JP4449496B2 - Acrylic copolymer emulsion and emulsion acrylic adhesive - Google Patents

Description

  The present invention relates to an acrylic copolymer emulsion suitable for an emulsion type acrylic pressure-sensitive adhesive for film labels.

From the viewpoint of environmental problems, resource saving, and cost reduction, the transition from solvent-based to water-based is also being promoted in the field of adhesives.
When comparing a water-based emulsion-type pressure-sensitive adhesive with a conventional solvent-type pressure-sensitive adhesive, the emulsion-type pressure-sensitive adhesive is generally inferior in terms of water resistance. This water resistance has two meanings: water-resistant adhesive strength and water whitening resistance.
The water-resistant adhesive strength means that the adhesive tape is not peeled when it is attached to an adherend and the adhesive tape comes into contact with water.
Further, water whitening means that the pressure-sensitive adhesive layer does not whiten when the pressure-sensitive adhesive tape or the like affixed to the adherend comes into contact with water. When the substrate constituting the pressure-sensitive adhesive tape is a transparent film, the pressure-sensitive adhesive When the layer is whitened, the aesthetics are impaired, so water whitening resistance is strictly required.

By the way, the water resistance so far refers to the water resistance after the adhesive tape or the like has been applied to the adherend. On the other hand, various demands on the adhesive tape or the like are becoming increasingly severe today. New “water resistance” in the state before wearing has been required.
That is, peel off the release sheet that constitutes the adhesive tape, etc., immerse it in water with the adhesive layer exposed, and then adhere to the adherend even if it is not immersed in water, It has come to be required to have. Such new “water resistance” is referred to as “water immersion resistance” in the present invention.
In addition, since it is not generally attached after being actually immersed in water, such a requirement is when adhesive tape etc. are left in harsh conditions such as high temperature and high humidity before being attached or stored. It is considered that it is assumed.

Patent Document 1: Japanese Patent Application Laid-Open No. 1-170677 proposes an aqueous emulsion containing copolymer particles having an average particle size of 0.1 μm or less and an intraparticle crosslinked structure. Certainly, the pressure-sensitive adhesive film obtained from such an emulsion has water resistance and moisture resistance equivalent to those of a solvent-type pressure-sensitive adhesive in the conventional sense.
However, when the pressure-sensitive adhesive surface provided on the film base material is immersed in water and then rubbed with a finger, there is a problem of insufficient adhesion to the film base material such that the pressure-sensitive adhesive layer is peeled off from the film base material.
Japanese Patent Laid-Open No. 1-170677

  The present invention solves the above-mentioned problems found in conventional emulsion-type acrylic pressure-sensitive adhesives, and has excellent adhesion to a film substrate even when the pressure-sensitive adhesive layer is brought into direct contact with water before sticking, and the adherend It is an object of the present invention to provide an emulsion-type acrylic pressure-sensitive adhesive that does not deteriorate the pressure-sensitive adhesive performance.

As a result of intensive studies to solve the above problems, the present inventors have completed the present invention.
That is, the present invention relates to an acrylic acid alkyl ester (a) having an alkyl group having 4 to 12 carbon atoms in an amount of 50 to 85% by weight and an alkyl group having an alkyl group having 1 to 4 carbon atoms in an alkyl methacrylate (b) 1 to 1 Acrylic acid containing 10% by weight, alkyl alkyl ester having 1 to 3 carbon atoms of alkyl group (c), 10 to 30% by weight, and acrylic acid and methacrylic acid in a weight ratio of 1/1 to 1/5 And an acrylic copolymer emulsion for pressure-sensitive adhesives having an average particle size of 0.08 to 0.15 μm, which is obtained by polymerizing an acrylic monomer containing 2 to 10% by weight of methacrylic acid (d) in water.

  Moreover, this invention relates to the emulsion type acrylic adhesive containing the acrylic copolymer emulsion as described in the said invention.

  According to the present invention, it is possible to provide an emulsion type acrylic pressure-sensitive adhesive that is excellent in adhesion to a film substrate even if the pressure-sensitive adhesive layer is directly brought into contact with water before sticking and does not deteriorate the adhesive performance to the adherend. It became so.

  Examples of the alkyl alkyl ester (a) (hereinafter also referred to as C4-C12 acrylic acid alkyl ester (a)) having 4 to 12 carbon atoms in the alkyl group include, for example, a butyl group, a pentyl group, Esters to which alkyl groups having 4 to 12 carbon atoms such as hexyl group, nonyl group, octyl group, decyl group and dodecyl group are bonded can be used. These alkyl groups may be linear or branched. It may be. Among these, particularly preferred alkyl acrylates having 4 to 12 carbon atoms in the alkyl group include 2-ethylhexyl acrylate and isooctyl acrylate, with 2-ethylhexyl acrylate being particularly preferred.

The alkyl group having 1 to 4 carbon atoms in the alkyl group (b) (hereinafter also referred to as C1 to C4 methacrylic acid alkyl ester (b)) includes, for example, methyl group, ethyl group as the alkyl group. Esters having an alkyl group having 1 to 4 carbon atoms such as a group, a propyl group, a butyl group, and an isobutyl group can be used. These alkyl groups may be linear or branched. Good. Among these, particularly preferable alkyl methacrylate is methacrylic acid methyl ester.

  Moreover, as the alkyl alkyl ester (c) (hereinafter also referred to as C1-C3 acrylic acid alkyl ester (c)) in which the alkyl group has 1 to 3 carbon atoms, examples of the alkyl group include a methyl group and an ethyl group. Esters to which an alkyl group having 1 to 3 carbon atoms such as a group or a propyl group is bonded can be used, and these alkyl groups may be linear or branched. Of these, a particularly preferred alkyl methacrylate is methyl acrylate.

The acrylic copolymer emulsion of the present invention is obtained by copolymerizing the above monomers (a) to (c), acrylic acid and methacrylic acid (d) in water, and is used for the copolymerization. When the total is 100% by weight,
C4 to C12 acrylic acid alkyl ester (a): 50 to 85% by weight,
C1-C4 methacrylic acid alkyl ester (b): 1 to 10% by weight,
It is important to copolymerize C1-C3 acrylic acid alkyl ester (c): 10 to 30% by weight, and acrylic acid and methacrylic acid (d): 2 to 10% by weight, and acrylic acid and methacrylic acid It is important that the weight ratio is 1/1 to 1/5.

When the C1-C4 methacrylic acid alkyl ester (b) is less than 1% by weight, the cohesive force of the pressure-sensitive adhesive layer is poor, and when it exceeds 10% by weight, the glass transition temperature is increased, leading to a decrease in adhesive force.
When the C1 to C3 acrylic acid alkyl ester (c) is less than 10% by weight, the adhesion to the substrate is deteriorated, and when it exceeds 30% by weight, the adhesive strength is reduced.
If the total of acrylic acid and methacrylic acid (d) is less than 2% by weight, the water resistance of the pressure-sensitive adhesive layer is poor, and if it exceeds 10% by weight, the adhesive strength is reduced.
Furthermore, in the ratio of acrylic acid to methacrylic acid, when the methacrylic acid is relatively less than the acrylic acid, and when the methacrylic acid is more than 5 times the acrylic acid, the water resistance of the pressure-sensitive adhesive layer is deteriorated.

  Furthermore, it is important that the dispersed particle size of the acrylic copolymer emulsion of the present invention is an average particle size of 0.08 to 0.15 μm. When the average particle size is smaller than 0.08 μm, the production stability is poor, and when it is larger than 0.15 μm, the adhesion to the substrate is degraded. Examples of methods for controlling the particle size include a method of increasing the amount of emulsifier, a method of previously adding the emulsifier to the reaction flask, a method of previously preparing the prepared pre-emulsion in the reaction flask, and the like.

  As the surfactant used when obtaining the acrylic copolymer emulsion of the present invention, a reactive surfactant, a non-reactive surfactant, etc. can be used alone or in combination of two or more, In view of water resistance and the like, it is preferable to use a reactive surfactant.

The following compounds can be illustrated as a reactive surfactant.
As anionic surfactants, long chain chains such as “Adekaria Soap SE-10N” manufactured by Asahi Denka Kogyo Co., Ltd., “Aqualon HS-10, HS-20” manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Alkyl skeleton made by Daiichi Kogyo Seiyaku Co., Ltd. “AQUALON KH-05, KH-10”, Asahi Denka Kogyo Co., Ltd. “ADEKA rear soap SR-10N”, etc. Examples include “KAYARAD”.

  Among the reactive surfactants, nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene phenyl ethers, sorbitan higher fatty acid esters, and glycerin higher fatty acid esters at the molecular ends or in the middle. It is limited to those having a heavy bond and capable of copolymerizing with the monomer. For example, “Adekaria Soap NE-10” manufactured by Asahi Denka Kogyo Co., Ltd., “Aqualon RN-10, RN-20, RN-50” manufactured by Daiichi Kogyo Seiyaku Co., Ltd., “Antox manufactured by Nippon Emulsifier Co., Ltd.” NA-16 "and the like.

When obtaining an acrylic copolymer emulsion, a non-reactive surfactant that does not impede water resistance can be added as an auxiliary.
For example, examples of the non-reactive surfactant include “New Coal SF Series”, “New Coal 2360”, “RA-9314”, “RA-9607” and the like manufactured by Nippon Emulsifier Co., Ltd. Such a non-reactive surfactant is preferably 0 to 50% by weight in a total amount of 100% by weight of the surfactant mainly composed of the reactive surfactant.

  As the polymerization initiator used in the present invention, a persulfate such as potassium persulfate or ammonium persulfate, a water-soluble thermal decomposition type superpolymerization catalyst such as an azobis cation salt or a hydroxyl group addition substance, or a redox polymerization catalyst is used. be able to. The redox polymerization catalyst includes a combination of an organic peroxide such as t-butyl hydroperoxide, benzoyl peroxide, cumene hydroperoxide and a reducing agent such as Rongalite, sodium metabisulfite, or potassium persulfate or ammonium persulfate. And Rongalite, a combination of sodium thiosulfate and ascorbic acid.

  Furthermore, when carrying out emulsion polymerization, various chain transfer agents can be used to control the molecular weight and molecular weight distribution of the resulting acrylic copolymer. As the chain transfer agent, mercaptan-based, thioglycol-based, and β-mercaptopropionic acid-based alkyl esters can be used. The amount used is preferably 0.01 to 0.3 parts by weight, more preferably 0.05 to 0.2 parts by weight, based on 100 parts by weight of the total amount of monomers.

Next, the pressure-sensitive adhesive of the present invention will be described.
The pressure-sensitive adhesive of the present invention comprises the above acrylic copolymer emulsion as a main component, and an appropriate tackifier such as, for example, for adjusting the adhesive strength as necessary for this acrylic copolymer emulsion, An appropriate amount of rosin resin, phenol resin, polyterpene, acetylene resin, petroleum hydrocarbon resin, ethylene vinyl acetate copolymer, synthetic rubber, natural rubber, or the like can be added. Further, a crosslinking agent, a viscosity modifier, an antifoaming agent, a leveling agent, a plasticizer, a filler, a neutralizing agent, a coloring agent, a silane coupling agent, an antiseptic, and the like may be added.
In addition, ethyleneimine, oxazoline, carbodiimide, zirconylammonium carbonate, epoxy group, and the like that can react with acrylic acid and carboxylic acid derived from methacrylic acid (d) in the acrylic copolymer emulsion are appropriately added as a crosslinking agent. Also good.

By applying the pressure-sensitive adhesive of the present invention onto a film substrate or a peelable sheet with various coating apparatuses such as a comma coater, reverse coater, slot die coater, lip coater, gravure chamber coater, curtain coater, and the like, and then drying. Various adhesive coated products such as adhesive sheets and adhesive labels can be obtained.
When the adhesive composition is applied directly on the film substrate, it is pasted with the peelable sheet after drying. When the adhesive composition is applied on the peelable sheet, it is pasted with the film substrate after drying. By combining them, various adhesive coatings can be obtained by either method.

Example 1
73 parts of 2-ethylhexyl acrylate, 3 parts of methyl methacrylate, 1 part of acrylic acid, 3 parts of methacrylic acid, 20 parts of methyl acrylate, 0.1 part of octyl thioglycolate with respect to 100 parts of these monomers, reactivity As an ammonia-neutralizing anionic surfactant, 2 parts of "Aqualon KH-10" manufactured by Daiichi Kogyo Seiyaku Co., Ltd. dissolved in 32 parts of ion-exchanged water was added and stirred to obtain an emulsion. This was placed in a dropping funnel.
A four-necked flask equipped with a stirrer, a condenser, a thermometer and the above dropping funnel was charged with 75 parts of ion-exchanged water and 0.2 part of “RA-9607” manufactured by Nippon Emulsifier Co., Ltd. The inside temperature was raised to 80 ° C. while stirring with gas, and 0.1 part of a 3% aqueous potassium persulfate solution was added as a solid content.
After 5 minutes, dropping of the emulsion was started from the dropping funnel, and in parallel with this, 0.35 part of 3% potassium persulfate aqueous solution was added dropwise from another dropping port over 3 hours.
While maintaining the internal temperature at 80 ° C., 60 minutes after completion of the emulsion dropping, 0.02 parts are divided into three portions with 1% t-butyl hydroperoxide aqueous solution and 1% Rongalite aqueous solution as solids every 30 minutes. Added.
Further, the mixture was aged at 80 ° C. for 60 minutes with stirring and then cooled and neutralized with aqueous ammonia to obtain an acrylic copolymer emulsion having an average particle size of 0.1 μm and a solid content of 45%. The average particle size was measured with Nikkiso Co., Ltd. Microtrac.
An antifoaming agent, a leveling agent, and a preservative are added to the obtained acrylic copolymer emulsion, and the pH is adjusted to 7.5 to 8 with aqueous ammonia, and 3000 mPa · s (BL type viscosity is further adjusted with a viscosity adjusting agent. (Measured at 60 rpm using a # 4 rotor) to obtain an emulsion-type acrylic pressure-sensitive adhesive.
This was coated with a comma coater so that the dry coating amount was 25 g / m ² , dried in a drying oven at 100 ° C. for 60 seconds, and laminated with a polyethylene terephthalate (PET) film having a thickness of 25 μm. And wound up to obtain an adhesive coated product.

(Example 2)
2-ethylhexyl acrylate 73 parts, methyl methacrylate 3 parts, acrylic acid 1 part, methacrylic acid 3 parts, methyl acrylate 15 parts, ethyl acrylate 5 parts, octyl thioglycolate 0.1 parts for all these monomers 1 part of “AQUALON KH-10” manufactured by Daiichi Kogyo Seiyaku Co., Ltd. as a reactive ammonia neutralizing anionic surfactant was added to 32 parts of ion-exchanged water and stirred to emulsify. Product was obtained and placed in a dropping funnel.
A four-necked flask equipped with a stirrer, condenser, thermometer and dropping funnel was charged with 75 parts of ion-exchanged water and 0.2 part of “RA-9607” manufactured by Nippon Emulsifier Co., Ltd. The inside temperature was raised to 80 ° C. while stirring with gas, and 0.1 part of a 3% aqueous potassium persulfate solution was added as a solid content. After 5 minutes, dropping of the emulsion was started from the dropping funnel, and in parallel with this, 0.35 part of 3% potassium persulfate aqueous solution was added dropwise from another dropping port over 3 hours.
While maintaining the internal temperature at 80 ° C., 60 minutes after completion of the emulsion dropping, 0.02 parts are divided into three portions with 1% t-butyl hydroperoxide aqueous solution and 1% Rongalite aqueous solution as solids every 30 minutes. Added.
Further, the mixture was aged at 80 ° C. for 1 hour with stirring and then cooled and neutralized with aqueous ammonia to obtain an acrylic copolymer emulsion having an average particle size of 0.1 μm and a solid content of 45%.
Using the resulting acrylic copolymer emulsion, a pressure-sensitive adhesive coated product was obtained in the same manner as in Example 1.

(Example 3)
Using the acrylic copolymer emulsion obtained in Example 1, Arakawa Chemical Co., Ltd. ("Superester E-865") (solid content 50%) as a rosin-based tackifier resin in Example 1 was used as a solid content of 5 In addition, an emulsion type acrylic pressure-sensitive adhesive having an average particle size of 0.1 μm was obtained, and a pressure-sensitive adhesive coated product was obtained in the same manner as in Example 1.

(Comparative Example 1)
93 parts of 2-ethylhexyl acrylate, 3 parts of methyl methacrylate, 1 part of acrylic acid, 3 parts of methacrylic acid, 0.1 part of octyl thioglycolate for all 100 parts of these monomers, reactive ammonia neutralizing anionic surface activity A solution obtained by dissolving 2 parts of “AQUALON KH-10” manufactured by Daiichi Kogyo Seiyaku Co., Ltd. in 32 parts of ion-exchanged water was added and stirred to emulsify to obtain an emulsion, which was placed in a dropping funnel.
A four-necked flask equipped with a stirrer, condenser, thermometer and dropping funnel was charged with 75 parts of ion-exchanged water and 0.2 part of “RA-9607” manufactured by Nippon Emulsifier Co., Ltd. The inside temperature was raised to 80 ° C. while stirring with gas, and 0.07 part of 3% aqueous potassium persulfate solution was added as a solid content. After 5 minutes, dropping of the emulsion was started from the dropping funnel, and in parallel with this, 0.35 part of 3% potassium persulfate aqueous solution was added dropwise from another dropping port over 3 hours.
While maintaining the internal temperature at 80 ° C., 60 minutes after completion of the emulsion dropping, 0.02 parts are divided into three portions with 1% t-butyl hydroperoxide aqueous solution and 1% Rongalite aqueous solution as solids every 30 minutes. Added.
Further, the mixture was aged at 80 ° C. for 1 hour with stirring and then cooled and neutralized with aqueous ammonia to obtain an acrylic copolymer emulsion having an average particle size of 0.1 μm and a solid content of 45%.
Using the resulting acrylic copolymer emulsion, a pressure-sensitive adhesive coated product was obtained in the same manner as in Example 1.

(Comparative Example 2)
73 parts of 2-ethylhexyl acrylate, 3 parts of methyl methacrylate, 1 part of acrylic acid, 3 parts of methacrylic acid, 20 parts of methyl acrylate, 0.1 part of octyl thioglycolate for 100 parts of these monomers, in reactive ammonia As a Japanese-type anionic surfactant, 2 parts of “AQUALON KH-10” manufactured by Daiichi Kogyo Seiyaku Co., Ltd. dissolved in 32 parts of ion-exchanged water was added and stirred to obtain an emulsion. Placed in dropping funnel.
A four-necked flask equipped with a stirrer, condenser, thermometer and dropping funnel was charged with 75 parts of ion-exchanged water and 0.05 part of “RA-9607” manufactured by Nippon Emulsifier Co., Ltd. The inside temperature was raised to 80 ° C. while stirring with gas, and 0.1 part of a 3% aqueous potassium persulfate solution was added as a solid content. After 5 minutes, dropping of the emulsion was started from the dropping funnel, and in parallel with this, 0.35 part of 3% potassium persulfate aqueous solution was added dropwise from another dropping port over 3 hours.
While maintaining the internal temperature at 80 ° C., 60 minutes after completion of the emulsion dropping, 0.02 parts are divided into three portions with 1% t-butyl hydroperoxide aqueous solution and 1% Rongalite aqueous solution as solids every 30 minutes. Added.
Further, after aging at 80 ° C. for 1 hour with stirring, the mixture was cooled and neutralized with aqueous ammonia to obtain an acrylic copolymer emulsion having an average particle size of 0.2 μm and a solid content of 45%.
Using the resulting acrylic copolymer emulsion, a pressure-sensitive adhesive coated product was obtained in the same manner as in Example 1.

(Comparative Example 3)
Example 1 An acrylic copolymer emulsion having an average particle size of 0.1 μm was obtained in the same manner as in Example 1 except that 4 parts of acrylic acid, which was 1 part, was obtained. Using the combined emulsion, a pressure-sensitive adhesive coated product was obtained in the same manner as in Example 1.

(Comparative Example 4)
58 parts of 2-ethylhexyl acrylate, 3 parts of methyl methacrylate, 1 part of acrylic acid, 3 parts of methacrylic acid, 35 parts of methyl acrylate, 0.1 part of octyl thioglycolate with respect to 100 parts of these monomers, in reactive ammonia As a Japanese-type anionic surfactant, 2 parts of “AQUALON KH-10” manufactured by Daiichi Kogyo Seiyaku Co., Ltd. dissolved in 32 parts of ion-exchanged water was added and stirred to obtain an emulsion. Placed in dropping funnel.
A four-necked flask equipped with a stirrer, condenser, thermometer and dropping funnel was charged with 75 parts of ion-exchanged water and 0.2 part of “RA-9607” manufactured by Nippon Emulsifier Co., Ltd. The inside temperature was raised to 80 ° C. while stirring with gas, and 0.07 part of 3% aqueous potassium persulfate solution was added as a solid content. After 5 minutes, dropping of the emulsion was started from the dropping funnel, and in parallel with this, 0.35 part of 3% potassium persulfate aqueous solution was added dropwise from another dropping port over 3 hours.
While maintaining the internal temperature at 80 ° C., 60 minutes after completion of the emulsion dropping, 0.02 parts are divided into three portions with 1% t-butyl hydroperoxide aqueous solution and 1% Rongalite aqueous solution as solids every 30 minutes. Added.
Further, the mixture was aged at 80 ° C. for 1 hour with stirring, then cooled and neutralized with aqueous ammonia to obtain an acrylic copolymer emulsion having an average particle size of 0.14 μm and a solid content of 45%.
Using the resulting acrylic copolymer emulsion, a pressure-sensitive adhesive coated product was obtained in the same manner as in Example 1.

[Test method]
(1) Normal adhesive strength The adhesive coated material is cut into a strip with a width of 25 mm, the release paper is peeled off, attached to a SUS plate in an atmosphere of 23 ° C., reciprocated once with a 2 kg roll, and then measured after 20 minutes. Provided. The adhesive strength was measured when peeled in the 180 ° direction at a speed of 300 mm / min in an atmosphere of 23 ° C.

(2) Water resistance 1 (Adhesion after water immersion)
The adhesive coated product is cut into a 25 mm width strip, the release paper is peeled off, immersed in warm water at 40 ° C. for 6 hours, taken out and immediately attached to a SUS plate in a 23 ° C. atmosphere, and reciprocated once with a 2 kg roll. Then, it was used for the measurement after 20 minutes. The adhesive strength was measured when peeled in the direction of 180 ° at a speed of 300 cm / min in an atmosphere of 23 ° C.

(3) Water resistance 2 (adhesion to substrate)
Cut the pressure-sensitive adhesive coating into a 25 mm wide strip, peel off the release paper, immerse in hot water at 40 ° C. for 3 hours, rub the pressure-sensitive adhesive layer with your fingers immediately, and rub the pressure-sensitive adhesive layer from the film substrate. It was confirmed whether it was taken.
Evaluation standard (circle): An adhesive layer does not peel from a film base material.
X: The pressure-sensitive adhesive layer is peeled off from the film substrate.

  Table 1 shows the test results of normal adhesive strength, post-immersion adhesive strength, and adhesion to a substrate using each pressure-sensitive adhesive coated product.

As shown in Table 1, when the pressure-sensitive adhesive layer is brought into direct contact with water before sticking, in the case of each comparative example, from the point of view of adhesive strength, the pressure-sensitive adhesive performance to the adherend does not decrease so much. I think. However, each of the comparative examples deteriorates the adhesion to the film substrate after water immersion. Therefore, when the adhesive coating after water immersion is removed from the adherend, part of the adhesive layer is transferred to the adherend. , Dirty adherend surface.
On the other hand, in the case of each Example, even if it immerses in water, the adhesiveness with respect to a base material does not fall, and it has the same adhesive performance as the case where it does not immerse in water.

Claims (2)

Acrylic acid alkyl ester (a) having 4 to 12 carbon atoms in the alkyl group (a) 50 to 85% by weight, methacrylic acid alkyl ester (b) having 1 to 4 carbon atoms in the alkyl group (b) 1 to 10% by weight, alkyl group Acrylic acid alkyl ester (c) having 1 to 3 carbon atoms of 10 to 30% by weight, acrylic acid and methacrylic acid (d) containing acrylic acid and methacrylic acid in a weight ratio of 1/1 to 1/5 An acrylic copolymer emulsion for pressure-sensitive adhesives having an average particle size of 0.08 to 0.15 μm, which is obtained by polymerizing an acrylic monomer containing 2 to 10% by weight in water. An emulsion-type acrylic pressure-sensitive adhesive containing the acrylic copolymer emulsion according to claim 1.