JP2019196492A - Adhesive tape - Google Patents

Abstract

To provide an adhesive tape suitably used for fixation of an optical film and having high constant load release property and high strain stress resistance to an adherend.SOLUTION: There is provided an adhesive tape having an adhesive layer containing: a polymer component containing 60 wt.% or more of a living radical-polymerized crosslinkable acrylic polymer obtained by living radical polymerization of at least a monomer mixture containing an acrylic alkylester monomer having 8 alkyl group carbon atoms and a crosslinkable functional group-containing monomer and having weight average molecular weight of 300,000 to 2,000,000 and molecular weight distribution (Mw/Mn) of 1.05 to 2.5; a tackifier resin; and a crosslinker. The acrylic alkylester monomer having 8 alkyl group carbon atoms is 2-ethyl hexyl acrylate, n-octyl acrylate or isooctyl acrylate. The content of the acrylic alkylester monomer having 8 alkyl group carbon atoms in the monomer mixture is 60 wt.% or more. A gel fraction of the adhesive layer is 50 wt.% or less.SELECTED DRAWING: None

Description

The present invention relates to a pressure-sensitive adhesive tape that is suitable for fixing an optical film and has both a high constant load peelability to an adherend and a high strain stress resistance.

In a portable electronic device (for example, a mobile phone, a portable information terminal, etc.) equipped with an image display device or an input device, an adhesive tape is used for assembly. Specifically, for example, an adhesive tape for bonding a cover panel for protecting the surface of a portable electronic device to an optical film of a touch panel module or a display panel module, or bonding a touch panel module and a display panel module. Is used.
Such an adhesive tape is used by being punched into a frame shape or the like and arranged around the display screen (for example, Patent Documents 1 and 2).

The adhesive tape used for fixing the optical film is required to have a strain stress resistance in addition to the adhesive force. That is, when the optical film fixed by the adhesive tape is exposed to a high temperature, the difference in the expansion / contraction behavior of the adhesive tape and the optical film is caused by the difference in the linear expansion coefficient between the adhesive tape and the optical film. When the adhesive tape and the optical film are firmly fixed, the stress generated by the difference in the expansion / contraction behavior remains in the optical film, causing optical distortion. When the adhesive tape and the optical film are loosely fixed, the occurrence of optical distortion can be suppressed, but there is a problem that the adhesive force becomes insufficient. Thus, in general, there was a trade-off relationship between adhesive force and strain stress resistance.

In particular, in the adhesion and fixing of components in recent large-sized portable electronic devices, it is necessary to attach a heavy component or member, and the load on the adhesive tape is increased. Further, in recent portable electronic devices, so-called narrowed frames have been promoted to narrow the periphery of the display screen to ensure a wider screen, and the width of the peripheral portion of the screen is extremely narrow in portable electronic devices with narrowed frames. Therefore, there is a demand for high adhesive force that can securely fix a member even if the bonding area is small, particularly high constant load peelability that is difficult to peel off when a constant load is applied.
Accordingly, the pressure-sensitive adhesive tape used for fixing the optical film of electronic equipment parts is required to have both high constant load peelability and high strain stress resistance on the adherend more than ever before.

JP 2009-242541 A JP 2009-258274 A

An object of this invention is to provide the adhesive tape which was used suitably for fixation of an optical film, and was compatible with the high constant load peelability with respect to a to-be-adhered body, and high strain-stress resistance in view of the said present condition.

The present invention provides a weight average molecular weight of 300,000 to 2,000,000 obtained by living radical polymerization of a monomer mixture containing at least an alkyl acrylate monomer having 8 alkyl groups and a crosslinkable functional group-containing monomer. It has a pressure-sensitive adhesive layer containing a polymer component containing 60% by weight or more of a living radical polymerization crosslinkable acrylic polymer having a molecular weight distribution (Mw / Mn) of 1.05 to 2.5, a tackifier resin, and a crosslinking agent. The acrylic tape alkyl ester monomer having an alkyl group carbon number of 8 is an adhesive tape, and is 2-ethylhexyl acrylate, n-octyl acrylate or isooctyl acrylate, and the acrylic group having an alkyl group carbon number of 8 in the monomer mixture. The acid alkyl ester monomer content is 60% by weight or more, and the viscosity The gel fraction of the adhesive layer is a pressure-sensitive adhesive tape is 50 wt% or less.
The present invention is described in detail below.

The inventors of the present invention have a weight average molecular weight of 300,000 to 300, obtained by living radical polymerization of a monomer mixture containing an alkyl acrylate alkyl ester monomer having an alkyl group having 8 carbon atoms as a main component and a crosslinkable functional group-containing monomer. By having an acrylic polymer having a molecular weight distribution (Mw / Mn) of 1.05 to 2.5 as a main component and a gel fraction of the pressure-sensitive adhesive layer to 50% by weight or less using a crosslinking agent, The present inventors have found that an adhesive tape capable of achieving both high constant load peelability and high strain stress resistance for an adherend is obtained, and the present invention has been completed.

The pressure-sensitive adhesive tape of the present invention has a pressure-sensitive adhesive layer containing a polymer component containing an acrylic polymer obtained by living radical polymerization (also referred to as “living radical polymerization crosslinkable acrylic polymer” in the present specification).
When the pressure-sensitive adhesive layer contains the living radical polymerization crosslinkable acrylic polymer, the pressure-sensitive adhesive tape of the present invention can achieve both high constant load peelability and strain stress resistance with respect to an adherend.

The living radical polymerization crosslinkable acrylic polymer is a living radical polymerization, preferably an organic tellurium polymerization, using as a raw material a monomer mixture containing at least an alkyl acrylate ester monomer having 8 alkyl groups and a crosslinkable functional group-containing monomer. It is an acrylic polymer obtained by living radical polymerization using an initiator.
Living radical polymerization is polymerization in which molecular chains grow without the polymerization reaction being hindered by side reactions such as termination reactions or chain transfer reactions. According to living radical polymerization, for example, a polymer having a more uniform molecular weight and composition than that of free radical polymerization or the like can be obtained, and the production of low molecular weight components and the like can be suppressed. The constant load peelability to the body is improved.

FIG. 1 shows a schematic diagram for explaining living radical polymerization. Living radical polymerization is polymerization in which molecular chains grow without the polymerization reaction being hindered by side reactions such as termination reaction or chain transfer reaction. In the living radical polymerization, the reaction proceeds without the growth terminal radical being deactivated and without generating new radical species during the reaction. In the middle of the reaction, all the polymer chains are polymerized while uniformly reacting with the monomer, and the composition of all the polymers approaches uniform. Therefore, the crosslinkable functional group-containing monomer 12 is included in all polymers of the living radical polymerization crosslinkable acrylic polymer 1. When such a living radical polymerization crosslinkable acrylic polymer 1 is crosslinked using a crosslinking agent, almost all polymers can participate in crosslinking between polymer chains. Since there are few low molecular weight components which do not contain a crosslinkable functional group containing monomer especially, even if it is a bridge | crosslinking with a gel fraction of 50 weight% or less, the probability that all the polymer chains will participate in bridge | crosslinking improves. FIG. 2 is a schematic diagram illustrating a case where a living radical polymerization crosslinkable acrylic polymer is crosslinked. In the living radical polymerization crosslinkable acrylic polymer, the composition of all polymers is uniform, and since the crosslinkable functional group-containing monomer is included, all polymer chains are involved in crosslinking. In FIG. 2, a hydroxyl group is shown as an example of the crosslinkable functional group. Thus, since almost all polymers can participate in crosslinking between polymer chains, it is possible to obtain an adhesive tape that can exhibit high constant load peelability to the adherend.

The effect of the present invention cannot be obtained even when an acrylic polymer obtained by conventional free radical polymerization is used.
FIG. 3 is a schematic diagram for explaining free radical polymerization. In free radical polymerization, radical species are continuously generated during the reaction and added to the monomer, and the polymerization proceeds. Therefore, in the free radical polymerization, a polymer 23 in which the growing terminal radical is deactivated during the reaction and a polymer 24 grown by the radical species newly generated during the reaction are generated. Therefore, when an acrylic polymer containing a crosslinkable functional group is produced by free radical polymerization, a polymer containing no relatively low molecular weight crosslinkable functional group-containing monomer is produced. Even if such a free radical polymerization crosslinkable acrylic polymer 2 is cross-linked using a cross-linking agent, a polymer that does not contain a crosslinkable functional group-containing monomer cannot participate in cross-linking between polymer chains. FIG. 4 shows a schematic diagram for explaining a case where a free radical polymerization crosslinkable acrylic polymer is crosslinked. In the free radical polymerization crosslinkable acrylic polymer, there is a polymer chain that cannot participate in crosslinking because the composition of the polymer is non-uniform and the polymer does not contain a relatively low molecular weight crosslinkable functional group-containing monomer. . In FIG. 4, a hydroxyl group is shown as an example of the crosslinkable functional group. When a thin adhesive tape is applied to an adherend and a load is applied, peeling occurs from a site that does not contain a crosslinkable functional group-containing monomer that cannot participate in crosslinking. I can't show my sexuality.

Among living radical polymerizations, living radical polymerization using an organic tellurium polymerization initiator has a crosslinkable functional group such as a carboxyl group, a hydroxyl group, an amino group, an amide group, and a nitrile group, unlike other living radical polymerizations. Without protecting any radically polymerizable monomer, it is possible to obtain a polymer having a uniform molecular weight and composition by polymerizing with the same initiator. For this reason, the radically polymerizable monomer which has a crosslinkable functional group can be copolymerized easily.

The organic tellurium polymerization initiator is not particularly limited as long as it is generally used for living radical polymerization, and examples thereof include organic tellurium compounds and organic telluride compounds.
Examples of the organic tellurium compound include (methylterranyl-methyl) benzene, (1-methylterranyl-ethyl) benzene, (2-methylterranyl-propyl) benzene, 1-chloro-4- (methylterranyl-methyl) benzene, 1-hydroxy- 4- (methylterranyl-methyl) benzene, 1-methoxy-4- (methylterranyl-methyl) benzene, 1-amino-4- (methylterranyl-methyl) benzene, 1-nitro-4- (methylterranyl-methyl) benzene, 1- Cyano-4- (methylterranyl-methyl) benzene, 1-methylcarbonyl-4- (methylterranyl-methyl) benzene, 1-phenylcarbonyl-4- (methylterranyl-methyl) benzene, 1-methoxycarbonyl-4- (methylterranyl-methyl) ) Benzene, 1- Enoxycarbonyl-4- (methylterranyl-methyl) benzene, 1-sulfonyl-4- (methylterranyl-methyl) benzene, 1-trifluoromethyl-4- (methylterranyl-methyl) benzene, 1-chloro-4- (1 -Methyl terranyl-ethyl) benzene, 1-hydroxy-4- (1-methyl terranyl-ethyl) benzene, 1-methoxy-4- (1-methyl teranyl-ethyl) benzene, 1-amino-4- (1-methyl terranyl-ethyl) Benzene, 1-nitro-4- (1-methylterranyl-ethyl) benzene, 1-cyano-4- (1-methylterranyl-ethyl) benzene, 1-methylcarbonyl-4- (1-methylterranyl-ethyl) benzene, 1- Phenylcarbonyl-4- (1-methylterranyl-ethyl) benzene, 1-meth Sicarbonyl-4- (1-methylterranyl-ethyl) benzene, 1-phenoxycarbonyl-4- (1-methylterranyl-ethyl) benzene, 1-sulfonyl-4- (1-methylterranyl-ethyl) benzene, 1-trifluoromethyl -4- (1-methylteranyl-ethyl) benzene, 1-chloro-4- (2-methylterranyl-propyl) benzene, 1-hydroxy-4- (2-methylterranyl-propyl) benzene, 1-methoxy-4- (2 -Methyl teranyl-propyl) benzene, 1-amino-4- (2-methyl teranyl-propyl) benzene, 1-nitro-4- (2-methyl teranyl-propyl) benzene, 1-cyano-4- (2-methyl teranyl-propyl) Benzene, 1-methylcarbonyl-4- (2-methylterranyl-propyl ) Benzene, 1-phenylcarbonyl-4- (2-methylterranyl-propyl) benzene, 1-methoxycarbonyl-4- (2-methylterranyl-propyl) benzene, 1-phenoxycarbonyl-4- (2-methylterranyl-propyl) benzene 1-sulfonyl-4- (2-methylterranyl-propyl) benzene, 1-trifluoromethyl-4- (2-methylterranyl-propyl) benzene, 2- (methylterranyl-methyl) pyridine, 2- (1-methylterranyl-ethyl) ) Pyridine, 2- (2-methylterranyl-propyl) pyridine, 2-methylterranyl-methyl ethanoate, methyl 2-methylterranyl-propionate, methyl 2-methylterranyl-2-methylpropionate, 2-methylterranyl-ethyl ethanoate, 2 -Methylterranil Ethyl propionate, 2-Mechiruteraniru -2-methylpropionic acid ethyl, 2-methyl-Terra alkylsulfonyl acetonitrile, 2-methyl-Terra sulfonyl propionitrile, 2-methyl-2-methyl-Terra sulfonyl propionitrile, and the like. The methyl terranyl group in these organic tellurium compounds may be an ethyl terranyl group, n-propyl terranyl group, isopropyl terranyl group, n-butyl terranyl group, isobutyl terranyl group, t-butyl terranyl group, phenyl terranyl group, etc. These organic tellurium compounds may be used alone or in combination of two or more.

Examples of the organic telluride compound include dimethyl ditelluride, diethyl ditelluride, di-n-propyl ditelluride, diisopropyl ditelluride, dicyclopropyl ditelluride, di-n-butyl ditelluride, di-sec-butyl ditelluride. , Di-tert-butylditelluride, dicyclobutylditelluride, diphenylditelluride, bis- (p-methoxyphenyl) ditelluride, bis- (p-aminophenyl) ditelluride, bis- (p-nitrophenyl) ditelluride, bis -(P-cyanophenyl) ditelluride, bis- (p-sulfonylphenyl) ditelluride, dinaphthyl ditelluride, dipyridyl ditelluride and the like can be mentioned. These organic telluride compounds may be used alone or in combination of two or more. Of these, dimethyl ditelluride, diethyl ditelluride, di-n-propyl ditelluride, di-n-butyl ditelluride and diphenyl ditelluride are preferable.

In addition, within the range which does not impair the effect of this invention, in addition to the said organic tellurium polymerization initiator, you may use an azo compound as a polymerization initiator for the purpose of acceleration | stimulation of a polymerization rate.
The azo compound is not particularly limited as long as it is generally used for radical polymerization. For example, 2,2′-azobis (isobutyronitrile), 2,2′-azobis (2-methylbutyronitrile) ), 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 1,1-azobis (cyclohexane-1-carbonitrile) ), 1-[(1-cyano-1-methylethyl) azo] formamide, 4,4′-azobis (4-cyanovaleric acid), dimethyl-2,2′-azobis (2-methylpropionate), Dimethyl-1,1′-azobis (1-cyclohexanecarboxylate), 2,2′-azobis {2-methyl-N- [1,1′-bis (hydroxymethyl) -2-hydroxyethyl Propionamide}, 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) propionamide], 2,2′-azobis [N- (2-propenyl) -2-methylpropionamide], 2 , 2′-azobis (N-butyl-2-methylpropionamide), 2,2′-azobis (N-cyclohexyl-2-methylpropionamide), 2,2′-azobis [2- (2-imidazoline-2 -Yl) propane] dihydrochloride, 2,2'-azobis {2- [1- (2-hydroxyethyl) -2-imidazolin-2-yl] propane} dihydrochloride, 2,2'-azobis [2 -(2-imidazolin-2-yl) propane], 2,2'-azobis (2-amidinopropane) dihydrochloride, 2,2'-azobis [N- (2-carboxyethyl) -2-methylpropionami Tetrahydrate, 2,2′-azobis (1-imino-1-pyrrolidino-2-methylpropane) dihydrochloride, 2,2′-azobis (2,4,4-trimethylpentane) and the like. It is done. These azo compounds may be used alone or in combination of two or more.

The monomer mixture used as the raw material of the living radical polymerization crosslinkable acrylic polymer contains at least an alkyl acrylate monomer having 8 alkyl groups and a crosslinkable functional group-containing monomer.
The content of the alkyl alkyl ester monomer having 8 alkyl groups in the monomer mixture is 60% by weight or more. By containing an acrylic acid alkyl ester monomer having 8 alkyl groups as the main component, the resulting pressure-sensitive adhesive tape of the present invention can exhibit high strain stress resistance. The content of the acrylic acid alkyl ester monomer having 8 alkyl groups in the monomer mixture is preferably 80% by weight or more.
The upper limit of the content of the acrylic acid alkyl ester monomer having 8 alkyl group carbon atoms in the monomer mixture is not particularly limited, but when considering the other monomer components, that is, the blending amount of the crosslinkable functional group-containing monomer, 99. About 99% by weight is the practical upper limit.

The alkyl acrylate alkyl ester monomer having 8 alkyl groups includes alkyl acrylate in which the alkyl group such as 2-ethylhexyl acrylate, n-octyl acrylate, and isooctyl acrylate is a structural isomer of an octyl group that does not include a ring structure. An ester monomer is mentioned. Of these, 2-ethylhexyl acrylate, n-octyl acrylate, and isooctyl acrylate are preferable, and 2-ethylhexyl acrylate is more preferable.

The crosslinkable functional group-containing monomer has a role of inserting a crosslinkable functional group into the living radical polymerization crosslinkable acrylic polymer.
Examples of the crosslinkable functional group include a hydroxyl group, a carboxyl group, a glycidyl group, an amino group, an amide group, and a nitrile group. Especially, since adjustment of the gel fraction of the said adhesive layer is easy, a hydroxyl group or a carboxyl group is preferable and a hydroxyl group is more preferable.

As a monomer which has a hydroxyl group, (meth) acrylic acid ester which has hydroxyl groups, such as 4-hydroxybutyl (meth) acrylate and 2-hydroxyethyl (meth) acrylate, is mentioned, for example.
As a monomer which has a carboxyl group, (meth) acrylic acid is mentioned, for example.
Examples of the monomer having a glycidyl group include glycidyl (meth) acrylate.
Examples of the monomer having an amide group include hydroxyethyl acrylamide, isopropyl acrylamide, dimethylaminopropyl acrylamide and the like.
Examples of the monomer having a nitrile group include acrylonitrile.

When a (meth) acrylic acid ester having a hydroxyl group is used as the crosslinkable functional group-containing monomer, the content in the monomer mixture is not particularly limited, but the preferred lower limit is 0.01% by weight and the preferred upper limit is 30% by weight. is there. When the content of the (meth) acrylic acid ester having a hydroxyl group is less than 0.01% by weight, the resulting pressure-sensitive adhesive layer may become too soft and the heat resistance may be lowered. The resulting pressure-sensitive adhesive layer may become too hard, and the pressure-sensitive adhesive tape may be easily peeled off or the strain stress resistance may be reduced.

When an acrylic monomer having a carboxyl group is used as the crosslinkable functional group-containing monomer, the content in the monomer mixture is not limited, but the preferred lower limit is 0.1% by weight and the preferred upper limit is 10% by weight. When the content of the acrylic monomer having a carboxyl group is less than 0.1% by weight, the resulting pressure-sensitive adhesive layer may become too soft and the heat resistance may be lowered. The pressure-sensitive adhesive layer is too hard, and the pressure-sensitive adhesive tape may be easily peeled off, or the strain stress resistance may be reduced.

The mixed monomer may contain a radical polymerizable monomer other than the alkyl acrylate ester monomer having 8 alkyl groups and the crosslinkable functional group-containing monomer. As said other radically polymerizable monomer, other (meth) acrylic acid ester is mentioned, for example. In addition to the acrylic monomer, a vinyl compound may be used as a monomer.

The other (meth) acrylic acid esters are not particularly limited, and methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, n-butyl (meth) acrylate, tert-butyl (meth) acrylate, n -(Meth) acrylic acid alkyl esters such as octyl methacrylate, isooctyl methacrylate, isononyl (meth) acrylate, isomyristyl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate, benzyl (Meth) acrylate, 2-butoxyethyl (meth) acrylate, 2-phenoxyethyl (meth) acrylate, glycidyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, poly B propylene glycol mono (meth) acrylate. These (meth) acrylic acid esters may be used alone or in combination of two or more.

The said vinyl compound is not specifically limited, For example, N-vinyl pyrrolidone, N-vinyl caprolactam, N-acryloyl morpholine, styrene, vinyl acetate etc. are mentioned. These vinyl compounds may be used alone or in combination of two or more.

In the living radical polymerization, a dispersion stabilizer may be used. Examples of the dispersion stabilizer include polyvinyl pyrrolidone, polyvinyl alcohol, methyl cellulose, ethyl cellulose, poly (meth) acrylic acid, poly (meth) acrylic acid ester, and polyethylene glycol.
As the living radical polymerization method, conventionally known methods are used, and examples thereof include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization and the like.
When a polymerization solvent is used in the living radical polymerization, the polymerization solvent is not particularly limited. For example, a nonpolar solvent such as hexane, cyclohexane, octane, toluene, xylene, water, methanol, ethanol, propanol, butanol, acetone, Highly polar solvents such as methyl ethyl ketone, methyl isobutyl ketone, tetrahydrofuran, dioxane, N, N-dimethylformamide can be used. These polymerization solvents may be used alone or in combination of two or more.
The polymerization temperature is preferably 0 to 110 ° C. from the viewpoint of the polymerization rate.

The living radical polymerization crosslinkable acrylic polymer has a weight-average molecular weight (Mw) lower limit of 300,000 and an upper limit of 2 million. When the weight average molecular weight is less than 300,000, the pressure-sensitive adhesive layer becomes too soft and heat resistance is lowered. If the weight average molecular weight exceeds 2,000,000, the viscosity at the time of coating becomes too high to be applied, which may cause uneven thickness of the pressure-sensitive adhesive layer. The minimum with a preferable weight average molecular weight (Mw) of the said living radical polymerization crosslinkable acrylic polymer is 400,000, and a preferable upper limit is 1.5 million.

The living radical polymerization crosslinkable acrylic polymer has a molecular weight distribution (Mw / Mn) of 1.05 to 2.5. When the molecular weight distribution exceeds 2.5, the low molecular weight components and the like generated in the living radical polymerization increase, so that the pressure-sensitive adhesive tape is easily peeled off and the constant load peelability to the adherend is lowered. A preferable upper limit of the molecular weight distribution is 2.0, a more preferable upper limit is 1.8, and a further preferable upper limit is 1.7.

The molecular weight distribution (Mw / Mn) is a ratio between the weight average molecular weight (Mw) and the number average molecular weight (Mn).
A weight average molecular weight (Mw) and a number average molecular weight (Mn) are measured as a polystyrene conversion molecular weight by the gel permeation chromatography (GPC) method. Specifically, the weight average molecular weight (Mw) and the number average molecular weight (Mn) are obtained by filtering a diluted solution obtained by diluting a living radical polymerization crosslinkable acrylic polymer with tetrahydrofuran (THF) 50 times with a filter, It is measured as a polystyrene-converted molecular weight by the GPC method using the obtained filtrate. In the GPC method, for example, 2690 Separations Model (manufactured by Waters) or the like can be used.

The pressure-sensitive adhesive layer may contain, as a polymer component, a polymer other than the living radical polymerization crosslinkable acrylic polymer, for example, a polymer obtained by free radical polymerization.
However, the lower limit of the content of the living radical polymerization crosslinkable acrylic polymer in the polymer component is 60% by weight, and the total amount of the polymer component (100% by weight) is the living radical polymerization crosslinkable acrylic polymer. Is preferred. By setting the content of the living radical polymerization crosslinkable acrylic polymer in the polymer component to 60% by weight or more, high constant load peelability to the adherend can be exhibited.
In addition, the tackifier resin mentioned later is not included in the polymer component.

The pressure-sensitive adhesive layer has a gel fraction of 50% by weight or less.
In the pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing a free radical polymerization acrylic polymer, if the gel fraction with excellent constant load peelability is set, the strain stress resistance decreases, and the gel fraction with excellent strain stress resistance Due to the trade-off relationship that, if set, the constant load peelability would be reduced, the gel fraction had to be adjusted within a somewhat narrow region between 15 and 35%.
On the other hand, in the pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing a living radical polymerization acrylic polymer, if the gel fraction is 80% by weight or more, the adhesive strength is reduced, and the performance that no adhesive remains at the time of peeling is exhibited. It has been known. This means that the adhesive strength increases when the gel fraction is less than 80% by weight. However, in adhesive tapes that have an adhesive layer containing living radical polymerization acrylic polymer as a polymer component, it is difficult to peel off even if it is thin, can exhibit high constant load peelability to the adherend, and has excellent strain stress resistance There was no known range of gel fractions.

As a result of intensive studies, the inventors have determined that the gel fraction of the pressure-sensitive adhesive layer containing a living radical polymerization crosslinkable acrylic polymer containing 2-ethylhexyl acrylate as a monomer component is 50% by weight or less. It has been found that a high constant load peelability and adhesive cohesive strength can be exhibited with respect to the adherend and that high strain stress resistance can be exhibited. This is because the living radical polymerization crosslinkable acrylic polymer has a uniform composition of all the polymers contained and has crosslinkable functional groups, so that all the polymers can participate in crosslinking between polymer chains. It is considered that the adhesive cohesive force can be exhibited and the constant load peeling force is improved.
When the gel fraction exceeds 50% by weight, the pressure-sensitive adhesive layer becomes hard and the constant load peelability to the adherend is lowered. The gel fraction is preferably 45% by weight or less, and more preferably 40% by weight or less.

The gel fraction is measured as follows. First, the adhesive tape was cut into a flat rectangular shape of 50 mm × 100 mm to prepare a test piece. After the test piece was immersed in ethyl acetate at 23 ° C. for 24 hours, the test piece was taken out from ethyl acetate and subjected to a condition of 110 ° C. For 1 hour. The weight of the test piece after drying is measured, and the gel fraction is calculated using the following formula (1). In addition, the release film for protecting an adhesive layer shall not be laminated | stacked on the test piece.
Gel fraction (% by weight) = 100 × (W2-W0) / (W1-W0) (1)
(W0: weight of substrate, W1: weight of test piece before immersion, W2: weight of test piece after immersion and drying)

In order to obtain a pressure-sensitive adhesive layer having a gel fraction in the above range, the pressure-sensitive adhesive layer contains a crosslinking agent. By appropriately adjusting the type or amount of the crosslinking agent, the gel fraction of the pressure-sensitive adhesive layer can be easily adjusted to the above range. The crosslinking agent is not particularly limited, and may be, for example, an isocyanate crosslinking agent, an aziridine crosslinking agent, an epoxy crosslinking agent, or a metal chelate crosslinking according to the type of crosslinking functional group of the living radical polymerization crosslinking acrylic polymer. An agent or the like is selected and used.
For example, when the living radical polymerization crosslinkable acrylic polymer has a hydroxyl group as a crosslinkable functional group, the living radical polymerization crosslinkable acrylic polymer can be cross-linked by using, for example, an isocyanate crosslinker as a crosslinker. . In addition, when the living radical polymerization crosslinkable acrylic polymer has a carboxyl group as a crosslinkable functional group, the living radical polymerization crosslinkable acrylic polymer can be obtained by using, for example, an epoxy crosslinking agent or an aziridine crosslinking agent as a crosslinking agent. It can be cross-linked. The living radical polymerization crosslinkable acrylic polymer has a uniform composition of all the polymers contained therein and has a crosslinkable functional group, so that all the polymers can participate in crosslinking between polymer chains. For this reason, even if it is a thin adhesive tape, it is hard to peel off and the adhesive tape which can exhibit high constant load peelability and adhesive cohesive force with respect to a to-be-adhered body can be obtained.
Especially, since it is excellent in the adhesive stability with respect to a base material, an isocyanate type crosslinking agent is preferable. Examples of the isocyanate-based crosslinking agent include Coronate HX (manufactured by Nippon Polyurethane Industry Co., Ltd.), Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.), and Mytec NY260A (manufactured by Mitsubishi Chemical Corporation).

The blending amount of the crosslinking agent is preferably 0.01 parts by weight, preferably 5 parts by weight, and more preferably 0.1 parts by weight with respect to 100 parts by weight of the living radical polymerization crosslinkable acrylic polymer. A more preferred upper limit is 3 parts by weight. Within this range, the gel fraction of the pressure-sensitive adhesive layer can be adjusted to 50% by weight or less.

The pressure-sensitive adhesive layer preferably further contains a tackifier resin. When the said adhesive layer contains tackifying resin, the constant load peelability with respect to the adherend of an adhesive tape improves. Especially, when using the tackifier which has a crosslinkable functional group, it can be bridge | crosslinked with the said living radical polymerization crosslinkable acrylic polymer via a crosslinking agent.

The tackifying resin has a preferred lower limit of hydroxyl value of 25 and a preferred upper limit of 55. When the hydroxyl value is out of the above range, the constant load peelability of the adhesive tape to the adherend may be lowered. A more preferred lower limit of the hydroxyl value is 30, and a more preferred upper limit is 50.
The hydroxyl value can be measured by JIS K1557 (phthalic anhydride method).

The tackifying resin has a preferable lower limit of the softening temperature of 70 ° C and a preferable upper limit of 170 ° C. When the softening temperature is less than 70 ° C., the tackifying resin may be too soft and the constant load peelability may be lowered. When the softening temperature exceeds 170 ° C., the pressure-sensitive adhesive layer becomes too hard, the pressure-sensitive adhesive tape is easily peeled off, and the constant load peelability to the adherend may be lowered. A more preferable lower limit of the softening temperature is 120 ° C.
The softening temperature is a softening temperature measured by the JIS K2207 ring and ball method.

The tackifying resin is not particularly limited, and examples thereof include rosin resins such as rosin ester resins, terpene resins such as terpene phenol resins, and petroleum resins. Of these, rosin ester resins and terpene phenol resins are preferable.
The above-mentioned rosin ester resins are rosin resins mainly composed of abietic acid, disproportionated rosin resins and hydrogenated rosin resins, dimers of polymer acids such as abietic acid (polymerized rosin resins), etc. It is the resin obtained by making it. A part of the hydroxyl group of the alcohol used for esterification is contained in the resin without being used for esterification, so that the hydroxyl value is adjusted to the above range. Examples of the alcohol include polyhydric alcohols such as ethylene glycol, glycerin, and pentaerythritol.
Resin esterified rosin resin is rosin ester resin, disproportionated rosin resin esterified disproportionated rosin ester resin, hydrogenated rosin resin esterified resin is hydrogenated rosin ester resin, polymerized rosin A resin obtained by esterifying the resin is a polymerized rosin ester resin.
The terpene phenol resin is a resin obtained by polymerizing terpene in the presence of phenol.

Examples of the disproportionated rosin ester resin include Superester A75 (hydroxyl value 23, softening temperature 75 ° C.) manufactured by Arakawa Chemical Industries, Superester A100 (hydroxyl value 16, softening temperature 100 ° C.) manufactured by Arakawa Chemical Co., Ltd. Examples thereof include ester A115 (hydroxyl value 19, softening temperature 115 ° C.), super ester A125 (hydroxyl value 15, softening temperature 125 ° C.) manufactured by the same company. Examples of the hydrogenated rosin ester resin include Pine Crystal KE-359 (hydroxyl value 42, softening temperature 100 ° C.) manufactured by Arakawa Chemical Industries, and ester gum H (hydroxyl value 29, softening temperature 70 ° C.) manufactured by the same company. It is done. Examples of the polymerized rosin ester resin include Pencel D135 (hydroxyl value 45, softening temperature 135 ° C.) manufactured by Arakawa Chemical Industries, Pencel D125 (hydroxyl value 34, softening temperature 125 ° C.) manufactured by Arakawa Chemical Co., Ltd. 42, softening temperature 160 ° C.) and the like.
Examples of the terpene resin include YS Polystar G150 (softening point 150 ° C.) manufactured by Yasuhara Chemical, YS Polyster T100 (softening point 100 ° C.), YS Polyster G125 (softening point 125 ° C.), YS Polystar Examples thereof include T115 (softening point 115 ° C.), YS Polystar T130 (softening point 130 ° C.) manufactured by the same company.
These tackifier resins may be used alone or in combination of two or more.

The content of the tackifying resin is preferably 5 parts by weight with respect to 100 parts by weight of the living radical polymerization crosslinkable acrylic polymer, and 40 parts by weight with a preferable upper limit. When the content is less than 5 parts by weight, the adhesive tape is easily peeled off, and the constant load peelability to the adherend may be lowered. Even if the content exceeds 40 parts by weight, the pressure-sensitive adhesive layer may become too hard due to an increase in the glass transition temperature (Tg), and the pressure-sensitive adhesive tape may be easily peeled off.

The pressure-sensitive adhesive layer may contain other resins such as additives such as a plasticizer, an emulsifier, a softener, a filler, a pigment, a dye, a silane coupling agent, and an antioxidant, if necessary. Good.

Since the pressure-sensitive adhesive tape of the present invention is difficult to peel off even if it is a thin pressure-sensitive adhesive tape, the pressure-sensitive adhesive layer and the substrate described later can be made thin according to the application.
The thickness of the pressure-sensitive adhesive layer is not particularly limited because it is set depending on the application, but a preferred lower limit is 1 μm and a preferred upper limit is 100 μm. When the thickness is less than 1 μm, the pressure-sensitive adhesive tape is easily peeled off, and the constant load peelability to the adherend may be lowered. When the said thickness exceeds 100 micrometers, a thin adhesive tape may not be obtained. The more preferable lower limit of the thickness of the pressure-sensitive adhesive layer is 3 μm, the more preferable upper limit is 75 μm, the still more preferable lower limit is 5 μm, and the still more preferable upper limit is 25 μm.

The pressure-sensitive adhesive tape of the present invention may be a support type having a base material or a non-support type having no base material. In the case of the support type, the pressure-sensitive adhesive layer may be formed on one side of the substrate, or the pressure-sensitive adhesive layer may be formed on both sides.

Although the said base material is not specifically limited, A resin film, a resin foam, paper, a nonwoven fabric, a yarn cloth cloth etc. are mentioned.
Examples of the resin film include polyolefin resin films such as polyethylene films and polypropylene films, polyester resin films such as PET films, and modified olefins such as ethylene-vinyl acetate copolymers and ethylene-acrylic acid ester copolymers. Examples thereof include a resin film, a polyvinyl chloride resin film, a polyurethane resin film, and a cycloolefin polymer resin film.
Examples of the resin foam include polyethylene foam, polypropylene foam, acrylic foam, urethane foam, and ethylene propylene rubber foam.
Examples of the yarn cloth cloth include a woven polyethylene flat yarn and a laminate of a resin film on the surface thereof.
Especially in the case of double-sided tapes used in the assembly of display modules, black-printed substrates to prevent light transmission, white-printed substrates to improve light reflectivity, metal-deposited film substrates, etc. Can also be used.

The thickness of the substrate is not particularly limited because it is set depending on the application, but for example, in the case of a film substrate, 1 to 100 μm is preferable, and 5 to 75 μm is more preferable. When the thickness of the substrate is less than 1 μm, the mechanical strength of the adhesive tape may be lowered. If the thickness of the base material exceeds 100 μm, the adhesive tape may become too stiff and it may be difficult to adhere and adhere together along the shape of the adherend.

The production method of the pressure-sensitive adhesive tape of the present invention is not particularly limited. For example, the living radical polymerization crosslinkable acrylic polymer is mixed with other compounding components such as the tackifying resin and the crosslinking agent as necessary, and stirred. Then, the pressure-sensitive adhesive solution is prepared, and subsequently this pressure-sensitive adhesive solution is applied to a release-treated PET film and dried to form a pressure-sensitive adhesive layer. The resulting pressure-sensitive adhesive layer is applied to one or both sides of the substrate. Examples thereof include a method of transferring and a method of directly coating and drying the substrate. The pressure-sensitive adhesive layer formed by coating and drying the PET film obtained by releasing the pressure-sensitive adhesive solution may be used as a non-support type pressure-sensitive adhesive tape without a substrate.

The use of the pressure-sensitive adhesive tape of the present invention is not particularly limited, but since an optical film can be fixed in a portable electronic device (for example, a mobile phone, a portable information terminal, etc.) because it can achieve both high constant load peelability and high strain stress resistance. In particular, it can be used suitably for the use.

ADVANTAGE OF THE INVENTION According to this invention, the adhesive tape which was used suitably for fixation of an optical film and was compatible with the high constant load peelability with respect to a to-be-adhered body, and high strain-stress resistance can be provided.

It is a schematic diagram explaining living radical polymerization. It is a schematic diagram explaining the case where a living radical polymerization crosslinkable acrylic polymer is bridge | crosslinked. It is a schematic diagram explaining free radical polymerization. It is a schematic diagram explaining the case where a free radical polymerization crosslinkable acrylic polymer is bridge | crosslinked. It is the schematic diagram which showed the test method which measures the grade of the optical film distortion in an Example. It is the schematic diagram which showed the test method of the constant load peeling test in an Example.

Hereinafter, embodiments of the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Preparation of acrylic polymer)
(Synthesis 1)
(Synthesis 1-1)
Tellurium (40 mesh, metal tellurium, manufactured by Aldrich) 6.38 g (50 mmol) was suspended in tetrahydrofuran (THF) 50 mL, and 1.6 mol / L n-butyllithium / hexane solution (Aldrich) 34 was added thereto. 4 mL (55 mmol) was slowly added dropwise at room temperature. The reaction solution was stirred until the metal tellurium disappeared completely. To this reaction solution, 10.7 g (55 mmol) of ethyl-2-bromo-isobutyrate was added at room temperature and stirred for 2 hours. After completion of the reaction, the solvent was concentrated under reduced pressure, followed by distillation under reduced pressure to obtain a yellow oily ethyl 2-methyl-2-n-butylteranyl-propionate.

(Synthesis 1-2)
In a glove box substituted with argon, in a reaction vessel, 19 μL of ethyl 2-methyl-2-n-butylteranyl-propionate prepared in Synthesis Example 1-1, V-60 (2,2′-azobisisobutyro Nitrile (manufactured by Wako Pure Chemical Industries, Ltd.) (1.4 mg) and ethyl acetate (1 mL) were added, the reaction vessel was sealed, and the reaction vessel was removed from the glove box. Subsequently, while flowing argon gas into the reaction vessel, mixed monomers shown in Table 1 (2EHA: 2-ethylhexyl acrylate, BA: butyl acrylate, EA: ethyl acrylate, AAc: acrylic acid, HEA: 2) -Hydroxyethyl acrylate) 100 g in total and 66.5 g of ethyl acetate as a polymerization solvent were added and a polymerization reaction was carried out at 60 ° C. for 20 hours to obtain a living radical polymerization crosslinkable acrylic polymer-containing solution.
The resulting living radical polymerization crosslinkable acrylic polymer was diluted 50 times with tetrahydrofuran (THF), and the resulting diluted solution was filtered through a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm). The filtrate was supplied to a gel permeation chromatograph (manufactured by Waters, 2690 Separations Model), and GPC measurement was performed under the conditions of a sample flow rate of 1 ml / min and a column temperature of 40 ° C., and the polystyrene equivalent molecular weight of the polymer was measured. The weight average molecular weight (Mw) and the molecular weight distribution (Mw / Mn) were determined. GPC KF-806L (Showa Denko) was used as the column, and a differential refractometer was used as the detector.

(Synthesis 2-6)
Preparation amount of ethyl 2-methyl-2-n-butylteranyl-propionate, preparation amount of V-60 (2,2′-azobisisobutyronitrile, manufactured by Wako Pure Chemical Industries, Ltd.), and composition of mixed monomer A living radical polymerization crosslinkable acrylic polymer-containing solution was obtained in the same manner as in Synthesis 1 except that the weight average molecular weight (Mw) and molecular weight distribution (Mw / Mn) were determined.

(Synthesis 7)
50 g of ethyl acetate was added as a polymerization solvent in the reaction vessel, and after bubbling with nitrogen, the reaction vessel was heated while flowing nitrogen and refluxing was started. Subsequently, a polymerization initiator solution obtained by diluting 150 mg of V-60 (2,2′-azobisisobutyronitrile, manufactured by Wako Pure Chemical Industries, Ltd.) 10 times with ethyl acetate as a polymerization initiator was placed in the reaction vessel. A total of 100 g of the mixed monomers shown in Table 1 was added dropwise over 2 hours. After completion of the dropwise addition, a polymerization initiator solution in which 150 mg of V-60 (2,2′-azobisisobutyronitrile, manufactured by Wako Pure Chemical Industries, Ltd.) as a polymerization initiator was diluted 10 times with ethyl acetate was again put in the reaction vessel. Then, a polymerization reaction was carried out for 4 hours to obtain a free radical polymerization polymer-containing solution.
In the same manner as in Synthesis 1, the weight average molecular weight (Mw) and the molecular weight distribution (Mw / Mn) were determined.

(Examples 1-6, Comparative Examples 1-3)
To the radical polymerization crosslinkable acrylic polymer-containing solution obtained above, ethyl acetate was added to 100 parts by weight of the nonvolatile content and stirred, and coronate L (isocyanate-based crosslinking agent, manufactured by Nippon Polyurethane Co., Ltd.) as a crosslinking agent, As a tackifying resin, Pencel D135 (polymerized rosin ester, manufactured by Arakawa Chemical Co., Ltd.) and YS Polystar G125 (terpene-based tackifying resin, manufactured by Yasuhara Chemical Co., Ltd.) were added in predetermined amounts shown in Table 2 and stirred, and the nonvolatile content was 30% by weight. An adhesive solution was obtained. The obtained pressure-sensitive adhesive solution was applied to a PET film having a thickness of 50 μm which had been subjected to a release treatment so that the paste thickness would be 7.5 μm after drying, and then dried at 70 ° C. for 10 minutes to obtain a pressure-sensitive adhesive tape. In addition, the release film for protecting an adhesive layer was laminated | stacked on the surface of the both sides of an adhesive layer.

The obtained adhesive tape was cut into a flat rectangular shape of 50 mm × 100 mm to prepare a test piece, and the release film was peeled off. The test piece was immersed in ethyl acetate at 23 ° C. for 24 hours, then taken out from the ethyl acetate and dried at 110 ° C. for 1 hour. The weight of the test piece after drying was measured, and the gel fraction was calculated using the following formula (1).
Gel fraction (% by weight) = 100 × (W2-W0) / (W1-W0) (1)
(W0: weight of substrate, W1: weight of test piece before immersion, W2: weight of test piece after immersion and drying)

(Evaluation)
The following evaluation was performed about the adhesive tape obtained by the Example and the comparative example. The results are shown in Table 2.

(1) Optical Film Optical Distortion Test FIG. 5 is a schematic diagram showing a test method for measuring the degree of optical film distortion. Whether or not the expansion and contraction deformation of the optical film due to temperature change can be alleviated by the pressure-sensitive adhesive layer was evaluated by a method in which a test sample as shown in FIG. 5 was exposed to a high temperature condition.
The release film on one surface of the test piece 30 obtained by punching the double-sided adhesive tape into a frame shape with a width of 2.5 mm is peeled and removed, and on the exposed adhesive layer, as shown in FIG. A PC frame 31 having a frame width of 5 mm and 100 mm × 63 mm and a BEF sheet 32 (TBEF II GMV2 (24)) of 88 mm × 51 mm were bonded together. At this time, the adhesion widths of the test piece 30 and the PC frame 31, and the test piece 30 and the BEF sheet 32 were adjusted to be 1 mm.
Next, the release film on the opposite surface of the test piece 30 was peeled and removed, and the glass plate 33 was bonded onto the exposed pressure-sensitive adhesive layer, and a 10 kg weight was applied for 10 seconds. Then, the test sample 34 was produced by leaving still at 23 degreeC and 50% of relative humidity for at least 24 hours.
Test sample 34 was placed in an 85 ° C. oven and allowed to stand for 96 hours. Thereafter, the temperature was slowly returned to room temperature over 30 minutes, and the optical film was evaluated for distortion according to the following criteria.
A: No distortion was observed. O: Distortion was observed but the image was not affected. X: Distortion was observed and the image was affected.

(2) Constant load peelability with respect to polycarbonate (PC) plate FIG. 6 is a schematic diagram showing a test method of a constant load peel test. As shown in FIG. 6, the obtained double-sided adhesive tape was cut into a strip shape having a width of 20 mm and a length of 50 mm to produce a test piece 41, and the release film was peeled off from the surface of the test piece 41. The pressure-sensitive adhesive layer was exposed and placed on the polycarbonate plate 40 so that the pressure-sensitive adhesive layer was opposed.
Next, the release film was peeled off from the back surface of the test piece 41, and a polyethylene terephthalate film (not shown) having a thickness of 23 μm was laminated on the exposed adhesive layer, and then 300 mm on the back surface of the test piece 41. The test sample 42 and the polycarbonate plate 40 are adhered by reciprocating a 2 kg rubber roller at a speed of 1 min / min, and the test sample 42 is left to stand for 24 hours under conditions of 23 ° C. and 50% relative humidity. Produced.
Next, the test sample 42 is put in an oven at 85 ° C., and as shown in FIG. 6, a load is applied to one end of the test piece 41 of the test sample 42 in a direction perpendicular to the sticking surface. Thus, the 50 g weight 43 was attached, and the time until the test piece 41 dropped from the polycarbonate plate 40 was measured. Based on the measured values, the constant load peelability was evaluated according to the following criteria.
○: Drop time was 1 hour or more ×: Drop time was less than 1 hour

ADVANTAGE OF THE INVENTION According to this invention, the adhesive tape which was used suitably for fixation of an optical film and was compatible with the high constant load peelability with respect to a to-be-adhered body, and high strain-stress resistance can be provided.

DESCRIPTION OF SYMBOLS 1 Living radical polymerization crosslinkable acrylic polymer 11 Monomer which does not contain a crosslinkable functional group 12 Crosslinkable functional group containing monomer 2 Free radical polymerization crosslinkable acrylic polymer 21 Monomer which does not contain a crosslinkable functional group 22 Crosslinkable functional group containing monomer 23 Polymer whose growth end radical was deactivated during the reaction 24 Polymer grown by radical species newly generated during the reaction 30 Test piece 31 PC frame 32 BEF sheet 33 Glass plate 34 Test sample 40 PC plate 41 Test piece 42 Test sample 43 50g weight

Claims (5)

A weight average molecular weight of 300,000 to 2,000,000, molecular weight distribution (Mw) obtained by living radical polymerization of a monomer mixture containing at least an alkyl acrylate monomer having 8 alkyl groups and a crosslinkable functional group-containing monomer. / Mn) A pressure-sensitive adhesive tape having a pressure-sensitive adhesive layer containing a polymer component containing 60% by weight or more of a living radical polymerization crosslinkable acrylic polymer of 1.05 to 2.5, a tackifier resin, and a crosslinking agent. And
The alkyl acrylate alkyl ester monomer having 8 alkyl groups is 2-ethylhexyl acrylate, n-octyl acrylate or isooctyl acrylate,
The content of the alkyl alkyl ester monomer having 8 alkyl groups in the monomer mixture is 60% by weight or more,
The pressure-sensitive adhesive tape, wherein the pressure-sensitive adhesive layer has a gel fraction of 50% by weight or less. The pressure-sensitive adhesive tape according to claim 1, wherein the tackifier resin has a hydroxyl value of 25 or more and 55 or less. The pressure-sensitive adhesive tape according to claim 1 or 2, wherein a softening temperature of the tackifying resin is 70 ° C or higher and 170 ° C or lower. The pressure-sensitive adhesive tape according to claim 1, wherein the tackifying resin is a rosin ester resin or a terpene phenol resin. The pressure-sensitive adhesive tape according to any one of claims 1 to 4, wherein a content of the tackifying resin is 5 parts by weight or more and 40 parts by weight or less with respect to 100 parts by weight of the living radical polymerization crosslinkable acrylic polymer.

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