CN102399501B - Re-stripping type adhesive piece - Google Patents

Abstract

The present invention provides a re-peelable adhesive sheet for affixing a label which can be easily peeled and removed in a recycling process and which can be easily peeled off by hand. This re-peelable adhesive sheet is characterized in that, in the re-peelable adhesive sheet obtained by laminating a release sheet, an adhesive layer, and a surface substrate, the adhesive layer is composed of a water-dispersible adhesive containing an aqueous emulsion and a crosslinking agent. The adhesive composition is formed. The aqueous emulsion contains an acrylic copolymer and an adhesion imparting agent. The monomer components constituting the acrylic copolymer include 2-ethylhexyl acrylate, acrylonitrile, and vinyl unsaturated with carboxyl groups. monomer, the content of the 2-ethylhexyl acrylate is more than 90% by mass in the monomer components, the content of the acrylonitrile is 0.5-5% by mass, and the gel rate of the adhesive layer is 40-80% by mass.

Description

Re-peelable adhesive sheet

technical field

The present invention relates to a re-peelable adhesive sheet that can be used for affixing a label on the surface of, for example, a bottle made of polyethylene terephthalate (hereinafter referred to as a PET bottle in some cases), and more specifically relates to an adhesive sheet for recycling. In the case of PET bottles, the re-peelable adhesive sheet for labeling can be easily peeled off.

Background technique

The re-peelable adhesive sheet or adhesive label has the function of being able to easily peel off the label attached to the adherend after a certain period of time, and can be used, for example, as a price tag for food and groceries with frequent price changes, and commodity logistics. In-process management labels or index labels are used to write necessary information by printing, etc., and can be peeled off when the purpose of information transmission and the like is no longer necessary (for example, Patent Documents 1 and 2).

In Patent Documents 1 and 2, a tackifier obtained by blending a tackifier and a polyglycidyl compound with an acrylic polymer having a carboxyl group is used.

On the other hand, various adhesive labels for beverage bottles are known as adhesive labels in a field different from the aforementioned adhesive labels.

PET bottles are widely used as containers for drinking water, soft drinks, juices, tea, black tea, sake, shochu, etc. In recent years, demands for recycling of such PET bottles have been remarkably increased from the viewpoint of environmental protection. Almost all PET bottles are pasted with stickers for displaying product names and contents, etc. When recycling PET bottles, the stickers need to be peeled off and removed during the regeneration process (hot water treatment, etc.) in the recycling facility . In addition, in order to effectively carry out the recycling process, it is desirable for each household to peel off the sticker before discarding the PET bottle. Therefore, the sticky label is required to have good adhesiveness to the PET bottle and good sticking operability, and at the same time, it is required to stick to the bottle with good adhesion and not easy to peel until the contents of the PET bottle are consumed. The opposite characteristic that the content can be easily peeled off after consumption.

In addition, after attaching the adhesive label to the empty bottle, when filling the contents, the inside of the bottle should be washed with water or weak alkaline cleaning solution before filling the contents. During this washing process, the adhesive label needs to be kept in an attached state without being peeled off.

As such an adhesive for labeling, in recent years, from the viewpoint of environmental sanitation, there has been a strong interest in a water-dispersible adhesive that does not use a solvent, and various studies have been conducted.

For example, Patent Document 3 discloses that an adhesive sheet made of an adhesive comprising an alkali-soluble polymer layer is used as a bottle label, but improvement in the balance between adhesiveness and re-peelability is required.

In addition, Patent Document 4 discloses a label characterized in that the label contains an alkali-soluble acrylic emulsion-type adhesive and a crosslinking agent, with respect to 100 parts by weight of the alkali-soluble acrylic emulsion-type adhesive agent, add 1-3 parts by weight of crosslinking agent. However, the label re-peelability and hot-water peelability were not sufficient when peeled by hand.

Further, in Patent Document 5, it is proposed that an adhesive resin is realized by using an acrylic copolymer containing 2-ethylhexyl acrylate as the main monomer component and a nitrogen-containing vinyl monomer as an adhesive resin. Appropriate adhesion and good re-peelability, but further design of the matching composition is required to obtain an adhesive with a balance of water resistance, adhesion and re-peelability.

[Prior Art Literature]

[Patent Document]

[Patent Document 1] JP-A-8-183935

[Patent Document 2] JP-A-8-225774

[Patent Document 3] JP-A-7-82537

[Patent Document 4] JP-A-2003-098969

[Patent Document 5] JP-A-2008-239872

Contents of the invention

The present invention is based on such circumstances, and an object of the present invention is to provide a re-peelable adhesive sheet for sticking labels, and a sticky label processed from the re-peelable sticky adhesive sheet for sticky labels has good stickability and sticking workability to bottles, At the same time, after the label is pasted, it is difficult to peel off from the bottle until the contents of the bottle are consumed, and after the contents of the bottle are consumed, it can be easily peeled off and removed during the regeneration process in the regeneration processing equipment, and it can be removed by hand. That is, it can be easily peeled off.

In order to achieve the above object, the inventors of the present invention conducted intensive studies and found that: in a re-peelable adhesive sheet having a structure laminated with a release sheet, an adhesive layer, and a surface substrate, the adhesive layer Contains an aqueous emulsion containing an acrylic copolymer and an adhesion-imparting agent, the monomer components constituting the acrylic copolymer include specific types and combinations of contents, and uses a gel of the adhesive layer The present invention has been accomplished by providing a water-dispersible adhesive composition having a rate within a specific range, thereby solving the above-mentioned problems.

That is, the present invention provides:

(1) A re-peelable adhesive sheet, characterized in that, in a re-peelable adhesive sheet obtained by laminating a release sheet, an adhesive layer, and a surface substrate, the adhesive layer is composed of an aqueous emulsion and a cross-linked A water-dispersible adhesive composition of an agent is formed, the aqueous emulsion contains an acrylic copolymer and an adhesion-imparting agent, and the monomer components constituting the acrylic copolymer include 2-ethylhexyl acrylate, acrylonitrile, and The ethylenically unsaturated monomer, the content of the 2-ethylhexyl acrylate is more than 90% by mass in the monomer components, the content of the acrylonitrile is 0.5-5% by mass, the adhesive The gel rate of the layer is 40-80% by mass;

(2) The re-peelable adhesive sheet according to (1) above, wherein the gel ratio is 40-60% by mass;

(3) The re-peelable adhesive sheet according to (1) or (2), wherein the content of the 2-ethylhexyl acrylate is 96% by mass or more;

(4) The re-peelable adhesive sheet according to (1) or (2), wherein the content of the ethylenically unsaturated monomer having a carboxyl group is 0.1 to 5% by mass;

(5) The re-peelable adhesive sheet according to (1) or (2), wherein the content of the acrylonitrile is 0.5-3% by mass;

(6) The re-peelable adhesive sheet according to (1) or (2), wherein the tackifier has a softening point of 80 to 160°C;

(7) The re-peelable adhesive sheet according to (1) or (2), wherein the crosslinking agent is selected from polyglycidyl compounds having two or more glycidyl groups in the molecule, and polyglycidyl compounds having two or more glycidyl groups in the molecule. One or more of the above oxazoline-based oxazoline-based compounds and carbodiimide-based compounds with two or more carbodiimide groups in the molecule;

(8) The re-peelable adhesive sheet according to (1) or (2), wherein the re-peelable adhesive sheet is used for affixing a label of a polyethylene terephthalate bottle;

(9) The re-peelable adhesive sheet according to claim 8, wherein, after being attached to a polyethylene terephthalate bottle, the adhesive layer is immersed in hot water at 80°C for 30 minutes. Peel off from this polyethylene terephthalate bottle within.

According to the present invention, the re-peelable adhesive sheet is formed by using the adhesive layer from a re-peelable water-based adhesive composition containing an aqueous emulsion containing acrylic acid and a crosslinking agent. The acrylic copolymer and the adhesion imparting agent contain, as the monomer components constituting the acrylic copolymer, 2-ethylhexyl acrylate, acrylonitrile, and an ethylenically unsaturated monomer having a carboxyl group as main components, thereby being able to Provided is a re-peelable adhesive sheet for sticking labels that can be easily peeled and removed in a recycling process in a recycling device and can be easily peeled off by hand.

Detailed ways

The present invention will be described in detail below.

The re-peelable adhesive sheet in the present invention can be removed from the PET bottle by immersing the PET bottle in hot water in the washing step of the PET bottle. The substrate sheet as the support body is not particularly limited. In order to easily separate the peeled adhesive label by utilizing the difference in specific gravity between the PET bottle and the adhesive label in hot water, a substrate with a specific gravity of less than 1 can be suitably used, for example, Non-fiber paper, crepe paper, water-resistant paper, etc., synthetic paper with holes inside, polypropylene fiber film, polyethylene film, foamed polyethylene film, and stretched or unstretched films can also be used appropriately.

Among them, from the viewpoint of good printability, rigidity, cost, labeling suitability, etc. as a label base material, a polyolefin-based synthetic resin film formed of polyethylene resin, polypropylene resin, etc. Synthetic paper made of polyolefin resin, etc.

The synthetic resin film as the base sheet may not be stretched, but may be stretched in a uniaxial direction or a biaxial direction such as the longitudinal direction or the transverse direction.

The thickness of the substrate sheet is not particularly limited, but is usually in the range of 10-200 μm, and preferably 25-150 μm from the viewpoint of ease of handling.

The base sheet may be colored or colorless and transparent. In addition, printing or printing may be performed on the surface or the back of the base sheet.

Therefore, a heat-sensitive recording layer; a print-receiving layer capable of thermal transfer, inkjet, laser printing, etc.; a printability enhancing layer, etc. can also be provided on the substrate sheet.

In addition, primer treatment or corona treatment may be performed in order to improve the adhesiveness (keying force) between the back surface (adhesive layer forming surface) of the base sheet and the adhesive layer.

In order to form the adhesive layer of the re-peelable adhesive sheet of the present invention, the adhesive composition contains an aqueous emulsion and a crosslinking agent. The aqueous emulsion contains an acrylic copolymer and an adhesion imparting agent. The monomer component contains 2-ethylhexyl acrylate, acrylonitrile, and an ethylenically unsaturated monomer having a carboxyl group.

In the present invention, the effect of the present invention can be realized by adjusting the content of acrylonitrile in the range of 0.5-5 mass%, preferably 0.5-4 mass%, more preferably 0.5-3 mass%. By making content of acrylonitrile more than the said minimum, the cohesive force of an adhesive layer becomes favorable when forming the adhesive layer of an adhesive sheet. Thereby, when the adhesive sheet is peeled from the adherend, it is possible to suppress the residue of the pasty substance of the adhesive or poor peeling, which is preferable. Moreover, by being below the said upper limit, it is possible to maintain favorable adhesiveness without impairing initial stage tackiness (tack property) or cohesiveness.

Acrylic acid, methacrylic acid, maleic acid, itaconic acid, etc. can be used as an ethylenically unsaturated monomer which has a carboxyl group. Among them, it is preferable to use acrylic acid and methacrylic acid from the viewpoint of easily achieving a balance between adhesiveness and re-peelability, and being easy to obtain.

It is preferable to use acrylic acid and methacrylic acid in combination from the viewpoint of being able to disperse crosslinking origins inside and outside the emulsion particles.

The content of the ethylenically unsaturated monomer having a carboxyl group is preferably 0.1 to 5% by mass, more preferably 0.5 to 2% by mass. By being 0.1% by mass or more, cohesion and mechanical stability can be improved; by being 5% by mass or less, the long-term stability of the re-peelable adhesive sheet before label processing can be improved, and the balance between re-peelability and adhesive force becomes good.

By making the content of 2-ethylhexyl acrylate to be 90% by mass or more in the monomer components constituting the acrylic copolymer, it is possible to impart a protective effect during re-peeling after sticking to the PET bottle for a certain period of time and then peeling off by hand. Moist feeling, prevents contamination of adherends. The content of 2-ethylhexyl acrylate is preferably 96% by mass or more, more preferably 97% by mass or more, from the viewpoint of obtaining a copolymer with a low Tg and achieving a balanced performance of adhesive force and re-peelability. , More preferably at least 98% by mass.

In addition, in order to control various properties of the pressure-sensitive adhesive layer, monomer components other than those described above may also be used appropriately. As other monomer components, it is preferable to use an alkyl (meth)acrylate having an alkyl group having 1 to 12 carbon atoms in addition to 2-ethylhexyl acrylate. For example, methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, ( Monomer components such as n-octyl methacrylate, isooctyl (meth)acrylate, isononyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl methacrylate, etc. , one or more of them can be used. Among them, the preferred monomer components are n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, isooctyl (meth)acrylate, n-butyl (meth)acrylate Octyl esters, particularly preferably n-butyl acrylate. The content of the monomer components is preferably 0 to 9.5% by mass of the monomer components constituting the acrylic copolymer. By being within this range, it is possible to stick to a PET bottle with good adhesiveness without impairing the re-peelability.

Further, in addition to the above-mentioned monomers, in order to improve the cohesive force of the adhesive layer, one selected from (poly)ethylene glycol di(meth)acrylate, methylenebisacrylamide, 1,6-hexanediol di( One or more types of polyfunctional monomers such as meth)acrylate, trimethylolpropane tri(meth)acrylate, and divinylbenzene. The content of these polyfunctional monomers can be added in an amount of about 0 to 2 parts by mass relative to 100 parts by mass of the above-mentioned total monomers. When the amount exceeds 2 parts by mass, the adhesion to the surface base material and re-peelability will be reduced.

When the acrylic copolymer in the adhesive layer of the re-peelable adhesive sheet of the present invention is prepared by emulsion polymerization using the above-mentioned monomer components, 2,2'-azobis (2-Methylpropylamidine) dihydrochloride (2,2'-アゾビス(2-Mecholpropionamidine), 2,2'-Azobisisobutylamidine dihydrochloride (2,2'- Azos such as アゾビス (2-Amijinopropan) ヒヒドロロライド), persulfates such as potassium persulfate and ammonium persulfate, peroxides such as benzoyl peroxide, tert-butyl hydroperoxide, and hydrogen peroxide or a redox initiator formed by a combination of persulfate and sodium bisulfite or a combination of peroxide and sodium ascorbate. Usually these polymerization initiators can be added in a prescribed amount at each stage of emulsion polymerization to carry out polymerization reaction.

When the aqueous emulsion of the acrylic copolymer in the adhesive layer of the re-peelable adhesive sheet of the present invention is prepared by emulsion polymerization, an appropriate amount of anionic or cationic emulsifier may be used in order to ensure polymerization stability. Specific examples of the anionic emulsifier include sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzenesulfonate, sodium alkyl polyoxyethylene ether sulfate, alkylphenol polyoxyethylene ether Sodium Sulfate etc. Examples of cationic emulsifiers include polyoxyethylene alkyl ethers, alkylphenol polyoxyethylene ethers, and the like. In addition, a radically polymerizable reactive emulsifier into which an acryl group, an acryloyl group, etc. have been introduced can also be used. These emulsifiers may be used alone or in combination.

The conditions of the emulsion polymerization are not particularly limited, and the conditions applicable to the usual emulsion polymerization can be applied as they are. Usually, after replacing the inside of the reactor with an inert gas, the temperature is raised while stirring under reflux, and the temperature is raised to a temperature range of about 40-100°C, and polymerization is carried out for about 1-8 hours after the start of the temperature rise.

The adhesive composition of the re-peelable adhesive sheet of this invention contains an adhesive agent as an essential component.

Examples of the tackifier to be used include rosin-based resins such as rosin, rosin phenol resins, and ester compounds thereof, hydrogenated rosin esters, terpene oligomers, terpene phenol resins, Adhesion-imparting agent for terpene-based resins such as aromatic modified terpene resins, C5-based petroleum resins, and C9-based petroleum resins. Among these, tackifiers having a softening point of 80 to 160° C. are preferred, or two or more of these tackifiers may be used in combination.

The number of parts to be mixed varies depending on the monomers used, and is usually added in an amount of 0.1 to 20 parts by mass, preferably 1 to 15 parts by mass, based on 100 parts by mass of the total amount of monomer components constituting the acrylic copolymer. By adding 0.1 parts by mass or more of the tackifier, favorable adhesive force and substrate adhesion can be obtained as substantial effects. By adding 20 parts by mass or less, it is possible to prevent the apparent Tg of the pressure-sensitive adhesive layer from becoming high, and to prevent a decrease in adhesive force and substrate adhesion.

The tackifier may be added as an emulsion-type tackifier to the aqueous emulsion of the acrylic copolymer after emulsion polymerization, or may be added before or during emulsion polymerization. In consideration of adhesiveness to surface substrates, it is preferable to coexist with monomer components during emulsion polymerization. When emulsification polymerization is carried out in the coexistence of monomer components, chain transfer to the tackifier is likely to occur, and there is a possibility that the gel fraction of the adhesive layer will decrease. In the present invention, by including a crosslinking agent as an essential component, the gel fraction In the range of 40-80% by mass, the desired effect can be obtained. The gel ratio described in the present invention is obtained by the measurement method in the examples described later.

In the present invention, the gel fraction can be adjusted to a range of 40-80% by mass by increasing or decreasing the amount of the crosslinking agent added after polymerization, and adjustment of the degree of polymerization by using a chain transfer agent during polymerization can also be used in combination. method of gelation. As the chain transfer agent, known chain transfer agents such as dodecyl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, thioglycolic acid- 2-ethylhexyl ester, 2,3-dimercapto-1-propanol.

As the adhesive layer, when the gel ratio is less than 40% by mass, secondary processing such as cutting and perforation of the adhesive label will deteriorate due to bleeding of the adhesive layer, and when it exceeds 80% by mass, sufficient gel content cannot be obtained. of adhesion. The preferable range of the gel fraction is 40-60% by mass.

The average particle diameter of the aqueous emulsion particles of the acrylic copolymer in the re-peelable adhesive sheet of the present invention is 80-500 nm, preferably 150-400 nm.

When the average particle diameter is within the above-mentioned range, an adhesive layer having a good balance of physical properties of the obtained adhesive layer, that is, adhesive force, re-peelability, and mechanical stability can be obtained.

By setting the average particle diameter to be 80 nm or more, stable emulsion ions can be obtained and an increase in the amount of surfactant used can be prevented. By making the average particle diameter 400 nm or less, the adhesiveness to a base material sheet can be acquired, and the fall of the water resistance of the obtained pressure-sensitive adhesive layer can be prevented.

The tackifier layer of the re-peelable adhesive sheet of the present invention contains a crosslinking agent as an essential component.

As a crosslinking agent, it is mainly a crosslinking agent that crosslinks with a carboxyl group derived from an ethylenically unsaturated monomer in an acrylic copolymer. From the viewpoint of less increase in adhesive strength over time and good stain resistance, epoxy-based compounds, oxazoline-based compounds, and carbodiimide-based compounds are mainly used. In addition, these crosslinking agents may be used alone or in combination of two or more. If necessary, aziridine-based compounds, polyisocyanates, melamine-based compounds, metal complex-based compounds, amine-based compounds, adipic acid may be used in combination. Other crosslinking agents such as hydrazine derivatives such as dihydrazide and sebacic acid dihydrazide.

These crosslinking agents are added in a ratio of 0.4 to 1 equivalent to 1 equivalent of carboxyl groups contained in the acrylic copolymer as the main resin component in the water-dispersible pressure-sensitive adhesive composition. By setting the addition amount to 0.4 equivalent or more, it is possible to prevent the gel fraction from being too low so that no substantial effect can be obtained, and to prevent the substrate adhesion and cohesive force from deteriorating. By being 1 equivalent or less, it is possible to prevent the crosslinking agent from penetrating into the adherend or substrate interface due to an excessively high gel fraction, prevent adherend contamination, decrease in substrate adhesiveness, and prevent decrease in alkali solubility.

As the epoxy-based compound, as long as it is a compound having two or more epoxy groups or glycidyl groups in the molecule, for example, bisphenol A epichlorohydrin type epoxy resin, sorbitol polyglycidyl ether ( Solbitor poly glider) (for example, "Denacor EX-611", "Denacor EX-612", "Denacor EX-614", "Denacor EX-614B", "Denacor EX-622" manufactured by Nagase Chemtex Co., Ltd.), Polyglycerol polyglycidyl ether (polyglycerol polyglycidyl ether) (for example, "Denacol EX-512" and "denacor EX-521" manufactured by Nagase Chemtex Co., Ltd.), pentaerythritol polyglycidyl ether (Pentaerythritol polyglycidyl ether) ) (e.g., "Denacol EX-411" manufactured by Nagase ChemTex Corporation, etc.), diglycerol polyglycidyl ether (Gigriselol Polygrishi Glycidyl Etel) (e.g., "Denakol EX-421" manufactured by Nagase ChemTex Corporation, etc.), Glycerol polyglycidyl ether (for example, "Denacol EX-313" and "Denacol EX-314" manufactured by Nagase Chemtex Co., Ltd.), trimethylolpropane polyglycidyl ether ( For example, "Denakol EX-321" manufactured by Nagase ChemTex Corporation, etc.), neopentyl glycol diglycidyl ether (e.g., "Denakol EX-211" manufactured by Nagase ChemTex Corporation, etc.), 1,6-hexanediol Diglycidyl ether (for example, "Denacol EX-212" manufactured by Nagase Chemtex Corporation, etc.), ethylene glycol diglycidyl ether (for example, "Denacol EX-810" and "Denacol EX-811" manufactured by Nagase ChemTex Corporation, etc.) ", etc.), diethylene glycol diglycidyl ether (for example, "Denacol EX-850" and "Denacol EX-851" manufactured by Nagase Chemtex Co., Ltd.), polyethylene glycol diglycidyl ether (for example, Nagasechem "Denacol EX-821", "Denacol EX-830", "Denacol EX-832", "Denacol EX-841", "Denacol EX-861" manufactured by Tex Corporation), propylene glycol diglycidyl ether (for example, Nagase "Denacol EX-911" manufactured by Chemtex Corporation, etc.), polypropylene glycol diglycidyl ether (for example, "Denacol EX-941" manufactured by Nagase Chemtex Corporation, "Denacol EX-920", "Denacol EX-931" etc. ), diglycidylaniline, N,N,N',N'-tetraglycidyl o-xylylenediamine, 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane wait.

As the oxazoline compound, an addition-polymerizable 2-oxazoline (such as 2-ethylpropenyl-2-oxazoline) having a substituent with an unsaturated carbon-carbon bond at the carbon position of the 2-position can be mentioned. oxazoline) and other unsaturated monomer copolymers, etc., as commercially available products, "Epocross WS-500", "Epocross WS-700", "Epocross K-2010E", "Epocross K-2010E" and " "EPOCROS K-2020E", "EPOCROS K-2030E", etc.

As the carbodiimide-based compound, as long as it is a compound containing at least two or more carbodiimide groups, examples include "Carbodilite V-02" and "Carbodilite V-02-L2" manufactured by Nisshinbo Co., Ltd. , "Calvodilite V-04", "Calvodilite V-06", "Calvodilite E-01", "Calvodilite E-02", "Calvodilite E-04", etc.

In addition, the adhesive layer in the re-peelable adhesive sheet of the present invention may appropriately contain a plasticizer (for example, liquid polybutene, mineral oil, lanolin, liquid polyisoprene, liquid polyacrylate, Dioctyl phthalate, glycerin, ethanolamine, etc.), preservatives, rust inhibitors, freeze-melt stabilizers, pigments, colorants, fillers (zinc oxide, titanium dioxide, calcium carbonate, clay, etc.), metal powders, Defoamers, tackifiers, surfactants, antioxidants, UV absorbers, etc.

The above-mentioned additives are mostly added to the aqueous emulsion after polymerization, and may also be added before or during emulsion polymerization.

The water-dispersed adhesive composition (aqueous emulsion containing an acrylic copolymer, an adhesion imparting agent, and a crosslinking agent) of the present invention has a solid content of 30-65% by mass, preferably 40-55% by mass.

In addition, the viscosity of the water-dispersed adhesive composition is 50-12000 mPa·s (BM type viscometer, 25°C), preferably 100-10000 mPa·s.

A pH in the range of 6-9 is further preferred. When the solid content, viscosity, and pH of the water-dispersed pressure-sensitive adhesive composition are within the above-mentioned ranges, it is preferable from the viewpoints of drying properties, coating properties, and handling properties.

There are no particular limitations on the method for producing the re-peelable adhesive sheet of the present invention. For example, a crosslinking agent and the like are mixed with the above-mentioned aqueous emulsion (if no tackifier is added during the emulsion polymerization of the acrylic copolymer, an emulsion-type tackifier is also mixed), and a tackifier such as polyacrylic acid is added and mixed as necessary. agent, and prepare an adhesive formed of a water-dispersible adhesive composition whose viscosity is adjusted to about 5,000-10,000 mPa·s at 25°C.

Next, a transfer coating method in which the adhesive is applied to the release sheet and dried to form an adhesive layer, and then the adhesive layer and the base sheet are bonded together can be employed. Furthermore, a direct coating method in which the adhesive is first applied directly to the surface of the substrate sheet, dried to form an adhesive layer, and then bonded to the release sheet can also be used.

Although it does not specifically limit as a release sheet, As a support base material, paper, synthetic paper, a synthetic resin film etc. are mentioned, for example.

As the paper, paper substrates such as fiberless paper, cellophane, coated paper, etc., paper substrates such as laminated papers of thermoplastic resins such as polyethylene and polypropylene laminated on these paper substrates, and fiber-free Paper substrates such as paper, cellophane, coated paper, etc., which have been sealed with fiber, starch, polyvinyl alcohol, styrene-acrylate resin, etc.; as plastic synthetic resin films, polyethylene resin, polypropylene resin, etc. Polyolefin resins such as resins, films made of polyester resins such as polybutylene terephthalate resins and polyethylene terephthalate resins, and corona discharge treatment on these synthetic resin films, etc. Films that are easy to be bonded are preferably films that have been subjected to a release treatment.

As the release treatment agent, rubber-based elastomers such as silicone resins, polyolefin resins (for release sheets other than polyolefin resins), isoprene resins, butadiene resins, alkyd resins, fluorine resins, etc., can be used. Known treating agents such as resins and long-chain alkyl-containing resins.

The thickness of the layer of the release treatment agent is preferably 0.05 to 2.0 μm, more preferably 0.1 to 1.5 μm.

The thickness of the support substrate of the release sheet is not particularly limited, and is usually 30-200 μm.

The method of applying the adhesive is not particularly limited, and conventionally known coating methods can be used, for example, using a knife coater, a roll coater, a roll knife coater, a gravure coater, Methods of coating devices such as electronic gravure coater, air knife coater, bar coater, die coater, curtain coater, etc.

The thickness of the adhesive layer is not particularly limited, and is usually 10-50 μm, preferably 12-30 μm. In addition, the re-peelable adhesive sheet of the present invention may be in the form of a flat sheet or rolled into a roll.

The re-peelable adhesive sheet of the present invention prepared as described above is characterized in that, after being attached to a PET bottle, it is sticky when immersed in hot water at 80°C in the recycling process of the recycling device. The agent layer peeled off from the PET bottle within 30 minutes.

The re-peelable adhesive sheet of the present invention can be easily peeled and removed from the PET bottle in the above-mentioned steps, and can be easily peeled off by hand, so it is particularly preferably used as a label for sticking PET bottles.

Example

Hereinafter, the present invention will be described in more detail by way of examples and comparative examples, but the present invention is not limited thereto. In addition, in the following examples and comparative examples, all parts or % represent parts by mass or % by mass.

Example 1

As monomer components, 98.4 parts of 2-ethylhexyl acrylate (hereinafter referred to as 2EHA), 0.2 parts of acrylic acid (hereinafter referred to as AA), 0.4 parts of methacrylic acid (hereinafter referred to as MAA), acrylonitrile (hereinafter referred to as 1.0 part of AN), 0.5 part of polyoxyethylene ether sulfate sodium salt (surfactant manufactured by Kao Corporation, trade name: Latemul E-118B), 0.5 part of polyoxyethylene alkyl alkyl ether ammonium salt (first Surfactant manufactured by Kogyo Pharmaceutical Co., Ltd., trade name: Aquaron KH-05) 0.1 part, polyoxyethylene alkyl ether (surfactant manufactured by Kao Corporation, trade name: Emalgen 103) 1 part, hydrogenated rosin ester (Istoman Adhesion-imparting agent manufactured by Chemicul Corporation, trade name: Forall 105) 2.0 parts, aromatic modified terpene resin (adhesion-imparting agent manufactured by Yasuhara Chemical Corporation, trade name: YS Resin TO-125) 0.5 parts, and 80 mass of ion-exchanged water The mixture was put into a reaction vessel equipped with a stirrer, a reflux condenser, a thermometer, a nitrogen gas introduction tube, and a dropping funnel, and stirred at room temperature to prepare an emulsion of a mixture of monomer components in advance.

In addition, 28 parts by mass of ion-exchanged water was added to a reaction device equipped with a stirrer, reflux condenser, thermometer, nitrogen gas introduction pipe and dropping funnel, and nitrogen gas was enclosed to raise the temperature until the internal temperature reached 80°C. At the same time, 10 parts by mass of % ammonium persulfate aqueous solution 0.5 parts by mass. Next, the emulsion of the mixture of the monomer components prepared beforehand was transferred to the dropping funnel, and it was dripped over 4 hours.

Simultaneously with this, 4 mass parts of 5 mass % ammonium persulfate aqueous solution was dripped, and the temperature in the reaction container was maintained at 80 degreeC, and emulsion polymerization was performed. After completion of the dropping, aging was carried out at 80° C. for 4 hours to obtain an aqueous emulsion (1) containing an acrylic copolymer and a tackifier.

Thereafter, it was cooled to room temperature, and water was added after neutralizing with 25% ammonia water to obtain an aqueous emulsion (2) having a solid content of 50% by mass and a pH of 8.0. Next, 0.5 part of polyoxyethylene alkylamine (manufactured by Lion Aczo Co., Ltd., trade name: Esomin C/25) was added as a plasticizer to obtain an aqueous emulsion (3).

Next, to 100 parts by mass of the aqueous emulsion (3), a polyacrylic acid-based thickener (ASE-60, manufactured by Romde Haus Co., Ltd.) was added to increase the viscosity at 25° C. to 8000 mPa·s.

Further, it was measured by adding a cross-linking agent (glycerol polyglycidyl ether manufactured by Nagase Chemtex Corporation with respect to 100 parts by mass of the acrylic copolymer in the above-mentioned aqueous emulsion (3), trade name: Denakor EX-313 (effective Component 99% or more)) Viscosity of an adhesive formed by 0.9 parts by mass of the obtained water-dispersed adhesive composition.

Using a roll-type knife coater, apply a coating thickness of 15 μm after drying on the release agent-treated surface of a release sheet (manufactured by Lintec Co., Ltd., cellophane after release treatment with silicone resin, product name: SP-8K Ao). The adhesive was applied in a manner and dried at 90° C. for 2 minutes to form an adhesive layer.

Then, the surface substrate synthetic paper (manufactured by ユポコーポレーション, product name: ユポ SGS80) with a print-receiving layer on one side is bonded to the surface that does not have a print-receiving layer, and at 23° C. and in an atmosphere of 50% relative humidity, It was left to stand for 7 days, thereby preparing a re-peelable adhesive sheet.

In addition, instead of the above-mentioned synthetic paper, it was bonded to the release-treated surface of a release sheet (manufactured by Lintec Co., Ltd., a polyester film that has been released with a silicone resin, product name: SP-PET3811), and placed at 23°C and a relative humidity of 50%. The adhesive sheet was prepared by leaving it standing for 7 days under an atmosphere, and the gel ratio was measured using the adhesive sheet.

The re-peelable adhesive sheet was bonded to a SUS board and a polyester board, respectively, and the adhesive force was measured. Next, the re-peelable adhesive sheet was processed into a label, and water resistance and re-peelability were measured.

Example 2

Except having changed 2-EHA and AN into the quantity shown in Table 1, it carried out similarly to Example 1. The results are shown in Table 1.

Example 3

Except having changed content of AA and MAA as shown in Table 1, it carried out similarly to Example 1, and produced the re-peelable adhesive sheet. The results are shown in Table 1.

Example 4

A re-peelable adhesive sheet was produced in the same manner as in Example 1, except that 1.0 part of carbodiimide (trade name: Carbodilite V-04) manufactured by Nisshinbo Co., Ltd. was used as a crosslinking agent. The results are shown in Table 1.

Example 5

In addition to using 2.0 parts of an oxazoline-based water-soluble polymer (manufactured by Nippon Shokubai Co., Ltd., trade name: EPOCROSS WS-700, solid content 25%) with a propenyl main chain as a crosslinking agent, it is the same as in Example 1 Then, a re-peelable adhesive sheet was produced. The results are shown in Table 1.

Comparative example 1, 2

Except having changed the quantity of AN into 0.4 part or not using it, and having changed 2-EHA into the quantity shown in Table 1, it carried out similarly to Example 1, and produced the re-peelable adhesive sheet for comparison. The results are shown in Table 1.

Comparative example 3

Except having used 8.0 parts of AN, and having changed 2-EHA into the quantity shown in Table 1, it carried out similarly to Example 1, and produced the re-peelable adhesive sheet for comparison. The results are shown in Table 1.

Comparative example 4, 5

Except not using Denacor EX-313 or using 0.3 parts, it carried out similarly to Example 1, and produced the re-peelable adhesive sheet for comparison. The results are shown in Table 1.

Comparative Example 6

Except having used 3.0 parts of denacol EX-313, it carried out similarly to Example 1, and produced the re-peelable adhesive sheet for comparison. The results are shown in Table 1.

Comparative Example 7

Except not adding Folar 105 and YS Resin TO-125, it carried out similarly to Example 1, and prepared the re-peelable adhesive sheet for comparison. The results are shown in Table 1.

Comparative Example 8

Except having used 2-EHA and n-butyl acrylate in the quantity shown in Table 1, it carried out similarly to Example 1, and produced the re-peelable adhesive sheet. The results are shown in Table 1.

Reference example 1, 2

In addition to using a commercially available alkali-soluble label adhesive (AN-free adhesive from Toagosei Co., trade name: RP-275, solid content 52-54%, viscosity 8000-18000mPa·s/25°C, pH 6.5-7.5) 100 parts by mass, respectively add cross-linking agent (polyglycerol polyglycidyl ether manufactured by Nagase Chemtex Corporation, trade name: denacol EX-521 (more than 99% active ingredient)) 1.0 parts or 3.0 parts to obtain Except for the above-mentioned adhesive, it carried out similarly to Example 1, and produced the re-peelable adhesive sheet for reference. The results are shown in Table 1.

The evaluation of each physical property and performance measured in the Example and the comparative example was performed as follows.

<Measurement of various physical properties>

(1) Viscosity

In accordance with JISK-6833, in an environment of 25°C, the viscosity of the adhesive composition was measured at 12 revolutions per minute using a BM-type viscometer (manufactured by Tokyo Keiki Co., Ltd.) (unit: mPa·s) .

(2) Gel rate

Wrap about 500 mg of the adhesive layer on a #300 SUS mesh, dip it in tetrahydrofuran for 72 hours, take it out together with the SUS mesh, dry it at 120°C for 3 hours, and calculate the adhesive layer by the mass ratio before dipping The gel rate (unit: mass %).

<Characteristics Test of Re-peelable Adhesive Sheet and Adhesive Label>

(1) Adhesion

Cut the re-peelable adhesive sheet into a width of 25mm, paste it on the SUS board and the polyester board (PET board), press it back and forth once with a roller with a mass of 2kg (19.6N), and place it at a relative humidity of 50% for 24 hours , the measured value when the peeling speed is 300mm/min and the peeling angle is 180°, and the unit is N/25mm.

(2) Water resistance

The re-peelable adhesive sheet was made into an adhesive label with a width of 25 mm×50 mm, and the adhesive label was attached to a PET bottle, and when it was immersed in water at 23° C. for 72 hours, peeling of the label was visually observed.

○: No peeling

×: peeled off

(3) Repeelability

[Hand peelability]

The same adhesive label as used for the water resistance test was attached to a PET bottle, and after being left for a week at 40° C. and a relative humidity of 80%, it was peeled off by hand to check re-peelability.

○: Good re-peelability, no paste residue

×: Can no longer be peeled off, with paste-like substance remaining

[hot water detachability]

Stick the same adhesive label as used in the water resistance test to the PET bottle, and when it is immersed in hot water at 80°C for 30 minutes, visually observe whether the label peels off naturally

◯: The label was completely peeled off.

Δ: Part of the label peeled off.

X: The label was not peeled off at all.

[use raw materials]

The numerical values of the monomer component and the crosslinking agent in Table 1 represent the amount of the active ingredient relative to 100 parts by mass of the total amount of the monomer component. The abbreviations and the like of the raw materials used are as follows.

2EHA: 2-Ethylhexyl Acrylate

n-BA: n-butyl acrylate

AA: Acrylic

MAA: methacrylic acid

AN: acrylonitrile

EX-313: Glycerol polyglycidyl ether manufactured by Nagase ChemTex Co., Ltd. (trade name: denacol EX-313 (99% or more active ingredients))

V-04: Carbodiimide manufactured by Nisshinbo Co., Ltd. (trade name: Carbodiline V-04 (active ingredient content 40%))

WS-700: Nippon Shokubai Co., Ltd. contains an oxazoline-based water-soluble polymer having an acrylic main chain (trade name: Epocross WS-700, solid content 25%)

EX-521: Polyglycerol polyglycidyl ether manufactured by Nagase Chemtex Co., Ltd. (trade name: denacol EX-521 (active ingredient 99% or more))

Industrial Applicability

The re-peelable adhesive sheet of the present invention is particularly useful as an adhesive label for bottles for various beverages, more specifically, for PET bottles. Since the adhesive layer used in the re-peelable adhesive sheet of the present invention is alkali-soluble, it is extremely useful in this field to easily perform the peeling operation of the attached label when recycling PET bottles.

Claims (9)

1. A re-peelable adhesive sheet, characterized in that, in the re-peelable adhesive sheet formed by laminating a release sheet, an adhesive layer, and a surface substrate, the adhesive layer is composed of an aqueous emulsion and a crosslinking agent Formed from a water-dispersible adhesive composition, the aqueous emulsion contains an acrylic copolymer and an adhesion-imparting agent, and the adhesion-imparting agent is 0.1-20 parts by mass, the monomer components constituting the acrylic acid copolymer include 2-ethylhexyl acrylate, acrylonitrile and ethylenically unsaturated monomers with carboxyl groups, the 2-ethylhexyl acrylate The content is more than 90% by mass of the total amount of 100% by mass of the monomer components, the content of the acrylonitrile is 0.5-5% by mass, and the gel ratio of the adhesive layer is 40-80% by mass, wherein , the cross-linking agent is a cross-linking agent that is cross-linked with the carboxyl group from the ethylenically unsaturated monomer in the acrylic copolymer, and relative to 1 equivalent of the carboxyl group, the amount of the cross-linking agent is The ratio of 0.4-1 equivalent, the determination method of the gel rate of the adhesive layer is as follows: 500 mg of the adhesive layer is wrapped in a #300 SUS screen, immersed in tetrahydrofuran for 72 hours, and taken out together with the SUS screen, After drying at 120°C for 3 hours, the gel fraction of the adhesive layer was calculated from the mass ratio before immersion. 2. The re-peelable adhesive sheet according to claim 1, wherein the gel rate is 40-60% by mass. 3. The re-peelable adhesive sheet according to claim 1 or 2, wherein the content of the 2-ethylhexyl acrylate is 96% by mass or more. 4. The re-peelable adhesive sheet according to claim 1 or 2, wherein the content of the ethylenically unsaturated monomer having a carboxyl group is 0.1 to 5% by mass. 5. The re-peelable adhesive sheet according to claim 1 or 2, wherein the content of the acrylonitrile is 0.5-3% by mass. 6. The re-peelable adhesive sheet according to claim 1 or 2, wherein the tackifier has a softening point of 80 to 160°C. 7. The re-peelable adhesive sheet according to claim 1 or 2, wherein the crosslinking agent is selected from polyglycidyl compounds having two or more glycidyl groups in the molecule, and polyglycidyl compounds having two or more oxazole groups in the molecule. One or more of the oxazoline-based compound of the line group, and the carbodiimide-based compound having two or more carbodiimide groups in the molecule. 8. The re-peelable adhesive sheet according to claim 1 or 2, wherein the re-peelable adhesive sheet is used for affixing a label of a bottle made of polyethylene terephthalate. 9. The re-peelable adhesive sheet according to claim 8, wherein after the adhesive layer is attached to a polyethylene terephthalate bottle, the adhesive layer is immersed in hot water at 80° C. within 30 minutes. Peel off from this polyethylene terephthalate bottle.