JP2024072387A - Alkali-peelable hot melt adhesive and container - Google Patents

Abstract

[Problem] To provide an alkali-peelable hot melt adhesive and a body-wrapped label that, even when applied in a thin film, has high adhesive strength and good followability (actual adhesion) of the hot melt to the displacement of the label caused by bottle expansion, and the label is not easily peeled off during long-term storage, and the adhered object can be easily peeled off from the container with a hot alkaline aqueous solution without leaving any adhesive residue.Solution] An alkali-peelable hot melt adhesive containing a styrene-based elastomer (A) containing a styrene-butadiene-styrene block copolymer (a1) and a styrene-ethylene-butylene-styrene block copolymer (a2), a rosin-based tackifier (B) having an acid value of 100 to 300 mgKOH/g, a process oil (C), and a specific amount of polypropylene wax (D) having a softening point of 100°C or higher. [Selected Figure] None

Description

The present invention relates to an alkali-removable hot melt adhesive and a container to which a label is attached using said adhesive.

In recent years, the production volume of polyethylene terephthalate (hereinafter referred to as PET) bottles has increased, along with the use of PET bottles for beverages. PET bottles usually have a plastic label attached to the outside of the body to display the product name, etc. There are several methods for attaching a plastic label to the outside of the body of a PET bottle, including the "wrap-around label method," "stretch label method," and "shrink label method."

In either case, it is required that used PET bottles are collected and can be recycled as raw materials. For example, the "Self-regulation Guidelines for Designated PET Bottles" issued by the PET Bottle Recycling Promotion Council lists the following indicators. That is, when pellets made by cutting bottles with labels are immersed in a 1.5% aqueous sodium hydroxide solution at 90°C at a pellet concentration of 10% (by weight) and stirred for 15 minutes, the label peels off from the PET pellets and no printing ink or adhesive remains on the PET pellets. In order to peel off the labels during the recycling process (alkali peelability), an alkali peelable hot melt adhesive has been developed and is used as an adhesive for labels on containers such as PET bottles.

On the other hand, if the contents contain carbon dioxide, and the bottle is left at high temperatures (40-50°C), such as during transportation in the summer, the PET bottle will expand. The expansion of the PET bottle places a load on the label wrapped around the bottle, which can cause the plastic film at the end of the label to shift from the plastic film located on the inside. Therefore, it is necessary for the label to not peel off even if the end of the label shifts (suitability for application). For this reason, the label needs to have high adhesive strength (peel strength) between the plastic films that make up the label base, and the hot melt adhesive needs to be able to follow the label's shift caused by bottle expansion.

Furthermore, in recent years, the plastic films and adhesives used in labels have become thinner (normal: 30-50 μm, thin: 5-15 μm) due to environmental considerations, and even if the adhesive layer is thin, there is a demand for high adhesive strength (peel strength) and conformability to misalignment between the plastic films that make up the label.

Patent Document 1 discloses a water-dispersible hot melt adhesive composition containing a copolyester. However, the copolyester described in Patent Document 1 has poor heat resistance and is partially thermally decomposed, resulting in a problem that the adhesive strength of the adhesive composition is not stable.

Patent Document 2 discloses a hot melt adhesive containing a thermoplastic elastomer (A), a rosin-based tackifier (B) having an acid value of 100 mgKOH/g or more and 300 mgKOH/g or less, a terpene phenol resin (C), a synthetic oil (D), and a polypropylene wax (E) graft-polymerized with maleic anhydride.

Patent Document 3 discloses a hot melt adhesive that contains a thermoplastic elastomer (A), a rosin-based tackifier (B) having an acid value of 100 mgKOH/g or more and 300 mgKOH/g or less, a synthetic oil (C), a wax (D) having a needle penetration of 10 dmm or less at 25°C, and a polyethylene glycol (E) having a number average molecular weight of 1000 or more.

Patent Document 4 discloses a hot melt adhesive that contains 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 nonionic surfactant (E).

Labels using the hot melt adhesives disclosed in References 2 to 4 have sufficient alkali peelability, adhesive strength between plastic films, and holding power, but there are problems in that the adhesive strength is significantly reduced by making the hot melt adhesive thin, and furthermore, the hot melt adhesive loses its ability to follow the label's displacement caused by bottle expansion, causing the label to peel off.

In other words, there was a demand for an alkali-peelable hot melt adhesive that, even when applied in a thin film, has high adhesive strength and the hot melt's ability to follow the displacement of the label caused by bottle expansion, so that the label does not peel off easily during long-term storage, and that allows the adhered material to be easily peeled off from the container using a hot alkaline aqueous solution without leaving any glue behind.

JP 11-512134 A JP 2010-90185 A JP 2010-280878 A JP 2012-1624 A

The object of the present invention is to provide a body-wrapped label that has high adhesive strength and high hot melt compliance (actual adhesion) with respect to label misalignment caused by bottle expansion, even when the hot melt adhesive is applied in a thin film, and that is particularly suitable for PET bottles for carbonated beverages, which have a large bottle expansion rate, and that is difficult to peel off during long-term storage, and that can be easily peeled off from the container with a hot alkaline aqueous solution without leaving any glue behind, and to provide an alkali-peeling hot melt adhesive for this purpose.

The present invention relates to the following alkali-removable hot-melt pressure sensitive adhesive and container.
[1] An alkali-peelable hot-melt pressure-sensitive adhesive comprising a styrene-based elastomer (A), a rosin-based tackifier (B), a process oil (C) and a polypropylene wax (D), wherein the styrene-based elastomer (A) comprises a styrene-butadiene-styrene block copolymer (a1) and a styrene-ethylene-butylene-styrene block copolymer (a2), the acid value of the rosin-based tackifier (B) is 100 to 300 mgKOH/g, 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 mass% in 100 mass% of the hot-melt pressure-sensitive adhesive.

[2] The alkali-peelable hot melt adhesive described in [1] above, in which the process oil (C) contains a naphthenic process oil.

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

[4] The container described in [3] above, characterized in that the label is a body-wrapped label.

[5] The container described in [3] above, characterized in that the label is made of polypropylene.

The present invention provides an alkali-peelable hot melt adhesive that has high adhesive strength and high compatibility with label displacement caused by bottle expansion even when the hot melt adhesive is applied in a thin film, and that makes it difficult for labels to peel off during long-term storage, particularly in PET bottles for carbonated beverages, which have a large bottle expansion rate, and that easily peels off from containers, etc., without leaving any adhesive residue, and does not reattach when immersed in a hot alkaline aqueous solution. Also provided is a container using the alkali-peelable hot melt adhesive of the present invention.

The alkali-peelable hot melt adhesive and container of the present invention are described in further detail below, but are not limited thereto.

In this specification, a numerical range specified using "~" is intended to include the numerical values before and after "~" as the lower and upper limits of the range.

(Styrene-based elastomer (A))
The styrene-based elastomer (A) is the base polymer of the alkali-peelable hot melt adhesive of the present invention. The styrene-based elastomer is a type of thermoplastic elastomer. A thermoplastic elastomer is a material that has the same properties as vulcanized rubber at room temperature and is elastic, and at high temperatures, it is a polymer material that can be used with existing molding machines as is, just like ordinary thermoplastic resins. Thermoplastic elastomers have both rubber components (soft segments: soft phase) that have elasticity in the molecule and molecular restraint components (hard segments: hard phase) that prevent plastic deformation, so they have properties intermediate between rubber and plastic.
Styrene elastomers generally have a polystyrene block and a rubber middle block, the polystyrene portion forms a physical crosslink (domain) and becomes a crosslinking point, and the middle rubber block gives the product rubber elasticity. The middle soft segment includes polybutadiene (B), polyisoprene (I) and polyolefin elastomer (ethylene propylene, EP), and depending on the arrangement with the hard segment polystyrene (S), they are divided into linear type and branched type (radial type).

Examples of styrene-based elastomers include styrene-butadiene-styrene block copolymer (hereinafter sometimes abbreviated as SBS), styrene-ethylene-butylene-styrene block copolymer (hereinafter sometimes abbreviated as SEBS), styrene-ethylene-propylene-styrene block copolymer (hereinafter sometimes abbreviated as SEPS), styrene-isoprene-styrene block copolymer (hereinafter sometimes abbreviated as SIS), and styrene-butylene-butadiene-styrene block copolymer (hereinafter sometimes abbreviated as SBBS).

The styrene-based elastomer (A) in the present invention simultaneously contains a styrene-butadiene-styrene block copolymer (a1) and a styrene-ethylene-butylene-styrene block copolymer (a2). By simultaneously containing SBS (a1) and SEBS (a2), it becomes possible to appropriately reduce the compatibility of the hot melt pressure-sensitive adhesive, and by reducing the compatibility, cohesive failure is promoted, and even when the bottle expands, the hot melt pressure-sensitive adhesive follows it, thereby suppressing peeling.
In addition, as long as SBS (a1) and SEBS (a2) are contained simultaneously, a styrene-based elastomer other than SBS (a1) and SEBS (a2) may be used in combination.

The content of the styrene-based elastomer (A) is preferably from 1.0 to 35 mass%, more preferably from 5 to 30 mass%, and even more preferably from 10 to 25 mass%, based on 100 mass% of the hot melt pressure-sensitive adhesive.
By containing the styrene-based elastomer (A) in the above range, both the alkali peelability and the adhesive strength can be achieved, which is preferable.
The mass ratio (a1)/(a2) of SBS (a1) to SEBS (a2) is preferably from 10/90 to 90/10, and more preferably from 20/80 to 80/20.
By containing SBS (a1) and SEBS (a2) in the above ranges, cohesive failure can be appropriately promoted and suitability for actual application can be imparted.

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

The content of the rosin-based tackifier (B) is preferably from 1.0 to 35 mass%, more preferably from 5 to 30 mass%, and even more preferably from 10 to 25 mass%, based on 100 mass% of the hot melt pressure-sensitive adhesive.
By containing the rosin-based tackifier (B) in the above range, both the alkali peelability and the suitability for actual application can be achieved, which is preferable.

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 Examples section.

(Process Oil (C))
The process oil (C) used in the present invention is an oil generally used as a plasticizer for rubber, thermoplastic elastomers, etc., that is, a process oil produced in petroleum refining, etc., and is roughly classified into paraffinic process oil, naphthenic process oil, and aromatic process oil. From the viewpoint of alkali stripping property, naphthenic oil is preferred.
Process oil is a mixture of aromatic rings, naphthenic rings, and paraffin chains, and naphthenic process oil in this application refers to process oil in which naphthenic ring carbons account for 35 to 46% by mass of the total carbon of the process oil. In addition, process oils in which aromatic carbons account for 30% by weight or more of the total carbon are classified as aromatic process oils, and process oils in which paraffin chain carbons account for 50% by weight or more of the total carbon are classified as paraffinic process oils.

The content of the process oil (C) is preferably from 15 to 50 mass%, more preferably from 20 to 45 mass%, and even more preferably from 25 to 40 mass%, based on 100 mass% of the hot melt pressure-sensitive adhesive.
By containing the process oil (C) in the above range, both alkali peelability and high adhesive strength can be achieved, which is preferable.

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

The content of the polypropylene wax (D) is 0.1 to 5 mass %, preferably 0.1 to 4 mass %, and more preferably 0.1 to 3 mass %, based on 100 mass % of the hot melt pressure sensitive adhesive.
By containing 0.1 to 5 mass % of the polypropylene wax (D) based on 100 mass % of the hot melt pressure sensitive adhesive, it is possible to obtain a hot melt pressure sensitive adhesive having excellent adhesive strength and practical application.

<Alkali-peelable hot melt adhesive>
The alkali peelable hot melt pressure sensitive adhesive of the present invention contains a styrene-based elastomer (A), a rosin-based tackifier (B), a process oil (C) and a polypropylene wax (D).

Any thermoplastic elastomer other than the styrene-based elastomer (A) can be used as long as the problem of the present invention can be solved.
Other examples of thermoplastic elastomers include olefin-based, urethane-based, polyester-based, polyamide-based, 1,2-butadiene-based, and vinyl chloride-based elastomers.

Furthermore, any tackifier other than the rosin-based tackifier (B) can be used as long as the problem of the present invention can be solved.
Other examples of the tackifier include terpene resins, alicyclic hydrocarbon resins, aliphatic petroleum resins, aromatic petroleum resins, etc. The tackifier resins may be used alone or in combination of two or more kinds.

If necessary, antioxidants to prevent thermal deterioration and thermal decomposition, coloring materials such as fluorescent whitening agents, etc. can be added to the alkali-peelable hot melt adhesive of the present invention.

Examples of antioxidants include 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, ethylene bis(oxyethylene) bis[3-(5-t-butyl-4-hydroxy-m-tolyl]propionate, tris(2,4-di-t-butylphenyl)phosphite, bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite, etc. These antioxidants may be used alone or in combination of two or more.

Fluorescent brightening agents include stilbene-based, coumarin-based, oxazole-based, and naphthalimide-based agents. These fluorescent brightening agents may be used alone or in combination of two or more types.

The alkali peelable hot melt adhesive of the present invention can be used as an adhesive for adhering paper, plastic film, etc. to various substrates such as glass, plastic, and metal. The alkali peelable hot melt adhesive of the present invention can easily peel off the attached paper, film, etc. with hot alkaline water, so that it is preferably used as an adhesive for labels on glass containers such as glass bottles used for soft drinks, seasonings, detergents, shampoos, edible oils, cosmetics, medicines, etc., and plastic containers such as PET (polyethylene terephthalate) bottles. However, the use of the adhesive of the present invention is not limited to this label use, and it can be used as an adhesive for all conventionally known uses such as packing tape, clear cases, and assembly. However, as specifically shown in the examples, the alkali peelable adhesive of the present invention satisfies the label peeling requirements with hot alkaline water in the "Voluntary Regulation Guideline for Designated PET Bottles" issued by the PET Bottle Recycling Promotion Council, and has the followability of a hot melt adhesive to the displacement of the label due to bottle expansion, so it is particularly preferable to use it as an adhesive for adhering labels to PET bottles, that is, as an adhesive suitable for recycling PET bottles.

OP, PE, PET, and even paper are usually used as label substrates for PET bottles. In addition, the labels are used with appropriate printing on the side opposite to the side to which the alkali-peelable hot melt adhesive is applied, i.e., the front side of the label, or on the side to which the alkali-peelable hot melt adhesive is applied, i.e., the back side of the label. The alkali-peelable hot melt adhesive of the present invention can be applied to the printed side of a label that has been printed, or of course to an unprinted label. In either case, it exhibits the desired adhesiveness, peelability, and hot alkaline water solubility. In addition, the printing may be performed on the entire back side of the label, or on only a part of the surface. The printing may be performed by any of the conventionally known printing methods, such as gravure printing and UV printing.

<Container>
The container in the present invention refers to one having a label attached thereto using the alkali-peelable hot-melt adhesive. As described above, the alkali-peelable hot-melt adhesive of the present invention is preferably used for attaching a label to a PET bottle, and in this case, the PET bottle to which the label is attached is the container in the present invention.

In PET bottles, in addition to those with a label attached to a part of the body of the PET bottle, a body-wrapped label that is wrapped around the body of the bottle to cover it in a circular shape is used, and the adhesive of the present invention is also preferably used for bonding these body-wrapped labels. OPP film is often used as such body-wrapped labels. The alkali-peelable hot melt adhesive of the present invention can provide good adhesion to body-wrapped labels such as OPP films, whether they are printed on the back or not. The alkali-peelable hot melt adhesive of the present invention may be applied to the entire back surface of the label, or the adhesive may be applied to only a part of the back surface of the label. Coating methods include the open wheel method, the closed gun method, and the direct coat method. The open wheel method and the direct coat method are preferred as methods that do not leave glue on the PET bottle when peeled off.

The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to the following examples. In the examples, "parts" refers to "parts by mass" and "%" refers to "% by mass" unless otherwise specified.

[Acid value]
The acid value was measured in accordance with JIS K5601-2-1 Acid Value (Titration Method). Specifically, 1 g of sample was precisely weighed, placed in a 250 ml flask, 50 ml of ethanol or an equal volume mixture of ethanol and ether was added, and the mixture was heated to dissolve, and titrated with 0.1N potassium hydroxide solution while shaking occasionally (indicator: phenolphthalein). The end point of the titration was the point at which the light pink color of the solution remained for 30 seconds. Next, a blank test was performed in the same manner to correct the value, and the acid value was calculated from the following formula.
Acid value = [amount of 0.1 N potassium hydroxide solution consumed (ml) x 5.611] / [amount of sample (g)]

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

The abbreviations used in Table 1 are as follows:
[Styrene-based elastomer (A)]
Styrene-butadiene-styrene block copolymer (a1)
D1118: Kraton D1118 (Kraton Polymers)
Styrene-ethylene-butylene-styrene block copolymer (a2)
G1726: Kraton G1726 (Kraton Polymers)

[Rosin-based tackifier (B)]
RHR301: (manufactured by Maruzen Yuka Shoji Co., Ltd.), unmodified hydrogenated rosin, acid value: 175 mgKOH/g
Haritac F: (manufactured by Harima Chemicals), unmodified hydrogenated rosin, acid value: 175 mgKOH/g
KE-604: Pine Crystal KE-604 (manufactured by Arakawa Chemical Industries, Ltd.), acid-modified rosin, acid value: 240 mgKOH/g

[Synthetic oil (C)]
N-90: Diana Fresia N-90 (Idemitsu Kosan Co., Ltd.) naphthenic process oil (paraffin: 48% by mass, naphthene: 46% by mass, aromatics: 6% by mass)
PW-90: Diana Process PW-90 (Idemitsu Kosan Co., Ltd.) paraffinic process oil (paraffin: 71% by mass, naphthene: 29% by mass, aromatics: 0% by mass)

[Polypropylene wax (D)]
660-P: Viscol 660-P (manufactured by Sanyo Chemical Industries, Ltd.), softening point: 145°C

[Other tackifiers]
FK125: Haritac FK125 (Harima Chemicals), rosin ester, acid value: 17 mgKOH/g
KR120: Pine Crystal KR120 (manufactured by Arakawa Chemical Industries, Ltd.), acid-modified rosin, acid value: 325 mgKOH/g
P-125: Alcon P-125 (manufactured by Arakawa Chemical Industries, Ltd.), alicyclic saturated hydrocarbon resin, acid value: none

[Other waxes]
PP1602: Ricothene PP1602 (Clariant Japan), maleic anhydride modified polypropylene wax, softening point: 98°C

Example 1
<Production 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 placed and heated to melt. Heating was performed carefully so that the contents would reach 130°C to 150°C. After melting, stirring was performed to obtain a homogeneous molten solution, and then while maintaining the temperature at 130°C to 150°C and continuing stirring, 5 parts of styrene-butadiene-styrene block copolymer (a1): D1118 and 15 parts of styrene-ethylene-butylene-styrene block copolymer (a2): G1726 were gradually added as styrene-based elastomer (A) to the molten mixture, and after the addition was completed, the mixture was heated and stirred at a temperature of 130°C to 150°C to completely melt the styrene-based elastomer (A). Thereafter, 50 parts of RHR301 were added as rosin-based tackifier (B), and a homogeneous molten mixture was obtained, which was then cooled to produce an alkali-peelable hot melt adhesive.

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

<Alkaline peelability>
(Sample preparation method)
A hot melt adhesive was applied to the printed surface of a label printed on a 30 μm thick OPP film in an amount of 5 to 15 g/m ² and a coating area of 15 cm ² (temperature condition: 150° C.) to obtain a label with a hot melt adhesive.
Thereafter, the hot melt adhesive label was attached to a 1.5 L round PET bottle at 150° C. using a labeler manufactured by Sakumi Labeler Co., Ltd. at a speed of 80 bpm.
Next, the PET bottle together with the hot melt adhesive label was crushed into approximately 8 mm x 8 mm squares to obtain pellets of PET with the label attached.
(Test method)
In a 1000 ml round flask, 180 g of a 2.0% by mass aqueous sodium hydroxide solution at 80 to 85° C. and 20 g of the pellets were placed and stirred at 120 rpm (stirring blade: propeller). After 10 minutes, the mixture was filtered through a filter, and the residual rate (area %) of the adhesive remaining on the PET pellets was visually observed.
(Evaluation criteria)
◎: The label with hot melt adhesive and the hot melt adhesive do not remain on the PET pellet: Very good ◯: The label with hot melt adhesive does not remain, but less than 10% of the hot melt adhesive remains on the PET pellet: Good △: 10% or more but less than 30% of the hot melt adhesive remains on the PET pellet: Usable ×: 30% or more of the hot melt adhesive remains on the PET pellet; Not usable

<Adhesive strength>
(Sample preparation method)
A label with a hot melt adhesive was obtained in the same manner as above. The label with the hot melt adhesive was attached to the non-printed surface of a 30 μm-thick OPP film at 23° C., pressed by rolling once back and forth with a hand roller, and cut to a width of 15 mm.
(Test method)
The test was performed in a thermostatic chamber at 23° C. with 180° peeling (peel speed: 300 mm/min).
(Evaluation criteria)
◎: 3.5N/15mm or more: Very good 〇: 2.5N/15mm or more and less than 3.5N/15mm: Good △: 1.5N/15mm or more and less than 2.5N/15mm: Usable ×: Less than 1.5N/15mm: Not usable

<Actual adhesion>
(Sample preparation method)
A label with a hot melt adhesive was obtained in the same manner as above. The label with the hot melt adhesive was then attached to a 1.5 L round PET bottle at 150° C. and a speed of 80 bpm using a labeler manufactured by Sakumi Labeler Co., Ltd. Carbonated water (commercially available) was filled into the resulting labeled bottle to obtain a sample to be used for evaluating the actual attachment property.
(Test method)
The bottle was placed in a thermostatic oven at 40° C., and the appearance was observed after one week.
(Evaluation criteria)
◎: Label misalignment is less than 5 mm: Very good ◯: Label misalignment is 5 mm to less than 10 mm: Good △: Label misalignment is 10 mm or more: Usable ×: Label peels off: Not usable

(Examples 2 to 19, Comparative Examples 1 to 11)
In accordance with the composition shown in Table 1, the styrene-based elastomer (A), the rosin-based tackifier (B), the process oil (C), the polypropylene wax (D) and other components were melted and mixed in the same manner as in Example 1 to prepare hot melt pressure sensitive adhesives, which were then evaluated in the same manner.

As can be seen from Examples 1 to 19 in Table 1, the hot melt adhesive of the present invention has high adhesive strength and good conformability (actual adhesion) to the label displacement caused by bottle expansion, even when the hot melt adhesive is applied as a thin film, the label is not easily peeled off, and further has alkali peelability.
On the other hand, the hot melt adhesives of Comparative Examples 1 to 11 did not provide satisfactory results in all of the alkaline peelability, adhesive strength, and suitability for actual application.

As explained above, the alkali-peelable hot melt adhesive of the present invention makes it possible to easily peel off the labels from containers that are no longer needed after use and to recycle them, and they can be easily separated by immersing them in a hot alkaline aqueous solution. It has also been found that the same performance is achieved not only with PET bottles but also with glass containers, making this hot melt adhesive suitable for recycling glass containers.

Claims (5)

An alkali peelable hot melt pressure sensitive adhesive comprising a styrene elastomer (A), a rosin tackifier (B), a process oil (C) and a polypropylene wax (D),
The styrene-based elastomer (A) comprises a styrene-butadiene-styrene block copolymer (a1) and a styrene-ethylene-butylene-styrene block copolymer (a2);
The acid value of the rosin-based tackifier (B) is 100 to 300 mgKOH/g;
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 mass% in 100 mass% of the hot melt pressure-sensitive adhesive;
Alkali-peelable hot melt adhesive. The alkali-peelable hot melt adhesive according to claim 1, wherein the process oil (C) contains a naphthenic process oil. A container to which a label is attached using the alkali-peelable hot melt adhesive according to claim 1 or 2. The container according to claim 3, characterized in that the label is a body-wrapped label. 4. The container of claim 3, wherein the label is made of polypropylene.