JP7460315B2 - Adhesive compositions, adhesives and adhesive sheets - Google Patents

Description

The present invention relates to an adhesive composition, adhesive, and adhesive sheet suitable for use in displays.

In recent years, various mobile electronic devices such as smartphones and tablet terminals are equipped with displays that use display modules that include liquid crystal elements, light emitting diodes (LED elements), organic electroluminescence (organic EL) elements, etc. Touch panels are increasingly being used.

In the above-mentioned display, a protective panel is usually provided on the front side of the display module. As electronic devices become thinner and lighter, the protective panels are being replaced from conventional glass plates to plastic plates such as acrylic plates and polycarbonate plates.

Here, a gap is provided between the protection panel and the display module so that even when the protection panel is deformed by an external force, the deformed protection panel does not hit the display module.

However, when the above-mentioned voids, i.e., air layers, exist, there is a large reflection loss of light due to the difference in refractive index between the protective panel and the air layer, and the difference in refractive index between the air layer and the display module. There is a problem that image quality deteriorates.

Therefore, it has been proposed to improve the image quality of the display by filling the gap between the protective panel and the display module with an adhesive layer. For example, Patent Document 1 discloses that an adhesive layer that fills the gap between a protective panel and a display module has a shear storage modulus (G') of 1.0×10 ⁵ Pa or less at 25° C. and 1 Hz. Discloses an adhesive layer having a gel fraction of 40% or more.

JP 2010-97070 A

However, when the storage modulus of the adhesive layer at room temperature is reduced as in Patent Document 1, the storage modulus at high temperatures drops more than necessary, causing problems under durable conditions. For example, when exposed to high temperature and humidity conditions, outgassing occurs from the plastic plate that serves as the protective panel, causing blisters such as air bubbles, lifting, and peeling. Furthermore, with conventional adhesive layers, there may be a problem that the adhesive layer whitens when it is returned to room temperature and humidity after being exposed to high temperature and humidity (humid heat) conditions.

The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide an adhesive composition, an adhesive, and an adhesive sheet that are excellent in both blister resistance and moist heat whitening resistance.

In order to achieve the above object, first, the present invention provides an adhesive composition characterized by containing a (meth)acrylic acid ester polymer (A) containing, as monomer units constituting the polymer, an alkyl (meth)acrylic acid ester, a reactive functional group-containing monomer having a reactive functional group in the molecule, and an N-vinyl carboxylic acid amide, and a crosslinking agent (B) (Invention 1).

In the adhesive composition according to the above invention (Invention 1), N-vinyl carboxylic acid amide is copolymerized with the (meth)acrylic acid ester polymer (A), so that the resulting adhesive has high adhesive strength and high cohesive strength, and is excellent in blister resistance. In addition, the presence of carboxylic acid amide, which is an excellent hydrophilic group, in the adhesive suppresses whitening of the adhesive when the adhesive is placed under high temperature and high humidity conditions and then returned to normal temperature and humidity. Therefore, the adhesive obtained by crosslinking the above adhesive composition is excellent in both blister resistance and humidity-heat whitening resistance.

In the above invention (invention 1), it is preferable that the (meth)acrylic acid ester polymer (A) does not contain a carboxyl group-containing monomer having a carboxyl group in the molecule as a monomer unit constituting the polymer. (Invention 2).

In the above inventions (Inventions 1 and 2), in the (meth)acrylic acid ester polymer (A), the reactive functional group-containing monomer and the N-vinylcarboxylic acid as monomer units constituting the polymer are The mass ratio to amide is preferably 95:5 to 50:50 (Invention 3).

In the above inventions (Inventions 1 to 3), the (meth)acrylic acid ester polymer (A) contains 5% by mass or more of the reactive functional group-containing monomer and 30% by mass as monomer units constituting the polymer. % or less (Invention 4).

In the above inventions (Inventions 1 to 4), it is preferable that the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is 200,000 or more and 2,000,000 or less (Invention 5).

Secondly, the present invention provides an adhesive obtained by crosslinking the adhesive composition (Inventions 1 to 5) (Invention 6).

The adhesive according to the above invention (invention 6) preferably has a gel fraction of 30% or more and 95% or less (invention 7).

The pressure-sensitive adhesive according to the above inventions (inventions 6 and 7) preferably has a dielectric constant of 6.5 or less at 1.0 MHz (invention 8).

In the above inventions (Inventions 6 to 8), it is preferable that a laminate in which a 50 μm thick adhesive layer made of the adhesive is sandwiched between a glass plate and a 1 mm thick acrylic resin plate is subjected to a durability test in which the laminate is stored for 120 hours under humid heat conditions of 85°C and 85% RH, and then the increase in haze value obtained by subtracting the haze value before the durability test from the haze value after storage for 24 hours at normal temperature and humidity of 23°C and 50% RH is less than 5 points (Invention 9).

Thirdly, the present invention provides an adhesive sheet (Invention 10) comprising two release sheets and an adhesive layer sandwiched between the release sheets so as to be in contact with the release surfaces of the two release sheets, the adhesive layer being made of the adhesive (Inventions 6 to 9).

Fourthly, the present invention provides a laminate in which the adhesive layer of the adhesive sheet (invention 10) is sandwiched between a glass plate and a plastic plate, and the laminate is subjected to moist heat conditions of 85° C. and 85% RH. After conducting a durability test of storing for 120 hours, the haze value obtained by subtracting the haze value before the durability test from the haze value when stored for 24 hours at normal temperature and humidity of 23 ° C. and 50% RH is less than 5 points. Provided is a laminate characterized by the following.

The adhesive composition, adhesive, and adhesive sheet of the present invention are excellent in both blister resistance and resistance to wet heat whitening.

FIG. 1 is a cross-sectional view of a pressure-sensitive adhesive sheet according to an embodiment of the present invention. FIG. 1 is a sectional view of a display body according to an embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described.
[Adhesive composition]
The adhesive composition according to this embodiment (hereinafter sometimes referred to as "adhesive composition P") contains a (meth)acrylic acid ester polymer (A) containing, as monomer units constituting a polymer, a (meth)acrylic acid alkyl ester, a reactive functional group-containing monomer having a reactive functional group in the molecule, and N-vinyl carboxylic acid amide, and a crosslinking agent (B). In this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. The same applies to other similar terms. In addition, the term "polymer" is also intended to include the concept of a "copolymer."

The adhesive obtained by crosslinking the adhesive composition P according to the present embodiment has high adhesive strength because N-vinylcarboxylic acid amide is copolymerized in the (meth)acrylic acid ester polymer (A). It has high cohesive strength and excellent blister resistance. For example, a display using an adhesive layer obtained by crosslinking the adhesive composition P according to the present embodiment is placed under high temperature and high humidity conditions (e.g., 85° C., 85% RH), and is made of a plastic plate or the like. Even when outgas is generated from the display component, the generation of blisters such as bubbles, floating, and peeling at the interface between the adhesive layer and the display component is suppressed.

Furthermore, carboxylic acid amide is an excellent hydrophilic group. If such a hydrophilic group exists in an adhesive, even if the adhesive is placed under high temperature and high humidity conditions, the water that has entered the adhesive under the high temperature and high humidity conditions will return to normal temperature and humidity. It is estimated that it sometimes becomes easy to come off from the adhesive, and as a result, whitening of the adhesive is suppressed. Therefore, the adhesive obtained by crosslinking the adhesive composition P according to this embodiment also has excellent moist heat whitening resistance.

Here, in order to improve the moist heat whitening resistance of the adhesive, as a constituent monomer of the (meth)acrylic acid ester polymer (A), a hydroxyl group-containing monomer having a hydroxyl group in the molecule is added in excess of the amount that contributes to crosslinking. There is also a method of using large amounts. However, in this case, the dielectric constant of the resulting pressure-sensitive adhesive increases due to the high polarity of the component derived from the hydroxyl group-containing monomer. On the other hand, since N-vinylcarboxylic acid amide has low polarity, it is possible to suppress the dielectric constant to a low level while improving the wet heat whitening resistance of the resulting adhesive. Thereby, malfunctions of the touch panel due to the dielectric constant of the adhesive can be effectively suppressed, and the responsiveness of the touch panel can be improved.

1. Each component (1) (meth)acrylic acid ester polymer (A)
The (meth)acrylic acid ester polymer (A) in this embodiment includes a (meth)acrylic acid alkyl ester, a reactive functional group-containing monomer having a reactive functional group in the molecule, and a monomer unit constituting the polymer. , and N-vinylcarboxylic acid amide.

The (meth)acrylic acid ester polymer (A) in this embodiment can exhibit preferable adhesiveness by containing (meth)acrylic acid alkyl ester as a monomer unit constituting the polymer. The alkyl group may be linear or branched, or may have a cyclic structure.

From the viewpoint of adhesion, the (meth)acrylic acid alkyl ester is preferably a (meth)acrylic acid alkyl ester having an alkyl group with 1 to 20 carbon atoms. Examples of the (meth)acrylic acid alkyl ester having an alkyl group with 1 to 20 carbon atoms include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, myristyl (meth)acrylate, palmityl (meth)acrylate, stearyl (meth)acrylate, cyclohexyl (meth)acrylate, isobornyl (meth)acrylate, and adamantyl (meth)acrylate. These may be used alone or in combination of two or more.

Among the above, the (meth)acrylic acid alkyl esters are preferably those having an alkyl group with 5 to 20 carbon atoms. Such (meth)acrylic acid alkyl esters with a large number of carbon atoms are highly hydrophobic and can reduce the dielectric constant of the resulting adhesive. As the (meth)acrylic acid alkyl esters having an alkyl group with 5 to 20 carbon atoms, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, isobornyl (meth)acrylate, etc. are preferred, with 2-ethylhexyl (meth)acrylate being particularly preferred due to its high adhesiveness and hydrophobicity.

The (meth)acrylic acid ester polymer (A) preferably contains 40% by mass or more, and more preferably 50% by mass or more of (meth)acrylic acid alkyl ester as a monomer unit constituting the polymer. The content is preferably 55% by mass or more, and more preferably 65% by mass or more. When the above (meth)acrylic acid alkyl ester is contained in an amount of 40% by mass or more, the (meth)acrylic acid ester polymer (A) can exhibit suitable adhesiveness. Further, the (meth)acrylic acid ester polymer (A) preferably contains 90% by mass or less, particularly 85% by mass or less of (meth)acrylic acid alkyl ester as a monomer unit constituting the polymer. It is preferable that the content is more preferably 80% by mass or less. By controlling the above-mentioned (meth)acrylic acid alkyl ester to 90% by mass or less, a suitable amount of other monomer components can be introduced into the (meth)acrylic ester polymer (A).

In addition, when a (meth)acrylic acid alkyl ester in which the alkyl group has 5 to 20 carbon atoms is included, the number of carbon atoms in the alkyl group in the (meth)acrylic acid alkyl ester in which the alkyl group has 1 to 20 carbon atoms is included. The lower limit of the content of the (meth)acrylic acid alkyl ester having 5 to 20 is preferably 50% by mass or more, particularly preferably 70% by mass or more, and more preferably 85% by mass or more. It is preferable. Thereby, the dielectric constant of the resulting adhesive can be effectively reduced. On the other hand, the upper limit of the content ratio of the (meth)acrylic acid alkyl ester whose alkyl group has 5 to 20 carbon atoms in the (meth)acrylic acid alkyl ester whose alkyl group has 1 to 20 carbon atoms is not particularly limited. However, it may be 100% by mass.

As the above (meth)acrylic acid alkyl ester, monomers (hard monomers) whose glass transition temperature (Tg) as a homopolymer exceeds 0°C and monomers (soft monomers) whose glass transition temperature (Tg) as a homopolymer is 0°C or lower are used. It is also preferable to use them in combination with monomers). This is because the soft monomer ensures adhesiveness and flexibility while the hard monomer improves the cohesive force, thereby making it possible to improve the blister resistance. In this case, the mass ratio of hard monomer to soft monomer is preferably 5:95 to 40:60, particularly preferably 15:85 to 30:70.

The glass transition temperature (Tg) of the hard monomer as a homopolymer is preferably 40°C or higher, particularly preferably 60°C or higher, and even more preferably 80°C or higher. Further, the glass transition temperature (Tg) is preferably 300°C or lower, particularly preferably 200°C or lower, and even more preferably 130°C or lower.

Examples of the hard monomers include methyl acrylate (Tg 10°C), methyl methacrylate (Tg 105°C), isobornyl acrylate (Tg 94°C), isobornyl methacrylate (Tg 180°C), adamantyl acrylate (Tg 115°C), and methacrylic acid. Examples include adamantyl (Tg 141°C). These may be used alone or in combination of two or more.

Among the above-mentioned hard monomers, methyl acrylate, methyl methacrylate, and isobornyl acrylate are preferred from the viewpoint of enhancing the performance of the hard monomer while preventing adverse effects on other properties such as tackiness and transparency. Considering tackiness, methyl acrylate and methyl methacrylate are more preferred.

The glass transition temperature (Tg) of the above soft monomer as a homopolymer is preferably -20°C or lower, more preferably -40°C or lower, and even more preferably -60°C or lower. The glass transition temperature (Tg) is preferably -100°C or higher, more preferably -90°C or higher, and even more preferably -80°C or higher.

Preferred examples of the soft monomer include acrylic acid alkyl esters having a linear or branched alkyl group having 2 to 12 carbon atoms. Examples include 2-ethylhexyl acrylate (Tg-70°C), n-butyl acrylate (Tg-54°C), and 2-ethylhexyl acrylate (Tg-70°C) is particularly preferred from the viewpoint of hydrophobicity. These may be used alone or in combination of two or more.

Further, as the above-mentioned (meth)acrylic acid alkyl ester, it is also preferable that at least a part of the (meth)acrylic acid alkyl ester is a monomer having an alicyclic structure as an alkyl group (an alicyclic structure-containing monomer). Since the alicyclic structure-containing monomer has high hydrophobicity, it can be expected to improve the adhesion to a low-polar adherend, and the resulting pressure-sensitive adhesive can have even better adhesion. This results in better blister resistance.

The carbon ring of the alicyclic structure in the alicyclic structure-containing monomer may have a saturated structure or may have an unsaturated bond in part. Further, the alicyclic structure may be a monocyclic alicyclic structure or a polycyclic alicyclic structure such as a bicyclic or tricyclic ring. From the viewpoint of optimizing the distance between the obtained (meth)acrylic acid ester polymers (A) and imparting higher stress relaxation properties to the adhesive, the above alicyclic structure is a polycyclic alicyclic structure ( A polycyclic structure) is preferable. Furthermore, in consideration of the compatibility between the (meth)acrylic acid ester polymer (A) and other components, it is particularly preferable that the polycyclic structure has two to four rings. In addition, from the viewpoint of imparting stress relaxation properties as mentioned above, the number of carbon atoms in the alicyclic structure (referring to the total number of carbon atoms in the part forming the ring, and when multiple rings exist independently, , the total number of carbon atoms) is usually preferably 5 or more, particularly preferably 7 or more. On the other hand, the upper limit of the number of carbon atoms in the alicyclic structure is not particularly limited, but from the viewpoint of compatibility as described above, it is preferably 15 or less, and particularly preferably 10 or less.

Specific examples of the alicyclic structure-containing monomer include cyclohexyl (meth)acrylate, dicyclopentanyl (meth)acrylate, adamantyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyloxyethyl (meth)acrylate, and the like. Among these, dicyclopentanyl (meth)acrylate (number of carbon atoms in the alicyclic structure: 10), adamantyl (meth)acrylate (number of carbon atoms in the alicyclic structure: 10), or isobornyl (meth)acrylate (number of carbon atoms in the alicyclic structure: 7) are preferred, as they exhibit superior step conformability and blister resistance under humid and hot conditions, and isobornyl (meth)acrylate is particularly preferred. These may be used alone or in combination of two or more.

When the (meth)acrylic acid ester polymer (A) contains an alicyclic structure-containing monomer as a constituent monomer unit, the ratio of the alicyclic structure-containing monomer in the (meth)acrylic acid alkyl ester having an alkyl group with 1 to 20 carbon atoms is preferably 1 mass% or more, more preferably 5 mass% or more, and even more preferably 10 mass% or more. The ratio of the alicyclic structure-containing monomer is preferably 50 mass% or less, more preferably 40 mass% or less, and even more preferably 30 mass% or less. When the content of the alicyclic structure-containing monomer is within the above range, the resulting pressure-sensitive adhesive has better blister resistance and exhibits excellent adhesion to transparent conductive films and plastics.

The (meth)acrylic acid ester polymer (A) in this embodiment contains a reactive functional group-containing monomer as a monomer unit constituting the polymer. When the adhesive composition P is crosslinked, the reactive functional group derived from the reactive functional group-containing monomer in the (meth)acrylic acid ester polymer (A) and the reactive functional group of the crosslinking agent (B) react. As a result, a three-dimensional network structure as a crosslinked structure is formed. As a result, the resulting pressure-sensitive adhesive has a high cohesive force and has excellent blister resistance.

Preferable examples of reactive functional group-containing monomers include monomers having a hydroxyl group in the molecule (hydroxyl group-containing monomers), monomers having a carboxyl group in the molecule (carboxyl group-containing monomers), and monomers having an amino group in the molecule (amino group-containing monomers). Among these, hydroxyl group-containing monomers are particularly preferred because they have excellent reactivity with the crosslinking agent (B) and have little adverse effect on the adherend.

Examples of hydroxyl group-containing monomers include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and ) 3-hydroxybutyl acrylate, 4-hydroxybutyl (meth)acrylate, and other hydroxyalkyl (meth)acrylates. Among these, 2-hydroxyethyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate are preferred from the viewpoint of reactivity with the crosslinking agent (B) and copolymerizability with other monomers, and in particular ( 2-hydroxyethyl meth)acrylate is preferred. These may be used alone or in combination of two or more.

Examples of the carboxy group-containing monomer include ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. Among these, acrylic acid is preferred from the viewpoint of reactivity with the crosslinking agent (B) and copolymerizability with other monomers. These may be used alone or in combination of two or more.

Examples of amino group-containing monomers include aminoethyl (meth)acrylate and n-butylaminoethyl (meth)acrylate. These may be used alone or in combination of two or more.

The (meth)acrylic acid ester polymer (A) preferably contains a reactive functional group-containing monomer in an amount of 5% by mass or more, particularly preferably 10% by mass or more, as a monomer unit constituting the polymer. Preferably, the content is more preferably 15% by mass or more. Further, the (meth)acrylic acid ester polymer (A) preferably contains a reactive functional group-containing monomer in an amount of 30% by mass or less, and preferably contains a reactive functional group-containing monomer in an amount of 28% by mass or less, as monomer units constituting the polymer. is more preferable, and it is particularly preferable that the content is 25% by mass or less, and further preferably 20% by mass or less. When the (meth)acrylic acid ester polymer (A) contains a monomer containing a reactive functional group in the above amount as a monomer unit, a good crosslinked structure is formed in the resulting adhesive, resulting in an adhesive with excellent blister resistance. is obtained. In addition, particularly when the content of the hydroxyl group-containing monomer is 30% by mass or less, an increase in the dielectric constant of the resulting pressure-sensitive adhesive is suppressed by the action of the N-vinylcarboxylic acid amide.

On the other hand, it is also preferable that the (meth)acrylic acid ester polymer (A) does not contain a carboxy group-containing monomer as a monomer unit constituting the polymer. Since a carboxy group is an acid component, by not containing a carboxy group-containing monomer, even if the target to which the pressure-sensitive adhesive is applied contains a material that may be damaged by acid, such as a transparent conductive film or a metal film such as tin-doped indium oxide (ITO), the problem caused by the acid (corrosion, change in resistance, etc.) can be suppressed.

Here, "free of carboxyl group-containing monomers" means that the polymer does not substantially contain carboxyl group-containing monomers, and in addition to not containing any carboxyl group-containing monomers at all, it is acceptable to contain carboxyl group-containing monomers to the extent that the carboxyl group does not cause corrosion of the transparent conductive film, metal wiring, etc. Specifically, it is acceptable to contain carboxyl group-containing monomers as monomer units in the (meth)acrylic acid ester polymer (A) in an amount of 0.1% by mass or less, preferably 0.01% by mass or less, and more preferably 0.001% by mass or less.

The (meth)acrylic acid ester polymer (A) in this embodiment contains N-vinylcarboxylic acid amide as a monomer unit constituting the polymer. Thereby, the resulting adhesive has excellent both blister resistance and wet heat whitening resistance, and has a low dielectric constant.

Examples of N-vinyl carboxylic acid amides include N-vinyl formamide, N-vinyl acetamide, N-vinyl-N-methyl acetamide, N-vinyl-N-methyl formamide, N-vinyl-N-ethyl formamide, N-vinyl-N-ethyl acetamide, N-methyl-N-vinyl formamide, and N-methyl-N-vinyl acetamide. Among the above, N-vinyl acetamide is preferred from the viewpoints of blister resistance, resistance to wet heat whitening, and dielectric constant. These may be used alone or in combination of two or more.

The (meth)acrylic acid ester polymer (A) preferably contains 0.5% by mass or more, particularly 1% by mass or more of N-vinylcarboxylic acid amide as a monomer unit constituting the polymer. It is preferable that the content is more preferably 2% by mass or more. Further, the (meth)acrylic acid ester polymer (A) preferably contains 15% by mass or less, particularly 10% by mass or less of N-vinylcarboxylic acid amide as a monomer unit constituting the polymer. The content is preferably 8% by mass or less, and more preferably 8% by mass or less. When the (meth)acrylic acid ester polymer (A) contains N-vinylcarboxylic acid amide in the above amount as a monomer unit, the resulting adhesive has even better blister resistance and moist heat whitening resistance, Further, the dielectric constant can be effectively suppressed to a low level.

In the (meth)acrylic acid ester polymer (A), the mass ratio of the reactive functional group-containing monomer as a monomer unit constituting the polymer and the N-vinylcarboxylic acid amide is 95:5 to 50:50. The ratio is preferably 85:15 to 60:40, and even more preferably 80:20 to 65:35. When the mass ratio is within the above range, blister resistance, moist heat whitening resistance, and dielectric constant can be achieved in a well-balanced manner.

The (meth)acrylic acid ester polymer (A) also preferably contains a monomer having a nitrogen-containing heterocycle in the molecule as a monomer unit constituting the polymer. By having a monomer having a nitrogen-containing heterocycle present as a constituent unit in the polymer, a predetermined polarity is imparted to the adhesive, and it can be made to have excellent affinity even for adherends having a certain degree of polarity, such as glass.

Examples of monomers having a nitrogen-containing heterocycle include N-(meth)acryloylmorpholine, N-vinyl-2-pyrrolidone, N-(meth)acryloylpyrrolidone, N-(meth)acryloylpiperidine, N-(meth)acryloylpyrrolidine, N-(meth)acryloylaziridine, aziridinylethyl (meth)acrylate, 2-vinylpyridine, 4-vinylpyridine, 2-vinylpyrazine, 1-vinylimidazole, N-vinylcarbazole, and N-vinylphthalimide. Among these, N-(meth)acryloylmorpholine, which exhibits superior adhesive strength, is preferred, and N-acryloylmorpholine is particularly preferred. These may be used alone or in combination of two or more.

The (meth)acrylic acid ester polymer (A) preferably contains 0.5% by mass or more of a monomer having a nitrogen-containing heterocycle as a monomer unit constituting the polymer, more preferably 1% by mass or more, and even more preferably 3% by mass or more. The (meth)acrylic acid ester polymer (A) preferably contains 20% by mass or less of a monomer having a nitrogen-containing heterocycle as a monomer unit constituting the polymer, more preferably 15% by mass or less, and even more preferably 8% by mass or less. When the content of the monomer having a nitrogen-containing heterocycle is within the above range, the resulting adhesive can fully exhibit excellent adhesion to glass.

The (meth)acrylic acid ester polymer (A) may contain other monomers as monomer units constituting the polymer, if desired. As other monomers, monomers that do not contain reactive functional groups are preferred.

Examples of monomers containing no reactive functional group include alkoxyalkyl (meth)acrylates such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, vinyl acetate, and styrene. These may be used alone or in combination of two or more.

The (meth)acrylic acid ester polymer (A) is preferably a linear polymer. A linear polymer makes it easier for molecular chains to become entangled, which is expected to improve cohesive strength, resulting in an adhesive with superior blister resistance.

Moreover, it is preferable that the (meth)acrylic acid ester polymer (A) is a solution polymer obtained by a solution polymerization method. By being a solution polymer, a polymer with a high molecular weight can be easily obtained, and an improvement in cohesive force can be expected, so that an adhesive with better blister resistance can be obtained.

The polymerization form of the (meth)acrylic acid ester polymer (A) may be a random copolymer or a block copolymer.

The weight average molecular weight of the (meth)acrylic acid ester polymer (A) preferably has a lower limit of 200,000 or more, more preferably 300,000 or more, and even more preferably 400,000 or more. If the lower limit of the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is the above or higher, the resulting pressure-sensitive adhesive will have better blister resistance.

The upper limit of the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 2 million or less, particularly preferably 1.5 million or less, and more preferably 1 million or less. preferable. When the upper limit of the weight average molecular weight of the (meth)acrylic acid ester polymer (A) is below the above range, the resulting pressure-sensitive adhesive will have better adhesive strength and better coatability during production. Note that the weight average molecular weight in this specification is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

In addition, in the adhesive composition P, the (meth)acrylic acid ester polymer (A) may be used alone or in combination of two or more kinds.

The content of the (meth)acrylic acid ester polymer (A) in the adhesive composition P according to this embodiment is preferably 50% by mass or more as a lower limit, particularly preferably 60% by mass or more, and even more preferably 70% by mass or more. By setting the lower limit of the content of the (meth)acrylic acid ester polymer (A) as above, the adhesive strength of the obtained adhesive becomes better. In addition, the content of the (meth)acrylic acid ester polymer (A) is preferably 99.9% by mass or less as an upper limit, particularly preferably 99.8% by mass or less, and even more preferably 99.7% by mass or less. By setting the upper limit of the content of the (meth)acrylic acid ester polymer (A) as above, the content of the crosslinking agent (B) is ensured, thereby improving the cohesive strength of the adhesive and improving the blister resistance.

(2) Crosslinking agent (B)
The crosslinking agent (B) crosslinks the (meth)acrylic acid ester polymer (A) to form a three-dimensional network structure by heating the pressure-sensitive adhesive composition P. This improves the cohesive strength of the resulting pressure-sensitive adhesive and provides it with excellent blister resistance.

The crosslinking agent (B) may be any that reacts with the reactive functional group of the (meth)acrylic acid ester polymer (A), and examples thereof include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, amine-based crosslinking agents, melamine-based crosslinking agents, aziridine-based crosslinking agents, hydrazine-based crosslinking agents, aldehyde-based crosslinking agents, oxazoline-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, and ammonium salt-based crosslinking agents. Among the above, when the reactive functional group of the (meth)acrylic acid ester polymer (A) is a hydroxyl group, it is preferable to use an isocyanate-based crosslinking agent that has excellent reactivity with the hydroxyl group, and when the reactive functional group of the (meth)acrylic acid ester polymer (A) is a carboxyl group, it is preferable to use an epoxy-based crosslinking agent that has excellent reactivity with the carboxyl group. The crosslinking agent (B) may be used alone or in combination of two or more types.

The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of polyisocyanate compounds include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate, and their biuret and isocyanurate forms, as well as adducts which are reactants with low-molecular active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. Among these, trimethylolpropane-modified aromatic polyisocyanates, particularly trimethylolpropane-modified tolylene diisocyanate and trimethylolpropane-modified xylylene diisocyanate, are preferred from the viewpoint of reactivity with hydroxyl groups.

Examples of the epoxy crosslinking agent include 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane, N,N,N',N'-tetraglycidyl-m-xylylenediamine, and ethylene glycol diglycidyl ether. , 1,6-hexanediol diglycidyl ether, trimethylolpropane diglycidyl ether, diglycidylaniline, diglycidylamine, and the like. Among them, 1,3-bis(N,N-diglycidylaminomethyl)cyclohexane is preferred from the viewpoint of reactivity with carboxy groups.

The content of the crosslinking agent (B) in the adhesive composition P is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more, per 100 parts by mass of the (meth)acrylic acid ester polymer (A). The content is preferably 3 parts by mass or less, more preferably 2 parts by mass or less, and even more preferably 1 part by mass or less. By having the content of the crosslinking agent (B) in the above range, the degree of crosslinking becomes appropriate, and the blister resistance of the resulting adhesive becomes more excellent.

(3) Various additives The adhesive composition P may optionally contain various additives commonly used in acrylic adhesives, such as silane coupling agents, ultraviolet absorbers, antistatic agents, tackifiers, oxidizing agents, etc. Inhibitors, light stabilizers, softeners, fillers, refractive index modifiers, etc. can be added. Note that the polymerization solvent and dilution solvent described below are not included in the additives constituting the adhesive composition P.

Here, when the adhesive composition P contains a silane coupling agent, the adhesive obtained has improved adhesion to glass members and plastic plates. This makes the adhesive obtained more blister-resistant.

As the silane coupling agent, an organosilicon compound having at least one alkoxysilyl group in the molecule, which has good compatibility with the (meth)acrylic acid ester polymer (A) and has light transparency is used. preferable.

Examples of such silane coupling agents include silicon compounds containing polymerizable unsaturated groups such as vinyltrimethoxysilane, vinyltriethoxysilane, methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 2-( Silicon compounds having an epoxy structure such as 3,4-epoxycyclohexyl)ethyltrimethoxysilane, mercapto group-containing silicon compounds such as 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, and 3-mercaptopropyldimethoxymethylsilane , 3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane, and other amino group-containing silicon compounds; 3-chloropropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, or at least one of these, and an alkyl group-containing silicon compound such as methyltriethoxysilane, ethyltriethoxysilane, methyltrimethoxysilane, or ethyltrimethoxysilane. Examples include condensates of These may be used alone or in combination of two or more.

When the adhesive composition P contains a silane coupling agent, the content thereof is preferably 0.01 parts by mass or more based on 100 parts by mass of the (meth)acrylic acid ester polymer (A), In particular, it is preferably 0.05 parts by mass or more, and more preferably 0.1 parts by mass or more. Further, the content is preferably 2 parts by mass or less, particularly preferably 1 part by mass or less, and further preferably 0.5 parts by mass or less.

2. Manufacture of adhesive composition Adhesive composition P is produced by manufacturing a (meth)acrylic acid ester polymer (A), and combining the obtained (meth)acrylic acid ester polymer (A) with a crosslinking agent (B). It can be manufactured by mixing and adding additives if desired.

The (meth)acrylic acid ester polymer (A) can be produced by polymerizing a mixture of monomers constituting the polymer using a conventional radical polymerization method. The (meth)acrylic acid ester polymer (A) is preferably polymerized by a solution polymerization method using a polymerization initiator if desired. Examples of the polymerization solvent include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, and methyl ethyl ketone, and two or more of them may be used in combination.

Examples of the polymerization initiator include azo compounds and organic peroxides, and two or more types may be used in combination. Examples of azo compounds include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylbutyronitrile), 1,1'-azobis(cyclohexane 1-carbonitrile), 2 ,2'-azobis(2,4-dimethylvaleronitrile), 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2,2'-azobis(2-methylpropionate) , 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-hydroxymethylpropionitrile), 2,2'-azobis[2-(2-imidazolin-2-yl) Propane], etc.

Examples of organic peroxides include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di(2-ethoxyethyl)peroxy Examples include dicarbonate, t-butyl peroxyneodecanoate, t-butyl peroxy bivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, diacetyl peroxide and the like.

In addition, in the above polymerization process, the weight average molecular weight of the resulting polymer can be adjusted by adding a chain transfer agent such as 2-mercaptoethanol.

Once the (meth)acrylic acid ester polymer (A) is obtained, the crosslinking agent (B) and, if desired, a diluting solvent and additives are added to the solution of the (meth)acrylic acid ester polymer (A) and mixed thoroughly to obtain a solvent-diluted adhesive composition P (coating solution). Note that, if any of the above components is in a solid state or if precipitation occurs when mixed with other components in an undiluted state, the component may be dissolved or diluted alone in a diluting solvent before mixing with the other components.

Examples of the dilution solvent include aliphatic hydrocarbons such as hexane, heptane, and cyclohexane; aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as methylene chloride and ethylene chloride; alcohols such as methanol, ethanol, propanol, butanol, and 1-methoxy-2-propanol; ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; and cellosolve-based solvents such as ethyl cellosolve.

The concentration and viscosity of the coating solution prepared in this manner are not particularly limited as long as they are within a coating range, and can be appropriately selected depending on the situation. For example, the adhesive composition P is diluted to a concentration of 10 to 60% by mass. In addition, when obtaining a coating solution, addition of a dilution solvent etc. is not a necessary condition, and if adhesive composition P has a viscosity etc. which can be coated, it is not necessary to add a dilution solvent. In this case, the adhesive composition P becomes a coating solution using the polymerization solvent of the (meth)acrylic acid ester polymer (A) as a diluting solvent.

[Adhesive]
The pressure-sensitive adhesive according to the present embodiment is obtained by crosslinking the pressure-sensitive adhesive composition P. The crosslinking of the pressure-sensitive adhesive composition P can usually be carried out by a heat treatment. This heat treatment can also serve as a drying treatment for volatilizing a diluting solvent and the like from a coating film of the pressure-sensitive adhesive composition P applied to a desired object.

The heating temperature for the heat treatment is preferably 50 to 150°C, and more preferably 70 to 120°C. The heating time is preferably 10 seconds to 10 minutes, and more preferably 50 seconds to 2 minutes.

After the heat treatment, a curing period of about 1 to 2 weeks may be provided at room temperature (e.g., 23°C, 50% RH) if necessary. If this curing period is required, the adhesive will be formed after the curing period has elapsed. If no curing period is required, the adhesive will be formed after the heat treatment has been completed.

By the above heat treatment (and curing), the (meth)acrylic acid ester polymer (A) is sufficiently crosslinked via the crosslinking agent (B). The adhesive thus obtained has excellent blister resistance.

The adhesive according to this embodiment preferably has the following physical properties.
(1) Gel fraction The lower limit of the gel fraction of the adhesive according to the present embodiment is preferably 30% or more, more preferably 40% or more, and particularly preferably 50% or more. . When the lower limit of the gel fraction of the adhesive is above, the cohesive force of the adhesive becomes high and the blister resistance becomes more excellent. Further, the upper limit of the gel fraction of the adhesive according to the present embodiment is preferably 95% or less, particularly preferably 85% or less, and further preferably 80% or less. When the upper limit of the gel fraction of the adhesive is within the above range, the adhesive does not become too hard, exhibits good adhesive strength, and exhibits better adhesion to adherends. Here, the method for measuring the gel fraction of the adhesive is as shown in the test example described below.

(2) Dielectric Constant The dielectric constant of the adhesive according to the present embodiment at 1.0 MHz is preferably 6.5 or less as an upper limit, particularly preferably 6.2 or less, and more preferably 5.8 or less. The upper limit of the dielectric constant as described above can contribute to suppressing malfunction of the touch panel and improving the responsiveness. The adhesive according to the present embodiment obtained by using the (meth)acrylic acid ester polymer (A) having a component derived from N-vinyl carboxylic acid amide can achieve the low dielectric constant as described above.

The lower limit of the dielectric constant of the adhesive of this embodiment at 1.0 MHz is not particularly limited, but is usually preferably 3.5 or more, more preferably 3.8 or more, and even more preferably 4.0 or more. The method for measuring the dielectric constant of the adhesive is as shown in the test example described later.

(3) Humidity and heat whitening resistance The humidity and heat whitening resistance of the pressure-sensitive adhesive according to this embodiment can be quantitatively evaluated by the haze value. Specifically, a laminate in which a 50 μm thick pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to this embodiment is sandwiched between a glass plate and an acrylic resin plate with a thickness of 1 mm is subjected to a durability test in which the laminate is stored under humid heat conditions of 85° C. and 85% RH for 120 hours, and then the haze value (%) (measured according to JIS K7136:2000; the same applies below) when stored at normal temperature and humidity of 23° C. and 50% RH for 24 hours minus the haze value (%) before the durability test is preferably less than 5 points, particularly preferably less than 3 points, and more preferably less than 1 point. If the haze value increase is as above, it can be said that the increase in haze value is small even after being placed under humid heat conditions, and the whitening of the pressure-sensitive adhesive is suppressed.

As mentioned above, in a laminate in which an adhesive layer is sandwiched between a glass plate and an acrylic resin plate, compared to a laminate in which an adhesive layer is sandwiched between two glass plates, the acrylic resin plate is Since the permeated moisture tends to condense within the laminate, whitening tends to occur in the adhesive layer. However, the pressure-sensitive adhesive according to the present embodiment exhibits excellent moist heat whitening resistance even in the above-mentioned laminate.

[Adhesive sheet]
The adhesive sheet according to this embodiment is an adhesive sheet having at least an adhesive layer made of the adhesive described above, and is preferably an adhesive sheet having a release sheet laminated on one or both sides of the adhesive layer.

FIG. 1 shows a specific configuration of one example of the pressure-sensitive adhesive sheet according to this embodiment.
As shown in Fig. 1, an adhesive sheet 1 according to an embodiment is composed of two release sheets 12a and 12b, and an adhesive layer 11 sandwiched between the two release sheets 12a and 12b so as to be in contact with the release surfaces of the two release sheets 12a and 12b. Note that the release surface of the release sheet in this specification refers to a surface of the release sheet that has releasability, and includes both a surface that has been subjected to a release treatment and a surface that exhibits releasability even without being subjected to a release treatment.

1. Each member (1) Adhesive layer The adhesive layer 11 is composed of the above-mentioned adhesive, that is, it is composed of an adhesive formed by crosslinking the adhesive composition P.

The lower limit of the thickness of the adhesive layer 11 in the adhesive sheet 1 according to the present embodiment (value measured according to JIS K7130) is preferably 10 μm or more, more preferably 25 μm or more, and particularly 50 μm. It is preferable that it is above. When the lower limit of the thickness of the adhesive layer 11 is above, it is easy to exhibit desired adhesive force.

The thickness of the adhesive layer 11 is preferably 1000 μm or less as an upper limit, more preferably 600 μm or less, particularly preferably 300 μm or less, and even more preferably 150 μm or less. When the upper limit of the thickness of the adhesive layer 11 is as described above, the adhesive layer 11 has better resistance to moist heat whitening and is also more likely to exhibit excellent blister resistance. The adhesive layer 11 may be formed as a single layer, or may be formed by laminating multiple layers.

(2) Release Sheet The release sheets 12a and 12b protect the adhesive layer 11 until the adhesive sheet 1 is used, and are peeled off when the adhesive sheet 1 (adhesive layer 11) is used. In the adhesive sheet 1 according to this embodiment, one or both of the release sheets 12a and 12b are not necessarily required.

Examples of release sheets 12a and 12b include polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, and polybutylene. Terephthalate film, polyurethane film, ethylene vinyl acetate film, ionomer resin film, ethylene/(meth)acrylic acid copolymer film, ethylene/(meth)acrylic acid ester copolymer film, polystyrene film, polycarbonate film, polyimide film, fluorine A resin film or the like is used. Moreover, these crosslinked films are also used. Furthermore, a laminated film of these may be used.

It is preferable that the release surfaces of the release sheets 12a, 12b (particularly the surfaces in contact with the adhesive layer 11) are subjected to a release treatment. Examples of the release agent used in the release treatment include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents. It is preferable that one of the release sheets 12a and 12b be a heavy release type release sheet with a high peel force, and the other release sheet be a light release type release sheet with a low peel force.

There are no particular limitations on the thickness of the release sheets 12a and 12b, but it is usually about 20 to 150 μm.

2. Physical Properties (1) Haze Value The haze value of the adhesive layer 11 of the adhesive sheet 1 according to this embodiment is preferably 5% or less, more preferably 3% or less, particularly preferably 1% or less, and even more preferably 0.5% or less. When the haze value of the adhesive layer 11 is 5% or less, the transparency is very high and it is suitable for optical applications (displays). The haze value in this specification is a value measured in accordance with JIS K7136:2000.

(2) Transmitted hue b*
The pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1 according to this embodiment has a transmission hue b* defined by the CIE1976 L*a*b* color system, which is preferably -2.0 to 2.0, particularly preferably -1.5 to 1.5, and more preferably -1.0 to 1.0. When the transmission hue b* of the pressure-sensitive adhesive layer 11 is in the above range, the pressure-sensitive adhesive layer 11 has little coloring and is particularly suitable for display use. In this embodiment, the (meth)acrylic acid ester polymer (A) contains an appropriate amount of N-vinyl carboxylic acid amide as a monomer unit constituting the polymer, thereby making it possible to achieve the above transmission hue b*. The method for measuring the transmission hue b* in this specification is as shown in the test example described later.

(3) Adhesive Strength The adhesive strength of the adhesive sheet 1 according to the present embodiment to soda lime glass is preferably 5 N/25 mm or more as a lower limit, particularly preferably 10 N/25 mm or more, and further preferably 15 N/25 mm or more. When the adhesive strength of the adhesive sheet 1 is 5 N/25 mm or more, the blister resistance is more excellent. In addition, the adhesive strength of the adhesive sheet 1 according to the present embodiment to soda lime glass is preferably 50 N/25 mm or less as an upper limit, more preferably 45 N/25 mm or less, and particularly preferably 40 N/25 mm or less. When the adhesive strength of the adhesive sheet 1 is 50 N/25 mm or less, good reworkability is obtained, and when a bonding error occurs, expensive display body components can be reused.

Here, the adhesive strength in this specification basically refers to the adhesive strength measured by the 180-degree peeling method in accordance with JIS Z0237:2009. The measurement sample is 25 mm wide and 100 mm long, and the measurement sample is attached to the adherend and pressurized at 0.5 MPa and 50°C for 20 minutes, and then left to stand for 24 hours under normal pressure, 23°C, and 50% RH, and then measured at a peeling speed of 300 mm/min.

3. Manufacturing of adhesive sheet In one manufacturing example of the adhesive sheet 1, the adhesive composition P coating solution is applied to the release surface of one release sheet 12a (or 12b), heat treatment is performed to thermally crosslink the adhesive composition P, and a coating layer is formed, and then the release surface of the other release sheet 12b (or 12a) is superimposed on the coating layer. If a curing period is required, a curing period is provided, and if no curing period is required, the coating layer becomes the adhesive layer 11 as it is. This results in the adhesive sheet 1. The conditions for the heat treatment and curing are as described above.

As another example of manufacturing the adhesive sheet 1, a coating solution of the adhesive composition P is applied to the release surface of one of the release sheets 12a, heat treatment is performed to thermally crosslink the adhesive composition P, and the adhesive composition P is applied. A layer is formed to obtain a release sheet 12a with a coating layer. Further, a coating solution of the adhesive composition P is applied to the release surface of the other release sheet 12b, heat treatment is performed to thermally crosslink the adhesive composition P, and a coating layer is formed. A release sheet 12b is obtained. Then, the release sheet 12a with the coating layer and the release sheet 12b with the coating layer are pasted together so that both coating layers are in contact with each other. If a curing period is required, a curing period is provided, and if a curing period is not required, the laminated coating layers described above become the adhesive layer 11 as is. Thereby, the above-mentioned pressure-sensitive adhesive sheet 1 is obtained. According to this production example, even if the adhesive layer 11 is thick, it is possible to stably produce it.

As a method for applying the coating solution of the adhesive composition P, for example, a bar coating method, a knife coating method, a roll coating method, a blade coating method, a die coating method, a gravure coating method, etc. can be used.

[Display body]
As shown in FIG. 2, the display 2 according to the present embodiment includes a first display component 21 (one display component) and a second display component 22 (another display component). ), and an adhesive layer 11 located between them and bonding the first display component 21 and the second display component 22 to each other. In the display body 2 according to the present embodiment, the first display body constituent member 21 may have a step such as the printed layer 3 on the surface on the adhesive layer 11 side.

The adhesive layer 11 in the display body 2 is the adhesive layer 11 of the adhesive sheet 1 described above.

Examples of the display body 2 include a liquid crystal (LCD) display, a light emitting diode (LED) display, an organic electroluminescence (organic EL) display, and electronic paper, and may also be a touch panel. Further, the display body 2 may be a member that constitutes a part thereof.

The first display component 21 is preferably a protective panel made of a glass plate, a plastic plate, etc., or a laminate including them. In this case, the printed layer 3 is generally formed in the shape of a frame on the adhesive layer 11 side of the first display component 21.

The above glass plate is not particularly limited, and examples thereof include chemically strengthened glass, alkali-free glass, quartz glass, soda-lime glass, barium-strontium-containing glass, aluminosilicate glass, lead glass, borosilicate glass, barium borosilicate glass, etc. The thickness of the glass plate is not particularly limited, but is usually 0.1 to 5 mm, and preferably 0.2 to 2 mm.

The above-mentioned plastic plate is not particularly limited, and examples thereof include an acrylic plate, a polycarbonate plate, and the like. The thickness of the plastic plate is not particularly limited, but is usually 0.2 to 5 mm, preferably 0.4 to 3 mm.

In addition, various functional layers (transparent conductive film, metal layer, silica layer, hard coat layer, anti-glare layer, etc.) may be provided on one or both sides of the above glass plate or plastic plate, or optical members may be laminated thereon. In addition, the transparent conductive film and metal layer may be patterned.

The second display component 22 is preferably an optical member to be attached to the first display component 21, a display module (e.g., a liquid crystal (LCD) module, a light emitting diode (LED) module, an organic electroluminescence (OLED) module, etc.), an optical member as part of a display module, or a laminate including a display module.

Examples of the above-mentioned optical members include anti-scattering films, polarizing plates (polarizing films), polarizers, retardation plates (retardation films), viewing angle compensation films, brightness enhancement films, contrast enhancement films, liquid crystal polymer films, and diffusion films. , transflective film, transparent conductive film, etc. Examples of the anti-scattering film include a hard coat film in which a hard coat layer is formed on one side of a base film.

The material constituting the printing layer 3 is not particularly limited, and known materials for printing can be used. The lower limit of the thickness of the printed layer 3, that is, the height of the step, is preferably 3 μm or more, more preferably 5 μm or more, particularly preferably 7 μm or more, and most preferably 10 μm or more. preferable. When the lower limit value is equal to or higher than the above value, it is possible to sufficiently ensure concealment such as making the electrical wiring invisible to the viewer. Moreover, the upper limit is preferably 50 μm or less, more preferably 35 μm or less, particularly preferably 25 μm or less, and even more preferably 20 μm or less. When the upper limit is below the above value, it is possible to prevent deterioration in the step followability of the adhesive layer 11 with respect to the printed layer 3.

To manufacture the display body 2, as an example, one release sheet 12a of the adhesive sheet 1 is peeled off, and the exposed adhesive layer 11 of the adhesive sheet 1 is attached to the surface of the first display body component 21 on which the printing layer 3 is present.

Thereafter, the other release sheet 12b is peeled off from the adhesive layer 11 of the adhesive sheet 1, and the exposed adhesive layer 11 of the adhesive sheet 1 and the second display component member 22 are bonded together. Moreover, as another example, the bonding order of the first display body constituent member 21 and the second display body constituent member 22 may be changed.

In the above display body 2, even if outgassing occurs from the first display body component 21 and/or the second display body component 22 when the display body 2 is placed under high temperature and high humidity conditions (e.g., 85°C, 85% RH), the adhesive layer 11 has excellent blister resistance, so the occurrence of blisters such as air bubbles, floating, and peeling is suppressed at the interface between the adhesive layer 11 and the first display body component 21 and/or the second display body component 22.

In addition, since the adhesive layer 11 has excellent moisture and heat whitening resistance, the display body 2 may be placed under high temperature and high humidity conditions (e.g., 85° C., 85% RH) and then returned to normal temperature and humidity. Even in this case, whitening of the adhesive layer 11 is suppressed. According to the display 2 according to the present embodiment, in particular, one of the first display component 21 and the second display component 22 is a plastic plate with a thickness of 1 mm or more, and the other is a glass plate. Even if there is, excellent moisture and heat whitening resistance is exhibited.

Furthermore, since the dielectric constant of the adhesive layer 11 is kept low, even if the display body 2 is a touch panel, malfunctions of the touch panel due to the dielectric constant of the adhesive layer 11 can be effectively suppressed. Moreover, the responsiveness of the touch panel is good.

The embodiments described above are described to facilitate understanding of the present invention, and are not described to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design changes and equivalents that fall within the technical scope of the present invention.

For example, either or both of the release sheets 12a and 12b in the adhesive sheet 1 may be omitted, and a desired optical member may be laminated in place of the release sheets 12a and/or 12b. Also, the first display member 21 may not have a step.

The present invention will be explained in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

[Example 1]
1. Preparation of (meth)acrylic acid ester polymer (A) 60 parts by mass of 2-ethylhexyl acrylate, 5 parts by mass of 4-acryloylmorpholine, 15 parts by mass of isobornyl acrylate, 5 parts by mass of N-vinylacetamide, and 2-hydroxy acrylate A (meth)acrylic acid ester polymer (A) was prepared by copolymerizing 15 parts by mass of ethyl using a solution polymerization method. When the molecular weight of this (meth)acrylic acid ester polymer (A) was measured by the method described below, it was found to have a weight average molecular weight (Mw) of 500,000.

2. Preparation of Adhesive Composition 100 parts by mass (solid content equivalent; same applies hereinafter) of the (meth)acrylic ester polymer (A) obtained in the above step 1 and trimethylolpropane-modified trimethylammonium as a crosslinking agent (B). 0.15 parts by mass of diisocyanate (manufactured by Toyochem Co., Ltd., product name "BHS8515") and 3-glycidoxypropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd., product name "KBM-403") as a silane coupling agent. A coating solution of the adhesive composition was obtained by mixing with 0.30 parts by mass, thoroughly stirring, and diluting with methyl ethyl ketone.

Here, Table 1 shows each formulation (in terms of solid content) of the adhesive composition when the (meth)acrylic acid ester polymer (A) is 100 parts by mass (in terms of solid content). The details of the abbreviations and the like listed in Table 1 are as follows.
[(meth)acrylic acid ester polymer (A)]
2EHA: 2-ethylhexyl acrylate ACMO: 4-acryloylmorpholine IBXA: isobornyl acrylate NVA: N-vinylacetamide HEA: 2-hydroxyethyl acrylate MMA: methyl methacrylate BA: n-butyl acrylate
[Crosslinking agent (B)]
TDI: Trimethylolpropane-modified tolylene diisocyanate (manufactured by Toyochem, product name "BHS8515")
Epoxy system: 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane (manufactured by Mitsubishi Gas Chemical Co., Ltd., product name "TETRAD-C")

3. Manufacturing of adhesive sheet The coating solution of the adhesive composition obtained in the above step 2 was applied by a knife coater to the release-treated surface of a heavy-release type release sheet (manufactured by Lintec Corporation, product name "SP-PET752150"), one side of which was a polyethylene terephthalate film treated with a silicone-based release agent. The coating layer was then heat-treated at 90°C for 1 minute to form a coating layer.

Next, the coated layer on the heavy release type release sheet obtained above and a light release type release sheet (manufactured by Lintec, product name "SP-PET382120") in which one side of the polyethylene terephthalate film was released with a silicone release agent. are laminated so that the release-treated surface of the light-release release sheet is in contact with the coating layer, and cured for 7 days at 23°C and 50% RH to form a heavy-release release sheet/adhesive. A first pressure-sensitive adhesive sheet having a structure of layer (thickness: 25 μm)/light release type release sheet was produced.

The adhesive composition coating solution obtained in the above step 2 was applied by a knife coater to the release-treated surface of a heavy-release release sheet (manufactured by Lintec Corporation, product name "SP-PET752150"), one side of which was a polyethylene terephthalate film treated with a silicone-based release agent, and then heated at 90°C for 1 minute to form a coating layer (thickness: 25 μm). Similarly, the adhesive composition coating solution obtained in the above step 2 was applied by a knife coater to the release-treated surface of a light-release release sheet (manufactured by Lintec Corporation, product name "SP-PET382120"), one side of which was a polyethylene terephthalate film treated with a silicone-based release agent, and then heated at 90°C for 1 minute to form a coating layer (thickness: 25 μm).

Next, the heavy release type release sheet with the coating layer obtained above and the light release type release sheet with the coating layer obtained above were laminated together so that the two coating layers were in contact with each other, and cured for 7 days under conditions of 23°C and 50% RH to produce a second adhesive sheet consisting of heavy release type release sheet/adhesive layer (thickness: 50 μm)/light release type release sheet.

The thickness of the adhesive layer is a value measured using a constant pressure thickness measuring device (manufactured by Techlock Co., Ltd., product name "PG-02") in accordance with JIS K7130.

[Examples 2 to 3, Comparative Examples 1 to 4]
The first and second pressure-sensitive adhesive sheets were produced in the same manner as in Example 1, except that the types and ratios of the monomers constituting the (meth)acrylic acid ester polymer (A), the weight average molecular weight (Mw) of the (meth)acrylic acid ester polymer (A), and the type and amount of the crosslinking agent (B) were changed as shown in Table 1.

Here, the weight average molecular weight (Mw) mentioned above is the weight average molecular weight in terms of polystyrene measured using gel permeation chromatography (GPC) under the following conditions (GPC measurement).
<Measurement conditions>
・GPC measurement device: Tosoh Corporation, HLC-8020
・GPC column (passed in the following order): TSK guard column HXL-H manufactured by Tosoh Corporation
TSK gel GMHXL (x2)
TSK gel G2000HXL
・Measurement solvent: Tetrahydrofuran ・Measurement temperature: 40℃

[Test Example 1] (Measurement of gel fraction)
The first adhesive sheet (adhesive layer thickness: 25 μm) obtained in Examples and Comparative Examples was cut into a size of 80 mm x 80 mm, and the adhesive layer was wrapped in a polyester mesh (mesh size 200). The mass of the adhesive alone was calculated by weighing the mass using a precision balance and subtracting the mass of the mesh alone. Let the mass at this time be M1.

Next, the adhesive wrapped in the polyester mesh was immersed in ethyl acetate at room temperature (23°C) for 24 hours. Thereafter, the adhesive was taken out and air-dried for 24 hours at a temperature of 23°C and a relative humidity of 50%, and further dried in an oven at 80°C for 12 hours. After drying, the mass was weighed using a precision balance, and the mass of the adhesive alone was calculated by subtracting the mass of the mesh alone. Let the mass at this time be M2. Gel fraction (%) is expressed as (M2/M1)×100. The results are shown in Table 2.

[Test Example 2] (Measurement of haze value)
The adhesive layer of the first adhesive sheet (adhesive layer thickness: 25 μm) obtained in Examples and Comparative Examples was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name) in accordance with JIS K7136:2000. The haze value (%) was measured using "NDH-2000"). The results are shown in Table 2.

[Test Example 3] (Measurement of adhesive strength)
The light release type release sheet was peeled off from the first adhesive sheet (adhesive layer thickness: 25 μm) obtained in Examples and Comparative Examples, and the exposed adhesive layer was replaced with polyethylene terephthalate (PET) having an easily adhesive layer. ) film (manufactured by Toyobo Co., Ltd., product name "PET A4300", thickness: 100 μm) was laminated to the easily adhesive layer to obtain a laminate of release sheet/adhesive layer/PET film. The obtained laminate was cut to a width of 25 mm and a length of 100 mm, which was used as a sample.

In an environment of 23°C and 50% RH, the heavy release type release sheet was peeled off from the above sample, and the exposed adhesive layer was attached to soda lime glass (manufactured by Nippon Sheet Glass Co., Ltd.), and then pressure was applied for 20 minutes at 0.5 MPa and 50°C in an autoclave manufactured by Kurihara Seisakusho Co., Ltd. After leaving the sample for 24 hours under conditions of 23°C and 50% RH, the adhesive strength (N/25 mm) was measured using a tensile tester (Tensilon manufactured by Orientec Co., Ltd.) at a peel speed of 300 mm/min and a peel angle of 180 degrees. Measurements were performed in accordance with JIS Z0237:2009 under conditions other than those described here. The results are shown in Table 2.

[Test Example 4] (Measurement of transmitted hue b*)
The adhesive layer of the first adhesive sheet (adhesive layer thickness: 25 μm) obtained in Examples and Comparative Examples was measured using a simultaneous photometric spectrophotometer (manufactured by Nippon Denshoku Kogyo Co., Ltd., product name "SQ2000"). ) was used to measure the transmitted hue b* defined by the CIE1976L*a*b* color system. The results are shown in Table 2.

[Test Example 5] (Evaluation of blister resistance)
The adhesive layer of the second adhesive sheet (adhesive layer thickness: 50 μm) obtained in the Examples and Comparative Examples was sandwiched between a transparent conductive film of a polyethylene terephthalate film (manufactured by Oike Kogyo Co., Ltd., ITO film, thickness: 125 μm) having a transparent conductive film made of tin-doped indium oxide (ITO) provided on one side, and an acrylic resin plate made of polymethyl methacrylate (PMMA) (manufactured by Mitsubishi Rayon Co., Ltd., product name "Acrylite MR-200", thickness: 1 mm) to obtain a laminate.

The obtained laminate (sample) was autoclaved for 30 minutes at 50° C. and 0.5 MPa, and then left for 24 hours at normal pressure, 23° C., and 50% RH. Then, it was stored for 72 hours under high temperature and high humidity conditions of 85° C. and 85% RH. Thereafter, the adhesive layer was visually checked to see if there were any bubbles, floating, or peeling, and the blister resistance was evaluated according to the following criteria. The results are shown in Table 2.
〇…There were no bubbles, floating, or peeling.
×...Bubbles, floating, and peeling occurred.

[Test Example 6] (Evaluation of resistance to wet heat whitening)
The adhesive layer of the second adhesive sheet (adhesive layer thickness: 50 μm) obtained in the Examples and Comparative Examples was sandwiched between a 1.1 mm thick alkali-free glass plate and a 1 mm thick acrylic resin plate (manufactured by Mitsubishi Rayon Co., Ltd., product name "Acrylite MR-200") to obtain a laminate.

The obtained laminate (sample) was autoclaved for 30 minutes under conditions of 50°C and 0.5 MPa, and then left for 24 hours at normal pressure, 23°C, and 50% RH. The haze value (%) of this laminate was measured in accordance with JIS K7136:2000 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH2000").

Next, the laminate was stored for 120 hours under humid heat conditions of 85°C and 85% RH. It was then left for 24 hours at room temperature and humidity of 23°C and 50% RH. The haze value (%) of the laminate was measured in accordance with JIS K7136:2000 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH2000").

Based on the above results, the haze value increase (points) after the humid heat condition was calculated by subtracting the haze value before the humid heat condition from the haze value after the humid heat condition. Based on the results, the moist heat whitening resistance was evaluated based on the following criteria. The results are shown in Table 2.
◎...Haze value increase is less than 1.0 points 〇...Haze value increase is 1.0 points or more but less than 5.0 points ×...Haze value increase is 5.0 points or more

[Test Example 7] (Calculation of dielectric constant)
A 100 μm thick adhesive layer was formed on one side of a 50 μm thick polyethylene terephthalate film in the same manner as in the Examples and Comparative Examples, and a 50 μm thick polyethylene terephthalate film was attached to the adhesive layer, and then cut into a size of 50 mm×50 mm. The capacitance (C1) of the resulting laminate was measured using an impedance analyzer (HP-4194A, manufactured by Hewlett-Packard Japan). In addition, two 50 μm thick polyethylene terephthalate films were stacked and cut into a size of 50 mm×50 mm, and the capacitance (C2) was measured in the same manner. Then, the values of C1 and C2 were used to calculate the series-connected capacitor: 1/C1=1/C2+1/C3
The capacitance (C3) of the adhesive was calculated based on the capacitance C3. The dielectric constant _εs of the adhesive was calculated based on the capacitance C3 using the following formula. The results are shown in Table 2.

ε _s = (C3×d)/(ε ₀ ×S)
ε _s : Permittivity of adhesive ε ₀ : Permittivity of vacuum (8.854×10 ⁻¹² )
C3: Capacitance of adhesive S: Area of adhesive layer d: Thickness of adhesive layer

As can be seen from Table 2, the adhesive sheets obtained in the examples were excellent in both blister resistance and resistance to whitening due to moist heat, and also showed low dielectric constants.

The adhesive composition, adhesive, and adhesive sheet of the present invention can be suitably used, for example, to bond a protective panel made of a plastic plate to a desired display component.

REFERENCE SIGNS LIST 1... Adhesive sheet 11... Adhesive layer 12a, 12b... Release sheet 2... Display body 21... First display body constituent member 22... Second display body constituent member 3... Printed layer

Claims (9)

A (meth)acrylic acid ester polymer (A) containing , as monomer units constituting the polymer, an alkyl (meth)acrylic acid ester, a reactive functional group-containing monomer having a reactive functional group in the molecule, and an N-vinyl carboxylic acid amide;
A crosslinking agent (B),
In the (meth)acrylic acid ester polymer (A), a mass ratio of the reactive functional group-containing monomer and the N-vinyl carboxylic acid amide as monomer units constituting the polymer is 95:5 to 50:50;
The (meth)acrylic acid alkyl ester includes a monomer having a glass transition temperature (Tg) of more than 0° C. as a homopolymer, and a monomer having a glass transition temperature (Tg) of 0° C. or lower as a homopolymer.
1. An adhesive composition comprising: The adhesive according to claim 1, wherein the (meth)acrylic acid ester polymer (A) does not contain a carboxyl group-containing monomer having a carboxyl group in the molecule as a monomer unit constituting the polymer. sexual composition. The adhesive composition according to claim 1 or 2, characterized in that the (meth)acrylic acid ester polymer (A) contains 5% by mass or more and 30% by mass or less of the reactive functional group-containing monomer as a monomer unit constituting the polymer. The adhesive composition according to any one of claims 1 to 3, wherein the (meth)acrylic acid ester polymer (A) has a weight average molecular weight of 200,000 or more and 2,000,000 or less. An adhesive obtained by crosslinking the adhesive composition according to any one of claims 1 to 4. The adhesive according to claim 5, characterized in that the gel fraction is 30% or more and 95% or less. The adhesive according to claim 5 or 6, characterized in that the dielectric constant at 1.0 MHz is 6.5 or less. The adhesive according to any one of claims 5 to 7, characterized in that a laminate in which a 50 μm thick adhesive layer made of the adhesive is sandwiched between a glass plate and a 1 mm thick acrylic resin plate is subjected to a durability test in which the laminate is stored for 120 hours under humid heat conditions of 85°C and 85% RH, and then the increase in haze value, calculated by subtracting the haze value before the durability test from the haze value when the laminate is stored for 24 hours at normal temperature and humidity of 23°C and 50% RH, is less than 5 points. Two release sheets,
an adhesive layer sandwiched between the release sheets so as to be in contact with the release surfaces of the two release sheets,
A pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer is made of the pressure-sensitive adhesive according to any one of claims 5 to 8.

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