Hot-melt adhesive composition and adhesive tape

Abstract

To provide a technique related to a hot-melt adhesive composition and an adhesive tape suitable for sealing a food container formed of a paper material having relatively large surface roughness.SOLUTION: A hot-melt adhesive composition contains a triblock copolymer A, a triblock copolymer B and a rosin ester-based tackifier resin. The triblock copolymer A contains at least a segment A having methacrylate ester as the main body, and a segment B having acrylic acid ester as the main body, and has a weight average molecular weight of 70,000 or more. The triblock copolymer B contains at least a segment A having methacrylate ester as the main body, and a segment B having acrylic acid ester as the main body, and has a weight average molecular weight of less than 70,000. The rosin ester-based tackifier resin has a softening point of 70°C-80°C. A content of the triblock copolymer B to 100 pts.mass of the triblock copolymer A is 70 pts.mass or more, and a content of the rosin ester-based tackifier resin to 100 pts.mass of the triblock copolymer A is 75 pts.mass or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a hot melt pressure sensitive adhesive composition and a pressure sensitive adhesive tape. [Background technology]

[0002] BACKGROUND ART From the viewpoint of reducing environmental impact, there is an increasing demand for food containers made of paper materials such as pulp (for example, pulp molded containers) instead of food containers made of synthetic resins. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-233935 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional food containers made of paper are sometimes sealed with a fitting mechanism, but because the containers themselves are prone to deformation and the fitting is loose and easy to come off, there is a demand for fastening them with adhesive tape. However, when sealing food containers with adhesive tape, if the surface roughness of the paper material is large, conventional adhesive tape cannot exert sufficient adhesiveness.

[0005] The present invention has been made in consideration of the above-mentioned problems, and aims to provide a hot melt pressure sensitive adhesive composition and pressure sensitive adhesive tape suitable for sealing food containers made of paper materials with relatively high surface roughness. [Means for solving the problem]

[0006] One embodiment of the present invention is a hot melt pressure-sensitive adhesive composition, comprising: a triblock copolymer A, which contains at least a methacrylic acid ester-based segment A and an acrylic acid ester-based segment B, and has a weight-average molecular weight of 70,000 or more; a triblock copolymer B, which contains at least a methacrylic acid ester-based segment A and an acrylic acid ester-based segment B, and has a weight-average molecular weight of less than 70,000; and a rosin ester-based tackifying resin having a softening point of 70 to 80°C, wherein the content of the triblock copolymer B per 100 parts by mass of the triblock copolymer A is 70 parts by mass or more, and the content of the tackifying resin per 100 parts by mass of the triblock copolymer A is 75 parts by mass or more. Another aspect of the present invention is a pressure-sensitive adhesive tape comprising a substrate and a pressure-sensitive adhesive layer formed from the hot-melt pressure-sensitive adhesive composition of the above aspect and laminated on the substrate. The pressure-sensitive adhesive tape of the above embodiment may be used to seal a food container in which at least the container body is formed from a paper material, and the paper material has an arithmetic mean roughness (Ra) of 12 to 25 μm and a ten-point mean roughness (Rz) of 61 to 100 μm. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a technology relating to a hot melt pressure sensitive adhesive composition and a pressure sensitive adhesive tape suitable for sealing food containers made of paper materials with a relatively high surface roughness. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic cross-sectional view of a pressure-sensitive adhesive tape according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail. In this specification, the expression "a to b" in the description of a range of numerical values means that the range is from a to b, unless otherwise specified.

[0010] (adhesive tape) 1 is a schematic cross-sectional view of a pressure-sensitive adhesive tape 10 according to an embodiment. The pressure-sensitive adhesive tape 10 includes a substrate 20 and a pressure-sensitive adhesive layer 30.

[0011] The substrate 20 can be appropriately selected within a range that does not impair the effects of the present invention, but is preferably made of at least one material selected from the group consisting of polyethylene terephthalate (PET), polypropylene (PP), cellophane, and paper.

[0012] The thickness of the substrate 20 is not particularly limited, but can be, for example, 5 to 100 μm or 9 to 50 μm.

[0013] The surface of the substrate 20 may be subjected to an appropriate surface treatment. Examples of the surface treatment include a corona treatment to improve adhesion to the pressure-sensitive adhesive layer 30, which will be described later, and a release treatment applied to the surface opposite the pressure-sensitive adhesive layer 30.

[0014] The pressure-sensitive adhesive layer 30 is laminated on one main surface of the substrate 20. The pressure-sensitive adhesive layer 30 is formed from a hot-melt pressure-sensitive adhesive composition. The hot melt pressure-sensitive adhesive composition contains a triblock copolymer A, a triblock copolymer B, and a rosin ester tackifying resin. Each component of the hot melt pressure-sensitive adhesive composition will be described in detail below.

[0015] (Triblock copolymer A) The triblock copolymer A contains at least a segment A mainly made of a methacrylic acid ester and a segment B mainly made of an acrylic acid ester, and has a weight average molecular weight of 70,000 or more. Specific examples of the triblock copolymer A include MMA (methyl methacrylate) / nBA (n-butyl acrylate) / MMA (methyl methacrylate) copolymer, MMA (methyl methacrylate) / nBA-2EHA (n-butyl acrylate and 2-ethylhexyl acrylate) / MMA (methyl methacrylate) copolymer, and the like, such as the "CLARITY (registered trademark) series" manufactured by Kuraray Co., Ltd.

[0016] (Triblock copolymer B) The triblock copolymer B contains at least a segment A mainly made of a methacrylic acid ester and a segment B mainly made of an acrylic acid ester, and has a weight average molecular weight of less than 70,000. A specific example of the triblock copolymer B is an MMA (methyl methacrylate) / nBA (n-butyl acrylate) / MMA (methyl methacrylate) copolymer (for example, the "CLARITY (registered trademark) series" manufactured by Kuraray Co., Ltd.). The content of triblock copolymer B relative to 100 parts by mass of triblock copolymer A is 70 parts by mass or more.

[0017] (rosin ester tackifying resin) The softening point of the rosin ester tackifying resin is 70°C to 80°C. Examples of rosin ester-based tackifying resins include disproportionated rosin ester, polymerized rosin ester, hydrogenated rosin ester, and rosin phenol-based tackifying resins.

[0018] The content of the rosin ester tackifying resin is preferably 75 parts by mass or more based on 100 parts by mass of the triblock copolymer A.

[0019] The pressure-sensitive adhesive layer 30 may contain other components to the extent that the effects of the present invention are not impaired.

[0020] The pressure-sensitive adhesive tape 10 may include other layers that are conventionally known. Examples of such other layers include a primer layer that enhances adhesion between the substrate 20 and the pressure-sensitive adhesive layer 30, and a separator layer that is provided in contact with the pressure-sensitive adhesive layer 30 and is removed before use. In consideration of productivity and environmental impact, a straight winding (no separator) is preferred.

[0021] (Method of manufacturing adhesive tape) The pressure-sensitive adhesive tape 10 according to the embodiment can be produced by a conventionally known method. For example, the pressure-sensitive adhesive tape 10 can be produced by the following procedure.

[0022] First, a hot melt pressure-sensitive adhesive composition containing the triblock copolymer A, the triblock copolymer B, the rosin ester tackifying resin, and, if necessary, other additives is prepared (hot melt pressure-sensitive adhesive composition production process). Next, the hot melt pressure sensitive adhesive composition is applied onto the substrate, and then the applied composition is sequentially wound up to the required length by a winding roller (coating step). Finally, the rolled rod is cut to a required width to produce an adhesive tape (cutting step).

[0023] In addition to the above procedure, the adhesive tape may be produced by transferring an adhesive layer formed in advance on a separator to a substrate.

[0024] (Application) The pressure-sensitive adhesive tape according to the above-described embodiment is used to seal food containers made of paper material such as pulp, etc. The food containers are, for example, pulp-molded containers.

[0025] The calculated average roughness (Ra) of the paper material of the food container is 12 to 25 μm, and the ten-point average roughness (Rz) is 61 to 100 μm. The arithmetic average roughness (Ra) is calculated in accordance with JIS B 0601 using a small surface roughness measuring instrument. The ten-point average roughness (Rz) is also calculated in accordance with JIS B 0601 using a small surface roughness measuring instrument.

[0026] As described above, the adhesive tape of this embodiment has good adhesion to food containers made of paper materials having a specified surface roughness, and is therefore suitable for use in sealing such food containers.

[0027] In the food container described above, both the container body and the lid that closes the container body may be made of a paper material having the above-mentioned surface roughness, or the container body may be made of a paper material having the above-mentioned surface roughness and the lid may be made of a transparent plastic material, so that the contents contained in the container body can be seen. In other words, in the food container described above, at least the container body is made of a paper material. Furthermore, the above-mentioned food container may be in a form in which the container body and the lid are integrated and can be freely folded back via a hinge, or the container body and the lid may be separate parts and the lid may be fitted into the opening of the container body.

[0028] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations can also be adopted. [Example]

[0029] EXAMPLES The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these.

[0030] (container) Five types of pulp-molded containers (pulp food containers) A to E with different surface roughness were prepared. The surface roughness of the paper portion of each pulp-molded container was measured using a small surface roughness measuring device. Specifically, the surface roughness (arithmetic mean roughness (Ra) and ten-point mean roughness (Rz)) was measured at eight locations on the paper surface, and the average value for each was calculated. The results (average values) obtained for surface roughness are shown in Table 1.

[0031] [Table 1]

[0032] (adhesive tape) Hot melt adhesive compositions were prepared using the ingredients and blending amounts shown in Tables 2 to 4, and then coated onto a cellophane substrate. The adhesive tapes of Examples 1 to 18 and Comparative Examples 1 to 7, each 15 mm wide, were produced according to the procedure of the adhesive tape manufacturing method described above. In Comparative Example 8, a solvent-based rubber adhesive was coated onto a cellophane substrate, and in Comparative Example 9, an acrylic emulsion adhesive was coated onto a Japanese paper substrate to produce an adhesive tape having a width of 15 mm. The raw materials shown in Tables 2 to 4 are as follows. Elastomer: Natural rubber Aliphatic hydrocarbon resin: Quinton M100, Zeon Corporation Triblock copolymer A1: KURARITY LA3710 (MMA / nBA / MMA copolymer, weight average molecular weight 216,000), manufactured by Kuraray Co., Ltd. Triblock copolymer A2: KURARITY LA3320 (MMA / nBA / MMA copolymer, weight average molecular weight 155,000), manufactured by Kuraray Co., Ltd. Triblock copolymer A3: KURARITY LA2330 (MMA / nBA / MMA copolymer, weight average molecular weight 98,000), manufactured by Kuraray Co., Ltd. Triblock copolymer B1: KURARITY LA2114 (MMA / nBA / MMA copolymer, weight average molecular weight 68,000), manufactured by Kuraray Co., Ltd. Rosin ester tackifying resin 1: Super Ester A-75 (softening point: 70 to 80°C), manufactured by Arakawa Chemical Industries, Ltd. Rosin ester tackifying resin 2: Super Ester A-100 (softening point: 95 to 105°C), manufactured by Arakawa Chemical Industries, Ltd. Rosin ester tackifying resin 3: Super Ester A-125 (softening point: 120-130°C), manufactured by Arakawa Chemical Industries, Ltd. Phenolic antioxidant: STAB AO-60, manufactured by ADEKA Corporation Phosphite antioxidant: STAB PEP-36, manufactured by ADEKA Corporation

[0033] (Adhesion to pulp mold) Container A was used as the adherend. Three pieces of adhesive tape were prepared for each Example and Comparative Example. A test piece of adhesive tape was pressed onto the container A using a 300g pressure roller. One minute after pressing, the adhesive tape was peeled from the edge of the main body (bowl portion) toward the bottom, and the adhesive strength was measured using a universal tensile tester. The average adhesive strength of the three points was calculated, and a sample with an average adhesive strength of 1.0 N / 10 mm or more was considered to have passed. However, samples in which the adhesive failed cohesively during adhesive strength measurement were considered to have failed even if the average adhesive strength was 1.0 N / 10 mm or more.

[0034] (Sealability evaluation when dropped) 200 g of contents were placed in container C, and the lid was placed on top. Adhesive tape was attached in two places so as to straddle the outer edge of the lid and the main body (bowl portion). The adhesive tape had an area of 15 mm x 40 mm. Three samples were prepared. After 3 rounds of finger pressure (approximately 300g of pressure), 20 minutes later, Container C was hung from a support pole by a 10cm long string, and when Container C was lifted up to the support pole and dropped, the number of times until the adhesive tape peeled off was counted. The data for the 3 points was rounded up or down, and 5 times or more was considered a pass.

[0035] (Applicability evaluation) Test pieces of adhesive tape (15 mm wide, 100 mm long) were attached to the paper portion of pulp molded containers A to E, sealing them so that the adhesive tape was attached to both the lid and the body (bowl portion) in a length of 50 mm. When applying the adhesive tape, light pressure was applied with the pad of a finger. After application, the containers were left to stand for 24 hours in an environment of 40°C and 75% RH, and then the adhesiveness of the adhesive tape was evaluated according to the following evaluation criteria. A rating of 4 or higher was considered a pass. <Evaluation criteria> 5: There is no lifting of the adhesive tape over the entire application surface, or the lifting area is less than 1% of the application surface, and there is high resistance when peeling the adhesive tape 4: There is no lifting of the adhesive tape over the entire application surface, or the lifting area is less than 1% of the application surface, and the resistance when peeling the adhesive tape is low 3: The adhesive tape is floating over an area of 1% to less than 20% of the adhesive surface. 2: The adhesive tape is floating over 20% to less than 50% of the application surface. 1: The adhesive tape is floating over 50% or more of the application surface.

[0036] [Table 2]

[0037] [Table 3]

[0038] [Table 4] [Industrial Applicability]

[0039] The adhesive tape of this embodiment has good adhesion to food containers made of paper materials having a specified surface roughness, and can therefore be suitably used to seal such food containers. [Explanation of symbols]

[0040] 10 adhesive tape, 20 substrate, 30 adhesive layer

Claims

1. a triblock copolymer A containing at least a segment A mainly composed of a methacrylic acid ester and a segment B mainly composed of an acrylic acid ester, and having a weight average molecular weight of 70,000 or more; a triblock copolymer B containing at least a segment A mainly composed of a methacrylic acid ester and a segment B mainly composed of an acrylic acid ester, and having a weight average molecular weight of less than 70,000; and a rosin ester tackifying resin having a softening point of 70°C to 80°C, the content of the triblock copolymer B relative to 100 parts by mass of the triblock copolymer A is 70 parts by mass or more, the content of the rosin ester tackifying resin relative to 100 parts by mass of the triblock copolymer A is 75 parts by mass or more.

2. A pressure-sensitive adhesive tape comprising: a substrate; and a pressure-sensitive adhesive layer formed from the hot melt pressure-sensitive adhesive composition according to claim 1 laminated on the substrate.

3. 3. The pressure-sensitive adhesive tape according to claim 2, which is used to seal a food container, at least the container body being formed from a paper material, the paper material having an arithmetic mean roughness (Ra) of 12 to 25 μm and a ten-point mean roughness (Rz) of 61 to 100 μm.

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