TWI808307B - Electronic substrate and photocurable composition - Google Patents

Abstract

[Problem] Provide an electronic substrate having a flexible portion with excellent flexibility. [Solution] In an electronic substrate having a rigid substrate 12 and a flexible substrate 14 extending from the end of the rigid substrate 12 and capable of conductive connection, an elastic protection element is provided on at least one surface of the curved portion of the flexible substrate 14 from the end of the flexible substrate 14. 0~400μm electronic substrate.

Description

Electronic substrate and photocurable composition

The present invention relates to an electronic substrate having a flexible portion excellent in flexibility, and a photocurable composition excellent in flexibility and adhesion.

Electronic substrates having flexible parts generally use flexible substrates (including flexible printed circuits (Flexible Printed Circuits, hereinafter also referred to as “flexible substrates”)) as their flexible parts. A flexible substrate is known as a flexible substrate in which a metal conductor circuit such as copper foil is usually formed on a thin film of polyimide resin or polyester resin, and a cover film such as polyimide resin or polyester resin is used as a protective layer. For example, in Japanese Unexamined Patent Publication No. 7-106728 (Patent Document 1), a resin composition is used as a protective element for a connecting portion of a rigid portion and a flexible portion in a substrate having a rigid portion and a flexible portion.

In addition, electronic substrates having a rigid substrate and a flexible substrate disposed at the end of the rigid substrate are also used in image display devices such as liquid crystal display devices or plasma display devices, organic EL display devices, RGB inorganic LED mounted display devices, and the like. In this image display device, a panel as an image display part is used as a rigid substrate, and an electrically connected flexible substrate is provided at the end of the panel to apply voltage or signal to the panel. Here, an anisotropic conductive film is usually used for the connection between the panel and the flexible substrate, and a protective element for insulation protection or connection reinforcement is applied to the connection portion. Then, the other end portion of the flexible substrate is electrically connected to the circuit substrate (main board, etc.). Usually, since the circuit board is arranged on the inner surface of the panel, the flexible board extending from the panel is bent and connected to the circuit board. In recent years, the demand for miniaturization and narrower borders of image display devices has gradually increased. In order to save space in non-image display parts, the driver IC is not installed on the conventional panel, but a chip on film (chip on film) structure mounted on a flexible substrate.

Here, in order to control the bendability of the flexible substrate, Japanese Patent Application Laid-Open No. 2008-26528 (Patent Document 2) discloses that, in an image display device having a panel having an electrode lead-out portion, a flexible substrate connected to the electrode lead-out portion, and a protective layer covering the connection between the flexible substrate and the electrode lead-out portion, the wettability of the resin material on the flexible substrate is changed. With the above-mentioned composition, when the resin material is applied to the above-mentioned flexible substrate, there are regions where the resin material is stable and the protective layer is formed, and regions where the protective layer is not formed stably including the resin material. As a result, the flexible substrate is bent starting from the front end of the protective layer in the above-mentioned flexible substrate where the protective layer is formed, so that the region where the protective layer is formed can be controlled to a predetermined width. Therefore, the protrusion width of the bent portion of the flexible substrate protruding outward from the end of the panel can be controlled to be small. [Prior Technical Literature] 〔Patent Document〕

[Patent Document 1] Japanese Patent Application Laid-Open No. 7-106728 [Patent Document 2] Japanese Patent Laid-Open No. 2008-26528

[Problem to be solved by the invention]

Therefore, for image display devices, it is desired to achieve further miniaturization and narrower borders. Specifically, for a flexible substrate that is bent at an end portion of a rigid substrate constituting an image display device or the like, it is strongly required to further reduce the protrusion width of the above-mentioned bent portion. In response to such a requirement, although the above-mentioned technology minimizes the outer shape by controlling the outer shape of the protective layer, it becomes detrimental to the protective layer itself when narrowing the frame. Also, if the radius of curvature is forcibly reduced, the protective layer will be damaged or peeled off, making it difficult to reduce the protruding width of the above-mentioned bent portion.

The present invention was made in order to solve the above-mentioned problems. That is, the object is to provide an electronic substrate having a flexible portion excellent in flexibility and durability, and a photocurable composition used for the flexible portion excellent in flexibility and adhesion. 〔A means to solve a problem〕

An electronic substrate and a photocurable composition according to an aspect of the present invention that achieve the above object are as follows.

An electronic substrate according to an aspect of the present invention is an electronic substrate having a rigid substrate and a flexible substrate extending from the end of the rigid substrate and capable of conductive connection, wherein an elastic protection member is provided on at least one surface of the curved portion of the flexible substrate from the end of the flexible substrate. 400 μm. Since the protruding width of the bent portion of the flexible substrate protruding from the end of the rigid substrate is in the range of 100 to 400 μm, even if the flexible substrate is bent with a small radius of curvature from the end of the rigid substrate, since there is a set elastic protection element, it is difficult to cause a problem at the bent portion. As a result, compared with conventional ones, the protruding amount of the bent portion of the flexible substrate from the end of the rigid substrate is reduced and excellent in durability.

The Martens hardness (Martens hardness) of the elastic protection element measured by a nanoindentation (nanoindentation) test is 0.1-0.5 N/mm ² . Since the Martens hardness of the above-mentioned elastic protection element is in the range of 0.1-0.5N/ ^mm2 , the above-mentioned elastic protection element extending from the end of the rigid substrate to the flexible substrate has excellent flexibility. Compared with conventional ones, the radius of curvature of the flexible substrate becomes smaller when it is bent. Therefore, the protruding width of the bent portion of the flexible substrate protruding outward from the end of the rigid substrate (that is, the amount of protrusion of the flexible substrate from the end of the rigid substrate) is smaller than conventional ones, and excellent in durability.

The Young's modulus of the elastic protection element is preferably 0.1-3.0 MPa. Since the elastic protective element having the Young's modulus in the above-mentioned range has moderate hardness, the radius of curvature of the flexible substrate can be reduced compared with conventional ones. As a result, the protruding width of the bent portion of the flexible substrate protruding outward from the end of the rigid substrate can be reduced compared to conventional ones, and can be excellent in durability.

The peeling force F of the above-mentioned elastic protective member shows the relationship of the following formula (1). F＞100×ln(E)＋250・・・（1） In the formula, F: peeling force (N/m), E: Young's modulus (MPa) Since the peeling force F of the above-mentioned elastic protection element has the relationship of the above formula (1), when the flexible substrate is bent from the end of the rigid substrate, the protection element will not peel off from the rigid substrate and the flexible substrate compared with conventional ones, and the radius of curvature of the flexible substrate can be reduced. As a result, the protruding width of the bent portion of the flexible substrate protruding outward from the end of the rigid substrate becomes smaller than that of conventional ones, and can be excellent in durability.

The flexible substrate is a resin film having a thickness of 15 to 200 μm, and when the flexible substrate is bent, a wiring body is provided on at least one of the curved inner surface or the outer surface of the flexible substrate. The aforementioned resin film is, for example, a polyimide film or a polyester film. Even if the flexible substrate is a resin film having the above thickness, the protruding width of the bent portion of the flexible substrate can be made smaller than conventional ones. Furthermore, since the elastic protection element is provided on the curved inner surface of the flexible substrate, it is possible to suppress damage to the wiring body when the flexible substrate is bent with a reduced radius of curvature.

A photocurable composition according to an aspect of the present invention is a photocurable composition that is coated on an electronic substrate and cured by irradiation with light to form an elastic protective layer. It is characterized in that it contains a monofunctional alicyclic (meth)acrylate monomer, a monofunctional aliphatic (meth)acrylate monomer, a monofunctional highly polar monomer, a thermoplastic elastomer, and a radical polymerization initiator. The measured Martens hardness is in the range of 0.1 to 0.5 N/mm ² . The photocurable composition according to one aspect of the present invention contains the above-mentioned components and has an uncured viscosity within the above-mentioned range, so it is easy to precisely control the coating amount on the electronic substrate, and the coating workability is excellent. As a result, in addition to reducing the possibility of excessive coating on the electronic substrate, since the cured body has a Marker hardness in the above-mentioned range, there is no possibility that the hardened body hinders bending, and the flexible substrate can be bent with a small radius of curvature.

The peeling force F of the cured body after curing of the above-mentioned photocurable composition shows the relationship of the following formula (1). F＞100×ln(E)＋250・・・（1） In the formula, F: peeling force (N/m), E: Young's modulus (MPa) The peeling force F of the cured body of the photocurable composition after curing has the relationship of the above formula (1), and the cured body obtained by curing the photocurable composition has excellent adhesion and flexibility to rigid substrates and flexible substrates. Even if the flexible substrate is bent with a small radius of curvature, it is difficult to peel off, and the durability of the electronic substrate can be improved.

The peeling force F of the hardened body after hardening of the said photocurable composition shows the relationship of following (2) formula. F＜100×ln（E）＋760・・・（2） F: peel force (N/m) E: Young's modulus (MPa) The peeling force F of the cured body of the photocurable composition after curing has the relationship of the above formula (2), and the cured body obtained by curing the photocurable composition does not have more than necessary strong adhesion to the rigid substrate and the flexible substrate. Therefore, the durability of the electronic substrate against the deformation of the flexible substrate is improved, and it can be torn off from the substrate and has excellent repairability.

An electronic substrate according to an aspect of the present invention is formed by coating the photocurable composition described above on the boundary region between the rigid substrate and the flexible substrate. When hardening, a photocurable composition exhibiting moderate flexibility is applied to the above-mentioned cross-border region. Even compared with conventional ones, the protruding amount of the flexible substrate from the end of the rigid substrate becomes smaller, and the protective element is difficult to peel off from the rigid substrate and the flexible substrate. As a result, the protruding width of the bent portion of the flexible substrate protruding outward from the end of the rigid substrate becomes smaller than that of conventional ones, and can be excellent in durability. In addition, since the photocurable composition hardens both the rigid substrate and the flexible substrate by attaching them, peeling of the rigid substrate and the flexible substrate can be prevented, and moisture or foreign matter can be prevented from entering from the boundary between the rigid substrate and the flexible substrate. [Effect of the invention]

In the electronic substrate according to an aspect of the present invention, even if the protruding width of the bent portion of the flexible substrate protruding from the end of the rigid substrate is reduced, the protective element is not damaged or peeled off. Moreover, the photocurable composition of one aspect of the present invention has low viscosity when uncured, so it is easy to apply and has excellent workability, and the cured product after curing can exhibit desired hardness and durability and moderate flexibility.

[Form for implementing the invention]

〔Electronic substrate〕 One aspect of the present invention will be described in detail based on the embodiment. An electronic substrate 10 according to an embodiment of the present invention will be described using FIGS. 1 to 3 . An electronic substrate 10 according to an embodiment of the present invention, as shown in FIG. 1 , has a rigid substrate 12 and a flexible substrate 14 extending from the end of the rigid substrate 12 and capable of conductive connection. Moreover, the electronic substrate 10, as shown in FIG. Next, as shown in FIG. 3, when the flexible substrate 14 protrudes from the end of the rigid substrate 12 and bends toward one surface side of the rigid substrate 12, the protruding width 40 of the bent portion of the flexible substrate 14 protruding from the end of the rigid substrate 12 is 100 to 400 μm. From the viewpoint of miniaturization of devices using electronic substrates, when the flexible substrate 14 protrudes from the end of the rigid substrate 12 and bends toward one surface side of the rigid substrate 12, the protruding width of the bent portion of the flexible substrate 14 protruding from the end of the rigid substrate 12 is preferably 100 to 350 μm, more preferably 150 to 350 μm.

Since the protruding width 40 of the bending portion 16 of the flexible substrate 14 protruding from the end of the rigid substrate 12 is in the range of 100 to 400 μm, compared with conventional ones, the durability against deformation of the connecting portion of the rigid substrate 12 and the flexible substrate 14 can be maintained, and the space of the substrate can be saved. Therefore, when the electronic substrate 10 according to one embodiment of the present invention is used in an image display device, for example, the non-display portion of the panel can be further reduced, thereby achieving miniaturization or narrower frame of the image display device.

The electronic substrate 10 used in an image display device is taken as an example for description below with reference to FIGS. 2 and 3 . Therefore, the electronic substrate 10 according to an embodiment of the present invention is not limited to the electronic substrate described in FIGS. 1 to 3 . As shown in FIG. 2 and FIG. 3 , for example, electrodes of a rigid substrate 12 of a liquid crystal display panel or an LED mounting panel with various functional layers laminated on a glass substrate are electrically connected to a flexible substrate 14 through an anisotropic conductive film 15 . In more detail, in the case of a liquid crystal display panel, the rigid substrate 12 is formed by sequentially laminating a polarizer 12a, a glass substrate 12b with a first transparent electrode, a glass substrate 12d with a second transparent electrode, a liquid crystal layer 12c sandwiched between the first glass substrate 12b and second glass substrate 12d, a sealing material 13 for encapsulating liquid crystal, a polarizer 12e provided on the back side of the second glass substrate 12d, and a backlight element 12f. In the electronic substrate 10 of the present invention, the flexible substrate 14 is provided via the anisotropic conductive film 15 at the end of the glass substrate 12d with the second transparent electrode. Furthermore, in order to prevent short circuit or peeling of the anisotropic conductive film 15 , elastic protection members 20 a , 20 b are provided so as to cover the anisotropic conductive film 15 . Also, the structure of the electronic substrate 10 is not limited to the above-mentioned structure, and any structure may be used as long as the rigid substrate 12 is harder than the flexible substrate 14 . As an example, for example, glass epoxy resin substrates, phenol resin substrates, silicon substrates, ceramic substrates, etc. may be used. In the case of a TFT liquid crystal display, the glass substrate 12b with the first transparent electrode becomes the first transparent electrode and the glass substrate with the color filter, and the glass substrate 12d with the second transparent electrode becomes the second transparent electrode and the glass substrate with the TFT.

FIG. 2 is a partially enlarged cross-sectional view showing a state before bending the flexible substrate 14 . The photocurable composition to be described later is applied to at least one of the inner side or the outer side of the bending part 16 at the connecting part of the rigid substrate 12 and the flexible substrate 14, and is cured by, for example, ultraviolet rays to form the elastic protection elements 20a, 20b. On the side of the glass substrate 12b with the first transparent electrode, an elastic protective element 20a is provided to cover the front end of the glass substrate 12b with the first transparent electrode, the anisotropic conductive film 15, and a part of the cross-border region 30a of the flexible substrate 14. In this regard, on the side of the glass substrate 12d with the second transparent electrode, an elastic protective element 20b is provided to cover the front end of the glass substrate 12d with the second transparent electrode, the anisotropic conductive film 15, and a part of the cross-border region 30b of the flexible substrate 14. Therefore, the conduction connection just The flexible substrate 12 and the anisotropic conductive film 15 of the flexible substrate 14 are encapsulated via the elastic protection elements 20a, 20b.

Next, bend the flexible substrate 14 in the direction of the white hollow arrow shown in FIG. 2 , as shown in FIG. 3 . As shown in FIG. 3 , in the part where the flexible substrate 14 and the elastic protection elements 20a, 20b are formed, the flexible substrate 14 and the elastic protection elements 20a, 20b have a set thickness and flexibility, protrude from the end of the rigid substrate 12 and bend to form a bending part 16. During this bending, the distance from the bent portion 16 of the flexible substrate 14 protruding from the end of the rigid substrate 12 to the protruding end is referred to as the protruding width 40 . Therefore, as mentioned above, the protrusion width 40 is 100-400 μm, preferably 100-350 μm, more preferably 150-350 μm. Also, the end of rigid board 12 refers to the end that protrudes most in the bending direction in the area where flexible board 14 and rigid board 12 overlap when viewed from the front of rigid board 12 (that is, in plan view). On the other hand, the protruding end of the bent part 16 of the flexible substrate 14 refers to the protruding end of the flexible substrate 14 farthest from the end of the rigid substrate 12 in the same plan view as above, and shows the surface of the base material (resin film) of the outer flexible substrate 14 forming the bend. Here, the plan view is taken as an example, but the direction of observing the above-mentioned terminal portion and the protruding end is not limited to the surface side, and may be observed from the side, for example.

〈Flexible substrate〉

The flexible substrate 14 according to one embodiment of the present invention is a substrate formed of a resin film such as a polyimide film or a polyester film, and usually at least wiring is formed on the resin film. In the flexible substrate 14 according to one embodiment of the present invention, it is preferable to provide a wiring body on a polyimide film. In addition, the thickness of the flexible substrate 14 is preferably 15-200 μm. Due to the formation of the set elastic protection element, even if the flexible substrate 14 is a polyimide film with the above-mentioned thickness, the protruding width 40 of the bending portion 16 of the flexible substrate 14 can be reduced compared with conventional ones.

In addition, the flexible substrate 14 may have a photoresist layer outside the wiring. It is also possible to further mount electronic components to form a so-called chip on film. In this case, the above-mentioned electronic components are preferably arranged avoiding the most curved portion of the curved portion.

<Elastic Protective Element> The elastic protective element according to an embodiment of the present invention preferably has a Martens hardness of 0.1-0.5 N/mm ² as measured by a nanoindentation test. Since the Martens hardness of the above-mentioned elastic protection element is in the range of 0.1-0.5N/ ^mm2 , extending from the end of the rigid substrate to the flexible substrate, the above-mentioned elastic protection element not only has excellent flexibility, but also has elongation and compressibility, and can reduce the radius of curvature when bending the flexible substrate compared with conventional ones. More specifically, when the above-mentioned elastic protection element is disposed inside the flexible substrate, the elastic protection element can be compressed during bending to reduce the radius of curvature. On the other hand, when the above-mentioned elastic protection element is arranged outside the flexible substrate, the elastic protection element can be stretched with weak stress during bending, so that the radius of curvature can be reduced. Therefore, the protrusion width 40 (that is, the amount of protrusion of the flexible substrate from the end of the rigid substrate) of the bent portion of the flexible substrate protruding outward from the end of the rigid substrate can be reduced compared to conventional ones.

The aforementioned Martens hardness is preferably 0.1 to 0.3 N/mm ² . Using the elastic protective layer material having the above hardness, the radius of curvature can be reduced with weak stress. Therefore, the load on a flexible substrate or a rigid substrate is small, and it is suitable for a glass substrate or a thin substrate that is easily broken, for example. Also, when the above-mentioned Martens hardness is in the range of 0.3 to 0.5 N/mm ² , since the radius of curvature is reduced, the stress becomes larger, but it is resistant to high-strength friction, and is suitable for large-scale substrates or applications where shocks such as vibration are applied.

The Young's modulus of the elastic protective element according to an embodiment of the present invention is 0.1-3.0 MPa, preferably 0.1-1.0 MPa, more preferably 0.1-0.3 MPa. In addition, the measuring method of Young's modulus is mentioned later. Due to the use of the elastic protection element with the Young's modulus in the above range, it has proper hardness, so compared with the conventional one, the radius of curvature of the flexible substrate can be reduced. As a result, the protruding width of the bent portion of the flexible substrate protruding outward from the end of the rigid substrate can be made smaller than conventionally.

Therefore, in order to protect the flexible substrate, the elastic protective layer has a predetermined strength. At this time, if the strength of the elastic protective layer is excessively increased, it is understood that the elastic protective layer is easily peeled off from the flexible substrate when the flexible substrate is bent to form a predetermined protrusion width. The inventors of the present invention have worked hard to find that once the relationship between the strength (Young's modulus) of the elastic protective layer and the peeling force between the elastic protective layer and the flexible substrate is within the set range, even when the flexible substrate is bent to the set protrusion width, peeling will not occur. That is, the peeling force F of the above-mentioned elastic protection element to the flexible substrate can be expressed as the following formula (1). F＞100×ln(E)＋250・・・（1） In the formula, F: peeling force (N/m), E: Young's modulus (MPa) The above-mentioned peeling force F of the elastic protective element has the relationship of the above formula (1), when the flexible substrate is bent from the end of the rigid substrate, the protective element will not peel off from the rigid substrate and the flexible substrate compared with conventional ones, and the radius of curvature of the flexible substrate can be reduced. As a result, durability against deformation can be maintained, and at the same time, the protruding width of the bent portion of the flexible substrate protruding outward from the end of the rigid substrate can be made smaller than in the prior art. The method of measuring the peeling force will be described later.

The relationship between Young's modulus and peeling force described later is shown in FIG. 8 . This figure is a figure made according to a sample of an embodiment of the present specification. As shown in FIG. 8 , F=100×ln(E)+250 was obtained as a regression line for determining the durability against deformation. Since the peeling force F of the elastic protective element satisfies the condition of the above formula (1), when the flexible substrate is bent from the end of the rigid substrate, the protective element will not peel off, and the radius of curvature of the flexible substrate can be reduced compared with conventional ones. Furthermore, F=100×ln(E)+760 was obtained as a regression line for determining the pros and cons of repairability. Since the peeling force F of the elastic protection element satisfies the conditions of the above formula (2), it can have the desired hardness and adhesion, and can be torn off from the base material at the same time, and the process can be corrected (repaired). In the case of a peeling force exceeding this regression line, the adhesion of the elastic protection element to the flexible substrate is too strong, and the elastic protection element is broken when peeling is attempted, thus making it difficult to repair.

Furthermore, the elastic protection element of an embodiment of the present invention, as shown in FIG. 9 , has three preferred ranges. That is to say, for the elastic protection element of the present invention, Young's modulus E (MPa) is 1.0≦E≦3.0, peeling force F (N/m) is 250≦F≦800 range C is particularly preferred, Young's modulus E (MPa) is 0.3≦E≦1.0, peeling force F (N/m) is 140≦F≦740 range B, Young's modulus E (MPa) is 0.1≦E≦0.3, peeling force F (N/m) is more preferably in the range A of 80≦F≦550. Using an elastic protection element with the properties of the above-mentioned range C, the stress becomes larger due to the reduction of the radius of curvature, but it is resistant to high-strength friction, and is suitable for large-scale substrates or applications where shocks such as vibration are applied. On the other hand, using the elastic protective member having the properties of the above-mentioned range A, the radius of curvature can be reduced with weak stress. Therefore, the load on a flexible substrate or a rigid substrate is small, and it is suitable for a glass substrate or a thin substrate that is easily broken, for example. Therefore, especially in the case of high level, miniaturization, and common frame, it is better to have the properties of the range A. On the other hand, range B is an elastic protection element having intermediate properties, and is preferable from the viewpoint of being easy to use in a wide range of applications.

〔Photocurable composition〕 A photocurable composition according to an embodiment of the present invention is a photocurable composition that is coated on an electronic substrate and cured by irradiation with light to form a protective layer. It includes a monofunctional alicyclic (meth)acrylate monomer, a monofunctional aliphatic (meth)acrylate monomer, a monofunctional highly polar monomer, a thermoplastic elastomer, and a radical polymerization initiator. .0MPa range.

Here, "a monofunctional alicyclic (meth)acrylate monomer" means that a monofunctional alicyclic acrylate monomer and a monofunctional alicyclic methacrylate monomer are included. "Monofunctional aliphatic (meth)acrylate monomer" means a monofunctional aliphatic acrylate monomer and a monofunctional aliphatic methacrylate monomer. Similarly, "monofunctional highly polar monomers" means monofunctional highly polar acrylate monomers, monofunctional highly polar methacrylate monomers, and acrylamide monomers.

The photocurable composition according to one embodiment of the present invention contains the above-mentioned components and has an uncured viscosity in the above-mentioned range, which is easy to apply and has excellent workability. Since the cured body after curing has a Young's modulus in the above-mentioned range, the hardened body has desired flexibility. Furthermore, the cured body of the photocurable composition of the present invention can also be used as an elastic protection member for the above-mentioned electronic substrate 10 .

The photocurable composition according to one embodiment of the present invention has an uncured viscosity of 10 to 5000 mPa․ from the viewpoint of coatability s range, preferably 50-2000 mPa․ s range, more preferably 90~1000 mPa․ range of s. Especially in the case where a non-contact coating device such as a jet dispenser is used to apply a photocurable composition to a predetermined thickness on a predetermined area of a coating object with unevenness, the viscosity is 90 to 1000 mPa in order to control the coating amount with high precision․ s is preferred.

From the viewpoint of providing the desired flexibility of the cured body, the Young's modulus of the cured body of the photocurable composition after curing is in the range of 0.1 to 3.0 MPa, preferably in the range of 0.1 to 1.0 MPa, more preferably in the range of 0.1 to 0.3 MPa.

The peeling force F of the cured body of the photocurable composition after curing is expressed by the following formula (1). F＞100×ln(E)＋250・・・（1） In the formula, F: peeling force (N/m), E: Young's modulus (MPa) The peeling force F of the cured body of the photocurable composition after curing has the relationship of the above formula (1), and the cured body obtained by curing the photocurable composition has desired hardness and is excellent in durability.

The peeling force F of the cured body of the photocurable composition after curing is expressed by the following formula (2). F＜100×ln（E）＋760・・・（2） F: peel force (N/m) E: Young's modulus (MPa) The peeling force F of the hardened body of the above-mentioned photocurable composition after curing has the relationship of the above formula (2), and the hardened body obtained by curing the above-mentioned photocurable composition has desired hardness and adhesion, and can be peeled off from the substrate, and has excellent process correctability (repairability).

Furthermore, as shown in FIG. 9, the hardened body of the photocurable composition according to an embodiment of the present invention can be largely divided into three preferable ranges. That is, the above-mentioned hardened body of the present invention preferably has a Young's modulus E (MPa) of 1.0≦E≦3.0, a peeling force F (N/m) of 250≦F≦800 in the range C, a Young's modulus E (MPa) of 0.3≦E≦1.0, and a peeling force F (N/m) of 140≦F≦740. (N/m) is more preferably in the range A of 80≦F≦550. If an elastic protective element having a hardened body in the above-mentioned range C is formed, the radius of curvature decreases and the stress increases, but it is resistant to high-strength friction and is suitable for large-scale substrates or applications where shocks such as vibrations are applied. On the other hand, if an elastic protection member having a hardened body having properties in the above-mentioned range A is formed, the radius of curvature can be reduced with weak stress. Therefore, the load on a flexible substrate or a rigid substrate is small, and it is suitable for a glass substrate or a thin substrate that is easily broken, for example. Therefore, especially in the case of high level, miniaturization, and shared frame, it is better to have the properties of the range A. On the other hand, range B is a hardened body having intermediate properties, and is preferable from the viewpoint of being easy to use in a wide range of applications.

The content and components of the photocurable composition will be described below.

Monofunctional cycloaliphatic (meth)acrylate monomers: The monofunctional alicyclic (meth)acrylate monomer is a liquid composition and is a component for dissolving thermoplastic elastomers. Due to the preparation of the monofunctional alicyclic (meth)acrylate monomer, the adhesive force of the hardened body of the photocurable composition after curing can be improved, and the adhesive residue can be reduced when peeling off the hardened body from the adhered object. Also, it has the effect of making the hardened body tough and increasing the Young's modulus. Moreover, increasing the proportion of this component can improve moisture resistance.

Monofunctional alicyclic (meth)acrylate monomers, such as isobornyl acrylate, cyclohexyl acrylate, dicyclopentenyl acrylate, 3,3,5-trimethylcyclohexyl acrylate, 4-tertiary butylcyclohexyl acrylate, etc.

Monofunctional aliphatic (meth)acrylate monomers: The monofunctional aliphatic (meth)acrylate monomer is a liquid composition, which is a component for dissolving the above-mentioned monofunctional aliphatic (meth)acrylate monomer and thermoplastic elastomer. By blending the monofunctional aliphatic (meth)acrylate monomer, the flexibility of the hardened body obtained after curing the photocurable composition can be improved, and the Young's modulus can be reduced.

Monofunctional aliphatic (meth)acrylate monomers, for example, aliphatic ether (meth)acrylate monomers such as ethoxydiethylene glycol acrylate, 2-ethylhexyldiethylene glycol acrylate, and butoxyethyl acrylate, or aliphatic hydrocarbon (meth)acrylate monomers such as dodecyl acrylate, octadecyl acrylate, isostearyl acrylate, decyl acrylate, isodecyl acrylate, isononyl acrylate, and n-octyl acrylate. By using the aliphatic hydrocarbon (meth)acrylate monomer, the compatibility with the soft segment of the thermoplastic elastomer can be improved, and the viscosity of the photocurable composition can be reduced.

Monofunctional highly polar monomers: The monofunctional high polarity monomer is a liquid composition, and the adhesiveness of the hardened body obtained after the photocurable composition is cured can be improved by blending the monofunctional high polarity monomer.

Monofunctional highly polar monomers, for example, hydroxyl-containing acrylate monomers, glycidyl-containing acrylate monomers, acrylamide-based monomers, tertiary amine-containing (meth)acrylate monomers, and imide-based (meth)acrylate monomers. In the photocurable composition, nitrogen-containing monomers such as acrylamide-based monomers, tertiary amino group-containing (meth)acrylate monomers, and imide-based (meth)acrylate monomers are preferred from the viewpoint of storage stability and adhesion improvement. Examples include acryloyl morpholine, dimethylaminoethyl (meth)acrylate, and N-acryloyloxy ethyl hexahydrophthalimide.

The monofunctional highly polar monomer is preferably 0.5% by mass to 12.75% by mass, more preferably 2 to 8.5% by mass, in the photocurable composition from the viewpoint of adhesiveness. When it is less than 0.5% by mass, the peeling force is reduced and the deformation is large, and it is easy to peel off at the joint between the rigid substrate and the flexible substrate. When it is greater than 12.75% by mass, the compatibility with thermoplastic elastomers is reduced. Therefore, there are concerns from the viewpoint of storage stability such as easy increase in viscosity over time, and concerns that the moisture resistance of the hardened body will decrease due to the increase in highly polar segments. In the case of 2 to 8.5% by mass, since the viscosity is low and the change in viscosity is small, a photocurable composition with high adhesion can be obtained.

The effect of improving the above-mentioned adhesion becomes remarkable for a photocurable composition having a Young's modulus of 0.3 MPa or less. This is because the shearing force of the photocurable composition of 0.3 MPa or less tends to be weak, and only the monofunctional (meth)acrylate monomer tends to lower the adhesion.

The photocurable composition according to one embodiment of the present invention may further appropriately contain polyfunctional monomers such as polyfunctional aliphatic (meth)acrylate monomers, polyfunctional cyclic (meth)acrylate monomers, and bismaleimide. From the viewpoint of the strength of the hardened body of the photocurable composition after curing and the reactivity of the photocurable composition, one or more of polyfunctional aliphatic (meth)acrylate monomers, polyfunctional cyclic (meth)acrylate monomers, and bismaleimide are preferably present in the photocurable composition in an amount of 0% by mass to 4.25% by mass alone or in total. When it exceeds 4.25% by mass, the residual viscosity of the hardened body is small, but on the other hand, there is a possibility that the hardened body shrinks during hardening (warping) or increases in hardness.

The aforementioned polyfunctional aliphatic (meth)acrylate monomers are, for example, difunctional aliphatic (meth)acrylate monomers. Examples of the difunctional aliphatic (meth)acrylate monomers include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, glycerol di(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 3-methyl-1,5-pentanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, etc. From the viewpoint of high compatibility with the soft segment of the thermoplastic elastomer, a difunctional aliphatic hydrocarbon di(meth)acrylate monomer having reactive groups at both ends is preferable.

Specific examples of the above multifunctional cyclic (meth)acrylate monomers include ethoxylated bisphenol A di(meth)acrylate, propoxylated bisphenol A di(meth)acrylate, propoxylated ethoxylated bisphenol A di(meth)acrylate, ethoxylated isocyanurate di/tri(meth)acrylate, ε-caprolactone modified ginseng-(2-acryloxyethyl)isocyanurate, and the like. The polyfunctional cyclic (meth)acrylate monomer is preferably a ginseng-(2-hydroxyethyl)isocyanurate-based (meth)acrylate monomer from the viewpoint of improving adhesion.

The aforementioned bismaleimides, such as 4,4'-diphenylmethane bismaleimide, 4-methyl-1,3-phenylene bismaleimide, 2,2-bis[4-(4-maleiminophenol)phenyl]propane, bis(3-ethyl-5-methyl-4-maleiminophenyl)methane, 1,6-bis(maleimino)hexane , 1,6'-bismaleimido-(2,2,4-trimethyl)hexane. Aliphatic bismaleimides such as 1,6-bis(maleimido)hexane, 1,6'-bismaleimido-(2,2,4-trimethyl)hexane are preferable from the viewpoint of hardly impairing the compatibility and photocurability of the photocurable composition.

Thermoplastic Elastomers: Examples of the above-mentioned thermoplastic elastomer include styrene-based thermoplastic elastomers, olefin-based thermoplastic elastomers, ester-based thermoplastic elastomers, urethane-based thermoplastic elastomers, amide-based thermoplastic elastomers, vinyl chloride thermoplastic elastomers, fluororesin-based thermoplastic elastomers, ionomer-based thermoplastic elastomers, and the like. The thermoplastic elastomer of the present invention is preferably a styrene-based thermoplastic elastomer.

The styrene-based thermoplastic elastomer, any one of the above-mentioned monofunctional alicyclic (meth)acrylate monomer, the above-mentioned monofunctional aliphatic (meth)acrylate monomer, and the above-mentioned monofunctional high-polarity monomer dissolved in the photocurable composition. Therefore, the styrene-based thermoplastic elastomer can improve the repairability of the cured body after curing of the monofunctional alicyclic (meth)acrylate monomer, the monofunctional aliphatic (meth)acrylate monomer, and the monofunctional highly polar monomer, and reduce moisture permeability. In addition, the styrene-based thermoplastic elastomer is a component that dissolves in any of the above-mentioned monofunctional alicyclic (meth)acrylate monomer, the above-mentioned monofunctional aliphatic (meth)acrylate monomer, and the above-mentioned monofunctional high-polarity monomer, and provides the rubber elasticity (softness and elongation) of the hardened body. In one embodiment of the present invention, the dissolved state may be in a uniform liquid state, and may be white turbid or cloudy in other colors in addition to being colorless and transparent.

Styrene-based thermoplastic elastomers are solid when they are alone, and have no adhesiveness at room temperature. However, they can be uniformly dispersed in the photocurable composition and its hardened body by dissolving in the above-mentioned monofunctional alicyclic (meth)acrylate monomer, the above-mentioned monofunctional aliphatic (meth)acrylate monomer, and the above-mentioned monofunctional highly polar monomer, and can be included as a component of an adhesive photocurable composition.

The amount of the styrene-based thermoplastic elastomer added is preferably 10 to 35% by mass, more preferably 10 to 20% by mass, and more preferably 10 to 15% by mass in the photocurable composition. When the blending of the styrene-based thermoplastic elastomer is less than 10% by mass, the repairability may be lowered. On the other hand, when it exceeds 35 mass %, the viscosity of a photocurable composition may increase, and coating may become difficult. If it is 20 mass % or less, fluidity|fluidity will be suitable and coating will be easy.

Specific examples of styrene-based thermoplastic elastomers include styrene-butadiene-styrene block copolymer (SBS), styrene-isoprene-styrene block copolymer (SIS), styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), styrene-isobutylene-styrene block copolymer (SIBS), styrene-ethylene-ethylene-propylene-styrene block copolymer (SEEPS), and these of the modified body.

Among these, it is preferable to use SEBS, SEPS, and SIBS in which the soft segment does not have an unsaturated bond, because the cured product of the photocurable composition has excellent tolerance. In addition, among SEBS and SEPS, the one with a higher proportion of soft segment can improve the transparency of the hardened body. Specifically, it is preferable that the mass ratio of the soft segment is 80 to 95% by mass relative to the total mass of the thermoplastic elastomer. In this way, for example, the parallel light transmittance (wavelength 550 nm) of the elastic protection element with a thickness of 0.5 mm can be increased to more than 90%.

In this specification, the weight-average molecular weight of the styrene-based thermoplastic elastomer is measured using the GPC method (Gel Permeation Chromatography; gel permeation chromatography) based on a calibration curve (calibration curve) measured with standard polystyrene. In one embodiment of the present invention, it is preferable to use a styrene-based thermoplastic elastomer having a weight average molecular weight of less than 200,000 from the viewpoint of easy adjustment to a viscosity suitable for coating.

Free radical polymerization initiator: The radical polymerization initiator, specifically, is preferably a photoradical polymerization initiator that hardens a monofunctional aliphatic (meth)acrylate monomer, a monofunctional alicyclic (meth)acrylate monomer, and a monofunctional highly polar monomer, for example, by photoreaction with light. When the photocurable composition contains a photoradical polymerization initiator, by irradiating the photocurable composition with light, for example, the photocurable composition coated on the object to be coated can be photocured to form a coating film. The photoradical polymerization initiator may be, for example, photopolymerization initiators such as benzophenones, thioxanthenes, acetophenones, acylphosphines, oxime esters, and alkylphenols. The amount of the photoradical polymerization initiator added is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass, based on 100 parts by mass of the total content of all monomers including monofunctional groups and polyfunctional groups.

Other ingredients: In the photocurable composition of one embodiment of the present invention, other components such as various additives may be further appropriately formulated within a range not departing from the gist of one embodiment of the present invention. For example, thixotropic agents such as silica and alumina, plasticizers such as olefin oils and paraffin oils, silane coupling agents or polymerization inhibitors, defoamers, light stabilizers, antioxidants, antistatic agents, fillers, etc.

The above-mentioned embodiment is an example of one embodiment of the present invention, and within the range not departing from the gist of the present invention, the embodiment can be changed, or known techniques can be added or combined, and these techniques are also included in the scope of the present invention. [Example]

One embodiment of the present invention will be described in more detail below based on examples (comparative examples). The following photocurable compositions of Samples 1 to 29 and their hardened bodies were produced, and evaluated by the following evaluation methods.

〈Sample making〉 Make a sample as shown below.

Sample 1: Lauryl acrylate, isocamphoryl acrylate, N-acryloxyethylcyclohexanedimethylimide, and 1,9-nonanediol diacrylate were prepared as acrylate-based monomers. Next, thermoplastic elastomer SIBS (styrene-isobutylene-styrene block copolymer) (trade name "SIBSTAR102T", manufactured by Kaneka Co., Ltd.) was added to the above-mentioned monomer, and stirred for 24 hours to dissolve the thermoplastic elastomer in the above-mentioned monomer. The deployment ratio at this time is shown in Table 1. Next, with 100 parts by mass of the "resin component" composed of the above-mentioned monomer and thermoplastic elastomer, 0.40 parts by mass and 3.60 parts by mass of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide as a photoradical polymerization initiator and 2-hydroxy-2-methylpropiophenone were added to the resin component to obtain the photocurable composition of Sample 1.

The obtained photocurable composition of Sample 1 was irradiated with ultraviolet rays under the following conditions to form an elastic protective member of a cured body of Sample 1.

Samples 2 to 28: The photocurable compositions of samples 2 to 28 were prepared in the same manner as sample 1 except that the thermoplastic elastomer and monomers of sample 1 were changed to the types and formulations (parts by mass) listed in Tables 2 to 4. The photocurable compositions of samples 2 to 28 were similarly irradiated with ultraviolet rays to sample 1 to form elastic protective members of samples 2 to 28 on the polyimide film.

For sample 29, the product name "Loctite 3523" manufactured by Henkel Japan Co., Ltd., which is a photocurable composition mainly composed of a urethane methacrylate resin and a (meth)acrylate monomer, which does not contain a thermoplastic elastomer, was used.

The compositions and evaluation results of samples 1-29 are shown in Tables 1-4 below. The evaluation method will be described later.

[Table 1]

[Table 2]

[table 3]

[Table 4]

The raw materials used in Tables 1-4 are shown below. 〈Thermoplastic elastomer〉 SIBSTAR102T: trade name "SIBSTAR102T", styrene content 15% by mass, weight average molecular weight 90,000, styrene-isobutylene-styrene block copolymer, manufactured by Kaneka Co., Ltd. SIBSTAR103T: trade name "SIBSTAR103T", styrene content 30% by mass, weight average molecular weight 90,000, styrene-isobutylene-styrene block copolymer, manufactured by Kaneka Co., Ltd. SIBSTAR073T: Trade name "SIBSTAR073T", styrene content 30% by mass, weight average molecular weight 70,000, styrene-isobutylene-styrene block copolymer, manufactured by Kaneka Co., Ltd. SEPTON2063: trade name "SEPTON2063", styrene content 13% by mass, weight average molecular weight 120,000, styrene-ethylene-pentene-styrene block copolymer, manufactured by KURARAY Co., Ltd. EPFD AT501: trade name "EPFD AT501", styrene content 40% by mass, weight average molecular weight 90,000, epoxy-modified styrene-butadiene-styrene copolymer, manufactured by DIACEL Co., Ltd. Multifunctional Polymers> TE-2000: trade name "TE-2000", polybutadiene (acrylic group equivalent weight 2000) with methacrylic group introduced at the terminal, manufactured by Nippon Soda Co., Ltd.

<Various tests and evaluations>

Viscosity (mPa･s): The viscosity of the uncured photocurable composition was measured at 23° C. and 107 rpm using a rotational viscometer (Bohlin Instruments, Bohlin V88 Viscometer, Cone Plate “CP5°/30”).

Preserve stability: The photocurable composition was left to stand in an environment of 25° C. for 2 weeks, and the case where precipitation or separation could not be visually confirmed was rated as “A”, and the case where precipitation or separation was visually confirmed was rated as “B”.

Tensile elongation at break (%), tensile strength (MPa), 100% tensile elongation stress (MPa), and Young's modulus (MPa): The mechanical strength of the hardened body was measured in accordance with partially modified JIS K 6251:2010. Coat the photocurable composition with a thickness of 1mm on the polyester film treated with silicon release type, and use an LED with a wavelength of 365nm to irradiate with 200mW/ ^cm2 ultraviolet rays for 15 seconds to harden the photocurable composition. Tensile test was carried out at a speed of 200mm/min, and the tensile elongation at break (elongation at break), tensile strength (maximum tensile stress), 100% tensile elongation stress, and Young's modulus (elasticity) were measured. Apply the following formula (1), formula (2) and formula (3) respectively to calculate the tensile elongation at break, tensile strength, and 100% tensile elongation stress. The Young's modulus is obtained by dividing the tensile stress by the strain within the stretching ratio limit. TS＝Fm／S ・・・Formula (1) Eb＝(L1－L0)／L0×100 ・・・Formula (2) TS100＝F100／S ・・・Formula (3) TS: Tensile strength (MPa) Fm: Maximum tensile force (N) S: Initial cross-sectional area of the sample (mm ² ) Eb: Tensile elongation at break (%) L0: Initial distance between marking lines (mm) L1: Distance between marking lines at break (mm) TS100: 100% elongation tensile stress (MPa) F100: 100% elongation tension (N)

Martens Hardness (N/mm ² ): A nanoindentation test of the hardened body was performed using a nanoindenter (ENT-2100, manufactured by Elionix). The sample used was a hardened body prepared as follows: a photocurable composition was coated on a polyimide film with a thickness of 50 μm to a thickness of 100 μm, and the cured body was cured by irradiating ultraviolet rays with an illuminance of 200 mW/cm ² for 15 seconds using an LED with a wavelength of 365 nm. Next, using the aforementioned nanoindenter, the Martens hardness of the hardened body was measured under the conditions of a maximum indentation load of 0.1 mN and an indentation speed of 0.01 mN/sec. As a result, when the average value of the Martens hardness measured at 5 points is between 0.1 N/mm ² and 0.3 N/mm ² , it is rated as "A", when it is more than 0.3 N/mm ^{2 and less than 0.5 N/mm 2 , it is rated as "B", when it is more than 0.5 N/mm 2 and} 1.0 N/mm ² , it is rated as "C", and when it exceeds 1.0 N/ ^{mm 2 ,} it is rated as "D".

Moisture permeability (g/ ^m2・24hr): According to JIS Z0208: 1976, the resin composition is coated on a silicon release-treated polyester film with a thickness of 1mm, and the moisture permeability (water vapor transmission rate) of the hardened body is measured at a temperature of 40°C and a relative humidity of 90%RH using an LED with a wavelength of 365nm and irradiating with 200mW/ ^cm2 ultraviolet rays for 15 seconds to harden. In the measurement of water vapor transmission rate, if there is a case where the sample weight decreases, correct the decrease amount.

Volume resistivity (Ω・m): Volume resistivity was measured using a digital multimeter R6871E manufactured by ADVANTEST. A photocurable composition was coated on a silicon release-treated polyester film with a thickness of 100 μm, and the cured body was cured by irradiating with 200 mW/ ^cm2 ultraviolet rays for 15 seconds using an LED with a wavelength of 365 nm. The resistance value above the upper limit of the measurement was evaluated as "A", and the volume resistivity within the measurement range was recorded in the table.

Warpage: The photocurable composition was coated on a polyimide film with a thickness of 50 μm to a thickness of 100 μm, and cured by irradiating with 200 mW/cm ² ultraviolet rays for 15 seconds using an LED with a wavelength of 365 nm. Cut this hardened body into 20mm×60mm, and when one end of the long side is pressed, if the other end does not float, the evaluation is "A", and the evaluation is "B" if the other end is floating.

Peel force (N/m): Measured by partially modifying the 180-degree peel test method of JIS K 6852-2:1999. A photocurable composition was coated on a polyimide film with a thickness of 50 μm in a thickness of 1 mm. Using an LED with a wavelength of 365 nm, it was irradiated with 200 mW/cm ² ultraviolet rays for 15 seconds to harden, then cut into widths of 26 mm, and peeled off at a peeling speed of 300 mm/min and a peeling angle of 180 degrees to measure the peeling force (adhesion strength).

High temperature and high humidity resistance test: Coat the resin composition with a thickness of 1 mm on a polyimide film with a thickness of 50 μm, use an LED with a wavelength of 365 nm, irradiate it with 200 mW/cm ² ultraviolet rays for 15 seconds to harden, and cut into a width of 26 mm. When these were left under high temperature and high humidity at 85° C. and 85% RH for 1,000 hours, those without floating or peeling were evaluated as “A”, and those with visible floating or peeling were evaluated as “B”.

Repair test: On a polyimide film with a thickness of 50 μm, a resin composition was coated to form a thickness of 500 μm and a width of 2 mm, and was cured by irradiating with 200 mW/cm ² ultraviolet rays for 15 seconds using an LED with a wavelength of 365 nm. When the hardened body was peeled off from the polyimide film, the evaluation was "A" when it was peeled off without being cracked visually, and the evaluation was "B" when it could not be peeled off.

Bending test (inner side): FIG. 4 is an explanatory diagram of a measurement method of the bending test (inner side). The photocurable composition was coated on the polyimide film 50 with a thickness of 50 μm to a thickness of 100 μm, and cured by irradiating with 200 mW/cm ² ultraviolet rays for 15 seconds using an LED with a wavelength of 365 nm to obtain a cured body 56 . This cured body 56 is cut into 26 mm x 40 mm, and a double-sided adhesive tape 54 with a thickness of 50 μm is pasted on the end of the hardened body 56 in the range of 26 mm x 5 mm, and then attached to the end of the glass substrate 52 with a thickness of 1 mm to make a sample (S100). When the sample piece is bent toward the non-adhesive tape side of the glass substrate 52 with the hardened body 56 as the inner side with a load of 50 g (S102), the protrusion width 40 protruding from the end of the glass substrate 52 (that is, the "protrusion length" protruding from the end of the glass substrate 52) is measured (S104). If the protrusion width (protrusion length) is less than 400 μm, the evaluation is “A”, if it is more than 400 μm but less than 500 μm, it is evaluated as “B”, and if it is more than 500 μm, it is evaluated as “C”.

Bending test (outer side): FIG. 5 is an explanatory diagram of a measurement method of the bending test (outer side). The photocurable composition was coated on the polyimide film 50 with a thickness of 50 μm to a thickness of 100 μm, and cured by irradiating with 200 mW/cm ² ultraviolet rays for 15 seconds using an LED with a wavelength of 365 nm to obtain a cured body 56 . This cured body 56 is cut into 26 mm x 40 mm, and a double-sided adhesive tape 54 with a thickness of 50 μm is pasted on the end of the polyimide film 50 within a range of 26 mm x 5 mm, and attached to the end of the glass substrate 52 with a thickness of 1 mm to make a sample (S200). In the sample piece, when the polyimide film 50 is inside and the glass substrate 52 is bent toward the non-adhesive tape side with a load of 50 g (S202), the "protrusion length" protruding from the end of the glass substrate 52 is measured (S204). If the protrusion width 40 (extrusion length) is less than 400 μm, the evaluation is “A”, if it is more than 400 μm but less than 500 μm, it is evaluated as “B”, and if it is more than 500 μm, it is evaluated as “C”.

Bending resistance test: The bending resistance test will be described using FIGS. 6 and 7 . As shown in FIG. 6 , a photocurable composition was coated on a polyimide film 50 with a thickness of 50 μm to a thickness of 1 mm, and cured by irradiating ultraviolet light at 200 mW/cm ² for 15 seconds using an LED with a wavelength of 365 nm to obtain a cured body 56 . Thereafter, as shown in FIG. 7 , this hardened body 56 was cut into 20 mm×100 mm, and a 1 kg hammer was attached to one end of the cut sample. From one end on the opposite side of the hammer, pinch 20mm and do 180. Back and forth bending test. That is, at a bend angle of 180°. , The radius of curvature is less than 10 mm. After the hardening body 56 is bent inside (the left side figure of FIG. 7 ), the state of the hardening body 56 being bent outside (the right side figure of FIG. 7 ) is 1 cycle, and the curved part is visually observed after 100 cycles. The evaluation benchmarks are as follows.

A: There is no crack and no peeling.

B: No cracks, but peeling.

C: There are cracks and no peeling.

D: There are cracks and peeling.

Light transmittance (%): For each sample, a pair of glass plates was prepared, one glass plate was coated with a photocurable composition, sandwiched by another glass plate, and hardened to a thickness of 0.5mm, and a sample piece was prepared in which the hardened body was sandwiched by a pair of glass plates. Here, the reason why the sample is sandwiched by glass plates is that the transmittance will be affected when the surface of the hardened body has diffuse reflection. Next, the parallel light transmittance (light transmittance) at a wavelength of 550 nm was measured for each sample sheet using an ultraviolet-visible spectrophotometer (“UV-1600” manufactured by Shimadzu Corporation).

Insulation reliability test: A JIS2-type comb-shaped substrate with copper wiring at a wiring interval of 0.318 mm is applied to a glass epoxy resin substrate with a resin composition at a thickness of 100 μm. Using an LED with a wavelength of 365 nm, irradiate with 200 mW/cm ² ultraviolet rays for 15 seconds to harden and make a sample. In an environment of 85° C. and 85% RH, a voltage of 50 V was applied to the substrate for 120 hours.

In all the above tests, the "thickness" of the photocurable composition is the thickness after hardening.

<Analysis of test results>

For samples 1-29, take Young's modulus on the abscissa and peel force on the ordinate, and plot the relationship between Young's modulus and peel force, as shown in Figure 8. Considering the results of the bending test (inner side), the bending test (outer side), and the bending resistance test, it can be seen from the graph in FIG. 8 that the peeling force F of the hardened body of the photocurable composition or the elastic protection member has the following relationship of (1). F＞100×ln(E)＋250・・・（1） In the formula, F: peeling force (N/m), E: Young's modulus (MPa)

Since the peeling force F of the above-mentioned elastic protection element has the relationship of the above formula (1), when the flexible substrate is bent from the end of the rigid substrate, the protection element will not peel off from the rigid substrate and the flexible substrate compared with conventional ones, and the radius of curvature of the flexible substrate can be reduced. As a result, the protruding width of the bent portion of the flexible substrate protruding outward from the end of the rigid substrate becomes smaller than that of conventional ones, and can be excellent in durability.

Also, for samples 1-29, take Young's modulus on the abscissa and peel force on the ordinate, and plot the relationship between Young's modulus and peel force, as shown in FIG. 8 . Considering the results of the repair test, it can be seen from the graph of FIG. 8 that the peeling force F of the hardened body of the photocurable composition has the relationship of the following formula (2). F＜100×ln（E）＋760・・・（2） F: peel force (N/m), E: Young's modulus (MPa)

The peeling force F of the cured body of the photocurable composition after curing has the relationship of the above formula (2), and the cured body obtained by curing the photocurable composition does not have more than necessary strong adhesion to the rigid substrate and the flexible substrate. Therefore, the durability of the electronic substrate against the deformation of the flexible substrate is improved, and it can be torn from the substrate and has excellent repairability.

Furthermore, for samples 1-29, take Young's modulus on the abscissa and peel force on the ordinate, and plot the relationship between Young's modulus and peel force, as shown in FIG. 9 . Considering the results of the bending test (inner side), bending test (outer side), and bending resistance test, it can be seen from the graph in Fig. 9 that the cured body of the photocurable composition has a Young's modulus E (MPa) of 1.0≦E≦3.0 and a peeling force F (N/m) of 250≦F≦800. The Young's modulus E (MPa) of 0.3≦E≦1.0 and the peeling force F (N/m) of 140≦F≦740 The range B is more preferable, and the range A in which the Young's modulus E (MPa) is 0.1≦E≦0.3 and the peeling force F (N/m) is 80≦F≦550 is more preferable. Using an elastic protection element with the properties of the above-mentioned range C, the stress becomes larger due to the reduction of the radius of curvature, but it is resistant to high-strength friction, and is suitable for large-scale substrates or applications where shocks such as vibration are applied. On the other hand, using the elastic protective member having the properties of the above-mentioned range A, the radius of curvature can be reduced with weak stress. Therefore, the load on a flexible substrate or a rigid substrate is small, and it is suitable for a glass substrate or a thin substrate that is easily broken, for example. Therefore, especially in the case of high level, miniaturization, and common frame, it is better to have the properties of the range A. On the other hand, range B is an elastic protection element having intermediate properties, and is preferable from the viewpoint of being easy to use in a wide range of applications. Also, the sample piece of sample 25 was hard and brittle, and the Young's modulus could not be measured. The specimens of samples 23 and 27 were cracked during peeling, and the peeling force could not be measured.

Viscosity: It was observed that the viscosity of samples 13, 18, 20, and 26 in which the concentration of the thermoplastic elastomer was 15% by mass or less and the sum of the monofunctional highly polar monomer and the polyfunctional monomer was 12.75% by mass or more was slightly higher. On the other hand, it can be seen that the remaining samples have low viscosity and are suppressed.

Martens hardness (N/mm ² ): For samples 1 to 29, the relationship between the Martens hardness and the peeling force can be seen. Considering the results of the bending test (inside), bending test (outside), and bending resistance test, it can be seen that the cured product of the light-curable composition has a Martens hardness of "A". In addition to flexibility, the value of the 100% tensile elongation stress is also small, and the elongation is excellent. ) are also small, which is better from these points of view.

In addition, when the Martens hardness is not less than 0.1 N/mm ² and not more than 0.3 N/mm ² , the peeling force F (N/m) is in the range of 80<F<556. When the Martens hardness is more than 0.3 N/mm ² and less than 0.5 N/mm ² , the peeling force F (N/m) is in the range of 200<F<896.

warping: Warpage was observed for samples 26, 28. Compared with other samples, it can be seen that samples 26 and 28 contain more polyfunctional monomers or polyfunctional polymers, and the Young's modulus is larger than 3 MPa.

Light transmittance (%): The light transmittance of sample 7 in which the mass ratio of the soft segment was 87% by mass of SEPS was 95%. On the other hand, the transmittance of the other samples was 86% or less, and the cured body was cloudy white, showing poor light transmittance.

Insulation reliability test: In all the photocurable compositions according to one embodiment of the present invention, no short circuit of copper wiring was observed. On the other hand, the surface of the copper wiring of sample 29 was discolored and turned brown.

10: Electronic substrate 12: Rigid substrate 12a: polarizer 12b: a glass substrate with a first transparent electrode 12c: liquid crystal layer 12d: a glass substrate with a second transparent electrode 12e: polarizer 12f: Backlight component 13: Encapsulation material 14: Flexible substrate 15: Anisotropic conductive film 16: Bending part 20a, 20b: Elastic protection elements 30a, 30b: Transboundary area 40: protruding width

[FIG. 1] is a perspective view of an electronic substrate according to an embodiment of the present invention. [FIG. 2] is a section along line II of FIG. 1, and is a partially enlarged sectional view illustrating the structure of the flexible substrate and the hardened body. [FIG. 3] is a partially enlarged sectional view taken along line II of FIG. 1 and illustrating a state in which the flexible substrate is bent. [ Fig. 4 ] is an explanatory diagram illustrating a bending test method in which the surface forming the hardened body functioning as an elastic protective member is turned inside, which is one of the evaluation methods of the examples in this specification. [ Fig. 5 ] is an explanatory diagram for explaining a bending test method in which the surface of the hardened body serving as an elastic protective element is turned outward by bending, which is one of the evaluation methods of the examples in this specification. [ FIG. 6 ] is a schematic structural diagram illustrating the structure of a sample piece in a bending resistance test, which is one of the evaluation methods of the examples provided in this specification. [ Fig. 7 ] is an explanatory diagram illustrating an outline of a bending resistance test. [FIG. 8] is a graph showing the relationship between the Young's modulus and the peeling force of the elastic protective member. [Fig. 9] is a graph showing the relationship between the Young's modulus and the peeling force of the elastic protection elements and the specified range.

10: Electronic substrate

12: Rigid substrate

14: Flexible substrate

16: Bending part

Claims (7)

An electronic substrate having a rigid substrate and an electronic substrate extending from the end of the rigid substrate and a flexible substrate that can be conductively connected, characterized in that an elastic protection element is provided from the end of the flexible substrate on at least one surface of the bending portion of the flexible substrate, and when the flexible substrate protrudes from the end of the rigid substrate and bends toward one surface side of the rigid substrate, the protrusion width of the bending portion of the flexible substrate protruding from the end of the rigid substrate is 100 to 400 μm, The above elastic protection element has a Martens hardness of 0.1-0.5 N/mm ² measured by a nano-indentation test. Such as the electronic substrate of claim 1, wherein the peeling force F of the above-mentioned elastic protection element shows the relationship of the following formula (1), F>100×ln(E)+250‧‧‧(1) In the formula, F: peeling force (N/m), E: Young’s modulus (MPa). The electronic substrate according to claim 1, wherein the flexible substrate is a resin film having a thickness of 15-200 μm, and when the flexible substrate is bent, a wiring body is provided on the curved inner surface of the flexible substrate. A photocurable composition, which is hardened by being coated on an electronic substrate and then irradiated with light to form an elastic protective layer, is characterized in that it contains a monofunctional alicyclic (meth)acrylate monomer, a monofunctional aliphatic (meth)acrylate monomer, a monofunctional highly polar monomer, a thermoplastic elastomer, and a radical polymerization initiator. The hardness is in the range of 0.1~0.5N/mm ² . As the photocurable composition of claim 4, wherein, the above photocurable composition The peeling force F of the hardened body after hardening shows the relationship of the following formula (1), F>100×ln(E)+250‧‧‧(1) In the formula, F: peeling force (N/m), E: Young’s modulus (MPa). Such as the photocurable composition of claim 4, wherein the peeling force F of the hardened body of the above photocurable composition shows the relationship of the following formula (2), F<100×ln(E)+760‧‧‧(2) F: peeling force (N/m) E: Young's modulus (MPa). The electronic substrate according to any one of claims 1 to 3, which is formed by coating the photocurable composition according to any one of claims 4 to 6 on the cross-border region between the above-mentioned rigid substrate and the above-mentioned flexible substrate.

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