JP7115752B2 - adhesive composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to an adhesive composition that is melted and softened to exert an adhesive action by being sandwiched between substrates to be adhered and thermocompressed, and in particular, it relates to an adhesive composition that is transparent when adhered and then peeled off. The present invention relates to an adhesive composition used for applications where the trace becomes opaque and the peeling can be visually confirmed.

Conventionally, various methods have been proposed for easily determining whether or not a container, packaging film, sealed letter, certificate, or the like has been opened intentionally or at random, as well as measures to prevent such opening. For example, Japanese Patent Application Laid-Open No. 2017-107001 discloses an example using heat-sensitive microcapsules. The pressure-sensitive adhesive used for sealing has the disadvantage that the property that the adhesive strength is reduced by heating is abused and is opened, so this is made easy by a method in which the microcapsules are destroyed and colored when heated. However, it is difficult to apply it to the method of sealing by thermocompression bonding because there is a risk of color development during thermocompression bonding.

In addition, there is a case where the seal is destroyed by opening the sealed part to which the seal is affixed, making it easy to determine whether the seal has been opened or not. Alternatively, the sticking seal must be the sealing agent itself. In any case, since the sticking seal is stuck using an adhesive, it is unavoidable that the peeling strength is lowered by heating and the package is opened.

Further, Japanese Patent No. 5082008 is cited as a technique involving breakage of a part of the substrate upon opening. Although the direct purpose of the patent is an easy-open container, since a part of the lid separated by the perforation is removed after opening, the change in appearance occurs and can be distinguished visually. In addition, Japanese Patent No. 2936969 discloses a lid material in which a film layer, a base layer, and a heat-seal layer containing inorganic powder are sequentially laminated on a substrate, and delamination between the base layer and the heat-seal layer occurs when the package is opened. It is possible to leave a trace of the heat-sealed layer that has delaminated at the unsealed portion. As described above, there are many proposals for making it possible to easily visually determine whether or not the package has been opened.

Japanese Patent Application Laid-Open No. 2017-107001 Japanese Patent No. 5082008 Japanese Patent No. 2936969

The present invention utilizes the properties of the adhesive itself, which is transparent when adhered and does not involve chemical changes or damage to the substrate when peeled off, which could not be performed with the conventional adhesive composition. An object of the present invention is to provide an adhesive composition capable of judging whether or not it has been opened.

The adhesive composition of the present invention, which has been made to solve the above problems, is an adhesive composition that melts with compatibility at a predetermined heating temperature and has an olefinic polymer and a thermoplastic polyurethane or/and a thermal adhesive composition that have mutually different refractive indices. It comprises a thermoplastic resin in which the weight ratio of plastic polyester is 80/20 to 20/80, fine particles having an average particle size of 0.3 to 20 μm and being incompatible with the thermoplastic resin, and a solvent. Characterized by

Further, in the present invention, it is preferable that the content of the fine particles is 0.5 to 30 parts by weight per 100 parts by weight of the thermoplastic resin.

Furthermore, it is preferable that the fine particles are a rubber composition.

According to the present invention, the adhesive composition from which the solvent sandwiched between the substrates to be adhered has been removed and dried is subjected to thermocompression bonding at a predetermined heating temperature to melt and soften to exhibit a transparent and strong adhesive effect, When peeled off, the adhesive surface remaining on the peeled surface becomes opaque and its trace can be visually confirmed, especially in the food, medical, and other fields where virginity is required, such as containers and packaging. It can be widely used as an adhesive for openings of

4A and 4B are photographs showing the state of bonding and peeling in Example 1 of the present invention. 13A and 13B are photographs showing the state of adhesion and peeling in Example 2 of the present invention. 4A and 4B are photographs showing the state of adhesion and peeling in Comparative Example 1 of the present invention. 10A and 10B are photographs showing the states at the time of adhesion and at the time of peeling in Comparative Example 2 of the present invention.

The adhesive composition of the present invention includes at least two types of thermoplastic resins that are compatible and melt at a predetermined heating temperature and have different refractive indices, and an average particle size that is incompatible with the thermoplastic resin. is composed of fine particles having a diameter of 0.3 to 20 μm and a solvent.

The thermoplastic resin is selected according to the type of the base material to be adhered, etc. However, in order to make the adhesive surface remaining on the peeled surface opaque when peeled off and to visually confirm the trace, it is necessary to use both of them. An adhesive composition having a difference in refractive index is preferable, but the adhesive composition is sandwiched between substrates to be adhered, applied, and thermocompressed at a predetermined heating temperature to melt and soften, thereby exhibiting a transparent and strong adhesive effect. For this purpose, it is preferable to use materials with similar refractive indices, such as ethylene-vinyl acetate copolymer, ethylene-(meth)acrylic ester copolymer, ethylene-vinyl acetate copolymer modified with maleic anhydride, ethylene -(meth)acrylic acid ester copolymers-maleic anhydride copolymers, ethylene-(meth)acrylic acid copolymers and metal salts thereof, ethylene-based (co)polymers such as ethylene-α olefin copolymers, Propylene-α-olefin copolymers and unsaturated carboxylic acid-modified products thereof, thermoplastic polyurethanes, etc. Ethylene-vinyl acetate copolymers, ethylene-(meth)acrylic acid ester copolymers, anhydrous ethylene-vinyl acetate copolymers Modified maleic acid, ethylene-(meth)acrylic acid ester copolymer-maleic anhydride copolymer, ethylene-(meth)acrylic acid copolymer and its metal salt, ethylene-α olefin copolymer, propylene-α At least one selected from olefin polymers such as olefin copolymers and unsaturated carboxylic acid modified products thereof, and at least one selected from thermoplastic polyurethanes and thermoplastic polyesters can be used in combination.

Further, the weight ratio of the olefinic polymer and thermoplastic polyurethane or/and thermoplastic polyester is preferably 80/20 to 20/80.

Further, the fine particles are preferably incompatible with the thermoplastic resin, and particularly preferably fine particles whose surfaces easily diffusely reflect sunlight, for example, fine particles of rubber or silica are preferably used. As for silica, plate-like silica is most preferable from the viewpoint of improvement of peel strength or degree of discoloration before and after peeling.

Examples of fine rubber particles include natural rubber, butadiene rubber, isoprene rubber, styrene-butadiene rubber, fluororubber, silicone rubber, and chlorosulfonated polyethylene. However, the particles themselves melt when heated and pressed. Rubber fine particles having a vulcanized and crosslinked structure are particularly preferred. As the silica component, for example, silicon dioxide or a compound containing silicon dioxide as a main component is preferable, regardless of whether it is a synthetic product or a natural product.

Further, the fine particles used in the present invention preferably have an average particle size of 0.3 to 20 μm. If the average particle size is less than 0.3 microns, the rate of discoloration before and after peeling is small, and if it exceeds 20 μm, depending on the thickness of the adhesive, the substrates to be bonded will not be smooth during thermal compression bonding, and during peeling. This is because there is little discoloration change and it becomes difficult to distinguish.

Furthermore, the amount of the fine particles to be blended is preferably 0.5 to 30 parts by weight per 100 parts by weight of the thermoplastic resin. This is because if the amount is less than 0.5 parts by weight, the improvement in peel strength and discoloration are poor, and if the amount exceeds 30 parts by weight, the thermocompression bondability deteriorates.

In addition, the adhesive composition of the present invention can be applied by dissolving or dispersing it in water and/or an organic solvent. Aqueous dispersions are particularly preferred from the standpoint of environmental hygiene, safety, and the like. The constituent components of these adhesive compositions may be appropriately selected from commercially available products, or those prepared by the methods described in JP-A-58-127752 and JP-A-58-118843 may be used as necessary. . Of course, as a small amount of organic solvent, a hydrophilic solvent such as alcohols, ketones, and esters may be used in combination.

Examples of substrates to be adhered suitable for use with the adhesive composition of the present invention include containers with lids, packaging films, plastic films, sheets, foils, and papers used for sealed letters, certificates, and the like. In particular, polyethylene phthalate, polynaphthalene phthalate, polypropylene, polycarbonate, polystyrene, ethylene-vinyl alcohol copolymer, polyamide, polyvinyl chloride, etc. films, sheets, metal deposits thereof , inorganic deposits, corona discharges, surface-treated products thereof, and the like are suitable.

In addition, the plastic film or sheet, which is the base material to be adhered, may be stretched in order to improve transparency, strength, heat resistance and tear resistance, such as gas barrier properties, tear resistance and thermocompression bonding. Another plastic film may be laminated for homogenization of the coating and improvement of peeling feeling.

In these base materials to be adhered, the portion to be adhered is required to be so transparent that the change after peeling can be visually determined, but other portions may be opaque.

In this embodiment, the adhesive is made of at least two different kinds of thermoplastic resins. Since a smooth adhesive surface is formed, it can be visually observed that the adhesive is adhered through the transparent base material to be adhered.

Next, when the lid, which is the base material to be adhered, is opened and the adhered state is peeled off, the surface unevenness, voids, etc. change due to peeling resistance when the adhered portion is peeled off, so the peeled surface diffusely reflects and becomes opaque (this implementation (White in the form of )) It can be visually confirmed that the adhesive state has been released and the lid has been opened. In particular, in the present embodiment, since different types of thermoplastic resins are combined as adhesives, changes such as surface unevenness and voids are likely to appear when the adhesive is peeled off. Exposed on the peeled surface to increase opacification.

In addition, even if the base material to be bonded has some voids or irregularities that diffusely reflect light before bonding, it is softened and fluidized by applying sufficient heat and pressure during thermocompression bonding, resulting in smooth diffused light reflection. The difference between the voids caused by the peeling resistance at the time of peeling and the irregular reflection of light due to the unevenness of the surface becomes remarkable, and the peeling can be visually confirmed.

In addition, it is preferable to select a combination of adhesives having a small difference in refractive index as much as possible. This is because if the adhesive itself is opaque before peeling, it will be difficult to determine the color change after peeling. When it is unavoidable to use materials with a large difference in refractive index, it is necessary to make a large difference in the amounts used. It is particularly preferable to use the ethylene-based (co)polymer and the thermoplastic polyurethane together as the thermoplastic resin component because it can be blended in a wide range of ratios and can expand the target range of substrates to be adhered.

Next, examples of the present invention will be described.

For example, the present invention is applied to Examples 1 to 3 in Table 1, which is the present invention when the surfaces to be bonded to each other between the lid and the container body of a transparent food container made of polyethylene terephthalate with a thickness of 200 μm are used as the adhesive base material. First, the adhesive composition of the present invention was applied to at least one adhesive surface of a base material to be adhered using a bar coater #10 (film thickness: 22.90 μm) manufactured by Daiyu Kizai Co., Ltd. and dried with hot air using a hand dryer to obtain a base material for thermocompression. Then, the adhesive-coated surface of the base material to be adhered and the base material to be adhered to which the adhesive is not applied are overlapped (with the lid on the container body), and heated at 120 ° C., 130 ° C., 140 ° C. and 150 ° C. At the temperature, a pressure of 0.5 MPa was applied, and each was thermally compressed for 2 seconds and left at room temperature. The ethylene-vinyl acetate copolymer used had a refractive index of 1.4, and the polyurethane used had a refractive index of 1.5.

After that, the adhesive surface was peeled off by hand, and the state of the peeled surface was visually observed through the base material coated with the adhesive. In addition, the peeling state at that time (interfacial peeling: 90% or more of the adhesive remains on the adhesive coated surface, adhesive peeling: the adhesive peels off from the coated substrate, cohesive peeling: the adhesive itself breaks) and the 15 mm width The T peel strength was measured with a peel strength tester. Table 1 shows the composition conditions of Examples and Comparative Examples. The unit in the table represents the weight converted to solid content (excluding water or solvent). The ethylene-vinyl acetate copolymer used in the examples was Mitsui Chemicals' aqueous dispersion "Chemipearl V100 (registered trademark)", and the polyurethane used was Dai-ichi Kogyo Seiyaku's aqueous dispersion "Superflex E2000 (registered trademark)." As the rubber particles, Shin-Etsu Chemical Co., Ltd.'s silicone rubber "KM series" was used, but the rubber particles are not limited to these. The amount of fine particles added in the table is the amount (parts by weight) added per 100 parts by weight of the thermoplastic resin.

Next, for the above examples and comparative examples, the adhesive surface was peeled off by hand, and the state of the peeled surface was visually observed through the base material coated with the adhesive. In addition, the peeling state at that time (interfacial peeling: 90% or more of the adhesive remains on the adhesive coated surface, adhesive peeling: the adhesive peels off from the coated substrate, cohesive peeling: the adhesive itself breaks) and the 15 mm width The T peel strength (N) was measured with a peel strength tester. The results are shown in the drawing.

As shown in FIG. 1 and the figure, in Examples 1 and 2, the film was sufficiently transparent before peeling off (“right side” and hereinafter the same) regardless of the heating temperature of 120° C., 130° C., 140° C., and 150° C. After peeling off (the same applies hereinafter for the “left side”), whitening was observed remarkably. On the other hand, Comparative Example 1 containing no fine particles as shown in FIG. 3 and Comparative Example 2 containing more than the proper weight ratio as shown in FIG. 4 were sufficiently transparent before peeling, but after peeling. did not obtain bleaching.

From these facts, the adhesive composition of the present invention is transparent when adhered, and when peeled off, it does not cause chemical changes or damage to the substrate. It was confirmed to provide an adhesive composition that can be judged whether or not it is present.

Claims (3)

A thermoplastic resin having a weight ratio of 80/20 to 20/80 between an olefin polymer and a thermoplastic polyurethane that are compatible and melt and have different refractive indices, and an average particle size of 0.3 to 20 μm. An adhesive composition comprising rubber fine particles incompatible with the thermoplastic resin in and a solvent,
The adhesive composition is applied between substrates to be bonded, dried, and subjected to thermocompression bonding in a state in which the solvent is removed, thereby melting and softening in a compatible state to form a transparent adhesive layer, thereby forming a transparent adhesive layer. The adhesive composition is characterized in that when the adhesion between the substrates to be adhered is peeled, a diffuse reflection surface is formed on the peeling surface due to the peeling resistance and the peeling surface becomes opaque, so that the presence or absence of opening can be visually confirmed. thing. 2. The adhesive composition according to claim 1, wherein the amount of said fine rubber particles compounded is 0.5 to 30 parts by weight per 100 parts by weight of said thermoplastic resin. 3. The adhesive composition according to claim 1, wherein said olefin polymer is an ethylene polymer.

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