JP2007197694A - Emulsion type adhesive and adhesive sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an adhesive sheet taking a plastic or paper as a substrate, easily peeling off from bonded materials at directly after the pasting with the various bonded materials but showing a strong bonding property after passing a suitable time through, and an emulsion type adhesive used preferably for forming the adhesive layer of such the adhesive sheet. <P>SOLUTION: This emulsion type adhesive is provided by containing a polymer emulsion obtained by performing a radical polymerization of a radically polymerizable unsaturated monomer forming a polymer having ≤0°C glass transition point in the presence of a surfactant in water, containing polymer emulsion having ≥70 wt.% tetrahydrofuran extraction rate of the coated film directly after its drying and 200,000 to 600,000 weight-average molecular weight of soluble portion, and inorganic particles (A) and/or already cross-linked organic particles (B) having ≥99% gel fraction, and having 0.5 to 15 Pa s viscosity. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an emulsion-type pressure-sensitive adhesive and a pressure-sensitive adhesive sheet using the emulsion-type pressure-sensitive adhesive. Specifically, in a pressure-sensitive adhesive sheet based on plastic or paper, a pressure-sensitive adhesive sheet that can be easily peeled off from the adherend immediately after being bonded to various adherends, and exhibits strong adhesiveness after an appropriate time has elapsed, and The present invention relates to an emulsion-type pressure-sensitive adhesive that can be preferably used for forming a pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet.

Various flat panel displays (FPDs) have been used as display devices in various fields. For example, FPDs are not only used indoors, including personal computer displays and liquid crystal televisions, but are also used in vehicles such as car navigation displays. Examples of these FPDs include a liquid crystal display (LCD), a plasma display (PDP), a rear projection display (RPJ), an EL display, and a light emitting diode display.
In these display devices, an antireflection film for preventing reflection from an external light source, a protective film (protective film) for preventing scratches on the surface of the display device, and the like are used.
Further, the FPD is not only used as a display device, but may be used as an input device by providing a touch panel function on the surface thereof. A protective film, an antireflection film, an ITO vapor deposition resin film, and the like are also used for this touch panel.
Further, the LCD of the FPD has a polarizing film or a retardation film laminated on a glass member for a liquid crystal cell.

Various films used for the display device are used by being adhered to an adherend with an adhesive. Since it is used for a display device, the pressure-sensitive adhesive is required to be excellent in transparency. Accordingly, a solvent-type pressure-sensitive adhesive mainly composed of an acrylic resin having excellent transparency has been suitably used.
By the way, among the various films described above, the polarizing film generally has a three-layer structure in which both surfaces of a polarizer mainly composed of polyvinyl alcohol are sandwiched between triacetyl cellulose protective films. Both the polarizer and the triacetylcellulose-based protective film containing polyvinyl alcohol as a main component remarkably expand and contract due to heat change and humidity change. As a result, the polarizing film also undergoes significant dimensional changes due to heat changes and humidity changes.
Therefore, the pressure-sensitive adhesive for sticking the polarizing film to the glass member for the liquid crystal cell resists the dimensional change of the polarizing film, and the polarizing film does not float or peel from the glass member for the liquid crystal cell. Toughness is required to keep the sticking state.
Moreover, after a polarizing film is affixed on the glass member for liquid crystal cells, the presence or absence of air at the affixing interface and the presence or absence of dust at the affixing interface are inspected. And when there is air and dust, a polarizing film etc. are peeled off from a glass member, and a new polarizing film etc. are stuck again. Therefore, when peeling a polarizing film, it is calculated | required not to leave an adhesive on a glass member.

In recent years, from the viewpoint of protecting the global environment (suppressing the emission of volatile organic compounds), improving the working environment, and effectively using resources, the use of water-based emulsion adhesives has been studied as an alternative to solvent-based adhesives.
However, when compared with the solvent type, the emulsion type is a polymer in the form of particles in the first place, so when a crosslinking reaction is performed in the presence of a crosslinking agent, a polymer or oligomer component having a low molecular weight contacts the crosslinking agent. It is difficult to form and remains as it is without contributing to crosslinking. Therefore, the adhesive strength is generally high immediately after being attached to the adherend as an adhesive sheet (initial stage), and as described above, no adhesive is left on the glass member, and the removability is poor. It was.

Various ideas have been made and proposed to improve these. For example, in JP-A-2000-281989 (Patent Document 1), JP-A-2004-203997 (Patent Document 2), and JP-A-2005-179435 (Patent Document 3), a sticky note or a cardboard surface tack sheet is assumed. Thus, a pressure-sensitive adhesive that can be re-peeled is disclosed so that no glue remains on the adherend immediately after being attached to a flat surface or an uneven surface and after a lapse of time. However, these satisfy the requirement for FPD in that the adhesive strength is low in the initial stage, but they do not meet the requirement that a strong adhesive strength after the pasting is required. Thus, it has been difficult to use an emulsion-type pressure-sensitive adhesive for FPD.
JP 2000-281989 A JP 2004-203997 A JP 2005-179435 A

  The present invention relates to a pressure-sensitive adhesive sheet made of plastic or paper as a base material, which can be easily peeled off from an adherend immediately after being bonded to various adherends and exhibits strong adhesiveness after an appropriate time. An object of the present invention is to provide an emulsion-type pressure-sensitive adhesive that can be preferably used for forming a sheet and a pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet.

In order to solve the above-mentioned problems, the present inventor has intensively studied to arrive at the present invention.
That is, the first invention comprises a radically polymerizable unsaturated monomer capable of forming a polymer having a glass transition temperature of 0 ° C. or lower in water in the presence of a surfactant, and a coating film immediately after drying. A polymer emulsion having a tetrahydrofuran extraction ratio of 70% by weight or more and a weight-average molecular weight of soluble component of 200,000 to 600,000,
Inorganic particles (A) and / or pre-crosslinked organic particles (B) having a gel fraction of 99% or more,
The present invention relates to an emulsion-type pressure-sensitive adhesive having a viscosity of 0.5 to 15 Pa · s.

  In the second invention, the inorganic particles (A) and the crosslinked organic particles (B) having a gel fraction of 99% or more have an average particle diameter of 0.01 to 50 μm and a true specific gravity of 0.9 to 6. The total amount of (A) and (B) is 0.1 to 100 parts by weight with respect to 100 parts by weight of the dry weight of the polymer emulsion.

  According to a third aspect of the invention, the tetrahydrofuran extraction rate after the dried coating film of the polymer emulsion is allowed to stand at 50 to 70 ° C. for one week is 60% by weight or more. The present invention relates to an emulsion type adhesive.

  In addition, in the fourth invention, 0 to 50% by weight of a radically polymerizable reactive surfactant and 50 to 50% of a non-reactive surfactant having no radical polymerizability in a total of 100% by weight of the surfactant. The emulsion-type pressure-sensitive adhesive according to any one of the first to third inventions, characterized by containing 100% by weight.

Further, in the fifth invention, the polymer emulsion contains a radical polymerizable unsaturated monomer capable of forming a polymer having a glass transition temperature of 0 ° C. or lower, a surfactant and water, and has an average particle size of 0.5. A monomer emulsion of ~ 2 μm,
While adding to a surfactant aqueous solution or water containing water and a surfactant,
The present invention relates to an emulsion-type pressure-sensitive adhesive according to any one of the first to fourth inventions, characterized by radical polymerization.

  The sixth invention relates to the emulsion-type pressure-sensitive adhesive according to the fifth invention, wherein the monomer emulsion further contains a tackifying resin.

  Further, according to a seventh invention, an adhesive layer formed from the emulsion-type adhesive according to any one of the first to sixth inventions is provided on at least one surface of the sheet-like substrate excluding the foamed substrate. It is an adhesive sheet, and the ratio of the 180 degree peeling force after 20 minutes and 24 hours after sticking to the adherend is (peeling force after 20 minutes) / (peeling force after 24 hours) = 0.2-0. It is related with the adhesive sheet characterized by being 6.

  Furthermore, an eighth invention relates to the pressure-sensitive adhesive sheet according to the seventh invention, wherein the sheet-like substrate is an optical plastic film.

  According to the present invention, a pressure-sensitive adhesive sheet based on plastic or paper can be easily peeled off from an adherend immediately after being bonded to various adherends, and exhibits strong adhesiveness after an appropriate time. It has become possible to provide an emulsion-type pressure-sensitive adhesive that can be preferably used for forming a sheet and a pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet.

  The radical polymerizable unsaturated monomer used for forming the polymer emulsion of the present invention is mainly composed of a (meth) acrylic acid alkyl ester having an alkyl group having 1 to 14 carbon atoms, and such (meta) ) Alkyl acrylate esters include methyl acrylate, ethyl acrylate, propyl acrylate, iso-propyl acrylate, butyl acrylate, iso-butyl acrylate, hexyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, acrylic Examples thereof include acrylic acid esters of linear or branched aliphatic alcohols such as acid decyl and dodecyl acrylate, and corresponding methacrylic acid esters. Preferably, the (meth) acrylic acid alkyl ester used has an alkyl group having 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and is mainly composed of n-butyl acrylate. Further preferred. The (meth) acrylic acid alkyl ester is contained in an amount of 70 to 99.9% by weight in a total of 100% by weight of the radical polymerizable unsaturated monomer, and is contained in one kind or two or more kinds.

  Further, as the radical polymerizable unsaturated monomer used in the present invention, it is preferable to contain a carboxyl group-containing monomer in an amount of 0.1 to 20% by weight in a total of 100% by weight of the radical polymerizable unsaturated monomer, The content is more preferably 0.2 to 5% by weight, and further preferably 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, the formed emulsion particles become unstable. On the other hand, when the proportion exceeds 20% by weight, the water resistance of the resulting adhesive decreases or the release sheet Causes repelling above.

  In addition, as the radical polymerizable unsaturated monomer used in the present invention, a monomer other than the above can be used as necessary. Examples of such a monomer include (meth) acrylic acid. Alcoholic hydroxyl group-containing monomers such as 2-hydroxyethyl, 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, polyethylene glycol acrylate, vinyl group-containing vinyl monomers, vinyl acetate, styrene , Vinyl monomers such as butadiene, epoxy group-containing monomers such as glycidyl acrylate and glycidyl methacrylate, N- (1,1-dimethyl-3-oxobutyl) acrylamide, N-hydroxyalkyl (meth) acrylamide, N-alkoxy (Meth) acyl such as alkyl (meth) acrylamide and methylol acrylamide Examples include a ruamide monomer, an alkoxysilyl group-containing monomer, and acetoacetoxyethyl methacrylate. These can be used in a proportion of 0 to 10% by weight in a total of 100% by weight of the radical polymerizable unsaturated monomer. 1 type (s) or 2 or more types can be used.

The glass transition temperature (Tg) of the polymer obtained by polymerizing the radical polymerizable unsaturated monomer of the present invention is important to be 0 ° C. or lower, and preferably −10 ° C. or lower. When Tg exceeds 0 ° C., it is easy to cause inconvenience that adhesiveness to various adherends cannot be secured.
The Tg of a polymer obtained by polymerizing a radically polymerizable unsaturated monomer can be easily calculated by a conventionally known theoretical formula, for example, the FOX formula.

The present invention relates to a pressure-sensitive adhesive that exhibits strong adhesion after 24 hours after being bonded to various adherends. Tetrahydrofuran of a coating film immediately after drying obtained from a polymer emulsion constituting the pressure-sensitive adhesive It is important that the extraction rate into the water and the weight average molecular weight of the soluble component are in specific ranges.
In the present invention, the tetrahydrofuran (hereinafter abbreviated as “THF”) extraction rate of the coating immediately after drying is applied to a PET film so that the dry film thickness is about 20 g / m ² . The composition of the dried film / PET film obtained by drying at 25 ° C. for 24 hours was wrapped in a 200 mesh stainless steel net, and after being immersed in THF at 25 ° C. for 2 days, the weight of the component eluted into THF was calculated as follows: Divided by the weight of the dried film before immersion.
Moreover, the weight average molecular weight (Mw) of the soluble part in THF measures the component eluted in the said THF by the gel permeation chromatography (GPC) of polystyrene conversion.
In the present invention, it is extremely important that the coating film immediately after drying obtained from the polymer emulsion has a THF extraction rate of 70% by weight or more and the weight average molecular weight of the soluble component is in the range of 200,000 to 600,000. It is.
When the THF extraction rate is less than 70% by weight, the fluidity of the pressure-sensitive adhesive layer becomes low, and the adhesive strength after the pressure-sensitive adhesive sheet is bonded to the adherend and allowed to elapse for 24 hours is not preferable.
Furthermore, if the THF-soluble component has a weight average molecular weight of less than 200,000, the cohesive strength of the polymer cannot be obtained, and thus the adhesive strength cannot be ensured. On the other hand, when it exceeds 600,000, the adhesion to the adherend is lowered, which is not preferable.

Moreover, in order to improve the heat-resistant aging stability of an adhesive sheet, the THF extraction rate of the coating film after leaving the dried coating film obtained from the polymer emulsion in a 50-70 degreeC environment for one week is 60 weight%. % Or more is preferable.
In general, in a polymer emulsion for a pressure-sensitive adhesive, a pressure-sensitive adhesive layer is formed by applying a pressure-sensitive adhesive composition containing the emulsion onto a substrate and drying to remove the solvent.
In the case of a crosslinkable polymer emulsion, a functional group for causing interparticle crosslinking is generally introduced into the resin component constituting the polymer emulsion, and a crosslinking reaction occurs during the drying. . However, usually, the crosslinking reaction is not completed at the time of drying, and functional groups that contribute to crosslinking remain. Even after the pressure-sensitive adhesive layer is formed, the cross-linking reaction further proceeds with time, particularly with heat. This causes a change in the molecular weight of the resin and the like, causing the adverse effect that the physical properties of the adhesive change immediately after drying and after aging.
The pressure-sensitive adhesive sheet is often used after a long time after production, and the temporal stability of the pressure-sensitive adhesive sheet is important.
In order to obtain a strong adhesive force after 24 hours, the pressure-sensitive adhesive sheet was affixed to the adherend, and the THF extraction rate of the polymer emulsion coating film after drying for 1 week in an environment of 50 to 70 ° C. was It is preferably 60% by weight or more. If it is less than 60% by weight, the fluidity of the polymer is lowered, so that there is a problem that a strong adhesive force cannot be obtained.

The surfactant used in the present invention is not particularly limited as long as it has a function of emulsifying a radically polymerizable unsaturated monomer in an aqueous medium, and is a reactive surfactant having a polymerization property, polymerization. Non-reactive surfactants that do not have the property are used alone or in combination of several kinds. These may be ionic or nonionic. Non-reactive surfactants include ether types such as polyoxyethylene alkyl ether, polyoxyalkylene alkyl ether, polyoxyalkylene polycyclic phenyl ether, ester type, ether-ester type, polyoxyethylene glyceryl ether fatty acid ester Nonionic surfactants such as polyoxyethylene hydrogenated castor oil fatty acid ester, polyoxyethylene trimethylolpropane fatty acid ester, amino acid derivative, polyglycerin fatty acid ester, and silicon-based surfactant. Ionic surfactant sulfates and salts thereof can also be used.
The reactive surfactant is one that can be copolymerized with a radically polymerizable unsaturated monomer, such as polyoxyalkylene alkenyl ether, ammonium salt or sodium salt of polyoxyalkylene alkenyl ether sulfate, polyoxyethylene- Examples include 1- (allyloxymethyl) alkyl ether, ammonium salt or sodium salt of polyoxyethylene-1- (allyloxymethyl) alkyl ether sulfate.
As such commercial products, “Adekaria Soap SE-10N” manufactured by Asahi Denka Kogyo Co., Ltd., “Aqualon HS-10, HS-20” manufactured by Daiichi Kogyo Seiyaku Co., Ltd. Examples include “AQUALON KH-10, KH-20” manufactured by Pharmaceutical Co., Ltd., “ADEKA rear soap SR-10N” manufactured by Asahi Denka Kogyo Co., Ltd., and Nippon Kayaku Co., Ltd. “KAYARAD” having a phosphate ester skeleton. .

The amount of the surfactant used is not particularly limited, but is preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the radical polymerizable unsaturated monomer, and 0.5 to 2 parts by weight. More preferably, it is a part. When the amount is less than 0.1 part by weight, the polymerization stability of the polymer emulsion is lowered, and aggregates are easily generated. On the other hand, when it exceeds 5 parts by weight, the water resistance is lowered, which is not preferable.
In the present invention, in order to control the emulsion particle size, a part of the surfactant to be used may be added to the polymerization vessel in advance.
The presence of the reactive surfactant has little effect on the molecular weight of the polymer produced, but reduces the extraction rate of the coating film immediately after drying the polymer emulsion into THF, and in the THF after heating the polymer emulsion coating. In order to further reduce the extraction rate, it is not preferable to use it alone. The amount of the surfactant used is 0.1 to 5 parts by weight of the surfactant with respect to 100 parts by weight of the radical polymerizable unsaturated monomer, and the radical polymerization is performed in 100% by weight of the surfactant. The reactive surfactant is preferably contained in a proportion of 0 to 50% by weight and the non-reactive surfactant is contained in a proportion of 50 to 100% by weight. The reactive surfactant is preferably contained in a proportion of 0 to 30% by weight and non-reactive. More preferably, the surfactant is contained in a proportion of 70 to 100% by weight.
When the ratio of the reactive surfactant exceeds 50% by weight, the extraction ratio of the coating film immediately after drying the polymer emulsion into THF tends to be less than 70% by weight, which is not preferable because the heat resistant aging property of the pressure-sensitive adhesive sheet is lowered. .

The polymer emulsion of the present invention can be obtained by a conventionally known emulsion polymerization method in the presence of a polymerization initiator.
As the polymerization initiator, either water-soluble or water-insoluble one can be used. As those generally used, water-soluble thermal decomposition 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 organic oxides such as t-butyl hydroperoxide, benzoyl peroxide, cumene hydroperoxide and combinations of reducing agents such as Rongalite and sodium metabisulfite, or sodium persulfate, ammonium persulfate and Rongalite. A combination of sodium thiosulfate, a combination of hydrogen peroxide and ascorbic acid, or the like can be used. The amount of the initiator used is usually 0.02 to 3 parts by weight, preferably 0.1 to 1 part by weight, based on 100 parts by weight of the radical polymerizable unsaturated monomer.
As a method for adding a polymerization initiator, the whole amount is charged in a reaction vessel, the reaction may be started, a part thereof is charged in a reaction vessel, and the remainder may be added in portions or added dropwise. The entire amount may be added in portions or added dropwise. In the case of divided addition or dropwise addition, it may be used in a state mixed with a radical polymerizable unsaturated monomer.

  In the present invention, mercaptan-based, thioglycol-based, β-mercaptopropionic acid-based alkyls are used as chain transfer agents to control the molecular weight and molecular weight distribution of a copolymer composed of radically polymerizable unsaturated monomers. Esters can be used. One of the characteristics of the present invention is that the weight-average molecular weight of the THF-soluble component of the coating film immediately after drying of the polymer emulsion is 200,000 to 600,000. Therefore, the amount of chain transfer agent used is also important. Increasing the amount of chain transfer agent can reduce the molecular weight of the polymer, but if the weight-average molecular weight of the THF soluble component is less than 200,000, the cohesive force of the polymer becomes extremely small, so it is not usually used as an adhesive. . When the chain transfer agent is used, the addition amount is 0 to 0.1 parts by weight with respect to 100 parts by weight of the radically polymerizable unsaturated monomer while adjusting the molecular weight so as to be within the above range.

  In the present invention, a tackifier resin may be used, dissolved in a radical polymerizable monomer at the time of polymerization, added after polymerization, or both of them. The purpose of addition at the time of polymerization is to utilize the chain transfer effect of the tackifier resin in addition to the improvement of the adhesive strength. As the tackifier resin, at least one or more of rosin resins, terpene resins, aromatic petroleum resins, aliphatic petroleum resins and the like can be used. 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. Aromatic petroleum resins include styrene oligomers and α-methylstyrene / styrene copolymers. The amount of tackifying resin used is preferably 0 to 30% by weight, more preferably 1 to 10% by weight, based on 100 parts by weight of the radical polymerizable unsaturated monomer.

The polymerization reaction for obtaining the polymer emulsion is usually performed in a temperature range of 40 to 90 ° C. over 1 to 6 hours.
The method for supplying the radically polymerizable unsaturated monomer into the reaction system is not particularly limited, and the entire amount may be charged in the reaction vessel in advance, or a part thereof is charged in the reaction vessel. The remainder may be added in portions or added dropwise, or the entire amount may be added in portions or added dropwise.
In the case of divided addition or dropwise addition, it may be in the form of monomer only, or may be mixed with water and a surfactant to form a monomer emulsion.
In the present invention, a monomer emulsion having an average particle size of 0.5 to 2 μm is prepared using a radical polymerizable unsaturated monomer, a surfactant and water, and the surfactant containing water and a surfactant is used. It is preferable to carry out radical polymerization while adding to the aqueous agent solution or water.
The purpose of subjecting the radically polymerizable unsaturated monomer to polymerization as a finely divided monomer emulsion is to increase the THF extraction rate of the coating film immediately after drying formed from the produced polymer emulsion.
It has been found that even when the composition of the reaction system is the same, the extraction rate of the produced polymer emulsion into the THF of the dried coating film can be adjusted by the degree of refinement of the monomer emulsion. It is because. It is possible to increase the extraction rate by refining the monomer emulsion, and the average particle size after refining is preferably 0.5 to 2 μm, more preferably 0.5 to 1 μm. preferable. When it is larger than 2 μm, the extraction rate is reduced, and the heat resistant aging property of the pressure-sensitive adhesive sheet is deteriorated.
As a method for miniaturization, it is common to use a disperser such as an ultrasonic emulsifier or a homomixer.

When using a tackifying resin, it is preferable that the tackifying resin is contained in the monomer emulsion. When the tackifier resin is used for polymerization in a state where it is contained in a fine monomer emulsion, in addition to improving the adhesion of the resulting polymer emulsion, particularly to polyolefins, etc., it also stabilizes the polymerization reaction. Since it is excellent in property, control of the amount of tackifying resin becomes easy.
As a method for incorporating the tackifier resin into the monomer emulsion, after previously dissolving or dispersing the tackifier resin in the radical polymerizable unsaturated monomer, water and a surfactant are added and mixed, Examples of the method include a body emulsion, but the method is not limited thereto.

An emulsion-type pressure-sensitive adhesive can be obtained by adding several kinds of additives to the obtained polymer emulsion.
The present invention relates to a pressure-sensitive adhesive sheet that does not leave a pressure-sensitive adhesive on an adherend when an adhesion error occurs, and can be easily peeled off. In order to reduce initial adhesive force, inorganic particles (A ) And / or containing crosslinked organic particles (B) having a gel fraction of 99% or more.

  Examples of the inorganic particles (A) that can be used in the present invention include calcium carbonate, iron oxide, calcium carbonate, magnesium oxide, magnesium hydroxide, basic magnesium carbonate, silica powder, hydrotalcite, glass beads, alumina, diatomaceous earth, and zircon oxide. , Synthetic silica, aluminum hydroxide, bentonite, calcium silicate, zeolite, kaolin clay, pyrophyllite (rholite clay), talc, serinite, attapulgite, mica, calcium sulfate, zircon silicate, carbon black, calcium sulfite, acetylene Black, titanium oxide, furnace black, graphite powder, potassium titanate, carbon fiber, barium sulfate, silicon nitride, silicon carbide, barium carbonate, antimony trioxide, barium titanate, molybdenum disulfide, zinc oxide, etc. Examples include mechanical particles.

In the present invention, in addition to inorganic particles (A), pre-crosslinked organic particles (B) having a gel fraction of 99% or more can also be used.
In addition, the gel fraction here means the value calculated from the weight change before and after being immersed for 24 hours at room temperature using toluene as an extraction solvent.
When the gel fraction of the crosslinked organic particles is less than 99%, it tends to be dissolved or swelled easily in the pressure-sensitive adhesive, which causes a change in particle diameter and makes the physical properties of the pressure-sensitive adhesive unfavorable.
As such pre-crosslinked organic particles (B) having a gel fraction of 99% or more, pre-crosslinked type made of polyolefin, polystyrene, polycarbonate, urethane resin, acrylic resin, Teflon (registered trademark), fatty acid amide, or the like. Organic particle | grains are mentioned.

In the present invention, the particle diameter of the particles (A) and (B) is very important for controlling the initial adhesive force, and is preferably 0.01 to 50 μm, more preferably 0.01 to 30 μm. More preferably, the thickness is 0.01 to 20 μm. When it is smaller than 0.01 μm, the initial adhesive strength does not decrease, and thus good removability cannot be obtained. On the other hand, when it is larger than 50 μm, the adhesive strength is too low to attach the adhesive sheet to the adherend.
The true specific gravity of the particles is preferably 0.9-6. When the true specific gravity of the particles is smaller than 0.9 or larger than 6, in both cases, the problem of separation of the pressure-sensitive adhesive component other than the particles from the particles tends to occur, and the stability of the pressure-sensitive adhesive decreases.
The amount of the particles used is preferably 0.1 to 100 parts by weight of the total of (A) and (B) with respect to 100 parts by weight of the dry weight of the polymer emulsion. More preferably, it is 1 to 30 parts by weight. Moreover, only 1 type may be used for the kind of particle | grains, and 2 or more types may be used together.
When the amount of particles used is less than 0.1 parts by weight, the initial adhesive force does not decrease, and therefore good removability cannot be obtained. On the other hand, when it exceeds 100 parts by weight, the adhesive force is too low and it becomes difficult to attach the adhesive sheet to the adherend.

  Further, in the present invention, a crosslinking agent can be used for the purpose of crosslinking the crosslinkable functional group in the emulsion particles. Examples of crosslinking agents include hydrazide compounds, semicarbazide derivatives, isocyanate compounds, oxazoline compounds, carbodiimide compounds, aziridine compounds, complexable metal compounds, and the like. It can mix | blend at the time of manufacture of an adhesive.

  In the present invention, several kinds of additives can be further blended as necessary. Specifically, wetting agents (surfactants to prevent repellency, etc.), antifoaming agents, neutralizing agents, plasticizers, thickeners, colorants, preservatives, rust inhibitors, solvents, water repellents, etc. Is mentioned.

  In the present invention, since the particles (A) and / or (B) are contained in the pressure-sensitive adhesive, the viscosity as the emulsion pressure-sensitive adhesive is very important. Depending on the specific gravity and particle size of the particles, precipitation of the particles is likely to occur. Due to this separation phenomenon, defects such as coating film defects at the time of coating or localized particles in the pressure-sensitive adhesive layer after drying occur. If the viscosity of the pressure-sensitive adhesive is too low, uniformity of the particles in the liquid cannot be obtained. Therefore, it is important that the viscosity of the emulsion-type pressure-sensitive adhesive is 0.5 Pa · s or more, and 1 Pa · s or more. Is preferred. As the viscosity increases, the stability of the particles improves. On the other hand, if the viscosity is too high, the fluidity of the pressure-sensitive adhesive is deteriorated, and poor stirring is likely to occur. .

Moreover, you may add the emulsion of tackifying resin to the emulsion type adhesive of this invention as needed, for example in order to aim at the further improvement of adhesive performance. This method is preferable from the viewpoint that the amount of the tackifying resin in the pressure-sensitive adhesive is extremely easy to control.
In order to prepare an emulsion-type pressure-sensitive adhesive, it is preferable to well disperse the additive using a homomixer or the like.

A pressure-sensitive adhesive sheet can be obtained by coating the emulsion-type pressure-sensitive adhesive of the present invention on a sheet-like substrate excluding a foamed substrate and drying it.
In the pressure-sensitive adhesive sheet of the present invention, an emulsion-type pressure-sensitive adhesive is coated on a release paper, dried, and provided with a pressure-sensitive adhesive layer. Then, the pressure-sensitive adhesive layer and the sheet-like substrate are bonded together, and the pressure-sensitive adhesive layer is formed into a sheet shape It can also be obtained by a transfer method on a substrate, a so-called transfer method.
The method of coating the emulsion-type pressure-sensitive adhesive on the sheet-like substrate or release paper is not particularly limited, and includes a roll coater such as a comma coater, a blade coater, and a gravure coater, a slot die coater, a lip coater, and a curtain coater. A conventionally known coating apparatus can be used.
Examples of sheet-like substrates excluding foamed substrates include paper, cellophane, various plastic sheets (polyester film, polycarbonate film, triacetate film, cycloolefin film, polyacrylic film, etc.), glass plates, etc. It is done. Moreover, various base materials can also be used independently, and the thing in the multilayer state formed by laminating | stacking a several thing can also be used. Further, the surface can be peeled off.
In the present invention, an optical plastic film can be particularly preferably used as the sheet-like substrate, and an adhesive sheet for optical use can be obtained.

The present invention does not leave a pressure-sensitive adhesive on the adherend when an adhesion error or the like occurs, and can be easily peeled off. It is shown.
Since the work process of “peeling” is repeatedly performed manually, it is generally required that the peel force at the time immediately after application is about 2 to 6 N / 25 mm.
On the other hand, when there is no adhesion mistake or the like, it is generally preferable that the adhesive strength is 10 N / 25 mm or more after 24 hours have elapsed since the application.
Therefore, in the present invention, the ratio of the 180-degree peel force after 20 minutes and 24 hours after application to the adherend is (20-minute peel force) / (24-hour peel force) = 0.2-0. .6 is preferred.
When the ratio of the peeling force is smaller than 0.2, the end portion of the pressure-sensitive adhesive sheet is easily peeled off immediately after pasting.
On the other hand, when it is larger than 0.6, the removability immediately after pasting is lowered.
The obtained pressure-sensitive adhesive sheet is excellent in removability immediately after sticking, final tough adhesive force, and stability over time of the pressure-sensitive adhesive sheet, so that it can be used not only for display devices such as FPD but also for film sheets for building interior and exterior. It is useful for various applications.

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. The number of ethylene oxide repeating ethylene oxide structures is abbreviated as “EO number”.
Example 1
2-ethylhexyl acrylate: 40.5 parts, butyl acrylate: 40.5 parts, ethyl acrylate: 15 parts, methyl methacrylate: 3 parts, acrylic acid: 1 part, octyl thioglycolate as a chain transfer agent: 0.04 part was mixed and dissolved to obtain a monomer mixture. To this monomer mixture, 1.5 parts of polyoxyethylene alkyl ether sulfate having 12 alkyl carbon atoms and 18 EO number, which is a non-reactive surfactant, and 39 parts deionized water are added. The monomer emulsion obtained by stirring was charged into a dropping tank.
A polymerization vessel equipped with a heating device, a stirrer, a reflux cooling device, a thermometer, a nitrogen introduction tube and a dropping tank was charged with 12 parts of deionized water and stirred under a nitrogen atmosphere to raise the internal temperature to 78 ° C. Then, 0.062 part of 5% potassium persulfate aqueous solution was added as a solid content. After 5 minutes, 0.188 parts of the above-mentioned monomer emulsion and 5% aqueous ammonium persulfate aqueous solution as solids were added dropwise from separate dropping tanks over 4 hours for 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 in a 5% aqueous solution. It was added in 3 portions every 10 minutes. The mixture was further reacted with stirring for 1 hour, neutralized with aqueous ammonia, and filtered through a 175 mesh nylon filter cloth to obtain a polymer emulsion.
The obtained polymer emulsion had a nonvolatile content of 61.5%, a viscosity of 0.11 Pa · s, and an average particle size of 0.62 μm.
The nonvolatile content was measured by measuring the weight ratio after drying at 150 ° C. for 20 minutes in an electric oven, and the average particle size was measured by “Microtrack” manufactured by Nikkiso Co., Ltd.
Further, in order to measure the THF extraction rate, the obtained polymer emulsion was applied to a PET film so that the dry film thickness was about 20 g / m ² and dried at 25 ° C. for 24 hours. The obtained sample (dry film / PET film) was cut to prepare two 3 cm × 10 cm coated products. One of them was wrapped in a 200 mesh stainless steel mesh without aging, soaked in THF at 25 ° C. for 2 days, and then the weight average molecular weight of the portion dissolved in THF was measured by gel permeation chromatography. Was 520000. Moreover, the THF extraction rate of the coating film immediately after drying was 71.3% by weight.
The other sample was aged for 7 days in an environment of 60 ° C., then wrapped in a 200 mesh stainless steel mesh, immersed in THF at 25 ° C. for 2 days, and the THF extraction rate was measured. % By weight.
Further, to 100 parts of the polymer emulsion obtained above, hydrous magnesium silicate having an average particle size of 1.5 μm: 20 parts, antifoaming agent: 0.1 part, sodium dioctylsulfosuccinate as a wetting agent: 0.1 part, antiseptic The resulting mixture was further thickened with a thickener to 5 Pa · s (BL type viscometer, measured at 25 ° C. with # 4 rotor / 60 rpm) to obtain an emulsion-type pressure-sensitive adhesive. The pressure-sensitive adhesive was prepared with a homomixer.
The obtained pressure-sensitive adhesive is coated on a release paper with a comma coater so as to have a dry film thickness of 20 g / m ² , dried in a drying oven at 100 ° C. for 75 seconds, laminated with a 50 μm thick PET film and wound up. A pressure-sensitive adhesive sheet was obtained. The obtained adhesive sheet was allowed to stand for 24 hours or more in an atmosphere of 23 ° C.-65% RH. Further, a part of the mixture was heated for 7 days in an environment of 60 ° C. Table 1 shows the properties of the polymer emulsion, and Table 2 shows the results of measuring the adhesive strength of the pressure-sensitive adhesive sheet before and after heating.
<Measurement of adhesive strength>
Two types of adhesive sheets before and after heating were cut into strips each having a width of 25 mm, the release paper was peeled off, affixed to a stainless steel plate (hereinafter abbreviated as “SUS plate”), and reciprocated once with a 2 kg roll. A sample was obtained.
For each measurement sample, the peel strength when peeled in the 180 ° direction at a rate of 300 mm / min in an atmosphere at 23 ° C. was measured 20 minutes and 24 hours after application.

(Example 2)
Example 1 except that the hydrous magnesium silicate used in Example 1 was changed to “GR-400” (manufactured by Negami Kogyo Co., Ltd.), which is a crosslinked acrylic fine particle having a gel fraction of 100% and an average particle size of 14 μm. The same experiment was conducted.

(Example 3)
The same experiment as in Example 1 was performed, except that the monomer emulsion prepared in Example 1 was further refined with a homomixer and charged into the dropping tank as a monomer emulsion having an average particle size of 0.7 μm. It was.

Example 4
2-ethylhexyl acrylate: 40.5 parts, butyl acrylate: 40.5 parts, ethyl acrylate: 15 parts, methyl methacrylate: 3 parts, acrylic acid: 1 part, octyl thioglycolate as a chain transfer agent: 0.03 part, polymerization rosin ("Pencel D-160" manufactured by Arakawa Chemical Co., Ltd.) having a softening point of about 150 ° C: 3 parts were mixed and dissolved to obtain a monomer mixture. To this monomer mixture, 1.5 parts of polyoxyethylene alkyl ether sulfate having 12 alkyl carbon atoms and 18 EO number, which is a non-reactive surfactant, and 39 parts deionized water are added. The monomer emulsion obtained by stirring was charged into a dropping tank.
A polymerization vessel equipped with a heating device, a stirrer, a reflux cooling device, a thermometer, a nitrogen introduction tube and a dropping tank was charged with 12 parts of deionized water and stirred under a nitrogen atmosphere to raise the internal temperature to 78 ° C. Then, 0.062 part of 5% potassium persulfate aqueous solution was added as a solid content. After 5 minutes, 0.188 parts of the above-mentioned monomer emulsion and 5% aqueous ammonium persulfate aqueous solution as solids were added dropwise from separate dropping tanks over 4 hours for 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 in a 5% aqueous solution. It was added in 3 portions every 10 minutes. The mixture was further reacted with stirring for 1 hour, neutralized with aqueous ammonia, and filtered through a 175 mesh nylon filter cloth to obtain a polymer emulsion.
Thereafter, the same experiment as in Example 1 was performed.

(Example 5)
The same experiment as in Example 4 was performed, except that the monomer emulsion prepared in Example 4 was further refined with a homomixer and charged into the dropping tank as a monomer emulsion having an average particle size of 0.6 μm. It was.

(Comparative Example 1)
In Example 1, the same experiment as in Example 1 was performed except that the chain transfer agent octyl thioglycolate was not used.

(Comparative Example 2)
In Example 1, the same experiment as in Example 1 was performed except that hydrous magnesium silicate was not used.

(Comparative Example 3)
A monomer mixture was obtained by mixing and dissolving butyl acrylate: 4 parts, methyl methacrylate: 93 parts, acrylic acid: 3 parts and benzoyl peroxide: 0.4 part as a polymerization initiator.
A polymerization vessel equipped with a heating device, a stirrer, a reflux cooling device, a thermometer, a nitrogen introducing tube and a dropping tank, deionized water: 330 parts, alkyl carbon number 12 which is a non-reactive surfactant, EO number 18 Polyoxyethylene alkyl ether sulfate: 4 parts were charged, and the above monomer mixture was further charged with stirring under a nitrogen atmosphere, and then the internal temperature was raised to 78 ° C. to initiate the reaction. After maintaining the internal temperature at 80 ° C. and reacting for 5 hours, neutralize with aqueous ammonia and filter with a 100 mesh nylon filter cloth to obtain an acrylic polymer emulsion having an average particle size of 20 μm and a gel fraction of 30%. Obtained.
In place of the hydrous magnesium silicate used in Example 1, an experiment similar to Example 1 was performed except that the polymer emulsion obtained above was used in an amount equivalent to 5 parts in terms of nonvolatile content.

(Comparative Example 4)
2-ethylhexyl acrylate: 40.5 parts, butyl acrylate: 40.5 parts, ethyl acrylate: 15 parts, methyl methacrylate: 3 parts, acrylic acid: 1 part, octyl thioglycolate as a chain transfer agent: 0.04 part was mixed and dissolved to obtain a monomer mixture. To this monomer mixture, 1.5 parts of polyoxyethylene alkyl ether sulfate having 12 alkyl carbon atoms and 18 EO number, which is a non-reactive surfactant, and 39 parts deionized water are added. The monomer emulsion obtained by stirring was charged into a dropping tank.
A polymerization vessel equipped with a heating device, a stirrer, a reflux cooling device, a thermometer, a nitrogen introduction tube and a dropping tank was charged with 12 parts of deionized water and stirred under a nitrogen atmosphere to raise the internal temperature to 78 ° C. Then, 0.187 part of 5% potassium persulfate aqueous solution was added as solid content. After 5 minutes, 0.563 parts of the above monomer emulsion and 5% ammonium persulfate aqueous solution as solids were added dropwise from separate dropping tanks over 4 hours for 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 in a 5% aqueous solution. It was added in 3 portions every 10 minutes. The mixture was further reacted with stirring for 1 hour, neutralized with aqueous ammonia, and filtered through a 175 mesh nylon filter cloth to obtain a polymer emulsion.
Thereafter, the same experiment as in Example 1 was performed.

(Comparative Example 5)
2-ethylhexyl acrylate: 40.5 parts, butyl acrylate: 40.5 parts, ethyl acrylate: 15 parts, methyl methacrylate: 3 parts, acrylic acid: 1 part is mixed and dissolved to prepare a monomer mixture. Obtained. To this monomer mixture, 1.5 parts of polyoxyethylene alkyl ether sulfate having 12 alkyl carbon atoms and 18 EO number, which is a non-reactive surfactant, and 39 parts deionized water are added. The monomer emulsion obtained by stirring was charged into a dropping tank.
A polymerization vessel equipped with a heating device, a stirrer, a reflux cooling device, a thermometer, a nitrogen introduction tube and a dropping tank was charged with 12 parts of deionized water and stirred under a nitrogen atmosphere to raise the internal temperature to 78 ° C. Then, 0.187 part of 5% potassium persulfate aqueous solution was added as solid content. After 5 minutes, 0.563 parts of the above monomer emulsion and 5% ammonium persulfate aqueous solution as solids were added dropwise from separate dropping tanks over 4 hours for 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 in a 5% aqueous solution. It was added in 3 portions every 10 minutes. The mixture was further reacted with stirring for 1 hour, neutralized with aqueous ammonia, and filtered through a 175 mesh nylon filter cloth to obtain a polymer emulsion.
Thereafter, the same experiment as in Example 1 was performed.

(Comparative Example 6)
The viscosity of the emulsion-type pressure-sensitive adhesive in Example 1 was changed to 0.3 Pa · s. However, when the obtained pressure-sensitive adhesive was allowed to stand for 1 day, the polymer emulsion and the hydrous magnesium silicate were separated, and the subsequent experiment was stopped.

  The pressure-sensitive adhesive sheet obtained according to the present invention is a pressure-sensitive adhesive sheet that can be easily peeled off from the adherend immediately after being bonded to various adherends, and exhibits strong adhesiveness after an appropriate period of time. It can be seen that even when the sheet is heated, the adhesive strength is excellent.

Claims (8)

A radically polymerizable unsaturated monomer capable of forming a polymer having a glass transition temperature of 0 ° C. or lower is radically polymerized in water in the presence of a surfactant, and the tetrahydrofuran extraction ratio of the coating immediately after drying is 70% by weight. A polymer emulsion having a weight-average molecular weight of 200,000 to 600,000 in a soluble part,
Inorganic particles (A) and / or pre-crosslinked organic particles (B) having a gel fraction of 99% or more,
An emulsion-type pressure-sensitive adhesive having a viscosity of 0.5 to 15 Pa · s.   The inorganic particles (A) and the crosslinked organic particles (B) having a gel fraction of 99% or more have an average particle diameter of 0.01 to 50 μm and a true specific gravity of 0.9 to 6, and (A) and (B) The emulsion-type pressure-sensitive adhesive according to claim 1, wherein the total amount is from 0.1 to 100 parts by weight based on 100 parts by weight of the dry weight of the polymer emulsion.   The emulsion-type pressure-sensitive adhesive according to claim 1 or 2, wherein the dry extraction film of the polymer emulsion is allowed to stand at 50 to 70 ° C for one week, and the tetrahydrofuran extraction rate is 60% by weight or more.   A total of 100% by weight of the surfactant contains 0 to 50% by weight of a radically polymerizable reactive surfactant and 50 to 100% by weight of a non-reactive surfactant having no radical polymerizability. The emulsion-type pressure-sensitive adhesive according to any one of claims 1 to 3. Monomer emulsion having an average particle size of 0.5 to 2 μm, wherein the polymer emulsion contains a radical polymerizable unsaturated monomer capable of forming a polymer having a glass transition temperature of 0 ° C. or less, a surfactant, and water The
While adding to a surfactant aqueous solution or water containing water and a surfactant,
The emulsion-type pressure-sensitive adhesive according to any one of claims 1 to 4, wherein the emulsion-type pressure-sensitive adhesive is obtained by radical polymerization.   The emulsion-type pressure-sensitive adhesive according to claim 5, wherein the monomer emulsion further contains a tackifying resin.   A pressure-sensitive adhesive sheet in which a pressure-sensitive adhesive layer formed from the emulsion-type pressure-sensitive adhesive according to any one of claims 1 to 6 is provided on at least one surface of a sheet-like base material excluding a foamed base material, The pressure-sensitive adhesive sheet is characterized in that the ratio of the 180-degree peel force after 20 minutes and 24 hours after sticking is (peel force after 20 minutes) / (peel force after 24 hours) = 0.2 to 0.6. .   The pressure-sensitive adhesive sheet according to claim 7, wherein the sheet-like substrate is an optical plastic film.