CN114651052A - Adhesive composition for optical use - Google Patents

Abstract

The purpose of the present invention is to provide an optical adhesive composition having excellent level difference absorption and excellent processability. The adhesive composition for optical use of the present invention is characterized by containing a (meth) acrylic block copolymer, wherein the (meth) acrylic block copolymer contains: a high Tg segment having a glass transition temperature of 0 ℃ or higher and 100 ℃ or lower, and a low Tg segment having a glass transition temperature of-100 ℃ or higher and lower than 0 ℃, wherein the (meth) acrylic block copolymer has a peak of tan delta in a region of 0 ℃ or higher and a peak of tan delta in a region of lower than 0 ℃. Here, the glass transition temperature is calculated by the FOX equation using the monomer component composition constituting each segment.

Description

Adhesive composition for optical use

Technical Field

The present invention relates to an adhesive composition for optical use. More specifically, the present invention relates to an optical adhesive composition which can be preferably used for bonding optical members, manufacturing optical products, and the like.

Background

In recent years, image display devices such as liquid crystal display devices (LCDs) and organic EL display devices, and input devices such as touch panels used in combination with the image display devices have been widely used. In the production of such image display devices and input devices (also referred to as "optical products"), for example, transparent adhesive compositions (also referred to as "optical adhesive compositions") are used for applications in which optical members are bonded to each other. For example, an adhesive sheet having an adhesive layer formed from an optical adhesive composition is used for attaching a touch panel, a lens, or the like to an image display device such as a Liquid Crystal Display (LCD) or an organic EL display device.

Among the optical members, there are increasing optical members including members having a height difference such as a printing height difference. For example, in an image display device provided with a touch panel, a transparent and conductive printed layer such as patterned ITO (indium tin oxide) is formed on the surface of an optical member. In addition, a black concealing portion is usually printed in a frame shape on the outer peripheral edge portion of the surface protective film. In such applications, the optical adhesive composition is required to have a property of filling in a level difference such as a printing level difference, that is, excellent level difference absorbability (also referred to as "level difference followability").

Further, the use of optical members having a level difference or a gap other than the above-mentioned printing level difference is increasing, and the demand for an optical adhesive composition having excellent level difference absorbability is increasing. For example, in order to provide sensors such as a camera on a panel, the number of cases where a hole is provided in an optical member such as a polarizing plate is increasing, and the optical adhesive composition used in such cases is required to fill in a level difference that occurs at the boundary between the optical member and the hole. Further, Micro LED displays, which are attracting attention as next-generation displays, are manufactured by laying LED elements on a substrate at high density, and the optical adhesive composition used for this purpose is required to fill gaps and level differences between the LED elements.

In order to improve the level difference absorption, an attempt has been made to improve flexibility by lowering the elastic modulus of the optical adhesive composition (for example, patent document 1). However, such an optical pressure-sensitive adhesive composition having a low elastic modulus has a problem that processability such as shape stability and handling property is deteriorated although the composition is excellent in level difference absorption property. For example, in an optical member laminate having a pressure-sensitive adhesive layer formed from an optical pressure-sensitive adhesive composition having a low elastic modulus, the pressure-sensitive adhesive layer easily overflows from the end during storage, and dust adheres to the overflowing pressure-sensitive adhesive layer, which may cause a problem in workability.

In order to improve processability, it is necessary to increase the elastic modulus of the pressure-sensitive adhesive layer and harden it, but there is a trade-off relationship that the level difference absorbency is lowered when the pressure-sensitive adhesive layer is hardened, and a problem that it is difficult to solve the balance between the level difference absorbency and processability.

In order to improve the processability of an adhesive layer having a low elastic modulus, a method of increasing the elastic modulus at around room temperature by blending a tackifier resin having a high glass transition temperature with an adhesive and lowering the elastic modulus in a temperature range exceeding the glass transition temperature is known, and the improvement of the processability by such a tackifier resin is insufficient. In addition, when a tackifier resin is used, compatibility with the adhesive composition may be a problem, and it may be difficult to add a large amount of the tackifier resin to a level that satisfies the target elastic modulus.

Documents of the prior art

Patent document

Patent document 1: international publication WO2016/170875

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical adhesive composition having excellent level difference absorption and excellent processability.

Means for solving the problems

As a result of intensive studies to achieve the above object, the present inventors have found that a (meth) acrylic block copolymer having a high Tg segment and a low Tg segment in a specific glass transition temperature range is used as a polymer contained in an optical pressure-sensitive adhesive composition, whereby a high storage modulus is exhibited at room temperature (for example, 25 ℃), hardness is high, and processability is good, and a storage modulus is remarkably reduced in a region exceeding 50 ℃ to cause high fluidity, and a level difference absorption property is good. The present invention has been completed based on these findings.

That is, the invention provides in 1 st aspect an optical adhesive composition characterized in that,

comprising a (meth) acrylic block copolymer,

the (meth) acrylic block copolymer contains: a high Tg segment having a glass transition temperature of 0 ℃ or higher and 100 ℃ or lower, and a low Tg segment having a glass transition temperature of-100 ℃ or higher and lower than 0 ℃,

the (meth) acrylic block copolymer has a peak of tan delta in a region of 0 ℃ or higher and a peak of tan delta in a region of less than 0 ℃.

Wherein the glass transition temperature is calculated from the composition of the monomer components constituting each segment by the FOX formula.

The adhesive composition for optical use of the present invention contains a (meth) acrylic block copolymer having the high Tg segment and the low Tg segment, and having tan δ peaks in the region at 0 ℃ or higher and the region at less than 0 ℃, respectively, whereby the (meth) acrylic block copolymer exhibits a high storage modulus, hardness, and good processability as a whole as the (meth) acrylic block copolymer because only the low Tg segment is converted and fluidized at room temperature (e.g., 25 ℃) and the high Tg segment is not converted. In addition, in the region exceeding 50 ℃, the high Tg segment also undergoes transition and fluidization, and the storage modulus of the entire (meth) acrylic block copolymer decreases, resulting in high fluidity.

When the pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition for optical use of the present invention is bonded to an optical member having a level difference, the adhesive layer becomes high in fluidity by being bonded under heating conditions (for example, 50 ℃ or higher) such as autoclave, and can adhere without leaving a gap by sufficiently following the level difference. Thereafter, when the steel sheet is returned to room temperature (e.g., 25 ℃) and stored, the storage modulus increases, and the processability becomes good.

In the optical adhesive composition according to claim 1, the maximum value of the peak of tan δ in the region of 0 ℃ or higher is preferably 0.5 to 3.0. This configuration is preferable in that the (meth) acrylic block copolymer can achieve excellent processability and shape stability.

In the optical adhesive composition according to claim 1, the (meth) acrylic block copolymer is preferably an ABA type triblock copolymer. This configuration is suitable in that the (meth) acrylic block copolymer is easily produced.

The following is preferred: in the ABA type triblock copolymer in the optical adhesive composition according to claim 1 of the present invention, the a segment is the high Tg segment and the B segment is the low Tg segment. This configuration is suitable in that the aforementioned operational effects of the present invention can be easily obtained.

In the optical adhesive composition according to claim 1, the monomer component constituting the high Tg segment in the (meth) acrylic block copolymer preferably contains at least 1 selected from the group consisting of an alkyl (meth) acrylate having a linear alkyl group having 1 to 3 carbon atoms, an alkyl (meth) acrylate having a branched alkyl group having 3 or 4 carbon atoms, and an alicyclic monomer, and more preferably an alkyl (meth) acrylate having a branched alkyl group having 3 or 4 carbon atoms. The alicyclic monomer is preferably a cycloalkyl (meth) acrylate having a cycloalkyl group of 4 to 10 carbon atoms, which may have a substituent. This constitution is suitably controlled so that the high Tg segment has a predetermined glass transition temperature and the (meth) acrylic block copolymer has a peak of tan δ in a region of 0 ℃ or higher, and the aforementioned operational effects of the present invention can be easily obtained.

In the optical adhesive composition according to claim 1, the monomer component constituting the low Tg segment in the (meth) acrylic block copolymer preferably contains at least 1 selected from the group consisting of an alkyl (meth) acrylate having a linear or branched alkyl group having 4 to 18 carbon atoms and a hydroxyl group-containing monomer. This constitution is suitably controlled so that the low Tg segment has a predetermined glass transition temperature and the (meth) acrylic block copolymer has a peak of tan δ in a region lower than 0 ℃, and the aforementioned operational effects of the present invention can be easily obtained.

The optical adhesive composition according to claim 1 of the present invention preferably contains 1% by weight or more of a hydroxyl group-containing monomer based on the total amount (100% by weight) of monomer components constituting the low Tg segment in the (meth) acrylic block copolymer. This configuration is suitable in that the low Tg segment is controlled to a predetermined glass transition temperature, and the aforementioned effects of the present invention can be easily obtained.

In the optical adhesive composition according to claim 1, the weight average molecular weight of the (meth) acrylic block copolymer is preferably 20 ten thousand or more. This configuration is preferable in that the optical adhesive composition of the present invention can easily obtain good hardness and processability at around room temperature.

In the optical adhesive composition according to claim 1, the molecular weight distribution of the (meth) acrylic block copolymer is preferably greater than 1 and 5 or less. This structure is preferable in that the (meth) acrylic block copolymer in the adhesive composition for optical use of the present invention has high uniformity and a highly transparent adhesive can be easily obtained.

In the optical pressure-sensitive adhesive composition according to claim 1, the ratio of the storage modulus at 25 ℃ to the storage modulus at 50 ℃ (storage modulus at 25 ℃/storage modulus at 50 ℃) is preferably 3 or more. This constitution is preferable in that the adhesive composition for optical use of the present invention has a sufficiently large difference between the storage modulus at room temperature (25 ℃) and the storage modulus at heating (50 ℃), has high fluidity at heating and exhibits excellent level difference absorption, and has excellent processability by hardening at room temperature.

In the optical pressure-sensitive adhesive composition according to claim 1 of the present invention, the storage modulus at 25 ℃ is preferably 1MPa or more and the storage modulus at 50 ℃ is preferably 0.5MPa or less. This constitution is preferable in that the adhesive composition for optical use of the present invention has a sufficiently large difference between the storage modulus at room temperature (25 ℃) and the storage modulus at heating (50 ℃), has high fluidity at heating and exhibits excellent level difference absorption, and has excellent processability by hardening at room temperature.

In addition, the 2 nd aspect of the present invention provides an optical adhesive layer formed from the optical adhesive composition of the 1 st aspect of the present invention.

In addition, the 3 rd aspect of the present invention provides an optical adhesive sheet having the optical adhesive layer of the 2 nd aspect of the present invention.

The optical pressure-sensitive adhesive layer and/or the optical pressure-sensitive adhesive sheet described above can be suitably used for producing an optical member laminate described later.

In addition, the 4 th aspect of the present invention provides an optical member laminate comprising: the pressure-sensitive adhesive layer for optical use includes a1 st substrate formed of an optical member, a2 nd substrate formed of an optical member having a level difference on a main surface, and the pressure-sensitive adhesive layer for optical use of the 2 nd aspect of the present invention, wherein the pressure-sensitive adhesive layer for optical use is laminated between any main surface of the 1 st substrate and the main surface of the 2 nd substrate having the level difference.

In the optical member laminate according to claim 4 of the present invention, the 1 st substrate has a level difference on a main surface thereof, and the optical adhesive layer is laminated between the main surface of the 1 st substrate having the level difference and the main surface of the 2 nd substrate having the level difference.

In addition, the height difference of the 2 nd substrate may be a height difference due to a hole provided in a main surface, and in this case, the 2 nd substrate is preferably a polarizing plate.

The height difference of the 1 st substrate is preferably a printing height difference provided on the main surface.

In addition, the height difference of the 2 nd substrate may be a height difference due to the LED chips provided on the main surface, and in this case, the 2 nd substrate is preferably an LED panel.

In addition, the 5 th aspect of the present invention provides an optical product including the optical member laminate.

In the optical member laminate and the optical device having the above-described configurations, the optical pressure-sensitive adhesive layer sufficiently follows the height difference of the 2 nd substrate to be in close contact without a gap, and the optical pressure-sensitive adhesive layer is hardened during storage at room temperature and has excellent workability.

In addition, according to the 6 th aspect of the present invention, there is provided the method for producing an optical member laminate as described above,

the method comprises the following steps: a step of attaching the optical adhesive sheet according to claim 3 of the present invention to the principal surface of the 2 nd substrate having the level difference,

And a step of laminating any main surface of the 1 st substrate on the optical pressure-sensitive adhesive layer of the optical pressure-sensitive adhesive sheet, and heating and pressing the laminate at 50 ℃ or higher.

This method is suitable for manufacturing the aforementioned optical member laminate.

ADVANTAGEOUS EFFECTS OF INVENTION

The optical adhesive composition of the present invention has the above-described structure, and therefore has excellent level difference absorption properties and excellent processability. Therefore, the optical adhesive composition of the present invention is useful as an optical adhesive layer and an optical adhesive sheet used for, in particular, bonding of optical members having a level difference, production of optical products such as image display devices, and the like.

Drawings

Fig. 1 is a schematic view (sectional view) showing one embodiment of an optical member laminate of the present invention.

Fig. 2 is a schematic view (sectional view) showing another embodiment of the optical member laminate of the present invention.

Fig. 3 is a schematic view (sectional view) showing another embodiment of the optical member laminate of the present invention.

Fig. 4 is a schematic view (cross-sectional view) showing another embodiment of the optical member laminate (Micro LED display device) of the present invention.

Fig. 5 is a schematic view (sectional view) showing one embodiment of an optical article (image display device) of the present invention.

Detailed Description

[ adhesive composition for optical use ]

The adhesive composition for optical use of the present invention contains a (meth) acrylic block copolymer. The (meth) acrylic block copolymer further contains: a high Tg segment having a glass transition temperature of 0 ℃ or higher and 100 ℃ or lower and a low Tg segment having a glass transition temperature of-100 ℃ or higher and lower than 0 ℃, and having tan delta peaks in a region of 0 ℃ or higher and a region of lower than 0 ℃.

In the present specification, a "high Tg segment having a glass transition temperature of 0 ℃ or higher and 100 ℃ or lower" is simply referred to as a "high Tg segment", a "low Tg segment having a glass transition temperature of-100 ℃ or higher and lower than 0 ℃ is simply referred to as a" low Tg segment ", a peak of tan δ in a region of 0 ℃ or higher is simply referred to as a" high temperature region tan δ peak ", a peak of tan δ in a region lower than 0 ℃ is simply referred to as a" low temperature region tan δ peak ", a (meth) acrylic block copolymer having the high Tg segment, the low Tg segment, the high temperature region tan δ peak, and the low temperature region tan δ peak is referred to as a" (meth) acrylic block copolymer a ", and an optical adhesive composition containing the (meth) acrylic block copolymer a is referred to as an" optical adhesive composition a ".

The term "(meth) acrylic acid" means "acrylic acid" and/or "methacrylic acid" ("one or both of acrylic acid" and methacrylic acid "), and the same applies to the following. The "(meth) acryloyl group" means an "acryloyl group" and/or a "methacryloyl group" ("acryloyl group" and "methacryloyl group" are one or both), and the same applies to the following.

The "segment" of the high Tg segment and the low Tg segment refers to a partial structure of each block unit constituting the (meth) acrylic block copolymer a.

The structure of the (meth) acrylic block copolymer a of the present invention may be a linear block copolymer, a branched (star-like) block copolymer, or a mixture thereof. The structure of such a block copolymer may be appropriately selected depending on the physical properties of the block copolymer to be required, and a linear block copolymer is preferable from the viewpoint of cost and ease of production. The linear block copolymer may have any structure (arrangement), and is preferably selected from the group consisting of (A-B)_nType, (A-B)_nA block copolymer having at least 1 structure selected from the group consisting of A type (n is an integer of 1 or more, for example, an integer of 1 to 3). In these structures, a and B denote segments composed of different monomer compositions. In the present specification, the segment represented by a constituting the linear block copolymer may be referred to as an "a segment", and the segment represented by B may be referred to as a "B segment".

Among these, from the viewpoints of ease of production, physical properties of the optical adhesive composition a, and the like, an AB type diblock copolymer represented by a-B and an ABA type triblock copolymer represented by a-B-a are preferable, and an ABA type triblock copolymer is more preferable. In the ABA type triblock copolymer, it is considered that the cross-linked structure of the block copolymers is higher due to pseudo cross-linking of the a segments at both ends, the cohesive force of the block copolymer is improved, and higher adhesion (adhesion) can be expressed. In the ABA type triblock copolymer, the 2a segments located at both ends may be the same or different.

When the (meth) acrylic block copolymer a is an ABA type triblock copolymer, at least 1 of the 2a segments and 1B segment (total of 3) may be a high Tg segment and at least 1 of the other may be a low Tg segment. From the viewpoints of ease of production, physical properties of the optical adhesive composition a, and the like, an ABA type triblock copolymer having the high Tg segment as the a segment and the low Tg segment as the B segment is preferable. In this case, an ABA type triblock copolymer in which at least 1 of the 2a segments is a high Tg segment and the B segment is a low Tg segment is preferable, and an ABA type triblock copolymer in which two of the 2a segments are high Tg segments and the B segment is a low Tg segment is more preferable.

The glass transition temperature (Tg) of the high Tg segment constituting the (meth) acrylic block copolymer A is 0 ℃ or more and 100 ℃ or less as described above. When the Tg of the high Tg segment is in this range, the storage modulus at room temperature (25 ℃) of the optical adhesive composition a tends to be easily controlled to be high, the composition is hard and excellent in processability, and the storage modulus significantly decreases in a region exceeding 50 ℃ and the composition tends to be a high-fluidity adhesive composition. From the viewpoint of improving the processability at room temperature (25 ℃) of the optical adhesive composition a, the Tg of the high Tg segment is preferably 4 ℃ or more, more preferably 6 ℃ or more, further preferably 8 ℃ or more, further more preferably 10 ℃ or more, and particularly preferably 12 ℃ or more. On the other hand, from the viewpoint that the storage modulus (G') of the optical pressure-sensitive adhesive composition a is significantly reduced in a region exceeding 50 ℃ and high fluidity is easily obtained, the Tg of the high Tg segment is preferably 90 ℃ or less, more preferably 85 ℃ or less, further preferably 60 ℃ or less, further more preferably 50 ℃ or less, and particularly preferably 35 ℃ or less.

The Tg of the low Tg segment constituting the (meth) acrylic block copolymer A is-100 ℃ or higher and lower than 0 ℃ as described above. When the glass Tg of the low Tg segment is in this range, only the low Tg segment tends to be fluidized at room temperature (25 ℃) to ensure processability, and a suitable adhesive force tends to be imparted to the optical adhesive composition a. From the viewpoint that the storage modulus of the optical adhesive composition A is not easily lowered at room temperature (25 ℃) and the processability can be improved, the Tg of the low Tg segment is preferably not less than-95 ℃, more preferably not less than-90 ℃, and still more preferably not less than-80 ℃. On the other hand, the Tg of the low Tg segment is preferably-5 ℃ or lower, more preferably-10 ℃ or lower, still more preferably-20 ℃ or lower, still more preferably-30 ℃ or lower, and particularly preferably-40 ℃ or lower, from the viewpoint of improving the appropriate adhesive strength and processability of the optical adhesive composition A at room temperature (25 ℃).

The difference between the Tg of the high Tg segment and the Tg of the low Tg segment constituting the (meth) acrylic block copolymer a (Tg of the high Tg segment — Tg of the low Tg segment) is not particularly limited, and from the viewpoint of easily controlling the storage modulus at room temperature (25 ℃) of the optical adhesive composition a to be high, being hard and excellent in processability, and being an adhesive composition having high fluidity with the storage modulus significantly decreasing in a region exceeding 50 ℃, it is preferably 30 ℃ or more, more preferably 35 ℃ or more, more preferably 40 ℃ or more, more preferably 45 ℃ or more, further preferably 50 ℃ or more, particularly preferably 55 ℃ or more, preferably 120 ℃ or less, more preferably 115 ℃ or less, more preferably 110 ℃ or less, more preferably 105 ℃ or less, further preferably 100 ℃ or less, and particularly preferably 95 ℃ or less.

The glass transition temperatures (Tg) of the high Tg segment and the low Tg segment constituting the (meth) acrylic block copolymer a are calculated by the following Fox equation. The calculated glass transition temperature is calculated based on the kind and amount of each monomer component constituting the high Tg segment or the low Tg segment of the (meth) acrylic block copolymer a, and therefore, can be adjusted by selecting the kind and amount of the monomer component of each segment, and the like.

The glass transition temperature (calculated Tg) can be calculated by the following Fox equation [ 1 ].

1/calculation of Tg W1/Tg (1) + W2/Tg (2) +. cndot. + Wn/Tg (n) [ 1]

Here, W1, W2, · · Wn means the weight percentages (% by weight) of the monomer components (1), (2) and (n) to the total monomer components of the copolymer, and Tg (1), (2) and (Tg) · Wn (n) represent the glass transition temperatures (in absolute temperature K) of homopolymers of the monomer components (1), (2) and (n).

The glass transition temperature of the homopolymer is known from various documents, catalogs and the like, and is described, for example, in j.brandup, e.h.immergut, e.a.grucke: Polymer Handbook: JOHNWILEY & SONS, INC. For monomers having no numerical value in various documents, values measured by ordinary thermal analysis, for example, differential thermal analysis, dynamic viscoelasticity measurement method, and the like can be used.

The temperature range in which the high-temperature region tan δ peak of the (meth) acrylic block copolymer a appears is 0 ℃ or higher (for example, 0 ℃ or higher and 100 ℃ or lower) as described above. When the peak tan δ in the high temperature region is in this temperature range, the storage modulus at room temperature (25 ℃) of the optical adhesive composition a tends to be easily controlled to be high, hard and excellent in processability, and the storage modulus tends to be significantly reduced in a region exceeding 50 ℃ to be a high-fluidity adhesive composition. The temperature at which the high-temperature region tan δ peak appears is preferably 3 ℃ or more, more preferably 6 ℃ or more, further preferably 9 ℃ or more, further more preferably 12 ℃ or more, and particularly preferably 15 ℃ or more, from the viewpoint of improving the processability of the optical adhesive composition a at room temperature (25 ℃). On the other hand, from the viewpoint that the storage modulus (G') of the optical pressure-sensitive adhesive composition a is significantly reduced in a region exceeding 50 ℃ and thus high fluidity is easily achieved, the temperature at which the tan δ peak appears in the high-temperature region is preferably 90 ℃ or less, more preferably 80 ℃ or less, further preferably 70 ℃ or less, further preferably 65 ℃ or less, and particularly preferably 60 ℃ or less.

The temperature region in which the low temperature region tan δ peak of the (meth) acrylic block copolymer a appears is lower than 0 ℃ (e.g., -100 ℃ or higher and lower than 0 ℃) as described above. When the peak tan δ in the low temperature region is in this temperature range, only the low Tg segment tends to flow at room temperature (25 ℃), whereby appropriate adhesive force can be imparted to the optical adhesive composition a while ensuring processability. The temperature at which the tan δ peak appears in the low temperature region is preferably-95 ℃ or higher, more preferably-90 ℃ or higher, further preferably-80 ℃ or higher, and further preferably-70 ℃ or higher, from the viewpoint that the storage modulus of the optical adhesive composition a is not easily lowered at room temperature (25 ℃) and the processability can be improved. On the other hand, the temperature at which the tan δ peak appears in the low temperature region is preferably-5 ℃ or less, more preferably-10 ℃ or less, further preferably-20 ℃ or less, further more preferably-30 ℃ or less, and particularly preferably-40 ℃ or less, from the viewpoint of improving the appropriate adhesive strength and processability of the adhesive composition a for optical use at room temperature (25 ℃).

The maximum value of the tan δ peak in the high temperature region is not particularly limited, but is preferably 0.5 to 3.0. When the maximum value of the high-temperature region tan δ peak is in this range, it is preferable in that excellent processability and shape stability of the (meth) acrylic block copolymer can be achieved. The maximum value of the high-temperature region tan δ peak is preferably 0.6 or more, and more preferably 0.7 or more, from the viewpoint of achieving excellent workability. In addition, the maximum value of the tan δ peak in the high temperature region is preferably 2.5 or less, more preferably 2.2 or less, from the viewpoint of less occurrence of scratches.

The maximum value of the tan δ peak in the low temperature region is not particularly limited, but is preferably 0.1 to 2.0. When the maximum value of the low temperature region tan δ peak is within this range, it is preferable in that the excellent processability and shape stability of the (meth) acrylic block copolymer can be achieved. The maximum value of the high-temperature region tan δ peak is preferably 0.2 or more, and more preferably 0.3 or more, from the viewpoint of achieving excellent workability. In addition, the maximum value of the tan δ peak in the low temperature region is preferably 1.5 or less, and more preferably 1 or less, from the viewpoint of preventing scratches from being easily generated.

The high-temperature region tan δ peak and the low-temperature region tan δ peak, and the temperature and maximum value at which these peaks occur, are measured by dynamic viscoelasticity measurement described in examples described later.

The (meth) acrylic block copolymer a is composed of a plurality of segments (including a high Tg segment and a low Tg segment) obtained by polymerizing a monomer component including a monomer (acrylic monomer) having a (meth) acryloyl group in the molecule.

The (meth) acrylic block copolymer a or each segment thereof preferably contains 70% by weight or more, more preferably 80% by weight or more, and particularly preferably 90% by weight or more of an acrylic monomer with respect to the total amount (100% by weight) of the monomer components.

The acrylic monomer constituting the (meth) acrylic block copolymer a or each segment thereof (including the high Tg segment and the low Tg segment) includes, as the most major monomer units in terms of weight ratio, monomer components derived from an alkyl acrylate having a linear or branched alkyl group and/or an alkyl methacrylate having a linear or branched alkyl group.

Examples of the alkyl (meth) acrylate having a linear or branched alkyl group, that is, the alkyl (meth) acrylate having a linear or branched alkyl group contained in the monomer component for forming the segment, which is used for forming the segment of the (meth) acrylic block copolymer a include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, sec-butyl (meth) acrylate, isobutyl (meth) acrylate, tert-butyl (meth) acrylate, pentyl (meth) acrylate, isopentyl (meth) acrylate, hexyl (meth) acrylate, heptyl (meth) acrylate, octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, and the like, Alkyl (meth) acrylates having a linear or branched alkyl group having 1 to 20 carbon atoms, such as nonyl (meth) acrylate, isononyl (meth) acrylate, decyl (meth) acrylate, isodecyl (meth) acrylate, undecyl (meth) acrylate, dodecyl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl (meth) acrylate, heptadecyl (meth) acrylate, octadecyl (meth) acrylate, isostearyl (meth) acrylate, nonadecyl (meth) acrylate, and eicosyl (meth) acrylate. As the alkyl (meth) acrylate for the segment, one kind of alkyl (meth) acrylate may be used, or two or more kinds of alkyl (meth) acrylates may be used. In the present embodiment, as the alkyl (meth) acrylate for the segment, at least one selected from the group consisting of methyl acrylate, n-butyl acrylate, and 2-ethylhexyl acrylate, t-butyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, and isononyl acrylate is preferably used.

The segment of the (meth) acrylic block copolymer a may contain a monomer unit derived from an alicyclic monomer. Examples of the alicyclic monomer used as the monomer unit for forming the segment, that is, the alicyclic monomer contained in the monomer component for forming the segment include cycloalkyl (meth) acrylates having a cycloalkyl group having 4 to 10 carbon atoms, (meth) acrylates having a bicyclic hydrocarbon ring, and (meth) acrylates having a hydrocarbon ring of at least three rings. The cycloalkyl group, bicyclic hydrocarbon ring, or tricyclic or higher hydrocarbon ring may have a substituent. Examples of the substituent include a halogen atom (e.g., a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom), a linear or branched alkyl group having 1 to 6 carbon atoms (e.g., a methyl group, an ethyl group, an n-propyl group, and an isopropyl group), and the like. The number of the substituents is not particularly limited, and may be suitably selected from 1 to 6. When the number of the substituents is 2 or more, 2 or more substituents may be the same or different.

Examples of the cycloalkyl (meth) acrylate include cyclopentyl (meth) acrylate, cyclohexyl (meth) acrylate, 3, 5-trimethylcyclohexyl (meth) acrylate, cycloheptyl (meth) acrylate, and cyclooctyl (meth) acrylate. Examples of the (meth) acrylic acid ester having a bicyclic hydrocarbon ring include bornyl (meth) acrylate and isobornyl (meth) acrylate. Examples of the (meth) acrylic ester having a hydrocarbon ring of at least three rings include dicyclopentyl (meth) acrylate, dicyclopentyloxyethyl (meth) acrylate, tricyclopentyl (meth) acrylate, 1-adamantyl (meth) acrylate, 2-methyl-2-adamantyl (meth) acrylate, and 2-ethyl-2-adamantyl (meth) acrylate. As the alicyclic monomer for the segment, one alicyclic monomer may be used, or two or more alicyclic monomers may be used. In the present embodiment, the alicyclic monomer for segment is preferably a cycloalkyl (meth) acrylate having 4 to 10 carbon atoms and optionally having a substituent (e.g., a linear or branched alkyl group having 1 to 6 carbon atoms), and more preferably at least one selected from the group consisting of cyclohexyl acrylate and 3,3, 5-trimethylcyclohexyl (meth) acrylate.

The segment of the (meth) acrylic block copolymer a may contain a monomer unit derived from a hydroxyl group-containing monomer. The hydroxyl group-containing monomer is a monomer having at least one hydroxyl group in the monomer unit. When the segment in the (meth) acrylic block copolymer a has a hydroxyl group-containing monomer unit, the optical adhesive composition a can easily obtain adhesiveness and appropriate cohesive strength.

Examples of the hydroxyl group-containing monomer used for forming the monomer unit of the segment, that is, the hydroxyl group-containing monomer contained in the monomer component used for forming the segment include hydroxyl group-containing (meth) acrylates, vinyl alcohols, and allyl alcohols. Examples of the hydroxyl group-containing (meth) acrylate include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, hydroxyoctyl (meth) acrylate, hydroxydecyl (meth) acrylate, hydroxylauryl (meth) acrylate, and (4-hydroxymethylcyclohexyl) methyl (meth) acrylate. As the hydroxyl group-containing monomer for the segment, one kind of hydroxyl group-containing monomer may be used, or two or more kinds of hydroxyl group-containing monomers may be used. In the present embodiment, the hydroxyl group-containing monomer for the segment is preferably a hydroxyl group-containing (meth) acrylate, and more preferably at least one selected from the group consisting of 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, and 4-hydroxybutyl methacrylate.

The segment of the (meth) acrylic block copolymer a may contain a monomer unit derived from a nitrogen atom-containing monomer. The nitrogen atom-containing monomer is a monomer having at least one nitrogen atom in the monomer unit. When the segment of the (meth) acrylic block copolymer a has a nitrogen atom-containing monomer unit, the optical adhesive composition a can easily obtain hardness and good adhesion reliability.

Examples of the nitrogen atom-containing monomer for forming the segment, that is, the nitrogen atom-containing monomer contained in the monomer component for forming the segment include N-vinyl cyclic amides and (meth) acrylamides. Examples of the N-vinyl cyclic amide as the nitrogen atom-containing monomer include N-vinyl-2-pyrrolidone, N-vinyl-2-piperidone, N-vinyl-3-morpholinone, N-vinyl-2-caprolactam, N-vinyl-1, 3-oxazin-2-one, and N-vinyl-3, 5-morpholinodione. Examples of the (meth) acrylamide as the nitrogen atom-containing monomer include (meth) acrylamide, N-ethyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N-butyl (meth) acrylamide, N-octyl (meth) acrylamide, N-dimethyl (meth) acrylamide, N-diethyl (meth) acrylamide, N-dipropyl (meth) acrylamide, and N, N-diisopropyl (meth) acrylamide. As the nitrogen atom-containing monomer for the acrylic polymer, one nitrogen atom-containing monomer may be used, or two or more nitrogen atom-containing monomers may be used. In the present embodiment, N-vinyl-2-pyrrolidone is preferably used as the nitrogen atom-containing monomer for the segment.

The segment of the (meth) acrylic block copolymer a may contain a monomer unit derived from a carboxyl group-containing monomer. The carboxyl group-containing monomer is a monomer having at least one carboxyl group in the monomer unit. When the segment of the (meth) acrylic block copolymer a contains a carboxyl group-containing monomer unit, the optical adhesive composition a may have good adhesion reliability.

Examples of the carboxyl group-containing monomer used for forming the monomer unit of the segment, that is, the carboxyl group-containing monomer contained in the monomer component used for forming the segment include (meth) acrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid, and isocrotonic acid. As the carboxyl group-containing monomer for the segment, one kind of carboxyl group-containing monomer may be used, or two or more kinds of carboxyl group-containing monomers may be used. In the present embodiment, acrylic acid is preferably used as the carboxyl group-containing monomer for the segment.

Further, examples of the monomer unit for forming the segment include the above-mentioned alkyl (meth) acrylate, alicyclic monomer, hydroxyl group-containing monomer, nitrogen atom-containing monomer, and monomer other than the carboxyl group-containing monomer (may be referred to as "other monomer"). Examples of the other monomer include alkoxyalkyl (meth) acrylates [ e.g., 2-methoxyethyl (meth) acrylate, 2-ethoxyethyl (meth) acrylate, methoxytriethylene glycol (meth) acrylate, 3-methoxypropyl (meth) acrylate, 3-ethoxypropyl (meth) acrylate, 4-methoxybutyl (meth) acrylate, 4-ethoxybutyl (meth) acrylate, etc. ]; epoxy group-containing monomers [ e.g., glycidyl (meth) acrylate, methylglycidyl (meth) acrylate, etc. ]; sulfonic acid group-containing monomers [ e.g., sodium vinylsulfonate, etc. ]; a phosphoric acid group-containing monomer; aromatic hydrocarbon group-containing (meth) acrylates [ e.g., phenyl (meth) acrylate, phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, etc. ]; vinyl esters [ e.g., vinyl acetate, vinyl propionate, etc. ]; aromatic vinyl compounds [ e.g., styrene, vinyltoluene, etc. ]; olefins or dienes [ e.g., ethylene, propylene, butadiene, isoprene, isobutylene, etc. ]; vinyl ethers [ e.g., vinyl alkyl ethers, etc. ]; vinyl chloride, and the like.

The content of the other monomer in the monomer units constituting the segment of the (meth) acrylic block copolymer a is not particularly limited as long as it is 30% by weight or less with respect to the total amount (100% by weight) of the monomer components, and is appropriately selected within a range not impairing the effects of the present invention.

The monomer component constituting the high Tg segment of the (meth) acrylic block copolymer a is preferably an alkyl (meth) acrylate selected from the group consisting of alkyl (meth) acrylates having a linear alkyl group having 1 to 3 carbon atoms (hereinafter, sometimes referred to as "alkyl (meth) acrylate") from the viewpoint of easily controlling the Tg of the high Tg segment within a predetermined range and of imparting desired physical properties to the (meth) acrylic block copolymer aIs a (meth) acrylic acid C_1-3Linear alkyl ester) ", an alkyl (meth) acrylate having a branched alkyl group having 3 or 4 carbon atoms (hereinafter, may be referred to as" (meth) acrylic acid C_3-4Branched alkyl ester ") and an alicyclic monomer. Since homopolymers of these monomers have a relatively high Tg, it is easy to control the Tg of the high Tg segment to the range defined in the present invention by containing a monomer selected from these monomers as a monomer component constituting the high Tg segment.

The alicyclic monomer is preferably a cycloalkyl (meth) acrylate having 4 to 10 carbon atoms and optionally having a substituent (e.g., a linear or branched alkyl group having 1 to 6 carbon atoms), more preferably a cycloalkyl acrylate having 4 to 10 carbon atoms and optionally having a substituent (e.g., a linear or branched alkyl group having 1 to 6 carbon atoms), and particularly preferably a cyclohexyl acrylate (Tg of homopolymer: 15 ℃) and 3,3, 5-trimethylcyclohexyl (meth) acrylate (Tg of homopolymer: 52 ℃).

When the alicyclic monomer is contained as the monomer component constituting the high Tg segment, the content of the alicyclic monomer relative to the total amount (100 wt%) of the monomer components is preferably 10 wt% or more (for example, 10 to 100 wt%), more preferably 20 wt% or more, more preferably 30 wt% or more, more preferably 40 wt% or more, more preferably 50 wt% or more, more preferably 60 wt% or more, more preferably 70 wt% or more, more preferably 80 wt% or more, further preferably 90 wt% or more, and particularly preferably 95 wt% or more, from the viewpoint of easily controlling the Tg of the high Tg segment to a predetermined range and of imparting desired physical properties to the (meth) acrylic block copolymer a.

As the aforementioned (meth) acrylic acid C_1-3Straight chain alkyl esters, preferably acrylic acid C_1-3The linear alkyl ester, particularly preferably methyl acrylate (Tg of the homopolymer: 8 ℃ C.).

As the aforementioned (meth) acrylic acid C_3-4Branched alkyl esters, preferably C acrylic acid_3-4Branched alkyl esters, particularly preferredTert-butyl acrylate (Tg of homopolymer: 35 ℃ C.).

The high Tg segment contains a (meth) acrylic acid C as a monomer component_1-3Linear alkyl ester and/or (meth) acrylic acid C_3-4In the case of branched alkyl esters, C is the alkyl (meth) acrylate_1-3Linear alkyl ester and/or (meth) acrylic acid C_3-4The content of the branched alkyl ester relative to the total amount (100% by weight) of the monomer components is preferably 10% by weight or more (e.g., 10 to 100% by weight), more preferably 20% by weight or more, more preferably 30% by weight or more, more preferably 40% by weight or more, more preferably 50% by weight or more, more preferably 60% by weight or more, more preferably 70% by weight or more, more preferably 80% by weight or more, further preferably 90% by weight or more, and particularly preferably 95% by weight or more, from the viewpoint of easily controlling the Tg of the high Tg segment to a predetermined range and imparting desired physical properties to the (meth) acrylic block copolymer a.

The monomer component constituting the low Tg segment of the (meth) acrylic block copolymer a is preferably an alkyl (meth) acrylate selected from the group consisting of alkyl (meth) acrylates having a linear or branched alkyl group having 4 to 18 carbon atoms (hereinafter, may be referred to as "C (meth) acrylate"), from the viewpoint of easily controlling the Tg of the low Tg segment in a predetermined range and of imparting desired physical properties to the (meth) acrylic block copolymer a_4-18Alkyl ester ") and hydroxyl group-containing monomers. Namely, (meth) acrylic acid C_4-18Since the homopolymer of the alkyl ester has a relatively low Tg, the Tg of the low Tg segment can be easily controlled to the range specified in the present invention by containing the homopolymer as a monomer component constituting the low Tg segment. On the other hand, the hydroxyl group-containing monomer also has a relatively low Tg, and the (meth) acrylic block copolymer a is easy to obtain adhesiveness and appropriate cohesive force. Therefore, it is more preferable that the monomer component constituting the low Tg segment of the (meth) acrylic block copolymer a further contains (meth) acrylic acid C_4-18Both alkyl esters and hydroxyl-containing monomers.

As the aforementioned (meth) acrylic acidC_4-18Alkyl esters, preferably acrylic acid C_4-18Alkyl esters, particularly preferably butyl acrylate (homopolymer Tg: -55 ℃ C.), 2-ethylhexyl acrylate (homopolymer Tg: -70 ℃ C.), n-hexyl acrylate (homopolymer Tg: -57 ℃ C.), n-octyl acrylate (homopolymer Tg: -65 ℃ C.), isononyl acrylate (homopolymer Tg: -58 ℃ C.).

The low Tg segment contains a (meth) acrylic acid C as a monomer component_4-18In the case of alkyl esters, for (meth) acrylic acid C_4-18The content of the alkyl ester relative to the total amount (100 wt%) of the monomer components is preferably 10 wt% or more (e.g., 10 to 100 wt%), more preferably 20 wt% or more, more preferably 30 wt% or more, more preferably 40 wt% or more, more preferably 50 wt% or more, more preferably 60 wt% or more, more preferably 70 wt% or more, more preferably 80 wt% or more, further preferably 90 wt% or more, and particularly preferably 95 wt% or more, from the viewpoint of easily controlling the Tg of the low Tg segment to a predetermined range and imparting desired physical properties to the (meth) acrylic block copolymer a.

As the hydroxyl group-containing monomer, a hydroxyl group-containing alkyl (meth) acrylate is preferred, and 4-hydroxybutyl acrylate (homopolymer Tg: -65 ℃ C.) and 2-hydroxyethyl acrylate (homopolymer Tg: -15 ℃ C.) are particularly preferred.

When the hydroxyl group-containing monomer is contained as the monomer component constituting the low Tg segment, the content of the hydroxyl group-containing monomer relative to the total amount (100 wt%) of the monomer components is preferably 1 wt% or more, more preferably 1.5 wt% or more, more preferably 2 wt% or more, further preferably 2.5 wt% or more, and particularly preferably 3 wt% or more, from the viewpoint of easily controlling the Tg of the low Tg segment to a predetermined range and providing desired physical properties to the (meth) acrylic block copolymer a. On the other hand, the content of the hydroxyl group-containing monomer with respect to the total amount (100 wt%) of the monomer components is preferably 50 wt% or less, more preferably 40 wt% or less, more preferably 30 wt% or less, more preferably 20 wt% or less, further preferably 10 wt% or less, and particularly preferably 5 wt% or less.

The (meth) acrylic block copolymer A contains a (meth) acrylic acid C as a monomer component constituting the low Tg segment_4-18In the case of both the alkyl ester and the hydroxyl group-containing monomer, the hydroxyl group-containing monomer and (meth) acrylic acid C_4-18Ratio of alkyl esters (hydroxyl group-containing monomer/(meth) acrylic acid C)_4-18Alkyl ester), the lower limit value is preferably 1/99, more preferably 1.5/98.5, more preferably 2/98, further preferably 2.5/97.5, and particularly preferably 3/97, and the upper limit value is 50/50, more preferably 40/60, more preferably 30/70, and further preferably 20/80.

The (meth) acrylic block copolymer a can be produced by the living radical polymerization method of the monomer components described above. The living radical polymerization method is preferable in that the production of a polymer having a uniform composition and a precise control of molecular weight distribution is facilitated because the simplicity and versatility of the conventional radical polymerization method are maintained and the termination reaction and chain transfer are not easily caused, and the growth of the growth terminal is not inactivated.

In the living radical polymerization method, a high Tg segment is prepared first, and then a monomer of a low Tg segment is polymerized with the high Tg segment; it is also possible to first make the low Tg segment and then polymerize the monomers of the high Tg segment with the low Tg segment.

When the (meth) acrylic block copolymer a is an ABA type triblock copolymer, it is preferable to first produce an a segment and then polymerize a monomer of a B segment with the a segment, from the viewpoint of ease of production.

The living radical polymerization method may be any known method without particular limitation, and there are a method using a transition metal catalyst (ATRP method) depending on the method of stabilizing the polymerization growth end; a method (RAFT method) using a sulfur-based reversible addition fragmentation chain transfer agent (RAFT agent); a method using an organotellurium compound (TERP method), and the like. Among these methods, the RAFT method is preferably used from the viewpoints of the diversity of monomers that can be used, the ease of controlling the molecular weight, the absence of metal residues in the optical adhesive composition, and the like.

The RAFT method may be any known method without particular limitation, and includes, for example: step 1 (1 st RAFT polymerization) of polymerizing a monomer component using, for example, a RAFT agent to prepare a1 st segment; and a step 2 (2 nd RAFT polymerization) of adding a monomer component having a different composition from the monomer component in the step 1 to the 1 st segment obtained in the step 1 and polymerizing the mixture to add the 2 nd segment to the 1 st segment. After the 2 nd RAFT polymerization, the 3 rd and 4 th RAFT polymerizations can be carried out in the same manner as the 2 nd RAFT polymerization, and the 3 rd and 4 th segments can be added.

The steps 1 and 2 can be carried out by a known conventional method, and examples thereof include a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, a polymerization method by heat or active energy ray irradiation (a thermal polymerization method, an active energy ray polymerization method), and the like. Among them, the solution polymerization method is preferable in view of transparency, water resistance, cost, and the like. In addition, from the viewpoint of suppressing inhibition of polymerization by oxygen, it is preferable that polymerization be carried out while avoiding contact with oxygen. For example, it is preferable to carry out the polymerization under a nitrogen atmosphere.

When the (meth) acrylic block copolymer a is an ABA type triblock copolymer, it is preferable to prepare an a segment in the step 1 and add a B segment to the obtained a segment in the step 2. In this case, the a segment is preferably a high Tg segment, and the B segment is preferably a low Tg segment.

The RAFT agent may be a known RAFT agent without any particular limitation, and is preferably a compound (trithiocarbonate, dithioester, dithiocarbonate) represented by, for example, the following formula (1), formula (2), or formula (3).

Formula (1), formula (2), or formula (3) [ formulae (1) to (3) ]]In, R^1aAnd R^1bThe same or different, represents a hydrogen atom, a hydrocarbon group, or a cyano group. R^1cRepresents a hydrocarbon group optionally having a cyano group. For as the above R^1a、R^1bAnd R^1cExamples of the hydrocarbon group(s) of (1) to (20) include hydrocarbon groups having 1 to (20) carbon atoms (linear, branched, or cyclic saturated or unsaturated hydrocarbon groups, etc.), and among them, hydrocarbon groups having 1 to (12) carbon atoms are preferable. Specific examples of the hydrocarbon group include linear, branched, or cyclic alkyl groups having 1 to 18 carbon atoms (preferably 1 to 12 carbon atoms) such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a cyclohexyl group, a dodecyl group, and an octadecyl group; aryl groups having 6 to 12 carbon atoms such as phenyl groups; and arylalkyl groups having 7 to 10 total carbon atoms such as benzyl and phenethyl. For as the above R^1cExamples of the hydrocarbon group having a cyano group include groups in which 1 to 3 of hydrogen atoms of the hydrocarbon group are substituted with a cyano group.

In the formulae (1) to (3), R²Represents a hydrocarbon group, or a group in which a part of hydrogen atoms of the hydrocarbon group is substituted with a carboxyl group (for example, carboxyalkyl group). Examples of the hydrocarbon group include hydrocarbon groups having 1 to 20 carbon atoms (linear, branched, or cyclic saturated or unsaturated hydrocarbon groups, etc.), and among them, hydrocarbon groups having 1 to 12 carbon atoms are preferable. Specific examples of the hydrocarbon group include linear, branched, or cyclic alkyl groups having 1 to 18 carbon atoms (preferably 1 to 12 carbon atoms) such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group, a cyclohexyl group, a dodecyl group, and an octadecyl group; and arylalkyl groups having 7 to 10 total carbon atoms such as benzyl and phenethyl.

In the RAFT method, polymerization is carried out by reaction of a raw material monomer so as to be inserted between a sulfur atom in a RAFT agent represented by formulae (1) to (3) and a methylene group adjacent to the sulfur atom.

The aforementioned RAFT agents are most commercially available. Commercially unavailable can be readily synthesized by known or otherwise conventional methods. In the present invention, the RAFT agent may be used alone in 1 kind, or may be used in combination in 2 or more kinds.

Examples of the RAFT agent include trithiocarbonates such as dibenzyltrithiocarbonate and S-cyanomethyl-S-dodecyltrithiocarbonate; dithioesters such as cyanoethyl dithiopropionate, benzyl dithiobenzoate, and ethoxyethyl dithiobenzoate; dithiocarbonates such as O-ethyl-S- (1-phenylethyl) dithiocarbonate, O-ethyl-S- (2-propoxyethyl) dithiocarbonate, and O-ethyl-S- (1-cyano-1-methylethyl) dithiocarbonate are preferable, and trithiocarbonates are more preferable, trithiocarbonates having a structure symmetrical to the left and right in formula (1), and dibenzyl trithiocarbonate and bis {4- [ ethyl- (2-acetoxyethyl) carbamoyl ] benzyl } trithiocarbonate are particularly preferable.

The step 1 may be carried out by polymerizing the monomer component in the presence of a RAFT agent. In step 1, the RAFT agent is used in an amount of usually 0.05 to 20 parts by weight, preferably 0.05 to 10 parts by weight, based on 100 parts by weight of the total amount of the monomer components. In the case of such an amount, the reaction can be easily controlled, and the weight average molecular weight of the obtained segment can be easily controlled.

The step 2 may be performed by adding a monomer component to the polymerization reaction mixture obtained in the step 1 and then polymerizing the mixture.

The RAFT process is preferably carried out in the presence of a polymerisation initiator. As the polymerization initiator, for example, a general organic polymerization initiator can be mentioned, specifically, a peroxide and an azo compound can be mentioned, and among these, an azo compound is preferable. The polymerization initiators may be used in 1 kind alone or in combination of 2 or more kinds.

Examples of the peroxide-based polymerization initiator include benzoyl peroxide and tert-butyl peroxymaleate.

Examples of the azo compound include 2,2 ' -azobisisobutyronitrile, 2 ' -azobis (4-methoxy-2, 4-dimethylvaleronitrile), 2 ' -azobis (2-cyclopropylpropionitrile), 2 ' -azobis (2, 4-dimethylvaleronitrile), 2 ' -azobis (2-methylbutyronitrile), 1 ' -azobis (cyclohexane-1-carbonitrile), 2- (carbamoylazo) isobutyronitrile, 2-phenylazo-4-methoxy-2, 4-dimethylvaleronitrile, 2 ' -azobis (2-amidinopropane) dihydrochloride, 2 ' -azobis (N, N ' -dimethyleneisobutyl) amidine, 2,2 ' -azobis (isobutylamide) dihydrate, 4 ' -azobis (4-cyanovaleric acid), 2 ' -azobis (2-cyanopropanol), dimethyl-2, 2 ' -azobis (2-methylpropionate), 2 ' -azobis [ 2-methyl-N- (2-hydroxyethyl) propionamide ].

The amount of the polymerization initiator used is usually 0.001 to 2 parts by weight, preferably 0.002 to 1 part by weight, based on 100 parts by weight of the total amount of the monomer components. In such an amount, the weight average molecular weight of the resulting segment can be easily controlled.

The RAFT method may be bulk polymerization without using a polymerization solvent, but preferably uses a polymerization solvent. Examples of the polymerization solvent include aromatic hydrocarbons such as benzene, toluene, and xylene; aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, and n-octane; alicyclic hydrocarbons such as cyclopentane, cyclohexane, cycloheptane, and cyclooctane; halogenated hydrocarbons such as chloroform, carbon tetrachloride, 1, 2-dichloroethane, and chlorobenzene; ethers such as diethyl ether, diisopropyl ether, 1, 2-dimethoxyethane, dibutyl ether, tetrahydrofuran, dioxane, anisole, phenylethyl ether, and diphenyl ether; esters such as ethyl acetate, propyl acetate, butyl acetate, and methyl propionate; ketones such as acetone, methyl ethyl ketone, diethyl ketone, methyl isobutyl ketone, and cyclohexanone; amides such as N, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone; nitriles such as acetonitrile and benzonitrile; sulfoxides such as dimethyl sulfoxide and sulfolane. The polymerization solvent may be used alone in 1 kind or in combination of 2 or more kinds.

The amount of the polymerization solvent to be used is not particularly limited, and is, for example, preferably 0.01mL or more, more preferably 0.05mL or more, further preferably 0.1mL or more, preferably 50mL or less, more preferably 10mL or less, further preferably 1mL or less, based on 1g of the monomer component.

The reaction temperature in the RAFT method is usually 60 to 120 ℃, preferably 70 to 110 ℃, and is usually carried out in an inert gas atmosphere such as nitrogen. The reaction can be carried out under any of normal pressure, increased pressure and reduced pressure, and is usually carried out under normal pressure. The reaction time is usually 1 to 20 hours, preferably 2 to 14 hours.

The polymerization conditions of the RAFT method described above can be applied to step 1 and step 2, respectively.

After completion of the polymerization reaction, the target (meth) acrylic block copolymer a can be isolated from the obtained reaction mixture by a common separation and purification means, such as removal of the residual monomer or the like using a solvent.

When the high Tg segment or the low Tg segment of the (meth) acrylic block copolymer a is produced in the step 1, the weight average molecular weight (Mw) of the high Tg segment or the low Tg segment is not particularly limited, but is preferably 10,000 to 1,000,000, more preferably 50,000 to 500,000, and further preferably 100,000 to 300,000. An Mw of the high Tg segment or the low Tg segment within this range is suitable for the above-described effects of the present invention.

The Mw described above is the sum Mw of two or more high Tg segments or low Tg segments in the (meth) acrylic block copolymer a.

The weight average molecular weight (Mw) of the (meth) acrylic block copolymer A is not particularly limited, but is preferably 20 ten thousand (200,000) or more, more preferably 300,000 to 5,000,000, and still more preferably 400,000 to 2,500,000. An Mw of the (meth) acrylic block copolymer a within this range is suitable for the above-described effects of the present invention.

The molecular weight distribution (Mw/Mn) of the (meth) acrylic block copolymer a is not particularly limited, but is preferably greater than 1, more preferably 1.5 or more, further preferably 2 or more, particularly preferably 2.5 or more, preferably 5 or less, more preferably 4.5 or less, further preferably 4 or less, particularly preferably 3.5 or less.

The weight average molecular weight (Mw) and the molecular weight distribution (Mw/Mn) are measured by GPC methods described in examples described later.

The content of the high Tg segment in the (meth) acrylic block copolymer a is preferably 10% by weight or more, more preferably 20% by weight or more, further preferably 25% by weight or more, particularly preferably 30% by weight or more, preferably 95% by weight or less, more preferably 90% by weight or less, further preferably 85% by weight or less, of the total 100% by weight of the (meth) acrylic block copolymer a.

The content of the low Tg segment in the (meth) acrylic block copolymer a is preferably 5% by weight or more, more preferably 10% by weight or more, further preferably 15% by weight or more, preferably 60% by weight or less, more preferably 50% by weight or less, further preferably 40% by weight or less, and particularly preferably 30% by weight or less, of the total 100% by weight of the (meth) acrylic block copolymer a.

The content of the low Tg segment and the low Tg segment or the ratio thereof is preferably within the above range for the above effects of the present invention.

The content of each segment and the ratio thereof can be calculated from the weight average molecular weight (Mw) of each segment obtained in each step of the RAFT method or the (meth) acrylic block copolymer a, and can be controlled by the feed ratio of the monomers at the time of forming each segment, the polymerization ratio of each monomer, and the like.

The content of the (meth) acrylic block copolymer a in the optical adhesive composition a is not particularly limited, and is preferably 50% by weight or more (for example, 50 to 100% by weight), more preferably 60% by weight or more, further preferably 80% by weight or more, and particularly preferably 90% by weight or more, relative to the total amount (total weight, 100% by weight) of the optical adhesive composition a, from the viewpoint of obtaining excellent processability at room temperature (25 ℃) and excellent level difference absorption in a region exceeding 50 ℃.

The optical adhesive composition a may contain additives in addition to the (meth) acrylic block copolymer a within a range not to impair the effects of the present invention. Examples of such additives include a polymerization initiator, a silane coupling agent, a solvent, a crosslinking accelerator, a tackifier resin (a rosin derivative, a polyterpene resin, a petroleum resin, an oil-soluble phenol, and the like), an anti-aging agent, a filler, an ultraviolet absorber, an antioxidant, a chain transfer agent, a plasticizer, a softener, a surfactant, an antistatic agent, and a rust preventive. The additives may be used alone or in combination of 2 or more.

Examples of the polymerization initiator include a photopolymerization initiator (photoinitiator) and a thermal polymerization initiator. The polymerization initiators may be used alone or in combination of 2 or more.

The photopolymerization initiator is not particularly limited, and examples thereof include benzoin ether type photopolymerization initiators, acetophenone type photopolymerization initiators, α -ketol type photopolymerization initiators, aromatic sulfonyl chloride type photopolymerization initiators, photoactive oxime type photopolymerization initiators, benzoin type photopolymerization initiators, benzil type photopolymerization initiators, benzophenone type photopolymerization initiators, ketal type photopolymerization initiators, and thioxanthone type photopolymerization initiators.

Examples of the benzoin ether-based photopolymerization initiator include benzoin methyl ether, benzoin ethyl ether, benzoin propyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2-dimethoxy-1, 2-diphenylethan-1-one, and anisole methyl ether. Examples of the acetophenone photopolymerization initiator include 2, 2-diethoxyacetophenone, 2-dimethoxy-2-phenylacetophenone, 1-hydroxycyclohexylphenyl ketone, 4-phenoxydichloroacetophenone and 4- (tert-butyl) dichloroacetophenone. Examples of the α -ketol photopolymerization initiator include 2-methyl-2-hydroxypropiophenone and 1- [4- (2-hydroxyethyl) phenyl ] -2-methylpropan-1-one. Examples of the aromatic sulfonyl chloride-based photopolymerization initiator include 2-naphthalenesulfonyl chloride. Examples of the optically active oxime-based photopolymerization initiator include 1-phenyl-1, 1-propanedione-2- (o-ethoxycarbonyl) -oxime and the like. Examples of the benzoin-based photopolymerization initiator include benzoin and the like. Examples of the benzil-based photopolymerization initiator include benzil and the like. Examples of the benzophenone-based photopolymerization initiator include benzophenone, benzoylbenzoic acid, 3' -dimethyl-4-methoxybenzophenone, polyvinyl benzophenone, and α -hydroxycyclohexyl phenyl ketone. Examples of the ketal-based photopolymerization initiator include benzildimethylketal. Examples of the thioxanthone-based photopolymerization initiator include thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2, 4-dimethylthioxanthone, isopropylthioxanthone, 2, 4-diisopropylthioxanthone, and dodecylthioxanthone.

The amount of the photopolymerization initiator is not particularly limited, and is preferably 0.01 to 1 part by weight, more preferably 0.05 to 0.5 part by weight, based on 100 parts by weight of the monomer component constituting the (meth) acrylic block copolymer a.

Examples of the thermal polymerization initiator include azo polymerization initiators, peroxide polymerization initiators (e.g., dibenzoyl peroxide, t-butyl peroxymaleate, etc.), redox polymerization initiators, and the like. Among them, azo polymerization initiators are preferred. Examples of the azo polymerization initiator include 2,2 '-azobisisobutyronitrile, 2' -azobis-2-methylbutyronitrile, dimethyl 2,2 '-azobis (2-methylpropionate), and 4, 4' -azobis-4-cyanovaleric acid.

The amount of the azo polymerization initiator is not particularly limited, but is preferably 0.05 to 0.5 parts by weight, more preferably 0.1 to 0.3 parts by weight, based on 100 parts by weight of the monomer components constituting the acrylic polymer a.

The optical adhesive composition a may contain a silane coupling agent within a range not to impair the effects of the present invention. When the silane coupling agent is contained in the optical pressure-sensitive adhesive composition a, the adhesion reliability to glass (especially, the adhesion reliability to glass in a high-temperature and high-humidity environment) is improved, and it is preferable.

The silane coupling agent is not particularly limited, and preferred examples thereof include γ -glycidoxypropyltrimethoxysilane, γ -glycidoxypropyltriethoxysilane, γ -aminopropyltrimethoxysilane and N-phenyl-aminopropyltrimethoxysilane. Among them, gamma-glycidoxypropyltrimethoxysilane is preferable. Further, as a commercially available product, for example, a product name "KBM-403" (manufactured by shin-Etsu chemical Co., Ltd.) can be given. The silane coupling agent may be used alone or in combination of 2 or more.

The content of the silane coupling agent in the optical adhesive composition a is not particularly limited, and is preferably 0.01 to 1 part by weight, more preferably 0.03 to 0.5 part by weight, based on 100 parts by weight of the (meth) acrylic block copolymer a.

The optical adhesive composition a may contain a solvent. The solvent is not particularly limited, and examples thereof include esters such as ethyl acetate and n-butyl acetate; aromatic hydrocarbons such as toluene and benzene; aliphatic hydrocarbons such as n-hexane and n-heptane; alicyclic hydrocarbons such as cyclohexane and methylcyclohexane; and ketones such as methyl ethyl ketone and methyl isobutyl ketone. The solvent may be used alone or in combination of 2 or more.

The optical adhesive composition a may be an adhesive composition having any form, and examples thereof include emulsion type, solvent type (solution type), active energy ray-curable type, and hot-melt type (hot-melt type). Among them, the optical pressure-sensitive adhesive composition a is preferably a solvent-type pressure-sensitive adhesive composition or an active energy ray-curable pressure-sensitive adhesive composition, and more preferably a solvent-type pressure-sensitive adhesive composition.

The method for producing the optical adhesive composition a is not particularly limited, and examples thereof include known methods. For example, the solvent-based optical adhesive composition a is prepared by mixing the (meth) acrylic block copolymer a, a solvent, and components added as necessary (for example, the aforementioned silane coupling agent, crosslinking agent, solvent, additives, and the like). The active energy ray-curable adhesive composition a for optical use is prepared by mixing the (meth) acrylic block copolymer a with components added as needed (for example, the photopolymerization initiator, the silane coupling agent, the crosslinking agent, the solvent, the additives, and the like described above).

The storage modulus at 25 ℃ (G' 25) of the optical adhesive composition a is not particularly limited, but is preferably 1MPa or more, more preferably 1.5MPa or more, more preferably 2MPa or more, more preferably 2.5MPa or more, more preferably 3MPa or more from the viewpoint of improving processability at room temperature, and is preferably 50MPa or less, more preferably 45MPa or less, more preferably 40MPa or less, more preferably 35MPa or less, more preferably 30MPa or less from the viewpoint of improving adhesion reliability at room temperature.

The storage modulus at 50 ℃ (G' 50) of the optical adhesive composition a is not particularly limited, but is preferably 0.5MPa or less, more preferably 0.45MPa or less, more preferably 0.4MPa or less, more preferably 0.35MPa or more, and more preferably 0.3MPa or less from the viewpoint of improving the level difference absorption in the region exceeding 50 ℃, and is preferably 0.0001MPa or more, more preferably 0.0005MPa or more, more preferably 0.001MPa or more, more preferably 0.005MPa or more, and more preferably 0.01MPa or more from the viewpoint of improving the handling property in the region exceeding 50 ℃.

The ratio (G '25/G' 50) of the storage modulus at 25 ℃ to the storage modulus at 50 ℃ of the optical adhesive composition a is not particularly limited, and is preferably 3 or more, more preferably 5 or more, more preferably 10 or more, further preferably 15 or more, and particularly preferably 20 or more from the viewpoint of improving processability at room temperature and improving the level difference absorption in a region exceeding 50 ℃, and is preferably 100 or less, more preferably 95 or less, more preferably 90 or less, further preferably 85 or less, and particularly preferably 80 or less from the viewpoint of adhesion reliability, handling property, and the like.

The storage modulus at 25 ℃ (G '25) and the storage modulus at 50 ℃ (G' 25) and the ratio thereof (G '25/G' 50) are measured by the dynamic viscoelasticity measurement described in the examples described later.

The optical pressure-sensitive adhesive layer of the present invention is formed from an optical pressure-sensitive adhesive composition a. In the present specification, the optical pressure-sensitive adhesive layer formed from the optical pressure-sensitive adhesive composition a is sometimes referred to as an "optical pressure-sensitive adhesive layer a".

The optical pressure-sensitive adhesive layer a is not particularly limited, and is formed by applying (coating) the optical pressure-sensitive adhesive composition a on an appropriate support such as a substrate or a release film, and heating, drying and/or curing as necessary. For example, when the optical adhesive layer a is formed from a solvent-based optical adhesive composition a, the optical adhesive layer a is formed by applying (coating) the optical adhesive composition a on a support and heating and drying the optical adhesive composition a. When the pressure-sensitive adhesive layer a is formed from the active energy ray-curable pressure-sensitive adhesive composition a, the pressure-sensitive adhesive layer a is formed by applying (coating) the pressure-sensitive adhesive composition a on a support and irradiating the support with an active energy ray. If necessary, the heating and drying may be performed after the irradiation with the active energy ray.

In the above-described coating (application), a known coating method can be used. For example, a conventional coater, specifically, a gravure roll coater, a reverse roll coater, a kiss roll coater, a dip roll coater, a bar coater, a knife coater, a spray coater, a comma coater, a direct coater, or the like can be used.

The gel fraction of the optical adhesive layer A is 50 to 90 wt%, preferably 50 to 80 wt%, and more preferably 50 to 70 wt%. When the gel fraction is 90 wt% or less, the cohesive force of the optical pressure-sensitive adhesive layer a is reduced to some extent, and the optical pressure-sensitive adhesive layer a is softened, so that the pressure-sensitive adhesive layer easily follows the level difference portion, and excellent level difference absorption is obtained. On the other hand, by setting the gel fraction to 50 wt% or more, it is possible to suppress the occurrence of a problem that the pressure-sensitive adhesive layer becomes too soft and the workability of the pressure-sensitive adhesive sheet is lowered, and also, it is possible to suppress the occurrence of bubbles and floating under a high-temperature environment or a high-temperature and high-humidity environment and to improve the adhesion reliability. The gel fraction can be controlled by, for example, the kind and content (amount) of the crosslinking agent.

The gel fraction (the ratio of the solvent-insoluble component) can be determined as an ethyl acetate-insoluble component. Specifically, the insoluble content of the pressure-sensitive adhesive layer was determined as a weight fraction (unit: weight%) of the insoluble content in ethyl acetate at room temperature (23 ℃) for 7 days, relative to the sample before immersion. More specifically, the gel fraction is a value calculated by the following "method for measuring gel fraction".

(method of measuring gel fraction)

About 1g of the pressure-sensitive adhesive layer was collected, and the weight thereof was measured and used as "the weight of the pressure-sensitive adhesive layer before impregnation". Next, the collected pressure-sensitive adhesive layer was immersed in 40g of ethyl acetate for 7 days, and then all the components insoluble in ethyl acetate (insoluble portion) were recovered, and the recovered insoluble portion was dried at 130 ℃ for 2 hours to remove ethyl acetate, and then the weight thereof was measured as "dry weight of insoluble portion" (weight of pressure-sensitive adhesive layer after immersion). Then, the obtained value is substituted into the following formula to calculate.

Gel fraction (% by weight) ═ [ (dried weight of insoluble portion)/(weight of adhesive layer before impregnation) ] × 100

The melting point of the optical pressure-sensitive adhesive layer A is not particularly limited, but is preferably-60 to 20 ℃, more preferably-40 to 10 ℃, and still more preferably-30 to 0 ℃. When the melting point is higher than 20 ℃, the adhesive force at room temperature cannot be exhibited.

The melting point is not particularly limited, and for example, the pressure-sensitive adhesive layer can be measured by Differential Scanning Calorimetry (DSC) in accordance with JIS K7121 as a measurement sample. Specifically, the measurement was carried out at-80 ℃ to 80 ℃ under a temperature rise rate of 10 ℃ per minute using a device name "Q-2000" manufactured by TA instruments, for example, as a measurement device.

The thickness of the optical pressure-sensitive adhesive layer A is not particularly limited, but is preferably 10 to 1mm, more preferably 100 to 500 μm, and still more preferably 150 to 350 μm. By setting the thickness to 10 μm or more, the pressure-sensitive adhesive layer can easily follow the level difference portion, and the level difference absorbability can be improved. Further, by setting the thickness to 1mm or less, the adhesive layer is less likely to be deformed, and workability is improved.

The adhesive sheet for optical use of the present invention has at least 1 optical adhesive layer a. In the present specification, an optical pressure-sensitive adhesive sheet having an optical pressure-sensitive adhesive layer a is sometimes referred to as "optical pressure-sensitive adhesive sheet a". The term "adhesive sheet" includes "adhesive tape". That is, the optical adhesive sheet a may be a tape-shaped adhesive tape.

The optical adhesive sheet a may be a single-sided adhesive sheet in which only one side of the sheet is an adhesive layer surface (adhesive surface) (i.e., the optical adhesive layer a surface), or may be a double-sided adhesive sheet in which both sides of the sheet are adhesive layer surfaces. The optical pressure-sensitive adhesive sheet a is not particularly limited, but from the viewpoint of use for bonding adherends to each other, a double-sided pressure-sensitive adhesive sheet is preferable, and a double-sided pressure-sensitive adhesive sheet in which both surfaces of the sheet are the surfaces of the optical pressure-sensitive adhesive layer a is more preferable.

The optical adhesive sheet a may be an adhesive sheet having no substrate (base layer), a so-called "substrate-free type" adhesive sheet (sometimes referred to as "substrate-free adhesive sheet"), or an adhesive sheet having a substrate (sometimes referred to as "substrate-attached adhesive sheet"). Examples of the substrate-less pressure-sensitive adhesive sheet include a double-sided pressure-sensitive adhesive sheet formed only from the optical pressure-sensitive adhesive layer a, a double-sided pressure-sensitive adhesive sheet formed from the optical pressure-sensitive adhesive layer a and a pressure-sensitive adhesive layer other than the optical pressure-sensitive adhesive layer a (which may be referred to as "other pressure-sensitive adhesive layer"), and the like. Examples of the pressure-sensitive adhesive sheet having a substrate include a single-sided pressure-sensitive adhesive sheet having an optical pressure-sensitive adhesive layer a on one side of the substrate, a double-sided pressure-sensitive adhesive sheet having an optical pressure-sensitive adhesive layer a on both sides of the substrate, and a double-sided pressure-sensitive adhesive sheet having an optical pressure-sensitive adhesive layer a on one side of the substrate and another pressure-sensitive adhesive layer on the other side.

Among the above, a substrate-less pressure-sensitive adhesive sheet is preferable, and a substrate-less double-sided pressure-sensitive adhesive sheet (substrate-less double-sided pressure-sensitive adhesive sheet) having no substrate and formed only of the optical pressure-sensitive adhesive layer a is more preferable, from the viewpoint of improvement of optical properties such as transparency. In addition, when the optical adhesive sheet a is an adhesive sheet having a substrate, there is no particular limitation, and from the viewpoint of processability, a double-sided adhesive sheet (substrate-attached double-sided adhesive sheet) having the optical adhesive layer a on both sides of the substrate is preferable.

The "substrate (base material layer)" is a portion to be bonded to an adherend (optical member or the like) together with the pressure-sensitive adhesive layer when the optical pressure-sensitive adhesive sheet a is used (bonded) on the adherend, and does not include a release film (separator) to be released when the pressure-sensitive adhesive sheet is used (bonded).

The optical adhesive sheet a may be a substrate-attached adhesive sheet as described above. Examples of such a substrate include various optical films such as a plastic film, an Antireflection (AR) film, a polarizing plate, and a retardation plate. Examples of the material of the plastic film and the like include plastic materials such as polyester resins such as polyethylene terephthalate (PET), acrylic resins such as polymethyl methacrylate (PMMA), polycarbonate, cellulose Triacetate (TAC), polysulfone, polyarylate, polyimide, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, ethylene-propylene copolymers, cyclic olefin polymers such as "ARTON" (a cyclic olefin polymer, manufactured by JSR Corporation) and "ZEONOR" (a cyclic olefin polymer, manufactured by Zeon Corporation). These plastic materials may be used alone or in combination of 2 or more. The "substrate" is a portion to be attached to an adherend (optical member or the like) together with the pressure-sensitive adhesive layer when the pressure-sensitive adhesive sheet is attached to the adherend. A release film (separator) that is peeled off at the time of use (at the time of attachment) of the adhesive sheet is not included in the "substrate".

The substrate is preferably transparent. The total light transmittance of the substrate in the visible light wavelength region (according to JIS K7361-1) is not particularly limited, and is preferably 85% or more, more preferably 88% or more. The haze of the base material (according to jis k7136) is not particularly limited, but is preferably 1.5% or less, and more preferably 1.0% or less. Examples of such transparent substrates include PET films and non-oriented films such as "ARTON" trade name and "ZEONOR" trade name.

The thickness of the substrate is not particularly limited, but is preferably 12 to 75 μm. The substrate may have any form of a single layer or a plurality of layers. The surface of the substrate may be subjected to a known and conventional surface treatment such as physical treatment such as corona discharge treatment and plasma treatment, and chemical treatment such as undercoating treatment.

The optical adhesive sheet a may have another adhesive layer (an adhesive layer other than the optical adhesive layer a). The other pressure-sensitive adhesive layer is not particularly limited, and examples thereof include pressure-sensitive adhesive layers formed of known or conventional pressure-sensitive adhesives such as urethane-based pressure-sensitive adhesives, acrylic-based pressure-sensitive adhesives, rubber-based pressure-sensitive adhesives, silicone-based pressure-sensitive adhesives, polyester-based pressure-sensitive adhesives, polyamide-based pressure-sensitive adhesives, epoxy-based pressure-sensitive adhesives, vinyl alkyl ether-based pressure-sensitive adhesives, and fluorine-based pressure-sensitive adhesives. The above-mentioned binders may be used singly or in combination of 2 or more.

The optical adhesive sheet a may have other layers (for example, an intermediate layer, a primer layer, and the like) in addition to the optical adhesive layer a, other adhesive layers, and a substrate within a range in which the effects of the present invention are not impaired.

The optical adhesive sheet a may be provided with a release film (separator) on the adhesive surface until the time of use. The mode of protecting the pressure-sensitive adhesive surface of the optical pressure-sensitive adhesive sheet a with the release film is not particularly limited, and each pressure-sensitive adhesive surface may be protected with 2 sheets of release film, or may be protected with 1 sheet of release film having both surfaces as release surfaces by winding the sheet into a roll. The release film is used as a protective material for the pressure-sensitive adhesive layer and is released when attached to an adherend. In the optical psa sheet a, the release film also functions as a support for the psa layer. The release film need not be provided.

The release film is not particularly limited, and examples thereof include a substrate having a release-treated layer, a low-adhesion substrate made of a fluoropolymer, and a low-adhesion substrate made of a nonpolar polymer. Examples of the substrate having a release-treated layer include plastic films and papers which are surface-treated with a release-treating agent such as silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide. Examples of the fluorine-based polymer in the low adhesion base material composed of the above-mentioned fluorine-based polymer include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, chlorofluoroethylene-vinylidene fluoride copolymer, and the like. Examples of the nonpolar polymer include olefin resins (e.g., polyethylene, polypropylene, and the like). The separator is formed by a known or conventional method. The thickness of the separator is not particularly limited.

Examples of the method for producing the optical adhesive sheet a include known and conventional methods. The method for producing the optical adhesive sheet a is not particularly limited, and varies depending on the composition of the optical adhesive layer a, and examples thereof include the following methods (1) to (3).

(1) An optical adhesive composition a containing a (meth) acrylic block copolymer a, if necessary, a polymerization initiator, a silane coupling agent, other additives, and the like is applied (coated) on a substrate or a separator, and cured (for example, heat curing, curing by irradiation with active energy rays such as ultraviolet rays, and the like) to produce an optical adhesive sheet a.

(2) An optical pressure-sensitive adhesive composition a (solution) obtained by dissolving a (meth) acrylic block copolymer a and, if necessary, additives and the like in a solvent is applied (coated) onto a substrate or a separator, and dried and/or cured to produce a pressure-sensitive adhesive sheet.

(3) The optical adhesive sheet a produced in (1) above was further dried.

In the case of curing by active energy rays (photocuring), since photopolymerization reaction is inhibited by oxygen in the air, it is preferable to block oxygen by, for example, bonding a separator or performing photocuring in a nitrogen atmosphere.

The optical adhesive sheet a is not particularly limited, but from the viewpoint of productivity, an optical adhesive composition a (solution) containing a (meth) acrylic block copolymer a and a solvent is preferably applied (coated) onto a substrate or a separator and dried and/or cured to produce an adhesive sheet.

The optical adhesive sheet a is not particularly limited, but from the viewpoint of productivity, an optical adhesive sheet produced from an optical adhesive composition a containing a (meth) acrylic block copolymer a and a polymerization initiator (a polymerization initiator such as a photopolymerization initiator or a thermal polymerization initiator) by a curing reaction with heat or active energy rays is also preferable. In addition, from the viewpoint of obtaining a thick pressure-sensitive adhesive layer, it is preferable to produce the pressure-sensitive adhesive layer from a pressure-sensitive adhesive composition containing a photopolymerization initiator by a curing reaction with active energy rays.

The thickness (total thickness) of the optical adhesive sheet A is not particularly limited, but is preferably 10 μm to 1mm, more preferably 100 to 500 μm, and still more preferably 150 to 350 μm. By setting the thickness to 10 μm or more, the pressure-sensitive adhesive layer can easily follow the level difference portion, and the level difference absorbability can be improved. The thickness of the optical adhesive sheet a does not include the thickness of the release film.

The optical adhesive sheet a preferably has high transparency. The haze (according to JIS K7136) of the optical adhesive sheet a is, for example, preferably 1.0% or less, and more preferably 0.7% or less. When the haze is 1.0% or less, the optical product or optical member to which the optical adhesive sheet a is attached has good transparency and appearance.

The total light transmittance (total light transmittance in the visible light wavelength region) (according to JIS K7361-1) of the optical adhesive sheet a is not particularly limited, but is preferably 90% or more, and more preferably 91% or more. By setting the total light transmittance to 90% or more, the optical product and the optical member to which the optical adhesive sheet a is attached have good transparency and appearance.

The haze and the total light transmittance can be measured, for example, by attaching a glass plate or the like to the pressure-sensitive adhesive sheet and using a haze meter.

Therefore, from the viewpoint of improving optical properties such as transparency, the optical adhesive sheet a is preferably an adhesive sheet having a haze of 1.0% or less and a total light transmittance of 90% or more. From the viewpoint of improving optical properties such as transparency and the like and from the viewpoint of use for bonding adherends to each other, the optical pressure-sensitive adhesive sheet a is preferably a double-sided pressure-sensitive adhesive sheet having a haze of 1.0% or less and a total light transmittance of 90% or more, and particularly preferably a substrate-less double-sided pressure-sensitive adhesive sheet having only the optical pressure-sensitive adhesive layer a, a haze of 1.0% or less and a total light transmittance of 90% or more.

The optical adhesive sheet a has excellent processability at room temperature because it has the optical adhesive layer a.

Further, since the optical adhesive sheet a has the optical adhesive layer a, the level difference absorption property is excellent in a region exceeding 50 ℃. For example, the level difference absorbability is excellent not only for a level difference of 5 to 10 μm but also for a level difference exceeding 40 μm. Further, the film has a level difference absorbability even for a level difference exceeding 80 μm.

Further, the optical adhesive sheet a has excellent adhesion reliability because it has the optical adhesive layer a.

The term "optical use" in the optical adhesive composition a, the optical adhesive layer a, and the optical adhesive sheet a means an optical adhesive composition, an optical adhesive layer, and an optical adhesive sheet used for optical applications, more specifically, applications for bonding optical members (applications for bonding optical members), applications for producing products using optical members (optical products), and the like.

The optical member is not particularly limited as long as it has optical characteristics (e.g., polarization, light refraction, light scattering, light reflection, light transmittance, light absorption, light diffraction, optical rotation, visibility, etc.), and examples thereof include members constituting optical products such as a display device (image display device) and an input device, members used in these devices (optical products), and examples thereof include a polarizing plate, a wavelength plate, a retardation plate, an optical compensation film, a brightness enhancement film, a light guide plate, a reflection film, an antireflection film, a transparent conductive film (ITO film, etc.), an appearance film, a decorative film, a surface protection plate, a prism, a lens, a color filter, a transparent substrate (front surface transparent member, etc.), and members obtained by folding these members.

Examples of the display device (image display device) include a liquid crystal display device, an organic EL (electroluminescence) display device, a PDP (plasma display panel), electronic paper, and a Micro LED display device. The input device may be a touch panel.

The optical member is not particularly limited, and examples thereof include members formed of glass, acrylic resin, polycarbonate, polyethylene terephthalate, a metal film, and the like (for example, sheet-shaped, film-shaped, plate-shaped members, and the like). As described above, the "optical member" also includes members (such as an appearance film, a decorative film, and a surface protection plate) that ensure visibility of a display device and an input device as an adherend and perform decoration and protection.

The optical adhesive sheet a is particularly preferably used for bonding a highly rigid optical member, and particularly preferably used for bonding an optical member made of glass. That is, the optical adhesive sheet a is preferably an optical adhesive sheet used for bonding an optical member made of glass, such as a glass sensor, a glass display panel (LCD, etc.), or a glass plate with a transparent electrode of a touch panel, and more preferably an optical adhesive sheet used for bonding a glass sensor and a glass display panel.

The method of bonding an optical member with the optical adhesive sheet a is not particularly limited, and examples thereof include the following.

(1) Method for attaching optical members to each other via optical adhesive sheet A

(2) Method for bonding optical member to member other than optical member via optical adhesive sheet A

(3) Method for bonding optical adhesive sheet A including optical member to optical member or member other than optical member

The optical adhesive sheet a including an optical member in the above-described embodiment (3) is preferably a substrate-attached adhesive sheet having an optical member as a substrate, that is, an optical member-attached adhesive sheet.

The optical member-attached pressure-sensitive adhesive sheet is also a pressure-sensitive adhesive type optical member having an optical pressure-sensitive adhesive layer a on an optical member.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the embodiments.

In fig. 1, an optical member laminate 10 according to one embodiment of the present invention is an optical member laminate including a1 st substrate 11 formed of an optical member, a2 nd substrate 12 formed of an optical member and having a height difference D on a main surface thereof, and an optical adhesive layer a laminated between any main surface of the 1 st substrate 11 and the main surface of the 2 nd substrate 12 having the height difference D.

In fig. 2, in the optical member laminate 20 according to another embodiment of the present invention, the 1 st substrate 21 has a height difference D 'on the main surface, and the optical adhesive layer a is laminated between the main surface of the 1 st substrate 21 having the height difference D' and the main surface of the 2 nd substrate 22 having the height difference D.

The optical member constituting the 1 st substrate and the 2 nd substrate includes the optical member. The height difference between the 1 st substrate and the 2 nd substrate on the main surface is not particularly limited, and includes, for example: a printing height difference of a transparent and conductive printing layer such as an ITO (indium tin oxide) layer, a printing layer provided for appearance, decoration, or the like, provided on a main surface of the substrate; a height difference due to hole processing at one or more locations on a main surface of a substrate (for example, a polarizing plate); a height difference due to light emitting elements (for example, LED elements) arranged on the main surface of the substrate. In the optical member laminate of the present invention, the optical pressure-sensitive adhesive layer a sufficiently follows the height difference, and is closely adhered without a gap such as a bubble.

Preferred embodiments of the optical member laminate of the present invention include the following optical member laminate 30: in fig. 3, the 2 nd substrate 32 is a polarizing plate having a height difference due to a hole H provided on a main surface, the 1 st substrate 31 is an optical member (for example, a transparent cover member) having a printed height difference D 'on a main surface, and an optical adhesive layer a is laminated between the main surface having the height difference D' of the 1 st substrate 31 and the main surface having the hole H of the 2 nd substrate 32.

In addition, another preferred embodiment of the optical member laminate of the present invention includes the following optical member laminate 40(Micro LED display device): in fig. 4, the 2 nd substrate 42 is an LED panel having a level difference due to the LED chip L provided on the main surface, and the optical adhesive layer a is laminated between the main surface of the 1 st substrate 41 and the main surface of the 2 nd substrate 42 having the LED chip L.

The optical product of the present invention is characterized by comprising the optical member laminate. Examples of the optical product include an image display device such as a liquid crystal display device, an organic EL (electroluminescence) display device, a PDP (plasma display panel), electronic paper, a Micro LED display device, and an input device such as a touch panel.

Preferred embodiments of the optical product of the present invention include the following image display device 50: in fig. 5, an image display device is formed by laminating an image display panel having a polarizing plate 52 perforated on the surface of an image display unit 53 and a front surface transparent member 51, and the front surface transparent member 51 is bonded to the perforated polarizing plate 52 of the image display panel via an optical adhesive layer a.

In the image display device having the above configuration, the optical pressure-sensitive adhesive layer sufficiently follows a height difference generated at a boundary of the hole provided in the polarizing plate to be closely attached without a gap, and the optical pressure-sensitive adhesive layer is hardened during storage at room temperature and has excellent workability.

The optical member laminate of the present invention can be preferably produced by a method including the following steps.

(1) A step of attaching an optical adhesive sheet A to the principal surface of the 2 nd substrate having the level difference (step 1)

(2) A step of laminating any of the main surfaces of the first substrate 1 on the optical pressure-sensitive adhesive layer A of the optical pressure-sensitive adhesive sheet A, and heating and pressing the laminate at 50 ℃ or higher (step 2)

The optical adhesive sheet a can be applied to the principal surface of the 2 nd substrate having the level difference in the 1 st step by a known method. When the optical adhesive sheet a has a release film, it is peeled after the 1 st step.

The lamination of the 1 st substrate to the optical pressure-sensitive adhesive layer a in the 2 nd step may be performed by a known method.

In the step 2, the optical pressure-sensitive adhesive layer a becomes highly fluid by heating and pressing at 50 ℃ or higher, and can sufficiently follow the height difference of the substrate to be in close contact without a gap. The heating is carried out at 50 ℃ or higher, preferably 60 ℃ or higher, more preferably 70 ℃ or higher. The pressurization is not particularly limited, and is carried out, for example, at 1.5atm or more, preferably at 2atm or more, and more preferably at 3atm or more. The heating and pressurizing can be performed using, for example, an autoclave.

When the optical member laminate of the present invention produced in the aforementioned step 2 is returned to room temperature (25 ℃), the optical pressure-sensitive adhesive layer a has a high storage modulus, a stable shape, and improved processability such as handleability.

Examples

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

The following measurement of the weight average molecular weight (Mw) and the molecular weight distribution (Mw/Mn) of the product was performed in terms of standard polystyrene by gel permeation chromatography (GCP method) under the following measurement conditions.

The measurement device: HLC-8320GPC (manufactured by Tosoh corporation)

Column: TS Kgel GMH-H (S), (Tosoh corporation)

Mobile phase solvent: tetrahydrofuran (THF)

Flow rate: 1.0cm³/min

Column temperature: 40 deg.C

Example 1

(preparation of Polymer RAFT solution A1)

In a reaction vessel equipped with a condenser tube, a nitrogen inlet tube, a thermometer, and a stirrer, 100 parts by weight of cyclohexyl acrylate (CHA) as a monomer component, 0.5 parts by weight of dibenzyl trithiocarbonate (DBTC) as a RAFT agent, and 100 parts by weight of ethyl acetate as a polymerization solvent were charged, and 0.2 parts by weight of 2, 2' -Azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was charged to perform solution polymerization in a nitrogen atmosphere, thereby obtaining a polymeric RAFT solution a1 having an Mw of 20 ten thousand.

(preparation of acrylic triblock copolymer-containing adhesive solution B1)

In a reaction vessel equipped with a condenser, a nitrogen inlet tube, a thermometer, and a stirrer, 97 parts by weight of n-Butyl Acrylate (BA), 3 parts by weight of 4-hydroxybutyl acrylate (4HBA), 100 parts by weight of the polymer RAFT solution a1 obtained above, and 100 parts by weight of ethyl acetate as a polymerization solvent were charged as monomer components, and 0.2 part by weight of 2, 2' -Azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was charged, and solution polymerization was performed in a nitrogen atmosphere, thereby obtaining a binder solution B1 containing an ABA-type acrylic triblock copolymer having an Mw of 51 ten thousand and an Mw/Mn of 2.06.

With respect to the calculated glass transition temperature (Tg) based on the FOX formula, the Tg of segment A of the ABA type acrylic triblock copolymer was 15 ℃ and the Tg of segment B was-55 ℃.

(preparation of adhesive sheet)

A75 μm thick polyethylene terephthalate (PET) film (Diafil MRF75, manufactured by Mitsubishi chemical corporation) having a silicone-based release layer provided on the surface thereof was used as a substrate, and an adhesive solution B1 containing an acrylic triblock copolymer was applied to the substrate and dried at 130 ℃ for 3 minutes to form an adhesive layer having a thickness of 150 μm. A PET film (diafil MRE75, manufactured by mitsubishi chemical) having a thickness of 75 μm and having one surface subjected to a silicone release treatment was bonded to the pressure-sensitive adhesive layer to obtain a pressure-sensitive adhesive sheet having release films attached to both surfaces thereof.

Example 2

(preparation of Polymer RAFT solution A2 and adhesive sheet)

A polymer RAFT solution a2 having an Mw of 14 ten thousand was obtained in the same manner as in example 1, except that Methyl Acrylate (MA) was used instead of cyclohexyl acrylate (CHA).

(preparation of acrylic triblock copolymer-containing adhesive solution B2)

A pressure-sensitive adhesive solution B2 containing an acrylic triblock copolymer having Mw of 29 ten thousand and Mw/Mn of 2.9 was obtained in the same manner as in example 1, except that a polymer RAFT solution a2 was used instead of the polymer RAFT solution a1, and a pressure-sensitive adhesive sheet was produced in the same manner as in example 1.

With respect to the calculated glass transition temperature (Tg) based on the FOX formula, the Tg of segment A of the ABA type acrylic triblock copolymer was 8 ℃ and the Tg of segment B was-55 ℃.

Example 3

(preparation of adhesive sheet and adhesive solution B3 containing acrylic triblock copolymer)

In a reaction vessel equipped with a condenser, a nitrogen inlet tube, a thermometer, and a stirrer, 97 parts by weight of 2-ethylhexyl acrylate (2EHA), 3 parts by weight of 4-hydroxybutyl acrylate (4HBA), 100 parts by weight of the polymer RAFT solution a1 obtained in example 1, and 100 parts by weight of ethyl acetate as a polymerization solvent were charged, 0.2 parts by weight of 2, 2' -Azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was charged, and solution polymerization was performed in a nitrogen atmosphere to obtain an adhesive solution 3 containing an ABA-type acrylic triblock copolymer having an Mw of 35 ten thousand and an Mw/Mn of 2.5, and an adhesive sheet was prepared in the same manner as in example 1.

For the calculated glass transition temperature (Tg) based on the FOX formula, the Tg of segment A of the ABA type acrylic triblock copolymer was 15 ℃ and the Tg of segment B was-70 ℃.

Example 4

(preparation of Polymer RAFT solution A3)

A polymer RAFT solution a3 having an Mw of 18 ten thousand was obtained in the same manner as in example 1, except that 50 parts by mass of cyclohexyl acrylate (CHA) and 50 parts by mass of 3,3, 5-trimethylcyclohexyl acrylate (TMCHA) were used as monomers.

(preparation of adhesive sheet and adhesive solution B4 containing acrylic triblock copolymer)

A pressure-sensitive adhesive solution B4 containing an ABA type acrylic triblock copolymer having Mw of 40 ten thousand and Mw/Mn of 4.3 was obtained in the same manner as in example 3, except that a polymer RAFT solution A3 was used instead of the polymer RAFT solution a1, and a pressure-sensitive adhesive sheet was produced in the same manner as in example 1.

With respect to the calculated glass transition temperature (Tg) based on the FOX formula, the Tg of segment A of the ABA type acrylic triblock copolymer was 32 ℃ and the Tg of segment B was-70 ℃.

Example 5

(preparation of Polymer RAFT solution A4)

A polymer RAFT solution a4 having an Mw of 16 ten thousand was obtained in the same manner as in example 1, except that 60 parts by mass of Methyl Acrylate (MA) and 40 parts by mass of tert-butyl acrylate (t-BA) were used.

(preparation of adhesive sheet and adhesive solution B5 containing acrylic triblock copolymer)

A pressure-sensitive adhesive solution B5 containing an ABA type acrylic triblock copolymer having Mw of 37 ten thousand and Mw/Mn of 3.9 was obtained in the same manner as in example 3, except that a polymer RAFT solution a4 was used instead of the polymer RAFT solution a1, and a pressure-sensitive adhesive sheet was produced in the same manner as in example 1.

For the calculated glass transition temperature (Tg) based on the FOX formula, the Tg of segment A of the ABA type acrylic triblock copolymer was 18 ℃ and the Tg of segment B was-70 ℃.

Comparative example 1

(preparation of adhesive sheet and adhesive solution C1 containing acrylic random copolymer)

In a reaction vessel equipped with a condenser tube, a nitrogen gas inlet tube, a thermometer, and a stirrer, 97 parts by weight of n-Butyl Acrylate (BA), 3 parts by weight of 4-hydroxybutyl acrylate (4HBA), and 122 parts by weight of ethyl acetate as a polymerization solvent as monomer components were charged, 0.2 parts by weight of 2, 2' -Azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was charged, and solution polymerization was performed in a nitrogen atmosphere to obtain a pressure-sensitive adhesive solution C1 containing an acrylic random copolymer having an Mw of 60 ten thousand, and a pressure-sensitive adhesive sheet was prepared in the same manner as in example 1.

The calculated glass transition temperature (Tg) of the acrylic random copolymer obtained on the basis of the FOX formula was-55 ℃.

Comparative example 2

(preparation of tackifying resin solution D1)

In a reaction vessel equipped with a condenser tube, a nitrogen inlet tube, a thermometer, and a stirrer, 100 parts by weight of cyclohexyl acrylate (CHA) as a monomer component, 1 part by weight of n-dodecylmercaptan (NDM) as a chain transfer agent, and 122 parts by weight of ethyl acetate as a polymerization solvent were charged, and 0.2 part by weight of 2, 2' -Azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was charged, and solution polymerization was performed in a nitrogen atmosphere, thereby obtaining a tackifier resin solution D1 containing an acrylic polymer having Mw of 2 ten thousand. The calculated glass transition temperature (Tg) based on the FOX formula was 15 ℃.

(preparation of adhesive sheet and adhesive solution containing tackifier resin)

An adhesive sheet was produced in the same manner as in example 1 except that 5 parts by weight of the tackifier resin solution D1 obtained above was mixed with 100 parts by weight of the adhesive solution C1 obtained in comparative example 1 and stirred to obtain an adhesive solution containing a tackifier resin.

Comparative example 3

(preparation of adhesive sheet and adhesive solution C2 containing acrylic random copolymer)

In a reaction vessel equipped with a condenser tube, a nitrogen introduction tube, a thermometer, and a stirrer, 50 parts by weight of 2-ethylhexyl acrylate (2EHA), 47 parts by weight of cyclohexyl acrylate (CHA), 3 parts by weight of 4-hydroxybutyl acrylate (4HBA), and 122 parts by weight of ethyl acetate as a polymerization solvent were charged as monomer components, 0.2 parts by weight of 2, 2' -Azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was charged, and solution polymerization was performed in a nitrogen atmosphere to obtain a pressure-sensitive adhesive solution C2 containing an acrylic random copolymer having an Mw of 80 ten thousand, and a pressure-sensitive adhesive sheet was prepared in the same manner as in example 1. The calculated glass transition temperature (Tg) based on the FOX equation was-36 ℃.

Comparative example 4

(preparation of adhesive sheet and adhesive solution C3 containing acrylic random copolymer)

In a reaction vessel equipped with a condenser tube, a nitrogen gas inlet tube, a thermometer, and a stirrer, 60 parts by weight of Butyl Acrylate (BA), 35 parts by weight of isobornyl methacrylate (IBXMA), 5 parts by weight of 4-hydroxybutyl acrylate (4HBA), and 122 parts by weight of ethyl acetate as a polymerization solvent were charged as monomer components, 0.2 parts by weight of 2, 2' -Azobisisobutyronitrile (AIBN) as a thermal polymerization initiator was charged, and solution polymerization was performed in a nitrogen atmosphere to obtain a pressure-sensitive adhesive solution C3 containing an acrylic random copolymer having an Mw of 90 ten thousand, and a pressure-sensitive adhesive sheet was prepared in the same manner as in example 1. The calculated glass transition temperature (Tg) based on the FOX formula was-11 ℃.

(evaluation)

For the pressure-sensitive adhesive sheets using the pressure-sensitive adhesive solutions obtained in the above examples and comparative examples, the storage modulus at 25 ℃ (G '25), the storage modulus at 50 ℃ (G' 50) and their ratio (G '25/G' 50), the peak temperature and maximum value of tan δ, the processability, and the level difference absorbency were measured or evaluated. The measurement or evaluation methods are shown below. The results of the measurement or evaluation are shown in table 1.

(1) Storage modulus [ G '25, G' 50, G '25/G' 50] and peak temperature and maximum value of tan delta

The storage modulus at 25 ℃ and 50 ℃ and the peak temperature and the maximum value of tan. delta. were determined by dynamic viscoelasticity measurement.

A plurality of adhesive sheets were laminated to a thickness of about 1.5mm to obtain a sample for measurement. In the measurement of the storage modulus of the laminated psa sheet, a sample having a thickness of about 1.5mm, which is obtained by alternately laminating a first psa layer and a second psa layer, was used as a measurement sample. Dynamic viscoelasticity was measured under the following conditions using an Advanced Rheological Expansion System (ARES) manufactured by Rheometric Scientific, and the storage modulus (G 'at 25 ℃ and 50 ℃ C.) was read from the measurement results'₂₅，G’₅₀) And the peak temperature and maximum value of tan δ.

(measurement conditions)

Deformation mode: torsion

Measuring frequency: 1Hz

Temperature rise rate: 5 ℃ per minute

Measuring temperature: a temperature ranging from-50 to 150 DEG C

Shape: parallel plates

(2) Workability

One release film was peeled from the pressure-sensitive adhesive sheet to expose one pressure-sensitive adhesive surface, and the pressure-sensitive adhesive surface was attached to a PET film (trade name "A4100" manufactured by Toyo Boseki Co., Ltd., thickness: 100 μm). Next, a sample for workability evaluation (having a structure of "PET film/pressure-sensitive adhesive layer/release film") was punched out from the PET film side using a press machine. The sample for evaluation of processability was measured at a temperature: after being left at 23 ℃ under an atmosphere of relative humidity 50% RH for 1 week, the release film on the opposite side of the PET film was observed for the presence of a shortage of the adhesive, and the processability (processability) was evaluated according to the following evaluation criteria.

Evaluation criteria for processability

O (good processability): no gel loss was observed.

X (poor processability): gel loss was observed.

(3) Height difference absorbency

The adhesive sheet was cut into a size of 40mm × 40mm, a release film having a thickness of 50 μm was peeled from one surface of the adhesive sheet, and the sheet was bonded to a glass plate having a thickness of 50mm × 50mm using a roll laminator (roll pressure: 0.2MPa, moving speed: 100 mm/min). In the same manner, the polarizing plate with the pressure-sensitive adhesive layer subjected to the punching process was cut out to a size of 30 × 30mm, and a release film of 50 μm provided on the pressure-sensitive adhesive layer was peeled off and bonded to a glass plate of 50mm × 50 mm.

A release film having a thickness of 38 μm was peeled from the other surface of the pressure-sensitive adhesive sheet, and the pressure-sensitive adhesive sheet was bonded to the polarizing plate by means of a vacuum laminator (0.1kPa, 60 ℃ C., 30 seconds). The sample was treated in an autoclave (50 ℃, 0.5MPa, 15 minutes), and then observed with a digital microscope having a magnification of 20 times, to confirm the presence or absence of air bubbles in the holes of the polarizing plate.

Evaluation criteria for level difference absorbency

Very good (excellent differential height absorption): no bubble was confirmed.

O (good level difference absorbency): it was confirmed that the number of bubbles having a diameter of several tens μm was less than 5.

X (poor height absorption): bubbles were confirmed.

[ Table 1]

(Table 1)

The following describes modifications of the present invention described above.

[ note 1] an optical adhesive composition characterized by containing a (meth) acrylic block copolymer,

the (meth) acrylic block copolymer contains: a high Tg segment having a glass transition temperature of 0 ℃ or higher and 100 ℃ or lower, and a low Tg segment having a glass transition temperature of-100 ℃ or higher and lower than 0 ℃,

the (meth) acrylic block copolymer has a peak of tan δ in a region of 0 ℃ or higher and a peak of tan δ in a region of less than 0 ℃.

Here, the glass transition temperature is calculated from the monomer component composition constituting each segment by the FOX equation.

[ appendix 2] the adhesive composition for optical use according to appendix 1, wherein the maximum value of tan δ in the region at 0 ℃ or higher is 0.5 to 3.0.

[ appendix 3] the optical adhesive composition according to appendix 1 or 2, wherein the (meth) acrylic block copolymer is an ABA triblock copolymer.

[ appendix 4] the adhesive composition for optical use according to appendix 3, wherein in the ABA type triblock copolymer, the A segment is the high Tg segment and the B segment is the low Tg segment.

[ appendix 5] the optical adhesive composition according to any one of appendix 1 to 4, wherein the monomer component constituting the high Tg segment in the (meth) acrylic block copolymer contains at least 1 selected from the group consisting of an alkyl (meth) acrylate having a linear alkyl group with 1 to 3 carbon atoms, an alkyl (meth) acrylate having a branched alkyl group with 3 or 4 carbon atoms, and an alicyclic monomer.

[ appendix 6] the adhesive composition for optical use according to appendix 5, wherein the (meth) acrylic block copolymer contains an alkyl (meth) acrylate having a branched alkyl group having 3 or 4 carbon atoms as a monomer component constituting the high Tg segment.

[ appendix 7] the adhesive composition for optical use according to appendix 5, wherein the alicyclic monomer contains: a cycloalkyl (meth) acrylate having a cycloalkyl group having 4 to 10 carbon atoms and optionally having a substituent.

[ appendix 8] the adhesive composition for optical use according to any one of appendix 1 to 7, wherein the (meth) acrylic block copolymer contains at least 1 selected from the group consisting of an alkyl (meth) acrylate having a linear or branched alkyl group having 4 to 18 carbon atoms and a hydroxyl group-containing monomer as a monomer component constituting the low Tg segment.

[ appendix 9] the adhesive composition for optical use according to any one of appendix 1 to 8, wherein the hydroxyl group-containing monomer is contained in an amount of 1 wt% or more based on the total amount (100 wt%) of monomer components constituting the low Tg segment in the (meth) acrylic block copolymer.

[ appendix 10] the adhesive composition for optical use according to any one of appendix 1 to 9, wherein the (meth) acrylic block copolymer has a weight average molecular weight of 20 ten thousand or more.

[ appendix 11] the adhesive composition for optical use according to any one of appendix 1 to 10, wherein the (meth) acrylic block copolymer has a molecular weight distribution of greater than 1 and 5 or less.

[ appendix 12] the adhesive composition for optical use according to any one of appendix 1 to 11, wherein a ratio of a storage modulus at 25 ℃ to a storage modulus at 50 ℃ (storage modulus at 25 ℃/storage modulus at 50 ℃) is 3 or more.

[ appendix 13] the adhesive composition for optical use according to any one of appendix 1 to 12, wherein the storage modulus at 25 ℃ is 1MPa or more and the storage modulus at 50 ℃ is 0.5MPa or less.

[ additional character 14] an optical adhesive layer comprising the optical adhesive composition according to any one of the additional characters 1 to 13.

[ additional character 15] an optical adhesive sheet having the optical adhesive layer described in additional character 14.

[ additional note 16] an optical member laminate comprising:

a1 st substrate formed of an optical member,

A2 nd substrate formed of an optical member having a height difference on a main surface, and

the adhesive layer for optical use described in supplementary note 14,

the optical adhesive layer is laminated between any main surface of the 1 st substrate and the main surface of the 2 nd substrate having the height difference.

[ appendix 17] the optical member laminate according to appendix 16, wherein the 1 st substrate has a height difference on a main surface,

the optical adhesive layer is laminated between the principal surface of the 1 st substrate having the level difference and the principal surface of the 2 nd substrate having the level difference.

[ additional note 18] the optical member laminate according to the additional note 16 or 17, wherein the 2 nd substrate has a height difference due to holes provided on a main surface.

[ addition 19] the optical member laminate according to addition 18, wherein the 2 nd substrate is a polarizing plate.

[ appendix 20] the optical member laminate according to any one of appendix 17 to 19, wherein the 1 st substrate has a printed height difference provided on a main surface.

[ additional note 21] the optical member laminate according to additional note 16, wherein the 2 nd substrate has a height difference due to the LED chips provided on the substrate.

[ addition 22] the optical member laminate according to addition 21, wherein the 2 nd substrate is an LED panel.

[ appendix 23] an optical product comprising the optical member laminate according to any one of appendix 16 to 22.

[ appendix 24] A method for producing an optical member laminate, characterized in that the method for producing an optical member laminate according to any one of appendix 16 to 22,

the manufacturing method comprises the following steps: a step of attaching the optical adhesive sheet described in item 15 to the principal surface of the 2 nd substrate having the level difference,

And a step of laminating any main surface of the 1 st substrate on the optical pressure-sensitive adhesive layer of the optical pressure-sensitive adhesive sheet, and heating and pressing the laminate at 50 ℃ or higher.

Industrial applicability

The optical adhesive composition of the present invention is useful as an optical adhesive layer and an optical adhesive sheet used for bonding optical members having a level difference, producing optical products such as image display devices, and the like.

Description of the reference numerals

10 optical member laminate

11 st substrate

12 nd 2 nd substrate

A optical adhesive layer

Difference in height of D

20 optical member laminate

21 st substrate

22 nd substrate

Difference in height of D

30 optical member laminate

31 st substrate

32 nd substrate (polarizing plate)

H hole

40 optical component Stack (Micro LED display)

41 st substrate

42 nd substrate

L LED chip

50 optical article (image display device)

51 front surface transparent member

52-hole polarizing plate

53 image display unit

H' piercing process

Claims (24)

1. An optical adhesive composition characterized by containing a (meth) acrylic block copolymer,

the (meth) acrylic block copolymer contains: a high Tg segment having a glass transition temperature of 0 ℃ or higher and 100 ℃ or lower, and a low Tg segment having a glass transition temperature of-100 ℃ or higher and lower than 0 ℃,

the (meth) acrylic block copolymer has a peak of tan delta in a region of 0 ℃ or higher and a peak of tan delta in a region of less than 0 ℃,

wherein the glass transition temperature is calculated by the formula FOX using the monomer component composition constituting each segment.

2. The adhesive composition for optical use according to claim 1, wherein the maximum value of tan δ in the region of 0 ℃ or higher is 0.5 to 3.0.

3. The optical adhesive composition according to claim 1 or 2, wherein the (meth) acrylic block copolymer is an ABA type triblock copolymer.

4. The optical adhesive composition according to claim 3, wherein in the ABA type triblock copolymer, the A segment is the high Tg segment and the B segment is the low Tg segment.

5. The optical adhesive composition according to any one of claims 1 to 4, wherein the monomer component constituting the high Tg segment in the (meth) acrylic block copolymer contains at least 1 selected from the group consisting of an alkyl (meth) acrylate having a linear alkyl group having 1 to 3 carbon atoms, an alkyl (meth) acrylate having a branched alkyl group having 3 or 4 carbon atoms, and an alicyclic monomer.

6. The optical adhesive composition according to claim 5, wherein an alkyl (meth) acrylate having a branched alkyl group having 3 or 4 carbon atoms is contained as a monomer component constituting the high Tg segment in the (meth) acrylic block copolymer.

7. The optical adhesive composition according to claim 5, wherein the alicyclic monomer contains: a cycloalkyl (meth) acrylate containing a cycloalkyl group having 4 to 10 carbon atoms, which optionally has a substituent.

8. The optical adhesive composition according to any one of claims 1 to 7, wherein at least 1 selected from the group consisting of alkyl (meth) acrylates having a linear or branched alkyl group having 4 to 18 carbon atoms and hydroxyl group-containing monomers is contained as a monomer component constituting the low Tg segment in the (meth) acrylic block copolymer.

9. The optical adhesive composition according to any one of claims 1 to 8, wherein the hydroxyl group-containing monomer is contained in an amount of 1 wt% or more based on the total amount (100 wt%) of monomer components constituting the low Tg segment in the (meth) acrylic block copolymer.

10. The optical adhesive composition according to any one of claims 1 to 9, wherein the (meth) acrylic block copolymer has a weight average molecular weight of 20 ten thousand or more.

11. The optical adhesive composition according to any one of claims 1 to 10, wherein the molecular weight distribution of the (meth) acrylic block copolymer is greater than 1 and 5 or less.

12. The optical adhesive composition according to any one of claims 1 to 11, wherein a ratio of a storage modulus at 25 ℃ to a storage modulus at 50 ℃ (storage modulus at 25 ℃/storage modulus at 50 ℃) is 3 or more.

13. The optical adhesive composition according to any one of claims 1 to 12, wherein the storage modulus at 25 ℃ is 1MPa or more and the storage modulus at 50 ℃ is 0.5MPa or less.

14. An optical adhesive layer comprising the optical adhesive composition according to any one of claims 1 to 13.

15. An optical adhesive sheet comprising the optical adhesive layer according to claim 14.

16. An optical member laminate comprising:

a1 st substrate formed of an optical member,

A2 nd substrate formed of an optical member having a height difference on a main surface, and

the adhesive layer for optical use according to claim 14,

the optical adhesive layer is laminated between an arbitrary main surface of the 1 st substrate and a main surface of the 2 nd substrate having the height difference.

17. The optical member stack according to claim 16,

the 1 st substrate has a height difference on a main surface,

the optical adhesive layer is laminated between the principal surface of the 1 st substrate having the height difference and the principal surface of the 2 nd substrate having the height difference.

18. The optical member laminate according to claim 16 or 17, wherein the 2 nd substrate has a height difference due to holes provided on a principal surface.

19. The optical member laminate according to claim 18, wherein the 2 nd substrate is a polarizing plate.

20. The optical member laminate according to any one of claims 17 to 19, wherein the 1 st substrate has a height difference that is a printed height difference provided on a main surface.

21. The optical member laminate according to claim 16, wherein the 2 nd substrate has a height difference due to the LED chips provided on the substrate.

22. The optical member laminate according to claim 21, wherein the 2 nd substrate is an LED panel.

23. An optical article comprising the optical member laminate according to any one of claims 16 to 22.

24. A method for producing an optical member laminate according to any one of claims 16 to 22,

the manufacturing method comprises the following steps: a step of attaching the optical adhesive sheet according to claim 15 to the principal surface of the 2 nd substrate having the level difference, and

and a step of laminating any main surface of the 1 st substrate on the optical pressure-sensitive adhesive layer of the optical pressure-sensitive adhesive sheet, and heating and pressing the laminate at 50 ℃ or higher.

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