesive strength by containing the styrene-based elastomer (A) in the above range.

In addition, the mass ratio ((a1)/(a2)) of SBS(a1) and SEBS(a2) is preferably 10/90 to 90/10, more preferably 20/80 to 80/20, and 25/75 to 25/75. 75/25 is particularly preferred.

By containing SBS (a1) and SEBS (a2) in a mass ratio within the above range, the alkali-releasable hot melt adhesive of the present disclosure can moderately promote cohesive failure and have real adhesive properties.

(Rosin-based tackifier (B))

The rosin-based tackifier (B) is not particularly limited as long as the acid value is 100 to 300 mgKOH/g. Unmodified untreated rosin, unmodified hydrogenated rosin, (meth)acrylic acid-modified rosin, hydrogenated (meth)acrylic acid-modified rosin, maleic acid-modified rosin, hydrogenated maleic acid-modified rosin. Rosin, fumaric acid-modified rosin, and hydrogenated fumaric acid-modified rosin are included. Preferably, it is unmodified hydrogenated rosin or hydrogenated (meth)acrylic acid-modified rosin, and more preferably, it is unmodified hydrogenated rosin. If the rosin-based tackifier (B) has an acid value of less than 100 mgKOH/g, it cannot exhibit sufficient alkali dispersibility, while if it has an acid value of more than 300 mgKOH/g, the viscosity and softening point of the hot melt adhesive become too high.

The content of the rosin-based tackifier (B) is 30 to 65% by mass based on 100% by mass of the hot melt adhesive. 35 to 60 mass% is preferable, and 40 to 55 mass% is more preferable.

The alkali-releasable hot-melt adhesive of the present disclosure is preferable because it can achieve both alkali-removable properties and actual adhesive properties by containing the rosin-based tackifier (B) in the above range.

Additionally, the acid value is the number of milligrams of potassium hydroxide (KOH) required to neutralize 1 g of sample. The method for measuring the acid value is described in detail in the later [Examples].

(Process Oil (C))

The process oil (C) used in the present disclosure is an oil commonly used as a plasticizer for rubber, thermoplastic elastomers, etc., a so-called process oil produced in petroleum refining, etc., and includes paraffinic process oil, naphthenic process oil, and aromatic process oil. It is largely distinguished by oil. From the viewpoint of alkali peelability, naphthenic oil is preferable.

Process oils are generally a mixture of aromatic rings, naphthenic rings, and paraffin chains. In this specification, a process oil with a naphthenic ring carbon content of 35 to 46% by mass of the total carbon is defined as a “naphthenic process oil,” and a process oil with an aromatic carbon content of 30% by mass or more of the total carbon is defined as an aromatic process oil. And, those containing more than 50% by mass of paraffin chain carbon in total carbon are defined as paraffinic and process oils.

The content of the process oil (C) is preferably 15 to 50% by mass, more preferably 20 to 45% by mass, and especially preferably 25 to 40% by mass, based on 100% by mass of the hot melt adhesive.

The alkali-removable hot-melt adhesive of the present disclosure is preferable because it can achieve both alkali-removability and high adhesive strength by containing the process oil (C) in the above range.

(polypropylene wax (D))

The polypropylene wax (D) is not particularly limited as long as it has a softening point of 100°C or higher. The softening point is preferably 125 to 165°C from the viewpoint of adhesive strength. In addition, the softening point is measured in accordance with JIS K-2207 (petroleum asphalt) 6.4 softening point test method (ring and ball method).

The content of polypropylene wax (D) is 0.1 to 5% by mass, preferably 0.1 to 4% by mass, and more preferably 0.1 to 3% by mass, based on 100% by mass of the hot melt adhesive.

The alkali peelable hot melt adhesive of the present disclosure may have excellent adhesive strength and actual adhesiveness by containing polypropylene wax (D) in the above range.

<Alkali peelable hot melt adhesive>

The alkali peelable hot melt adhesive of the present disclosure includes a styrene-based elastomer (A), a rosin-based tackifier (B), a process oil (C), and a polypropylene wax (D).

The alkali-removable hot melt adhesive of the present disclosure can be used in combination with any other thermoplastic elastomer other than the styrene-based elastomer (A) within the range capable of solving the problems of the present disclosure.

Other thermoplastic elastomers include olefin-based, urethane-based, polyester-based, polyamide-based, 1,2-butadiene-based, and vinyl chloride-based. These may be used individually, or two or more types may be used together.

The alkali-releasable hot melt adhesive of the present disclosure can also be used in combination with any other tackifier other than the rosin-based tackifier (B), within the range capable of solving the problems of the present disclosure. Other tackifiers include terpene resins, alicyclic hydrocarbon resins, aliphatic petroleum resins, and aromatic petroleum resins. These may be used individually, or two or more types may be used together.

The alkali-releasable hot melt adhesive of the present disclosure includes, if necessary, an antioxidant to prevent thermal degradation and thermal decomposition; Colorants such as fluorescent whitening agents can be added.

As antioxidants, pentaerythritol tetrakis[3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate], octadecyl-3-(3,5-di-t-butyl- 4-hydroxyphenyl)propionate, diethyl[[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]methyl]phosphonate, 4,6-bis(octylthiomethyl) -o-cresol, ethylenebis(oxyethylene)bis[3-(5-t-butyl-4-hydroxy-m-tryl]propionate, tris(2,4-di-t-butylphenyl)phosphite , and bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, etc. may be used individually or in combination of two or more types.

Examples of fluorescent whitening agents include stilbene-based, coumarin-based, oxazole-based, and naphthalimide-based. These may be used individually, or two or more types may be used together.

The alkali-removable hot melt adhesive of the present disclosure can be used as an adhesive for adhering paper, plastic films, etc. to various substrates such as glass, plastic, and metal. The alkali-removable hot-melt adhesive of the present disclosure can easily peel off attached paper, plastic films, etc. with hot alkaline water.

The alkali-releasable hot melt adhesive of the present disclosure having the above characteristics is used in applications such as soft drinks, seasonings, detergents, shampoos, cooking oils, cosmetics, and pharmaceuticals, and in glass containers such as glass bottles and PET (polyethylene terephthalate) bottles. It is suitable as an adhesive for labels on plastic containers, etc.

As shown in the [Examples] described later, the alkali peelable adhesive of the present disclosure satisfies the requirements for label peeling by hot alkaline water in the "Guidelines for Self-Regulation of Designated PET Bottles" issued by the PET Bottle Recycling Promotion Council, It has the ability to follow the hot melt adhesive against label misalignment due to bottle expansion. Therefore, the alkali-removable adhesive of the present disclosure is particularly suitable as an adhesive for attaching labels to PET bottles (an adhesive suitable for recycling of PET bottles).

Additionally, the use of the adhesive of the present disclosure is not limited to label use. The adhesive of the present disclosure can be used for all conventionally known adhesive applications, such as gum tape, clear cases, and assembly.

Substrates for labels for PET bottles usually include biaxially oriented polypropylene (OPP), polyethylene (PE), PET, and paper. The label may be a non-printed label, and may be at least a portion of the surface (i.e., the surface of the label) opposite to the surface on which the alkali-removable hot-melt adhesive of the substrate is applied, or the alkali-removable hot-melt adhesive of the substrate. It may be a printed label in which printing is performed on at least part of the surface on which the label is applied (i.e., the back side of the label). The alkali peelable hot melt adhesive of the present disclosure can be applied to the non-printing side of a non-printing label, the printing side or the non-printing side of a printed label, and can exhibit a predetermined adhesiveness/peelability/heat alkaline water solubility in any case. there is. Printing is performed by conventionally known printing methods such as gravure printing and UV printing.

<Courage>

The container in the present disclosure is one in which a label is attached to a container body, such as a PET bottle, using the alkali-removable hot melt adhesive of the present disclosure described above. As described above, the alkali-removable hot melt adhesive of the present disclosure is suitable for adhering labels to PET bottles. Accordingly, one embodiment of the container of the present disclosure includes a PET bottle with an attached label (labeled PET bottle).

Types of labeled PET bottles include labeled PET bottles in which a label is affixed to a portion of the body of the PET bottle, and body-wrapped PET bottles in which the label is wound so as to cover the body of the bottle in a circumferential shape. You can hold the bottle.

The adhesive of the present disclosure is also preferably used for adhering body wrap labels. For body wrapping labels, biaxially oriented polypropylene (OPP) film is widely used. The alkali-removable hot-melt adhesive of the present disclosure can provide good adhesion to body wrap labels such as OPP films, regardless of whether or not they are printed.

The alkali-removable hot melt adhesive of the present disclosure can be applied to part or the entire back side of a label. Application methods include an open wheel method, a closed gun method, and a direct coat method. As a method that leaves no adhesive paste on the main body of a container such as a PET bottle when the label is peeled off, the open wheel method and the direct coat method are preferable.

[Example]

Hereinafter, the present invention will be described in more detail through examples and comparative examples. However, the present invention is not limited to the following examples. In examples, unless otherwise specified, “part” represents “part by mass” and “%” represents “% by mass.”

[Acid value]

The acid value was measured in accordance with JIS K5601-2-1 acid value (timetric method). Specifically, 1 g of the sample was accurately weighed, placed in a 250 ml flask, 50 ml of ethanol or an equal volume mixture of ethanol and ether was added, and the sample was heated and dissolved. While this solution was occasionally shaken, 0.1N potassium hydroxide solution was added dropwise. Titration was performed using phenolphthalein as an indicator. The end point of titration was set at the point where the light pink color of the liquid remained for about 30 seconds. Next, a blank test was performed and corrected in the same manner, and the acid value was obtained from the following equation.

Acid value = [Consumption amount of 0.1N potassium hydroxide solution (ml) × 5.611] / [Sample amount (g)]

[Yeonhwa Branch]

The softening point was measured in accordance with JIS K-2207 (petroleum asphalt) 6.4 softening point test method (ring and ball method).

Each abbreviated name in Table 1-1 and Table 1-2 represents the following materials.

[Styrene-based elastomer (A)]

Styrene-butadiene-styrene block copolymer (a1)

·D1118: Clayton D1118 (manufactured by Clayton Polymer)

Styrene-ethylene-butylene-styrene block copolymer (a2)

·G1726: Clayton G1726 (manufactured by Clayton Polymer)

[Rosin-based tackifier (B)]

・RHR301: (manufactured by Maruzen Yukashoji Co., Ltd.), unmodified hydrogenated rosin, acid value: 175 mgKOH/g

Hari-Tac F: (manufactured by Harimakasei Co., Ltd.), unmodified hydrogenated rosin, acid value: 175 mgKOH/g

KE-604: Fine Crystal KE-604 (manufactured by Arakawa Chemical Co., Ltd.), acid-modified rosin, acid value: 240 mgKOH/g

[Synthetic oil (C)]

・N-90: Dianapressia N-90 (manufactured by Idemitsu Kosan Corporation) naphthenic process oil (paraffin: 48% by mass, naphthene: 46% by mass, aromatic: 6% by mass)

PW-90: Diana Process PW-90 (manufactured by Idemitsu Kosan Corporation) paraffinic process oil (paraffin: 71% by mass, naphthene: 29% by mass, aromatic: 0% by mass)

[Polypropylene wax (D)]

・660-P: Viscol 660-P (manufactured by Sanyo Kaseiko Co., Ltd.), softening point: 145°C

[Other tackifiers]

・FK125: Haritech FK125 (manufactured by Harimakasei Co., Ltd.), rosin ester, acid value: 17 mgKOH/g

KR120: Fine Crystal KR120 (manufactured by Arakawa Chemical Co., Ltd.), acid-modified rosin, acid value: 325 mgKOH/g

·P-125: Alcon P-125 (manufactured by Arakawa Chemical Co., Ltd.), alicyclic saturated hydrocarbon resin, acid value: none

[Other Wax]

PP1602: Lycocene PP1602 (manufactured by Clariant Japan), maleic anhydride modified polypropylene wax, softening point: 98°C

(Example 1)

<Manufacture of alkali peelable hot melt adhesive>

In a stainless steel beaker equipped with a stirrer, 28 parts of process oil (C): N-90 and 2 parts of polypropylene wax (D): 660-P were added and heated to melt. Heating was done carefully so that the contents reached 130-150°C. After melting, stirring was performed to obtain a uniform molten solution. While maintaining the temperature at 130 to 150°C and continuing stirring, 5 parts of styrene-butadiene-styrene block copolymer (a1): D1118 as styrene-based elastomer (A) and styrene-ethylene-butylene-styrene were added to this solution. Block copolymer (a2): 15 parts of G1726 was added slowly. After completion of addition, the mixture was heated and stirred at a temperature of 130 to 150°C to completely melt the styrene-based elastomer (A). After that, 50 parts of RHR301 was added as a rosin-based tackifier (B) to obtain a uniform molten mixture. This was naturally cooled to room temperature (20-25°C) to prepare an alkali-removable hot melt adhesive.

The adhesive strength (to OPP), alkali peelability, and actual adhesion of the obtained alkali peelable hot melt adhesive were evaluated by the following methods. The results are shown in Table 2-1 and Table 2-2.

<Alkali peelability>

(How to make samples)

As a label, a printed label (L1) was prepared by color printing on one side of an OPP film with a thickness of 30 μm. A hot melt adhesive was applied to the printing surface of this printed label (L1) under the conditions of a temperature of 150°C, a coating amount of 5 to 15 g/m2, and a coating area of 15 cm2, to obtain a label with an adhesive.

Using a labeler manufactured by Sakura Vera, the adhesive label was applied to cover the body of a 1.5 L round PET bottle in a circumferential shape under the conditions of a temperature of 150°C and a speed of 80 bpm, thereby obtaining a PET bottle with a label. This labeled PET bottle was pulverized into approximately 8 mm x 8 mm squares to obtain PET pellets containing the adhesive component and label component.

(Test Methods)

In a 1000 ml round flask, 180 g of a 2.0% by mass aqueous solution of sodium hydroxide at 80 to 85°C and 20 g of the above PET pellets were placed, and stirred at 120 rpm using a propeller as a stirring blade. After 10 minutes, this solution was filtered using a filter, and the residual percentage (area %) of the adhesive remaining in the PET pellet was determined by visual observation.

(Evaluation standard)

◎: Adhesive label and adhesive do not remain on PET pellets: Very good

○: No adhesive label remains, but less than 10% of the adhesive remains on the PET pellet: Good

△: More than 10% but less than 30% of adhesive remains in PET pellets: Practical

×: 30% or more of adhesive remains in PET pellets; Impractical

<Adhesive strength>

(How to make samples)

The adhesive label obtained as described above is attached to the non-printed side of a printed label (L1) printed in color on one side of an OPP film with a thickness of 30 μm at 23°C, and a hand roller is pressed on the printed label (L1). It was pressed back and forth and cut to a width of 15mm.

(Test Methods)

The printed label (L1) was peeled at 180° (peel speed: 300 mm/min) in a constant temperature room at 23°C, and the peel strength was measured.

(Evaluation standard)

◎: 3.5N/15mm or more: Very good

○: 2.5N/15mm or more, less than 3.5N/15mm: Good

△: More than 1.5N/15mm but less than 2.5N/15mm: Practical

×: Less than 1.5N/15mm: Not practical

<True adhesiveness>

(How to make samples)

The adhesive label obtained in the same manner as above was attached to cover the body of a 1.5L round PET bottle in a circumferential shape using a labeler manufactured by Sakumiravera Co., Ltd. under the conditions of a temperature of 150°C and a speed of 80 bpm, and the label was attached. I got a PET bottle. This labeled PET bottle was filled with carbonated water (commercially available product).

(Test Methods)

The labeled PET bottle (containing carbonated water) was placed in a constant temperature oven at 40°C, and its appearance was visually observed one week later.

(Evaluation standard)

◎: Label misalignment is less than 5 mm: Very good

○: Label misalignment is 5 mm or more but less than 10 mm: Good.

△: Label misalignment of 10 mm or more: Practical

×: Label peeled off: Not practical

(Examples 2 to 20, Comparative Examples 1 to 13)

A hot melt adhesive was manufactured and evaluated in the same manner as in Example 1, except that the composition was changed to that shown in Table 1-1 or Table 1-2.

[Table 1-1]

[Table 1-2]

[Table 2-1]

[Table 2-2]

From the data of Examples 1 to 20 shown in Table 1-1 and Table 2-1, the hot melt adhesive of the present disclosure has adhesive strength and hot melt followability against label misalignment due to expansion of the bottle, even when applied as a thin film ( It was found that the label had high thread adhesion, was difficult to peel off, and also had alkali peelability.

On the other hand, as shown in Table 1-2 and Table 2-2, the hot melt adhesives of Comparative Examples 1 to 13 did not provide results satisfying all of alkali peelability, adhesive strength, and actual adhesiveness.

As explained above, the present disclosure has high adhesive strength and high followability (actual adhesiveness) of the hot melt against label misalignment due to expansion of the bottle, even when a thin film of hot melt adhesive is applied, and the label is unlikely to peel when stored for a long period of time. It is possible to provide an alkali-releasable hot melt adhesive that is difficult and at the same time can be easily peeled off from the container using a thermal aqueous alkali solution and can be peeled off without leaving any adhesive paste. The present disclosure can also provide a container using this alkali-removable hot melt adhesive.

For example, when a labeled container using the alkali-removable hot melt adhesive of the present disclosure is recycled after becoming unnecessary, the label can be easily peeled from the container body, such as by immersing the labeled container in a hot aqueous alkali solution. The body and label can be easily distinguished.

The alkali-removable hot melt adhesive of the present disclosure is suitable as a label for a container, and is suitable as a body wrapping label for a PET bottle (particularly for a body wrapping label for a PET bottle for carbonated beverages with a high bottle expansion rate).

The alkali-removable hot melt adhesive of the present disclosure is not limited to PET bottles, but can exhibit similar performance in glass containers and is also suitable for recycling of glass containers.

Claims (5)

It is an alkali peelable hot melt adhesive containing styrene-based elastomer (A), rosin-based tackifier (B), process oil (C), and polypropylene wax (D).
The styrene-based elastomer (A) includes styrene-butadiene-styrene block copolymer (a1) and styrene-ethylene-butylene-styrene block copolymer (a2),
The acid value of the rosin-based tackifier (B) is 100 to 300 mgKOH/g, and the content of the rosin-based tackifier (B) is 30 to 65% by mass based on 100% by mass of the hot melt adhesive,
The softening point of the polypropylene wax (D) is 100°C or higher, and the content of the polypropylene wax (D) is 0.1 to 5% by mass based on 100% by mass of the hot melt adhesive,
Alkali release hot melt adhesive.
According to paragraph 1,
An alkali-releasable hot melt adhesive wherein the process oil (C) contains a naphthenic process oil.
A container in which a label is attached to the container body using the alkali peelable hot melt adhesive according to claim 1 or 2.
The container according to claim 3, wherein the label is a body wrap label.
The container according to claim 3, wherein the label is made of polypropylene.