JP2007254721A - Pressure-sensitive adhesive sheet and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pressure-sensitive adhesive sheet comprising a plastic sheet base material and a pressure-sensitive adhesive layer, excellent in water resistance, having the pressure-sensitive adhesive layer which can not be easily whitened and express a large adhesive strength. <P>SOLUTION: The pressure-sensitive adhesive sheet comprises the plastic sheet base material except foams and the pressure-sensitive adhesive layer laminated on at least one surface of the base material. The pressure-sensitive adhesive layer is formed of an emulsion type water-based pressure-sensitive adhesive agent comprising an acrylic polymer as a main component, contains ≤3 wt.% water soluble component and has ≤40 brightness L* after 24 hour immersion at 25°C when the thickness of the pressure-sensitive adhesive layer is 20μm, and the adhesive strength in 180°peeling against a polyethylene plate is ≥6N/25mm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a pressure-sensitive adhesive sheet including a plastic sheet substrate and a pressure-sensitive adhesive layer, and a method for producing the pressure-sensitive adhesive sheet. Specifically, the present invention relates to a pressure-sensitive adhesive sheet that is difficult to whiten even when immersed in water and has excellent whitening resistance and a method for producing the same.

In order to form a pressure sensitive adhesive sheet, a pressure sensitive adhesive is used.
The basic laminated structure of the pressure-sensitive adhesive sheet is (1) a single-sided pressure-sensitive adhesive sheet such as a base sheet / pressure-sensitive adhesive layer / release sheet, or (2) a release sheet / pressure-sensitive adhesive layer / base material. A double-sided pressure-sensitive adhesive sheet such as a sheet / pressure-sensitive adhesive layer / release sheet. In use, the release sheet is peeled off, and the pressure-sensitive adhesive layer is attached to the adherend.

The pressure-sensitive adhesive sheet is used for various applications, and various adhesive strengths are required.
After sticking, the environment in which it is used varies, and it may be placed under high humidity or exposed to cold or hot water. In such a case, water resistance may be required for the pressure-sensitive adhesive layer. For example, when used for application of optical materials, high humidity resistance over a long period of time is required. Therefore, it is required that the pressure-sensitive adhesive layer does not become clouded by the influence of water, that is, does not whiten.

Pressure-sensitive adhesives are broadly classified into solvent-type pressure-sensitive adhesives and water-based emulsion-type pressure-sensitive adhesives, and both are mainly composed of an acrylic polymer.
In general, a solvent-type pressure-sensitive adhesive is preferable to an aqueous emulsion-type pressure-sensitive adhesive for forming a pressure-sensitive adhesive layer having excellent water resistance. However, from the viewpoints of protecting the global environment (suppressing volatile compound emissions), improving the work environment, and effectively using resources, water can be used in place of solvent-type pressure-sensitive adhesives in fields that require high water resistance. There has been a demand for using pressure sensitive adhesives.

  By the way, when a large adhesive force is required (for example, when an adhesive force of 6 N / 25 mm or more is required at the time of 180-degree peeling to a polyethylene plate), a solvent-type pressure-sensitive adhesive containing an adhesion-imparting resin is used. Often used. The adhesion-imparting resin is dissolved in the solvent. Therefore, in the case of a solvent-type acrylic pressure-sensitive adhesive, it is easy to dissolve the adhesion-imparting resin in a solvent solution of an acrylic polymer. Since the acrylic polymer and the adhesion-imparting resin are sufficiently compatible, the dry coating film of the solvent-type acrylic pressure-sensitive adhesive, that is, the pressure-sensitive adhesive layer is generally excellent in transparency.

  On the other hand, the acrylic water-based emulsion-type pressure-sensitive adhesive has an acrylic polymer emulsion as a main component and water as a dispersion medium. However, the adhesion-imparting resin does not dissolve in water. Therefore, it is extremely difficult to obtain an acrylic aqueous emulsion pressure-sensitive adhesive by mixing the adhesion-imparting resin with an acrylic polymer emulsion as it is, and even if obtained, the dispersion stability is extremely poor.

Therefore, various ideas have been made to introduce the adhesion-imparting resin into the acrylic water-based emulsion type pressure-sensitive adhesive.
For example, it has been proposed that an adhesion-imparting resin is pre-emulsified and blended into an acrylic polymer emulsion. This method makes it possible to blend an adhesion-imparting resin, which is mostly solid, into an acrylic polymer emulsion.
However, according to this method, the pressure-sensitive adhesive layer obtained after drying the pressure-sensitive adhesive is not only inferior in transparency, but also the pressure-sensitive adhesive layer becomes more cloudy due to the influence of water. This is because in the process of drying the pressure-sensitive adhesive, the polymer particles derived from the acrylic polymer emulsion and the adhesion-imparting resin are difficult to mix, and the adhesion-imparting resin forms an independent domain and a uniform phase is not formed. Therefore, as a result, it is considered that the pressure-sensitive adhesive layer becomes cloudy and the water resistance is deteriorated.

In the following Patent Documents 1 to 3, an emulsion containing a radically polymerizable unsaturated monomer, an adhesion-imparting resin, a surfactant (preferably a reactive surfactant) and water is prepared in advance, and the emulsion is polymerized. Thus, a method for introducing an adhesion-imparting resin into an emulsion-type pressure-sensitive adhesive has been proposed.
For example, in Example 4 of JP 2000-313865 A (Patent Document 1), 100 parts by weight of a radical polymerizable unsaturated monomer, 5 parts of an adhesion-imparting resin, about 1.6 parts of a reactive surfactant and water are added. A method is described in which an emulsion containing it is obtained and this emulsion is polymerized to obtain an emulsion-type pressure-sensitive adhesive. However, since the surfactant used is a reactive surfactant and the amount thereof is large, the pressure-sensitive adhesive layer obtained from such an emulsion-type pressure-sensitive adhesive has insufficient transparency and water resistance. It is. Furthermore, since the amount of the adhesion-imparting resin is also small, it is impossible to obtain a pressure-sensitive adhesive sheet that can exhibit a large adhesive force of 6 N / 25 mm or more when peeled 180 degrees from the polyethylene plate.

  Examples 1 and 2 of JP 2001-031708 A (Patent Document 2) contain 100 parts by weight of a radical polymerizable unsaturated monomer, 10 parts of an adhesion-imparting resin, 1.5 parts of a reactive surfactant, and water. A method is described in which an emulsion is obtained, and the emulsion is dropped and polymerized in water containing 1.5 parts of a reactive surfactant to obtain an emulsion-type pressure-sensitive adhesive. However, since the surfactant used is a reactive surfactant and the total amount used is large, a pressure-sensitive adhesive layer obtained from such an emulsion-type pressure-sensitive adhesive is not transparent in terms of transparency. It is enough.

Furthermore, Example 1 of JP 2001-348551 A (Patent Document 3) contains 100 parts by weight of a radically polymerizable unsaturated monomer, 15 parts of an adhesion-imparting resin, 2.5 parts of a reactive surfactant, and water. A method for obtaining an emulsion and pressure-sensitive adhesive by polymerizing the emulsion is described. However, since the surfactant used is a reactive surfactant and the amount thereof is large, the pressure-sensitive adhesive layer obtained from such an emulsion-type pressure-sensitive adhesive is still not transparent in terms of transparency. It is enough.
JP 2000-313865 A JP 2001-031708 A JP 2001-348551 A

  The present invention is a pressure-sensitive adhesive sheet comprising a plastic sheet substrate and a pressure-sensitive adhesive layer, having a water-resistant adhesive layer that is excellent in water resistance and hardly whiten even when immersed in water, and is large An object of the present invention is to provide a pressure-sensitive adhesive sheet capable of expressing an adhesive force.

That is, the first invention is a pressure-sensitive adhesive sheet comprising a plastic sheet substrate other than a foam and a pressure-sensitive adhesive layer laminated on at least one surface of the substrate,
The pressure-sensitive adhesive layer is formed from an emulsion-type water-based pressure-sensitive adhesive mainly composed of an acrylic polymer, and the amount of water-soluble components contained in the pressure-sensitive adhesive layer is 3% by weight or less. Yes,
When the thickness of the pressure-sensitive adhesive layer is 20 μm, the lightness L * after being immersed in water at 25 ° C. for 24 hours is 40 or less, and the adhesive strength at the time of 180-degree peeling to the polyethylene plate is 6 N / 25 mm or more,
The present invention relates to a pressure-sensitive adhesive sheet.

  Further, the second invention is a radically polymerizable unsaturated monomer mainly composed of (meth) acrylic acid alkyl ester, wherein the emulsion-type water-based pressure-sensitive adhesive can form a polymer having a glass transition temperature of 0 ° C. or lower. (A) 100 parts by weight, 6-30 parts by weight of an adhesion-imparting resin (B) containing 60% by weight or more of a rosin-based adhesion-imparting resin, and 0.2-1.5 parts by weight of a non-reactive surfactant (C) The pressure-sensitive adhesive sheet according to the first aspect of the invention contains an acrylic polymer-containing composition emulsion obtained by polymerizing a monomer-containing composition emulsion containing a part and water.

The third invention is a pressure-sensitive adhesive sheet comprising a plastic sheet substrate other than a foam and a pressure-sensitive adhesive layer laminated on at least one surface of the substrate,
The pressure-sensitive adhesive layer is formed from an emulsion-type water-based pressure-sensitive adhesive mainly composed of an acrylic polymer, and the amount of water-soluble components contained in the pressure-sensitive adhesive layer is 3% by weight or less. Yes,
The emulsion-type water-based pressure-sensitive adhesive can form a polymer having a glass transition temperature of 0 ° C. or less, 100 parts by weight of a radically polymerizable unsaturated monomer (A) based on (meth) acrylic acid alkyl ester, 6-30 parts by weight of an adhesion-imparting resin (B) containing 60% by weight or more of a rosin-based adhesion-imparting resin, 0.2-1.5 parts by weight of a non-reactive surfactant (C), and water It contains an acrylic polymer-containing composition emulsion obtained by polymerizing a monomer-containing composition emulsion.
The present invention relates to a pressure-sensitive adhesive sheet.

  Furthermore, 4th invention is 2nd or 3rd invention in which the said emulsion type water-pressure-sensitive adhesive contains the crosslinking agent (D) which can react with the functional group in the said acrylic polymer containing composition emulsion. This relates to a pressure-sensitive adhesive sheet.

Furthermore, the fifth invention provides at least one surface of the plastic sheet substrate other than the foam,
100 parts by weight of radically polymerizable unsaturated monomer (A) mainly composed of alkyl (meth) acrylate capable of forming a polymer having a glass transition temperature of 0 ° C. or less, and 60% by weight or more of rosin-based adhesion-imparting resin It is obtained by polymerizing a monomer-containing composition emulsion containing 6 to 30 parts by weight of an adhesion-imparting resin (B), 0.2 to 1.5 parts by weight of a non-reactive surfactant (C), and water. Applying an emulsion-type water-based pressure-sensitive adhesive containing an acrylic polymer-containing composition emulsion, drying, and fusing emulsion particles derived from the acrylic polymer-containing composition emulsion to form a pressure-sensitive adhesive layer;
A pressure-sensitive adhesive sheet manufacturing method comprising:
The amount of water-soluble component contained in the pressure-sensitive adhesive layer is 3% by weight or less,
When the thickness of the pressure-sensitive adhesive layer is 20 μm, the lightness L * after being immersed in water at 25 ° C. for 24 hours is 40 or less, and the adhesive strength at the time of 180-degree peeling to the polyethylene plate is 6 N / 25 mm or more,
The present invention relates to a method for producing a pressure-sensitive adhesive sheet.

  According to the present invention, it is difficult to whiten even when immersed in water. Specifically, when the thickness of the pressure-sensitive adhesive layer is 20 μm, the lightness L * after being immersed in water at 25 ° C. for 24 hours is 40. The following pressure-sensitive adhesive sheet can be provided. Furthermore, this pressure-sensitive adhesive sheet has an excellent adhesive force, and specifically, can exhibit an adhesive force of 6 N / 25 mm or more when peeled by 180 degrees against a polyethylene plate.

The present invention provides a pressure-sensitive adhesive layer in which a pressure-sensitive adhesive layer formed from an emulsion-type water-based pressure-sensitive adhesive mainly composed of an acrylic polymer is laminated on at least one surface of a plastic sheet substrate other than a foam. It is an adhesive sheet.
Examples of the plastic sheet substrate in the present invention (hereinafter sometimes simply referred to as “substrate” or “sheet-like substrate”) include various plastic sheets or various plastic films having a flat shape. However, the base material which is a foam is excluded.
Various base materials can be used alone (single layer), or a plurality of base materials laminated and multilayered. Furthermore, a base material whose surface is peeled can also be used.
Although the thickness of a base material is not specifically limited, Generally, it is preferable that it is about 15-200 micrometers, and it is more preferable that it is about 25-80 micrometers.

  As various plastic sheets (various plastic films), for example, polyvinyl alcohol film, triacetyl cellulose film, polyolefin resin film (polypropylene, polyethylene, polycycloolefin, ethylene-vinyl acetate copolymer, etc.), polyester resin Film (polyethylene terephthalate (hereinafter referred to as “PET”), polybutylene terephthalate, etc.), polycarbonate resin film, polynorbornene resin film, polyarylate resin film, acrylic resin film, polyphenylene sulfide resin Film, polystyrene resin film, vinyl resin film, polyamide resin film, polyimide resin film, epoxy resin film Lum and the like can be used.

When the pressure-sensitive adhesive sheet according to the present invention is used in the optical field, the above-mentioned plastic film is an optical plastic film excellent in transparency. Specifically, when the thickness is 100 μm, the total light transmittance is 80% or more. An optical plastic film is preferable.
As the optical plastic film, a multilayer film can be used in addition to a single layer film.

Examples of the single layer optical film include a polyester film, a polycarbonate film, a triacetate film, and a cycloolefin film.
Examples of the multilayered optical film include a polarizing film, a retardation film, an elliptically polarizing film, an antireflection film, and a brightness enhancement film. As a polarizing film, the thing of the laminated structure which pinched | interposed the both surfaces of the polyvinyl alcohol-type polarizer with the triacetyl cellulose type protective film, for example is mentioned. As a retardation film, the thing of the structure which laminated | stacked the stretched polycarbonate film is mentioned, for example. Examples of the antireflection film include a laminated structure in which a PET film is coated with poly-4-fluoroethylene. Examples of the brightness enhancement film include a laminated structure in which a PET film is coated with diffusible fine particles.

The pressure-sensitive adhesive layer is formed from an emulsion-type water-based pressure-sensitive adhesive (hereinafter sometimes simply referred to as “water-based pressure-sensitive adhesive”), and has excellent water resistance and adhesiveness. is there.
That is, the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive sheet of the present invention is formed from an emulsion-type water-based pressure-sensitive adhesive mainly composed of an acrylic polymer, and the amount of water-soluble component contained is 3 % By weight or less.
In addition, this pressure sensitive adhesive layer
(1) The lightness L * after immersion in water (25 ° C., 24 hours) at a thickness of 20 μm of the pressure-sensitive adhesive layer is 40 or less, and
(2) Adhesive strength at the time of 180 degree peeling with respect to a polyethylene plate is 6 N / 25 mm or more.
It is possible to provide a pressure-sensitive adhesive sheet having the water resistance (1) and the adhesive property (2).

The acrylic polymer that constitutes the emulsion-type water-based pressure-sensitive adhesive is a polymer of a radically polymerizable unsaturated monomer mainly composed of an acrylic monomer by a conventionally known emulsion polymerization method using a surfactant and a polymerization initiator. Can be obtained.
As the radically polymerizable unsaturated monomer, it is preferable that the main component is a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms. This (meth) acrylic acid alkyl ester includes methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, iso-propyl (meth) acrylate, butyl (meth) acrylate, (meth) Linear or branched aliphatic such as iso-butyl acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, decyl (meth) acrylate, dodecyl (meth) acrylate Examples include acrylate esters of alcohol and the corresponding methacrylate esters. The alkyl group of the (meth) acrylic acid alkyl ester used preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and particularly preferably 2-ethylhexyl acrylate as a main component. . These can be used alone or in combination of two or more.
The (meth) acrylic acid alkyl ester is preferably contained in an amount of 70 to 99.9 wt% in a total of 100 wt% of the radical polymerizable unsaturated monomer.

  The radically polymerizable unsaturated monomer preferably contains 0.1 to 20% by weight, preferably 0.2 to 5% by weight of the carboxyl group-containing monomer in a total of 100% by weight of the radically polymerizable unsaturated monomer. It is more preferable to contain 0.2 to 2% by weight. Examples of the carboxyl group-containing monomer include acrylic acid, methacrylic acid, maleic anhydride, maleic acid, itaconic acid, and crotonic acid. When the proportion of the carboxyl group-containing monomer is less than 0.1% by weight, particles that are dispersoids constituting the acrylic polymer emulsion to be formed (hereinafter, particles that are dispersoids are referred to as “emulsion particles”) in water. In this case, the dispersion state is likely to be unstable, and the polymerization tends to be unstable. On the other hand, when the proportion of the carboxyl group-containing monomer exceeds 20% by weight, the adhesion between the emulsion particles is inhibited during drying and aging, and the pressure-sensitive adhesive layer tends to be whitened when immersed in water.

As the radically polymerizable unsaturated monomer, a monomer other than the above can be used as necessary. Examples of such monomers include
Alcoholic hydroxyl group-containing monomers such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and polyethylene glycol (meth) acrylate;
Epoxy group-containing monomers such as glycidyl acrylate and glycidyl methacrylate;
(Meth) acrylamide monomers such as N-hydroxyalkyl (meth) acrylamide, N-alkoxyalkyl (meth) acrylamide, methylolated acrylamide, N- (1,1-dimethyl-3oxobutyl) acrylamide, diacetone acrylamide;
Phosphoric group-containing vinyl monomers and vinyl monomers such as vinyl acetate, styrene and butadiene; and acetoacetoxyethyl methacrylate and alkoxysilyl group-containing monomers;
Etc. These monomers can be used in a proportion of 0 to 10% by weight in a total of 100% by weight of the radically polymerizable unsaturated monomers, and one or more can be used.

  From the above, as the radical polymerizable unsaturated monomer, (meth) acrylic acid alkyl ester (main component) is 70 to 99.9% by weight, carboxyl group-containing monomer is 0.1 to 20% by weight, and other than both It is preferable to use a monomer mixture containing the monomer in a proportion of 0 to 10% by weight.

In general, a pressure-sensitive adhesive layer is formed by applying a pressure-sensitive adhesive in a liquid state to a sheet-like substrate such as a plastic sheet, and then drying to remove a liquid medium contained in the pressure-sensitive adhesive. It is formed by.
In the case of a solvent-type pressure-sensitive adhesive, by removing the liquid medium, the contained polymer component is formed as it is to form a pressure-sensitive adhesive layer. On the other hand, in the case of an emulsion-type water-based pressure-sensitive adhesive, when the liquid medium is removed and through the subsequent aging process, the emulsion particles that are dispersoids approach, adhere to, and fuse together to form a film. Go through the process.

  In the present invention, it is important that the amount of the water-soluble component contained in the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive sheet is 3% by weight or less, and preferably 2.5% by weight or less. When the amount of the water-soluble component exceeds 3% by weight, the approach, adhesion, and fusion between the emulsion particles are inhibited during aging. Therefore, the pressure-sensitive adhesive layer containing the water-soluble component in an excess amount of more than 3% by weight cannot form a dense film structure. As a result, the sparse pressure-sensitive adhesive layer has poor water resistance and whitens when immersed in water at 25 ° C. for 24 hours, and the lightness L * is 40 or less at a pressure-sensitive adhesive layer thickness of 20 μm. A pressure-bonding sheet cannot be provided.

This lightness L * is represented by a numerical value from 0 to 100. L * = 0 means completely pure black, and L * = 100 means completely pure white. Generally, when L * is larger than 40, it is recognized as “white” when viewed by human eyes, so it cannot be used as an optical member that requires high water resistance or for outdoor use exposed to water. .
In the present invention and the following description, this lightness L * is 24 when the pressure-sensitive adhesive sheet formed by laminating a pressure-sensitive adhesive layer having a thickness of 20 μm on a plastic sheet substrate is immersed in water or at 25 ° C. It means the value L * measured after soaking in water for hours. That is, the brightness of a pressure-sensitive adhesive sheet (base material + pressure-sensitive adhesive layer) having a pressure-sensitive adhesive layer having a thickness of 20 μm before and after water immersion treatment (25 ° C., 24 hours). Specifically, it is a value measured by a reflection method using a multi-light source spectrocolorimeter before the water immersion treatment or immediately after the water immersion treatment is taken out.

Therefore, even if the pressure-sensitive adhesive layer constituting the pressure-sensitive adhesive sheet of the present invention is whitened when immersed in water at 25 ° C. for 24 hours, the pressure-sensitive adhesive sheet has a thickness of 20 μm. It is important that L * is 40 or less, and L * is more preferably 35 or less.
Even in the state before being immersed in water, L * of the pressure-sensitive adhesive sheet should not exceed 40 when the thickness of the pressure-sensitive adhesive layer is 20 μm.

The “water-soluble component” contained in the pressure-sensitive adhesive layer is contained in the pressure-sensitive adhesive layer formed by applying and drying the pressure-sensitive adhesive on the substrate and removing the volatile components. Among various components, those that are water-soluble are shown.
For example, a surfactant used in emulsion polymerization for obtaining an acrylic polymer, which itself has no radical polymerizability, is a so-called non-reactive surfactant that is water-soluble;
Neutralizing agents for neutralizing acrylic polymer emulsions that remain in the pressure-sensitive adhesive layer to be formed because they do not exhibit volatility such as ammonia;
In addition, the water-soluble component contained in an antifoamer, a wetting agent, an antiseptic | preservative, a thickener etc. which is mix | blended with a pressure sensitive adhesive is mentioned.
However, as will be described later, reactive surfactants, polymerization initiators, and crosslinking agents used in emulsion polymerization for obtaining acrylic polymers are excluded.

  It is important that the adhesive force of the pressure-sensitive adhesive sheet, that is, the adhesive force of the pressure-sensitive adhesive layer, is 6 N / 25 mm or more, and 7 N / 25 mm or more. Is more preferable, and 8 N / 25 mm or more is more preferable.

The emulsion-type water-based pressure-sensitive adhesive used for obtaining the pressure-sensitive adhesive sheet of the present invention is preferably composed mainly of (meth) acrylic acid alkyl ester capable of forming a polymer having a glass transition temperature of 0 ° C. or lower. 100 parts by weight of the radically polymerizable unsaturated monomer (A), 6-30 parts by weight of an adhesion-imparting resin (B) containing 60% by weight or more of a rosin-based adhesion-imparting resin, and a non-reactive surfactant (C) 0 An acrylic polymer-containing composition emulsion (hereinafter simply referred to as “polymer”) obtained by polymerizing a monomer-containing composition emulsion containing 2 to 1.5 parts by weight and water (hereinafter also simply referred to as “monomer emulsion”). It is also referred to as “emulsion”.).
As the radically polymerizable unsaturated monomer (A) used for the formation of the monomer-containing composition emulsion, it is preferable to use various monomers described above, which can form a polymer having a glass transition temperature of 0 ° C. or lower. Can do.

By the way, in order to form a dense pressure-sensitive adhesive layer, it is important to promote the fusion of emulsion particles during drying and aging that is optionally performed as necessary. Therefore, in order to promote the fusion of the emulsion particles, it is preferable to use interparticle crosslinking.
In order to generate cross-particle crosslinking, it is preferable to use a combination of monomers having a functional group capable of causing a crosslinking reaction as the radical polymerizable unsaturated monomer (A). Among these, it is preferable to use a monomer having a carboxyl group or a hydroxyl group in combination with a monomer having a functional group that can undergo a crosslinking reaction during film formation. These functional groups may have self-crosslinking properties.
Furthermore, cross-linking between particles can be generated also by using a cross-linking agent (D) described later.

  Monomers suitably used for forming interparticle crosslinks include epoxy group-containing monomers such as glycidyl acrylate and glycidyl methacrylate, N-hydroxyalkyl (meth) acrylamide, N-alkoxyalkyl (meth) acrylamide, methylolated acrylamide, dye Examples include monomers such as (meth) acrylamide monomers such as acetone acrylamide, alkoxysilyl group-containing monomers, and acetoacetoxyethyl methacrylate.

When the above-mentioned various radically polymerizable unsaturated monomers (A) are polymerized, the glass transition temperature (Tg) of the obtained polymer is preferably 0 ° C. or lower, more preferably −10 ° C. or lower, It is still more preferable that it is 20 degrees C or less. That is, in order to obtain a desired pressure-sensitive adhesive layer in the present invention, it is preferable to use a radically polymerizable unsaturated monomer whose glass transition temperature is 0 ° C. or less.
In other words, it is preferable to use an acrylic polymer that has a glass transition temperature of 0 ° C. or lower as the main component of the water-based pressure-sensitive adhesive.

As the adhesion-imparting resin (or tackifying resin) (B), a resin containing at least 60% by weight of a rosin resin in a total of 100% by weight of the adhesion-imparting resin (B) is used as the radical polymerizable unsaturated monomer (A). It is preferable to use 6 to 30 parts by weight relative to 100 parts by weight in total, more preferably 8 to 25 parts by weight, and even more preferably 10 to 20 parts by weight.
When the adhesion-imparting resin (B) is less than 6 parts by weight, a sufficient pressure-sensitive adhesive, specifically, a pressure-sensitive adhesive capable of expressing an adhesive force of 6 N / 25 mm or more when peeled 180 degrees against a polyethylene plate It becomes difficult to form a layer.
On the other hand, when the adhesion-imparting resin (B) exceeds 30 parts by weight, the water resistance of the pressure-sensitive adhesive layer decreases, and the lightness L * of the pressure-sensitive adhesive sheet after being immersed in water can be 40 or less. It becomes difficult to form an adhesive layer. In addition, since the amount of the adhesion-imparting resin (B) contained in the pressure-sensitive adhesive layer is too much, the pressure-sensitive adhesive layer becomes too soft and it is difficult to obtain a strong adhesive force.
Here, the adhesion-imparting resin (B) is preferably blended in the monomer emulsion. As a result, emulsion particles in which the adhesion-imparting resin (B) is incorporated into the formed polymer emulsion particles and the acrylic polymer and the adhesion-imparting resin (B) are integrated are obtained. It is possible to form a pressure-sensitive adhesive layer excellent in the above. On the other hand, if the adhesion-imparting resin (B) is added later to the formed polymer emulsion, adhesion is obtained, but a simple mixture of the acrylic polymer emulsion and the emulsion of the adhesion-imparting resin (B). Thus, since the fusion of both emulsion particles is difficult to proceed, the desired water resistance may not be obtained.

Even if the adhesion-imparting resin (B) is used in the range of 6 to 30 parts by weight based on 100 parts by weight of the radical polymerizable unsaturated monomer (A), the rosin-based resin occupying the adhesion-imparting resin (B). If the ratio is less than 60% by weight, the pressure-sensitive adhesive layer is poorly transparent in the first stage before being immersed in water and is not good in water resistance. From the viewpoint of transparency and water resistance, it is preferable to use only a rosin resin, but from the viewpoint of economy, it is preferable to use another adhesion-imparting resin in combination.
Examples of other adhesion-imparting resins that can be used in combination with the rosin resin include terpene resins, aromatic petroleum resins, and aliphatic petroleum resins. It is preferable to use a terpene resin in combination from the viewpoint of adhesive strength.
Examples of the rosin resin include natural rosin, rosin ester, hydrogenated rosin, hydrogenated rosin ester, polymerized rosin, polymerized rosin ester, disproportionated rosin, and disproportionated rosin ester.
Examples of the terpene resin include α-pinene resin, β-pinene resin, terpene phenol resin, hydrogenated terpene phenol resin and the like.
Examples of aromatic petroleum resins include styrene oligomers and α-methylstyrene / styrene copolymers.

The monomer-containing composition emulsion containing the radical-polymerizable unsaturated monomer (A) and the adhesion-imparting resin (B) further includes a non-reactive surfactant (C) instead of a reactive surfactant as an emulsifier. It is important to include.
In other words, as long as the mixed liquid of the radical polymerizable unsaturated monomer (A) and the adhesion-imparting resin (B) is simply emulsified in an aqueous medium, a so-called reactive surfactant having a radical polymerizable functional group can be used as a radical. Any non-reactive surfactant having no polymerizable functional group can be used. However, according to the knowledge of the present inventors, in order to obtain a pressure-sensitive adhesive layer having excellent water resistance, it is preferable to use the non-reactive surfactant (C) for the following reasons.

  That is, when polymerizing a monomer emulsion containing the radical polymerizable unsaturated monomer (A) and the adhesion-imparting resin (B), the reactive surfactant is copolymerized with the radical polymerizable unsaturated monomer (A), It is considered that the reactive surfactant that has lost the degree of freedom is immobilized in the vicinity of the surface of the emulsion particles of the resulting acrylic polymer-containing composition emulsion. The emulsion particles of this polymer emulsion are mainly composed of an acrylic polymer having a relatively high lipophilicity and an adhesion-imparting resin (B). Therefore, when the emulsion-type pressure-sensitive adhesive containing this polymer emulsion is dried and a pressure-sensitive adhesive layer is formed, the hydrophilic part derived from the surfactant immobilized in the vicinity of the surface of the emulsion particles is due to its hydrophilicity. It is presumed that the fusion between the emulsion particles of the polymer emulsion is inhibited without affinity with the lipophilic portion occupying most of the emulsion particles. As a result, it becomes difficult to obtain a pressure-sensitive adhesive layer having excellent water resistance from a pressure-sensitive adhesive containing a polymer emulsion obtained using a reactive surfactant.

On the other hand, when the non-reactive surfactant (C) is used, the surfactant is present in the vicinity of the surface of the emulsion particles of the polymer emulsion, but is not immobilized. It can move through the membrane in the course of the membrane. That is, since the non-reactive surfactant (C) does not inhibit the fusion between the lipophilic emulsion particles, the pressure-sensitive adhesive containing the polymer emulsion obtained by using the non-reactive surfactant (C). A dense and uniform pressure-sensitive adhesive layer can be formed from the agent. Since the pressure-sensitive adhesive layer is dense and uniform, it has excellent water resistance.
In addition, it has been considered that the use of a reactive surfactant as an emulsifier is most effective for improving the water resistance of a pressure-sensitive adhesive layer, without specially exemplifying special patent documents. . Therefore, the finding of the present invention that the use of reactive surfactants may rather adversely affect the water resistance of the pressure sensitive adhesive layer is groundbreaking and extremely important.

As the non-reactive surfactant (C), either ionic or non-ionic surfactants may be used, and each of them can be used alone or in combination.
Nonionic surfactants (C) include nonionic surfactants such as polyoxyalkylene alkyl ethers typified by polyoxyethylene alkyl ethers and polyoxyalkylene polycyclic phenyl ethers and other ether types. Examples thereof include oxyethylene glyceryl ether fatty acid ester, polyoxyethylene hydrogenated castor oil fatty acid ester, polyoxyethylene trimethylolpropane fatty acid ester, amino acid derivative, polyglycerin fatty acid ester, and silicon surfactant.
As the ionic surfactant among the non-reactive surfactant (C), an ionic surfactant such as a sulfate ester obtained by anionizing the nonionic surfactant or a salt thereof can be used.

The amount of the non-reactive surfactant (C) used is preferably 0.2 to 1.5 parts by weight with respect to a total of 100 parts by weight of the radical polymerizable unsaturated monomer (A), 0.5 to More preferably, it is 1 part by weight. When the non-reactive surfactant (C) is less than 0.2 parts by weight, the dispersion stability of the monomer emulsion is poor, and a layer containing the radical polymerizable unsaturated monomer (A) and the adhesion-imparting resin (B) It becomes easy to separate into an aqueous layer. Furthermore, when a monomer emulsion having poor dispersion stability is to be polymerized, the polymerization becomes unstable and a lot of aggregates are generated.
On the other hand, although the surfactant is not immobilized in the vicinity of the surface of the emulsion particles, if the non-reactive surfactant (C) exceeds 1.5 parts by weight, the resulting acrylic polymer-containing composition emulsion When drying, an excessive amount of the non-reactive surfactant (C) inhibits fusion between the emulsion particles, and decreases the transparency of the pressure-sensitive adhesive layer at the stage before being immersed in water, Further, the water resistance tends to be lowered.
In the production process, a part of the surfactant to be used may be previously added to the polymerization container in order to control the emulsion particle size of the polymer emulsion to be produced.

  The monomer emulsion contains a specific amount of the adhesion-imparting resin (B), a specific amount of the non-reactive surfactant (C), and water with respect to 100 parts by weight of the radical polymerizable monomer (A). The amount of water is not particularly limited, but is usually about 40 to 250 parts by weight with respect to 100 parts by weight of the radical polymerizable monomer (A).

In the monomer-containing composition emulsion, the 50% particle diameter of the emulsion particles is preferably 2 μm or less, more preferably 0.5 to 1.7 μm, and 0.8 to 1.5 μm. Further preferred. By controlling the stirring conditions and the like, the particle diameter of the emulsion particles of the monomer emulsion can be controlled.
In the present invention, “50% particle diameter” refers to a median diameter on a volume basis.

From the viewpoint of the transparency of the formed pressure-sensitive adhesive layer before it is immersed in water and the water resistance, the polymer emulsion preferably has a smaller emulsion particle size. On the other hand, if the 50% particle size of the emulsion particles of the monomer emulsion is too small, the stability of the monomer emulsion tends to decrease, and the polymerization stability also tends to decrease.
In general, a relatively large amount of surfactant is required to ensure dispersion stability of smaller emulsion particles. If the amount of the non-reactive surfactant (C) to be used is increased with respect to the radical polymerizable monomer (A) or the adhesion-imparting resin (B), the stability can be improved even with a monomer emulsion having a small particle size. The stability of the polymer emulsion can also be improved. However, when the amount of the non-reactive surfactant (C) is excessive, the transparency of the formed pressure-sensitive adhesive layer is lowered.
On the other hand, when the 50% particle size of the emulsion particles of the monomer emulsion exceeds 2 μm, the pressure-sensitive adhesive layer obtained from the water-based pressure-sensitive adhesive containing a polymer emulsion obtained by polymerizing the emulsion particles is the same as before being immersed in water. Already inferior in transparency at the stage.

When the composition (monomer emulsion) containing the radically polymerizable monomer (A) and the adhesion-imparting resin (B) is polymerized in water, the radically polymerizable monomer (A) and the adhesion-imparting resin (B) in water From the difference in diffusion rate, it is considered that the radical polymerizable monomer (A) preferentially forms a polymer emulsion alone and the adhesion-imparting resin (B) is easily left behind.
When a monomer emulsion that is so large that the 50% particle size of the emulsion particles exceeds 2 μm is polymerized, this tendency becomes stronger, and the acrylic polymer emulsion derived from the radical polymerizable monomer (A) and the adhesion-imparting resin (B) It becomes a state close to a simple mixture with an emulsion. In such a case, since the fusion between the emulsion particles is difficult to proceed, the formed pressure-sensitive adhesive layer is already poorly transparent before being immersed in water, and becomes more white and opaque when immersed in water. Tend to be.

The step of polymerizing the monomer-containing composition emulsion to obtain an acrylic polymer-containing composition emulsion is performed, for example, as follows.
First, the radical polymerizable monomer (A) and the adhesion-imparting resin (B) are sufficiently mixed, and preferably the adhesion-imparting resin (B) is sufficiently dissolved in the radical polymerizable monomer (A) and is not reacted with this mixture. The surfactant (C) and water are added and mixed with stirring. Here, it is preferable to obtain a monomer emulsion having a 50% particle diameter of emulsion particles of 2 μm or less by using a disperser such as an ultrasonic emulsifier or a homomixer as necessary.

Subsequently, a part or all of the obtained monomer emulsion is put into a dropping device,
(1) Put water in a reaction vessel equipped with heating and stirring means, and drop the monomer emulsion into the water to polymerize,
(2) Put water and a part of the monomer emulsion into a reaction vessel equipped with heating and stirring means, and drop the remaining monomer emulsion from the dropping device to polymerize,
(3) Water and a non-reactive surfactant can be placed in a reaction vessel equipped with heating and stirring means, and the monomer emulsion can be dropped into the aqueous surfactant solution for polymerization.
The polymerization reaction for obtaining an acrylic polymer-containing composition emulsion is usually carried out in a temperature range of 40 ° C. to 90 ° C. over 2 to 6 hours.

  In the case of the method exemplified as the above (3), the amount of the non-reactive surfactant that can be blended in the water in the reaction vessel is an amount that does not decrease the transparency of the formed pressure-sensitive adhesive layer. The amount of the non-reactive surfactant used for forming the monomer emulsion is preferably 0.2 to 1.5 parts by weight with respect to 100 parts by weight of the radically polymerizable monomer (A). It is preferable.

In the polymerization, it is preferable to use a polymerization initiator. As the polymerization initiator, either a water-soluble or water-insoluble one can be used, and a water-soluble polymerization initiator is preferably used.
As those generally used, water-soluble pyrolytic polymerization initiators such as persulfates such as potassium persulfate and ammonium persulfate, azobis cation salts or hydroxyl adducts, and redox initiators can be used. . Redox initiators include peroxides such as t-butyl hydroperoxide, benzoyl peroxide, cumene hydroperoxide and a combination of longalit, a reducing agent such as sodium metabisulfite, or sodium persulfate, ammonium persulfate and longalit, A combination with sodium thiosulfate, a combination of hydrogen peroxide and ascorbic acid, or the like can be used.
The amount of the polymerization initiator used is preferably 0.02 to 3 parts by weight and more preferably 0.1 to 1 part by weight with respect to 100 parts by weight of the radical polymerizable unsaturated monomer (A). .

As a method for adding a polymerization initiator, the whole amount may be charged in a reaction vessel and the reaction may be started, or a part thereof may be charged in a reaction vessel and the remainder may be added in portions or added dropwise. Then, the entire amount may be added in portions or added dropwise. In the case of divided addition or dropwise addition, a polymerization initiator may be used in a state of being mixed with the monomer emulsion.
Even if the polymerization initiator is water-soluble at the time of addition, since the initiator itself is incorporated into the polymer at the time of polymerization, it loses its water-solubility. Therefore, in the present invention, the polymerization initiator is excluded from the “water-soluble component contained in the pressure-sensitive adhesive layer”.

  Furthermore, in order to control the molecular weight and molecular weight distribution of the emulsion particles of the acrylic polymer-containing composition emulsion, mercaptan-based, thioglycol-based, and β-mercaptopropionic acid-based alkyl esters can be used as chain transfer agents. . When a chain transfer agent is used, it is used while adjusting the molecular weight of the acrylic polymer to be produced, within the range of 0 to 0.1 parts by weight of addition with respect to 100 parts by weight of the radical polymerizable unsaturated monomer (A). It is preferable.

  In the polymer emulsion obtained after polymerization, the proportion of small particle diameters of 0.05 μm or more and less than 0.4 μm is 60 to 98% by volume in the total 100% of the volume of all dispersed particles, and 0.4 μm or more and 5 μm. The proportion of the following large particle size is preferably 40 to 2% by volume, the proportion of the small particle size is 75 to 90% by volume, and the proportion of the large particle size is 25 to 10%. More preferably, it is volume%. When the proportion of small particle size particles of 0.05 μm or more and less than 0.4 μm is less than 60% by volume, that is, the proportion of large particle size particles of 0.4 μm or more and 5 μm or less is relatively larger than 40% by volume, The transparency of the formed pressure-sensitive adhesive layer tends to be lowered. On the other hand, when the proportion of the small particle size particles exceeds 98% by volume, the filling rate of the particles at the time of drying is lowered, and consequently the fusion property between the emulsion particles and the adhesion to the base material are lowered. There is a tendency that the water resistance and adhesiveness of the pressure-sensitive adhesive layer are reduced.

The emulsion-type water-based pressure-sensitive adhesive containing the acrylic polymer-containing composition emulsion obtained as described above is dried after being applied to a plastic sheet substrate, and in the course of drying or as necessary. In the aging process to be performed, it is preferable to crosslink the emulsion particles with each other.
For this purpose, for example, the following methods (1) and (2) can be preferably employed.
(1) After radical polymerization of the radically polymerizable unsaturated monomer (A), the radicals so that the functional groups derived from the monomer (A) can undergo a crosslinking reaction in the drying process and the aging process performed as necessary. The kind of functional group in the polymerizable unsaturated monomer (A) is selected.
For example, when a monomer having an acetoacetoxy group is used as one of the radically polymerizable unsaturated monomers (A), acrylic polymers constituting the emulsion particles can self-crosslink in the drying process or the like.

(2) The emulsion-type water-based pressure-sensitive adhesive (or polymer emulsion) contains a crosslinking agent (D) that can react with the functional group derived from the monomer (A).
As the crosslinking agent (D), a compound capable of reacting with a functional group derived from the radical polymerizable unsaturated monomer (A) in the polymer emulsion, for example, a hydroxyl group, a carboxyl group, an epoxy group, etc. during the drying process or aging is used. Can do.
Examples of such a crosslinking agent (D) include hydrazide compounds, semicarbazide derivatives, isocyanate compounds, carbodiimide compounds, aziridine compounds, complexable metal compounds, and the like.

The amount of the crosslinking agent (D) used is preferably 10 parts by weight or less with respect to 100 parts by weight in total of the acrylic polymer and the adhesion-imparting resin (B) contained in the polymer emulsion, and is 5 parts by weight or less. More preferably, it is more preferably 3 parts by weight or less.
In the drying process and the aging process, it is considered that the fusion between the emulsion particles and the cross-linking between the particles proceed in competition. Therefore, it is considered that when the interparticle cross-linking proceeds before the fusion between the emulsion particles hardly proceeds, the cross-linked portion becomes a kind of barrier to the fusion between the emulsion particles. Therefore, it is preferable that the amount of the crosslinking agent (D) is not too large.
In addition, even if the crosslinking agent (D) is in a water-soluble state in the pressure-sensitive adhesive before drying, radical polymerization in the crosslinking agent (D) and the polymer emulsion is performed during the drying and aging process. Since the functional group derived from the polymerizable unsaturated monomer (A) reacts, it loses water solubility. Therefore, in the present invention, the crosslinking agent (D) is excluded from the “water-soluble component contained in the pressure-sensitive adhesive layer”.

  The emulsion-type pressure-sensitive adhesive can optionally contain various additives in addition to the acrylic polymer-containing composition emulsion and the crosslinking agent (D) blended as necessary. Specifically, wetting agents (surfacing prevention surfactants, etc.), water-soluble antifoaming agents (low HLB surfactants), neutralizing agents, plasticizers, thickeners, colorants, preservatives, rust prevention And water-soluble components such as agents, and oil-soluble components such as solvents, colorants, and water repellents.

A wetting agent is a surfactant that has a high ability to reduce the surface tension of a water-based pressure-sensitive adhesive, and is usually included when a water-based pressure-sensitive adhesive is applied onto a release sheet that has been subjected to a water-repellent treatment. Is a component to be processed.
As the wetting agent, acetylene glycol surfactants, sodium dioctyl sulfosuccinate, silicon surfactants and the like are generally used.

Since the water-based pressure-sensitive adhesive tends to foam, it is common to add an antifoaming agent as an additive in order to obtain a uniform pressure-sensitive adhesive layer.
Examples of antifoaming agents include compositions containing inorganic oils, surfactants, inorganic compounds such as hydrophobic silica, and the like. Nonionic surfactants with low HLB are mainly used as surfactants.

For the purpose of improving the stability of polymer emulsion, it is preferable to neutralize acidic groups such as carboxyl groups of the emulsion particles with a neutralizing agent.
Examples of the neutralizing agent include aqueous ammonia, sodium hydroxide, and amine.

Furthermore, the water-based pressure-sensitive adhesive contains water, and bacteria and the like are easily propagated and easily rot. Accordingly, it is preferable to add a preservative to the aqueous pressure-sensitive adhesive.
Examples of water-soluble preservatives include isothiazoline derivatives, benzalkonium chloride, benzethonium chloride, sodium hypochlorite, povidone iodine, pyridinethiol derivatives, hydrogen peroxide, ethanol and the like.
These water-soluble various additive components are preferably mixed well into the polymer emulsion using a homomixer or the like.

In the present invention, as described above, the amount of the water-soluble component contained in the obtained pressure-sensitive adhesive layer needs to be 3% by weight or less. Therefore, it is preferable to control the amount of water-soluble additives among the various additives described above.
That is, the water-soluble additive (E) is originally a water-soluble substance and has reactivity with the monomer emulsion or emulsion particles of the polymer emulsion when the monomer emulsion is polymerized or when the aqueous pressure-sensitive adhesive is dried. And defined as non-volatile, the water-soluble additive (E), together with the water-soluble non-reactive surfactant in the polymer emulsion, is combined with the dry weight of the water-based pressure sensitive adhesive, i.e., non-volatile. It is preferably controlled so as to be 3% by weight or less, more preferably 2.5% by weight or less, in the total 100% by weight of the components. When it exceeds 3% by weight, it becomes difficult to obtain a pressure-sensitive adhesive layer having excellent water resistance.
In addition, since the reactive surfactant used in the emulsion polymerization, the polymerization initiator, and the crosslinking agent to be incorporated are incorporated into the structure of the polymer emulsion and lose water solubility, the water-soluble additive (E) Excluded.

  The pressure-sensitive adhesive sheet of the present invention is a plastic sheet other than the pressure-sensitive adhesive layer and the foam after the emulsion-type aqueous pressure-sensitive adhesive is coated on a release sheet and dried to provide a pressure-sensitive adhesive layer. It can be suitably obtained by a method in which a pressure-sensitive adhesive layer is transferred onto a sheet-like substrate, that is, a so-called transfer method. After the pressure-sensitive adhesive layer and the sheet-like base material are bonded together, it is preferable to further age as necessary.

  The method for coating the release sheet with the water-based pressure-sensitive adhesive is not particularly limited, and conventionally known roll coaters such as comma coaters, blade coaters, and gravure coaters, slot die coaters, lip coaters, curtain coaters, and the like. Can depend on coating equipment.

Drying is generally performed at 50 to 120 ° C. for 30 seconds to 5 minutes, and in particular, it is often around tens of seconds at around 100 ° C., but is not limited thereto, and the volatile components in the formed layer are removed. Any condition can be used as long as it can be sufficiently removed.
The dry thickness of the pressure-sensitive adhesive layer to be formed is preferably 5 to 70 μm, and more preferably 10 to 60 μm.

  In the pressure-sensitive adhesive sheet of the present invention, it is important that the emulsion particles forming the pressure-sensitive adhesive layer are sufficiently fused together. Specifically, it is important to fuse the emulsion particles derived from the acrylic polymer-containing composition emulsion until the lightness L * of the pressure-sensitive adhesive sheet after being immersed in water is 40 or less.

The emulsion-type water-based pressure-sensitive adhesive is dried, for example, at around 100 ° C. for several tens of seconds. If the fusion between the emulsion particles is insufficient under such conditions, the pressure-sensitive adhesive sheet after drying (this It is preferred to further age the precursor of a pressure-sensitive adhesive sheet according to the invention. By aging, the fusion of the emulsion particles proceeds, the shape of the polymer emulsion particles that have been in the form of particles collapses to form a uniform phase, and the lightness L * after immersion in water is 40 or less. The pressure-sensitive adhesive sheet of the invention can be obtained.
For example, this aging can be performed at 5 to 70 ° C. for about 1 to 30 days, and more specifically, for example, it is preferably performed at 25 ° C. for 7 days or 40 ° C. for about 3 days.

Since the obtained pressure-sensitive adhesive sheet has good transparency and water resistance, it has high water resistance such as laminated films, labels, tapes, window films, and other general-purpose products such as packaging materials and optical members such as polarizing plates. Useful for a wide range of applications that require adhesive strength.
This pressure-sensitive adhesive sheet includes a plastic sheet substrate and a pressure-sensitive adhesive layer, and may further include a release sheet or any other sheet or layer.

  Specific examples of the present invention will be described below together with comparative examples, but the present invention is not limited to the following examples. In the following examples and comparative examples, “parts” and “%” represent “parts by weight” and “% by weight”, respectively. In addition, the number of ethylene oxide repeating polyethylene oxide is defined as “EO number”.

Example 1
As radical polymerizable monomers, 2-ethylhexyl acrylate: 50.5 parts, butyl acrylate: 40.3 parts, ethyl acrylate: 5 parts, methyl methacrylate: 3 parts, acrylic acid: 1 part, acetoacetoxyethyl methacrylate: 0.2 part, “Super Ester A-125” (made by Arakawa Chemical Co., Ltd.) which is a rosin resin as an adhesion-imparting resin: 10 parts, “YS Resin PX1250” (made by Yasuhara Chemical Co., Ltd.) which is a terpene resin : 5 parts were mixed, and the adhesion-imparting resin was dissolved in the radical polymerizable monomer to obtain a mixture of both.
To this mixture, add 1 part of polyoxyethylene alkyl ether sulfate (alkyl carbon number 12, EO number 18), which is a water-soluble non-reactive surfactant, and 50 parts of deionized water, and stir using a homomixer. A monomer-containing composition emulsion having a 50% particle size of 5 μm was obtained. The theoretically required glass transition temperature of the polymer obtained from the composition of the radical polymerizable monomer is −57.1 ° C.
The obtained monomer-containing composition emulsion was charged into a dropping tank.

In a polymerization vessel equipped with a heating device, a stirrer, a reflux cooling device, a thermometer, a nitrogen introduction tube and a dropping tank, deionized water: 49 parts, polyoxyethylene alkyl ether sulfate having 12 alkyl carbons and 18 EO: 0.1 part was charged and stirred under a nitrogen atmosphere to raise the internal temperature to 78 ° C., and 0.105 part of 5% aqueous potassium persulfate solution was added as a solid content. After 5 minutes, the monomer-containing composition emulsion and a 5% aqueous solution of ammonium persulfate (0.315 parts as a solid content) were dropped from another dropping tank over 4 hours to carry out polymerization.
After completion of the dropping, the temperature is kept at 80 ° C. for 30 minutes, and then the internal temperature is set to 60 to 65 ° C. over 30 minutes, and t-butyl hydroperoxide: 0.1 part and Rongalite: 0.12 part every 10 minutes. It was added in three portions. The reaction was further continued for 1 hour with stirring, followed by neutralization with aqueous ammonia and filtration through a 175 mesh nylon filter cloth to obtain an acrylic polymer-containing composition emulsion containing an acrylic polymer and an adhesion-imparting resin. This emulsion had a non-volatile content of 50.1% and a viscosity of 120 mPa · s.
Here, the viscosity was measured using a BL type viscometer under the condition of # 4 rotor / 60 rpm at 25 ° C. (hereinafter the same). The nonvolatile content was determined from the weight ratio of the weight after drying at 150 ° C. for 20 minutes in an electric oven to the weight before drying.

The obtained polymer emulsion has a small particle component (peak) and a large particle component (peak), each having a maximum value at particle sizes of 0.190 μm and 3.276 μm, and a 50% particle size of 0.188 μm. Met. The emulsion particles contained in the small particle size component (peak) having a maximum value at a particle size of 0.190 μm are small particle size particles having a particle size of 0.05 μm or more and less than 0.4 μm, and the content ratio is obtained. When the total volume of the emulsion particles of the obtained polymer emulsion was 100% by volume, it was 85% by volume. The remaining 15% by volume of the particles were contained in a large particle size component (peak) having a maximum value at 3.276 μm, and were large particle size particles having a particle size of 0.4 μm to 5 μm.
Here, the particle sizes of the monomer emulsion and polymer emulsion were measured using “Microtrac” manufactured by Nikkiso Co., Ltd.

To 100 parts of the above polymer emulsion, antifoaming agent: 0.1 part (50% is a water-soluble component), water-soluble sodium dioctylsulfosuccinate: 0.1 part, preservative: 0.3 part ( 5% is a water-soluble component) and further thickener: 1 part (30% is a water-soluble component) is added and mixed thoroughly with a homomixer to obtain an emulsion-type water-based pressure-sensitive adhesive having a viscosity of 5000 mPa · s. It was.
The obtained emulsion-type water-based pressure-sensitive adhesive was coated on a release sheet whose surface was peeled using a doctor blade, dried at 100 ° C. for 75 seconds, and a pressure-sensitive adhesive layer having a dry film thickness of 20 μm was formed. Obtained. Next, a 50 μm thick PET film was bonded to the pressure sensitive adhesive layer and aged at 40 ° C. for 3 days to obtain a pressure sensitive adhesive sheet. The amount of the water-soluble component contained in the pressure-sensitive adhesive layer was 1.86%.

<Water resistance (whitening resistance) evaluation>
Before water immersion: The pressure sensitive adhesive sheet was peeled off, and L * of the pressure sensitive adhesive sheet was measured by a reflection method using a multi-light source spectrocolorimeter (manufactured by Suga Test Instruments Co., Ltd.).
After water immersion: Remove the release sheet of the pressure-sensitive adhesive sheet, soak in water at 25 ° C., leave it for 24 hours, take it out, and immediately use a multi-light source spectrocolorimeter (manufactured by Suga Test Instruments Co., Ltd.). Then, L * of the pressure-sensitive adhesive sheet was measured by a reflection method.

<Measurement of adhesive strength>
The pressure-sensitive adhesive sheet was cut into a strip having a width of 25 mm, and the release sheet was peeled off, attached to a polyethylene plate, and reciprocated once with a 2 kg roll to obtain a measurement sample. The obtained measurement sample was left in an atmosphere at 23 ° C. for 24 hours, and then the adhesive strength when peeled in the direction of 180 ° at a speed of 300 mm / min in the atmosphere at 23 ° C. was measured.

(Example 2)
In Example 1, the same experiment as in Example 1 was performed except that the aging condition was changed to 25 ° C./7 days.

(Example 3)
Polymerization was carried out in the same manner as in Example 1 except that the 50% particle size of the monomer emulsion was changed to 1.2 μm to obtain a polymer emulsion. The obtained polymer emulsion has a small particle component (peak) and a large particle component (peak), each having a maximum value at particle sizes of 0.203 μm and 1.244 μm, and a 50% particle size of 0.182 μm. Met.
The emulsion particles contained in the small particle size component (peak) having a maximum value at a particle size of 0.203 μm are small particle size particles having a particle size of 0.05 μm or more and less than 0.4 μm, and the content ratio is obtained. When the total volume of the emulsion particles of the obtained polymer emulsion was 100% by volume, it was 88% by volume. The remaining 12% by volume of particles were contained in a large particle size component (peak) having a maximum value at 1.244 μm, and were large particle size particles having a particle size of 0.4 μm or more and 5 μm or less.
Using the obtained polymer emulsion, the same experiment as in Example 1 was performed.

Example 4
Adhesion-imparting resin other than rosin resin: “Superester A-125” (Arakawa Chemical Co., Ltd.): 5 parts, terpene resin: “YS Resin PX1250” (Yasuhara Chemical Co., Ltd.): 10 parts Was a monomer emulsion having a 50% particle size of 1.2 μm in the same manner as in Example 1, and was similarly polymerized and filtered to obtain a polymer emulsion having a nonvolatile content of 50.3% and a viscosity of 120 mPa · s. Thereafter, the same experiment as in Example 1 was performed.

(Comparative Example 1)
In Example 1, the same experiment as in Example 1 was performed except that aging was not performed.

(Comparative Example 2)
To 100 parts of the polymer emulsion obtained in Example 1, 0.1 part of antifoaming agent (50% is a water-soluble component), 1 part of sodium dioctylsulfosuccinate, which is water-soluble as a wetting agent, preservative: 0. 3 parts (5% is a water-soluble component) was added, and further thickener: 1 part (30% was a water-soluble component) was added to obtain an emulsion-type water-based pressure-sensitive adhesive.
Thereafter, the same experiment as in Example 1 was performed.

(Comparative Example 3)
As radical polymerizable monomers, 2-ethylhexyl acrylate: 50.5 parts, butyl acrylate: 40.3 parts, ethyl acrylate: 5 parts, methyl methacrylate: 3 parts, acrylic acid: 1 part, acetoacetoxyethyl methacrylate: 0.2 part, “Super Ester A-125” (made by Arakawa Chemical Co., Ltd.) which is a rosin resin as an adhesion-imparting resin: 10 parts, “YS Resin PX1250” (made by Yasuhara Chemical Co., Ltd.) which is a terpene resin : 5 parts were mixed and dissolved to obtain a mixture of both. To this mixture, 1 part of ammonium salt of polyoxyethylene-1- (allyloxymethyl) alkyl ether sulfate, which is a reactive surfactant, and 50 parts of deionized water are added and stirred with a homomixer to give 50% A monomer emulsion having a particle size of 5 μm was obtained.
The obtained monomer emulsion was charged into a dropping tank.

  In a polymerization vessel equipped with a heating device, a stirrer, a reflux cooling device, a thermometer, a nitrogen introduction tube and a dropping tank, deionized water: 49 parts, polyoxyethylene alkyl ether sulfate having 12 alkyl carbons and 18 EOs: 0 .1 part was charged and stirred under a nitrogen atmosphere to raise the internal temperature to 78 ° C., and 0.105 part of 5% aqueous potassium persulfate solution was added as a solid content. After 5 minutes, the monomer emulsion and a 5% aqueous solution of ammonium persulfate (0.315 parts as a solid content) were dropped from another dropping tank over 4 hours to perform polymerization. After completion of dropping, the temperature is kept at 80 ° C. for 30 minutes, and then the internal temperature is set to 60 to 65 ° C. over 30 minutes, and t-butyl hydroperoxide: 0.1 part and Rongalite: 0.12 part are added every 10 minutes. Added in batches. Further, the mixture is reacted for 1 hour with stirring, neutralized with aqueous ammonia, filtered through a 175 mesh nylon filter cloth, and contains an acrylic polymer having a glass transition temperature (calculated value) of -57.1 ° C. An emulsion was obtained. This polymer emulsion had a non-volatile content of 50.1% and a viscosity of 120 mPa · s.

Thickener: 1 part (30% is a water-soluble component) was added to 100 parts of the resulting polymer emulsion to increase the viscosity to 5000 mPa · s to obtain an emulsion-type water-based pressure-sensitive adhesive. The pressure-sensitive adhesive was prepared using a homomixer.
Thereafter, the same experiment as in Example 1 was performed. The amount of water-soluble component contained in the pressure-sensitive adhesive layer was 0.6%.

(Comparative Example 4)
As the adhesion-imparting resin, “super ester A-125” (made by Arakawa Chemical Co., Ltd.) which is a rosin resin: 3.3 parts, “YS resin PX1250” (made by Yasuhara Chemical Co., Ltd.) which is a terpene resin: 1 .7 parts, except that the amount of polyoxyethylene alkyl ether sulfate having 12 carbon atoms and 18 EO number which is a water-soluble non-reactive surfactant used in Example 1 was changed to 1.5 parts. The same experiment as in Example 1 was performed.

(Comparative Example 5)
Instead of polyoxyethylene alkyl ether sulfate having 12 carbon atoms and 18 EO, which is a non-reactive surfactant used in Comparative Example 4, polyoxyethylene-1- (allyloxy), which is a reactive surfactant, is used. The same experiment as in Comparative Example 4 was performed except that an ammonium salt of methyl) alkyl ether sulfate was used.

(Comparative Example 6)
Adhesion-imparting resin is rosin resin "Super Ester A-125" (Arakawa Chemical Co., Ltd.): 25 parts, terpene resin "YS Resin PX1250" (Yasuhara Chemical Co., Ltd.): 15 parts The same experiment as in Example 1 was performed except that the change was made.

(Comparative Example 7)
The non-reactive surfactant used in Example 1 was prepared by using 15 parts of “Superester A-125” (produced by Arakawa Chemical Co., Ltd.), which is a rosin resin, without using a terpene resin. Instead of polyoxyethylene alkyl ether sulfate having 12 alkyl carbon atoms and 18 EO atoms, a reactive surfactant, polyoxyethylene-1- (allyloxymethyl) alkyl ether sulfate ammonium salt is 2.5. The same experiment as in Example 1 was performed except that the part was changed to use part.

(Comparative Example 8)
A mixture of a radical polymerizable monomer similar to that in Example 1 and a water-soluble non-reactive surfactant, an alkyl carbon number 12 and an EO number 18 polyoxyethylene alkyl, containing no adhesion-imparting resin in the monomer emulsion Ether sulfate: 1 part of a monomer-containing composition emulsion having a 50% particle size of 1.2 μm was obtained. Thereafter, in the same manner as in Example 1, a polymer emulsion having a non-volatile content of 50.2% and a viscosity of 110 mPa · s and containing no adhesion-imparting resin was obtained.
The particle size distribution of the obtained polymer emulsion was 100% by volume of particles contained in a peak having a maximum value at a particle size of 0.180 μm, and the particle size was 0.05 μm or more and less than 0.4 μm. The 50% particle size of the polymer emulsion was 0.185 μm.
Subsequently, 15 parts of rosin-based adhesion-imparting resin having an emulsified softening point of 150 ° C. and an average particle size of 0.52 μm was added to and mixed with 100 parts of the solid content of the obtained polymer emulsion. After mixing, the particle size distribution was determined in the same manner as in Example 1.
Thereafter, the same experiment as in Example 1 was performed on the basis of 100 parts of a mixture of a polymer emulsion containing no adhesion-imparting resin and an adhesion-imparting resin emulsion.

  The results obtained are shown in Table 1.

Claims (5)

A pressure-sensitive adhesive sheet comprising a plastic sheet substrate other than a foam and a pressure-sensitive adhesive layer laminated on at least one surface of the substrate,
The pressure-sensitive adhesive layer is formed from an emulsion-type water-based pressure-sensitive adhesive mainly composed of an acrylic polymer, and the amount of water-soluble components contained in the pressure-sensitive adhesive layer is 3% by weight or less. Yes,
When the thickness of the pressure-sensitive adhesive layer is 20 μm, the lightness L * after being immersed in water at 25 ° C. for 24 hours is 40 or less, and the adhesive strength at the time of 180-degree peeling to the polyethylene plate is 6 N / 25 mm or more,
A pressure-sensitive adhesive sheet.   The emulsion-type water-based pressure-sensitive adhesive can form a polymer having a glass transition temperature of 0 ° C. or less, 100 parts by weight of a radically polymerizable unsaturated monomer (A) based on (meth) acrylic acid alkyl ester, 6-30 parts by weight of an adhesion-imparting resin (B) containing 60% by weight or more of a rosin-based adhesion-imparting resin, 0.2-1.5 parts by weight of a non-reactive surfactant (C), and water The pressure-sensitive adhesive sheet according to claim 1, comprising an acrylic polymer-containing composition emulsion obtained by polymerizing the monomer-containing composition emulsion. A pressure-sensitive adhesive sheet comprising a plastic sheet substrate other than a foam and a pressure-sensitive adhesive layer laminated on at least one surface of the substrate,
The pressure-sensitive adhesive layer is formed from an emulsion-type water-based pressure-sensitive adhesive mainly composed of an acrylic polymer, and the amount of water-soluble components contained in the pressure-sensitive adhesive layer is 3% by weight or less. Yes,
The emulsion-type water-based pressure-sensitive adhesive can form a polymer having a glass transition temperature of 0 ° C. or less, 100 parts by weight of a radically polymerizable unsaturated monomer (A) based on (meth) acrylic acid alkyl ester, 6-30 parts by weight of an adhesion-imparting resin (B) containing 60% by weight or more of a rosin-based adhesion-imparting resin, 0.2-1.5 parts by weight of a non-reactive surfactant (C), and water It contains an acrylic polymer-containing composition emulsion obtained by polymerizing a monomer-containing composition emulsion.
A pressure-sensitive adhesive sheet.   The pressure-sensitive adhesive sheet according to claim 2 or 3, wherein the emulsion-type water-based pressure-sensitive adhesive contains a crosslinking agent (D) capable of reacting with a functional group in the acrylic polymer-containing composition emulsion. On at least one surface of the plastic sheet substrate other than the foam,
100 parts by weight of radically polymerizable unsaturated monomer (A) mainly composed of alkyl (meth) acrylate capable of forming a polymer having a glass transition temperature of 0 ° C. or less, and 60% by weight or more of rosin-based adhesion-imparting resin It is obtained by polymerizing a monomer-containing composition emulsion containing 6 to 30 parts by weight of an adhesion-imparting resin (B), 0.2 to 1.5 parts by weight of a non-reactive surfactant (C), and water. Applying an emulsion-type water-based pressure-sensitive adhesive containing an acrylic polymer-containing composition emulsion, drying, and fusing emulsion particles derived from the acrylic polymer-containing composition emulsion to form a pressure-sensitive adhesive layer;
A pressure-sensitive adhesive sheet manufacturing method comprising:
The amount of water-soluble component contained in the pressure-sensitive adhesive layer is 3% by weight or less,
When the thickness of the pressure-sensitive adhesive layer is 20 μm, the lightness L * after being immersed in water at 25 ° C. for 24 hours is 40 or less, and the adhesive strength at the time of 180-degree peeling to the polyethylene plate is 6 N / 25 mm or more,
A method for producing a pressure-sensitive adhesive sheet.