JP6201330B2 - Transparent double-sided adhesive sheet - Google Patents

Description

  The present invention can be suitably used for pasting constituent members of an image display device such as a personal computer, a mobile terminal (PDA), a game machine, a television (TV), a car navigation system, a touch panel, a pen tablet and the like. The present invention relates to a double-sided adhesive sheet. In particular, it is related with the transparent double-sided adhesive sheet which can be used conveniently for bonding the structural member for image display apparatuses which has a level | step-difference part on the bonding surface.

  In recent years, in order to improve the visibility of an image display device, an image display panel such as a liquid crystal display (LCD), a plasma display (PDP) or an electroluminescence display (ELD), and a protection disposed on the front side (viewing side) thereof. A gap between the panel and the touch panel member is filled with an adhesive sheet, a liquid adhesive, or the like to suppress reflection of incident light or outgoing light from a display image at an air layer interface.

As a method of filling the gaps between the constituent members for an image display device with an adhesive, a liquid adhesive resin composition containing an ultraviolet curable resin is filled into the gaps, and then cured by irradiation with ultraviolet rays. A method is known (Patent Document 1).
However, in such a method, not only the work when filling the liquid adhesive resin composition is complicated and inferior in productivity, but also an area where ultraviolet rays are difficult to reach, such as a part concealed in the printing concealment layer, is not adhesive. It was difficult to cure, and it was difficult to obtain stable quality.

  In view of this, filling the gaps between the constituent members for an image display device with an adhesive sheet is performed. For example, Patent Document 2 discloses a first adhesive layer and a second adhesive having different viscoelastic behavior as a transparent adhesive sheet that can be suitably used for bonding a transparent panel such as a protective panel or a touch panel to an image display panel. A value of the dynamic shear storage elastic modulus G ′ measured by temperature dispersion at a frequency of 1 Hz, which is an adhesive sheet having a structure in which each layer has one or more layers and these layers are laminated and integrated. However, the transparent adhesive sheet characterized by being in a specific range is disclosed.

  Patent Document 3 discloses a transparent double-sided PSA sheet having an intermediate resin layer (A) and a pressure-sensitive adhesive layer (B) as a front and back layer, and each layer is one or more types of (meta). A layer having an acrylic ester (co) polymer as a base resin, and a storage shear modulus (G ′ (A)) of the intermediate resin layer (A) at a frequency of 1 Hz in a temperature range of 0 ° C. to 100 ° C. There is disclosed a transparent double-sided PSA sheet that is higher than the pressure-sensitive adhesive layer (B) and has an indentation hardness (Asker C2 hardness) of the entire sheet of 10 to 80.

Patent Document 4 discloses a monomer (meth) acrylic copolymer containing a (meth) acrylic acid ester having a UV crosslinkable site as a thin (for example, 30 to 50 μm thick) pressure-sensitive adhesive sheet applicable to a surface having a step or a bump. A UV-crosslinkable pressure-sensitive adhesive sheet comprising a polymer, wherein the storage elastic modulus of the pressure-sensitive adhesive sheet before UV-crosslinking is 5.0 × 10 ⁴ Pa or more and 1.0 × 10 ⁶ Pa at 30 ° C. and 1 Hz. Below, it is 5.0 × 10 ⁴ Pa or less at 80 ° C. and 1 Hz, and the storage elastic modulus of the pressure-sensitive adhesive sheet after UV crosslinking is 1.0 × 10 ³ Pa or more at 130 ° C. and 1 Hz. An ultraviolet crosslinkable pressure-sensitive adhesive sheet is disclosed.

  Further, in Patent Document 5, as a method for producing a laminate for constituting an image display device having a constitution in which an image display device constituting member is laminated on at least one side of a transparent double-sided adhesive sheet, an adhesive that is primarily crosslinked by ultraviolet rays. A method is disclosed in which after the sheet is bonded to the image display device constituent member, the adhesive sheet is irradiated with ultraviolet rays through the image display device constituent member and subjected to secondary curing.

  In Patent Document 6, a composition in which 1000 to 125000 mPa · s of syrup obtained by partial polymerization of a radical polymerization monomer so as to have a polymer pass-through rate of 30 to 60% and a radical polymerization initiator is applied to a substrate. A method of obtaining a pressure-sensitive adhesive sheet by applying post-actinic radiation and curing is disclosed.

International Publication No. 2010/027041 International Publication No. 2010/044229 International Publication No. 2011/129200 JP 2011-184582 A Japanese Patent No. 4971529 Special table 2007-510035 gazette

  In the field of image display devices centering on mobile phones and mobile terminals, in addition to thinning and high precision, design diversification has progressed, and new problems have arisen accordingly. For example, a black concealment portion is conventionally printed in a frame shape on the peripheral portion of the surface protection panel. However, with the diversification of the design, the frame concealment portion other than black is printed. Forming in color is starting to take place. When the concealment part is formed with a color other than black, the concealability is low with a color other than black, and therefore the height of the concealment part, that is, the printing part tends to be higher than that of black. For this reason, an adhesive sheet for laminating components having such a printing unit is required to have a print level followability that can fill a corner to follow a large print level.

Also, as the thickness of the printing part increases, the part that contacts the printing part of the image display device is subjected to a greater stress than other parts, which may cause distortion and adversely affect the optical characteristics. Therefore, it is also required to suppress such distortion.
For this reason, a higher stress relaxation property (fluidity) is required for a filling member such as an adhesive sheet, but the storage stability of the adhesive sheet and the workability during handling are impaired only by increasing the fluidity. There is a possibility that the foaming reliability of the laminated member that has been bonded is lowered.

  In addition, the constituent members of the image display device include a member that generates gas (also referred to as “outgas”) over time under a high temperature or high humidity environment, such as a plastic protective panel. In the case where the constituent members of these image display devices are bonded together with a transparent double-sided adhesive sheet, the transparent double-sided adhesive sheet can have an adhesive force and a cohesive force that can sufficiently counter the gas pressure of outgas. It is also necessary to do so.

  Therefore, when the image display device constituting member having a stepped portion on the bonding surface is bonded via a transparent double-sided adhesive sheet, the present invention follows the stepped portion of the bonding surface to provide a transparent double-sided surface. The adhesive sheet can be filled, and distortion generated in the adhesive sheet can be reduced.Furthermore, the foaming resistance under high temperature and high humidity environment can be reduced without impairing the workability during handling. It is intended to provide a new transparent double-sided adhesive sheet that can be maintained.

The present invention relates to one or more (meth) acrylic acid ester (co) polymers, an ultraviolet polymerization initiator having a molar extinction coefficient at a wavelength of 365 nm of 10 or more and a molar extinction coefficient at a wavelength of 405 nm of 0.1 or less. The first feature is that it contains (A) and a visible light polymerization initiator (B) having a molar extinction coefficient of 10 or more at a wavelength of 405 nm,
The value (E ′ / G ′) obtained by dividing the dynamic storage elastic modulus (E ′) at 60 ° C. obtained by the tensile method by the dynamic storage elastic modulus (G ′) at 60 ° C. obtained by the shear method is 10 or more. A transparent double-sided adhesive sheet in a B-stage state is proposed, which has the second feature.

Since the transparent double-sided adhesive sheet proposed by the present invention contains an ultraviolet polymerization initiator (A) and a visible light polymerization initiator (B), visible light is applied to the uncrosslinked transparent double-sided adhesive sheet. By irradiating and cross-linking visible light, a transparent double-sided adhesive sheet in a B-stage state in which ultraviolet cross-linkability remains can be obtained. Or it can be set as the transparent double-sided adhesive sheet of the B stage state which left visible light crosslinkability by irradiating an ultraviolet-ray with respect to an uncrosslinked transparent double-sided adhesive sheet, and carrying out ultraviolet crosslinking.
In such a B-stage transparent double-sided adhesive sheet, the E ′ / G ′ of the sheet is 10 or more compared to the case where an elongation or compression stress is applied in a direction parallel to the sheet surface. This means that the direction perpendicular to the sheet surface, that is, when stress is applied through the sheet surface, is more easily deformed, and has high dimensional stability and high deformation sensitivity due to stress in the surface direction. It is possible to follow the stepped portion.
Therefore, if the image display apparatus constituent member provided with the stepped portion on the bonding surface is bonded using the transparent double-sided adhesive sheet proposed by the present invention, it follows the stepped portion of the bonding surface to every corner. It can be filled, and the distortion generated in the adhesive sheet can be reduced. Furthermore, the foaming resistance under high temperature and high humidity environment can be maintained without impairing the workability during handling. it can.

  In the invention disclosed in Patent Document 6, since a raw material having a low polymer conversion rate is used as a base resin, a monomer tends to remain in a low molecular weight product or in an unreacted state after curing, and a low molecular component is present after bonding of members. There is a possibility that the adherend is contaminated, or the cohesive force with the adherend interface is reduced, and the foaming resistance reliability at a high temperature cannot be sufficiently obtained. On the other hand, the transparent double-sided adhesive sheet proposed by the present invention uses a high molecular weight acrylate copolymer as a base resin, and since there are few low molecular weight components, these problems are solved. be able to.

  Hereinafter, an example of an embodiment of the present invention will be described. However, the present invention is not limited to the following embodiments.

<This adhesive sheet 1>
The transparent double-sided adhesive sheet (hereinafter referred to as “the present adhesive sheet 1”) according to the first embodiment of the present invention includes at least one (meth) acrylic acid ester (co) polymer and an ultraviolet region. Containing a UV polymerization initiator (A) that initiates crosslinking by light and a visible light polymerization initiator (B) that initiates crosslinking by light in the visible light region, and if necessary, a crosslinking agent (C). The adhesive composition further containing a tackifier (D) according to the requirements and, if necessary, the other component (E) (hereinafter referred to as “the present adhesive composition 1”) is primarily cured. A transparent double-sided adhesive sheet in a B-stage state having a single layer structure.

Since the present adhesive sheet 1 contains the ultraviolet polymerization initiator (A) and the visible light polymerization initiator (B), the uncrosslinked present adhesive composition 1 is visible when irradiated with visible light. By photocrosslinking, it can be first cured to form a transparent double-sided adhesive sheet in a B-stage state. In addition, the uncrosslinked present adhesive composition 1 may be subjected to ultraviolet crosslinking by irradiating with a light beam including ultraviolet rays to be primarily cured to obtain a transparent double-sided adhesive sheet in a B stage state.
Among these, from the viewpoint of increasing the unevenness followability of the present adhesive sheet 1, the uncrosslinked adhesive composition 1 is irradiated with visible light to be crosslinked with visible light, thereby leaving the ultraviolet reactivity. A transparent double-sided adhesive sheet is preferred.

Therefore, as an example of a preferable production method of the present adhesive sheet 1, one or more (meth) acrylic acid ester (co) polymers, an ultraviolet polymerization initiator (A) that initiates crosslinking by light in the ultraviolet region, It contains a visible light polymerization initiator (B) that initiates crosslinking by light in the visible light region, and if necessary, a crosslinking agent (C), if necessary, a tackifier (D), and if necessary, other Examples of the method for obtaining the present adhesive sheet 1 include forming the present adhesive composition 1 further containing the component (E) into a sheet shape on a release sheet and first curing it by irradiation with visible light. it can. However, it is not limited to such a manufacturing method.
In the above production method, when visible light is irradiated, in order to avoid the reaction of the ultraviolet polymerization initiator (A), visible light that does not substantially contain light in the ultraviolet region, for example, light in the wavelength region of less than 380 nm. Is preferably irradiated.
Here, “substantially not contained” is intended to include such a case even if light in the ultraviolet region is intentionally cut, and is intended to encompass such a case, for example, a wavelength region of 380 nm or more (for example, If the light intensity (for example, 350 nm wavelength) in the wavelength region of less than 380 nm is less than 10% with respect to the light intensity of 410 nm wavelength), it is not practically included.

<This adhesive sheet 2>
The transparent double-sided adhesive sheet (hereinafter referred to as “the present adhesive sheet 2”) according to the second embodiment of the present invention includes at least one (meth) acrylic acid ester (co) polymer and visible light. It contains a visible light polymerization initiator (B) that initiates crosslinking by light in the region, and if necessary, a crosslinking agent (C), a tackifier (D) if necessary, and other components (if necessary) An intermediate layer S1 obtained by first curing an adhesive composition further containing E) (hereinafter referred to as "the present adhesive composition 2");
Contains one or more (meth) acrylic acid ester (co) polymers and an ultraviolet polymerization initiator (A) that initiates crosslinking by light in the ultraviolet region, and if necessary, a crosslinking agent (C). The outermost layer S2 formed from an adhesive composition (hereinafter referred to as “the present adhesive composition 3”) that further contains a tackifier (D) and, if necessary, other components (E). ,
It is a transparent double-sided adhesive sheet in a B stage state.

Since the present adhesive sheet 2 only needs to include the intermediate layer S1 and the outermost layer S2, another layer may be interposed between the intermediate layer S1 and the outermost layer S2, or the intermediate layer S1. The outermost layer S2 may be provided on both front and back sides, or the outermost layer S2 may be provided on one side of the intermediate layer S1, and the other layer may be provided on the other side of the intermediate layer S1. May be.
Especially, it is preferable that it is the structure which has the structure (S2 / S1 / S2) provided with the outermost layer S2 in the front and back both sides of intermediate | middle layer S1.

  In the production process of the present adhesive sheet 2, for example, the intermediate layer S1 is cured by irradiating visible light and crosslinking the present adhesive composition 3 containing the visible light polymerization initiator (B) with visible light. Can do. At this time, since the outermost layer S2 can maintain an uncrosslinked state, it can maintain a flexible and fluid state. Therefore, even if this adhesive sheet 2 maintains handling (handling property) by hardening of intermediate | middle layer S1, even if there exists an uneven | corrugated level | step difference etc. in a bonding surface, outermost layer S2 fluidly follows this unevenness | corrugation. Can do. Thus, it can be said that the present adhesive sheet 2 is superior to the present adhesive sheet 1 from the viewpoint that the surface layer can be made more flexible and the unevenness reliability can be improved.

  In the present adhesive sheet 2 in the B-stage state, the present adhesive composition 3 of the outermost layer S2 may be in an uncrosslinked state, that is, in an uncured state, or partially if the ultraviolet reactivity remains. May be crosslinked, that is, cured.

(Outermost layer S2)
As the base resin in the present adhesive composition 3 that forms the outermost layer S2, the same base resin as that of the present adhesive sheet 1, that is, a (meth) acrylic acid ester (co) polymer can be used. Details will be described later.

The outermost layer S2 may contain a visible light polymerization initiator (B), but the visible light polymerization initiator (B) so that the crosslinking does not proceed when the intermediate layer S1 is crosslinked with visible light. The content of is preferably smaller.
Specifically, the (meth) acrylic in the outermost layer S2 with respect to the mass part (intermediate Bm) of the visible light polymerization initiator (B) per 100 parts by mass of the (meth) acrylic acid ester (co) polymer in the intermediate layer S1. The ratio (outermost Bm / intermediate Bm) of the number of parts (outermost Bm) of the visible light polymerization initiator (B) per 100 parts by weight of the acid ester (co) polymer is lower than 1, particularly less than 0.5. Preferably, it is low, especially lower than 0.05.

(Intermediate layer S1)
As the base resin in the adhesive composition 2 forming the intermediate layer S1, the base resin of the adhesive sheet 1, that is, a (meth) acrylic acid ester (co) polymer can be used. Details will be described later.
However, the base resin in the present adhesive composition 2 that forms the intermediate layer S1 may be the same resin as the base resin in the present adhesive composition 3 that forms the outermost layer S2, or may be a different resin. From the viewpoints of ensuring transparency and ease of production, and preventing refraction at the interface between the intermediate layer S1 and the outermost layer S2, the base resins are preferably the same resin.
Further, the visible light polymerization initiator (B), the crosslinking agent (C), the tackifier (D) and other components (E) in the adhesive composition 2 are the same as those of the adhesive sheet 1 respectively. Can be used. Details will be described later.

The intermediate layer S1 in the B stage state may be formed so as not to be cross-linked by other electromagnetic waves, may be formed so as to be further cross-linked by other electromagnetic waves, or may be further cross-linked by heat. It may be formed.
For example, the intermediate layer S1 may contain an ultraviolet polymerization initiator (A) in addition to the visible light polymerization initiator (B). If the intermediate layer S1 contains the ultraviolet polymerization initiator (A), the intermediate layer S1 can be further cross-linked by ultraviolet irradiation.

  However, since the light transmittance decreases as the content of the crosslinking initiator increases, the amount of the crosslinking initiator in the intermediate layer S1 is preferably lower than the content in the outermost layer S2.

(Dynamic storage modulus of each layer by shear method (G '))
In the present adhesive sheet 2, followability when bonding to uneven portions such as a step (referred to as “high printing step”) due to a printing portion having a height of 50 μm or more, smoothness after bonding, workability From the viewpoint of balancing, the dynamic storage elastic modulus (G ′) of the intermediate layer S1 by the shear method at 60 ° C. is lower than the dynamic storage elastic modulus (G ′) of the outermost layer S2 by the shear method at 60 ° C. It is preferable to become.
Among them, the ratio of the dynamic storage elastic modulus (G ′) by the shear method at 60 ° C. of the intermediate layer S1 to the dynamic storage elastic modulus (G ′) by the shear method at 60 ° C. of the outermost layer S2 is 1.5 to 1000. It is preferable that it is preferably 2 or more or 500 or less.

The dynamic storage elastic modulus (G ′) of the intermediate layer S1 by a shearing method at 60 ° C. is preferably 1.0 × 10 ³ Pa to 1.0 × 10 ⁷ Pa. By being 1.0 × 10 ³ Pa or more, the dimensional stability as an adhesive sheet is excellent, and by being 1.0 × 10 ⁷ Pa or less, distortion is caused in the adhesive sheet after bonding to the uneven surface. It is preferable because it hardly occurs.
From such a viewpoint, the dynamic storage elastic modulus (G ′) of the intermediate layer S1 by the shearing method at 60 ° C. is 5.0 × 10 ³ Pa or more or 5.0 × 10 ⁶ Pa or less, particularly 1 among them. It is preferably 0.0 × 10 ⁴ Pa or more or 1.0 × 10 ⁶ Pa or less.

  In order to adjust the dynamic storage elastic modulus (G ′) of each of the intermediate layer S1 and the outermost layer S2 by the above-described shearing method, for example, a copolymerization monomer that forms an acrylic acid (co) polymer that is a base polymer What is necessary is just to adjust the crosslinking degree by adjusting the kind and composition ratio of this, or adjusting the irradiation conditions of light.

(Layer thickness)
In the present adhesive sheet 2, the ratio of the total layer thickness of the intermediate layer S1 to the total layer thickness of the outermost layer S2 ((S1) / (S2)) is 0.1 <(S1) / (S2) <10. Is preferred.
If the ratio of the thickness of the intermediate layer S1 and the outermost layer S2 is in the above range, the contribution of the thickness of the adhesive sheet 2 does not become too large in the laminate for an image display device and the image display device described later. It is preferable because it is too flexible and the workability related to cutting and handling is not deteriorated. Further, it is preferable because the adhesion to the adherend and the wettability can be maintained without being inferior in conformity to unevenness and a bent surface.
From the standpoint of following the printing step and reducing optical distortion in the vicinity of the unevenness after pasting, it is even more preferable that 0.1 <(S1) / (S2) <1.

(Manufacturing method)
The adhesive sheet 2 can be manufactured by the following method.
For example, the adhesive composition 2 and the adhesive composition 3 are coextruded between two transparent release sheets to produce a two-layer laminated sheet, and the laminated sheet is irradiated with visible light. The intermediate layer S1 can be primarily cured to obtain the present adhesive sheet 2 in a B-stage state.
In the case of a three-layer configuration comprising the outermost layer S2, the intermediate layer S1, and the outermost layer S2, for example, the adhesive composition 2 and the adhesive composition 3 are coextruded between two transparent release sheets. A three-layer laminated sheet is prepared, and the intermediate layer S1 is primarily cured by irradiating the laminated sheet with visible light, whereby the B-staged adhesive sheet 2 can be obtained.

In the above production method, when the laminated sheet is irradiated with visible light, the adhesive composition 3 containing the ultraviolet polymerization initiator (A) is substantially irradiated with light having a wavelength in the ultraviolet region in order to avoid ultraviolet crosslinking. It is preferable to irradiate visible light that does not include, for example, visible light that substantially does not include light in a wavelength region of less than 380 nm.
As a method of irradiating visible light that does not substantially include light having a wavelength in the ultraviolet region, a light source that emits only visible light that does not include light having a wavelength in the ultraviolet region may be used. Irradiation may be performed using a light source through a filter that does not transmit light. Further, by laminating a film that does not transmit light having a wavelength in the ultraviolet region on one or both surfaces of the adhesive sheets 1 and 2, and irradiating light through the film, the wavelength in the ultraviolet region is changed to the adhesive sheet. You may make it not reach 1 and 2.
Note that the term “substantially not included” includes a case where light in the ultraviolet region is intentionally cut, so that it may be included to some extent. Therefore, it is intended to include such a case, for example, a wavelength region of 380 nm or more (for example, 410 nm) If the light intensity in the wavelength region of less than 380 nm (for example, 350 nm wavelength) is less than 10% with respect to the light intensity of the wavelength, it is not practically included.

  The manufacturing method of this adhesive sheet 2 is not limited to the said manufacturing method. For example, after the sheet S1 for forming the intermediate layer S1 is irradiated with visible light and crosslinked to form the intermediate layer S1, the outermost layer made of the adhesive composition 3 is formed on one side or both sides of the intermediate layer S1. The present adhesive sheet 2 may be produced by stacking S2.

<Features of Adhesive Sheets 1 and 2>
The adhesive sheets 1 and 2 contain one or more (meth) acrylic acid ester (co) polymers as a base resin, and are visible with an ultraviolet polymerization initiator (A) that initiates cross-linking by light in the ultraviolet region. A visible light polymerization initiator (B) that initiates crosslinking by light in the light region, and if necessary, a polyfunctional (meth) acrylate resin (C) as a crosslinking agent; And a tackifier (D), which are common in that they are B-stage transparent double-sided adhesive sheets.

  Here, the “B stage state” means an intermediate curing state of the adhesive sheet having adhesiveness or tackiness, that is, a state where the adhesive sheet is not finally cured, and is further cured (crosslinked) when irradiated with light. This means a state where the adhesiveness can be further increased. In this case, it includes a hot-melt type that is heated to soften and then cured by light irradiation (crosslinking). Further, a pressure-sensitive type that is cured (crosslinked) by light irradiation without heating is also included.

  In a conventional adhesive sheet in which a transparent double-sided adhesive sheet is primarily cured by UV crosslinking and then secondarily cured by UV crosslinking, a reaction residue in the primary curing causes the start of secondary curing. There was a limit to the amount of change in physical properties before and after curing. For example, it has been difficult to largely change the flexibility or fluidity in the B stage state, the adhesiveness or foam resistance after secondary curing, and the like before and after the secondary curing. On the other hand, in the present adhesive sheets 1 and 2, since the types of the crosslinking initiator that contributes to the primary curing and the crosslinking initiator that contributes to the secondary curing are different, at least before and after the secondary curing compared to the former. The amount of physical property change can be increased. Therefore, in the B stage state after primary curing (before secondary curing), higher fluidity can be imparted, and the bonding reliability to the uneven surface can be enhanced. On the other hand, after secondary curing, it can be firmly cured by irradiation with ultraviolet rays, so that the foam resistance after bonding can be enhanced.

  In addition, in a conventional method in which secondary curing is performed after primary curing using an adhesive material having both photocuring properties and thermosetting properties, a thermosetting agent such as an organic peroxide, an isocyanate compound, an epoxy compound, or an amine compound is used. When processing the composition, it not only causes gelation, but also requires a curing period of several days to complete the reaction, and thus has a problem of poor productivity. On the other hand, in the present adhesive sheets 1 and 2, since both the primary curing and the secondary curing are performed by photocrosslinking, there is an advantage that the problem in such a thermosetting process can be eliminated. .

  In addition, compared to the adhesive sheet not subjected to the primary cross-linking treatment, and the method of performing cross-linking treatment by applying heat or ultraviolet rays after bonding the adherend members using a hot melt adhesive resin sheet, in these methods In the stage before the crosslinking treatment, since the sheet shape is not maintained by crosslinking, there is a problem inferior in processability and storage stability as a sheet. On the other hand, in the present adhesive sheets 1 and 2, since it can be in a B stage state in which the shape is maintained by selectively using visible light to perform primary crosslinking, it is superior to the former. In addition, it has the advantage of being able to obtain excellent processability and storage stability.

(E '/ G')
The adhesive sheets 1 and 2 both have a value obtained by dividing the dynamic storage elastic modulus (E ′) at 60 ° C. obtained by the tension method by the dynamic storage elastic modulus (G ′) at 60 ° C. obtained by the shear method ( E ′ / G ′) can be 10 or more.

  The fact that E ′ / G ′ of the present adhesive sheets 1 and 2 is 10 or more means that the sheet surface is perpendicular to the sheet surface, that is, the sheet surface, compared with the case where an elongation or compressive stress is applied in the direction parallel to the sheet surface. This means that it is easier to deform when stress is applied. In general, the relationship between the dynamic storage elastic modulus (E ′) in the tensile direction and the dynamic storage elastic modulus (G ′) in the shear direction assumes that the material is an ideal elastic body (no volume change during deformation). In this case, E ′ / G ′ = 3. Even in a general resin member, E ′ / G ′ is usually about 3 or so. Therefore, if the value of E ′ / G ′ at 60 ° C. of the adhesive sheets 1 and 2 is 10 or more, the adhesive sheets 1 and 2 are more dimensionally stable than the conventional adhesive or adhesive sheet. It is high and has high deformation sensitivity due to stress in the surface direction, that is, excellent in unevenness followability at the time of bonding.

  From this viewpoint, E ′ / G ′ of the adhesive sheets 1 and 2 is preferably 10 or more, more preferably 15 or more, and particularly preferably 20 or more. On the other hand, there is no particular limitation on the upper limit. However, when E ′ / G ′ is 100 or less, it is preferable in terms of obtaining storage stability and anti-foaming reliability when the laminated body after bonding is stored in a high temperature or high humidity environment. E ′ / G ′ is preferably 100 or less, more preferably 70 or less, and even more preferably 50 or less.

  Examples of the method of setting E ′ / G ′ of the present adhesive sheets 1 and 2 to 10 or more include (I)... A method of adjusting an adhesive composition by filling fillers having different rigidity at 60 ° C., ( II) ・ ・ Method to adjust by laminating resin layers with different rigidity at 60 ℃, (III) ・ ・ Sensitivity to stress in tensile direction and shear direction by changing the degree of crosslinking in the sheet (in the vertical direction) The method of adjusting by making it different can be mentioned. However, it is not limited to these methods.

  In the method (I), a large amount of filler must be blended in order to develop the anisotropy of the elastic modulus, which may cause poor appearance due to poor dispersion. In the method (II), there are problems that the optical characteristics are deteriorated and the cost and productivity are deteriorated by laminating layers having different rigidity. On the other hand, since the method (III), that is, the method of varying the degree of crosslinking in the thickness direction of the sheet does not have these problems, the method (III) is adopted as a method for producing the present adhesive sheet 1. Is preferred.

(Dynamic storage elastic modulus (E ′) at 60 ° C. obtained by the tensile method)
The adhesive sheets 1 and 2 preferably have a dynamic storage elastic modulus (E ′) at 60 ° C. determined by a tensile method of 1.0 × 10 ⁴ Pa to 6.6 × 10 ⁵ Pa . It is more preferably 0 × 10 ⁴ Pa or more or 5.0 × 10 ⁵ Pa or less. However, it is not limited to these ranges.
If the dynamic storage elastic modulus (E ′) by the tension method is 1.0 × 10 ⁴ Pa or more, it is preferable in terms of the cutting property of the adhesive sheet. Moreover, if the dynamic storage elastic modulus (E ') by the said tension method is 6.6x10 < ⁵ > Pa or less, it is preferable at the point which can relieve | moderate the distortion which arises in an adhesive sheet after bonding to an uneven surface. .

  The dynamic storage elastic modulus (E ′) at 60 ° C. obtained by the tension method of the adhesive sheets 1 and 2 is, for example, using a dynamic viscoelasticity measuring device, tensile mode: vibration frequency 1 Hz, measurement temperature: 0 ° C. To 100 ° C., heating rate: 3 ° C./minute, and can be obtained by measuring the dynamic storage elastic modulus E ′ by the above-mentioned tension method at 60 ° C.

  As a method of adjusting the dynamic storage elastic modulus (E ′) at 60 ° C. obtained by the tension method for the adhesive sheets 1 and 2, for example, a copolymer for forming a (meth) acrylic acid ester copolymer which is a base polymer is used. Examples thereof include a method of adjusting the kind and composition ratio of the polymerization monomer, adjusting the addition amount of the crosslinking monomer, adjusting the degree of crosslinking by adjusting the light irradiation amount and the like. However, it is not limited to such a method.

(Dynamic storage elastic modulus (G ′) at 60 ° C. determined by the shear method)
The adhesive sheets 1 and 2 preferably have a dynamic storage elastic modulus (G ′) at 60 ° C. determined by a shearing method of 5.0 × 10 ² Pa to 1.0 × 10 ⁵ Pa, especially 5 It is particularly preferable that the pressure is 0.0 × 10 ³ Pa or more or 5.0 × 10 ⁴ Pa or less. However, it is not limited to these ranges.
A dynamic storage elastic modulus (G ′) by the shearing method of 5.0 × 10 ² Pa or more is preferable from the viewpoint of storage stability of the adhesive sheet. Moreover, if the dynamic storage elastic modulus (G ') by the said shearing method is 1.0 * 10 < ⁵ > Pa or less, it is preferable at the point of the followable | trackability to the adherend surface with an unevenness | corrugation.

  The dynamic storage elastic modulus (G ′) at 60 ° C. obtained by the shearing method of the adhesive sheets 1 and 2 is, for example, a measurement sample obtained by laminating an adhesive sheet to have a thickness of 1 mm to 2 mm using a rheometer. Strain: 0.5%, frequency: 1 Hz, temperature: −50 to 200 ° C., heating rate: 3 ° C./min, and measurement of dynamic storage elastic modulus (G ′) by the shear method at 60 ° C. Can be obtained.

  As a method for adjusting the dynamic storage elastic modulus (G ′) at 60 ° C. obtained by the shearing method for the adhesive sheets 1 and 2, for example, a copolymer for forming a (meth) acrylic acid ester copolymer as a base polymer is used. Examples thereof include a method of adjusting the kind and composition ratio of the polymerization monomer, adjusting the addition amount of the crosslinking monomer, adjusting the degree of crosslinking by adjusting the light irradiation amount and the like. However, it is not limited to this method.

(transparency)
The adhesive sheets 1 and 2 have a feature of being transparent. It is distinguished from a non-transparent adhesive sheet such as an adhesive sheet made of foamed resin or the like.

<Thickness>
The total thickness of the adhesive sheets 1 and 2 is preferably 50 μm to 1 mm, more preferably 100 μm or more or 500 μm or less.
If the total thickness of the adhesive sheets 1 and 2 is 50 μm or more, it is possible to follow unevenness such as a high printing level difference, and if the total thickness is 1 mm or less, the demand for thinning can be met.
Furthermore, from the viewpoint of filling the peripheral concealment layer in the conventional image display device with a higher printing height, specifically up to a step of about 50 μm, the total thickness of the adhesive sheets 1 and 2 is 100 μm or more. It is even more preferable that the thickness is 150 μm or more. On the other hand, from the viewpoint of meeting the demand for thinning, it is more preferably 500 μm or less, particularly 350 μm or less.

<Base resin>
As the base resin of the adhesive compositions 1, 2, and 3, from the viewpoint of tackiness, transparency and weather resistance, (meth) acrylic acid ester-based polymers (including copolymers, hereinafter referred to as “acrylic”) It is preferable to use an acid ester-based (co) polymer).

  The acrylic ester-based (co) polymer as the base resin is selected by appropriately selecting the kind of acrylic monomer or methacrylic monomer used for polymerizing the copolymer, the composition ratio, the polymerization conditions, and the like. ) And molecular weight, etc., can be appropriately adjusted for preparation.

Examples of acrylic monomers and methacrylic monomers used to polymerize acrylic ester (co) polymers include 2-ethylhexyl acrylate, n-octyl acrylate, isooctyl acrylate, n-butyl acrylate, ethyl acrylate, methyl methacrylate, methyl acrylate. Etc. Hydroxyethyl acrylate, acrylic acid, glycidyl acrylate, acrylamide, acrylonitrile, methacrylonitrile, fluorine acrylate, silicone acrylate, etc. having a hydrophilic group or an organic functional group can also be used.
Various vinyl monomers such as vinyl acetate, alkyl vinyl ether, and hydroxyalkyl vinyl ether that can be copolymerized with the above acrylic monomer and methacryl monomer can also be appropriately used for polymerization.

  As the polymerization treatment using these monomers, known polymerization methods such as solution polymerization, emulsion polymerization, bulk polymerization, suspension polymerization and the like can be employed. In this case, a thermal polymerization initiator or photopolymerization is used according to the polymerization method. An acrylic ester copolymer can be obtained by using a polymerization initiator such as an initiator.

  This adhesive composition 1, 2, 3 is non-solvent, that is, does not contain a solvent, can be hot-melt molded, and exhibits an appropriate adhesive strength at the stage of primary curing, and It is preferable that the surface of the adherend has flexibility so as to follow unevenness and foreign matter on the surface.

In addition, if the molecular weight of the base resin of the present adhesive composition 1, 2, 3 is too small, even if it is first cured, it may not exhibit adhesive strength or may be too soft and have poor handling properties. On the other hand, if the molecular weight is too large, it becomes hard at the stage of primary curing, and does not have the flexibility to follow irregularities and foreign matter on the surface of the adherend.
From such a viewpoint, the mass average molecular weight (Mw) of the base resin is preferably 100,000 to 700,000, more preferably 200,000 or more and 600,000 or less, and particularly preferably 250,000 or more or 500,000 or less.

The base resins of the adhesive compositions 1, 2, and 3 are acrylic acid having a ratio (Mw / Mn) of mass average molecular weight (Mw) to number average molecular weight (Mn) of 5 to 10, particularly 6 or 9 or less. It is more preferable to use an ester (co) polymer.
The large mass average molecular weight / number average molecular weight means that the molecular weight distribution is wide. If this value is about 5 to 10, each of the low molecular weight component and the high molecular weight component has fluidity and wettability. In order to exhibit performance commensurate with the molecular weight such as cohesive force, it is preferable because the workability and adhesion performance tend to be better than those having a narrow (uniform) molecular weight distribution.

Further, among acrylate-based (co) polymers, acrylate ester random copolymers, and among them, the glass transition temperature (Tg) of each monomer component constituting the random copolymer, that is, acrylate random copolymer Acrylic ester random copolymer containing two types of monomers having a large difference in glass transition temperature (also referred to as “Tg”) of a polymer polymerized by only a single monomer is used for each monomer component constituting Is preferred.
At this time, the difference in glass transition temperature (Tg) obtained by the differential scanning calorimetry (DSC) method of the two types of monomer components is preferably 25 to 300 ° C., particularly 40 ° C. or more or 200 ° C. or less, and particularly More preferably, the temperature is 60 ° C. or higher or 180 ° C. or lower, and further 100 ° C. or higher or 180 ° C. or lower. Specifically, the glass transition temperature (Tg) of one monomer is −100 ° C. to 0 ° C., particularly −80 ° C. to −20 ° C., and the glass transition temperature (Tg) of the other monomer component is 0 to 250 ° C. In particular, the temperature is preferably 20 to 180 ° C.
By using a copolymer containing two kinds of monomers having a large difference in glass transition temperature, a component having a low glass transition temperature functions as a fluid component, and a component having a high glass transition temperature functions as an aggregating component, respectively, An adhesive sheet having cohesive force can be obtained.

Examples of the copolymer component having a glass transition temperature (Tg) determined by the differential scanning calorimetry (DSC) method of −100 to 0 ° C. include 2-ethylhexyl acrylate, n-octyl acrylate, decyl acrylate, n-butyl acrylate, In addition to alkyl acrylates such as ethyl acrylate, 2-ethoxyethoxyethyl acrylate, diethylene glycol monobutyl ether acrylate, tetrahydrofurfuryl acrylate, alkoxylated tetrahydrofurfuryl acrylate, 4-hydroxybutyl acrylate glycidyl ether, methoxypolyethylene glycol monoacrylate, caprolactone acrylate, etc. An acrylic monomer containing an organic functional group of
On the other hand, examples of the copolymer component having a glass transition temperature (Tg) obtained by the differential scanning calorimetry (DSC) method of 0 to 250 ° C. include vinyl acetate, styrene, methyl methacrylate, isobornyl (meth) acrylate, and dicyclopenta. Dienyl (meth) acrylate, 4-ethoxylated cumylphenol (meth) acrylate, 3,3,5-trimethylcyclohexanol (meth) acrylate, cyclic trimethylolpropane formal (meth) acrylate, 2-hydroxypropyl methacrylate, tert -Butyl (meth) acrylate, cyclohexyl acrylate, neopentyl acrylate, cetyl acrylate, phenyl acrylate, toluyl acrylate, 2-phenoxyethyl methacrylate, diethylene glycol methyl acetate Methacrylate, 2-naphthyl acrylate, 2-methoxycarbonylphenyl acrylate, ethyl methacrylate, n-butyl methacrylate, sec-butyl methacrylate, isobutyl methacrylate, propyl methacrylate, isopropyl methacrylate, stearyl methacrylate, tetrahydrofurfuryl methacrylate, ethoxylated nonylphenol methacrylate, Cyclohexyl methacrylate, 4-tert-butylcyclohexyl methacrylate, benzyl methacrylate, phenethyl methacrylate, glycidyl methacrylate, hydroxyethyl methacrylate, acrylamide, hydroxyethyl acrylamide, N, N-dimethylacrylamide, N, N-dimethylaminoethyl acrylamide, acryloni Lil, and the like.

  In the acrylate copolymer as the base resin, a monomer component having a high Tg (that is, a monomer having a high glass transition temperature when the monomer is polymerized alone) and a monomer component having a low Tg (that is, the monomer By adjusting the ratio to the monomer having a low glass transition temperature when polymerized alone, the fluidity and cohesive force of the adhesive sheets 1 and 2 can be appropriately adjusted. For example, in order to give the present adhesive sheets 1 and 2 tackiness as a pressure-sensitive adhesive sheet and wettability to the uneven surface of the adherend or foreign matter, the amount of the monomer component having a low Tg may be increased. . Further, in order to obtain the handling and cutting properties of the present adhesive sheets 1 and 2, the amount of the monomer component having a high Tg may be increased.

  The adhesive sheets 1 and 2 can be softened with a plasticizer to lower the hardness, or an additive such as an oligomer can be used to appropriately adjust the hardness of the adhesive sheets 1 and 2.

<Ultraviolet polymerization initiator (A)>
As the ultraviolet polymerization initiator (A), any polymerization initiator may be used as long as it generates radicals by irradiation with ultraviolet rays, for example, light having a wavelength of 300 nm to 380 nm.
Therefore, the present adhesive sheets 1 and 2 have a wavelength absorption range for initiating an ultraviolet crosslinking reaction in ultraviolet rays, for example, in a wavelength range of 300 nm to 380 nm, by containing the ultraviolet polymerization initiator (A). Become.

In order for the present adhesive sheets 1 and 2 in the B stage state to be more flexible than the conventional double-sided adhesive sheet, the ultraviolet polymerization initiator (A) reacts to light in the visible light region. It is preferably an ultraviolet polymerization initiator that does not. In that case, since only the visible light polymerization initiator (B) can be selectively reacted by irradiation with visible light, for example, light having a wavelength range of 300 nm to 380 nm, primary curing only by visible light crosslinking is performed. be able to. At this time, since the ultraviolet polymerization initiator (A) is not photoexcited and does not contribute to the initiation of the primary curing reaction, the B stage state in which sufficient room for reaction by ultraviolet rays is left after the primary curing is performed. can do.
From this point of view, the ultraviolet polymerization initiator (A) is preferably one having a property in which radical generation is less likely to occur upon irradiation with light in a wavelength region with visible light (region having a wavelength of 380 nm or more). Specifically, those having a molar extinction coefficient at a wavelength of 365 nm of 10 or more are preferable.

  The ultraviolet polymerization initiator (A) is roughly classified into two types depending on the radical generation mechanism in the (meth) acrylic acid ester or vinyl ester system, and generates a radical by cleaving and decomposing the single bond of the photopolymerizable initiator itself. The “intramolecular cleavage type photopolymerizable initiator” (also referred to as “intramolecular cleavage type”), the photoexcited initiator and the hydrogen donor in the system form an exciplex, and the hydrogen of the hydrogen donor Can be broadly classified into “intermolecular hydrogen abstraction type photopolymerization initiator” (also referred to as “intermolecular hydrogen abstraction type”).

Among these, as the ultraviolet polymerization initiator (A), an intermolecular hydrogen abstraction type is particularly preferable.
The intermolecular hydrogen abstraction type can be reused as a reaction initiator because an initiator that has not reacted returns to the ground state even if excited once. For this reason, compared to the intramolecular cleavage type, the intermolecular hydrogen abstraction type tends to remain as an active species after the reaction. Therefore, it is suitable for use as a reaction initiator when ultraviolet light is applied after bonding and further crosslinking (secondary curing) is performed. In addition, the intermolecular hydrogen abstraction type is superior to the intramolecular cleavage type in that there are few decomposition products with a low molecular weight, and there are few outgases and elutions derived from the decomposition products.

The ultraviolet polymerization initiator (A) is preferably an ultraviolet polymerization initiator (A) having a molar extinction coefficient at a wavelength of 365 nm of 10 or more and a molar extinction coefficient at a wavelength of 405 nm of 0.1 or less. 2,2-dimethoxy-1,2-diphenylethane-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1- (4- (2 -Hydroxyethoxy) phenyl) -2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1- [4- {4- (2-hydroxy-2-methyl-propionyl) benzyl} phenyl] -2-methyl-propan-1-one, oligo (2-hydroxy-2-methyl-1- (4- (1-methylvinyl) phenyl) propanone), methyl phenylglyoxylic acid, 2-methyl-1- (4-Methylthiophenyl) -2-morpholinopropan-1-one Benzophenone, 4-methyl-benzophenone, 2,4,6-trimethylbenzophenone, 2,4,6-trimethylbenzophenone, 4-phenylbenzophenone, 3,3′-dimethyl-4-methoxybenzophenone, 4- (1,3 -Acryloyl-1,4,7,10,13-pentaoxotridecyl) benzophenone and the like. Any one of these or derivatives thereof may be used, or two or more of these may be used in combination.
Among them, benzophenone and its derivatives, which are intermolecular hydrogen abstraction type, are preferable because they have no decomposition products even after the reaction and are easily latent as reactive active species for bringing the composition into a B-stage state.

<Visible light polymerization initiator (B)>
The visible light polymerization initiator (B) is not particularly limited as long as it is a starting point for the polymerization reaction of the base resin by generating radicals by irradiation with visible light, for example, light having a wavelength range of 380 nm to 700 nm.
The visible light polymerization initiator (B) may generate radicals only by irradiation with visible light, or it may generate radicals by irradiation with light in a wavelength region other than the visible light region. May be.

  The visible light polymerization initiator (B) is preferably a photoinitiator having a molar extinction coefficient at a wavelength of 405 nm of 10 or more.

  The reactive radical generation mechanism of visible light polymerization initiators is broadly classified into two types: intramolecular cleavage type that cleaves and decomposes its own single bond to generate radicals, and radicals that excite hydrogen from hydroxyl groups in the system. Is classified into an intermolecular hydrogen abstraction type (also referred to as “hydrogen abstraction type”).

Of these, the intramolecular cleavage type is particularly preferable as the visible light polymerization initiator (B).
The intramolecular cleavage type decomposes when a radical is generated by light irradiation to form another compound, and once excited, it does not function as a reaction initiator. For this reason, when the intramolecular cleavage type is used as the visible light polymerization initiator (B) having an absorption wavelength in the visible light region, the adhesive sheet is 1 by irradiation with visible light compared to the case of using the intermolecular hydrogen abstraction type. After the subsequent crosslinking, a visible light reactive photopolymerization initiator (also referred to as “visible light curable photopolymerization initiator”) remains as an unreacted residue in the adhesive composition, and the adhesive sheet is expected. This is preferable because there is a low possibility of incurring aging and acceleration of crosslinking. Further, the coloring specific to the visible light curable photopolymerization initiator is also preferable because it becomes a reaction decomposition product, so that the visible light region absorption is eliminated and the color to be erased can be appropriately selected.

  The visible light polymerization initiator (B) is preferably a visible light polymerization initiator having a molar extinction coefficient at a wavelength of 405 nm of 10 or more and a molar extinction coefficient at a wavelength of 365 nm of 10 or more. Benzyl-2-dimethylamino-1- (4-morpholinophenyl) butan-1-one, 2- (4-methylbenzyl) -2-dimethylamino-1- (4-morpholinophenyl) butan-1-one, Bis (η5-2,4-cyclopentadiene-1-yl) -bis (2,6-difluoro-3- (1H-pyrrol-1-yl) phenyl) titanium, bis (2,4,6-trimethylbenzoyl) -Phenylphosphine oxide, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, thioxanthone, 2-chlorothioxanthone, 3-methylthioxanthone, 2,4-dimethylthioxone N-tone, 2-methylanthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 2-aminoanthraquinone, 1,2-octanedione, 1- (4- (phenylthio), 2- (o-benzoyloxime)), etc. Can be mentioned. Any one of these or derivatives thereof may be used, or two or more of these may be used in combination.

  Among these, bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide, 2,4,6-trimethylbenzoyl is an intramolecular cleavage type photopolymerization initiator, which becomes a degradation product after reaction and disappears. Diphenylphosphine oxide is preferable, and 2,4,6-trimethylbenzoyldiphenylphosphine oxide is more preferable from the viewpoint of solubility in the resin.

(Content of crosslinking initiator)
The content of the crosslinking initiator including the ultraviolet polymerization initiator (A) and the visible light polymerization initiator (B) is not particularly limited. As a guideline, 0.1 to 10 parts by weight, particularly 0.2 parts by weight or more and 5 parts by weight or less, particularly 0.5 parts by weight or more or 3 parts by weight or less, with respect to 100 parts by weight of the base resin constituting each layer. It is preferable to adjust the ratio. However, this range may be exceeded in balance with other elements.

  In the present adhesive resin composition 1, the content ratio of the ultraviolet polymerization initiator (A) and the visible light polymerization initiator (B) is 100 from the viewpoint that the physical property change before and after the secondary curing can be increased. : 1-1: 1, especially 50: 1 to 1.5: 1, more preferably 30: 1 to 2: 1. However, this range may be exceeded in balance with other elements.

The content ratio of the visible light polymerization initiator (B) in the outermost layer S2 to the content of the visible light polymerization initiator (B) in the intermediate layer S1 is preferably lower than 1, more preferably 0.5 or less. Particularly preferably, it is 0.3 or less.
The content ratio is preferable in that after the intermediate layer S1 is primarily cured with visible light, the outermost layer S2 can be in a B-stage state with sufficient room for ultraviolet reaction.

<Crosslinking agent (C)>
Depending on the type of the base resin, it is possible to perform crosslinking with visible light and crosslinking with ultraviolet light without a crosslinking agent. Therefore, what is necessary is just to add a crosslinking agent (C) as needed. However, it is preferable to contain a crosslinking agent from the viewpoint of increasing the change in physical properties before and after secondary curing.

As a crosslinking agent (C) mix | blended with this adhesive composition 1,2,3, for example, 1, 4- butanediol di (meth) acrylate, 1, 6-hexanediol di (meth) acrylate, 1,9- Nonanediol di (meth) acrylate, tricyclodecane dimethanol (meth) acrylate, bisphenol A polyethoxydi (meth) acrylate, bisphenol A polypropoxy di (meth) acrylate, bisphenol F polyethoxydi (meth) acrylate, ethylene glycol di (meth) Acrylate, trimethylolpropane trioxyethyl (meth) acrylate, tris (2-hydroxyethyl) isocyanurate tri (meth) acrylate, ε-caprolactone modified tris (2-hydroxyethyl) isocyanurate tri (meth) acrylate Rate, pentaerythritol tri (meth) acrylate, propoxylated pentaerythritol tri (meth) acrylate, ethoxylated pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, propoxylated pentaerythritol tetra (meth) acrylate, ethoxylated Pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, polyethylene glycol di (meth) acrylate, tris (acryloxyethyl) isocyanurate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate , Dipentaerythritol penta (meth) acrylate, tripentaerythritol hexa (meth) acrylate , Dipentaerythritol penta (meth) acrylate, neopentyl glycol di (meth) acrylate hydroxybivalate, di (meth) acrylate of ε-caprolactone adduct of neopentyl hydroxybivalate, trimethylolpropane tri (meta ) Acrylates, trimethylolpropane polyethoxytri (meth) acrylate, ditrimethylolpropane tetra (meth) acrylate and other UV curable polyfunctional monomers, as well as polyester (meth) acrylate, epoxy (meth) acrylate, urethane (meta And polyfunctional acrylic oligomers such as acrylate and polyether (meth) acrylate.
Among them, as a crosslinking monomer (crosslinking agent) used when crosslinking an acrylic ester (co) polymer in terms of reactivity and the strength of the obtained cured product, for example, it has 3 or more (meth) acryloyl groups. Polyfunctional (meth) acrylates are preferred.

Regarding the amount of the crosslinking agent (C), if the amount of the crosslinking agent is large, the reaction proceeds rapidly and it becomes difficult to control the reaction. Therefore, the amount of the crosslinking agent is adjusted so that the crosslinking can be stopped midway. preferable.
From this viewpoint, the amount of the crosslinking agent (C) is 0 to 30 parts by weight, particularly 20 parts by weight or less, especially 10 parts by weight or less, and especially 5 parts by weight or less, based on 100 parts by weight of the base resin constituting each layer. Is preferable.

<Tackifier (D)>
The present pressure-sensitive adhesive compositions 1, 2, and 3 may contain a tackifying resin tackifier (D) as necessary.
The tackifying resin (D) has an effect of adjusting the elastic modulus and glass transition temperature of the adhesive sheets 1 and 2 and adjusting the adhesive properties such as peeling force and tack. The peeling resistance shows a high value when the energy loss when the adhesive material is deformed at the time of peeling is highest, that is, near the dispersion peak of the Tan δ curve. In general, the pressure-sensitive adhesive composition has a Tanδ peak temperature lower than room temperature. Therefore, by adding the tackifying resin (D) to increase the glass transition temperature of the entire composition, it is only apparent from the room temperature to the high temperature range. Peel resistance can be increased.
Therefore, the tackifier resin (D) may be contained when it is desired to obtain an apparent peel resistance.

  The softening temperature of the tackifying resin (D) is preferably 60 ° C to 150 ° C, particularly preferably 60 ° C to 130 ° C. If the softening temperature is too high, the compatibility with the (meth) acrylic acid ester copolymer that is the adhesive main agent tends to be inferior. If the softening temperature is too low, it is difficult to obtain the effect of adjusting the adhesive properties. There is a risk of impairing the durability of the adhesive sheet in the environment.

  As a tackifying resin having a softening temperature of 60 ° C. to 150 ° C., styrene resin, rosin resin, terpene resin, and the like from the viewpoints of transparency, availability, compatibility with (meth) acrylate copolymer, and the like. Mention may be made of tackifying resins such as aliphatic hydrocarbon resins. One or two or more of these can be used in combination.

Among these, hydrogenated rosin ester resins are preferable from the viewpoint of heat yellowing and compatibility in a wide range of compounding ratios.
Hydrogenated rosin ester resins are available from Arakawa Chemical Co. (Pine Crystal), Pinova (Picolite), and the like.

<Others>
The pressure-sensitive adhesive compositions 1, 2, and 3 may contain known components blended in a normal pressure-sensitive adhesive composition as components other than those described above. For example, various additives such as an antioxidant, an anti-aging agent, and a hygroscopic agent can be appropriately blended as necessary.
Moreover, you may add reaction catalyst (A tertiary amine type compound, a quaternary ammonium type compound, a lauric acid tin compound, etc.) suitably as needed.

<Uses of the present adhesive sheets 1 and 2>
The adhesive sheets 1 and 2 are both transparent and have adhesiveness, and can be filled to every corner following the stepped portion of the bonding surface, so that the distortion generated in the adhesive sheet can be reduced. Further, the foaming resistance under high temperature and high humidity environment can be maintained without impairing the workability during handling. Therefore, for example, in an image display panel using an image display panel such as an LCD, PDP or EL, such as a personal computer, a mobile terminal (PDA), a game machine, a television (TV), a car navigation system, a touch panel, a pen tablet, etc. Can be suitably used for attaching a transparent panel such as a protective panel or a touch panel.

  For example, a display screen of a mobile phone employs a configuration in which a polarizing film or the like is laminated on a liquid crystal panel display (LCD), and a plastic protective panel is laminated thereon via an adhesive sheet. At this time, a concealing printing portion (thickness of about 5 μm to 80 μm) is attached to the rear surface of the protective panel, and the adhesive is placed in the corner of the stepped portion formed at the edge of the concealing printing portion. If the liquid does not enter sufficiently, bubbles remain and the visibility of the screen decreases.

  The adhesive sheets 1 and 2 can be applied without any bubbles remaining by filling the corners and filling the corners even if there are steps of about 50 to 80 μm as well as steps of about 5 to 20 μm. Can be worn. In addition, for example, it can be stuck so as not to foam even in a high temperature environment of about 85 ° C., and is extremely excellent in uneven followability. Therefore, the present adhesive sheets 1 and 2 can be suitably used for bonding an image display device constituent member having a stepped portion such as a high printing step or an uneven portion on the bonding surface.

Further, since the adhesive sheets 1 and 2 are excellent in shape retention and can be processed into an arbitrary shape in advance, it is preferable to cut them in advance according to the image display panel.
The cutting method at this time is generally punched with a Thomson blade, cut with a super cutter or laser, and half-cuts leaving either the front or back release film in a frame shape so that the release film can be easily peeled off. Is more preferable.

  More specifically, the present adhesive sheets 1 and 2 are used to directly bond the protective panel and the image display panel, or the touch panel body and the image display panel, or the touch panel body and the protective panel. Laminates or image display devices can be produced.

<Method for Producing Laminate for Constructing Image Display Device>
Next, an image display device constituting laminate having a constitution in which image display device constituting members are laminated on at least one surface of the present adhesive sheet 1 or 2 (referred to as “the present image display device constituting laminate”). The manufacturing method will be described.
The laminate for constituting the image display device has a structure in which the image display device constituting member is laminated on both surfaces of the adhesive sheet 1 or 2, and the image display device on one side of the adhesive sheet 1 or 2. It also includes a configuration in which constituent members are stacked and a release sheet or the like is stacked on the other surface.

The laminate for constituting an image display device can be manufactured through at least the following steps (1) and (2).
(1) By forming an uncrosslinked adhesive composition into a single-layer or multilayer sheet, irradiating the adhesive composition with visible light, and crosslinking the adhesive composition with visible light, B A step of forming the present adhesive sheet 1 or 2 in a stage state.
(2) An image display device constituent member is laminated on at least one surface of the B-stage state main adhesive sheet 1 or 2, and the transparent double-sided adhesive sheet is irradiated with ultraviolet rays through the image display device constituent member. And UV crosslinking.

(Process (1))
In the step (1), the present adhesive sheet 1 or 2 may be produced by the method described above. For example, the adhesive composition 1, 2, 3 in an uncrosslinked state is formed into a single-layer or multilayer sheet between two transparent release sheets, and visible through at least one transparent release sheet. What is necessary is just to irradiate the said adhesive composition with a light ray and to make the said adhesive composition crosslink visible light.
At this time, for example, the present adhesive compositions 1, 2, and 3 can be heated and melted (hot melt) and applied onto a transparent release resin sheet to form a single-layer or multilayer sheet.

When irradiating visible light, it is preferable to irradiate visible light which does not substantially contain light having a wavelength in the ultraviolet region, for example, light having a wavelength of less than 380 nm.
As described above, as a method of irradiating visible light that does not substantially include light having a wavelength in the ultraviolet region, a light source that emits only visible light that does not include light having a wavelength in the ultraviolet region may be used. You may make it irradiate through the filter which does not permeate | transmit the light of the wavelength of a area | region.
For example, a method of irradiating the adhesive composition with visible light through a transparent release sheet having a light transmittance at a wavelength of 380 nm of less than 10% and a light transmittance at a wavelength of 405 nm of 80% or more. be able to.
Note that the term “substantially not included” includes a case where light in the ultraviolet region is intentionally cut, so that it may be included to some extent. Therefore, it is intended to include such a case, for example, a wavelength region of 380 nm or more (for example, 410 nm) If the light intensity in the wavelength region of less than 380 nm (for example, 350 nm wavelength) is less than 10% with respect to the light intensity of the wavelength, it is not practically included.

  In step (1), in order to adjust the degree of visible light crosslinking, in addition to a method for controlling the amount of visible light irradiation, visible light is irradiated through a transparent release sheet, thereby reducing visible light transmission. It is also possible to adjust the degree of visible light crosslinking so as to block part.

  Here, as a transparent release sheet that can be used for such a purpose, that is, a transparent release sheet having a function of partially blocking the transmission of visible light, for example, a polyester-based, polypropylene-based, polyethylene-based cast film or stretched film. A film obtained by applying a silicone resin to a release treatment and the like can be appropriately selected and used, and in particular, release films having different peeling forces and release films having different thicknesses can be used.

  In addition, what is necessary is just to adjust suitably the thickness of a transparent double-sided adhesive sheet, the irradiation amount of visible light, an irradiation wavelength, an irradiation apparatus, etc.

(Process (2))
In the step (2), an image display device constituent member is laminated on at least one surface of the B-staged present adhesive sheet 1 or 2 obtained in the step (1), and the image display device constituent member is used to The transparent double-sided adhesive sheet is irradiated with ultraviolet rays to cause ultraviolet crosslinking.
In this way, the transparent double-sided adhesive sheet can be firmly cross-linked by irradiating the transparent double-sided adhesive sheet in the B stage state with ultraviolet rays through the image display device constituent member, The said transparent double-sided adhesive sheet can be firmly adhere | attached on the said image display apparatus structural member.

Here, examples of the image display device constituent member include a touch panel, an image display panel, a surface protection panel, a polarizing film, and the like, and any one of these or a laminate composed of a combination of two or more types. There may be.
As described above, the image display device constituting member may be laminated on one side of the adhesive sheet 1 or 2 and a release sheet or the like may be laminated on the other side.

In the step (2), it is necessary to irradiate ultraviolet rays through the image display device constituting member to cause an ultraviolet crosslinking reaction. For this purpose, the photoinitiator in the present adhesive sheets 1 and 2 must be excited, and a sufficient amount of light having a wavelength effective to generate radicals must be delivered. It is preferable that the image display apparatus constituent member when the adhesive sheet is irradiated with ultraviolet rays has a certain ultraviolet ray transmittance or more.
Specifically, for example, when a glass plate is laminated as an image display device constituent member on one side of the adhesive sheet 1 or 2 on the side irradiated with ultraviolet rays, the ultraviolet transmittance of the glass plate is not less than a certain value. Is preferred. For example, when a glass plate is laminated on one side of the adhesive sheet 1 or 2, and a protective sheet is laminated on the other side, the ultraviolet transmittance of at least either the glass plate or the protective sheet is high. It is preferable to be a certain value or more.
Therefore, when the transparent double-sided adhesive sheet is irradiated with ultraviolet rays through the image display device constituting member, the ultraviolet transmittance of the image display device constituting member, that is, the light transmittance in the wavelength range of 300 nm to 380 nm of the UV-A wave is 20. % Or more, preferably 30% or more, and more preferably 40% or more.

  Examples of the member having such light transmittance include those composed of polycarbonate resin, acrylic resin, polyvinyl chloride resin, polyester resin, cyclic polyolefin resin, styrene resin, and the like. According to the method for manufacturing a laminate for constituting an image display device of the present invention, since the plastic member can suppress foaming due to dimensional change due to temperature / humidity change and outgas emission and permeation, the resin member constituting the laminate In addition to the polycarbonate resin, acrylic resin and cyclic polyolefin resin, it can be used for resin members composed of triacetyl cellulose resin and the like.

(Laminated body for configuring the present image display device)
Examples of the image display device constituting member that can be used in the above manufacturing method include images such as a personal computer, a mobile terminal (PDA), a game machine, a television (TV), a car navigation system, a touch panel, a pen tablet, an LCD, a PDP, or an EL. The structural member of a display apparatus can be mentioned.

As a specific example, in an image display device for a mobile phone, a polarizing film or the like is laminated on a liquid crystal panel display (LCD), and a plastic protective panel is laminated thereon via an adhesive or a sheet. There is a case. At this time, PVA (polyvinyl alcohol) or triacetyl cellulose resin may be used as a constituent material of the polarizing film, and it has been found that these easily release outgas.
Therefore, if a laminate comprising the structure of the protective panel / the present adhesive sheet 1, 2 / polarizing film is produced, foaming by outgas emitted from the protective panel or the polarizing film even when used at high temperatures. Can be effectively suppressed.

  In addition, for example, release sheet / main adhesive sheet 1, 2 / touch panel, release sheet / main adhesive sheet 1, 2, protective panel, release sheet / main adhesive sheet 1, 2 / liquid crystal panel, liquid crystal panel / Adhesive sheet 1,2 / Touch panel, LCD panel / Adhesive sheet 1,2, Protective panel, Liquid crystal panel / Adhesive sheet 1,2 / Touch panel / Adhesive sheet 1,2 / Protective panel, Polarizing film / Adhesive sheets 1, 2 / touch panel, polarizing film / adhesive sheets 1, 2 / touch panel / adhesive sheets 1, 2 / protective panel, etc.

<Explanation of phrases>
In general, “sheet” refers to a product that is thin by definition in JIS, and whose thickness is small and flat for the length and width. In general, “film” is compared to the length and width. A thin flat product whose thickness is extremely small and whose maximum thickness is arbitrarily limited, and is usually supplied in the form of a roll (Japanese Industrial Standard JISK6900). However, since the boundary between the sheet and the film is not clear and it is not necessary to distinguish the two in terms of the present invention, in the present invention, even when the term “film” is used, the term “sheet” is included and the term “sheet” is used. In some cases, “film” is included.
In addition, the expression “panel” such as an image display panel and a protection panel includes a plate, a sheet, and a film.

In the present specification, when “X to Y” (X and Y are arbitrary numbers) is described, it means “preferably greater than X” or “preferably,” with the meaning of “X to Y” unless otherwise specified. The meaning of “smaller than Y” is also included.
Further, when described as “X or more” (X is an arbitrary number), it means “preferably larger than X” unless otherwise specified, and described as “Y or less” (Y is an arbitrary number). In the case, unless otherwise specified, the meaning of “preferably smaller than Y” is also included.

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

(Intermediate composition A)
Acrylate ester copolymer obtained by random copolymerization of 75 parts by mass of 2-ethylhexyl acrylate (Tg-70 ° C.), 20 parts by mass of vinyl acetate (Tg 32 ° C.) and 5 parts by mass of acrylic acid (Tg 105 ° C.) ( Mw: 400,000, Mn: 90,000, Mw / Mn: 4.4) 1 kg, UV-curable resin propoxylated pentaerythritol triacrylate (“ATM-4PL” manufactured by Shin-Nakamura Chemical Co., Ltd.) 250 g as a crosslinking agent, 3 g of 2,4,6-trimethylbenzoyldiphenylphosphine oxide (“Lucirin TPO” manufactured by BASF, 365 nm molar extinction coefficient 160, 405 nm molar extinction coefficient 60) as a visible light polymerization initiator, and 4 as an ultraviolet polymerization initiator -Methylbenzophenone (Lambson SpeedCureMBP, 365 nm molar extinction coefficient 30, 405 nm Le absorption coefficient 0.1 or less) were uniformly mixed with 10 g, the intermediate layer composition A was prepared.

(Intermediate layer composition B)
In the intermediate layer composition A, instead of 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 4-methylbenzophenone, UV polymerization initiator 4-methylbenzophenone (SpeedCureMBP manufactured by Lambson) was used as a photopolymerizable initiator. An intermediate layer composition B was prepared in the same manner as the intermediate layer composition A, except that 20 g of 365 nm molar extinction coefficient 30, 405 nm molar extinction coefficient 0.1 or less) was used.

(Intermediate layer composition C)
In the intermediate layer composition A, instead of 2,4,6-trimethylbenzoyldiphenylphosphine oxide and 4-methylbenzophenone, 2,4,6-trimethylbenzoyl as a visible light polymerization initiator was used as a photopolymerization initiator. An intermediate layer composition B was prepared in the same manner as the intermediate layer composition A except that 10 g of diphenylphosphine oxide ("Lucirin TPO" manufactured by BASF, 365 nm molar extinction coefficient 160, 405 nm molar extinction coefficient 60) was used.

(Adhesive layer composition A)
Acrylate ester copolymer obtained by random copolymerization of 75 parts by mass of 2-ethylhexyl acrylate (Tg-70 ° C.), 20 parts by mass of vinyl acetate (Tg 32 ° C.) and 5 parts by mass of acrylic acid (Tg 105 ° C.) ( Mw: 500,000, Mn: 90,000, Mw / Mn: 5.6) 1 kg, UV-curing resin propoxylated pentaerythritol triacrylate (“ATM-4PL” manufactured by Shin-Nakamura Chemical Co., Ltd.) as a crosslinking agent Then, 15 g of 4-methylbenzophenone (SpeedCureMBP manufactured by Lambson, 365 nm molar extinction coefficient 30, 405 nm molar extinction coefficient 0.1 or less) as an ultraviolet polymerization initiator was mixed to prepare an adhesive layer composition A.

(Adhesive composition B)
Acrylate ester copolymer (Mw: 350,000) obtained by random copolymerization of 69 parts by mass of butyl acrylate (Tg-55 ° C.), 30 parts by mass of vinyl acetate (Tg 32 ° C.) and 1 part by mass of acrylic acid (Tg 105 ° C.). , Mn: 70,000, Mw / Mn: 5.0) 1 kg, 70 g of propoxylated pentaerythritol triacrylate (“ATM-4PL” manufactured by Shin-Nakamura Chemical Co., Ltd.) as a crosslinking agent, and hydrogenated rosin resin as a tackifier (“Pine Crystal KR311” manufactured by Arakawa Chemical Co., Ltd .: softening temperature 77 ° C.) and 4-methylbenzophenone as an ultraviolet polymerization initiator (SpeedCureMBP manufactured by Lambson, 365 nm molar extinction coefficient 30, 405 nm molar extinction coefficient 0.1 or less) 20 g was mixed to prepare an adhesive layer composition B.

(Adhesive composition C)
Acrylate ester copolymer obtained by random copolymerization of 75 parts by mass of 2-ethylhexyl acrylate (Tg-70 ° C.), 20 parts by mass of vinyl acetate (Tg 32 ° C.) and 5 parts by mass of acrylic acid (Tg 105 ° C.) ( Mw: 400,000, Mn: 90,000, Mw / Mn: 4.4) 20 g per 1 kg of 4-methylbenzophenone 365 nm molar extinction coefficient 30, 405 nm molar extinction coefficient 0.1 or less) as an ultraviolet polymerization initiator By mixing, an adhesive layer composition C was prepared.

(Adhesive composition D)
In place of 4-methylbenzophenone in Adhesive Composition A, 2,4,6-trimethylbenzoyldiphenylphosphine oxide ("Lucirin TPO" manufactured by BASF), 365 nm molar extinction coefficient 160, 405 nm molar extinction was used as a photopolymerizable initiator. Adhesive composition D was prepared in the same manner as adhesive composition A except that 10 g of coefficient 60) was blended.

(Adhesive composition E)
Acrylate ester copolymer obtained by random copolymerization of 88 parts by mass of 2-ethylhexyl acrylate (Tg-70 ° C.), 11.5 parts by mass of acrylic acid (Tg 105 ° C.) and 0.5 parts by mass of 4-acryloyloxyethoxybenzophenone. The photopolymerization initiator 2,4,6-trimethylbenzoyldiphenylphosphine oxide ("Lucirin TPO" manufactured by BASF, for 1 kg of the union (Mw: 150,000, Mn: 50,000, Mw / Mn: 3.0), An adhesive layer composition E was prepared by adding 1 g of 365 nm molar extinction coefficient 160, 405 nm molar extinction coefficient 60).

<Example 1>
A UV cut polyethylene terephthalate film ("O700E100" manufactured by Mitsubishi Plastics) subjected to a peeling treatment (light transmittance at a wavelength of 380 nm was 0.7% and light transmittance at a wavelength of 405 nm was 87%) was produced.

Formed into a sheet by co-extrusion on one side of the release film treated to be peelable so that the adhesive layer composition A / intermediate layer composition A / adhesive layer composition A = 50 μm / 50 μm / 50 μm And the above-mentioned release film was laminated | stacked on the surface, and the laminated body was produced.
From both the front and back sides of the laminate, through a release film 1 and 2, a high-pressure mercury lamp is used to irradiate light with a high-pressure mercury lamp so that the integrated light quantity at a wavelength of 405 nm is 1000 mJ. A transparent double-sided adhesive sheet 1 (total thickness 150 μm) was produced. At this time, since light having a wavelength of 380 nm or less is blocked by the UV-cut polyethylene terephthalate film, only light (visible light) having a wavelength of 380 nm or more has reached the transparent double-sided PSA sheet.

<Example 2>
In Example 1, except that the adhesive layer composition B / intermediate layer composition A / adhesive layer composition B = 50 μm / 50 μm / 50 μm were coextruded and formed into a sheet shape, the same as in Example 1, A transparent double-sided adhesive sheet 2 (total thickness 150 μm) in a B-stage state was produced.

<Comparative Example 1>
Adhesive layer composition C / intermediate layer composition on one side of a release-treated polyethylene terephthalate film ("Bina 100GT" manufactured by Fujimori Kogyo Co., Ltd .: light transmittance at a wavelength of 365 nm of 87% and light transmittance at a wavelength of 405 nm of 90%) Product B / Adhesive layer composition C = Polyethylene terephthalate film coextruded to form 40 μm / 70 μm / 40 μm and formed into a sheet shape, and the surface was peeled off (“MRF75” manufactured by Mitsubishi Plastics, Inc .: light transmittance at a wavelength of 365 nm A laminate was prepared by laminating 88% and a light transmittance of 90% at a wavelength of 405 nm.
A transparent double-sided adhesive sheet 1 in a B-stage state is irradiated with a high-pressure mercury lamp through the polyethylene terephthalate film from both the front and back sides of the laminate so that the integrated light quantity at a wavelength of 365 nm is 1000 mJ, and is UV-crosslinked. A total thickness of 150 μm) was produced.

<Comparative example 2>
In Example 1, except that the adhesive composition D / intermediate composition C / adhesive composition D = 50 μm / 50 μm / 50 μm were coextruded and formed into a sheet shape in the same manner as in Example 1, but in the B-stage state. Transparent double-sided adhesive sheet 4 (total thickness 150 μm).

<Comparative Example 3>
A polyethylene terephthalate film (Mitsubishi Resin Co., Ltd.) formed by extruding into one side of the peeled polyethylene terephthalate film (“Bina 100GT” manufactured by Fujimori Kogyo Co., Ltd.) to form an adhesive composition D = 150 μm. “MRF75”) was laminated to prepare a transparent double-sided adhesive sheet 5 (total thickness 150 μm) before curing.

<Preparation of laminate for constituting image display device>
As an alternative member of an image display device constituent member having a high printing step, white printing with a width of 10 mm and a thickness of 80 μm is performed on a peripheral portion of 60 mm × 90 mm × thickness of 0.5 mm, and a peripheral portion of 80 μm. A glass substrate for evaluation formed with a printed level difference (light transmittance of 90% or more in a wavelength range of 300 nm to 380 nm) was produced.
And one peeling film of the transparent double-sided adhesive sheets 1-4 cut | judged to the predetermined | prescribed magnitude | size is peeled off, and pressure reduction (absolute pressure of 5 kPa) is performed so that the printed adhesive layer may be covered with the exposed adhesive surface. After heating to 80 ° C. and press-bonding, UV cross-linking is performed on the transparent double-sided adhesive sheets 1 to 4 through the glass substrate with a high-pressure mercury lamp so that the integrated light quantity at a wavelength of 365 nm is 1000 mJ. Thus, laminates 1 to 4 for constituting an image display device were produced.

<Evaluation>
The following evaluation was performed about the transparent double-sided adhesive sheets 1-5 obtained by the Example and the comparative example.

(Dynamic storage elastic modulus (E ′) at 60 ° C. obtained by the tensile method)
The dynamic storage elastic modulus (E ′) at 60 ° C. obtained by the tensile method was determined by cutting the transparent double-sided adhesive sheets 1 to 5 obtained in Examples and Comparative Examples into sample dimensions: width 4 mm × length 15 mm. Using a viscoelasticity measuring device (itkDVA-200, manufactured by IT Measurement Control Co., Ltd.), tensile mode: vibration frequency 1 Hz, measurement temperature: 0 ° C. to 100 ° C., temperature increase rate: 3 ° C./min, 60 ° C. The dynamic storage elastic modulus E ′ was measured by the tensile method in FIG.

(Dynamic storage elastic modulus (G ′) at 60 ° C. determined by the shear method)
The dynamic storage elastic modulus (G ′) at 60 ° C. obtained by the shearing method is a thickness of 1 mm to 2 mm using a plurality of transparent double-sided adhesive sheets 1 to 5 obtained in Examples and Comparative Examples. As a measurement sample, using a rheometer (“MARS” manufactured by Eihiro Seiki Co., Ltd.), a sticking jig: Φ25 mm parallel plate, strain: 0.5%, frequency The dynamic storage elastic modulus G ′ by a shear method at 60 ° C. was measured at 1 Hz, temperature: −50 to 200 ° C., and heating rate: 3 ° C./min.

(Evaluation of cutting processability and storage stability)
The transparent double-sided adhesive sheets 1 to 5 were cut with a 55 mm × 85 mm Thomson blade using a Thomson punching machine with the release film laminated. Immediately after cutting and after cutting 100 sheets, the shape of the edge was observed after storage for 1 week in a 25 ° C., 50% humidity environment.
Immediately after pasting or after storage, 10 or more pieces of glue protruding or crushed at the end were evaluated as “×”, and those having no glue protruding or crushed at the edge were “○”. It was determined.

(Printing level followability test)
As described above, when the laminates 1 to 4 for constituting an image display device were produced, the appearance of the laminates 1 to 4 was visually observed, and the transparent double-sided adhesive sheet was lifted or peeled near the printing step. “X” was evaluated, and “Δ” was evaluated when there was no streak or optical unevenness in the opening near the printing step, but “o” was evaluated when there was no lift or peeling.

(Foaming resistance test)
As an alternative member of an image display device constituent member having a high printing step, white printing with a width of 10 mm and a thickness of 80 μm is performed on a peripheral portion of 60 mm × 90 mm × thickness of 0.5 mm, and a peripheral portion of 80 μm. An evaluation glass substrate (light transmittance of 90% or more in the wavelength range of 300 nm to 380 nm of the opening) formed by forming a printing step was prepared.
In this way, 50 glass substrates for evaluation were prepared and printed on the transparent double-sided adhesive sheets 1 to 5 so that the ultraviolet rays of 365 nm reached 2000 mJ / cm 2 in the integrated light quantity through the printed glass substrates. A sample for foam resistance test was prepared by irradiation with ultraviolet rays.

Each sample was allowed to stand for one day in a normal state (temperature: 23 ° C., humidity: 50%), then cured for 6 hours in a thermostatic oven at a temperature of 85 ° C. and humidity of 25%, and the appearance after curing was visually observed.
The case where 5 or more new floats or foaming occurred after curing was evaluated as “×”, and the case where 5 sheets or less occurred but “△” was evaluated as “◯” when no new floatation or foaming occurred.

<Discussion>
Each of the adhesive sheets 1 and 2 (Examples 1 and 2) is a combination of a photopolymerization initiator (A) sensitive to visible light and a polymerization initiator (B) that reacts with ultraviolet rays. By adjusting the value of / G 'to 10 or more, it is possible to alleviate the distortion that occurs in the part in contact with the step part while having excellent cutting workability and storage stability, and to suppress the adverse effect on the optical characteristics I found out that Furthermore, since it can be set as the B stage state which left the room for ultraviolet crosslinking enough, the laminated body excellent in foaming-resistant reliability was obtained by irradiating with an ultraviolet-ray through a member after bonding.

Adhesive sheet 3 (Comparative Example 1) does not contain a visible light curable photopolymerization initiator (B), and is excellent in workability and storage stability by UV primary crosslinking. Since the fluidity at the time of bonding is impaired, the distortion that occurs in the portion in contact with the stepped portion cannot be sufficiently relaxed compared to the example of what can be bonded without bubbles to the printing step, and there is a slight amount near the uneven portion. As a result, uneven muscles were left.
Moreover, since the sensitivity of the secondary crosslinking reaction by ultraviolet rays is impaired by the primary crosslinking, the anti-foaming reliability was inferior to the examples.

  Adhesive sheet 4 (Comparative Example 2) contains only a visible light curable photopolymerization initiator, and the cross-linking reaction proceeds too much at the time of primary curing, so that flexibility at the time of bonding is impaired. As a result, the unevenness followability was poor. Moreover, there was hardly any room for secondary crosslinking, and foaming reliability was not obtained.

Since the adhesive sheet 5 (Comparative Example 3) has an E ′ / G ′ value of 10 or less, it is difficult to achieve both handleability and unevenness followability, and it has excellent flexibility and printing step uptake. It was inferior to workability. Further, since no primary cross-linking was performed, the entire sheet was prone to permanent deformation during storage, and the stability was poor.

Claims (9)

One or more (meth) acrylic acid ester (co) polymers, an ultraviolet polymerization initiator (A) having a molar extinction coefficient at a wavelength of 365 nm of 10 or more and a molar extinction coefficient at a wavelength of 405 nm of 0.1 or less; And a visible light polymerization initiator (B) having a molar extinction coefficient at a wavelength of 405 nm of 10 or more as a first feature,
The dynamic storage elastic modulus (E ′) at 60 ° C. determined by the tensile method is 1.0 × 10 ⁴ Pa to 6.6 × 10 ⁵ Pa, and the dynamic storage elastic modulus (G ′ at 60 ° C. determined by the shear method). ) Is 5.0 × 10 ² Pa to 1.0 × 10 ⁵ Pa, and the dynamic storage elastic modulus (E ′) at 60 ° C. determined by the tensile method is determined by the shear method. The second feature is that the value (E ′ / G ′) divided by the elastic modulus (G ′) is 10 or more and 100 or less ,
A transparent double-sided adhesive sheet that is in a B-stage state that remains visible-light-crosslinked and remains UV-crosslinkable, or in a B-stage state that remains UV-crosslinked and remains visible-light-crosslinkable .
  The transparent double-sided adhesive sheet according to claim 1, further comprising a polyfunctional (meth) acrylic ester resin (C) as a crosslinking agent.   The transparent double-sided adhesive sheet according to claim 1 or 2, further comprising a tackifier (D) containing a resin having a softening temperature of 60C to 150C. An intermediate layer S1 containing one or more (meth) acrylic acid ester (co) polymers and a visible light polymerization initiator (B) having a molar extinction coefficient of 10 or more at a wavelength of 405 nm;
One or more (meth) acrylic acid ester (co) polymers, an ultraviolet polymerization initiator (A) having a molar extinction coefficient at a wavelength of 365 nm of 10 or more and a molar extinction coefficient at a wavelength of 405 nm of 0.1 or less; An outermost layer S2 containing:
The transparent double-sided adhesive sheet according to any one of claims 1 to 3, wherein the transparent double-sided adhesive sheet according to any one of claims 1 to 3 is provided.   The (meth) acrylic acid ester (co) in the outermost layer S2 with respect to the mass part (intermediate Bm) of the visible light polymerization initiator (B) per 100 parts by mass of the (meth) acrylic acid ester (co) polymer in the intermediate layer S1 The transparent according to claim 4, wherein the ratio (outermost Bm / intermediate Bm) of the number of parts (outermost Bm) of the visible light polymerization initiator (B) per 100 parts by weight of the polymer is lower than 1. Double-sided adhesive sheet.   6. The ultraviolet polymerization initiator (A) is an intermolecular hydrogen abstraction type photoinitiator, and the visible light polymerization initiator (B) is a cleavage type photopolymerization initiator. The transparent double-sided adhesive sheet according to any one of the above.   An image display device constituent member is laminated on at least one side of the transparent double-sided adhesive sheet according to any one of claims 1 to 6, and the transparent double-sided adhesive sheet contains ultraviolet rays through the image display device constituent member. Is applied to the transparent double-sided adhesive sheet, and the laminate for image display device construction is provided with a construction obtained by ultraviolet crosslinking.   The image display device according to claim 7, wherein the image display device constituent member is a laminate formed of any one of a group consisting of a touch panel, an image display panel, a surface protection panel, and a polarizing film, or a combination of two or more types. Structural laminate.   The image display apparatus comprised using the laminated body of Claim 8.