JP2020076096A - Adhesive layer, adhesive composition, adhesive and adhesive sheet - Google Patents

Abstract

To provide an adhesive layer excellent not only in folding durability but also excellent in moist heat-resistant haze property while having excellent adhesive force to an adherend.SOLUTION: The adhesive layer is produced by curing [I] an adhesive composition containing (A) an acrylic resin, and has an adhesive force (α) of 25 N/25 mm or more, folding durability (β) of 100,000 times or more and a moist heat-resistant haze property (γ) of 1.0% or less, each as measured under predetermined conditions.SELECTED DRAWING: None

Description

  The present invention relates to a pressure-sensitive adhesive layer, a pressure-sensitive adhesive composition, a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet, and in particular, while being excellent in adhesive strength to an adherend, it is also excellent in bending durability, and further The present invention relates to a pressure-sensitive adhesive layer, a pressure-sensitive adhesive composition, a pressure-sensitive adhesive and a pressure-sensitive adhesive sheet which are also excellent in haze suppression (hereinafter, sometimes referred to as “moisture heat haze resistance”) under a humid heat environment.

In recent years, mobile devices such as televisions and monitors for personal computers, laptop computers, mobile phones, tablet terminals and wearable terminals usually have a protective layer formed of a plastic sheet or the like on the viewing side of the display, which is external. In order to prevent damage to the display due to impact, a space (air layer) is provided between the display and the protective layer.
However, there is a problem that reflection occurs at the interface between the protective layer and the air layer and at the interface between the air layer and the display, which causes a reduction in visibility.
Therefore, in recent years, an impact absorbing pressure-sensitive adhesive layer has been used instead of an air layer for the purpose of improving visibility and further reducing the thickness of a mobile device (plastic sheet) while ensuring impact resistance. ..

  In order for the pressure-sensitive adhesive layer to exhibit sufficient impact absorption performance, it is necessary to have a certain amount of thickness, but the solvent-based acrylic pressure-sensitive adhesive that has been commonly used in the past has been used for thick coating applications. In that case, since the thickness of the pressure-sensitive adhesive layer at the time of coating is large, there is a problem that coating dripping occurs or the solvent is hard to volatilize in the drying step after coating and remains as foam in the pressure-sensitive adhesive layer. was there.

On the other hand, it has been proposed to use a solventless adhesive, and a hot melt adhesive and an active energy ray-curable adhesive have been proposed (for example, Patent Document 1).
Among solvent-free pressure-sensitive adhesives, the hot-melt pressure-sensitive adhesive does not require a drying step for volatilizing the solvent after coating, and even in the case of thick coating, the pressure-sensitive adhesive layer can be efficiently used in a short time. Is what you can get.

JP, 2014-214280, A

In recent years, from the viewpoint of high functionality and multi-functionality of mobile devices and further diversification of design, it has been required to make a flat display curved and flexible, so that the board does not break even if it is bent. There is a demand for an adhesive that prevents cracks from entering the substrate when it is bent.
However, in the technique disclosed in the above-mentioned Patent Document 1, these bending durability are not taken into consideration, and improvement as a pressure-sensitive adhesive composition is required.
In addition, an adhesive with a low elastic modulus is conceivable from the viewpoint of improving the bending durability, but it is feared that the adhesive strength and the moist heat haze resistance will decrease by itself, and the bending durability, the adhesive strength, and the moist heat resistance Further improvement is required in order to make all of the haze excellent in balance.

  Therefore, in the present invention, under such a background, an adhesive layer having excellent adhesion to an adherend, excellent bending durability, and excellent moisture and heat haze resistance, and the adhesive layer are formed. An object is to provide an adhesive composition, an adhesive and an adhesive sheet.

  However, as a result of intensive studies conducted by the present inventors in view of such circumstances, the pressure-sensitive adhesive layer is a cured pressure-sensitive adhesive composition containing an acrylic resin, and the adhesive force is 25 N / 25 mm or more, The present invention has been completed by finding that an adhesive layer having a bending durability of 100,000 times or more and a moisture and heat haze resistance of 1.0% or less meets the object of the present invention.

  In the present invention, the acrylic resin contained in the pressure-sensitive adhesive composition contains at least two kinds of acrylic resins having different glass transition temperatures and having a weight average molecular weight of 10,000 or more. The glass transition temperature read from the temperature at which the loss tangent of the dynamic viscoelasticity is maximum is −20 ° C. or less, and the glass transition temperature of the acrylic resin having the highest glass transition temperature and the lowest glass transition temperature of the acrylic resin. It has been found that the object of the present invention is particularly satisfied when the difference in glass transition temperature of the acrylic resin is 20 ° C. or less.

That is, the present invention is a pressure-sensitive adhesive layer obtained by curing a pressure-sensitive adhesive composition [I] containing an acrylic resin (A), the adhesive force (α) below is 25 N / 25 mm or more, and the following bending The first gist is a pressure-sensitive adhesive layer having a durability (β) of 100,000 times or more and the following moisture-heat haze resistance (γ) of 1.0% or less.
Adhesive strength (α):
When a pressure-sensitive adhesive layer is formed on a polyethylene terephthalate sheet (thickness: 125 μm) that has been subjected to an easy-adhesion treatment, the pressure-sensitive adhesive layer side of the pressure-sensitive adhesive sheet is a 2 kg roller on non-alkali glass at 23 ° C. and 50% RH environment. 180 degree peel strength (N / 25 mm) measured at a peeling speed of 300 mm / min using an autograph, after reciprocating and pressure-bonding and leaving still at 23 ° C. and 50% RH for 30 minutes.
Folding durability (β):
When the pressure-sensitive adhesive layer is a pressure-sensitive adhesive sheet formed on a polyethylene terephthalate sheet (thickness 125 μm) that has been subjected to an easy-adhesion treatment, the pressure-sensitive adhesive layer side of the pressure-sensitive adhesive sheet is changed to transparent polyimide (thickness 50 μm) under an environment of 23 ° C. and 50% RH. The roller is reciprocated and pressure-bonded, and the distance between the sheets when the polyethylene terephthalate sheet side is folded is 5 mm at a speed of 40 times / min at 23 ° C. and 50% RH environment. The number of times the appearance has not changed after repeated bending tests.
Moisture and heat haze resistance (γ):
When a pressure-sensitive adhesive layer was formed on a polyethylene terephthalate sheet (thickness 125 μm) that was subjected to easy-adhesion treatment, it was bonded to non-alkali glass (thickness 1.1 mm) and then autoclaved (50 ° C., 0.5 MPa). , 20 minutes), and using the obtained test piece, a humidity and heat resistance test is performed for 7 days (168 hours) at 60 ° C. and 90% RH atmosphere, and a haze value after the humidity and heat resistance test and before the humidity and heat resistance test. Difference.

  Further, the present invention is a pressure-sensitive adhesive composition [I] containing an acrylic resin (A), wherein the acrylic resin (A) is an acrylic resin having a different glass transition temperature and a weight average molecular weight of 10,000 or more. It contains at least two kinds of resins, and the glass transition temperature (T) read from the temperature at which the loss tangent of the dynamic viscoelasticity of the acrylic resin (A) becomes maximum is −20 ° C. or less, and most A pressure-sensitive adhesive composition in which the temperature difference between the glass transition temperature (T1) of the acrylic resin (A1) having a high glass transition temperature and the glass transition temperature (T2) of the acrylic resin (A2) having the lowest glass transition temperature is 20 ° C. or less. The thing is the second gist.

  Further, in the present invention, a pressure-sensitive adhesive comprising the pressure-sensitive adhesive composition according to the second aspect is a third aspect, and an adhesive having a pressure-sensitive adhesive layer formed using the pressure-sensitive adhesive composition according to the second aspect. A sheet is the fourth gist.

  The pressure-sensitive adhesive layer of the present invention is a pressure-sensitive adhesive layer obtained by curing a pressure-sensitive adhesive composition [I] containing an acrylic resin (A), and the pressure-sensitive adhesive force (α) is 25 N / 25 mm or more, Since the bending durability (β) is 100,000 times or more and the moist-heat haze resistance (γ) is 1.0% or less, the adhesive strength to the adherend is excellent and the bending It has excellent durability and also has excellent resistance to moist heat and haze. Therefore, it is particularly useful as a pressure-sensitive adhesive or a pressure-sensitive adhesive sheet used for a touch panel, an image display device or the like, particularly for a touch panel or an image display device of a folding smartphone or the like.

  Further, the pressure-sensitive adhesive composition of the present invention, when used as a pressure-sensitive adhesive, has excellent adhesive strength to an adherend, but also has excellent bending durability, and is also excellent in moist-heat haze resistance. is there. Therefore, it is particularly useful as a pressure-sensitive adhesive or a pressure-sensitive adhesive sheet used for a touch panel, an image display device or the like, particularly for a touch panel or an image display device of a folding smartphone or the like.

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below, but these show one example of preferred embodiments.
In the present invention, "(meth) acrylic" means acrylic or methacrylic, "(meth) acryloyl" means acryloyl or methacryloyl, and "(meth) acrylate" means acrylate or methacrylate. ..

  The pressure-sensitive adhesive layer of the present invention is a pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition [I] containing the acrylic resin (A), and has an adhesive force (α) measured under the following measurement conditions and bending durability. Both (β) and the resistance to moisture and heat haze (γ) satisfy predetermined values.

<Adhesive strength (α)>
When the pressure-sensitive adhesive layer of the present invention is a pressure-sensitive adhesive sheet formed on a polyethylene terephthalate (PET) sheet (125 μm in thickness) which has been subjected to easy-adhesion treatment, the pressure-sensitive adhesive layer has a temperature of 23 ° C. on the pressure-sensitive adhesive layer side of the pressure-sensitive adhesive sheet. , 2kg roller reciprocatingly pressure-bonded to non-alkali glass under 50% RH environment, and after standing still at 23 ° C, 50% RH environment for 30 minutes, using autograph, peeling speed 300mm / min The measured 180 degree peel strength (N / 25 mm).

  The pressure-sensitive adhesive layer of the present invention has an adhesive force (α) measured by the above method of 25 N / 25 mm or more, preferably 28 N / 25 mm or more, and particularly preferably 30 N / 25 mm or more. The upper limit of the adhesive strength (α) is usually 100 N / 25 mm, preferably 50 N / 25 mm.

<Folding durability (β)>
The bending durability (β) is 23 when the pressure-sensitive adhesive layer of the invention is a pressure-sensitive adhesive sheet formed on a polyethylene terephthalate (PET) sheet (thickness: 125 μm) which has been subjected to an easy-adhesion treatment. Rolled back and forth with a roller on a transparent polyimide sheet (thickness 50 μm) under an environment of 50 ° C. and 50% RH, and 40 times so that the distance between the sheets when folded with the PET sheet side inside was 5 mm / A bending test is repeatedly performed at a rate of min at 23 ° C. and 50% RH to measure the number of times that there is no change in appearance. The above "no change in appearance" means that there are no cracks or cloudiness in any of the pressure-sensitive adhesive layer, the transparent polyimide, and the PET sheet. In addition, visually check the appearance for changes.

  The pressure-sensitive adhesive layer of the present invention has a bending durability (β) measured by the above method of 100,000 times or more, preferably 150,000 times or more, and particularly preferably 200,000 times or more.

<Moisture and heat haze resistance (γ)>
When the pressure-sensitive adhesive layer of the present invention is used as a pressure-sensitive adhesive sheet formed on a polyethylene terephthalate (PET) sheet (125 μm in thickness) for easy adhesion treatment, it is applied to non-alkali glass (thickness: 1.1 mm). After combining, autoclave treatment (50 ° C., 0.5 MPa, 20 minutes) was performed, and using the obtained test piece, a wet heat resistance test was performed for 7 days (168 hours) at 60 ° C. and 90% RH environment. The difference between the haze values after the moist-heat resistance test and before the moist-heat resistance test is calculated from the following formula.
The difference between the haze value (%) = H ₂ -H ₁
The above H ₁ represents the haze value before the moist heat resistance test, and H ₂ represents the haze value after the moist heat resistance test.

  The adhesive layer of the present invention has a moisture and heat haze resistance (γ) measured by the above method of 1.0% or less, preferably 0.8% or less, and particularly preferably 0.5% or less. The lower limit of the resistance to moisture and heat haze (γ) is usually 0.1%.

The pressure-sensitive adhesive layer is obtained by curing the pressure-sensitive adhesive composition [I], and the pressure-sensitive adhesive composition [I] easily forms a thick pressure-sensitive adhesive layer, and further contains a solvent substantially from the viewpoint of the environment. It is preferable to use a non-solvent type pressure-sensitive adhesive composition.
Hereinafter, each component contained in the pressure-sensitive adhesive composition [I] will be described.

<Acrylic resin (A)>
The pressure-sensitive adhesive composition [I] contains an acrylic resin (A). The acrylic resin (A) preferably has a glass transition temperature of -20 ° C or lower.
The acrylic resin (A) may be made of one type of acrylic resin, or may contain two or more types of acrylic resins having different glass transition temperatures. Among them, as the acrylic resin (A), it is preferable to contain two or more kinds of acrylic resins having different glass transition temperatures and different weight average molecular weights of 10,000 or more from the viewpoint of achieving both adhesive strength and bending durability.
Furthermore, the acrylic resin (A) contains at least two kinds of acrylic resins having different weight average molecular weights of 10,000 or more and having different glass transition temperatures, and the glass transition of the acrylic resin (A1) having the highest glass transition temperature. The temperature difference between the temperature (T1) and the glass transition temperature (T2) of the acrylic resin (A2) having the lowest glass transition temperature is preferably 20 ° C. or less.

  Such an acrylic resin (A) containing at least two kinds of acrylic resins having different glass transition temperatures is usually obtained by mixing separately produced acrylic resins having different glass transition temperatures. The acrylic resin (A) containing at least two kinds of acrylic resins having different glass transition temperatures can also be obtained by devising a polymerization method such as two-step polymerization.

The number of acrylic resins in the case of mixing the separately manufactured acrylic resins having different glass transition temperatures is usually 2 to 4 types, preferably 2 to 3 types, and particularly preferably 2 types. The greater the number of acrylic resins contained in the acrylic resin (A), the lower the productivity and the economic efficiency.
The acrylic resin used in the present invention will be described below.

  The acrylic resin is obtained by polymerizing a copolymerization component containing a hydroxyl group-containing monomer (a1), and preferably has a (meth) acrylic acid alkyl ester having an alkyl group having 5 to 14 carbon atoms. At least one type of copolymerizable monomer (a2) selected from a group-based monomer and a vinyl ester-based monomer, and a (meth) acrylic acid alkyl ester-based monomer and a vinyl ester-based monomer having an alkyl group having 1 to 4 carbon atoms At least one copolymerizable monomer (a3) (excluding (a1) and (a2)) and, if necessary, a functional group-containing ethylenically unsaturated monomer (a4) (excluding (a1) .) And other copolymerizable monomer (a5) as a polymerization component.

<Hydroxyl group-containing monomer (a1)>
Examples of the hydroxyl group-containing monomer (a1) include 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 5-hydroxypentyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, and 8-. Hydroxy (meth) acrylates such as hydroxyoctyl (meth) acrylate, caprolactone modified monomers such as caprolactone modified 2-hydroxyethyl (meth) acrylate, oxyalkylene modified monomers such as diethylene glycol (meth) acrylate and polyethylene glycol (meth) acrylate, 2 -Primary hydroxyl group-containing monomers such as acryloyloxyethyl-2-hydroxyethylphthalic acid; 2-hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, 3-chloro-2-hydroxypropyl (meth) acrylate, etc. And a secondary hydroxyl group-containing monomer; and a secondary hydroxyl group-containing monomer such as 2,2-dimethyl-2-hydroxyethyl (meth) acrylate. These may be used alone or in combination of two or more.

  Among the above-mentioned hydroxyl group-containing monomers (a1), 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, from the viewpoint of excellent balance between moist heat resistance and heat resistance. It is particularly preferable to use 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate.

  In addition, in the case of producing an acrylic resin (A2) described later, a hydroxyl group-containing monomer containing 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate from the viewpoint of compatibility of adhesive strength and bending durability. Is preferably used as a copolymerization component, and it is particularly preferable to include only 2-hydroxy (meth) acrylate and 4-hydroxybutyl (meth) acrylate as the hydroxyl group-containing monomer.

  In the present invention, the copolymerization ratio of 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate [2-hydroxyethyl (meth) acrylate / 4-hydroxybutyl (meth) acrylate] is on a weight basis. , 95/5 to 30/70, more preferably 80/20 to 40/60, particularly 75/25 to 45/65, and particularly 70/30 to 50/50. If the amount of 2-hydroxyethyl (meth) acrylate is too small, the adhesive force when used as a pressure-sensitive adhesive will decrease, and if it is too large, the bending durability when used as a pressure-sensitive adhesive will tend to decrease.

  In addition, as the hydroxyl group-containing monomer (a1) used in the present invention, it is preferable that the content ratio of di (meth) acrylate contained as an impurity in the hydroxyl group-containing monomer (a1) is small, and specifically, 0.5 wt. % Or less, preferably 0.2% by weight or less, and more preferably 0.1% by weight or less.

In the present invention, the content of the hydroxyl group-containing monomer (a1) is usually 5 to 60% by weight, preferably 8 to 45% by weight, particularly preferably 10 to 40% by weight, based on the whole copolymerization component, It is preferably from 11 to 35% by weight, particularly preferably from 12 to 30% by weight.
If the content is too low, the resistance to moist heat when used as a pressure-sensitive adhesive tends to decrease, and if it is too high, the self-crosslinking reaction of the acrylic resin tends to occur, and the heat resistance tends to decrease.

<At least one copolymerizable monomer (a2) selected from a (meth) acrylic acid alkyl ester-based monomer and a vinyl ester-based monomer having an alkyl group having 5 to 14 carbon atoms>
In the present invention, as a copolymerization component, further contain a copolymerizable monomer having a structure in which hydrogen abstraction is likely to occur in a high energy state such as high temperature or ultraviolet irradiation, and as a result, crosslinks are easily formed. In particular, it is particularly preferable to contain at least one copolymerizable monomer (a2) selected from a (meth) acrylic acid alkyl ester-based monomer and a vinyl ester-based monomer having an alkyl group having 5 to 14 carbon atoms. It is more preferable to use a (meth) acrylic acid alkyl ester-based monomer having a branched structure and an alkyl group having 5 to 14 carbon atoms, particularly preferably 2-ethylhexyl (meth) acrylate. These may be used alone or in combination of two or more.

The content of the copolymerizable monomer (a2) is preferably 15 to 90% by weight, particularly preferably 20 to 85% by weight, further preferably 30 to 80% by weight, particularly preferably 30 to 80% by weight, based on the whole copolymerization component. It is preferably 40 to 75% by weight, and most preferably 45 to 70% by weight.
When the content is too small, the step followability and durability when used as an adhesive tend to be deteriorated. On the other hand, when the amount of the copolymerizable monomer (a2) is too large, the adhesive strength when used as an adhesive tends to decrease.

<At least one copolymerizable monomer (a3) selected from a (meth) acrylic acid alkyl ester-based monomer and a vinyl ester-based monomer having an alkyl group having 1 to 4 carbon atoms>
In the present invention, as the copolymerization component, at least one copolymerizable monomer (a3) selected from a (meth) acrylic acid alkyl ester-based monomer and a vinyl ester-based monomer, which further has an alkyl group having 1 to 4 carbon atoms. It is preferable to contain (however, excluding (a1) and (a2)) from the viewpoint of improving cohesive strength and further improving adhesive strength when used as an adhesive.

Examples of the copolymerizable monomer (a3) include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, t-butyl (meth) acrylate, isobutyl (meth) acrylate, and n-propyl. (Meth) acrylate, isopropyl (meth) acrylate, vinyl propionate, vinyl acetate and the like can be mentioned. These copolymerizable monomers (a3) may be used alone or in combination of two or more.
Among the above-mentioned copolymerizable monomers (a3), it is preferable to use methyl (meth) acrylate, ethyl (meth) acrylate, and t-butyl (meth) acrylate from the viewpoint of improving cohesive force when used as an adhesive. ..

  Further, among the above-mentioned copolymerizable monomers (a3), at least one (meth) acrylate (a3-1) of methyl (meth) acrylate and ethyl (meth) acrylate is used in order to further exert the effect of the present invention. It is preferable to use.

  The content of the copolymerizable monomer (a3) is preferably 5 to 70% by weight, particularly preferably 10 to 60% by weight, further preferably 15 to 45% by weight, based on the whole copolymerization component. is there. If the content of the copolymerizable monomer (a3) is too small, the adhesive strength when used as a pressure-sensitive adhesive tends to decrease, and if it is too large, the bending durability tends to decrease when used as a pressure-sensitive adhesive. There is.

  The content of the component (a3) in the case of using at least one (meth) acrylate (a3-1) of methyl (meth) acrylate and ethyl (meth) acrylate is based on the total amount of the copolymerization components. , 5 to 40% by weight, particularly preferably 7 to 30% by weight, further preferably 10 to 25% by weight. If the content of (a3-1) is too large, the handling property during processing tends to decrease due to an increase in viscosity, and if it is too small, the adhesive strength tends to decrease when used as an adhesive.

<Functional group-containing ethylenically unsaturated monomer (a4)>
In the present invention, a functional group-containing ethylenically unsaturated monomer (a4) (excluding (a1)) can be used as a copolymerization component of the acrylic resin, if necessary.

Examples of the functional group-containing ethylenically unsaturated monomer (a4) include a functional group-containing monomer having a nitrogen atom, an acetoacetyl group-containing monomer, an isocyanate group-containing monomer, and a glycidyl group-containing monomer.
Among these, a functional group-containing monomer having a nitrogen atom is preferable, particularly preferably an amino group-containing monomer and an amide group-containing monomer, more preferably an amino group-containing monomer, from the viewpoint of imparting cohesive force and crosslinking promoting action. Is.

  Examples of the amino group-containing monomer include primary amino group-containing (meth) acrylates such as aminomethyl (meth) acrylate and aminoethyl (meth) acrylate; t-butylaminoethyl (meth) acrylate, t-butylamino. Secondary amino group-containing (meth) acrylates such as propyl (meth) acrylate; ethylaminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, diethylamino Examples thereof include tertiary amino group-containing (meth) acrylates such as propyl (meth) acrylate and dimethylaminopropylacrylamide.

  Examples of the amide group-containing monomer include (meth) acrylamide; N-methyl (meth) acrylamide, N-ethyl (meth) acrylamide, N-propyl (meth) acrylamide, Nn-butyl (meth) acrylamide, dye. N-alkyl (meth) acrylamides such as acetone (meth) acrylamide, N, N'-methylenebis (meth) acrylamide; N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N, N- N, N-dialkyl (meth) acrylamides such as dipropyl (meth) acrylamide, N, N-ethylmethylacrylamide, N, N-diallyl (meth) acrylamide; N-hydroxymethyl (meth) acrylamide, N-hydroxyethyl (meth ) Hydroxyalkyl (meth) acrylamides such as acrylamide; alkoxyalkyl (meth) acrylamides such as N-methoxymethyl (meth) acrylamide and N- (n-butoxymethyl) (meth) acrylamide;

  Examples of the acetoacetyl group-containing monomer include 2- (acetoacetoxy) ethyl (meth) acrylate and allyl acetoacetate.

  Examples of the isocyanate group-containing monomer include 2-acryloyloxyethyl isocyanate, 2-methacryloyloxyethyl isocyanate, and their alkylene oxide adducts.

  Examples of the glycidyl group-containing monomer include glycidyl (meth) acrylate and allylglycidyl (meth) acrylate.

  These functional group-containing ethylenically unsaturated monomers (a4) may be used alone or in combination of two or more.

  The content of the functional group-containing ethylenically unsaturated monomer (a4) is preferably 30% by weight or less, particularly preferably 20% by weight or less, further preferably 10% by weight or less, based on the whole copolymerization component. It is particularly preferably 5% by weight or less. If the content of the functional group-containing ethylenically unsaturated monomer (a4) is too large, the heat resistance of the resin tends to decrease.

<Other copolymerizable monomer (a5)>
In the present invention, other copolymerizable monomer (a5) can be used as a copolymerization component of the acrylic resin, if necessary.

  Examples of the other copolymerizable monomer (a5) include phenyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenyldiethylene glycol (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, and phenoxy. Aromatic (meth) acrylic acid ester type monomers such as polyethylene glycol-polypropylene glycol- (meth) acrylate and nonylphenol ethylene oxide adduct (meth) acrylate, acrylonitrile, methacrylonitrile, styrene, α-methylstyrene, stearic acid Vinyl, vinyl chloride, vinylidene chloride, alkyl vinyl ether, vinyl toluene, vinyl pyridine, vinyl pyrrolidone, itaconic acid dialkyl ester, fumaric acid dialkyl ester, allyl alcohol, acrylic chloride, methyl vinyl ketone, N-acrylamidomethyltrimethylammonium chloride, allyltrimethyl Examples thereof include monomers such as ammonium chloride and dimethylallyl vinyl ketone. These may be used alone or in combination of two or more.

  Further, when the purpose is to increase the molecular weight of the acrylic resin, for example, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate. A small amount of a compound having two or more ethylenically unsaturated groups such as propylene glycol di (meth) acrylate and divinylbenzene can also be used together. In this case, the compound having two or more ethylenically unsaturated groups has high reactivity, and normally does not remain unreacted when used as a copolymerization component of an acrylic resin. If the amount used is too large, these compounds having two or more ethylenically unsaturated groups will remain unreacted, and the acrylic resin tends to gel.

  The content of the other copolymerizable monomer (a5) is preferably 50% by weight or less, particularly preferably 40% by weight or less, and further preferably 20% by weight or less, based on the entire copolymerization component. .. If the content of the other copolymerizable monomer (a5) is too large, the heat resistance tends to decrease, or the adhesive strength tends to decrease.

  The acrylic resin used in the present invention can be produced by appropriately selecting and polymerizing the above-mentioned copolymerization component so as to have a desired glass transition temperature.

As the above-mentioned polymerization method, for example, conventionally known polymerization methods such as solution polymerization, suspension polymerization, bulk polymerization and emulsion polymerization can be used, but in the present invention, it is safe to produce by solution polymerization, It is preferable in that an acrylic resin can be stably produced with an arbitrary monomer composition.
Hereinafter, an example of a preferred method for producing the acrylic resin used in the present invention will be shown.

  First, the above-mentioned copolymerization component and polymerization initiator are mixed or dropped into an organic solvent, and solution polymerization is performed to obtain an acrylic resin solution.

〔Organic solvent〕
Examples of the organic solvent used in the polymerization reaction include aromatic hydrocarbons such as toluene and xylene, aliphatic hydrocarbons such as hexane, esters such as ethyl acetate and butyl acetate, N-propyl alcohol, isopropyl alcohol. And aliphatic ketones, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and other ketones. These may be used alone or in combination of two or more. Among these solvents, an organic solvent having a boiling point of 80 ° C. or less is used in that a solvent-free acrylic resin can be efficiently produced by distilling the solvent from the acrylic resin solution obtained by solution polymerization. Preferably.

Examples of the organic solvent having a boiling point of 80 ° C. or lower include hydrocarbon solvents such as n-hexane (67 ° C.), alcohol solvents such as methanol (65 ° C.), ethyl acetate (77 ° C.), methyl acetate. (54 ° C.) ester solvent, methyl ethyl ketone (80 ° C.), acetone (56 ° C.) ketone solvent, diethyl ether (35 ° C.), methylene chloride (40 ° C.), tetrahydrofuran (66 ° C.), etc. Of these, ethyl acetate, acetone, and methyl acetate are preferably used, and ethyl acetate and acetone are particularly preferable, from the viewpoints of versatility and safety.
The numerical value in parentheses following the name of each organic solvent is the boiling point of each organic solvent.

[Polymerization initiator]
As the polymerization initiator used in the polymerization reaction, it is possible to use an azo polymerization initiator or a peroxide polymerization initiator which is a usual radical polymerization initiator, and the azo polymerization initiator may be, for example, 2,2'-azobis (2-methylbutyronitrile), 2,2'-azobisisobutyronitrile, (1-phenylethyl) azodiphenylmethane, 2,2'-azobis (2,4-dimethylvaleronitrile) ), 2,2′-azobis (2-cyclopropylpropionitrile), 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), and the like, and as a peroxide-based polymerization initiator. Are, for example, benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, lauroyl peroxide, t-butyl peroxypivalate, t-hexyl peroxypivalate, t-hexyl peroxy neodecanoate, diisopropyl peroxy. Examples thereof include carbonate and diisobutyryl peroxide. These may be used alone or in combination of two or more.

  In the production of the acrylic resin, it is preferable to use an organic solvent having a boiling point of 80 ° C. or less as a reaction solvent for solution polymerization and to carry out the polymerization at a relatively low temperature, in which case the polymerization initiation with a high 10-hour half-life temperature is initiated. When the agent is used, the polymerization initiator tends to remain. If the polymerization initiator remains, gelation of the acrylic resin tends to occur in the step of distilling the solvent from the acrylic resin solution, which will be described later.

Therefore, from the viewpoint of stably performing the step of distilling off the solvent from the acrylic resin solution obtained by solution polymerization, use of a polymerization initiator having a 10-hour half-life temperature of 60 ° C. or lower among the above polymerization initiators. Are preferred, and particularly preferred are 2,2′-azobis (2,4-dimethylvaleronitrile) (52 ° C.) and 2,2′-azobis (2-cyclopropylpropionitrile) (49.6 ° C.). , 2,2′-azobis (4-methoxy2,4-dimethylvaleronitrile) (30 ° C.), t-butylperoxypivalate (54.6 ° C.), t-hexylperoxypivalate (53.2 ° C.), t-hexyl peroxy neodecanoate (44.5 ° C.), diisopropyl peroxy carbonate (40.5 ° C.) and diisobutyryl peroxide (32.7 ° C.), more preferably 2,2′-azobis (2,2). 4-dimethylvaleronitrile) (52 ° C.) and t-hexyl peroxypivalate (53.2 ° C.).
The numerical value in parentheses following the name of each compound is the 10-hour half-life temperature of each compound.

  The amount of the polymerization initiator used is usually 0.001 to 10 parts by weight, preferably 0.1 to 8 parts by weight, particularly preferably 0.5 to 6 parts by weight, based on 100 parts by weight of the polymerization component. It is more preferably 1 to 4 parts by weight, particularly preferably 1.5 to 3 parts by weight, most preferably 2 to 2.5 parts by weight. If the amount of the above-mentioned polymerization initiator used is too small, the polymerization rate of the acrylic resin tends to decrease, the amount of residual monomers tends to increase, and the weight average molecular weight of the acrylic resin tends to increase. If the amount used is too large, gelation of the acrylic resin tends to occur in the step of distilling the solvent from the acrylic resin solution described later.

[Polymerization conditions, etc.]
Regarding the polymerization conditions of the solution polymerization, the polymerization may be carried out according to the conventionally known polymerization conditions, and for example, the polymerization components and the polymerization initiator may be mixed or dropped in a solvent to carry out the polymerization under predetermined polymerization conditions.

  The polymerization temperature in the above polymerization reaction is usually 40 to 120 ° C., but in the present invention, it is preferably 50 to 90 ° C., particularly preferably 55 to 75 ° C., further preferably 60 to 70 from the viewpoint of stable reaction. ℃. If the polymerization temperature is too high, the acrylic resin tends to gel easily, and if it is too low, the activity of the polymerization initiator decreases, so that the polymerization rate tends to decrease and the residual monomer tends to increase.

Further, the polymerization time in the polymerization reaction (the time until the start of the follow-up heating in the case of performing the follow-up heating described later) is not particularly limited, but is preferably 0.5 hours or more from the last addition of the polymerization initiator, It is particularly preferably 1 hour or longer, more preferably 2 hours or longer, and particularly preferably 5 hours or longer. The upper limit of the polymerization time is usually 72 hours.
The polymerization reaction is preferably carried out while refluxing the solvent because it is easy to remove heat.

  In the production of the acrylic resin, in order to reduce the amount of the residual polymerization initiator, it is preferable that the polymerization initiator is thermally decomposed by the forced heating.

The above-mentioned heating temperature is preferably higher than the 10-hour half-life temperature of the above-mentioned polymerization initiator, specifically, usually 40 to 150 ° C, and 55 to 130 ° C from the viewpoint of suppressing gelation. Is preferred, and particularly preferred is 75 to 95 ° C. If the heating temperature for driving in is too high, the acrylic resin tends to turn yellow, and if it is too low, the polymerization components and the polymerization initiator remain, and the temporal stability and thermal stability of the acrylic resin tend to decrease.
Thus, the acrylic resin solution can be obtained.

  Since the acrylic resin used in the present invention is preferably a solvent-free acrylic resin containing no solvent, the solvent is then distilled off from the acrylic resin solution.

  The step of distilling the solvent from the acrylic resin solution can be carried out by a known general method.Examples of the method of distilling the solvent include, for example, a method of distilling the solvent by heating and a pressure reduction. Although there is a method of distilling off the solvent, etc., the method of distilling off by heating under reduced pressure is preferable from the viewpoint of efficiently distilling off the solvent.

  The temperature for heating to distill off the solvent is preferably 60 to 150 ° C., and in particular, the reaction solution after polymerizing the acrylic resin is kept at 60 to 80 ° C. to distill the solvent. And then distilling off the solvent at 80 to 150 ° C. is preferable in that the residual solvent amount is extremely reduced. From the viewpoint of suppressing gelation of the acrylic resin, it is preferable that the solvent is not distilled off at a temperature higher than 150 ° C.

The pressure in the case of distilling off the solvent under reduced pressure is preferably 20 to 101.3 kPa, and in particular, after distilling off the solvent in the reaction solution while maintaining it in the range of 50 to 101.3 kPa. It is preferable to distill off the residual solvent at 0 to 50 kPa in order to extremely reduce the amount of the residual solvent.
Thus, a solventless acrylic resin can be manufactured.

  The acrylic resin (A) used in the present invention preferably contains the acrylic resin (A1) having the highest glass transition temperature and the acrylic resin (A2) having the lowest glass transition temperature. These acrylic resins (A1) ) And (A2) are manufactured by the above manufacturing method and the like.

  The acrylic resins (A1) and (A2) contain a structural moiety derived from the hydroxyl group-containing monomer (a1), and the content of the structural moiety derived from the hydroxyl group-containing monomer (a1) in the acrylic resin is usually 5 to 5. It is 60% by weight, preferably 8 to 45% by weight, particularly preferably 10 to 40% by weight, further preferably 11 to 35% by weight, particularly preferably 12 to 30% by weight.

  Further, the acrylic resins (A1) and (A2) include, in addition to the structural portion derived from the hydroxyl group-containing monomer (a1), at least one (meth) acrylate (a3) of methyl (meth) acrylate and ethyl (meth) acrylate. -1) It is preferable to contain the structural part derived from. The content of the structural moiety derived from the (meth) acrylate (a3-1) is usually 5 to 40% by weight, preferably 7 to 30% by weight, particularly preferably 10 to 25% by weight, based on the acrylic resin. Is.

  It is particularly preferable that the acrylic resin (A1) contains a structural site derived from methyl (meth) acrylate and ethyl (meth) acrylate as the (meth) acrylate (a3-1) from the viewpoint of excellent adhesive strength.

  In addition, it is particularly preferable that the acrylic resin (A2) contains a structural site derived from ethyl (meth) acrylate as the (meth) acrylate (a3-1) from the viewpoint of excellent bending durability and adhesive strength.

  Here, the structural site ratio (composition ratio) derived from each component of the acrylic resin can be determined by, for example, NMR.

  The glass transition temperature (T1) of the acrylic resin (A1) is preferably −25 to −10 ° C., more preferably −23 to −12 ° C., and particularly preferably −21 to −15 ° C. .. If the glass transition temperature is too low, the adhesive strength tends to decrease, and if the glass transition temperature is too high, the bending durability tends to decrease.

  The glass transition temperature (T2) of the acrylic resin (A2) is lower than the glass transition temperature of the acrylic resin (A1), and is preferably −35 to −20 ° C., It is preferably −33 to −23 ° C., and particularly preferably −30 to −25 ° C. If the glass transition temperature is too low, the durability in the bent state tends to decrease, and if the glass transition temperature is too high, the bending durability tends to decrease.

  In the present invention, the glass transition temperature is a loss tangent (loss elastic modulus G ″ / storage elastic modulus G ′ = tan δ) when dynamic viscoelasticity is measured in a shear deformation mode using a dynamic viscoelasticity measuring device. It is calculated by reading the maximum temperature.

  The weight average molecular weight of the acrylic resins (A1) and (A2) is preferably 10,000 or more, particularly preferably 100,000 to 1,500,000, further preferably 200,000 to 1,000,000, and particularly preferably 250,000. ˜800,000, most preferably 300,000 to 600,000. If the weight average molecular weight is too small, the cohesive force tends to decrease and the durability tends to decrease. If it is too large, the viscosity will be too high, and the coatability and handling will tend to decrease.

  The degree of dispersion (weight average molecular weight / number average molecular weight) of the acrylic resins (A1) and (A2) is preferably 15 or less, particularly preferably 10 or less, further preferably 7 or less, and particularly preferably 5 It is below. If the dispersity is too high, the durability of the pressure-sensitive adhesive layer tends to deteriorate, and foaming or the like tends to occur. If it is too low, the handleability tends to deteriorate. The lower limit of the dispersity is usually 1.1 from the viewpoint of manufacturing limit.

The weight average molecular weight in the present invention is a weight average molecular weight in terms of standard polystyrene molecular weight, and is measured by high performance liquid chromatography (manufactured by Tosoh Corporation, "HLC-8320GPC", column: TSKgel GMHXL (exclusion limit molecular weight: 4 × 10 ^8). , Separation range: 100 to 4 × 10 ⁸ , theoretical plate number: 14000 plates / piece, packing material: styrene-divinylbenzene copolymer, packing particle size: 9 μm, column size: 7.8 mm ID × 30 cm ) And column: TSKgel G2000HXL (exclusion limit molecular weight: 1 × 10 ⁴ , separation range: 100 to 1 × 10 ⁴ , theoretical plate number: 16000 plates / column, packing material: styrene-divinylbenzene copolymer, packing Agent particle size: 5 μm, column size: 7.8 mm ID × 30 cm) is measured by using one in series, and the number average molecular weight can also be measured by the same method. The dispersity can be calculated from the weight average molecular weight and the number average molecular weight.

As described above, the acrylic resin (A) may consist of one type of acrylic resin, but preferably contains two or more types of acrylic resins having different glass transition temperatures.
As a method for obtaining the acrylic resin (A) by mixing the acrylic resin (A1) and the acrylic resin (A2), an acrylic resin (A1) solution and an acrylic resin (A2) solution are used. Examples of the method include a method of distilling off the solvent after mixing, a method of mixing the solventless acrylic resin (A1) and the solventless acrylic resin (A2), and the like. Among them, the method of mixing the acrylic resin (A1) solution and the acrylic resin (A2) solution and then distilling off the solvent is preferable from the viewpoint of workability.
Thus, the acrylic resin (A) used in the present invention is obtained.

  When the acrylic resin (A) contains two or more kinds of acrylic resins having different glass transition temperatures, the method for confirming these is, for example, using tetrahydrofuran (THF) and the acrylic resin (A). [Or, the pressure-sensitive adhesive composition [I]] is dissolved to prepare a sample solution of about 0.1% by weight. It can be confirmed by analyzing this sample solution by a gradient method with GPC using an ODS (octadecylsilyl) column. Examples of the gradient method include a method in which acetonitrile and THF are used as a mobile phase and the mixing ratio of acetonitrile and THF is changed.

  In the acrylic resin (A), the structural portion derived from the hydroxyl group-containing monomer (a1) is usually 5 to 60% by weight, preferably 8 to 45% by weight, particularly preferably 10 to 40% by weight, and further preferably 11 to 11. 35% by weight, particularly preferably 12 to 30% by weight.

  The acrylic resin (A) has a structural portion derived from (meth) acrylate (a3-1) in an amount of usually 5 to 40% by weight, preferably 7 to 30% by weight, particularly preferably 10 to 25% by weight. It includes.

  The glass transition temperature (T) of the acrylic resin (A) is preferably −20 ° C. or lower, more preferably −22 ° C. or lower, and particularly preferably −23 ° C. or lower from the viewpoint of excellent bending durability. .. If the glass transition temperature is too high, the bending durability tends to decrease. The lower limit of the glass transition temperature of the acrylic resin (A) is usually -45 ° C.

  When the acrylic resin (A) contains two or more kinds of acrylic resins having different glass transition temperatures, the glass transition temperature (T1) of the acrylic resin (A1) having the highest glass transition temperature and the highest glass transition temperature The temperature difference with the glass transition temperature (T2) of the low-acrylic resin (A2) is 20 ° C. or less, preferably 15 ° C. or less, and particularly preferably 10 ° C. or less, from the viewpoint of achieving both adhesive strength and bending durability. Furthermore, it is 8 ° C. or less. If the glass transition temperature difference is too large, the compatibility of the resin tends to decrease. The lower limit of the temperature difference is preferably 3 ° C., particularly preferably 4 ° C., and if the temperature difference is too small, either the adhesive strength or the bending durability tends to decrease.

  When the acrylic resin (A) contains the acrylic resin (A1) and the acrylic resin (A2), the content ratio of the acrylic resin (A1) and the acrylic resin (A2) [(A1) / (A2) )] Is preferably 70/30 to 30/70 in weight ratio, more preferably 65/35 to 40/60, and particularly preferably 60/40 to 50/50 in terms of the balance between adhesive strength and bending durability. .. When the content of the acrylic resin (A1) is too small [the content of the acrylic resin (A2) is too large], there is a tendency that the adhesive strength is reduced and the reliability in a high temperature and high humidity environment is lowered. If the content of the acrylic resin (A1) is too large [the content of the acrylic resin (A2) is too small], the bending durability tends to decrease.

  The total content of the acrylic resin (A1) and the acrylic resin (A2) with respect to the acrylic resin (A) is usually 50% by weight or more, preferably 80% by weight or more, more preferably 90% by weight or more. , And more preferably 100% by weight.

  Furthermore, the weight ratio of the amount of the hydroxyl group-containing monomer (a1) constituting the acrylic resin (A1) and the amount of the hydroxyl group-containing monomer (a1) constituting the acrylic resin (A2) is preferably 3: 1 to 1: 3, Particularly preferably, it is 2: 1 to 1: 2, more preferably 1: 1 to 1: 1.5. When the amount of the hydroxyl group-containing monomer (a1) constituting the acrylic resin (A1) is too small, the adhesive strength when used as a pressure-sensitive adhesive is lowered, and when the amount of the hydroxyl group-containing monomer (a1) is too large, it is used as the pressure-sensitive adhesive. In that case, the bending durability tends to decrease, and if the difference in the amount of the hydroxyl group-containing monomer (a1) between the two is too large, the compatibility of the resin tends to decrease and the wet heat resistance tends to decrease.

  The weight average molecular weight of the acrylic resin (A) is preferably 10,000 or more, particularly preferably 100,000 to 1,500,000, further preferably 200,000 to 1,000,000, particularly preferably 250,000 to 800,000, Most preferably, it is 300,000 to 600,000. If the weight average molecular weight is too small, the cohesive force tends to decrease and the durability tends to decrease. If it is too large, the viscosity will be too high, and the coatability and handling will tend to decrease.

When the acrylic resin (A) contains the acrylic resin (A1) and the acrylic resin (A2), the weight average molecular weight (Mw1) of the acrylic resin (A1) having the highest glass transition temperature and the highest glass The difference from the weight average molecular weight (Mw2) of the acrylic resin (A2) having a low transition temperature preferably satisfies the following formula.
(Mw1)-(Mw2) ≧ -100,000
The value obtained by subtracting (Mw2) from (Mw1) is preferably -100,000 or more, and particularly preferably 0 or more, from the viewpoints of achieving both adhesive strength, bending durability, and reliability in a bent state. If the value obtained by subtracting (Mw2) from (Mw1) is too small, the adhesive force and the reliability in the bent state tend to be lowered. The upper limit of the above formula is usually 2,000,000, and if it is too large, the compatibility of the resin tends to decrease.

  Further, the dispersity (weight average molecular weight / number average molecular weight) of the acrylic resin (A) is preferably 15 or less, particularly preferably 10 or less, further preferably 7 or less, and particularly preferably 5 or less. .. If the dispersity is too high, the durability of the pressure-sensitive adhesive layer tends to deteriorate, and foaming or the like tends to occur. If it is too low, the handleability tends to deteriorate. The lower limit of the dispersity is usually 1.1 from the viewpoint of manufacturing limit.

  The acid value of the acrylic resin (A) is preferably 0.001 to 2 mgKOH / g, particularly preferably 0.001 to 1 mgKOH / g, and further preferably 0.001 to 0.5 mgKOH / g. If the acid value is too high, the thermal stability tends to decrease.

  Here, the acid value in the present invention is obtained by neutralization titration based on JIS K0070.

  It is preferable that the acrylic resin (A) is a solventless acrylic resin that does not substantially contain a solvent, particularly preferably an acrylic resin ( The solvent content of A) is not more than 2% by weight, more preferably 0.00001 to 2% by weight, particularly preferably 0.0001 to 1% by weight, most preferably 0.001 to 0.1% by weight. is there. If the solvent content is too high, bubbles tend to be generated in the pressure-sensitive adhesive layer when used as a pressure-sensitive adhesive, and the durability tends to deteriorate.

  Further, the residual monomer amount in the acrylic resin (A) is preferably 2% by weight or less, particularly preferably 0.00001 to 1.5% by weight, further preferably 0.0001 to 1.2% by weight. is there. If the residual monomer amount is too large, the molecular weight increases when heated, and the coatability and adhesive properties tend to deteriorate, or air bubbles occur in the adhesive, and durability tends to decrease.

  The solvent content and the amount of residual monomers in the acrylic resin (A) are those obtained by diluting the acrylic resin (A) 20 times with toluene, and measuring the gas chromatography / mass fragment detector (GC: manufactured by Agilent Technologies, 7890A). GC system, MSD: manufactured by Agilent Technologies, 5975 inert).

  Further, in the present invention, the content of volatile matter (usually the solvent and the residual monomer are main components) in the acrylic resin (A) is preferably 2% by weight or less, and particularly preferably 0.00001. ˜1.5 wt%, and more preferably 0.0001 to 1.2 wt%. If the amount of residual monomer is too large, the molecular weight of the acrylic resin will increase when heated, and the coatability will decrease, and when it is used as an adhesive, the adhesive physical properties will decrease, and bubbles will occur, resulting in durability. Tends to decrease.

The volatile matter content in the acrylic resin (A) is a value calculated from the weight change before and after heating the acrylic resin in a hot air dryer at 130 ° C. for 1 hour, It is calculated by the following formula.
Volatile content (% by weight) = (Wa-Wb) / Wa × 100
The Wa is the weight of the acrylic resin before heating, and the Wb is the weight of the acrylic resin after heating.

  The acrylic resin (A) is a main component of the pressure-sensitive adhesive composition [I], and the content with respect to the pressure-sensitive adhesive composition [I] is 80% by weight or more based on the whole. From the viewpoint of reliability during durability, it is preferably 90 to 99.9% by weight, more preferably 95 to 99.9% by weight.

<Photopolymerization initiator>
The pressure-sensitive adhesive composition [I] of the present invention forms a pressure-sensitive adhesive layer by curing, but when curing is performed by an active energy ray described later, it stabilizes the reaction upon irradiation with the active energy ray. It is preferable to use a photopolymerization initiator from the viewpoint that it is possible.

  The photopolymerization initiator is not particularly limited as long as it generates a radical by the action of light, and examples thereof include acetophenones, benzoins, benzophenones, thioxanthones, and acylphosphine oxides. Can be given. These photopolymerization initiators can be used alone or in combination of two or more. Among these photopolymerization initiators, hydrogen abstraction type benzophenone and intramolecular cleavage type acetophenone type photopolymerization initiators are preferably used because they can be efficiently crosslinked intermolecularly or intramolecularly.

  The amount of the photopolymerization initiator blended is preferably 0.01 to 10 parts by weight, particularly preferably 0.1 to 5 parts by weight, and further preferably 100 parts by weight of the acrylic resin (A). 0.5 to 2 parts by weight. If the blending amount is too small, the curing speed tends to be low or the curing tends to be insufficient, and if it is too large, the curability is not improved and the economical efficiency tends to be lowered.

  Further, as auxiliary agents of these photopolymerization initiators, for example, triethanolamine, triisopropanolamine, 4,4′-dimethylaminobenzophenone (Michler's ketone), 4,4′-diethylaminobenzophenone, 2-dimethylaminoethylbenzoic acid, Ethyl 4-dimethylaminobenzoate, (n-butoxy) ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, 2-ethylhexyl 4-dimethylaminobenzoate, 2,4-diethylthioxanthone, 2, It is also possible to use 4-diisopropylthioxanthone together. These auxiliaries may be used alone or in combination of two or more.

<Active energy ray curable monomer>
In addition, when curing with active energy rays, it is preferable to use an active energy ray-curable monomer, whereby the cohesive force of the entire pressure-sensitive adhesive layer can be adjusted and stable pressure-sensitive adhesive properties can be obtained.

  As the active energy ray-curable monomer, a polyfunctional monomer having two or more ethylenically unsaturated groups in one molecule is preferable, and for example, hexanediol di (meth) acrylate, butanediol di (meth) acrylate, ( Poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (Meth) acrylate, trimethylolpropane tri (meth) acrylate, tetramethylolmethane tri (meth) acrylate, isocyanuric acid ethylene oxide modified tri (meth) acrylate, allyl (meth) acrylate, vinyl (meth) acrylate and urethane (meth) Examples thereof include acrylate. The above polyfunctional monomers may be used alone or in combination of two or more.

  The amount of the polyfunctional monomer blended is preferably 0 to 10 parts by weight, particularly preferably 0.1 to 7.5 parts by weight, and further preferably 0, relative to 100 parts by weight of the acrylic resin (A). 0.5 to 5 parts by weight.

<Other optional ingredients>
As a constituent component of the pressure-sensitive adhesive composition [I] of the present invention, other optional components may be included in addition to the above-mentioned photopolymerization initiator and active energy ray-curable monomer.

  Examples of other optional components include carbodiimide compounds, antioxidants, plasticizers, tackifiers, cross-linking agents, cross-linking accelerators, silane coupling agents, antistatic agents, and functional dyes. These may be used alone or in combination of two or more. The content of the other optional components may be in the range that does not impair the effects of the present invention, and is preferably 0.1 to 10% by weight in the pressure-sensitive adhesive composition [I].

The pressure-sensitive adhesive composition [I] of the present invention is produced using the above-mentioned components, for example, as follows.
The pressure-sensitive adhesive composition [I] of the present invention can be obtained by mixing the acrylic resin (A) and the above-mentioned constituents, but before or after the solvent distillation step in the production of the acrylic resin (A). The above-mentioned photopolymerization initiator, active energy ray-curable monomer, and other optional components can be blended inside (in the state where the solvent remains) or after the solvent is distilled off. Above all, it is preferable to blend the solvent-free acrylic resin (A) after the solvent is distilled off.
When the carbodiimide-based compound is blended, the resin composition obtained is obtained by blending it with the acrylic resin (A) before the photopolymerization initiator, the active energy ray-curable monomer, and other optional components. It is preferable from the viewpoint of chemical stability of the product. Particularly preferably, the acrylic resin (A) and the carbodiimide compound are mixed at 0 to 140 ° C, and more preferably 20 to 100 ° C.

  When the obtained pressure-sensitive adhesive composition [I] contains a solvent, the solvent-free pressure-sensitive adhesive composition is obtained by distilling the solvent in the same manner as the above-mentioned method of distilling the solvent from the acrylic resin. The product [I] is obtained.

  The acid value of the solventless pressure-sensitive adhesive composition is 0.001 to 0.3 mgKOH / g, preferably 0.001 to 0.15 mgKOH / g, and particularly preferably 0.001 to 0.1 mgKOH / g. ..

  The pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition [I] satisfies all of the above-mentioned pressure-sensitive adhesive strength (α), bending durability (β), and moist-heat haze resistance (γ). Therefore, it is useful as an adhesive layer of an adhesive sheet. The pressure-sensitive adhesive composition [I] is also useful as a material component of a pressure-sensitive adhesive, and is particularly useful as a material component of a hot-melt pressure-sensitive adhesive.

<Adhesive sheet>
The pressure-sensitive adhesive composition [I] of the present invention comprises a pressure-sensitive adhesive sheet having a cured pressure-sensitive adhesive layer provided on a base sheet, a double-sided pressure-sensitive adhesive sheet having the pressure-sensitive adhesive layer provided on a release sheet, and a pressure-sensitive adhesive layer. It is preferably used as an optical member with an adhesive layer provided on the optical member. Examples of the curing method include a method of curing with active energy rays, a method of curing by crosslinking with a crosslinking agent, and a method of combining these.

The pressure-sensitive adhesive sheet can be produced, for example, as follows.
In the present invention, the "sheet" is not particularly distinguished from "film" or "tape", and is meant to include these.

  First, the pressure-sensitive adhesive composition [I] is applied to one side or both sides of the base material sheet in a molten state by heating, and then cooled, or the pressure-sensitive adhesive composition is melted by heating and the base material is heated by a T-die or the like. A pressure-sensitive adhesive layer is formed on one surface or both surfaces of the base material sheet so as to have a predetermined thickness by a method such as extrusion onto a sheet and lamination. Then, if necessary, a release sheet may be attached to the surface of the pressure-sensitive adhesive layer to prepare a pressure-sensitive adhesive sheet.

  In addition, after forming the pressure-sensitive adhesive layer on the base material sheet, if necessary, active energy ray irradiation treatment is performed, and further aging is performed to form a pressure-sensitive adhesive layer in which the pressure-sensitive adhesive composition [I] is cured (crosslinked). A PSA sheet having the same can be produced.

Alternatively, a double-sided pressure-sensitive adhesive sheet without a substrate can be prepared by forming a pressure-sensitive adhesive layer on the release sheet and bonding the release sheet to the opposite pressure-sensitive adhesive layer surface.
When the pressure-sensitive adhesive sheet or double-sided pressure-sensitive adhesive sheet obtained is used, the release sheet is peeled from the pressure-sensitive adhesive layer before use.

  Examples of the base sheet include polyester resins such as polyethylene naphthalate, polyethylene terephthalate, polybutylene terephthalate and polyethylene terephthalate / isophthalate copolymers; polyolefin resins such as polyethylene, polypropylene and polymethylpentene; polyvinyl fluoride, Polyvinylidene fluoride, polyfluorinated ethylene resins such as polyfluorinated ethylene; polyamides such as nylon 6, nylon 6,6; polyvinyl chloride, polyvinyl chloride / vinyl acetate copolymers, ethylene-vinyl acetate copolymers, ethylene-vinyl Vinyl copolymers such as alcohol copolymers, polyvinyl alcohol and vinylon; Cellulose resins such as cellulose triacetate and cellophane; Acrylic resins such as polymethylmethacrylate, polyethylmethacrylate, polyethylacrylate and polybutylacrylate. Polystyrene; polycarbonate; polyarylate; a sheet made of at least one synthetic resin selected from the group consisting of polyimide, aluminum, copper, iron metal foil, fine paper, paper such as glassine paper, glass fiber, natural fiber, Examples include woven and non-woven fabrics made of synthetic fibers. These base sheets can be used as a single layer or as a multi-layer body in which two or more kinds are laminated. Among these, a sheet made of synthetic resin is preferable from the viewpoint of weight reduction and the like.

  Further, as the release sheet, for example, various synthetic resin sheets exemplified as the above-mentioned supporting base material, paper, cloth, non-woven fabric and the like which have been subjected to release treatment can be used. A silicon-based release sheet is preferably used as the release sheet.

  The coating method of the pressure-sensitive adhesive composition [I] is not particularly limited as long as it is a general coating method, and examples thereof include roll coating, die coating, gravure coating, comma coating, screen printing and the like. There is a method of.

  By irradiating with an active energy ray, the acrylic resin (A) in the pressure-sensitive adhesive composition [I] forms a crosslinked structure in at least one of intramolecular and intermolecular.

  As the active energy rays, for example, light rays such as far-ultraviolet rays, ultraviolet rays, near-ultraviolet rays, infrared rays, electromagnetic waves such as X-rays and γ-rays, electron rays, proton rays, neutron rays, etc. can be used, but curing speed, irradiation Ultraviolet rays are preferred because of the availability of the device and the price.

When curing by irradiating with ultraviolet rays, a high pressure mercury lamp, an ultra high pressure mercury lamp, a carbon arc lamp, a metal halide lamp, a xenon lamp, a chemical lamp, an electrodeless discharge lamp, an LED lamp, etc. that emits light in the wavelength range of 150 to 450 nm are used. Then, the ultraviolet rays of 30 to 3000 mJ / cm ² , preferably 100 to 1500 mJ / cm ² may be irradiated.

  The aging treatment is preferably carried out particularly when a crosslinking agent is used in the pressure-sensitive adhesive composition [I]. The conditions of the aging treatment are usually a temperature of room temperature (23 ° C.) to 100 ° C. and a time of usually 1 To 30 days, and specifically, it may be carried out under the conditions of, for example, 23 ° C. for 1 to 20 days, preferably 23 ° C. for 3 to 10 days, and 40 ° C. for 1 to 7 days.

  In the present invention, the pressure-sensitive adhesive layer-carrying optical member can be obtained by laminating and forming the pressure-sensitive adhesive layer on the optical member. Further, the optical members can be attached to each other using the double-sided pressure-sensitive adhesive sheet.

  The gel fraction of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is preferably 10 to 100% by weight, particularly preferably 30 to 90% by weight, particularly preferably 50 to 80% by weight from the viewpoint of durability and adhesive strength. % Is preferable. If the gel fraction is too low, the cohesive force will decrease and the durability will tend to decrease. On the other hand, if the gel fraction is too high, the adhesive force tends to decrease due to the increase in cohesive force, and the bending durability tends to decrease.

  The gel fraction is a measure of the degree of crosslinking (degree of curing), and is calculated by the following method, for example. That is, a polymer sheet as a base material (for example, a polyethylene terephthalate (PET) film) having a pressure-sensitive adhesive layer formed thereon (without a separator) is wrapped with a 200-mesh SUS wire mesh, and toluene is used. The gel fraction is defined as the weight percentage of the insoluble adhesive layer remaining in the wire mesh relative to the weight of the adhesive layer before immersion in toluene at 23 ° C. for 24 hours. However, the weight of the base material is subtracted.

  In adjusting the gel fraction within the above range, for example, adjusting the amount of active energy ray irradiation or the amount of photopolymerization initiator, or adjusting the type and amount of the active energy ray-curable monomer, and crosslinking. When an agent is used, it can be achieved by adjusting the kind and amount of the crosslinking agent.

  The thickness of the pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet is usually preferably 15 to 3000 μm, more preferably 20 to 1000 μm, and particularly preferably 50 to 350 μm. If the thickness of the pressure-sensitive adhesive layer is too thin, the shock absorbing property tends to decrease, and if it is too thick, the thickness of the entire optical member tends to increase and the practicality tends to decrease.

  The film thickness in the present invention is obtained by subtracting the measured value of the thickness of the constituent members other than the adhesive layer from the measured value of the thickness of the entire adhesive layer-containing laminate by using "ID-C112B" manufactured by Mitutoyo Corporation. It is the value obtained by.

The pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition [I] of the present invention is excellent in adhesive strength and bending durability, and is also excellent in moist-heat haze resistance. In addition, the pressure-sensitive adhesive prepared using the pressure-sensitive adhesive composition [I] has excellent adhesive strength, bending durability, and moisture / heat haze resistance, so that it is used as a pressure-sensitive adhesive having double-sided adhesive applications, impact resistance, and strong adhesiveness. It can be preferably used. Specifically, glass or ITO transparent electrode sheets, optical sheets such as polyethylene terephthalate (PET), polycarbonate (PC), polymethylmethacrylate (PMMA), polarizing plates, retardation plates, optical compensation films, brightness enhancement films, etc. It is useful as a pressure-sensitive adhesive component for the application of optical members. Further, it can be suitably used for an image display device such as a touch panel including these optical members, particularly for a touch panel and an image display device such as a foldable smartphone.
The pressure-sensitive adhesive composition [I] of the present invention can also be used as various pressure-sensitive adhesives for labels and pressure-sensitive adhesives for masking, and is particularly preferably used for electronic parts and the like.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.
In the examples, "part" and "%" mean weight basis. The weight average molecular weight of the acrylic resin was measured according to the method for measuring the weight average molecular weight of the acrylic resin described above.
The glass transition temperature of the acrylic resin was measured as follows.
The content of the structural portion of the acrylic resin after completion (after polymerization) is substantially the same as the content of the polymerization component.
Further, for reference, the glass transition temperature calculated by the Fox calculation formula is also shown.

<Glass transition temperature (Tg) of acrylic resin>
A pressure-sensitive adhesive sheet having a thickness of about 650 μm was produced in an uncrosslinked state by coating a polyester release sheet with the acrylic resin solution before solvent distillation and drying the polyester release sheet. The dynamic viscoelasticity of the produced pressure-sensitive adhesive sheet was measured under the following conditions, and the temperature at which the loss tangent (loss elastic modulus G ″ / storage elastic modulus G ′ = tan δ) became maximum was read to determine the glass transition of the acrylic resin. The temperature (Tg) was used.
・ Measurement equipment: DVA-225 (IT-Measurement Control Co., Ltd.)
・ Deformation mode: Shear / strain: 0.1%
・ Measuring temperature: -100 to 20 ° C
・ Measurement frequency: 1 Hz

  Prior to the examples, an acrylic resin (A1) and an acrylic resin (A2) were manufactured as follows.

<Manufacture of acrylic resin (A1)>
[Acrylic resin (A1-1)]
In a 2 L flask equipped with a condenser, 24 parts of ethyl acetate (boiling point 77 ° C.) as a polymerization solvent and 2,2′-azobis (2,4-dimethylvaleronitrile) (ADVN, half temperature 52 ° C.) as a polymerization initiator were added. 01 parts of the mixture was heated under reflux in a flask, and 39.0 parts of 2-ethylhexyl acrylate (2EHA), 6.0 parts of methyl acrylate (MA), 6.0 parts of ethyl acrylate (EA), and 2-hydroxyethyl acrylate (HEA). A solution prepared by previously mixing 9.0 parts, 6 parts of acetone and 0.1 part of ADVN was added dropwise over 3 hours. Thirty minutes after the dropping, 0.1 part of ADVN was added dropwise over 1 hour and reacted to obtain an acrylic resin (A1-1) solution. The obtained acrylic resin (A1-1) had a glass transition temperature of -22 ° C and a weight average molecular weight of 535,000.

[Acrylic resin (A1-2) to (A1-4), (A1-6)]
Acrylic resins (A1-2) to (A1-4), (A1-4), (A1) were prepared according to the production method of (A1-1) except that the polymerization components of the acrylic resin (A1-1) were changed as shown in Table 1. A1-6) solution was obtained.

[Acrylic resin (A1-5)]
In a 2 L flask with a condenser, ethyl acetate 37 parts (boiling point 77 ° C.) as polymerization solvent, methyl ethyl ketone 63 parts (boiling point 80 ° C.), and 2,2′-azobisisobutyronitrile (AIBN, half temperature) as a polymerization initiator. (65 ° C.) 0.3 part was heated under reflux in a flask, and a solution in which 100 parts of methyl methacrylate (MMA), 3 parts of ethyl acetate and 0.3 part of AIBN were mixed in advance was added dropwise over 2 hours. 60 minutes after the dropping, 0.2 part of AIBN was added and reacted to obtain an acrylic resin (A1-5) solution. The weight average molecular weight of the obtained acrylic resin (A1-5) was 47,000. The glass transition temperature of the acrylic resin (A1-5) cannot be measured by the above measuring method.

  The results of the monomer composition (structural unit derived from the finished component), weight average molecular weight, and glass transition temperature (Tg) of the obtained acrylic resin (A1) are also shown in Table 1 below.

<Manufacture of acrylic resin (A2)>
[Acrylic resin (A2-1)]
In a 2 L flask equipped with a condenser, 24 parts of ethyl acetate (boiling point 77 ° C.) as a polymerization solvent and 2,2′-azobis (2,4-dimethylvaleronitrile) (ADVN, half temperature 52 ° C.) as a polymerization initiator were added. 01 parts of the mixture was heated under reflux in a flask, 39.0 parts of 2-ethylhexyl acrylate (2EHA), 12.0 parts of ethyl acrylate (EA), 6.0 parts of 2-hydroxyethyl acrylate (HEA), 4-hydroxybutyl acrylate. A solution in which 3.0 parts of (4HBA), 6 parts of acetone, and 0.6 parts of ADVN were mixed in advance was added dropwise over 3 hours. After 30 minutes from the dropping, 0.1 part of ADVN was dropped over 1 hour and reacted to obtain an acrylic resin (A2-1) solution. The obtained acrylic resin (A2-1) had a glass transition temperature of -28 ° C and a weight average molecular weight of 562,000.

[Acrylic resin (A2-2) to (A2-7)]
The acrylic resin (A2-1) to (A2-7) solution was prepared according to the production method of (A2-1) except that the polymerization components of the acrylic resin (A2-1) were changed as shown in Table 2. Obtained.

  The resin composition (structural unit derived from the finished component), weight average molecular weight, and glass transition temperature (Tg) of the resulting acrylic resin (A2) are also shown in Table 2 below.

  Using the acrylic resin (A1) and acrylic resin (A2) obtained above, pressure-sensitive adhesive compositions of Examples and Comparative Examples were produced.

<Example 1>
Acrylic resin (A1-1) solution (60 parts in terms of solid content) and acrylic resin (A2-1) solution (40 parts in terms of solid content) were mixed to obtain acrylic resin (A-1). It was The difference in glass transition temperature between the acrylic resin (A1-1) and the acrylic resin (A2-1) in the acrylic resin (A-1) is 6 ° C., and the glass transition of the acrylic resin (A-1) is The temperature was -23 ° C.
Next, the solvent of this acrylic resin (A-1) solution was distilled out of the system in a flask equipped with a reflux liquid extraction tube, and the pressure was reduced to 90 kPa for 1 hour and further to 10 kPa to 90 The solvent was distilled off by holding at 2 ° C for 2 hours.
With respect to 100 parts of the acrylic resin (A-1) obtained by distilling off the solvent, 5 parts of trimethylolpropane triacrylate (polyfunctional monomer) was used as a photopolymerization initiator, and Omnirad 184 (IGM Resins BV Company). (Manufactured by IGM Resins BV) and 0.25 parts (manufactured by IGM Resins Co., Ltd.) were mixed to obtain a pressure-sensitive adhesive composition [I-1].

<Example 2>
Acrylic resin (A-2) is obtained by mixing an acrylic resin (A1-2) solution (55 parts in terms of solid content) and an acrylic resin (A2-2) solution (45 parts in terms of solid content). It was The difference in glass transition temperature between the acrylic resin (A1-2) and the acrylic resin (A2-2) in the acrylic resin (A-2) is 5 ° C., and the glass transition of the acrylic resin (A-2) is 5 ° C. The temperature was -23 ° C.
Next, in the same manner as in Example 1, the solvent was distilled off from the acrylic resin (A-2) solution.
With respect to 100 parts of the acrylic resin (A-2) obtained by distilling off the solvent, 5 parts of trimethylolpropane triacrylate (polyfunctional monomer) was used as a photopolymerization initiator, and Omnirad 184 (IGM Resins BV Company). 0.25 parts of benzophenone and 0.25 parts of benzophenone were mixed to obtain an adhesive composition [I-2].

<Example 3>
An acrylic resin (A1-3) solution (55 parts in terms of solid content) and an acrylic resin (A2-3) solution (45 parts in terms of solid content) were mixed to obtain an acrylic resin (A-3). It was The difference in glass transition temperature between the acrylic resin (A1-3) and the acrylic resin (A2-3) in the acrylic resin (A-3) is 6 ° C., and the glass transition of the acrylic resin (A-3) is The temperature was -22 ° C.
Next, in the same manner as in Example 1, the solvent was distilled off from the acrylic resin (A-3) solution.
With respect to 100 parts of the acrylic resin (A-3) obtained by distilling off the solvent, 5 parts of trimethylolpropane triacrylate (polyfunctional monomer) was used as a photopolymerization initiator, and Omnirad 184 (IGM Resins BV Company). (Manufactured by IGM Resins BV) and 0.25 parts (manufactured by IGM Resins Co., Ltd.) were mixed to obtain an adhesive composition [I-3].

<Example 4>
The acrylic resin (A1-1) solution (60 parts in terms of solid content) and the acrylic resin (A2-4) solution (40 parts in terms of solid content) were mixed to obtain an acrylic resin (A-4). It was The difference in glass transition temperature between the acrylic resin (A1-1) and the acrylic resin (A2-4) in the acrylic resin (A-4) is 4 ° C., and the glass transition of the acrylic resin (A-4) is The temperature was -22 ° C.
Next, in the same manner as in Example 1, the solvent was distilled off from the acrylic resin (A-4) solution.
With respect to 100 parts of the acrylic resin (A-4) obtained by distilling off the solvent, 5 parts of trimethylolpropane triacrylate (a polyfunctional monomer), Omnirad as a photopolymerization initiator
184 (IGM Resins BV) 0.25 parts and Omnirad 754 (IGM Resins BV) 0.5 part were mixed to obtain an adhesive composition [I-4].

<Comparative Example 1>
The solvent of the acrylic resin (A1-1) solution was distilled off in the same manner as in Example 1.
With respect to 100 parts of the acrylic resin (A1-1) obtained by distilling off the solvent, 5 parts of trimethylolpropane triacrylate (polyfunctional monomer) was used as a photopolymerization initiator, and Omnirad 754 (IGM Resins BV Company). (Manufactured by Mitsui Chemicals, Ltd.) was mixed to obtain an adhesive composition [I′-1].

<Comparative example 2>
The solvent of the acrylic resin (A1-4) solution was distilled off in the same manner as in Example 1.
With respect to 100 parts of the acrylic resin (A1-4) obtained by distilling off the solvent, 5 parts of trimethylolpropane triacrylate (polyfunctional monomer), as a photopolymerization initiator, Omnirad 754 (IGM Resins BV Company). (Manufactured by Mitsui Chemical Co., Ltd.) was mixed to obtain an adhesive composition [I′-2].

<Comparative example 3>
The solvent of the acrylic resin (A2-5) solution was distilled off in the same manner as in Example 1.
With respect to 100 parts of the acrylic resin (A2-5) obtained by distilling off the solvent, 5 parts of trimethylolpropane triacrylate (polyfunctional monomer) was used as a photopolymerization initiator, and Omnirad 184 (IGM Resins BV Company). (Manufactured by IGM Resins BV) and 0.25 part of Omnirad 754 (manufactured by IGM Resins BV) were mixed to obtain an adhesive composition [I′-3].

<Comparative example 4>
Acrylic resin (A1-5) solution (10 parts in terms of solid content) and acrylic resin (A2-6) solution (90 parts in terms of solid content) were mixed to give acrylic resin (A'-1). Obtained.
Next, the solvent was distilled off from the acrylic resin (A'-1) solution.
With respect to 100 parts of the acrylic resin (A′-1) obtained by distilling off the solvent, 10 parts of trimethylolpropane triacrylate (polyfunctional monomer) was used as a photopolymerization initiator, and Omnirad 184 (IGM Resins BV. (Manufactured by the same company) and 0.75 part of Omnirad 754 (manufactured by IGM Resins BV) were mixed to obtain an adhesive composition [I′-4].

<Comparative Example 5>
Acrylic resin (A1-6) solution (60 parts in terms of solid content) and acrylic resin (A2-7) solution (40 parts in terms of solid content) were mixed to give acrylic resin (A'-2). Obtained.
Next, the solvent was distilled off from the acrylic resin (A'-2) solution.
With respect to 100 parts of the acrylic resin (A′-2) obtained by distilling off the solvent, 5 parts of trimethylolpropane triacrylate (polyfunctional monomer) was used, and Omnirad 184 (IGM Resins B.V. 0.25 parts (manufactured by the same company) and 0.5 parts of Omnirad 754 (manufactured by IGM Resins BV) were mixed to obtain an adhesive composition [I′-5].

  The compounding compositions of the pressure-sensitive adhesive compositions of Examples 1 to 4 and Comparative Examples 1 to 5 obtained above are shown in Table 3 below.

  Using the obtained pressure-sensitive adhesive compositions of Examples 1 to 4 and Comparative Examples 1 to 5, a substrateless double-sided pressure-sensitive adhesive sheet and a pressure-sensitive adhesive layer-attached PET sheet were produced as follows.

<Preparation of substrate-less double-sided PSA sheet and PET sheet with PSA layer>
The pressure-sensitive adhesive composition obtained above was sandwiched between polyester-based release sheets (thickness: 176 μm), and pressed while heating at 100 ° C. so that the pressure-sensitive adhesive layer had a thickness of 160 μm. Then, the substrateless double-sided pressure-sensitive adhesive sheet was obtained by irradiating ultraviolet rays at a peak illuminance of 150 mW / cm ² and an integrated exposure amount of 1000 mJ / cm ² (500 mJ / cm ² × 2 passes). At this time, the pressure-sensitive adhesive composition becomes a pressure-sensitive adhesive.
Further, the release sheet on one surface is peeled from the pressure-sensitive adhesive layer of the substrateless double-sided pressure-sensitive adhesive sheet obtained above, and pressed against an easily-adhesive-treated polyethylene terephthalate (PET) sheet (thickness 125 μm) to obtain the thickness of the pressure-sensitive adhesive layer. A PET sheet with an adhesive layer having a thickness of 160 μm was obtained.

Using the substrate-less double-sided pressure-sensitive adhesive sheets of Examples 1 to 4 and Comparative Examples 1 to 5 and the PET sheet with a pressure-sensitive adhesive layer obtained above, gel fraction, pressure-sensitive adhesive strength, bending durability, and humidity / heat resistance haze were used. The sex was evaluated. The results are shown in Table 4 below.
Since the compatibility with Comparative Examples 4 and 5 was poor, only the gel fraction and the haze value before the moist-heat resistance test were evaluated.

(Gel fraction)
After cutting the above-mentioned substrateless double-sided pressure-sensitive adhesive sheet into a size of 40 mm × 40 mm, a peak illuminance: 150 mW / cm ² and an integrated exposure amount: 2000 mJ / cm ² (1000 mJ / cm ² × 2) with a high-pressure mercury UV irradiation device. Pass) and leave it for 30 minutes under the condition of 23 ° C. × 50% RH, and then one release sheet is peeled off, and the pressure-sensitive adhesive layer side is a SUS mesh sheet having a size of 50 mm × 100 mm (200 mm). (The mesh), the other release sheet is peeled off, the sample is wrapped by folding it back from the center with respect to the longitudinal direction of the SUS mesh sheet, and then immersed in a sealed container containing 250 g of toluene for 24 hours. Then, the weight percentage of the insoluble adhesive layer remaining on the SUS mesh sheet with respect to the weight of the adhesive layer before immersion in toluene was taken as the gel fraction (%).

〔Adhesive force〕
The PET sheet with the pressure-sensitive adhesive layer was cut into a size of width 25 mm × length 100 mm, and a high-pressure mercury UV irradiation device provided a peak illuminance: 150 mW / cm ² , integrated exposure dose: 2000 mJ / cm ² (1000 mJ / cm After irradiating with ultraviolet rays for ² × 2 passes), the release sheet is peeled off, and the pressure-sensitive adhesive layer side is placed on non-alkali glass (“Eagle XG” manufactured by Corning, thickness 1.1 mm) at 23 ° C. and 50% RH. Under a pressure of 2 kg rubber roller 2 times, and left standing for 30 minutes under the condition of 23 ° C. × 50% RH, and then 180 degree peel strength (N) at room temperature (23 ° C.) at a peeling speed of 300 mm / min. / 25 mm) was measured.

[Folding durability]
Regarding the PET sheet with the pressure-sensitive adhesive layer, the pressure-sensitive adhesive layer side of the pressure-sensitive adhesive sheet is pressed against a transparent polyimide sheet (thickness 50 μm) under an environment of 23 ° C. and 50% RH to form a “PET sheet / pressure-sensitive adhesive layer / polyimide sheet” layer. A test piece having the constitution was obtained.
After that, the above test piece was irradiated with ultraviolet rays from the PET sheet side with a high-pressure mercury UV irradiation device at a peak illuminance: 150 mW / cm ² , and an integrated exposure amount: 2000 mJ / cm ² (1000 mJ / cm ² × 2 passes). Then, it was cut into a size of 40 mm in width and 120 mm in length, and a repeated bending test was performed as follows.
The repeated bending test was carried out in an environment of 23 ° C. and 50% RH with the PET sheet side facing inward, and the test conditions are as follows.
[Test conditions] Test equipment: Sheet-shaped no-load U-shaped expansion / contraction tester DLDM111LH (manufactured by Yuasa System Equipment Co., Ltd.) Bending speed: 40 times / min Bending diameter: 5 mm It was measured and evaluated according to the following criteria.
◎ ・ ・ ・ 200,000 times or more ○ ・ ・ ・ 100,000 times or more, less than 200,000 times × ・ ・ ・ Less than 100,000 times

[Moisture heat haze resistance]
The PET sheet with the pressure-sensitive adhesive layer was cut into a size of width 30 mm × length 50 mm, and a high-pressure mercury UV irradiation device was used to obtain a peak illuminance: 150 mW / cm ² and an integrated exposure dose: 2000 mJ / cm ² (1000 mJ / cm ² After irradiating with ultraviolet rays for ² x 2 passes), the release sheet is peeled off, and the pressure-sensitive adhesive layer side is stuck to non-alkali glass ("Eagle XG" manufactured by Corning Co., thickness 1.1 mm) and then autoclaved. Treatment (50 ° C., 0.5 MPa, 20 minutes), standing for 30 minutes under the condition of 23 ° C. × 50% RH, and a test piece having the constitution of “alkali-free glass / adhesive layer / PET sheet” It was made.

Using the obtained test piece, a moist-heat resistance test was performed for 7 days (168 hours) in an atmosphere of 60 ° C. and 90% RH, and a haze value was measured before the start of the moist-heat resistance test and immediately after the moist-heat resistance test. The haze value is a value of diffuse transmittance (DT) and total light transmittance (TT) obtained by measuring diffuse transmittance and total light transmittance using Haze MATER NDH2000 (manufactured by Nippon Denshoku Industries Co., Ltd.). Was substituted into the following formula 1 to calculate the haze value. Then, the difference in haze value was calculated from the following formula 2. This machine complies with JIS K7361-1.
[Formula 1]
Haze value (%) = (DT / TT) × 100
[Formula 2]
The difference between the haze value (%) = H ₂ -H ₁
The above H ₁ indicates a haze value before the moist heat resistance test, and H ₂ indicates a haze value immediately after the moist heat resistance test.

As can be seen from Table 4 above, in Examples 1 to 4, all of the adhesive strength, bending durability, and moist heat haze resistance were excellent with good balance.
On the other hand, in Comparative Examples 1 to 3, none of the adhesive strength, the bending durability, and the wet heat haze resistance were excellent in a well-balanced manner. Further, in Comparative Examples 4 and 5, the compatibility was poor and the transparency was poor.

  The pressure-sensitive adhesive layer of the present invention and the pressure-sensitive adhesive composition forming the same are excellent in adhesive strength, bending durability, and moisture and heat haze resistance, and thus are suitably used for touch panels, image display devices, etc., shock absorbing sheets, etc. be able to.

Claims (9)

A pressure-sensitive adhesive layer obtained by curing the pressure-sensitive adhesive composition [I] containing an acrylic resin (A), having the following adhesive strength (α) of 25 N / 25 mm or more and the following bending durability (β): A pressure-sensitive adhesive layer, which is 100,000 times or more and has the following moist heat resistance (γ) of 1.0% or less.
Adhesive strength (α):
When the pressure-sensitive adhesive layer is a pressure-sensitive adhesive sheet formed on a polyethylene terephthalate sheet (thickness 125 μm) that has been subjected to an easy-adhesion treatment, the pressure-sensitive adhesive layer side of the pressure-sensitive adhesive sheet is a non-alkali glass with a 2 kg roller at 23 ° C. and 50% RH. 180 degree peel strength (N / 25 mm) measured at a peeling speed of 300 mm / min using an autograph, after reciprocating and pressure bonding, and leaving still at 23 ° C. and 50% RH for 30 minutes.
Folding durability (β):
When the pressure-sensitive adhesive layer is a pressure-sensitive adhesive sheet formed on a polyethylene terephthalate sheet (thickness: 125 μm) that has been subjected to an easy-adhesion treatment, the pressure-sensitive adhesive layer side of the pressure-sensitive adhesive sheet is changed to a transparent polyimide (thickness: 50 μm) under an environment of 23 ° C. and 50% RH. The rollers are reciprocated and pressure-bonded, and the distance between the sheets when the polyethylene terephthalate sheet side is folded is 5 mm at a speed of 40 times / min at 23 ° C. and 50% RH environment. The number of times the appearance has not changed after repeated bending tests.
Moisture and heat haze resistance (γ):
When a pressure-sensitive adhesive layer is formed on a polyethylene terephthalate sheet (thickness 125 μm) that has been subjected to an easy-adhesion treatment, it is bonded to non-alkali glass (thickness 1.1 mm) and then autoclaved (50 ° C., 0.5 MPa). , 20 minutes), and using the obtained test piece, a humidity and heat resistance test is performed for 7 days (168 hours) at 60 ° C. and 90% RH atmosphere, and a haze value after the humidity and heat resistance test and before the humidity and heat resistance test. Difference.   The acrylic resin (A) contains at least two kinds of acrylic resins having different glass transition temperatures and having a weight average molecular weight of 10,000 or more, and the loss tangent of dynamic viscoelasticity of the acrylic resin (A) is The glass transition temperature (T) read from the maximum temperature is −20 ° C. or lower, and the glass transition temperature (T1) of the acrylic resin (A1) having the highest glass transition temperature and the acrylic resin having the lowest glass transition temperature. The pressure-sensitive adhesive layer according to claim 1, wherein the glass transition temperature (T2) of the resin (A2) has a temperature difference of 20 ° C or less.   A pressure-sensitive adhesive composition [I] containing an acrylic resin (A), wherein the acrylic resin (A) contains at least two acrylic resins having different glass transition temperatures and having a weight average molecular weight of 10,000 or more. The acrylic resin (A) has a glass transition temperature (T) of −20 ° C. or lower read from the temperature at which the loss tangent of the dynamic viscoelasticity of the acrylic resin (A) is maximum, and has the highest glass transition temperature. A pressure-sensitive adhesive composition, wherein the temperature difference between the glass transition temperature (T1) of the resin (A1) and the glass transition temperature (T2) of the acrylic resin (A2) having the lowest glass transition temperature is 20 ° C. or less.   The glass transition temperature (T1) read from the temperature at which the loss tangent of the dynamic viscoelasticity of the acrylic resin (A1) is maximum is -25 to -10 ° C, and the pressure-sensitive adhesive according to claim 3. Agent composition.   The glass transition temperature (T2) read from the temperature at which the loss tangent of dynamic viscoelasticity of the acrylic resin (A2) is maximum is −35 to −20 ° C. 5. Adhesive composition.   The content ratio (weight ratio) of the acrylic resin (A1) and the acrylic resin (A2) is 70/30 to 30/70, and the acrylic resin (A1) and the acrylic resin (A2) are contained in a ratio of 70/30 to 30/70. Adhesive composition.   The acrylic resin (A2) is an acrylic resin copolymerized with a hydroxyl group-containing monomer containing 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate as a copolymerization component. The pressure-sensitive adhesive composition according to any one of claims 3 to 6.   A pressure-sensitive adhesive comprising the pressure-sensitive adhesive composition according to any one of claims 3 to 7.   A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed by using the pressure-sensitive adhesive composition according to claim 3.