JP5516939B2 - Water-dispersed acrylic pressure-sensitive adhesive composition and pressure-sensitive adhesive tape - Google Patents

Description

  The present invention relates to a water-dispersed acrylic pressure-sensitive adhesive composition in which acrylic copolymer emulsion particles are dispersed in an aqueous medium, and a pressure-sensitive adhesive tape having the pressure-sensitive adhesive composition as a pressure-sensitive adhesive layer.

  Adhesive tape is used as a bonding means with excellent workability and high bonding reliability in parts such as office automation equipment, home appliances, and automobiles for parts fixing and labeling for displaying product information. On the other hand, from the viewpoint of protecting the global environment, assembly products such as OA equipment are often disassembled after use and recycled and reused. At this time, when the parts are joined with the adhesive tape or when the label is attached, an operation for peeling the adhesive tape or the label is required, and the adhesive can be removed without breaking the residue or the supporting substrate. Characteristics (so-called removability) are required. Further, in recent years, suppression of emission of volatile organic compounds (so-called VOC) has been strongly demanded. In the pressure-sensitive adhesive tape, a solventless type pressure-sensitive adhesive has attracted attention, and replacement of a solvent-type pressure-sensitive adhesive with a water-dispersed pressure-sensitive adhesive has been desired.

  As a releasable pressure-sensitive adhesive tape using a water-dispersed acrylic pressure-sensitive adhesive, for example, a pressure-sensitive adhesive tape using acrylic acid and methacrylic acid in combination is disclosed (see Patent Document 1). However, when preparing the double-sided pressure-sensitive adhesive tape having high adhesive strength, it is difficult to ensure sufficient removability of the pressure-sensitive adhesive tape. Moreover, the adhesive tape which uses the water-dispersed acrylic adhesive composition which used acrylic acid and methacrylic acid together as an adhesive tape excellent in the adhesiveness to a base material or a to-be-adhered body is disclosed (patent document 2). reference). However, the pressure-sensitive adhesive tape has a large increase in adhesive strength over time after being stuck, and it has been difficult to ensure removability. In particular, there has been a problem that the increase in adhesion to a metal surface such as stainless steel is large.

  Furthermore, these adhesive tapes have a rough surface when a pressure sensitive adhesive tape using an emulsion-type adhesive is used for the purpose of fixing a highly breathable member having a rough surface such as urethane foam or nonwoven fabric. There is a problem that it is difficult to adhere to a highly air permeable member having the above.

JP 2006-265537 A JP-A-2005-248059

  The problem to be solved by the present invention is that it has good adhesion and holding power to various adherends, and is suitable for the adhesive residue and the support base material to be hardly broken at the time of peeling. An object of the present invention is to provide a water-dispersed emulsion-type pressure-sensitive adhesive capable of forming a pressure-sensitive adhesive tape having removability.

  Moreover, it is an adhesive tape used for the purpose of fixing a highly air permeable member having a rough surface such as a foam or a nonwoven fabric such as urethane, and can form an adhesive tape that sufficiently adheres to the highly air permeable member having a rough surface. The object is to provide a water-dispersed emulsion-type pressure-sensitive adhesive. Furthermore, it is providing the water-dispersed acrylic adhesive which can form the adhesive tape excellent also in water resistance.

  In the present invention, by using 2-ethylhexyl acrylate as the main monomer of the high molecular weight acrylic copolymer constituting the main acrylic copolymer emulsion in the water-dispersed acrylic pressure-sensitive adhesive composition, the nonwoven fabric is obtained. By securing the impregnation property and suitable removability of the adhesive, and further using (meth) acrylate having an alkyl group having 4 to 8 carbon atoms, the strong adhesiveness is improved while maintaining the removability. be able to. In addition, by using methacrylic acid and acrylic acid in combination with the composition of the main monomer, stable strong adhesion can be secured from a highly polar metal-based adherend to a low-polarity olefin-based adherend. . Furthermore, by using the methacrylic acid and acrylic acid together with the nitrogen-containing vinyl monomer, the acid groups can be present not only on the surface of the emulsion particles but also on the inside of the particles at the same level or higher. According to the acrylic copolymer emulsion particles, the cohesive force between the emulsion particles can be secured by the acid groups present on the particle surface, and the cohesive force inside the emulsion particles can be improved by the acid groups present inside the particles. Therefore, it is possible to form a pressure-sensitive adhesive layer that does not easily cause the pressure-sensitive adhesive layer to fall off or have adhesive residue at the time of re-peeling even with strong adhesive strength. Normally, if the adhesive layer has a portion with low cohesive strength, the portion with low cohesive strength has high fluidity, so that the adhesion of the adhesive to the adherend easily progresses over time, and is stuck for a long time. In the case where the pressure-sensitive adhesive composition increases excessively, it becomes difficult to re-peel, but according to the pressure-sensitive adhesive composition containing the acrylic copolymer emulsion of the present invention, the cohesive strength in the pressure-sensitive adhesive layer is low. A part can be reduced and deterioration of the removability over time can be suitably suppressed. In the present invention, the above-mentioned acrylic copolymer is used as an acrylic copolymer in the water-dispersed acrylic copolymer, and the main component as a high molecular weight acrylic copolymer having a weight average molecular weight of 500,000 to 1,200,000. As a result, a particularly excellent cohesion is realized. By using this in combination with a low molecular weight acrylic copolymer having a weight average molecular weight of 5,000 to 250,000 containing the same monomer as the main monomer of the high molecular weight acrylic copolymer, it is possible to cause adhesion without causing phase separation. Suitable fluidity can be imparted to the agent layer, and adhesion to the adherend can be improved. Thereby, cohesion force required for re-peelability and the characteristic which fully adheres to rough surfaces, such as foams and nonwoven fabrics, such as urethane, can be made to balance more suitably.

  According to the water-dispersed acrylic pressure-sensitive adhesive composition of the present invention, the discharge of volatile organic compounds (so-called VOC) and the odor of organic solvents can be greatly reduced, and it adheres firmly to adherends such as metals. , Adhesive tape that does not excessively increase the adhesive strength even when stuck for a long period of time, does not undergo special treatment such as heating when peeling, and does not destroy the so-called adhesive residue or supporting substrate Can be obtained.

  Moreover, according to the pressure-sensitive adhesive tape comprising the water-dispersed acrylic pressure-sensitive adhesive composition of the present invention, it can be sufficiently adhered and fixed to a highly breathable member having a rough surface such as a foamed material such as urethane or a nonwoven fabric. Furthermore, suitable adhesiveness and removability can be realized even in a high humidity environment.

<Water-dispersed acrylic pressure-sensitive adhesive composition>
The water-dispersed acrylic pressure-sensitive adhesive composition of the present invention is a water-dispersed acrylic pressure-sensitive adhesive composition in which acrylic copolymer emulsion particles are dispersed in an aqueous medium, and forms the acrylic copolymer emulsion particles. The acrylic copolymer to be used has a molecular weight distribution obtained by GPC measurement of a component dissolved in tetrahydrofuran, and the obtained molecular weight distribution consists of a high molecular weight acrylic copolymer (a) and a low molecular weight acrylic copolymer (b). The weight average molecular weight in terms of standard polystyrene of each peak when it has two peaks and the waveforms are separated into waveforms is (a) a range of 500 to 1,200,000 and (b) a range of 5000 to 250,000.

(High molecular weight acrylic copolymer (a))
The high molecular weight acrylic copolymer (a) having a weight average molecular weight of 500,000 to 1,200,000 used in the present invention is 2-ethylhexyl acrylate, (meth) acrylate having 4 to 8 carbon atoms, and acrylic acid. An acrylic copolymer containing methacrylic acid and a nitrogen-containing vinyl monomer as monomer components is used. In the present invention, by using a high molecular weight acrylic copolymer of the composition as the main acrylic copolymer that forms the water-dispersed acrylic copolymer emulsion, it is suitable even with high adhesive strength. An excellent cohesive force capable of re-peeling can be secured.

  In this invention, the re-peelability suitable for an adhesive tape can be provided to a high molecular weight acrylic copolymer (a) by using 2-ethylhexyl acrylate as a monomer component. As content of 2-ethylhexyl acrylate, it is preferable that it is 10-90 mass%, and it is more preferable that it is 20-80 mass%. By keeping the content of 2-ethylhexyl acrylate within this range, it is easy to suppress the adhesion between the pressure-sensitive adhesive and the adherend over time, and the adhesive strength hardly rises excessively. it can.

  Moreover, by using together with 2-ethylhexyl acrylate and using the (meth) acrylate which has a C4-C8 alkyl group, strong adhesiveness can be improved greatly, maintaining removability. Examples of the (meth) acrylate having an alkyl group having 4 to 8 carbon atoms include n-butyl (meth) acrylate, isobutyl (meth) acrylate, t-butyl (meth) acrylate, isooctyl (meth) acrylate, and n-octyl (meta ) (Meth) acrylates such as acrylates can be used. Among them, acrylate monomers having an alkyl group having 4 to 8 carbon atoms are preferably used, and n-butyl acrylate can be particularly preferably used. It is also preferable to use n-butyl acrylate and t-butyl methacrylate in combination. The amount of (meth) acrylate having an alkyl group having 4 to 8 carbon atoms is preferably 10 to 80% by mass, and more preferably 20 to 70% by mass.

  In the present invention, a monomer that forms the high molecular weight acrylic copolymer (a) in order to more suitably express the effects of the above-mentioned 2-ethylhexyl acrylate and (meth) acrylate having 4 to 8 carbon atoms. The sum of the contents of 2-ethylhexyl acrylate and (meth) acrylate having an alkyl group having 4 to 8 carbon atoms is preferably 50 to 98% by mass, and particularly preferably 80 to 98% by mass. . The ratio of the content of 2-ethylhexyl acrylate in the monomer component forming the acrylic copolymer and the (meth) acrylate having a C 4-8 alkyl group is (2-ethylhexyl acrylate / C 4 -C The mass ratio represented by (meth) acrylate having 8 alkyl groups is preferably 9/1 to 2/8, and particularly preferably 75/25 to 25/75.

  In the present invention, (meth) acrylate monomers other than those described above may be used in combination as the (meth) acrylate monomer that forms the high molecular weight acrylic copolymer (a). Examples of other (meth) acrylate monomers include (meth) acrylate monomers such as methyl (meth) acrylate and ethyl (meth) acrylate, and one or more of these may be used in combination. . Especially, it is preferable to use together (meth) acrylate which has a C2-C2 alkyl group, such as methyl (meth) acrylate and ethyl (meth) acrylate, and it is preferable that it is 1-10 mass% as usage-amount. .

  In the present invention, acrylic acid and methacrylic acid are used in combination as a monomer having an acid group in the high molecular weight acrylic copolymer (a) in order to introduce acid groups into and on the surface of the acrylic copolymer emulsion. To do. The carboxyl group of acrylic acid and methacrylic acid is easy to ensure cohesive force by interaction between carboxyl groups, there are many means for increasing cohesive force with many reactive crosslinking agents, and interaction with the nitrogen-containing vinyl monomer described later. It has the advantage that it can be expressed. Furthermore, in the present invention, acrylic acid tends to be oriented in the vicinity of the particle surface and methacrylic acid is oriented inside the particle by using acrylic acid having relatively high hydrophilicity and methacrylic acid that is more hydrophobic than acrylic acid. The acid groups can be arranged in a well-balanced manner on the surface and inside of the acrylic copolymer emulsion particles. The presence of acid groups in the vicinity of the particle surface can ensure cohesion between emulsion particles, and the presence of acid groups present in the particles can improve cohesion within emulsion particles. Thereby, since the obtained adhesive layer can reduce a part with low cohesive force and can suppress the deterioration of removability with time, it is difficult for the adhesive layer to fall off or have adhesive residue at the time of re-exfoliation.

  The content of acrylic acid and methacrylic acid in the high molecular weight acrylic copolymer (a) is the sum of the contents of methacrylic acid and acrylic acid in the monomer component forming the high molecular weight acrylic copolymer (a). It is 0.5-10 mass%, Preferably, it is 0.5-5 mass%, More preferably, it is 1.5-3.5 mass%. By setting it within this range, the crosslinking reaction with the crosslinking agent easily proceeds well. Further, when the pressure-sensitive adhesive layer is formed, a cohesive force suitable for the pressure-sensitive adhesive layer is ensured, and the holding power and the removability are easily compatible. Furthermore, the cohesive force necessary for ensuring water resistance and the hydrophobicity of the pressure-sensitive adhesive layer surface can be ensured.

  The combined ratio of methacrylic acid and acrylic acid is such that the molar equivalent ratio of methacrylic acid / acrylic acid is preferably 0.2 or more, more preferably 3 or more, further preferably 4 or more, and 6 or more. It is more preferable that By setting the combined ratio within the above range, the amount of surface acid groups and the amount of internal acid groups in the acrylic copolymer emulsion particles can be suitably controlled.

  In addition, the high molecular weight acrylic copolymer (a) may contain other carboxyl group-containing monomers as monomers having an acid group within a range not inhibiting the distribution of acid groups in the acrylic copolymer emulsion particles. You may use together. As other carboxyl group-containing monomers, for example, one or more selected from carboxyl group-containing vinyl monomers such as itaconic acid, maleic acid, maleic anhydride, phthalic acid, phthalic anhydride, and crotonic acid can be used. When these carboxyl group-containing monomers are used in combination, it is preferable that the total amount of the carboxyl group-containing monomers including acrylic acid and methacrylic acid is in the range of 0.5 to 10% by mass.

  In the high molecular weight acrylic copolymer (a) used in the present invention, a nitrogen-containing vinyl monomer is further used as a monomer component of the acrylic copolymer. The nitrogen-containing vinyl monomer is presumed to produce an effect of drawing a carboxyl group that is easily oriented on the particle surface into the particle by interacting with an acid group, particularly a carboxyl group, in the acrylic copolymer emulsion particles. In order to produce this effect, the content of the nitrogen-containing vinyl monomer is preferably set to the above lower limit or more. On the other hand, when the content is increased, the reactivity with the crosslinking agent described later tends to decrease, but by setting the content to the upper limit or less, necessary reactivity can be ensured. When the content is within this range, the acid group distribution in the acrylic copolymer emulsion particles can be easily converged to a suitable distribution range.

  Examples of the nitrogen-containing vinyl monomer include one or more selected from N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, acrylonitrile, acrylamide, N, N-dimethylacrylamide and dimethylaminoethyl (meth) acrylate. Can be used.

  The content of the nitrogen-containing vinyl monomer in the monomer component forming the high molecular weight acrylic copolymer (a) is 0.1 to 4.5% by mass, preferably 0.5 to 4% by mass, more preferably. Can be suitably expressed in the range of 0.5 to 3.5% by mass.

  Although the ratio of the nitrogen-containing vinyl monomer and the vinyl monomer having a carboxyl group in the high molecular weight acrylic copolymer (a) is not particularly limited, the monomer constituting the high molecular weight acrylic copolymer (a) The molar ratio X / Y is preferably 1/1 to 1/20, where X is the number of moles of the nitrogen-containing vinyl monomer in the component, and Y is the number of moles of the vinyl monomer having a carboxyl group. ~ 1/5 is more preferable, and 1/1 to 1/3 is still more preferable. If it is in the said range, reaction with the vinyl monomer which has a carboxyl group, and the crosslinking agent mentioned later will advance easily. Furthermore, it becomes easy to converge the distribution of carboxyl groups in the acrylic copolymer emulsion to a range described later.

  In the high molecular weight acrylic copolymer (a) used in the present invention, monomers other than those described above can be used as necessary. Examples of such monomers include a hydroxyl group-containing monomer, (meth) Alcoholic hydroxyl group-containing monomers such as 2-hydroxyethyl acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate can be used as appropriate. As keto group or aldehyde group-containing monomer, diacetone acrylamide, diacetone methacrylamide, acrolein, formyl styrene, vinyl methyl ketone, vinyl ethyl ketone, vinyl isobutyl ketone, diacetone acrylate, diacetone methacrylate, acetonitrile acrylate, 2-hydroxypropyl Examples include acrylate acetoacetate and butanediol acrylate acetate. As the silane monomer, 3-methacryloxypropylmethyldimethoxysilane [for example, KBM-502 manufactured by Shin-Etsu Chemical Co., Ltd.], 3-methacryloxypropyltrimethoxysilane [for example, KBM-503 manufactured by Shin-Etsu Chemical Co., Ltd.], 3 -Methacryloxypropylmethyldiethoxysilane [for example, KBE-502 manufactured by Shin-Etsu Chemical Co., Ltd.], 3-methacryloxypropyltriethoxysilane [for example, KBE-503 manufactured by Shin-Etsu Chemical Co., Ltd.], 3-acryloxypropyltri And methoxysilane [for example, KBM-5103 manufactured by Shin-Etsu Chemical Co., Ltd.]. Moreover, N methylol acrylamide etc. are mentioned as a methylol group containing monomer. Examples of the phosphoric acid group-containing monomer include Sipomer PAM-100, PAM-200, and PAM-300 manufactured by Rhodia Nikka Co., Ltd., and 20% by mass or less in the monomer component forming the acrylic copolymer. It can be used at a ratio of 1 type or 2 types or more.

  The weight average molecular weight of the high molecular weight acrylic copolymer (a) used in the present invention is 500 to 1,200,000, preferably 60 to 1,000,000. By setting it within the range, it is possible to balance both the flexibility when the pressure-sensitive adhesive impregnates the nonwoven fabric and the cohesive force necessary for removability.

  The said weight average molecular weight is standard polystyrene conversion by a gel permeation chromatography (GPC). As an example of measurement conditions, HLC-8220GPC (manufactured by Tosoh Corporation) is used, the column is TSKgel GMHXL (manufactured by Tosoh Corporation), the column temperature is 40 ° C., the eluent is tetrahydrofuran, the flow rate is 1.0 mL / min, and standard polystyrene. Can be measured by using TSK standard polystyrene.

  In order to adjust the molecular weight, a chain transfer agent may be used in the polymerization. Examples of the chain transfer agent include known chain transfer agents such as lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, and 2,3-dimethylcapto-1-propanol. Can be used.

(Low molecular weight acrylic copolymer (b))
The low molecular weight acrylic copolymer (b) having a weight average molecular weight of 5000 to 250,000 used in the present invention contains 2-ethylhexyl acrylate as a monomer component. In the present invention, by using 2-ethylhexyl acrylate as a monomer component as the low molecular weight acrylic copolymer (b) used in combination with the high molecular weight acrylic copolymer (a), the above high molecular weight acrylic copolymer is used. Compatibility with the coalescence (a) can be ensured, and suitable removability can be easily imparted to the adhesive tape. In addition, the monomer component other than the monomer component and the blending ratio are the same as those of the high molecular weight acrylic copolymer (a), so that compatibility between the two components can be easily ensured, and the cohesive force due to the combined use of the copolymer can be ensured. Degradation is difficult to occur. The content of 2-ethylhexyl acrylate in the monomer component constituting the low molecular weight acrylic copolymer (b) is preferably 10 to 90% by mass, and more preferably 20 to 80% by mass. By setting the content of 2-ethylhexyl acrylate in this range, suitable removability can be maintained.

  Further, in the low molecular weight acrylic copolymer (b) as well as the high molecular weight acrylic copolymer (a), it has an alkyl group having 4 to 8 carbon atoms in combination with 2-ethylhexyl acrylate (meth). Preference is given to using acrylates. By using the (meth) acrylate having an alkyl group having 4 to 8 carbon atoms in combination, it becomes easy to combine removability and strong adhesiveness. As the (meth) acrylate having an alkyl group having 4 to 8 carbon atoms, the (meth) acrylate exemplified in the high molecular weight acrylic copolymer (a) can be exemplified, and among them, n-butyl acrylate can be preferably used. It is also preferable to use n-butyl acrylate and t-butyl methacrylate in combination. The amount of (meth) acrylate having an alkyl group having 4 to 8 carbon atoms is preferably 10 to 80% by mass, and more preferably 20 to 70% by mass. Moreover, when using together the (meth) acrylate which has a C4-C8 alkyl group, the sum of content of 2-ethylhexyl acrylate and the (meth) acrylate which has a C4-C8 alkyl group is 50- It is preferably 98% by mass, particularly preferably 80 to 98% by mass, and the ratio of the content of 2-ethylhexyl acrylate and (meth) acrylate having an alkyl group having 4 to 8 carbon atoms is (2- It is preferably 9/1 to 2/8 in mass ratio represented by ethylhexyl acrylate / (meth) acrylate having an alkyl group having 4 to 8 carbon atoms, and particularly preferably 75/25 to 25/75. preferable.

  Moreover, as a (meth) acrylate monomer which forms a low molecular weight acrylic copolymer (b), you may use together 1 type (s), such as methyl (meth) acrylate and ethyl (meth) acrylate, or 2 types or more, for example. Especially, it is preferable to use together (meth) acrylate which has a C2-C2 alkyl group, such as methyl (meth) acrylate and ethyl (meth) acrylate, and it is preferable that it is 1-10 mass% as usage-amount. .

  The low molecular weight acrylic copolymer (b) preferably contains a monomer having an acid group as a monomer other than those described above. Examples of the monomer having an acid group include one or two selected from carboxyl group-containing vinyl monomers such as acrylic acid, methacrylic acid, itaconic acid, maleic acid, maleic anhydride, phthalic acid, phthalic anhydride, and crotonic acid. The above can be used. Among them, acrylic acid is preferable because it tends to impart flexibility to the resulting pressure-sensitive adhesive layer and contributes to improvement of adhesion, and methacrylic acid is easy to ensure cohesive force and contribute to improvement of removability. Can be used. It is also preferable to use acrylic acid and methacrylic acid in combination.

  The content of the monomer having an acid group in the low molecular weight acrylic copolymer (b) is 0.5 to 10% by mass in the monomer component forming the low molecular weight acrylic copolymer (b). Preferably, it is 0.5-5 mass%, More preferably, it is 1.5-3.5 mass%. By setting it within this range, the crosslinking reaction with the crosslinking agent easily proceeds well. Further, when the pressure-sensitive adhesive layer is formed, a cohesive force suitable for the pressure-sensitive adhesive layer is ensured, and the holding power and the removability are easily compatible. Furthermore, the cohesive force necessary for ensuring water resistance and the hydrophobicity of the pressure-sensitive adhesive layer surface can be ensured.

  When methacrylic acid and acrylic acid are used in combination, the molar equivalent ratio of methacrylic acid / acrylic acid is preferably 0.2 or more, more preferably 3 or more, and even more preferably 4 or more, More preferably, it is 6 or more. It becomes easy to contribute to the improvement of the cohesive force in an adhesive layer by making a combined use ratio into the said range.

  In the low molecular weight acrylic copolymer (b) used in the present invention, a nitrogen-containing vinyl monomer may be used as the monomer component of the acrylic copolymer in order to improve the prevailing power of the pressure-sensitive adhesive layer. good. Examples of the nitrogen-containing vinyl monomer include one or more selected from N-vinylpyrrolidone, N-vinylcaprolactam, acryloylmorpholine, acrylonitrile, acrylamide, N, N-dimethylacrylamide and dimethylaminoethyl (meth) acrylate. Can be used.

  Content in the case of using a nitrogen-containing vinyl monomer is 0.1-4.5 mass% in the monomer component which forms a low molecular-weight acrylic copolymer (b), Preferably, it is 0.5-4 The effects of the present invention can be suitably expressed by adjusting the mass%, more preferably 0.5 to 3.5 mass%.

  Although the ratio of the nitrogen-containing vinyl monomer and the vinyl monomer having a carboxyl group in the low molecular weight acrylic copolymer (b) is not particularly limited, the monomer constituting the low molecular weight acrylic copolymer (b) The molar ratio represented by the number of moles of nitrogen-containing vinyl monomer in the component / number of moles of vinyl monomer having a carboxyl group is preferably 1/1 to 1/20, more preferably 1/1 to 1/5. 1/1 to 1/3 is more preferable. If it is in the said range, reaction with the vinyl monomer which has a carboxyl group, and the crosslinking agent mentioned later will advance easily. Furthermore, it becomes easy to converge the distribution of carboxyl groups in the acrylic copolymer emulsion to a range described later.

  In the low molecular weight acrylic copolymer (b) used in the present invention, monomers other than those described above can be used as necessary. Examples of such monomers include the above high molecular weight acrylic copolymers. One or two or more of the hydroxyl group-containing monomer, keto group or aldehyde group-containing monomer, silane monomer, methylol group-containing monomer, and phosphate group-containing monomer exemplified in (a) may be used. It can be used in a proportion of 20% by mass or less in the monomer component forming the copolymer (b).

  The weight average molecular weight of the low molecular weight acrylic copolymer (b) used in the present invention is preferably 5000 to 250,000, more preferably 50,000 to 250,000. If it is less than 5000, the cohesive force required for re-peelability and heat resistance is insufficient, and if it exceeds 250,000, it is difficult to ensure the property of sufficiently adhering to rough surfaces such as foams such as urethane and nonwoven fabric.

  The said weight average molecular weight is standard polystyrene conversion by a gel permeation chromatography (GPC). As an example of measurement conditions, HLC-8220GPC (manufactured by Tosoh Corporation) is used, the column is TSKgel GMHXL (manufactured by Tosoh Corporation), the column temperature is 40 ° C., the eluent is tetrahydrofuran, the flow rate is 1.0 mL / min, and standard polystyrene. Can be measured by using TSK standard polystyrene.

  In order to adjust the molecular weight, a chain transfer agent may be used for the polymerization. As the chain transfer agent, known chain transfer agents exemplified in the high molecular weight acrylic copolymer (a) can be used.

(Copolymer ratio)
The water-dispersed acrylic pressure-sensitive adhesive composition of the present invention is a composition comprising an acrylic copolymer emulsion in which emulsion particles of the acrylic copolymer are dispersed in an aqueous medium, and the acrylic copolymer emulsion particles Is a composition containing the high molecular weight acrylic copolymer (a) and the low molecular weight acrylic copolymer (b).

  The content ratio of the high molecular weight acrylic copolymer (a) and the low molecular weight acrylic copolymer (b) in the water-dispersed acrylic pressure-sensitive adhesive composition is as follows: high molecular weight acrylic copolymer (a): low molecular weight The weight ratio represented by the acrylic copolymer (b) is 100: 3 to 100: 50, preferably 100: 10 to 100: 45, and more preferably 100: 10 to 100: 25. When the blending ratio of the low molecular weight acrylic copolymer (b) is less than 100: 3, it becomes difficult to ensure the property of sufficiently adhering to a rough surface such as a foam or a nonwoven fabric such as urethane, and when exceeding 100: 50, The cohesive force necessary for removability and heat resistance is insufficient.

  The weight ratio of each acrylic copolymer can be obtained from the molecular weight distribution obtained when GPC measurement is performed on a component of the acrylic copolymer in the acrylic copolymer emulsion that dissolves in ethyl acetate. The water-dispersed acrylic pressure-sensitive adhesive composition of the present invention has a molecular weight distribution obtained when GPC measurement is performed on a component dissolved in ethyl acetate of the acrylic copolymer in the acrylic copolymer emulsion constituting the composition. Have two peaks, and the molecular weight of each peak in terms of standard polystyrene is in the range of 500,000 to 1,200,000 and 5,000 to 250,000, respectively. In the present invention, the component based on the peak having a molecular weight in terms of standard polystyrene in the range of 500,000 to 1,200,000 is the high molecular weight acrylic copolymer (a), and the molecular weight in terms of standard polystyrene is in the range of 5000 to 250,000. The component based on the peak is a low molecular weight acrylic copolymer (b), and the above weight ratio is the weight ratio of the molecular weight distribution obtained from the molecular weight distribution based on each peak separated by the waveform. It is.

(Production method)
The acrylic copolymer emulsion can be produced by an emulsion polymerization method for obtaining an emulsion-type pressure-sensitive adhesive. In the emulsion polymerization, an appropriate amount of an anionic or nonionic emulsifier or other dispersion stabilizer is used in order to ensure polymerization stability. Especially an emulsifier is not restrict | limited, A well-known emulsifier can be used. Examples of the anionic emulsifier include sodium lauryl sulfate, ammonium lauryl sulfate, sodium dodecylbenzene sulfonate, sodium polyoxyethylene alkyl ether sulfate, sodium polyoxyethylene alkyl phenyl ether sulfate and the like. Examples thereof include ethylene alkyl ether and polyoxyethylene alkyl phenyl ether.
Furthermore, it is preferable to use an emulsifier having a polymerizable unsaturated group in the molecule, which is known as a “reactive emulsifier”. Specifically, Latemul S-180 [manufactured by Kao Corporation], Latemu PD-104 [manufactured by Kao Corporation], Aqualon HS-10 [manufactured by Daiichi Kogyo Seiyaku Co., Ltd.], Aqualon HS-20 [No. Ichi Kogyo Seiyaku Co., Ltd.], Aqualon KH-10 [Daiichi Kogyo Seiyaku Co., Ltd.], Aqualon KH-1025 [Daiichi Kogyo Seiyaku Co., Ltd.], Aqualon KH-05 [Daiichi Kogyo Seiyaku Co., Ltd. )], Aqualon RN-10 [Daiichi Kogyo Seiyaku Co., Ltd.], Aqualon RN-20 [Daiichi Kogyo Seiyaku Co., Ltd.], Aqualon ER-10 [Daiichi Kogyo Seiyaku Co., Ltd.], Aqualon ER-20 [Daiichi Kogyo Seiyaku Co., Ltd.], New Frontier A-229E [Daiichi Kogyo Seiyaku Co., Ltd.], Adeka Soap SE-10 [Asahi Denka Kogyo Co., Ltd.], Adeka Soap SE -20 [Asahi Denka Kogyo Co., Ltd.], Adeka Asopu SR-10 N [Asahi Denka Co., Ltd.], ADEKAREASOAP SR-20 N [Asahi Denka Co., Ltd.], and the like. It is preferable to use a reactive emulsifier because the water resistance of the coating is improved in addition to the polymerization stability.

  Among the emulsion polymerization methods, it is preferable to use a dropping polymerization method. Moreover, in order to make it easy to introduce an acid group into the particle, a dropping polymerization method may be selected and controlled by changing the composition of the emulsion to be dropped in the first half and the second half of the dropping. Specifically, the acid monomer can be introduced into the particles by increasing the ratio of the acid monomer in the first half of the dropping and decreasing the ratio of the acid monomer in the second half of the dropping.

  The polymerization initiator used in the emulsion polymerization is not limited, and a known polymerization initiator can be used. Specifically, 2,2 ′,-azobis (2-methylpropionamidine) dihydrochloride, 2,2′-azobis (2-methylpropionamidine) disulfate, 2,2′-azobis (2-amidinopropane) ) Dihydrochloride, 2,2′-azobis [N- (2-arboxyethyl) -2-methylpropionamidine] hydrate, 2,2′-azobis (N, N′-dimethyleneisobutylamidine) Azo initiators such as hydrochloride, 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride, persulfate initiators such as potassium persulfate, ammonium persulfate, sodium persulfate Agents, benzoyl peroxide, t-butyl hydroperoxide, peroxide initiators such as hydrogen peroxide, carbonyl initiators such as aromatic carbonyl compounds, persulfate and sodium hydrogensulfite Combination with helium, and the like redox initiators such as a combination of a peroxide and sodium ascorbate.

  In the preparation of the water-dispersed acrylic pressure-sensitive adhesive composition of the present invention, a raw material such as a monomer for obtaining one acrylic copolymer is supplied to a reaction vessel to perform a first-stage polymerization reaction. Subsequently, the acrylic emulsion containing each acrylic copolymer is prepared by supplying a raw material such as a monomer for obtaining the other acrylic copolymer to the reaction vessel and performing the second stage polymerization reaction. Adjust. In particular, the polymerization of the high molecular weight acrylic copolymer (a) is the first stage, and the polymerization of the low molecular weight acrylic copolymer (b) is the second stage. Since it becomes easy, it is preferable.

  In each polymerization reaction of the first stage and the second stage, it is preferable to use a chain transfer agent in order to adjust the molecular weight. Examples of the chain transfer agent used include lauryl mercaptan, glycidyl mercaptan, mercaptoacetic acid, 2-mercaptoethanol, thioglycolic acid, 2-ethylhexyl thioglycolate, 2,3-dimethylcapto-1-propanol and the like can be preferably used. Moreover, the chain transfer agent used in each polymerization reaction of the first stage and the second stage may be the same or different.

  The content of the chain transfer agent is 0. 100 parts by mass with respect to 100 parts by mass of the monomer used for adjusting the high molecular weight acrylic copolymer (a) or the low molecular weight acrylic copolymer (b) obtained in each polymerization reaction. It is preferable that it is 001-0.5 mass part, and it is more preferable that it is 0.02-0.2 weight part.

  In the first stage and second stage polymerization reactions, (the mass of the chain transfer agent used in the first stage polymerization reaction / the acrylic copolymer obtained by the first stage polymerization reaction) The content ratio of the first-stage chain transfer agent expressed by the sum of the masses of the monomers used is obtained by (the mass of the chain transfer agent used in the second-stage polymerization reaction / the second-stage polymerization reaction). It is preferable to make it less than the content ratio of the second-stage chain transfer agent represented by the sum of the monomer masses used in the acrylic copolymer). By reducing the content ratio of the first-stage chain transfer agent from that of the second stage, it becomes easier to suppress the unreacted chain transfer agent remaining in the reaction vessel in the first-stage polymerization reaction, and the high molecular weight Polymerization of the acrylic copolymer (a) is facilitated. Therefore, the content ratio of the first-stage chain transfer agent is less than that of the second stage, and the polymerization of the high molecular weight acrylic copolymer (a) is performed in the first stage, and the low molecular weight acrylic copolymer (b ) Is preferably the second stage.

  The content ratio of the second-stage chain transfer agent is preferably 1.1 to 10 times the content ratio of the first-stage chain transfer agent, more preferably 3.1 to 10 times. Preferably, it is 4 to 6 times. By setting it as the said range, it becomes easy to obtain the molecular weight distribution which has two peaks.

  The monomer composition used in the first stage polymerization reaction and the monomer composition used in the second stage polymerization reaction may be the same or different, but the resulting high molecular weight acrylic copolymer In order to improve the compatibility between (a) and the low molecular weight acrylic copolymer (b), it is preferable to contain a common monomer species as a main component, and to have the same monomer composition.

  The mass ratio of the total amount of monomers used in the high molecular weight acrylic copolymer (a) and the total amount of monomers used in the low molecular weight acrylic copolymer (b) is (a) :( b) = 100 : 3 to 100: 50 is preferable, 100: 10 to 100: 45 is more preferable, and 100: 10 to 100: 25 is still more preferable. By setting it as the said range, it becomes easy to keep the ratio of a high molecular weight acrylic copolymer (a) and a low molecular weight acrylic copolymer (b) in the target range.

  The timing of transition from the first stage polymerization reaction to the second stage polymerization reaction is preferably such that the polymerization rate after supplying all the first stage monomers to the reaction vessel is 90% or more. Is more preferably 95% or more. By setting it as the said range, it becomes easy to keep the molecular weight of the acrylic copolymer of the 1st step and the 2nd step in the target range.

(Aqueous medium)
The aqueous medium used in the present invention may be water alone or a mixed solvent of water and a water-soluble solvent. The above-mentioned “mixed solvent of water and water-soluble solvent” usable in the present invention is a mixed solvent of a water-soluble solvent mainly composed of water, and the water-soluble solvent with respect to the total amount of the mixed solvent. The content of is preferably 10% by weight or less, more preferably 5% by weight or less. Examples of the water-soluble solvent include alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, ethyl carbitol, ethyl cellosolve, butyl cellosolve, or polar solvents such as N-methylpyrrolidone, which may be used alone. Two or more kinds may be used in combination.

(Distribution of acid groups)
The water-dispersed acrylic pressure-sensitive adhesive composition of the present invention is a composition comprising an acrylic copolymer emulsion in which emulsion particles of the acrylic copolymer are dispersed in an aqueous medium. The acrylic copolymer emulsion particles in the water-dispersed acrylic pressure-sensitive adhesive composition include the acid group amount (AN _SUR ) on the surface of the acrylic copolymer emulsion particles and the acid group amount inside the acrylic copolymer emulsion particles. _{(aN iN)} and the ratio _{of, (aN iN) / (aN} SUR) is desirably 1 or more acrylic copolymer emulsion particles. In the present invention, by using an acrylic copolymer in which the amount of acid groups inside is equal to or greater than the amount of acid groups on the surface, adhesive residue can be reduced and excessive increase in adhesive strength over time can be suppressed. Thus, an adhesive tape having suitable removability can be realized. According to the water-dispersed acrylic pressure-sensitive adhesive composition using such acrylic copolymer emulsion particles, excellent removability is achieved even when a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer is used. Therefore, it is possible to realize a pressure-sensitive adhesive tape excellent in both characteristics of conflicting strong adhesion and re-peeling. Furthermore, adhesive tapes with excellent water resistance can be obtained by securing cohesive force by acid group orientation both between and within the particles and reducing the hydrophilicity of the pressure-sensitive adhesive layer surface by improving the amount of acid groups on the particle surface (improving hydrophobicity). be able to. The acid group amount ratio (AN _IN ) / (AN _SUR ) is preferably 1.3 or more, more preferably 1.5 or more, and further preferably 2.0 or more. On the other hand, the upper limit is not particularly limited as long as there is a surface acid group amount (A _SUR ) that can ensure cohesion between the acrylic copolymer emulsion particles, but the ratio is preferably 10 or less, and preferably 5 or less. Is more preferable. When it is within the above-mentioned upper limit range, the interaction between the particles easily proceeds, the cohesive force between the particles is easily increased, and the removability and water resistance are improved.

(Measurement method of acid group distribution)
The distribution of acid groups in the acrylic copolymer emulsion particles used in the present invention is measured by the following method. The method for measuring the distribution of acid groups of the acrylic copolymer emulsion particles in the present invention is preferably a potentiometric titration because it is a simple operation with little measurement error. The acid group can be measured by potentiometric titration according to the method disclosed in Japanese Patent Application Laid-Open No. 2007-003454, and is measured in detail by the following method.

  In the present invention, a method for measuring the distribution of acid groups in the acrylic copolymer emulsion particles using potentiometric titration is shown below.

  The acidic sample dispersion used for potentiometric titration can be prepared by mixing acrylic copolymer emulsion particles (solid content) and ion-exchanged water at a mass ratio represented by (acrylic copolymer emulsion / ion-exchanged water). Adjust to / 100. Extraction of the acrylic copolymer emulsion particles from the water-dispersed acrylic pressure-sensitive adhesive composition may be performed in a state of being dispersed in an aqueous medium or in a state of being separated from the aqueous medium. In addition, extraction is easy if the acrylic copolymer emulsion is prepared and then extracted before the additives are added. The acidic sample dispersion to be adjusted is preferably an acidic sample dispersion having a pH of 4 or less. From the water-dispersed acrylic pressure-sensitive adhesive composition neutralized with ammonia water or the like, acrylic acid is dispersed in an aqueous medium. When extracting the copolymer emulsion, it is preferable to adjust the pH to 4 or less by adding a weak acid such as formic acid or butyric acid to the sample dispersion as necessary.

  For titration, an automatic potentiometric titrator can be used. Examples of the automatic potentiometric titrator include AT-610, AT-420N-WIN manufactured by Kyoto Electronics Co., Ltd.

Calculation of the acid group amount (AN _SUR ) and the internal acid group amount (AN _IN ) on the surface of the acrylic copolymer emulsion particles is calculated based on a titration curve obtained by potentiometric titration. When potentiometric titration is performed with the X-axis as the base dropping amount and the Y-axis as the pH, between the titration start point P ₀ and the titration end point P ₃ , the minimum point P ₁ and the minimum point P at which the pH becomes minimum after the base titration starts. titration curve having an inflection point P ₂ appearing next to ₁ (FIG. 1) is obtained. The local minimum point P ₁ and the inflection point P ₂ are more clearly converted to a differential curve (FIG. 2) of a titration curve in which the X-axis is a base dropping amount (mL) and the Y-axis is ΔE / mL. easily read the ₁ and _{P 2.}

The region of P _{0 to} P ₁ in the titration curve is a region where the free acid in the aqueous phase of the sample dispersion is neutralized, and the pH value decreases as the free acid in the aqueous phase is neutralized. shows the minimum value P ₁ that the pH value becomes minimum when neutralized. Therefore, the amount of base dripped in this region is the titration amount required to neutralize the acid in the aqueous phase. From the base titration and the base concentration of the inorganic base solution used for the titration, the acid group amount (AN _AQUA ) [meq / g] in the aqueous phase in the sample dispersion is calculated.

In the water-dispersed acrylic pressure-sensitive adhesive composition, since the acid used for polymerizing the acrylic copolymer generally remains, the acrylic copolymer emulsion particles are extracted in a state dispersed in an aqueous medium. Free acid is present in the aqueous phase of the sample dispersion. On the other hand, when only the acrylic copolymer emulsion particles are separated and dispersed in ion-exchanged water, there is a possibility that P ₀ = P ₁ because there is theoretically no acid in the aqueous phase. .

When the acid in the aqueous phase is neutralized, the acid groups on the surface of the acrylic copolymer emulsion particles that are easily neutralized are then neutralized. Since this becomes the region of P _{1 to} P ₂ of the titration curve, the amount of base dripped in this region is the titration amount required to neutralize the acid groups on the surface of the acrylic copolymer emulsion particles. The acid group amount (AN _SUR ) [meq / g] on the surface of the acrylic copolymer emulsion particles is calculated from the base titration and the base concentration of the inorganic base solution used for the titration.

When the acid groups on the surface of the acrylic copolymer emulsion particles are neutralized, neutralization of the acid groups inside the acrylic copolymer emulsion particles, which are difficult to neutralize, begins. This is the inflection point P ₂ in the titration curve. Appears as The amount of acid groups (AN _IN ) inside the acrylic copolymer emulsion particles is determined by titration of the total amount of acid groups present inside the emulsion particles when the emulsion particles form particles stably. Therefore, it is preferable to calculate from the above calculation result and the total acid group amount (AN _TOTAL ) in the sample dispersion by the following formula.
AN _IN = AN _TOTAL- (AN _SUR + AN _AQUA )

  In the inorganic base solution used for the titration, potassium hydroxide or sodium hydroxide can be preferably used as the inorganic base used for titration, and potassium hydroxide is particularly preferably used. The concentration of the inorganic base used for titration is preferably adjusted in the range of 0.1 to 2 mol / L.

  As other titration conditions, it is preferable to perform titration by intermittent constant rate titration, the intermittent time is 10 seconds, the maximum dripping amount is 20 mL, the single injection amount at the intermittent injection is preferably 0.16 mL / time, and the injection speed Is preferably 5 seconds / mL, the potential for collecting data is 4 mL, and the titration for detecting pH is preferably performed every 0.16 mL.

  To illustrate a specific measurement method, a water-dispersed acrylic pressure-sensitive adhesive composition containing 3 g of acrylic copolymer emulsion particles (solid content) was weighed into a 300 mL polyethylene beaker with a dropper, Ion exchange water is poured into the polyethylene beaker until the total amount of the test sample reaches 100 g and stirred. Then, the electrode and the temperature assurance electrode are immersed. The tip of the titration nozzle is higher than the liquid level, and is 2 cm away from the electrode so that the titration reagent does not reach the electrode. Under the above conditions, automatic potentiometric titration is started with stirring. After the measurement is completed, meq / g is calculated from the titration amount at the equivalent point automatically printed on the obtained titration curve.

The total acid group amount (AN _TOTAL ) in the acidic sample dispersion can be obtained by a measurement method based on potentiometric titration with an inorganic acid solution as shown below, even when calculated from the theoretical amount of acid groups calculated from the charged amount. The obtained value may be used. A method for measuring the total amount of acid groups (AN _TOTAL ) in the sample dispersion by potentiometric titration is described below.

  For the preparation of the sample dispersion, potassium hydroxide is added to a sample dispersion equivalent to the acidic sample dispersion used above until pH 13 and all acid groups including the inside of the particles are neutralized. When the dispersion of acrylic copolymer emulsion particles is a basic sample dispersion having a pH of 13, all acid groups inside are drawn out to the surface of the emulsion particles by electrostatic interaction. Therefore, by performing back titration of the basic sample dispersion with an inorganic acid solution, the acid groups on the surface of the acrylic copolymer emulsion particles and the acid groups on the inside can be titrated equally, and the total amount of acid groups in the sample dispersion Can be calculated.

  The acid used for the titration is preferably sulfuric acid, and the concentration is preferably 0.1 mol / L. As the potentiometric titration apparatus, an apparatus similar to the above can be preferably used.

When potentiometric titration is performed with the X-axis being the acid dropping amount and the Y-axis being the pH, the inflection points Q ₁ , Q ₂ , Q _{3 are in the} order of the acid titration from the titration start point Q ₀ to the titration end point Q _4. A titration curve is obtained (FIG. 3). By converting these inflection points into differential curves (FIG. 4) of titration curves in which the X axis is the acid drop amount (mL) and the Y axis is ΔE / mL, the inflection points can be read more clearly. X-coordinate at these inflection points _{Q1, Q} 2, _{Q 3} is an acid dropped quantity at each _point, acid dropping amount in Q 0 to Q ₁ neutralizing the residue of potassium hydroxide used in adjusting to pH13 This is the titration amount required to do this. The acid dripping amount in Q _{1 to} Q ₂ is a titration amount required to neutralize all acid groups present in the acrylic copolymer emulsion particles, and the acid dripping amount in Q _{2 to} Q ₃ is the water phase. This is a titration amount required to neutralize the acid groups therein. Therefore, the total amount of acid groups in the acidic sample dispersion is converted into meq / g based on the amount of acid dropped in Q _{1 to} Q ₃ and the concentration of acid used for titration. (AN _TOTAL ) is calculated.

  As a specific measurement method, a water-dispersed acrylic pressure-sensitive adhesive composition containing 3 g of acrylic copolymer emulsion particles (solid content) was weighed into a 300 mL polyethylene beaker with a dropper, and then Ion exchange water is poured into a polyethylene beaker until the total amount of the test sample reaches 100 g and stirred. Subsequently, 1N potassium hydroxide is added and stirred until the test sample reaches pH 13. Then, the electrode and the temperature assurance electrode are immersed. The potentiometric automatic titration is started in the same manner as the titration conditions described above. After the measurement is completed, meq / g is calculated from the titration amount at the equivalent point automatically printed on the obtained titration curve.

  The introduction of acid groups into the acrylic copolymer emulsion particles can be controlled by appropriately selecting the monomer composition and polymerization method. As the monomer composition, acid groups can be introduced into the particles by increasing the hydrophobicity of the acid monomer. Moreover, an acid group can also be introduce | transduced inside a particle | grain by copolymerizing the nitrogen-containing monomer which interacts with an acid group. On the other hand, as the polymerization method, a so-called dropping polymerization method can be selected and controlled by changing the composition of the emulsion to be dropped in the first half and the second half of the dropping. Specifically, the acid monomer can be introduced into the particles by increasing the ratio of the acid monomer in the first half of the dropping and decreasing the ratio of the monomer having an acid group in the second half of the dropping.

  In addition, the average particle diameter of the acrylic copolymer emulsion particles in the present invention is not particularly limited, but since it may be difficult to introduce acid groups into the emulsion particles if it is 150 nm or less, the lower limit is The particle diameter is preferably more than 150 nm, more preferably 200 nm or more, and even more preferably 300 nm or more. Moreover, as an upper limit, it is preferable that it is 1000 nm or less, It is more preferable that it is 800 nm or less, It is more preferable that it is 600 nm or less, It is still more preferable that it is 400 nm or less.

  Here, the average particle diameter of the particles means a 50% median diameter of the emulsion particles on the volume basis, and the numerical values are based on values obtained by measurement by a dynamic light scattering method. If the average particle size becomes too small, the surface area of the particles increases and the proportion of the particle surface in contact with water increases. As a result, for example, when a carboxyl group is used as the acid group, the carboxyl group is easily ionized into a carboxylate anion, and the tendency of the carboxyl group to localize on the particle surface is increased.

For this reason, the ratio (AN _IN ) / (AN _SUR ) between the amount of acid groups on the surface of the resulting acrylic copolymer emulsion and the amount of acid groups inside (AN _SUR ) may not be within the desired range as described above. . Accordingly, the average particle diameter is preferably more than 150 nm. On the other hand, when the average particle size becomes too large, an excessively large average particle size is not preferable in order to promote fusion between the emulsion particles after forming the pressure-sensitive adhesive layer, and it is preferable to suppress the average particle size to 1000 nm or less.

(Tackifying resin)
In the water-dispersed acrylic pressure-sensitive adhesive composition of the present invention, it is preferable to use a tackifying resin in order to adjust the strong adhesiveness of the pressure-sensitive adhesive layer obtained. As the tackifier resin used in the present invention, an emulsion type tackifier resin can be preferably used from the viewpoint of use in an aqueous dispersion type pressure-sensitive adhesive composition. Examples of the emulsion type tackifying resin include rosin, polymerized rosin, polymerized rosin ester, rosin phenol, stabilized rosin ester, disproportionated rosin ester, terpene, terpene phenol, petroleum resin, etc. Can be illustrated.

  Among these, a polymerized rosin ester-based tackifier resin and a rosin phenol-based tackifier resin are preferable, and it is particularly preferable to blend these in combination. Specifically, polymerized rosin ester-based tackifier resins are Superester E-650 [Arakawa Chemical Industries, Ltd.], Superester E-788 [Arakawa Chemical Industries, Ltd.], Superester E-786. 60 [Arakawa Chemical Industries, Ltd.], Super Ester E-865 [Arakawa Chemical Industries, Ltd.], Super Ester E-865NT [Arakawa Chemical Industries, Ltd.], Harrier Star SK-508 [Harima Chemicals ( Co., Ltd.] Harrier Star SK-508H [Harima Kasei Co., Ltd.], Harrier Star SK-816E [Harima Kasei Co., Ltd.], Harrier Star SK-822E [Harima Kasei Co., Ltd.], Harrier Star SK- 323NS [manufactured by Harima Chemicals Co., Ltd.] and the like, and rosin phenolic tackifying resins are Tamanoru E-100 [manufactured by Arakawa Chemical Industries, Ltd.], Tamanoru E 200 [(manufactured by Arakawa Chemical Industry Ltd.), Tamanol E-200NT Arakawa Chemical Industries, Ltd.], and the like.

  When these are used in combination, the ratio of the polymerized rosin ester-based tackifier resin (A) to the rosin phenol-based tackifier resin (B) is 5 / in a mass ratio represented by (A) / (B). 1 to 1/5 is preferable, 3/1 to 1/3 is more preferable, and 3/1 to 1/1 is still more preferable. If it is in the said range, heat resistance and removability can be improved with sufficient balance.

  The softening point of the tackifying resin is preferably 120 to 180 ° C, more preferably 140 to 180 ° C. Heat resistance improves by mix | blending a tackifying resin with a high softening point.

  In the blend ratio of the acrylic copolymer / tackifying resin, the acrylic copolymer / tackifying resin = 100/10 to 100/40 is preferable, and the acrylic copolymer / tackifying resin = 100 is more preferable. / 15 to 100/35. If it is in the said range, heat resistance and removability can be improved with sufficient balance.

(Crosslinking agent)
In the water-dispersed acrylic pressure-sensitive adhesive composition of the present invention, it is preferable to use a crosslinking agent for the purpose of improving the cohesive strength of the resulting pressure-sensitive adhesive layer. Examples of the crosslinking agent include known isocyanate crosslinking agents, epoxy crosslinking agents, aziridine crosslinking agents, polyvalent metal salt crosslinking agents, metal chelate crosslinking agents, keto-hydrazide crosslinking agents, oxazoline crosslinking agents, and carbodiimide crosslinking agents. A crosslinking agent, a silane crosslinking agent, a glycidyl (alkoxy) epoxysilane crosslinking agent, or the like can be used. Among them, a type of crosslinking agent that is added after the completion of polymerization and causes the crosslinking reaction to proceed is preferable. Examples thereof include an isocyanate-based crosslinking agent, an epoxy-based crosslinking agent, an oxazoline-based crosslinking agent, a carbodiimide-based crosslinking agent, and a glycidyl (alkoxy) epoxysilane-based crosslinking agent. Specifically, in the isocyanate-based cross-linking agent, Bernock DNW-5000 [manufactured by DIC Corporation], Bernock DNW-5010 [manufactured by DIC Corporation], Bernock DNW-5100 [manufactured by DIC Corporation], Bernock DNW- 5500 [manufactured by DIC Corporation], Aquanate 100 [manufactured by Nippon Polyurethane Industry Co., Ltd.], Aquanate 105 [manufactured by Nippon Polyurethane Industry Co., Ltd.], Aquanate 110 [manufactured by Nippon Polyurethane Industry Co., Ltd.], Aquanate 120 [manufactured by Nippon Polyurethane Industry Co., Ltd.], Aquanate 130 [manufactured by Nippon Polyurethane Industry Co., Ltd.], Aquanate 200 [manufactured by Nippon Polyurethane Industry Co., Ltd.], Aquanate 210 [manufactured by Nippon Polyurethane Industry Co., Ltd.], LS2319 [manufactured by Sumika Bayer Urethane Co., Ltd.], LS2336 [Sumika Bayer Ure Tanhydr Co., Ltd.], Bayhydur 3100 [manufactured by Sumika Bayer Urethane Co., Ltd.] and the like, and epoxy crosslinking agents include Denacol EX-832 [Nagase Kasei Kogyo Co., Ltd.], Denacol EX-841 [Nagase Kasei] Kogyo Co., Ltd.], Tetrad C [Mitsubishi Gas Chemical Co., Ltd.], Tetrad X [Mitsubishi Gas Chemical Co., Ltd.], etc. Catalyst manufactured], Epocross WS-700 [manufactured by Nippon Shokubai Co., Ltd.], Epocross K-2010E [manufactured by Nippon Shokubai Co., Ltd.], Epocross K-2020E [manufactured by Nippon Shokubai Co., Ltd.], Epocross K-2030E [(stock) ) Manufactured by Nippon Shokubai Co., Ltd., and carbodiimide-based crosslinking agents include Carbodilite SV-02 [Nisshinbo Co., Ltd.], Carbodilite V-02 [Nisshinbo ( )], Carbodilite V-02-L2 [Nisshinbo Co., Ltd.], Carbodilite V-04 [Nisshinbo Co., Ltd.], Carbodilite E-01 [Nisshinbo Co., Ltd.], Carbodilite E-02 [Nisshinbo Co., Ltd.] )], Carbodilite E-03A [Nisshinbo Co., Ltd.], Carbodilite E-04 [Nisshinbo Co., Ltd.], and glycidyl (alkoxy) epoxysilane crosslinking agents, 2- (3,4-epoxycyclohexylethyltrimethoxy) Silane [KBM-303; Shin-Etsu Silicone Co., Ltd.], γ-glycidoxypropyltrimethoxysilane [KBM-403; Shin-Etsu Silicone Co., Ltd.], γ-glycidoxypropylmethyldiethoxysilane [KBE-402 Manufactured by Shin-Etsu Silicone Co., Ltd.], γ-glycidoxypropyltriethoxysilane [KBE-403; Manufactured by Co., Ltd.] and the like. As an index of the degree of cross-linking, the degree of cross-linking is adjusted using the value of the gel fraction that measures the insoluble content after the pressure-sensitive adhesive layer has been immersed in toluene for 24 hours. The gel fraction is preferably 20 to 45% by mass. More preferably in the range of 25 to 45% by mass, and still more preferably in the range of 28 to 38% by mass, re-peelability and strong adhesiveness can be ensured with a good balance.

  Among them, it is preferable to use a crosslinking agent that reacts with the above-mentioned vinyl monomer having an acid group, and the above-mentioned isocyanate-based crosslinking agent, epoxy compound, oxazoline compound, carbodiimide-based crosslinking agent, glycidyl (alkoxy) epoxysilane compound, and the like are preferable. . The present invention is a technique characterized by ensuring the cohesive force of the acrylic copolymer over the whole by orienting an appropriate amount of acid groups both on the emulsion particle surface and inside the particle. By using a cross-linking agent that reacts with an acid group, an improvement in cohesion can be suitably achieved.

(Additive)
In the water-dispersed acrylic pressure-sensitive adhesive composition of the present invention, as an additive, a base (such as aqueous ammonia) or an acid for adjusting pH within a range that does not impair the desired effect of the present invention as necessary. Plasticizers, softeners, antioxidants, fillers such as glass and plastic fibers, balloons, beads, and metal powders, colorants such as pigments and dyes, pH adjusters, film formation aids, leveling agents, thickening agents Known agents such as an agent, a water repellent, and an antifoaming agent can be optionally added to the pressure-sensitive adhesive composition.

(Solid content concentration)
Further, the solid content concentration of the water-dispersed acrylic pressure-sensitive adhesive composition of the present invention is not particularly limited, but from the viewpoints of manufacturing cost and transportation cost, and drying properties when dried and used. From the viewpoint of superiority, the solid content concentration is preferably 40 to 70% by weight.

(Initial gel fraction)
The water-dispersed acrylic pressure-sensitive adhesive composition of the present invention has an uncrosslinked gel fraction (hereinafter referred to as “solid content”) when the aqueous medium is removed from the composition so that the crosslinking reaction does not proceed. The initial gel fraction) is preferably 15% by mass or less, more preferably 10% by mass or less, further preferably 5% by mass or less, and more preferably 3% by mass or less. Even more preferred. In the present invention, by making the initial gel fraction of the water-dispersed acrylic pressure-sensitive adhesive composition within this range, impregnation into the base material is suitable, and good removability is easily realized. Also, using a water-dispersed acrylic pressure-sensitive adhesive composition having an initial gel fraction within the range, after removing the aqueous medium so as not to proceed with the crosslinking reaction, the crosslinking reaction is allowed to proceed to form a pressure-sensitive adhesive layer. By doing so, an adhesive tape having excellent resilience resistance can be formed.

  The initial gel fraction can be adjusted by the polymerization temperature at the time of preparing the water-dispersed acrylic pressure-sensitive adhesive composition, the kind of initiator and the amount used. When the initial gel fraction is 15% by mass or less, it is preferable to use, for example, an azo initiator, a persulfate initiator, and a peroxide initiator as the initiator. Of these, azo initiators and persulfate initiators such as ammonium persulfate can be preferably used.

  The initial gel fraction is measured by removing the aqueous medium from the water-dispersed acrylic pressure-sensitive adhesive composition containing no crosslinking agent to obtain a solid content, and then measuring the insoluble content by immersing the solid content in toluene for 24 hours. be able to.

  When adjusting the initial gel fraction, it is preferable to appropriately adjust the polymerization temperature during emulsion polymerization according to the polymerization initiator used. For example, when ammonium persulfate is used, the initial gel fraction is 15% by mass. In the following, the polymerization temperature is preferably less than 70 ° C, more preferably less than 65 ° C.

<Adhesive tape>
(Constitution)
The pressure-sensitive adhesive tape of the present invention is a pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer made of the above water-dispersed acrylic pressure-sensitive adhesive composition. The pressure-sensitive adhesive layer may be a single-layer pressure-sensitive adhesive layer or a multilayer composed of a plurality of pressure-sensitive adhesive layers and sheets such as a double-sided pressure-sensitive adhesive tape. A double-sided pressure-sensitive adhesive tape can be suitably used in two or more member fixing applications.

(Adhesive layer)
The pressure-sensitive adhesive layer in the pressure-sensitive adhesive tape of the present invention is a layer obtained by removing the solvent from the water-dispersed acrylic pressure-sensitive adhesive composition. The preferable thickness of the pressure-sensitive adhesive layer added to both sides when the double-sided pressure-sensitive adhesive tape is formed is 30 to 300 μm, more preferably 50 to 200 μm.

  The pressure-sensitive adhesive layer in the present invention preferably has a temperature having a convex peak value on the tangent loss in the dynamic viscoelastic spectrum, which is −60 ° C. to −5 ° C., and is −30 ° C. to −10 ° C. It is more preferable. When it exists in this range, it becomes easy to balance re-peelability and strong adhesiveness in a well-balanced manner.

  The above-mentioned dynamic viscoelastic characteristics are measured between the parallel disks that are the measuring unit of the test machine using a viscoelasticity tester (manufactured by Rheometrics, trade name: Ares 2KSTD) in the measurement of dynamic viscoelasticity. A test piece is sandwiched in between and a storage elastic modulus (G ′) and a loss elastic modulus (G ″) from −50 ° C. to 150 ° C. are measured at a frequency of 1 Hz. The test piece is an adhesive having a thickness of 0.5 to 2.5 mm. May be sandwiched between the parallel disks alone, but the laminate of the base material and the adhesive may be stacked in layers and sandwiched between the parallel disks. When the thickness of the pressure-sensitive adhesive is adjusted to the above range, even if a base material is sandwiched in the middle, measurement can be performed without affecting the dynamic viscoelastic spectrum of the pressure-sensitive adhesive.

  As an index of the degree of cross-linking of the pressure-sensitive adhesive layer after drying and cross-linking, the degree of cross-linking is adjusted using the value of the gel fraction for measuring the insoluble content after the pressure-sensitive adhesive layer is immersed in toluene for 24 hours. The gel fraction is preferably 20 to 45% by mass. More preferably in the range of 25 to 45% by mass, and still more preferably in the range of 28 to 38% by mass, re-peelability and strong adhesiveness can be ensured with a good balance.

(Nonwoven fabric)
When forming a double-sided pressure-sensitive adhesive tape, it is preferable to use a nonwoven fabric as the core. The nonwoven fabric has a tensile strength, a tear strength, and an interlayer strength in order to balance re-peelability and adhesion. It is preferable to use a nonwoven fabric in a specific range.

  The tensile strength of the nonwoven fabric is preferably 10 to 50 N / 20 mm in both the MD direction (longitudinal direction; flow direction) and the TD direction (lateral direction; width direction), more preferably 15 to 40 N / 20 mm, and more preferably 25 to 40 N / 20 mm. Even more preferred. In the double-sided pressure-sensitive adhesive tape of the present invention, by setting the tensile strength of the nonwoven fabric base material within the above range, the tape is hardly broken at the time of re-peeling and is also difficult to peel off when attached to a curved surface or the like. In addition, the above-mentioned tensile strength was measured using a Tensilon tensile tester on a sample having a vote line length of 100 mm and a width of 20 mm under a measurement condition of a tensile speed of 300 mm / min in an environment of 23 ° C. and 50% RH. The maximum strength.

  The tear strength of the nonwoven fabric is preferably 1 N or more as the tear strength specified in JIS-P-8116. By setting the tear strength to 1 N or more, it is possible to remarkably suppress the breakage of the nonwoven fabric that occurs when the starting point of breakage occurs due to the instantaneous tearing in the peeling process and expands, and the base material is difficult to cut. As a result, the removability of the double-sided pressure-sensitive adhesive tape adhered to the adherend for a long time can be greatly improved. The upper limit of the tear strength is not particularly defined, but a tear strength of about 3N is usually assumed as the upper limit for a substrate using a nonwoven fabric. Preferably it is 1.2-2.5N, More preferably, it is 1.5-2.5N.

  The interlayer strength of the nonwoven fabric is preferably 1 N / 15 mm or more. The interlayer strength is measured by first sticking a 24 mm wide adhesive film (cellophane tape: CT405AP-24 manufactured by Nichiban) on both sides of a 25 × 150 mm non-woven fabric. The length of the adhesive film is longer than that of the nonwoven fabric. Both ends of the sample are cut off, the cellophane tape is peeled off from one end of the sample adjusted to 15 × 150 mm, and the nonwoven fabric layer is peeled off by about 30 mm. Three samples of each of the vertical direction and the horizontal direction are prepared. Measurement temperature and humidity: 23 ° C., 50% RH, Measuring instrument: Tensilon RTA-100 manufactured by Orientec, specimen gripping interval: 20 mm, the sample is sandwiched between chucks, speed: 100 mm / min, measurement distance: 50 mm The integrated average load is read, and the average value of the three sheets in the vertical direction and the horizontal direction is set as the interlayer strength (N / 15 mm). The upper limit of interlaminar strength is not particularly specified, but an interlaminar strength of about 4N is usually assumed as the upper limit for a substrate using a nonwoven fabric.

  As a material of the nonwoven fabric, a known and conventional nonwoven fabric used as a nonwoven fabric for an adhesive tape can be used. Typical examples include Manila hemp; pulp; chemical fibers such as rayon, acetate fiber, polyester fiber, polyvinyl alcohol fiber, polyamide fiber; and mixtures thereof. Furthermore, you may perform the impregnation process which used the viscose impregnation and the thermoplastic resin as a binder as needed.

  Among these, hemp alone or a mixture of hemp and vinylon, rayon, polyester, pulp or the like is preferable. As the hemp, Manila hemp is preferable from the viewpoint of strength. The content of Manila hemp is preferably 50% by mass or more, and more preferably 70% by mass or more.

  For the purpose of improving the strength of the nonwoven fabric, it is preferable to add a known and usual reinforcing agent in the nonwoven fabric manufacturing process. As the reinforcing agent, an internal additive reinforcing agent or an external additive reinforcing agent may be used alone or in combination. As the internal reinforcement, polyacrylamide resins, urea-formaldehyde resins, melamine-formaldehyde resins, epoxy-polyamide resins, and the like can be used. In particular, a polyamidoamine / epichlorohydrin resin which is an epoxy-polyamide resin is preferable because it significantly increases the interlayer strength of the nonwoven fabric. The addition amount of the internal additive reinforcing agent is preferably 0.2 to 1%, more preferably 0.3 to 0.5% with respect to the nonwoven fabric. On the other hand, as the external additive reinforcing agent, a thermoplastic resin such as starch; viscose, carboxymethylcellulose, polyvinyl alcohol, polyacrylamide or the like can be used. Especially, in order to raise the interlayer strength of a nonwoven fabric base material, it is preferable to use the above-mentioned internal additive reinforcement agent.

The basis weight of the nonwoven fabric described above is preferably from 10 to 30 g / ^{m 2,} it is rather more preferable is 13~25g / ^{m 2,} and still more preferably 14~20g / ^{m 2.} It is preferable that density is 0.15~0.35g / ^{m 2,} and more preferably 0.2 to 0.3 g / ^{m 2.} In the case of this range, it is possible to improve the balance between the difficulty of cutting the nonwoven fabric and the impregnation property of the pressure-sensitive adhesive into the nonwoven fabric, and the removability can be further improved.

  The paper making method of the nonwoven fabric is not particularly limited, but can be obtained by a known wet method, and various paper machines using a circular net paper machine, a short net paper machine, a long net paper machine, an inclined short net paper machine, etc. The method is used. Among them, in order to make it difficult to cut the nonwoven fabric, it is preferable to increase the isotropy of strength and elongation in the MD direction and the TD direction, and an inclined short net paper machine that easily increases the isotropy is preferable.

  It is preferable that an acrylic copolymer having a glass transition temperature (Tg) of −10 ° C. or lower is fixed to the nonwoven fabric used to form the double-sided pressure-sensitive adhesive tape. Compared to ordinary non-woven fabric that does not have an acrylic copolymer fixed, when the acrylic copolymer is fixed, the surface of the non-woven fabric is coated with acrylic, so it has a chemical affinity with the acrylic pressure-sensitive adhesive composition. Property is improved, and the effect of strengthening the bond between the nonwoven fabric substrate and the pressure-sensitive adhesive is born. As a result, in the re-peeling process of peeling the pressure-sensitive adhesive tape that has been stuck to the adherend for a long period of time, the pressure-sensitive adhesive is less likely to fall off the nonwoven fabric substrate. Moreover, usually, when a nonwoven fabric is treated with an acrylic fiber processing agent, the tensile strength of the nonwoven fabric tends to increase, but the tear strength is greatly reduced, and it becomes easy to break. However, when an acrylic copolymer having a low glass transition temperature is used, the tear strength is increased at a temperature in the vicinity of −10 ° C., which greatly contributes to the improvement of removability.

  Furthermore, the glass transition temperature of the acrylic copolymer fixed to the nonwoven fabric is preferably −10 ° C. or lower, preferably −15 ° C. or lower, and more preferably −20 ° C. or lower. When an acrylic copolymer having a high glass transition temperature exceeding −10 ° C. is fixed to a nonwoven fabric substrate, the brittleness of the nonwoven fabric substrate becomes strong and the tear strength of the nonwoven fabric substrate decreases. As a result, the nonwoven fabric substrate is significantly easily broken when re-peeling. On the other hand, in the case of an acrylic copolymer having a low glass transition temperature of −10 ° C. or lower, an effect of relaxing the stress applied to the nonwoven fabric substrate during the re-peeling process is produced, and the nonwoven fabric substrate is difficult to break.

(Manufacturing process of adhesive tape)
In order to laminate the pressure-sensitive adhesive layer on the nonwoven fabric, a method in which the pressure-sensitive adhesive solution is directly applied to the nonwoven fabric substrate using a roll coater, a die coater or the like, followed by a drying step, and a separator is bonded (hereinafter referred to as a direct coating method). ) Or a method of coating a pressure-sensitive adhesive solution once on a separator, transferring it to a non-woven fabric after passing through a drying step (hereinafter referred to as a transfer method). In the production process of double-sided tape, compared to the direct coating method in which the nonwoven fabric is impregnated with the adhesive in the solution state, the transfer method impregnates the nonwoven fabric with the adhesive layer after drying, so that the impregnation property tends to deteriorate. is there. However, since the acrylic copolymer having the constitution of the present invention is excellent in impregnation into a nonwoven fabric, it is possible to ensure excellent impregnation even in a transfer method.

(Characteristics of adhesive tape)
The tensile strength of the pressure-sensitive adhesive tape of the present invention is preferably 20 N / 20 mm or more and less than 50 N / 20 mm in both the MD direction (longitudinal direction; flow direction) and the TD direction (transverse direction; width direction). More preferably, it is 20 N / 20 mm or more and less than 40 N / 20 mm, More preferably, it is 30 N / 20 mm or more and less than 40 N / 20 mm. In the case of 20 N / 20 mm or more, the adhesive tape is stuck for a long period of time, and becomes remarkably difficult to tear when peeled again. On the other hand, when the tensile strength is excessively high, the so-called waist as the adhesive tape becomes strong, and therefore, it tends to occur without being able to withstand the repulsive force, and is preferably less than 50 N / 20 mm. In particular, in the case where an adhesive tape is used for an application that requires a repulsive force such as a curved surface, it is preferably less than 40 N / 20 mm.

  In addition, the above-mentioned tensile strength was measured using a Tensilon tensile tester on a sample having a vote line length of 100 mm and a width of 20 mm under a measurement condition of a tensile speed of 300 mm / min in an environment of 23 ° C. and 50% RH. The maximum strength.

  The 180 degree peel adhesive strength of the adhesive tape is determined by JIS-Z-0237, and a stainless steel plate is used as the adherend. [A] A sample left for 1 hour in an environment of 23 ° C. and 50%, and [B] 1 day in an environment of 23 ° C. and 50% after being left for 10 days in an environment of 60 ° C. and 0 to 5%. When preparing samples that were allowed to stand for a period of time and measuring the adhesive strength ([A] and [B]) when the adhesive tape samples [A] and [B] were peeled off at a speed of 1000 m / min in the direction of 180 degrees Further, the adhesive strength of [A] is preferably 12 to 19 N / 20 mm, and the difference in adhesive strength of [B]-[A] is preferably within 10 N / 20 mm. In the case of the adhesive strength in this range, it becomes easy to achieve both re-peelability and strong adhesiveness in a balanced manner. In addition, the adhesive tape at the time of evaluation adjusts an adhesive tape sample by cut | disconnecting to 20 mm width x 100 mm length, and in the case of a double-sided adhesive tape, a double-sided adhesive tape is lined with a 25-micrometer-thick PET film, and 20-mm width A double-sided adhesive tape sample is prepared by cutting to a length of × 100 mm.

<Application>
The pressure-sensitive adhesive tape of the present invention has a peeling resistance that can withstand the repulsive force of the adherend, a resistance that can withstand a load applied in the shear direction, an adhesive reliability under severe environmental conditions such as a high humidity environment, and a space between parts in a small area. It is also excellent in strong adhesive force that can stably fix between members, such as fixing. In addition, it has excellent removability in the case of inadequate adhesion in the work process and separation between members during recycling. Unlike conventional adhesives based on solution-polymerized acrylic resins, the use of water-dispersed acrylic adhesive compositions can also be expected to reduce volatile organic compounds. It can be suitably used as an adhesive tape that fixes parts in various products in industrial applications such as building materials, OA, and home appliance industries.

(Production Example 1: Preparation of emulsion (A))
In a container, 60 g of ion exchange water and surfactant Aqualon KH-1025 [Daiichi Kogyo Seiyaku Co., Ltd .; active ingredient 25%] 16 g and surfactant Latemul PD-104 [Kao Co., Ltd .; active ingredient 20%] 30 g was added and dissolved uniformly. There, 182 g of n-butyl acrylate, 182 g of 2-ethylhexyl acrylate, 20 g of methyl methacrylate, 6 g of N-vinylpyrrolidone, 2.5 g of acrylic acid [80% active ingredient], 10 g of methacrylic acid [80% active ingredient], lauryl mercaptan 0 .16 g was added and emulsified to obtain 508.66 g of an emulsified liquid (A).

(Production Example 2: Preparation of emulsion (I))
In a container, 15 g of ion exchange water and surfactant Aqualon KH-1025 [Daiichi Kogyo Seiyaku Co., Ltd .; active ingredient 25%] and 4 g of surfactant Latemul PD-104 [Kao Co., Ltd .; active ingredient 20%] 7.5 g was added and dissolved uniformly. There, 45.5 g of n-butyl acrylate, 45.5 g of 2-ethylhexyl acrylate, 5 g of methyl methacrylate, 1.5 g of N-vinylpyrrolidone, 0.63 g of acrylic acid [active ingredient 80%], methacrylic acid [80% active ingredient] ] 2.5 g and lauryl mercaptan 0.20 g were added and emulsified to obtain 127.18 g of an emulsified liquid (I).

(Production Example 3: Preparation of Emulsion (U))
In a container, 75.00 g of ion-exchanged water and surfactant Aqualon KH-1025 [Daiichi Kogyo Seiyaku Co., Ltd .; active ingredient 25%] 20.00 g and surfactant Latemul PD-104 [manufactured by Kao Corp .; effective Ingredient 20%] 37.50 g was added and dissolved uniformly. There, 227.5 g of n-butyl acrylate, 227.5 g of 2-ethylhexyl acrylate, 25.00 g of methyl methacrylate, 7.50 g of N-vinyl pyrrolidone, 3.13 g of acrylic acid [active ingredient 80%], methacrylic acid [active ingredient 80%] 12.50 g and lauryl mercaptan 0.20 g were added and emulsified to obtain 635.83 g of an emulsion (U).

(Production Example 4: Preparation of emulsion (e))
In a container, 75.00 g of ion-exchanged water and surfactant Aqualon KH-1025 [Daiichi Kogyo Seiyaku Co., Ltd .; active ingredient 25%] 20.00 g and surfactant Latemul PD-104 [manufactured by Kao Corp .; effective Ingredient 20%] 37.50 g was added and dissolved uniformly. There, 227.5 g of n-butyl acrylate, 227.5 g of 2-ethylhexyl acrylate, 25.00 g of methyl methacrylate, 7.50 g of N-vinyl pyrrolidone, 15.63 g of acrylic acid [active ingredient 80%], 0.20 g of lauryl mercaptan Was added and emulsified to obtain 635.83 g of an emulsified liquid (E).

(Production Example 5: Preparation of emulsion (o))
In a container, 75.00 g of ion-exchanged water and surfactant Aqualon KH-1025 [Daiichi Kogyo Seiyaku Co., Ltd .; active ingredient 25%] 20.00 g and surfactant Latemul PD-104 [manufactured by Kao Corp .; effective Ingredient 20%] 37.50 g was added and dissolved uniformly. There, 231.25 g of n-butyl acrylate, 231.25 g of 2-ethylhexyl acrylate, 25.00 g of methyl methacrylate, 3.13 g of acrylic acid [80% active ingredient], 12.50 g of methacrylic acid [80% active ingredient], lauryl Mercaptan (0.20 g) was added and emulsified to obtain 635.83 g of an emulsion (O).

Example 1
<Production of acrylic copolymer emulsion (A)>
In a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, a thermometer, and a dropping funnel, 290 g of ion-exchanged water was added, and the temperature was raised to 60 ° C. while blowing nitrogen. While stirring, a part [3.18 g] of the emulsion (a), 5.00 g of an aqueous ammonium persulfate solution (3% active ingredient), and 5 g of an aqueous sodium hydrogen sulfite solution (3% active ingredient) were added, and the temperature was maintained at 60 ° C. The polymerization was performed in 1 hour.

  Subsequently, 505.48 g of the remaining emulsified liquid (A) and 32 g of an aqueous ammonium persulfate solution (active ingredient 1.25%) were dropped using a separate funnel over 6.4 hours while maintaining the reaction vessel at 60 ° C. Polymerized. After completion of the dropwise addition, the reaction vessel was stirred for 2 hours while maintaining the temperature at 60 ° C. The polymerization rate at this stage was 99%.

  Subsequently, 127.18 g of the emulsified liquid (I) and 8 g of an aqueous ammonium persulfate solution (active ingredient 1.25%) were dropped and polymerized over a period of 1.6 hours using a separate funnel while keeping the reaction vessel at 60 ° C. . After completion of the dropwise addition, the reaction vessel was stirred for 2 hours while maintaining the temperature at 60 ° C. The polymerization rate at this stage was 99%.

  The contents were cooled and then adjusted with aqueous ammonia (10% active ingredient) so that the pH was 7.0. This was filtered through a 200-mesh wire mesh to obtain an acrylic copolymer emulsion (A). Here, the solid content concentration in the obtained acrylic copolymer emulsion (A) was 53%, and the average particle size was 309 nm. Moreover, the weight average molecular weight by GPC measurement of the acrylic copolymer in the acrylic copolymer emulsion (A) was 620,000. Further, as a result of waveform separation of the peak obtained by GPC measurement, the weight average molecular weight based on the first peak is 730,000, and the weight average molecular weight based on the second peak is 200,000. Met. Further, the weight ratio was calculated from the area ratio of the molecular weight distribution based on each peak separated by waveform, and the result was 8: 2.

<Production of water-dispersed acrylic pressure-sensitive adhesive composition (1)>
In the acrylic copolymer emulsion (A) [solid content: 500 g], Surfynol PSA-336 [manufactured by Air Products Japan Co., Ltd .; active ingredient 100%] 2.5 g as a leveling agent, as an antifoaming agent Surfynol DF-110D [manufactured by Air Products Japan Ltd .; active ingredient 100%] 2.5 g, epoxy compound tetrad C [manufactured by Mitsubishi Gas Chemical Co., Ltd.] 0.15 g as a cross-linking agent, emulsion as a tackifying resin Type polymerized rosin ester tackifier resin super ester E-865NT [manufactured by Arakawa Chemical Industries, Ltd .; softening point 160 ° C.] solid content 50 g, emulsion type rosin phenol tackifier resin Tamanol E-200NT [Arakawa Chemical Industries, Ltd. ); Softening point 150 ° C.] Add 50 g of solids and filter through 100 mesh wire mesh Water-dispersible acrylic pressure-sensitive adhesive composition of the present invention (1) was obtained.

(Comparative Example 1)
<Production of acrylic copolymer emulsion (B)>
In a reaction vessel equipped with a stirrer, a reflux condenser, a nitrogen inlet tube, a thermometer, and a dropping funnel, 290 g of ion-exchanged water was added, and the temperature was raised to 60 ° C. while blowing nitrogen. While stirring, a part of the emulsion (3.18 g), 5.00 g of an aqueous ammonium persulfate solution (3% active ingredient) and 5 g of an aqueous sodium hydrogen sulfite solution (3% active ingredient) were added, and the temperature was maintained at 60 ° C. The polymerization was performed in 1 hour. Subsequently, the remaining 632.65 g of the emulsion and 40 g of ammonium persulfate aqueous solution [active ingredient 1.25%] were dropped and polymerized using a separate funnel over 8 hours while maintaining the reaction vessel at 60 ° C. After completion of the dropping, the reaction vessel was stirred for 2 hours while maintaining the temperature at 60 ° C., and then the contents were cooled, and subsequently adjusted with ammonia water (active ingredient 10%) so that the pH became 7.0. This was filtered through a 200-mesh wire mesh to obtain an acrylic copolymer emulsion (B). Here, the solid content concentration in the obtained acrylic copolymer emulsion (B) was 53%, and the average particle size was 315 nm. Moreover, the weight average molecular weight of the acrylic copolymer in the acrylic copolymer emulsion (B) was 720,000.

<Production of water-dispersed acrylic pressure-sensitive adhesive composition (2)>
In the acrylic copolymer emulsion (B) [solid content: 500 g], Surfynol PSA-336 [manufactured by Air Products Japan Co., Ltd .; active ingredient 100%] 2.5 g as a leveling agent, as an antifoaming agent Surfynol DF-110D [manufactured by Air Products Japan Ltd .; active ingredient 100%] 2.5 g, epoxy compound tetrad C [manufactured by Mitsubishi Gas Chemical Co., Ltd.] 0.15 g as a cross-linking agent, emulsion as a tackifying resin Type polymerized rosin ester tackifier resin super ester E-865NT [manufactured by Arakawa Chemical Industries, Ltd .; softening point 160 ° C.] solid content 50 g, emulsion type rosin phenol tackifier resin Tamanol E-200NT [Arakawa Chemical Industries, Ltd. ); Softening point 150 ° C.] Add 50 g of solids and filter through 100 mesh wire mesh Water-dispersible acrylic pressure-sensitive adhesive composition (2) was obtained.

(Comparative Example 2)
<Production of water-dispersed acrylic pressure-sensitive adhesive composition (3)>
An acrylic copolymer emulsion (C) was produced in the same manner as in Comparative Example 1 except that the emulsion (E) was used instead of the emulsion (U) used in Comparative Example 1. Type acrylic pressure-sensitive adhesive composition (3) was obtained. Here, in the obtained acrylic copolymer emulsion (C), the solid content concentration was 53%, and the average particle size was 338 nm. The weight average molecular weight of the acrylic copolymer in the acrylic copolymer emulsion (C) was 730,000.

(Comparative Example 3)
<Production of water-dispersed acrylic pressure-sensitive adhesive composition (4)>
An acrylic copolymer emulsion (D) was produced in the same manner as in Comparative Example 1 except that the emulsion (O) was used instead of the emulsion (U) used in Comparative Example 1, and the aqueous dispersion was dispersed. Type acrylic pressure-sensitive adhesive composition (4) was obtained. Here, the solid content concentration in the obtained acrylic copolymer emulsion (D) was 53%, and the average particle size was 336 nm. Moreover, the weight average molecular weight of the acrylic copolymer in the acrylic copolymer emulsion (D) was 730,000.

[Method for preparing non-woven fabric substrate]
A solution containing 90% Manila hemp, 10% polyester, and 0.5% polyamidoamine / epichlorohydrin resin was made with an inclined short net paper machine to a basis weight of 17 g / m ² and a density of 0.28 g / cm ³ , A nonwoven fabric base material having a tensile strength of 25.3 N / 20 mm in the MD direction and 23.5 N / 20 mm in the TD direction was obtained.
[Method for preparing double-sided adhesive tape]
The water-dispersed acrylic pressure-sensitive adhesive composition was applied onto a 75 μm-thick polyester film that had been peeled off so that the thickness after drying was 65 μm, and dried at 100 ° C. for 5 minutes. The pressure-sensitive adhesive sheet was transferred to both surfaces of the above-mentioned nonwoven fabric substrate, and was laminated with a 90 ° C. hot roll at a pressure of 4 kgf / cm to obtain a double-sided pressure-sensitive adhesive tape. In addition, this double-sided adhesive tape was used for the test after aging at 40 ° C. for 2 days.

  The obtained water-dispersed acrylic pressure-sensitive adhesive composition and pressure-sensitive adhesive tape were evaluated as follows. The obtained results are shown in the table.

[Evaluation method]
(Weight average molecular weight of acrylic copolymer)
About the obtained acrylic copolymer emulsion, GPC measurement was performed under the following conditions, and the weight average molecular weight of the acrylic copolymer in the water-dispersed acrylic pressure-sensitive adhesive composition was measured.
Measuring device: HLC-8220GPC (manufactured by Tosoh Corporation)
GPC column configuration: The following four columns (all manufactured by Tosoh Corporation)
(1) TSK-GEL HXL-H (guard column)
(2) TSK-GEL GMHXL
(3) TSK-GEL GMHXL
(4) TSK-GEL GMHXL
Sample concentration: diluted with tetrahydrofuran to 4 mg / mL Mobile phase solvent: tetrahydrofuran Flow rate: 1.0 mL / min
Injection volume: 100 μL
Column temperature: 40 ° C

(Average particle diameter of acrylic copolymer emulsion particles)
The obtained acrylic copolymer emulsion was measured with a Nikkiso Co., Ltd. Microtrac UPA type particle size distribution measuring device, and the average particle size of the acrylic copolymer emulsion particles in the water-dispersed acrylic pressure-sensitive adhesive composition was measured. The value of the diameter (50% median diameter on a volume basis) was determined.

(Rough surface adhesion evaluation 1 (Removability of double-sided adhesive tape affixed to the rough surface))
The double-sided pressure-sensitive adhesive tape sample was prepared by backing the double-sided pressure-sensitive adhesive tape with ECS urethane foam (5 mm thickness manufactured by Inoac Co., Ltd.) and cutting it into a width of 20 mm × 100 mm. Next, a stainless steel plate was used as an adherend, and one-way reciprocating pressure application was performed with a 2 kg roller in an environment of 23 ° C. and 50%, and the plate was allowed to stand in an environment of 60 ° C. for 10 days. Then, it left still in 23 degreeC * 50% RH environment for 1 hour, and the removability at the time of peeling a double-sided adhesive tape sample at a speed | rate of 25 m / min in the direction of 135 degree | times was evaluated. The re-peelability was evaluated according to the following criteria.
(Double-circle): The adhesive tape residual area by the adhesive residue to a to-be-adhered body, cutting | disconnection of a nonwoven fabric, and peeling of a double-sided adhesive tape from urethane foam is less than 5% of the sticking area.
○: Adhesive residue on the adherend, cutting of the nonwoven fabric, and residual area of the adhesive tape due to peeling of the double-sided adhesive tape from the urethane foam is 5% or more and less than 25% of the applied area.
Δ: Adhesive residue on the adherend, cutting of the nonwoven fabric, and residual area of the adhesive tape due to peeling of the double-sided adhesive tape from the urethane foam is 25% or more and less than 75% of the applied area.
X: The adhesive adhesive remains on the adherend, the non-woven fabric is cut, and the residual area of the adhesive tape due to the peeling of the double-sided adhesive tape from the urethane foam is 75% or more of the sticking area.

(Rough surface adhesion evaluation 2 (Adhesive strength to ECS urethane foam))
The double-sided pressure-sensitive adhesive tape sample was prepared by backing the double-sided pressure-sensitive adhesive tape with a PET film having a thickness of 25 μm and cutting it into a width of 20 mm × 100 mm. Next, ECS urethane foam (5 mm thickness, manufactured by Inoac Co., Ltd.) fixed to a stainless steel plate is used as an adherend, and a one-time reciprocating pressure application is performed with a 2 kg roller in an environment of 5 ° C. for 1 hour in an environment of 5 ° C. I left it alone. Then, the adhesive force when the double-sided pressure-sensitive adhesive tape sample was peeled off at a speed of 300 m / min in the 180 degree direction was measured. In addition, the measurement of adhesive force was implemented based on JIS-Z-0237.

(Adhesive strength evaluation)
The double-sided pressure-sensitive adhesive tape sample was prepared by backing the double-sided pressure-sensitive adhesive tape with a PET film having a thickness of 25 μm and cutting it into a width of 20 mm × 100 mm. Next, a stainless steel plate was used as an adherend, and pressure bonding was performed once and again with a 2 kg roller in an environment of 23 ° C. and 50%, and left for 1 hour in an environment of 23 ° C. and 50%. Then, the adhesive force when the double-sided pressure-sensitive adhesive tape sample was peeled off at a speed of 300 m / min in the 180 degree direction was measured. In addition, the measurement of adhesive force was implemented based on JIS-Z-0237.

  As can be seen from the above table, the pressure-sensitive adhesive tape using the water-dispersed acrylic pressure-sensitive adhesive composition of the present invention in the examples has a good adhesive force and excellent reproducibility even for a highly breathable member having a rough surface. It also had releasability. On the other hand, the pressure-sensitive adhesive tape of the comparative example was poor in removability for a highly breathable member having a rough surface.

It is a conceptual diagram of a titration curve obtained by potentiometric titration with a basic solution of an acrylic copolymer emulsion. It is a conceptual diagram of a differential curve based on a titration curve obtained by potentiometric titration with a basic solution of an acrylic copolymer emulsion. It is a conceptual diagram of a titration curve obtained by potentiometric titration with an acidic solution of an acrylic copolymer emulsion. It is a conceptual diagram of a differential curve based on a titration curve obtained by potentiometric titration with an acidic solution of an acrylic copolymer emulsion.

Claims (8)

A water-dispersed acrylic pressure-sensitive adhesive composition comprising an aqueous medium, an acrylic copolymer and a crosslinking agent , wherein the acrylic copolymer emulsion particles are dispersed in the aqueous medium,
As the acrylic copolymer forming the acrylic copolymer emulsion particles, a high molecular weight acrylic copolymer (a) having a weight average molecular weight of 500,000 to 1,200,000 and a weight average molecular weight of 5,000 to 250,000 A certain low molecular weight acrylic copolymer (b),
The high molecular weight acrylic copolymer (a) comprises 2-ethylhexyl acrylate, (meth) acrylate having a C 4-8 alkyl group other than 2-ethylhexyl acrylate, acrylic acid, methacrylic acid, and a nitrogen-containing vinyl monomer. It is obtained by polymerizing what is contained as a monomer component ,
The low molecular weight acrylic copolymer (b) is obtained by polymerizing a polymer containing 2-ethylhexyl acrylate as a monomer component,
The content ratio of the high molecular weight acrylic copolymer (a) and the low molecular weight acrylic copolymer (b) is represented by the high molecular weight acrylic copolymer (a): the low molecular weight acrylic copolymer (b). The water-dispersed acrylic pressure-sensitive adhesive composition is 100: 3 to 100: 50 by weight ratio. The sum of the high molecular weight of 2-ethylhexyl acrylate monomer component forming the acrylic copolymer (a), and 2-ethylhexyl having an alkyl group of 4-8 carbon atoms other than acrylate content of the (meth) acrylate The content of methacrylic acid and acrylic acid is 0.5 to 10 mass%, and the content of the nitrogen-containing vinyl monomer is 0.15 to 4.5 mass%. Water-dispersed acrylic pressure-sensitive adhesive composition. The ratio of the content of acrylic acid and methacrylic acid in the monomer component forming the high molecular weight acrylic copolymer (a) is 2 or more in molar equivalent ratio represented by (methacrylic acid / acrylic acid). The water-dispersed acrylic pressure-sensitive adhesive composition according to claim 1 or 2. The ratio of the content of 2-ethylhexyl acrylate in the monomer component forming the high molecular weight acrylic copolymer (a) and (meth) acrylate having an alkyl group having 4 to 8 carbon atoms other than 2-ethylhexyl acrylate is The mass ratio represented by (Methyl acrylate having an alkyl group having 4 to 8 carbon atoms other than 2 -ethylhexyl acrylate / 2-ethylhexyl acrylate ) is 9/1 to 2/8. The water-dispersed acrylic pressure-sensitive adhesive composition according to any one of the above. The water-dispersed acrylic pressure-sensitive adhesive composition according to any one of claims 1 to 4 , wherein the low molecular weight acrylic copolymer (b) contains acrylic acid, methacrylic acid, and a nitrogen-containing vinyl monomer as monomer components. Of claim 1-5 wherein the water-dispersible acrylic pressure-sensitive adhesive composition from the crosslinking reaction by removing the aqueous medium so as not to proceed with solids only the time solids of the gel fraction of more than 15 wt% The water-dispersed acrylic pressure-sensitive adhesive composition according to any one of the above. Adhesive tape having a pressure-sensitive adhesive layer obtained by coating the aqueous dispersion type acrylic pressure-sensitive adhesive composition according dried to claim 1-6. The pressure-sensitive adhesive tape according to claim 7 , wherein the pressure-sensitive adhesive layer has a gel fraction of 20 to 45%.

Images