JP2014189702A - Aqueous re-releasable tackifier and re-releasable tacky sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tackifier entailing, even in a case where a neutral paper is used as a surface substrate for a re-releasable tacky sheet, neither a cohesive force gain nor a tackifying force loss after an extended storage period.SOLUTION: The provided aqueous re-releasable tackifier includes: (A) acrylic particles having a 50% average particle diameter of 20-60 μm; (B) acrylic particles having a glass transition point of -70 to -45°C and a 50% average particle diameter of 0.1-0.6 μm; and (C) a curative, whereas the acrylic particles (B) are obtained by polymerizing a monomer mixture including acrylic acid, methyl methacrylate, and 2-ethylhexyl acrylate in the presence of (D) an anionic reactive emulsifier and (E) a nonionic inert emulsifier having an ethylene oxide unit repeating number of 7 to 20.

Description

  The present invention relates to an aqueous pressure-sensitive adhesive having removability.

  Conventionally, the re-peelable pressure-sensitive adhesive sheet is generally composed of a base material and a pressure-sensitive adhesive layer. As the base material, plastic film, synthetic paper, paper, metal foil or the like is used. In particular, re-peelable pressure-sensitive adhesive sheets using paper substrates are widely used in food and product logistics management labels, delivery address labels, form printing raw materials such as copy sheets, and adhesive tapes. ing.

The paper used for the base material used to be acid paper made by using aluminum sulfate for fixing rosin-based sizing agents, but aluminum sulfate is weakly acidic. There was a problem that some cellulose was hydrolyzed and the paper deteriorated with time.
Therefore, in recent years, neutral paper made using a neutral sizing agent has been widely used in consideration of the storage stability of paper.
By the way, calcium carbonate is easy to control the particle size, particle size distribution, and particle shape, has high whiteness and opacity, and is low in cost. However, since it dissolves under acidic conditions, it has not been used with acidic paper. However, since neutral paper does not have the above-mentioned restrictions, calcium carbonate can be used as a filler.

  Under these circumstances, neutral paper has come to be used as a base material for the re-peelable pressure-sensitive adhesive sheet. However, the water-based acrylic pressure-sensitive adhesive generally used for the re-peelable pressure-sensitive adhesive sheet has a carboxyl group in order to promote copolymerization and obtain a desired pressure-sensitive adhesive strength. When calcium carbonate is ionized, it moves to the pressure-sensitive adhesive layer over time. As the calcium ions migrated as described above undergo a crosslinking reaction with the carboxyl group, there arises a problem that the adhesive strength of the re-peelable pressure-sensitive adhesive sheet is greatly reduced.

  Therefore, in Patent Document 1, a surface base material containing a calcium component in a paper layer, an adhesive layer mainly composed of an acrylic copolymer, and an adhesive sheet obtained by sequentially laminating a release sheet, calcium in the surface base material is disclosed. The adhesive sheet which suppressed that the component and the carboxylic acid component of the acryl-type copolymer in an adhesive layer suppressed ionization is disclosed.

JP 2002-338909 A

  However, conventional aqueous pressure-sensitive adhesives contain sulfates and phosphates, but the crosslinking by calcium ions has been insufficiently suppressed. Further, when a metal sequestering agent is used, the viscosity of the pressure-sensitive adhesive is lowered, so that there is a problem that a general coating apparatus (for example, a comma coater) cannot be used for coating the pressure-sensitive adhesive.

  An object of the present invention is to provide a re-peelable pressure-sensitive adhesive with good coatability, which is capable of producing a re-peelable pressure-sensitive adhesive sheet whose adhesive strength does not easily decrease over time even when neutral paper is used as a substrate.

The present invention relates to acrylic particles (A) having a D50 average particle diameter of 20 to 60 μm and acrylic particles (B) having a glass transition temperature of −70 to −45 ° C. and a D50 average particle diameter of 0.1 to 0.6 μm. ) And a curing agent (C),
The acrylic particles (B) are nonionic non-reactive in which a monomer mixture containing acrylic acid, methyl methacrylate and 2-ethylhexyl acrylate is anionic reactive emulsifier (D) and the number of repeating ethylene oxide units is 7 to 20. An aqueous re-peelable pressure-sensitive adhesive formed by polymerization in the presence of an emulsifier (E).

  According to the present invention having the above-described configuration, the acrylic particles (B) mainly contributing to the adhesive force are made hydrophobic so that the effect of suppressing the carboxyl group and the crosslinking reaction when calcium ions migrate to the adhesive layer. Obtained. That is, hydrophobicity is improved by using a hydrophobic monomer 2-ethylhexyl acrylate and a nonionic non-reactive emulsifier having a specific range of ethylene oxide chain as an emulsifier, and an anionic reactive emulsifier is also used. As a result, the cohesive force of the acrylic particles (B) was improved, and a desired adhesive force was obtained.

  According to the present invention, it is possible to provide a re-peelable pressure-sensitive adhesive having good coating properties, which can create a re-peelable pressure-sensitive adhesive sheet that hardly deteriorates in adhesive strength even when neutral paper is used as a substrate.

  First, terms of the present invention will be described. The sheet | seat of an adhesive sheet is synonymous with a film and a tape. The monomer is an ethylenically unsaturated monomer.

  The aqueous re-peelable pressure-sensitive adhesive of the present invention comprises an acrylic particle (A) having a D50 average particle diameter of 20 to 60 μm, an acrylic particle (B) having a D50 average particle diameter of 0.1 to 0.6 μm, and curing. Nonionic non-reactive emulsifier (E) in which the acrylic particles (B) contain an agent (C), and the monomer mixture comprises an anion-reactive emulsifier (D) and a repeating number of ethylene oxide units of 7 to 20 The glass transition temperature is -70 to -45 ° C.

  The aqueous re-peelable pressure-sensitive adhesive of the present invention is preferably used as a re-peelable pressure-sensitive adhesive sheet by forming a pressure-sensitive adhesive layer by coating and drying. Common materials such as paper, plastic and synthetic paper can be used for the base material of the pressure-sensitive adhesive sheet. In the present invention, particularly when neutral paper is used as the base material, an effect is obtained in which the adhesive strength hardly decreases with time.

  In the aqueous re-peelable pressure-sensitive adhesive of the present invention, the acrylic particles (B) having a small average particle size have a role of maintaining adhesion to the adherend and mainly obtaining an adhesive force, and having a large average particle size. The acrylic particles (A) protrude from the pressure-sensitive adhesive layer in a convex shape, thereby suppressing excessive adhesion between the acrylic particles (B) and the adherend and mainly having a removability.

The acrylic particles (A) have a D50 average particle diameter of 20 to 60 μm. In order to obtain this average particle size, it is preferable to synthesize a raw material monomer mixture by suspension polymerization in the presence of an emulsifier and a suspension dispersant.
The monomer mixture is preferably a carboxyl group-containing monomer or other monomer.

  Examples of the carboxyl group-containing monomer include acrylic acid (Tg 106 ° C.), methacrylic acid (Tg 186 ° C.), itaconic acid (Tg 100 ° C.), maleic acid (Tg 130 ° C.), and the like. Of these, the use of acrylic acid is preferred. Tg is the glass transition temperature of the homopolymer.

  The carboxyl group-containing monomer is preferably used in an amount of 0.5 to 5 parts by weight, more preferably 1 to 3 parts by weight in the monomer mixture. By being in the range of 0.5 to 5 parts by weight, the polymerization stability and the cohesive force in the particles can be further improved.

The other monomers are preferably (meth) acrylic acid alkyl esters and other vinyl monomers.
Examples of the (meth) acrylic acid alkyl ester include methyl acrylate (Tg 8 ° C.), ethyl acrylate (Tg −22 ° C.), butyl acrylate (Tg −52 ° C.), and acrylic acid-2-ethylhexyl (Tg −70). Acrylic esters such as methyl methacrylate (Tg 105), ethyl methacrylate (Tg 65 ° C.), butyl methacrylate (Tg 20 ° C.), 2-ethylhexyl methacrylate (Tg −10 ° C.), cyclohexyl methacrylate And methacrylates such as (Tg 66 ° C.).
Examples of the other vinyl monomers include aromatic monomers such as styrene (Tg 65 ° C.), α-methylstyrene (Tg 168 ° C.), and benzyl methacrylate (Tg 54 ° C.); vinyl acetate (Tg 29 ° C.). Vinyl ester such as vinyl pyrrolidone (Tg 180 ° C.); glycidyl group-containing monomer such as glycidyl methacrylate (Tg 41 ° C.); 2-hydroxyethyl methacrylate (Tg 55 ° C.) Hydroxyl group-containing monomers such as dimethylaminoethyl methacrylate (Tg 18 ° C.); carboxylic acid amide group-containing monomers such as acrylamide (Tg 153 ° C.); acrylonitrile (Tg) Cyano group-containing monomers such as 100 ° C; polyfunctional vinyl monomers such as diallyl phthalate (Tg 90 ° C); I can get lost.
Among these monomers, 2-ethylhexyl acrylate is more preferable.

  The other monomer is preferably used in an amount of 95 to 99.5 parts by weight, and more preferably 97 to 99 parts by weight in the monomer mixture. By being in the range of 95 to 99.5 parts by weight, it becomes easier to balance the adhesive force and the cohesive force. Adhesive force improves more by becoming 95 weight part or more.

  The glass transition temperature of the acrylic particles (A) is preferably -70 to -65 ° C. By being in the said range, the tack with respect to a to-be-adhered body can be improved more.

In the present invention, the glass transition temperature (Tg) of the particles (copolymer) is a calculated value obtained by the following mathematical formula (1).
Formula (1) 1 / Tg = [(W1 / Tg1) + (W2 / Tg2) +... (Wn / Tgn)] / 100
However, W1: wt% of monomer 1, Tg1: glass transition temperature (° K) of homopolymer that can be formed only from monomer 1, W2: wt% of monomer 2, Tg2: monomer 2 Glass transition temperature (° K) of homopolymer that can be formed only from monomer, Wn:% by weight of monomer n, Tgn: Glass transition temperature (° K) of homopolymer that can be formed only from monomer n. Note that W1 + W2 +... + Wn = 100. Moreover, only a monomer is used for calculation of Tg, and a reactive emulsifier is not included even if copolymerization is possible.

  In the present invention, the glass transition temperature of the homopolymer was based on “Kyozo Kitaoka,“ Introduction to Synthetic Resins for Paints ”, published by Kobunshi Publishing, May 25, 1974”.

  The suspension polymerization preferably uses an emulsifier and a suspension dispersant in combination. As the emulsifier, an anionic emulsifier and a nonionic emulsifier can be used, but an anionic emulsifier is preferable because a stable suspension (a dispersion of acrylic particles (A)) can be produced.

The emulsifier is preferably a reactive emulsifier having an ethylenically unsaturated group and a reactive emulsifier having no ethylenically unsaturated group. The emulsifier is preferably an anionic emulsifier or a nonionic emulsifier due to its ionicity.
Examples of the reactive emulsifier include sodium vinyl sulfonate, polyoxyethylene ammonium sulfate acrylate, polyoxyethylene sulfonate sodium methacrylate, ammonium polyoxyethylene alkenyl phenyl sulfonate, polyoxyethylene alkenyl phenyl sulfate, sodium allyl alkyl sulfosuccinate. And anionic reactive emulsifiers such as sodium acrylate and polyoxypropylene sulfonic acid soda, and nonionic reactive emulsifiers such as polyoxyethylene alkenyl phenyl ether and polyoxyethylene methacryloyl ether.

  Examples of the non-reactive emulsifier include dodecyl benzene sulfonate, lauryl sulfate, alkyl diphenyl ether sulfonate, dialkyl sulfosuccinate, polyoxyethylene alkyl phenyl ether sulfate, polyoxyethylene polycyclic phenyl ether sulfate, polyoxy Anionic emulsifiers such as ethylene alkyl ether sulfate, polyoxyethylene alkyl phenyl ethers such as polyoxyethylene nonylphenyl ether and polyoxyethylene octylphenyl ether; polyoxyethylene lauryl ether, polyoxyethylene stearyl ether, polyoxyethylene Polyoxyethylene alkyl ethers such as oleyl ether; polyoxypolycyclic phenyl such as polyoxyethylene distyrenated phenyl ether Ether such; and nonionic emulsifiers such as polyoxyethylene sorbitan fatty acid esters.

  The emulsifier is preferably used in an amount of 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the monomer mixture. When it is in the range of 0.1 to 10 parts by weight, removability and polymerization stability can be further improved.

  The suspension dispersant is preferably used for enhancing the polymerization stability during suspension polymerization. Specifically, the suspension dispersant is a water-soluble protective colloid, for example, polyvinyl alcohols such as partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, and modified polyvinyl alcohol; hydroxyethyl cellulose, hydroxypropyl cellulose, carboxy Cellulose derivatives such as methylcellulose salt; and the like.

  The suspension dispersant is preferably used in an amount of 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the monomer mixture.

  In the present invention, it is preferable to use an oil-soluble polymerization initiator for suspension polymerization. Specifically, for example, benzoyl peroxide, lauroyl peroxide, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, t-butylperoxybivalate, t-butylperoxybenzoate, t-butylperoxy-2- Ethyl hexanoate, 2,2'-azobisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 2,2 ' -Azobis-4-methoxy-2,4-dimethylvaleronitrile, 2,2'-azobismethylisobutyrate and the like.

  The oil-soluble polymerization initiator is preferably 0.1 to 1.2 parts by weight, more preferably 0.3 to 0.8 parts by weight with respect to 100 parts by weight of the monomer mixture. By being in the range of 0.1 to 1.2 parts by weight, stable suspension polymerization can be easily obtained.

  In the present invention, the reaction temperature of the suspension polymerization is preferably 70 ° C. or higher, more preferably 80 ° C. or higher and 96 ° C. or lower.

In the present invention, a chain transfer agent may be used in the suspension polymerization for adjusting the molecular weight.
As the chain transfer agent, for example, a compound having a thiol group or a hydroxyl group is generally known. Examples of the compound having a thiol group include mercaptans such as lauryl mercaptan, 2-mercaptoethyl alcohol, dodecyl mercaptan and mercaptosuccinic acid, mercaptopropionate alkyl such as n-butyl mercaptopropionate and octyl mercaptopropionate, and mercaptopropion. And mercaptopropionic acid alkoxyalkyl such as methoxybutyl acid. Examples of the compound having a hydroxyl group include alcohols such as methyl alcohol, n-propyl alcohol, isopropyl alcohol, t-butyl alcohol, and benzyl alcohol. Among these, alcohols such as isopropyl alcohol are preferable from the viewpoint of further reducing the odor and aggregates of the pressure-sensitive adhesive.

  The chain transfer agent is preferably 0.01 to 0.1 parts by weight, more preferably 0.03 to 0.07 parts by weight, based on 100 parts by weight of the monomer mixture. It becomes easy to adjust to a desired molecular weight by being in the range of 0.01 to 0.1 parts by weight.

  The solvent used in the suspension polymerization in the present invention is preferably water, but a hydrophilic solvent such as alcohol can be used as long as the effects of the present invention are obtained.

  The acrylic particles (A) are preferably neutralized with a basic compound. As the basic compound, ammonia, and as the amines, monoethylamine, dimethylethanolamine, methylpropanolamine and the like are preferable.

  As for D50 average particle diameter of acrylic particle | grains (A), 20-60 micrometers is preferable. By being in the said range, it becomes easy to make adhesive force and removability compatible. The D50 average particle size is a D50 average particle size measured with a light scattering particle size measuring device “Microtrack 9320HRA (trade name); manufactured by Nikkiso Co., Ltd.”. The measurement is diluted with water and adjusted so that the measured concentration falls within the optimum concentration gauge width displayed on the screen.

  In the present invention, the gel fraction of the acrylic particles (A) is preferably 30 to 95% by weight, and more preferably 50 to 90% by weight. By being in the range of 30 to 95% by weight, in addition to further improving the adhesive force and removability, the anchoring property to the adherend is further improved.

In the present invention, the method for measuring the gel fraction (% by weight) is as follows. That is, the aqueous re-peelable pressure-sensitive adhesive is coated on a polyethylene terephthalate (PET) film so that the dry film thickness is about 200 μm, and then dried at 23 ° C. for 7 days. Next, the weight of the 200 mesh wire mesh is measured (the weight is M). The pressure-sensitive adhesive sheet is cut into a size of 5 cm × 5 cm, and the weight of the test piece bonded to the 200 mesh wire net is measured (the weight is A). The 200 mesh is a mesh specified by JIS G-3555.
The specimen is left in 50 ml of ethyl acetate at 50 ° C. for 1 day. Then, after taking out and drying at 100 degreeC for 20 minutes, a weight is measured (the weight is set to T).
Subsequently, a polyethylene terephthalate (PET) film is taken out from the test piece, the pressure-sensitive adhesive layer is removed using ethyl acetate, and the weight of the PET film is measured (the weight is defined as K). The obtained numerical value is substituted into the following mathematical formula (1) to obtain the gel fraction.
Formula (1) (TMK) × 100 / (AMK)

The acrylic polymer (B) mainly contributes to adhesive strength in the pressure-sensitive adhesive layer. The D50 average particle diameter is 0.1 to 0.6 μm, and the glass transition temperature is −70 to −45 ° C.
The acrylic particles (B) are preferably synthesized by emulsion polymerization of a monomer mixture.
The monomer mixture includes at least acrylic acid, methyl methacrylate, and 2-ethylhexyl acrylate. Hydrophobic acrylic polymer (B) by using hydrophobic monomer 2-ethylhexyl acrylate and nonionic non-reactive emulsifier having ethylene oxide chain in specific range as emulsifier Ion migration can be suppressed.

  The acrylic acid is preferably used in an amount of 0.5 to 2 parts by weight, more preferably 0.8 to 1.1 parts by weight, based on 100 parts by weight of the monomer mixture. By being in the range of 0.5 to 2 parts by weight, the polymerization stability is further improved during emulsion polymerization, and the crosslinking reaction with calcium ions can be further suppressed.

  Methyl methacrylate is preferably used in an amount of 1 to 19 parts by weight, more preferably 5 to 10 parts by weight, based on 100 parts by weight of the monomer mixture. By being in the range of 1 to 19 parts by weight, it becomes easy to balance the adhesive force and the cohesive force.

  2-ethylhexyl acrylate is preferably used in an amount of 80 to 98 parts by weight, more preferably 89 to 94 parts by weight, based on 100 parts by weight of the monomer mixture. By being in the range of 80 to 98 parts by weight, the adhesive strength and the polymerization stability are further improved.

  Other monomers that can be used in the monomer mixture are vinyl acetate (Tg 29 ° C), methyl acrylate (Tg 8 ° C), ethyl acrylate (Tg-22 ° C), butyl acrylate (Tg-52 ° C). ) And the like. However, it is preferable that the use is minimized or not used in consideration of the decrease in hydrophobicity. Even when used at a minimum, 5% by weight or less is preferable. In addition, the monomer illustrated by acrylic particle (A) can further be used for the said monomer mixture, if it exists in the range with which the effect of this invention is acquired.

  The glass transition temperature of the acrylic particles (B) is preferably -70 to -45 ° C. By being in the said range, adhesive force and cohesive force can be improved more.

  As the emulsifier used in the emulsion polymerization for obtaining the acrylic particles (B), an anionic emulsifier and a nonionic emulsifier can be used. However, in the present invention, an anionic reaction is performed in order to improve hydrophobicity and impart cohesion. The nonionic non-reactive emulsifier is used in order to improve the hydrophobicity. Specifically, it is preferable to use a nonionic non-reactive emulsifier (E) having a repeating number of ethylene oxide units of 7 to 20. By emulsion polymerization of the monomer mixture in the presence of these emulsifiers, the acrylic particles (B) can be shifted to hydrophobicity, and good cohesive strength, adhesive strength and removability can be obtained. .

  As the anionic reactive emulsifier (D), the emulsifier exemplified for the acrylic particles (A) can be used.

  The anionic reactive emulsifier (D) is preferably used in an amount of 0.1 to 10 parts by weight, more preferably 0.5 to 5 parts by weight, based on 100 parts by weight of the monomer mixture. By being in the range of 0.1 to 10 parts by weight, hydrophobicity, removability and polymerization stability are further improved.

The nonionic non-reactive emulsifier (E) uses an emulsifier having an ethylene oxide unit repeat number (hereinafter referred to as the number of EO units) of 7 to 20 among the emulsifiers exemplified for the acrylic particles (A). When the number of EO units is in the above range, both the hydrophobicity and polymerization stability of the acrylic particles (B) can be achieved.
Other emulsifiers can be used in combination as long as the effects of the present invention are obtained.

  The nonionic non-reactive emulsifier (E) is preferably used in an amount of 0.1 to 5 parts by weight, more preferably 0.5 to 3 parts by weight, based on 100 parts by weight of the monomer mixture. Hydrophobicity, removability, and polymerization stability are further improved by being in the range of 0.1 to 5 parts by weight.

  In the present invention, the polymerization initiator used for emulsion polymerization is preferably a radical polymerization initiator. The radical polymerization initiator is preferably a peroxide, but more preferably a combination of a peroxide and a reducing agent (hereinafter also referred to as a redox initiator). When the redox initiator is used, the molecular structure of the acrylic particles (B) tends to be a linear structure with few branches, the removability is improved, and the adhesive strength, particularly the adhesive strength to rough surfaces such as corrugated cardboard, is increased. It can be improved.

  Examples of the peroxide include persulfates such as potassium persulfate, ammonium persulfate, and sodium persulfate, and tertiary butyl hydroperoxide.

  Examples of the reducing agent include sodium pyrosulfite, L-ascorbic acid, iron (II) salt and the like.

  As a combination of redox initiators, for example, a combination of peroxide and ascorbic acid (a combination of hydrogen peroxide water and ascorbic acid), a combination of peroxide and iron (II) salt (hydrogen peroxide water and A combination of iron (II) salt and the like, and a combination of persulfate and sodium hydrogen sulfite. In the present invention, a combination of ammonium persulfate and sodium pyrosulfite is preferable from the viewpoint of further improving removability.

  The use amount of the radical polymerization initiator is preferably 0.2 to 1 part by weight, more preferably 0.2 to 0.6 part by weight based on 100 parts by weight of the monomer mixture. The polymer formation and removability can be further improved by being 0.2 to 1 part by weight. In addition, when using a redox initiator, it is preferable to use it by peroxide / reducing agent = 2/1 (weight ratio).

  In the emulsion polymerization of the acrylic particles (B), a chain transfer agent can be used to adjust the molecular weight in the same manner as the acrylic particles (A).

  The solvent used in the emulsion polymerization in the present invention is preferably water, but a hydrophilic solvent can be used for alcohol or the like as long as the effects of the present invention are obtained.

  The acrylic particles (B) are preferably neutralized with a basic compound. A basic compound can be used similarly to the acrylic particles (A).

  0.1-0.6 micrometer is preferable and, as for D50 average particle diameter of an acryl-type particle | grain (B), 0.2-0.5 micrometer is more preferable. By being in the range of 0.1 to 0.6 μm, it becomes easy to make the viscosity appropriate for the emulsion, and the applicability of the pressure-sensitive adhesive can be further improved, and the removability can be further improved. In addition, this D50 average particle diameter was calculated | required using the dynamic light scattering method (Microtrac NPA150 by Microtrac). The measurement was diluted with water, and the measurement concentration was adjusted to fall within the optimum concentration gauge width displayed on the screen.

  The aqueous re-peelable pressure-sensitive adhesive of the present invention contains acrylic particles (A) and acrylic particles (B), so that the acrylic particles (A) form a large number of protrusions on the surface of the pressure-sensitive adhesive layer. Since the acrylic particles (A) hitting the protruding portions (convex portions) have little tack, the acrylic particles (B) whose adhesion is inhibited by the acrylic particles (A) is responsible for the adhesion to the adherend. The present invention is a pressure-sensitive adhesive that can be re-peeled while obtaining a certain level of adhesive strength.

The blending of the acrylic particles (A) and the acrylic particles (B) is (A) / (B) = weight ratio.
75/25 to 25/75 is preferred. By being in the said range, adhesive force and removability can be obtained at a higher level.

  In the present invention, the curing agent (C) may be a compound having a functional group capable of reacting with a carboxyl group. Specific examples include oxazoline compounds, carbodiimide compounds, epoxy compounds, aziridine compounds, isocyanate compounds, melamine compounds, metal compounds such as metal complexes, amine compounds, and the like. Among these, carbodiimide compounds are more preferable because of good removability after aging.

  The curing agent (C) is not particularly limited as long as it uses an amount that allows the gel fraction of the pressure-sensitive adhesive layer to be 45 to 90% by weight. Usually, the amount is about 0.1 to 5.0 parts by weight with respect to 100 parts by weight in total of the acrylic particles (A) and the acrylic particles (B).

The aqueous re-peelable pressure-sensitive adhesive of the present invention can contain a tackifying resin in order to further improve the adhesive strength. Tackifying resins can be classified mainly into natural resin and synthetic resins.
The natural resin is preferably, for example, rosin resin (rosin, rosin ester, rosin phenol, colorless rosin derivative, etc.), terpene resin (terpene, aromatic modified terpene, terpene phenol, etc.) and the like.
The synthetic resin is preferably, for example, a petroleum resin (including styrene, α-methylstyrene, and aliphatic), and others (including phenolic resin, xylene resin, and ketone resin). Of these, rosin resin, terpene resin and petroleum resin are preferable, and rosin resin is more preferable. When the rosin resin is used, tack, removability, and adhesive stability over time can be further improved. The tackifying resin is preferably a water dispersion type.

The aqueous re-peelable pressure-sensitive adhesive of the present invention includes various additives used in general water-based pressure-sensitive adhesives such as an antifoaming agent, a wetting agent, a color pigment, a thickener, a plasticizer, an oxidation agent, if necessary. An inhibitor, an ultraviolet absorber, a preservative, etc. can be blended.

  In the present invention, the gel fraction of the aqueous re-peelable pressure-sensitive adhesive is preferably 45 to 90% by weight, and more preferably 60 to 80% by weight. When the gel fraction is in the range of 45 to 90% by weight, removability and anchoring properties can be achieved at a higher level.

In the present invention, the method for measuring the gel fraction (% by weight) is as follows. That is, the aqueous re-peelable pressure-sensitive adhesive is coated on a polyethylene terephthalate (PET) film so that the dry film thickness is about 200 μm, and then dried at 23 ° C. for 7 days. Next, the weight of the 200 mesh wire mesh is measured (the weight is M). The pressure-sensitive adhesive sheet is cut into a size of 5 cm × 5 cm, and the weight of the test piece bonded to the 200 mesh wire net is measured (the weight is A). The 200 mesh is a mesh specified by JIS G-3555.
The specimen is left in 50 ml of ethyl acetate at 50 ° C. for 1 day. Then, after taking out and drying at 100 degreeC for 20 minutes, a weight is measured (the weight is set to T).
Subsequently, a polyethylene terephthalate (PET) film is taken out from the test piece, the pressure-sensitive adhesive layer is removed using ethyl acetate, and the weight of the PET film is measured (the weight is defined as K). The obtained numerical value is substituted into the following mathematical formula (1) to obtain the gel fraction.
Formula (1) (TMK) × 100 / (AMK)

The re-peelable pressure-sensitive adhesive sheet of the present invention will be described. The re-peelable pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer formed from an aqueous re-peelable pressure-sensitive adhesive. In the present invention, the pressure-sensitive adhesive sheet is also referred to as a pressure-sensitive adhesive film or a pressure-sensitive adhesive tape, and a product obtained by separating these is also referred to as a pressure-sensitive adhesive label.

The re-peelable pressure-sensitive adhesive sheet of the present invention is a method in which an aqueous re-peelable pressure-sensitive adhesive is applied to a peelable sheet and dried, and then bonded to a base material, or an aqueous re-peelable type is directly applied to a base material, It can manufacture by the method of bonding with a peelable sheet after drying.

As the substrate, high-quality paper, coated paper, impregnated paper, synthetic paper, and the like can be used, and there are acidic paper and neutral paper according to a method of fixing a sizing agent to paper. In the present invention, when a neutral paper is used as the base material, a re-peelable pressure-sensitive adhesive sheet is obtained in which the adhesive strength hardly decreases with time.
As the peelable sheet, paper and plastic film that have been peeled with silicone or the like can be used.

  For the application of the pressure-sensitive adhesive, known coating apparatuses such as a roll coater such as a comma coater, a blade coater, and a gravure coater, a slot die coater, a lip coater, and a curtain coater can be used. The thickness of the pressure-sensitive adhesive layer is preferably 0.1 to 200 μm.

  The re-peelable pressure-sensitive adhesive sheet of the present invention can be widely used for delivery tag labels, industrial and household slip labels, building materials, and household masking tapes.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated in detail, this invention is not limited only to a following example. In the following, “part” indicates “part by weight”, and “%” indicates “% by weight”.

<Example 1>
"Manufacture of acrylic particles (A)"
A 2 L four-necked flask (hereinafter referred to as a reaction vessel) equipped with a reflux condenser, a stirrer, a thermometer, a nitrogen inlet tube, and a raw material inlet, with 700 parts of ion-exchanged water and a concentration of 5% Gohsenol KH as a suspension dispersant 100 parts of an aqueous solution of -17 (partially saponified polyvinyl alcohol manufactured by Nippon Synthetic Chemical Co., Ltd.) and 33.3 parts of an aqueous solution of New Coal 707SF (anion non-reactive emulsifier manufactured by Nippon Emulsifier Co., Ltd. (nonvolatile content 30%)) And dissolved by stirring.
Next, in another container, 490 parts of 2-ethylhexyl acrylate (hereinafter abbreviated as “2EHA”), 10 parts of acrylic acid (hereinafter abbreviated as “AA”), and perbutyl PV (manufactured by NOF Corporation) as an oil-soluble initiator. (Purity 70%)) 1.7 parts was added and stirred and mixed, and after confirming that the oil-soluble initiator was dissolved, this mixed solution was added to the reaction vessel and stirred for 1 hour.
Next, 400 parts of ion-exchanged water was added to the reaction vessel, and heating was started under a nitrogen atmosphere. After confirming the start of the reaction, the reaction was carried out for 4 hours while maintaining the internal temperature at 75 ° C. Cooling was started after completion of the reaction. After cooling to room temperature, it was neutralized with aqueous ammonia to obtain a dispersion of acrylic particles having a non-volatile content of 26.0%, a pH of 8.0, a viscosity of 100 mPa · s, and a D50 average particle size of 50 μm. The theoretical Tg of the glass transition temperature calculated from the monomer composition was -68.1 ° C. In addition, the D50 average particle diameter and glass transition temperature calculated | required the method demonstrated in the front | former stage.

"Manufacture of acrylic particles (B)"
23 parts of ion-exchanged water is placed in a 2 L reaction vessel equipped with a reflux condenser, stirrer, thermometer, nitrogen inlet tube, and raw material inlet, and the internal temperature becomes 70 ° C. while stirring while introducing nitrogen. Until heated.
Next, in another container, 90 parts of 2EHA, 9 parts of methyl methacrylate (hereinafter abbreviated as “MMA”), 1 part of AA, Aqualon KH-10 as an emulsifier (Ethylene Oxide unit made by Daiichi Kogyo Seiyaku Co., Ltd.) 2 parts of anion-reactive emulsifier having 10 repetitions (hereinafter referred to as the number of EO units), 1 part of Emulgen 1118S-70 (18 nonionic non-reactive emulsifier with EO units of 18 (non-volatile content 70%)), citric acid A mixture of 3 parts of sodium and 21 parts of ion-exchanged water was emulsified with a homomixer to prepare a monomer emulsion.
5% of the monomer emulsion was added to the reaction vessel, and at the same time, 0.4 parts of 5% ammonium persulfate (hereinafter abbreviated as “APS”) aqueous solution and 2% sodium pyrosulfite (hereinafter referred to as “polymerization initiator”). Emulsion polymerization was started by adding 0.5 part of an aqueous solution (abbreviated as “SMBS”).
Ten minutes after the addition of the polymerization initiator, 95% of the monomer emulsion, 3.6 parts of 5% APS aqueous solution and 4.5 parts of 2% SMBS aqueous solution were added dropwise simultaneously over 5 hours. During this time, the inside of the flask was kept at 70 ° C.
After completion of dropping, the reaction was continued at 70 ° C. for 3 hours. Thereafter, cooling is started, and aqueous ammonia is added at room temperature to neutralize, whereby an emulsion of acrylic particles (B) having a non-volatile content of 58.0%, a pH of 7.0, a viscosity of 250 mPa · s, and a D50 average particle size of 0.36 μm. Got.
The theoretical Tg of the glass transition temperature calculated from the monomer composition was −60.1 ° C.

"Composition of aqueous re-peeling adhesive"

  The resulting acrylic particles (A) and acrylic particles (B) were mixed so that (A) / (B) = 30/70 (in terms of non-volatile content weight). Furthermore, preservative: 0.3 part, wetting agent: 0.7 part, antifoaming agent: 1.0 with respect to a total of 100 parts (in terms of nonvolatile content) of acrylic particles (A) and acrylic particles (B). Prepared so that the viscosity becomes 3000 mPa · s (BL type viscometer, measured at # 3 rotor / 12 rpm at 25 ° C.) using a thickener and aqueous ammonia in a homomixer. A composition was obtained.

  For a total of 100 parts of the acrylic particles (A) and acrylic particles (B) in the composition, the carbodilite V-04 of the curing agent (C) (carbodiimide compound manufactured by Nisshinbo Chemical Co., Ltd. (non-volatile content: 40%) )) Was added in an amount of 0.2 in terms of nonvolatile content to obtain an aqueous re-peelable pressure-sensitive adhesive.

[Example 2]
When the acrylic particles (A) were produced, the aqueous re-peelable pressure-sensitive adhesive was obtained in the same manner as in Example 1 except that the D50 average particle diameter was changed from 50 μm to 20 μm by changing the stirring speed from 300 rpm to 600 rpm. It was.

[Example 3]
The same procedure as in Example 1 except that 2EHA was changed to 96.7 parts, MMA was changed to 8.3 parts, and 4 parts of butyl acrylate (hereinafter abbreviated as “BA”) was added in the synthesis of acrylic particles (B). And an aqueous re-peelable pressure-sensitive adhesive was obtained.

[Example 4]
An aqueous re-peelable pressure-sensitive adhesive was obtained in the same manner as in Example 1 except that 2EHA was reduced to 80 parts and MMA was increased to 19 parts when the acrylic particles (B) were produced.

[Example 5]
An aqueous re-peelable pressure-sensitive adhesive was obtained in the same manner as in Example 1 except that the amount of 2EHA was increased to 98 parts and the amount of MMA was reduced to 1 part when the acrylic particles (B) were produced.

[Example 6]
Except for reducing the amount of Aqualon KH-10 to 1 part during the production of acrylic particles (B) and newly using 1 part of Hytenol LA-10 (anion non-reactive emulsifier manufactured by Daiichi Kogyo Seiyaku Co., Ltd.). Was carried out in the same manner as in Example 1 to obtain an aqueous re-peelable pressure-sensitive adhesive.

[Example 7]
When producing the acrylic particles (B), Emulgen 1118S-70 [nonionic non-reactive emulsifier having an EO unit number of 18 mol (nonvolatile content 70%) manufactured by Kao Corporation] was used as Emulgen 1108S [EO unit manufactured by Kao Corporation]. It was carried out in the same manner as in Example 1 except that it was changed to several 8 moles of nonionic non-reactive emulsifier (non-volatile content 100%)] to obtain an aqueous re-peelable pressure-sensitive adhesive.

[Example 8]
When producing acrylic particles (B), only an APS aqueous solution having a concentration of 5% was used as a polymerization initiator, and the reaction vessel internal temperature was changed to 85 ° C. Got.

[Example 9]
Example 1 except that the D50 average particle size was changed from 0.36 μm to 0.18 μm by increasing the amount of monomer emulsion added to the flask from 5% to 10% during the production of acrylic particles (B). In the same manner as above, an aqueous re-peelable pressure-sensitive adhesive was obtained.

[Example 10]
Except for changing the D50 average particle size from 0.36μm to 0.54μm by reducing the amount of monomer emulsion added to the flask from 5% to 1.5% during the production of acrylic particles (B) In the same manner as in Example 1, an aqueous re-peelable pressure-sensitive adhesive was obtained.

[Example 11]
The ratio of the acrylic particles (A) and the acrylic particles (B) constituting the re-peelable pressure-sensitive adhesive is changed from (A) / (B) = 30/70 (non-volatile weight conversion) to (A) / (B ) = Except for changing to 50/50, the same procedure as in Example 1 was performed to obtain an aqueous re-peelable pressure-sensitive adhesive.

[Example 12]
The ratio of acrylic particles (A) and acrylic particles (B) constituting the re-peelable pressure-sensitive adhesive is (A) / (B) = 30/70 (in terms of non-volatile content) (A) / (B) = Except having changed to 70/30, it carried out similarly to Example 1, and obtained the water-based re-peeling type adhesive.

[Example 13]
Carbodilite V-04 (aqueous solution type) was changed to Carbodilite E-04 (Carbodiimide compound manufactured by Nisshinbo Chemical Co., Ltd., emulsion type, nonvolatile content 40%) in the same manner as in Example 1, except that the aqueous re-peelable pressure-sensitive adhesive Got.

[Comparative Example 1]
When producing acrylic particles (A), the stirring speed was changed from 300 rpm to 50 rpm, except that the D50 average particle size was changed from 50 μm to 150 μm, in the same manner as in Example 1 to obtain an aqueous re-peelable pressure-sensitive adhesive It was.

[Comparative Example 2]
An aqueous re-peelable pressure-sensitive adhesive was obtained in the same manner as in Example 1 except that 2EHA was changed to BA when the acrylic particles (B) were produced.

[Comparative Example 3]
The same procedure as in Example 1 was performed except that MMA was changed to styrene (St) during the production of the acrylic particles (B). However, the reaction was difficult to proceed, and a large amount of aggregates were generated. Stopped.

[Comparative Example 4]
An aqueous re-peelable pressure-sensitive adhesive was obtained in the same manner as in Example 1 except that 2EHA was reduced to 72 parts and MMA was increased to 27 parts during the production of acrylic particles (B).

[Comparative Example 5]
Example except that the anion reactive emulsifier Aqualon KH-10 was changed to the anion non-reactive emulsifier Hitenol LA-10 [Daiichi Kogyo Seiyaku Co., Ltd., polyoxyethylene lauryl ether ammonium sulfate] during the production of the acrylic particles (B). In the same manner as in Example 1, an aqueous re-peelable pressure-sensitive adhesive was obtained.

[Comparative Example 6]
When producing the acrylic particles (B), Emulgen 1118S-70 (nonionic non-reactive emulsifier having an EO unit number of 18 mol made by Kao Corporation (nonvolatile content 70%)) was used as Emulgen 1150S-70 [50 EO units made by Kao Corporation]. Mole nonionic non-reactive emulsifier (nonvolatile content 70%)] was carried out in the same manner as in Example 1 to obtain an aqueous re-peelable pressure-sensitive adhesive.

By applying the aqueous re-peelable pressure-sensitive adhesive obtained in Examples and Comparative Examples on a peelable sheet to a thickness of 20 μm using an applicator, and drying it in a drying oven at 100 ° C. for 3 minutes. An adhesive layer was formed. Next, a commercially available neutral paper (basis weight 80 g / m ² , containing about 15% calcium carbonate) was bonded to the pressure-sensitive adhesive layer to prepare a re-peelable pressure-sensitive adhesive sheet.

  In Table 1, the usage-amount of an emulsifier and a polymerization initiator shows each nonvolatile content with respect to a total of 100 parts of monomers. Moreover, the usage-amount of the hardening | curing agent was displayed with the amount of non volatile matters with respect to a total of 100 parts of acrylic particle | grains (A) and (B). Moreover, the D50 average particle diameter of acrylic particle | grains (A) and (B) was measured by the method demonstrated in the front | former stage.

<Adhesive strength>
The obtained re-peelable pressure-sensitive adhesive sheet was prepared in a size of 25 mm in width and 100 mm in length to obtain a test piece. In accordance with JIS Z0237 under a 23 ° C., 50% RH environment, a test piece was attached to a stainless steel plate (SUS304BA) to obtain a test sample. A test sample 30 minutes after application was measured for normal adhesive strength at a peeling angle of 180 ° and a pulling speed of 300 mm / min.

  Separately, the obtained releasable pressure-sensitive adhesive sheet was allowed to stand for 3 days in a 60 ° C.-95% RH environment. Next, the re-peelable pressure-sensitive adhesive sheet was allowed to stand for 5 hours in an environment of 23 ° C. and 50% RH. Thereafter, the test piece was prepared in a size of 25 mm in width and 100 mm in length. Then, the adhesive strength was measured by the same method as described above, and the adhesive strength was determined as time passed.

In order to determine the decrease in the adhesive strength with respect to the use of neutral paper as the substrate, evaluation was performed using the following mathematical formula (3).
Formula (3) Adhesive strength retention rate (%) = (Post-adhesive strength / normal adhesive strength) × 100

  The gel fraction in Table 2 was measured by the method described in the preceding paragraph.

From the results of Table 2, the examples using the aqueous re-peelable pressure-sensitive adhesive of the present invention were able to maintain good adhesive strength even after wet heat aging. On the other hand, the comparative example could not satisfy all the evaluation items.

Claims (4)

Acrylic particles (A) having a D50 average particle diameter of 20 to 60 μm, acrylic particles (B) having a glass transition temperature of −70 to −45 ° C. and a D50 average particle diameter of 0.1 to 0.6 μm, and curing Agent (C),
The acrylic particles (B) are nonionic non-reactive in which a monomer mixture containing acrylic acid, methyl methacrylate and 2-ethylhexyl acrylate is anionic reactive emulsifier (D) and the number of repeating ethylene oxide units is 7 to 20. An aqueous re-peelable pressure-sensitive adhesive obtained by polymerization in the presence of an emulsifier (E).   The aqueous re-peelable pressure-sensitive adhesive according to claim 1, wherein the acrylic particles (A) and the acrylic particles (B) have a weight ratio of (A) / (B) = 75/25 to 25/75.   The aqueous re-peelable pressure-sensitive adhesive according to claim 1 or 2, wherein the curing agent (C) is a compound having a carbodiimide group. A re-peelable pressure-sensitive adhesive sheet comprising a base material and a pressure-sensitive adhesive layer formed from the aqueous re-peelable pressure-sensitive adhesive according to claim 1.