JP2000169815A - Heat-sensitive adhesive agent, heat-sensitive adhering sheet and use of the sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heat-sensitive adhering agent having excellent adhesiveness and water resistance and readily peelable from the surface on a container such as a plastic bottle or a glass bottle by using an alkali solution and useful for a label, and a heat-sensitive adhering sheet. SOLUTION: This heat-sensitive adhering agent contains a copolymer obtained by copolymerizing 0.5-15 wt.% of an ethylenic unsaturated carboxylic acid with 85-99.5 wt.% of the other vinyl-based monomer, a rosin polymer and a solid plasticizer and has >=20 (KOH mg/g) acid value. Further, the adhering agent contains 20-150 pts.wt. of the rosin polymer and 100-400 pts.wt. of the solid plasticizer based on 100 pts.wt. of the copolymer. The heat-sensitive adhering sheet is obtained by coating the heat-sensitive adhering agent on the surface of a plastic film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a heat-sensitive adhesive which is non-tacky at room temperature but develops tackiness by heating, and after tackiness is developed, the tackiness is maintained for a while even if a heating source is removed. The present invention relates to a heat-sensitive adhesive sheet. The present invention also relates to a plastic bottle to which the heat-sensitive adhesive sheet is attached, and further relates to a method of peeling the sheet from the plastic bottle.

[0002]

2. Description of the Related Art Water-dispersible adhesives are often used in conventional heat-sensitive adhesives so that they do not have tackiness after application and drying. For example, "Glue manual"
As described in (12th edition, published by the Society of Polymer Publishing, 1980), a water-dispersed adhesive having a basic skeleton of a thermoplastic resin, a tackifier and a solid plasticizer is used as a composition. You. Among the compositions, the thermoplastic resin is a source of adhesive strength and adhesive strength.

[0003] In addition, a solid plasticizer is basically a solid at room temperature and therefore does not impart plasticity to the resin. By melting by heating to swell or soften the resin, it is non-adhesive and heat-sensitive at room temperature. The adhesive has a function of expressing tackiness by heating. At this time, when the tackifier is present, the tackiness is more remarkably exhibited, and the practical characteristics are improved.

On the surface of a container such as a plastic bottle or a glass bottle, a label provided with an adhesive layer on the entire back surface of the substrate,
Alternatively, a label or the like provided with an adhesive layer at both ends or around the back surface of the substrate is attached. Conventionally, casein-based adhesives, starch-based adhesives, polyvinyl alcohol-based adhesives, hot melt adhesives, and the like have been used for these labels. In these conventional adhesives, application and label attachment are performed integrally, that is, immediately after the adhesive is applied to the base material, the adhesive surface of the label is attached to the adherend. Has to be managed at the same time, and the work is extremely complicated and difficult. On the other hand, in the case of a heat-sensitive adhesive, the application step and the sticking step can be separated and independent, and each step can be independently managed. Use of conductive adhesives is increasing.

On the other hand, in recent years, in the field of containers and packaging, it has been desired to establish a new recycling or returnable system of the waste in the field of containers and packaging from the viewpoints of global environment protection and resource protection. With the enforcement of the Act on the Promotion of Commercialization (the so-called Containers and Packaging Recycling Law) (April 1998), there has been a demand for removing labels from the container surface and reusing the container itself or the raw materials of the container. More and more. However, the above-described heat-sensitive adhesive is generally more resistant to an alkaline solution than a starch-based adhesive or the like, and it is difficult to peel off a label from a container to be adhered with an alkaline solution, or the label substrate is There is a problem that even if the adhesive is peeled off, only the adhesive remains adhered to the container and cannot be easily removed.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object the following:
Provide a heat-sensitive adhesive and a heat-sensitive adhesive sheet for labels that are excellent in adhesiveness and water resistance and can be easily peeled off from the surface of a container such as a plastic bottle or a glass bottle with an alkaline solution, and further propose a method of using the sheet. The purpose is to:

[0007]

That is, the first invention is to provide a copolymer of 0.5 to 15% by weight of an ethylenically unsaturated carboxylic acid and 85 to 99.5% by weight of another vinyl monomer. A heat-sensitive adhesive comprising a copolymer, a polymerized rosin and a solid plasticizer, and having an acid value of 20 (KOH mg / g) or more.

According to a second aspect of the present invention, there is provided a thermosensitive thermosensitive recording medium according to the first aspect, comprising 20 to 150 parts by weight of a tackifier and 100 to 400 parts by weight of a solid plasticizer based on 100 parts by weight of the copolymer. Adhesive.

A third invention is a heat-sensitive adhesive sheet obtained by applying the heat-sensitive adhesive according to the first or second invention on a plastic film.

A fourth invention is a plastic bottle to which the heat-sensitive adhesive sheet according to the third invention is adhered.

A fifth invention is a method for peeling a heat-sensitive adhesive sheet from a plastic bottle according to the fourth invention using an alkaline solution.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The heat-sensitive adhesive of the present invention contains a polymerized rosin as a tackifier having a function of improving the tackiness, and contains 0.5 to 15% by weight of an ethylenically unsaturated carboxylic acid and 85% by weight. It is important that the heat-sensitive adhesive contains an acid value of 20 (KOH mg / g) or more, containing a copolymer obtained by copolymerizing ビ ニ ル 99.5% by weight of another vinyl monomer. is there. As the polymerized rosin, those having a softening temperature of 100 ° C. or higher are preferable from the viewpoint of blocking resistance. If the amount of the ethylenically unsaturated carboxylic acid is less than 0.5% by weight, the alkali releasability is poor, and if it exceeds 15% by weight, the water resistance is poor.
The copolymerization ratio of the ethylenically unsaturated carboxylic acid is preferably from 1 to 10% by weight, more preferably from 1 to 5% by weight. The heat-sensitive adhesive has an acid value of 20 (KOH
When the amount is less than (mg / g), the alkali peelability is poor. The acid value of the heat-sensitive adhesive is preferably 25 to 75 (KOH mg / g).

The ethylenically unsaturated carboxylic acids used in the present invention include acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, crotonic acid, aconitic acid and the like. May be used alone or in combination of two or more. In the present invention, other vinyl monomers used for copolymerization with the ethylenically unsaturated carboxylic acid include styrene, α
-Aromatic vinyl compounds such as methylstyrene and vinyltoluene, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate and the like, alkyl methacrylates, methyl acrylate, acrylic acid Ethyl, alkyl acrylates such as n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, vinyl cyanide compounds such as acrylonitrile and methacrylonitrile, vinyl ester compounds such as vinyl acetate, cyclohexyl methacrylate, acrylic Cyclic alkyl esters of acrylic acid or methacrylic acid such as cyclohexyl acid, and various functional monomers, for example, acrylamide, methacrylamide, glycidyl acrylate, 2-hydroacrylic acid Examples thereof include silyl, 2-hydroxyethyl methacrylate, sodium styrene sulfonate, N-methylolacrylamide, N-butoxymethylacrylamide, methylpropanesulfonic acid acrylamide, diaminoethyl methacrylate, acrylonitrile, and the like, and styrene, cyclohexyl methacrylate, methacrylic acid. Methyl, t-butyl methacrylate, 2-acrylic acid
Ethylhexyl, ethyl acrylate, cyclohexyl methacrylate, and acrylamide are preferred, and styrene is particularly preferred as one of the essential components of the copolymer. These other vinyl monomers are used for imparting an appropriate cohesive force to the copolymer, and are used for copolymerization in the range of 85 to 99.5% by weight. Outside this range, good adhesive strength cannot be obtained.

The copolymer used in the present invention is produced, for example, by a usual emulsion polymerization method. That is, water,
In a dispersion system comprising a surfactant, a monomer having an ethylenically unsaturated carboxylic acid as an essential component and a radical polymerization catalyst as a basic component, a monomer is polymerized, and a production method is performed to obtain an aqueous dispersion of polymer particles. is there.

Examples of the solid plasticizer used in the present invention include diphenyl phthalate, dihexyl phthalate, dicyclohexyl phthalate, dicyclohexyl terephthalate, dihydroabiethyl phthalate, dimethyl isophthalate, sucrose benzoate, and ethylene glycol dibenzoate. Trimethylolethane tribenzoate, glyceride tribenzoate, pentaerythritol tetrabenzoate, sucrose octaacetate, tricyclohexyl citrate, N-cyclohexyl-p-toluenesulfonamide, and the like.
Usually, dicyclohexyl phthalate is preferably used.

The particle size of the solid plasticizer greatly affects the smoothness of the surface to which the heat-sensitive adhesive is applied. If the particle size is too large, the smoothness of the surface to which the heat-sensitive adhesive is applied deteriorates. Since there is an effect such as an increase in time, the volume average particle size is preferably in the range of 1 to 15 μm, and is preferably adjusted to the maximum particle size of 50 μm or less.

The heat-sensitive adhesive of the present invention comprises a copolymer 100
The polymerized rosin is preferably contained in an amount of 20 to 150 parts by weight, more preferably 30 to 120 parts by weight, based on the weight of the rosin. The solid plasticizer is preferably contained in an amount of 100 to 400 parts by weight, more preferably 200 to 350 parts by weight, based on 100 parts by weight of the copolymer.

The heat-sensitive adhesive of the present invention may further contain a filler or the like, as long as the object of the present invention is not hindered. For example, inorganic substances such as titanium oxide, alumina, kaolin and talc, paraffin, Organic substances such as natural waxes, synthetic waxes, and natural fats and oils, resin powders, and the like can be used as they are, or as emulsions or water dispersions. Further, if necessary, a dispersant, an antifoaming agent, a thickener and the like can be used.

A heat-sensitive adhesive sheet in an aqueous dispersion state is applied to a substrate and dried to obtain a heat-sensitive adhesive sheet. The heat-sensitive adhesive can be applied to the substrate using various coating apparatuses such as a gravure coater, an air doctor coater, a floating knife coater, a die coater, and a lip coater. For example, it may be provided so as to cover one entire surface of the base material, or may be provided so as to cover both ends or the periphery of one surface of the base material, and a stripe shape on one surface of the base material, They may be provided in a lattice or dot shape. As the base material, conventionally known high-quality paper, coated paper, art paper, vapor-deposited paper or the like, or synthetic paper, polyolefin resin such as polyethylene or polypropylene, or polyester resin represented by PET, polystyrene resin, poly Plastics such as a vinyl chloride resin or a polyamide resin represented by nylon, and a base material such as a metal plate (foil) can be used. In addition, it is general to provide a printing layer using various inks on the surface of the base material on which the heat sensitivity is not applied, and the application or printing of the heat-sensitive adhesive may be performed first. When printing after applying the heat-sensitive adhesive first, it is preferable to use an ultraviolet-curable or electron-beam-curable ink so that the heat-sensitive adhesive is not particularly activated by the heat of drying the ink. Of course, it can be used without printing. Alternatively, it is also possible to form a heat-sensitive adhesive sheet by providing a print layer on a transparent plastic film and providing a heat-sensitive adhesive layer on the print layer.

Among the heat-sensitive adhesive sheets of the present invention, those having a plastic film as a base material are particularly used by sticking to a plastic bottle. That is, the heat-sensitive adhesive sheet using paper as the base material in the peeling step after the application, the alkali solution passing through the base material can directly contribute to the peeling of the heat-sensitive adhesive, while the plastic film and the base material The heat-sensitive adhesive sheet does not allow the alkaline solution to pass through the substrate.
Therefore, it is more difficult to secure water resistance and easy peelability with an alkaline solution when using a plastic film as the substrate than when using paper as the substrate. When the heat-sensitive adhesive sheet attached to the plastic bottle is peeled off, it is preferable to make the bottle into small pieces before the peeling step in order to promote the peeling. When the heat-sensitive adhesive sheet having a plastic film as a substrate is peeled off from a container as an adherend, it is preferable to immerse the film in an alkaline solution or spray an alkaline solution. In particular,
The heat-sensitive adhesive sheet affixed to the adherend together with the adherend is 80
By dipping in a 1.5% caustic soda solution and stirring for about 15 minutes, the heat-sensitive adhesive layer swells or dissolves, and the adhesive force between the heat-sensitive adhesive sheet and the adherend is reduced. When the substrate and the heat-sensitive adhesive are peeled off from the adherend, or when the substrate is peeled off first and then the heat-sensitive adhesive remains on the adherend, the heat-sensitive adhesive is removed from the adherend. Peel or dissolve.

The heat-sensitive adhesive of the present invention can be applied not only to a plastic film but also to a paper substrate, and the obtained heat-sensitive adhesive sheet can be stuck not only to a plastic bottle but also to a glass bottle. Yes, the sheet can be similarly peeled off with an alkaline solution, and the container itself or container material can be easily recycled.

[0022]

The present invention will be specifically described below with reference to examples. However, the scope of the present invention is not limited at all by the following Examples. In the examples, “parts” means “parts by weight” and “%” means “% by weight”. [Examples 1 to 7 and Comparative Examples 1 to 4] First, a solid plasticizer, a polymerized rosin, or a polymerized rosin ester were added to a pebble mill pot according to the formulations shown in Table 1 (each formulation was expressed by a nonvolatile content ratio). , A maleic acid resin solution and water were added, and after pulverizing for 20 hours, a copolymer and an additive were added and mixed and stirred for 5 minutes to prepare a heat-sensitive resin composition. The obtained heat-sensitive adhesive was applied onto the corona-treated surface of the OPP film so that the coating amount at the time of drying was 10 g / m ^2, and dried at 40 ° C. for 2 minutes to obtain a heat-sensitive adhesive sheet. The sheet was not tacky after drying. Table 1 shows the results of evaluation of the adhesive strength, water resistance and alkali peelability of the heat-sensitive adhesive sheet.

[0023]

[Table 1]

The evaluation of the adhesive strength, water resistance and alkali peeling property of the coated product was carried out by the following methods. Adhesive strength: The heat-sensitive adhesive sheet was stuck to an untreated 50 μm PET film at 120 ° C. for 2 seconds at 2 kg / cm ² using a heat sealing machine and left for 1 day in an environment of 23 ° C.-65%.
Adhesive strength was measured by peeling at 180 degrees according to JIS Z-0237, and judged according to the following criteria. ◎ ・ ・ ・ ・ ・ ・ 200g / 15mm or more. ○ ・ ・ ・ ・ ・ ・ 50g / 15mm or more and less than 200g / 15mm. × ・ ・ ・ ・ ・ ・ Less than 50g / 15mm.

Water resistance: The heat-sensitive adhesive sheet was heated at 150 ° C. for 30 seconds to develop tackiness, then immediately adhered to a PET bottle, left for 1 day in an environment of 23 ° C.-65%, and then left at 1 cm × 1c
m, immersed in warm water of 40 ° C. for 20 minutes, taken out the PET bottle cut out to a predetermined size, and visually observed the peeling state of the heat-sensitive sheet. A: The sheet does not peel off from the PET bottle at all. Δ: The sheet is partially peeled from the PET bottle. ×: The sheet peels off from the PET bottle.

Alkali peelability; heat-sensitive adhesive sheet
After heating at 30 ° C for 30 seconds to develop tackiness,
Affixed to a T bottle, and after one day, the bottle with a heat-sensitive adhesive sheet was cut into a size of 1 cm × 1 cm and heated to 80 ° C. 1.
After immersion in a 5% aqueous solution of caustic soda and stirring for 15 minutes,
The small piece of the ET bottle was taken out, and the peeled state of the heat-sensitive adhesive sheet and the remaining state of the adhesive were visually observed. A: The sheet peels off from the small pieces of the PET bottle, and no adhesive remains on the small pieces. Δ ... The sheet peels off from the small piece of the PET bottle,
Some adhesive remains on the small pieces. X: The sheet does not peel off from the small pieces of the PET bottle.

[0027]

As compared with the conventional heat-sensitive adhesive sheet coated with a heat-sensitive adhesive, 0.5 to 15% by weight of ethylenically unsaturated carboxylic acid and other vinyl monomers 85
A heat-sensitive adhesive sheet comprising a copolymer obtained by copolymerization of 〜99.5% by weight, a polymerized rosin and a solid plasticizer, and coated with the heat-sensitive adhesive of the present invention having an acid value of 20 or more is ,
Without impairing the adhesive strength and water resistance, the industrial significance of being able to be easily peeled off from the adherend with an alkaline solution, and that the adherend can be easily recycled and returned,
Extremely large.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09J 135/00 C09J 135/00 193/04 193/04 F-term (Reference) 4J004 AA02 AA06 AA07 AA10 AA17 AB01 AB03 CA02 CA03 CA04 CA05 CA06 CB02 CC02 FA06 4J040 BA201 BA202 DB041 DB042 DB071 DB072 DE021 DE022 DF041 DF042 DF051 DF052 DF071 DF072 DF101 DF102 GA05 GA11 GA14 GA25 HB31 HB32 HB33 HB34 HD17 JA09 LA06

Claims (5)

[Claims] 1. An ethylenically unsaturated carboxylic acid of 0.5 to 1
5% by weight and other vinyl monomers 85 to 99.5
A heat-sensitive adhesive comprising a copolymer obtained by copolymerization of a weight%, a polymerized rosin, and a solid plasticizer, and having an acid value of 20 (KOH mg / g) or more. 2. 20 to 150 parts by weight of a polymerized rosin and 100 to 40 parts by weight of a solid plasticizer based on 100 parts by weight of a copolymer.
The heat-sensitive adhesive according to claim 1, comprising 0 parts by weight. 3. A heat-sensitive adhesive sheet obtained by coating the heat-sensitive adhesive according to claim 1 on a plastic film. 4. A plastic bottle to which the heat-sensitive adhesive sheet according to claim 3 is adhered. 5. A method for peeling a heat-sensitive adhesive sheet from a plastic bottle according to claim 4, using an alkaline solution.