JP7645622B2 - Dry Films and Laminates - Google Patents

Description

The present invention relates to a dry film, and more specifically, to a dry film that can be suitably used in the manufacture of glass substrate/resin layer laminates, etc., as a cover window for a flexible display element.

In the field of electronic devices such as display elements such as liquid crystal displays (LCDs) and organic light-emitting diode displays (OLEDs) and electronic paper, flexible panels that have flexibility are beginning to be adopted in addition to conventional flat panels. In particular, in recent years, there has been progress in the development of electronic devices equipped with foldable displays.

Instead of the conventional glass substrate, it has been proposed to use organic polymer materials such as polyimide for the cover windows of flexible devices such as those described above, and some of these have been put to practical use. However, these polymer materials are inferior in rigidity and hardness to glass substrates, and when used in flexible panels, they can cause wrinkles and kinks when repeatedly bent, and the surface can easily become scratched.

It has also been proposed to make the conventional glass substrate into an ultra-thin glass substrate of about several tens of microns, which would allow the display panel to maintain its flatness and luxurious feel while still being flexible. Although ultra-thin glass has a certain degree of bending radius, it has problems with low compressive strength and impact resistance, which are inherent properties of glass. As a result, in recent years, attempts have been made to use chemically strengthened ultra-thin glass.

However, although chemically strengthened ultra-thin glass is superior to ordinary ultra-thin glass in terms of compressive strength, bending strength, impact resistance, etc., it is inferior in puncture resistance (resistance to breakage when pressed with a sharp object), so in practice, a structure has been proposed in which the chemically strengthened ultra-thin glass is sandwiched between a protective film such as a polyester film, with a flexible adhesive in between.

Incidentally, in the technical field of display substrates, the use of composite substrates in which a polyimide resin layer is laminated onto a glass substrate has been proposed as a material that combines water vapor barrier properties with flexibility (for example, Patent Documents 1 to 3).

Special Publication No. 2002-534305 Special Publication No. 2015-533685 JP 2019-214159 A

For applications such as cover windows for displays used in flexible devices, laminates in which a resin film is laminated onto ultra-thin bendable glass have been proposed. However, as mentioned above, soft materials are used for the resin film or adhesive in terms of adhesion to the ultra-thin glass and shock absorption. Therefore, when used as a cover window, there are problems such as insufficient surface hardness, causing scratches and dents on the display surface, and loss of the texture such as flatness and luxurious feel that are advantages of using ultra-thin glass. In addition, there are problems such as the need for a process to bond the ultra-thin film and the resin film together via an adhesive, and the fact that a certain thickness is required to give the adhesive shock absorption properties, making it impossible to reduce the total thickness of the cover window.

In the course of intensive research into the above-mentioned problems, the inventors focused on polyimide, which has excellent transparency, and produced a laminate of a glass substrate/polyimide layer by applying polyimide varnish to a glass substrate and drying it. The inventors found that the laminate had both high surface hardness and high impact resistance. However, when they tried to produce a laminate of an ultra-thin glass substrate/polyimide layer in the same manner, the inventors noticed a new problem that the laminate curved due to drying shrinkage when drying the coating film of the polyimide varnish.
In order to prevent the laminate from curving, the inventors tried to make a polyimide varnish into a dry film and laminate a polyimide layer onto an ultra-thin glass substrate using the dry film, but they found that this resulted in a new problem in that sufficient adhesion between the polyimide layer and the ultra-thin glass substrate was not obtained. In particular, the adhesion was insufficient for fluorinated polyimides, which have excellent transparency.

The present invention was made in response to these problems, and its purpose is to provide a dry film that can easily and simply manufacture a glass substrate/resin layer laminate without using an adhesive, and that can provide a laminate that is free of curvature (warping) while maintaining texture such as flatness and a luxurious feel, has excellent adhesion between the glass substrate and the resin layer, and is also excellent in surface hardness and impact resistance.

The inventors of the present invention have further conducted intensive research in order to provide a dry film that can solve all of the above problems, and as a result have discovered that by combining a specific epoxy compound with a polyimide containing a certain amount of fluorine or less to form a resin layer in a dry film, the resulting glass substrate/resin layer laminate maintains texture such as flatness and a luxurious feel while also exhibiting excellent adhesion between the glass substrate and the resin layer, as well as excellent surface hardness and impact resistance. The present invention has been completed based on this discovery. That is, the gist of the present invention is as follows.

[1] A dry film comprising a substrate and a resin layer releasably provided on the substrate,
The resin layer comprises a polyimide having a fluorine content of 25% by mass or less, and an epoxy compound having an epoxy equivalent of 1000 g/eq or less and a molecular weight of 10,000 or less.
[2] The dry film according to [1], wherein the polyimide has a YI value of 5.0 or less when made into a single layer film having a thickness of 50 μm.
[3] The dry film according to [1] or [2], wherein the polyimide has a haze of 2.0 or less when made into a single layer film having a thickness of 50 μm.
[4] The dry film according to any one of [1] to [3], wherein the epoxy compound has a softening point of 150° C. or less.
[5] The dry film according to any one of [1] to [4], wherein the epoxy compound is contained in an amount of 1 to 50 mass% based on the total amount of solids in the resin layer.
[6] The dry film according to any one of [1] to [5], wherein the resin layer further contains a bluing agent.
[7] A laminate comprising a glass substrate and a resin layer provided in contact with one of the main surfaces of the glass substrate,
The resin layer is a laminate comprising a resin layer of the dry film according to any one of [1] to [6].
[8] The laminate according to [7], wherein the glass substrate is chemically strengthened glass.
[9] The laminate according to [7] or [8], which is used as a cover window of a flexible display element.
[10] A method for producing a laminate including a glass substrate and a resin layer provided on one of the main surfaces of the glass substrate so as to be in contact with the surface, comprising the steps of:
The dry film according to any one of [1] to [6] is attached to one of the main surfaces of a glass substrate so that the resin layer of the dry film is in contact with the main surface of the glass substrate;
peeling the base material from the dry film to form a resin layer on the glass substrate;
The resin layer is heated to a temperature equal to or higher than the softening point temperature of the epoxy compound.
A method for producing a laminate, comprising:

According to the present invention, by forming a dry film by combining a specific epoxy compound with a polyimide having a certain amount of fluorine or less to form a resin layer, it is possible to realize a dry film that, even when used as a laminate of a glass substrate/resin layer, maintains the texture such as flatness and a luxurious feel, is free of curvature (warping), has excellent adhesion between the glass substrate and the resin layer, and provides a laminate with excellent surface hardness and impact resistance.

1 is a schematic cross-sectional view showing an embodiment of a dry film according to the present invention; FIG. 4 is a schematic cross-sectional view showing another embodiment of the dry film according to the present invention. 1 is a schematic cross-sectional view showing an embodiment of a laminate according to the present invention. FIG. 4 is a schematic cross-sectional view showing another embodiment of a laminate according to the present invention. FIG. 4 is a schematic cross-sectional view showing another embodiment of a laminate according to the present invention.

[Dry film]
The dry film according to the present invention will be described with reference to the drawings. Fig. 1 is a schematic cross-sectional view showing one embodiment of the dry film according to the present invention. The dry film 1 according to the present invention includes a substrate 10 and a resin layer 20 provided on the substrate 10. In the present invention, in order to prevent dust or the like from adhering to the surface of the resin layer 20 when the dry film is formed, and in consideration of the handling of the dry film 1, a protective film 30 may be further provided on the surface of the resin layer 20 opposite to the surface that contacts the substrate 10, as shown in Fig. 2. Each component constituting the dry film according to the present invention will be described below.

<Substrate>
The substrate can be any substrate that can support the resin coating film when forming the resin layer described below, and can be suitably used, for example, a polyester film such as polyethylene terephthalate or polyethylene naphthalate, a polyimide film, a polyamideimide film, a polypropylene film, a polystyrene film, or other thermoplastic resin film. Among these, polyester films are preferred from the viewpoints of heat resistance, mechanical strength, handling, etc. A laminate of these films can also be used as the substrate.

In addition, from the viewpoint of improving mechanical strength, it is preferable that the thermoplastic resin film described above is a film that has been oriented uniaxially or biaxially.

The surface of the substrate on which the resin layer is to be formed may be subjected to a release treatment so that the resin layer can be easily peeled off from the substrate when the dry film is used. For example, a release agent such as wax, silicone wax, or silicone-based resin is dissolved or dispersed in an appropriate solvent to prepare a coating liquid, which is then applied to the substrate surface by a known method such as a coating method such as roll coating or spray coating, gravure printing, or screen printing, and then dried, thereby performing the release treatment.

The thickness of the substrate is not particularly limited, but is generally selected from the range of 10 to 150 μm depending on the application.

<Resin Layer>
The resin layer releasably provided on the above-mentioned substrate will be described. The resin layer contains polyimide and an epoxy compound as essential components. As described below, the dry film of the present invention is a coating film obtained by applying a resin composition containing polyimide and an epoxy compound to a substrate and drying it. Considering the practicality of the dry film, the coating film must be dried to the extent that the coating film is not sticky, i.e., to the extent that the tack is eliminated. However, the dried coating film (i.e., the resin layer) has almost no tack, and when the dry film is attached (laminated) to a glass substrate, the adhesion between the resin layer and the glass substrate, which is the adherend, is poor. In particular, fluorinated polyimide is known as a highly transparent polyimide that is preferably used for optical applications such as display elements, but when fluorinated polyimide is made into a dry film, the adhesion to the adherend is significantly reduced. In the present invention, by using a polyimide with a fluorine content of a certain value or less and using a specific epoxy compound in combination, the adhesion to the glass substrate, which is the adherend, can be improved even when the dry film is made. Below, the components constituting the resin composition according to the present invention will be described.

<Polyimide>
Polyimide has a structure represented by the following formula (1) in which polyamic acid, which is a reaction product of carboxylic anhydride and diamine, is imidized. The constitutional unit represented by formula (1) is a constitutional unit formed by the reaction of a tetracarboxylic acid compound with a diamine compound.

In the above formula (1), X's each independently represent a divalent organic group, preferably a divalent organic group having 4 to 40 carbon atoms, more preferably a divalent organic group having a cyclic structure having 4 to 40 carbon atoms. Examples of the cyclic structure include an alicyclic ring, an aromatic ring, and a heterocyclic structure.
The organic group may have a hydrogen atom substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, in which case the number of carbon atoms in the hydrocarbon group and the fluorine-substituted hydrocarbon group is preferably 1 to 8. However, even when fluorine-substituted, the fluorine content of the polyimide must be 25 mass% or less. When the fluorine content increases, the optical properties (light transmittance, YI value, haze) of the polyimide are improved, but the adhesion to the glass substrate cannot be maintained.
In an embodiment of the present invention, the polyimide may contain a plurality of types of X, and the plurality of types of X may be the same or different from each other.
Examples of X include groups represented by the following formulas, in which a hydrogen atom in each group is substituted with a methyl group, a fluoro group, a chloro group or a trifluoromethyl group, and a chain hydrocarbon group having 6 or less carbon atoms.

In the above formula, * represents a bond, and A ¹ , A ² and A ³ each independently represent a single bond, -O-, -S-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ -, -SO ₂ -, -CO- or N(Q)-, where Q represents a monovalent hydrocarbon group having 1 to 12 carbon atoms which may be substituted with a halogen atom.
As an example, A ¹ and A ³ are single bonds, -O- or -S-, and A ² is -CH ₂ -, -C(CH ₃ ) ₂ -, -C(CF ₃ ) ₂ - or SO ₂ -. The bonding positions of ^{A 1} and A ² to each ring, and the bonding positions of A ² and A ³ to each ring are each independently preferably meta or para positions to each ring, more preferably para positions.

で表される基がより好ましい。
また、Ａ^１、Ａ^２およびＡ^３は、積層体の表面硬度および柔軟性を高めやすい観点から、互いに独立して、単結合、－Ｏ－またはＳ－であることが好ましく、単結合またはＯ－であることがより好ましい。 Among the above groups, from the viewpoint of the surface hardness and bending resistance of the laminate, a group represented by the following formula:

A group represented by the following formula is more preferred.
From the viewpoint of easily increasing the surface hardness and flexibility of the laminate, A ¹ , A ² and A ³ are preferably each independently a single bond, —O— or S—, and more preferably a single bond or O—.

In a preferred embodiment of the present invention, at least a part of the multiple Xs in the above formula (1) are constitutional units represented by formula (2).

In formula (2), * represents a bond, R ¹ to R ⁸ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and the hydrogen atoms contained in R ¹ to R ⁸ each independently may be substituted with a halogen atom.

R ¹ to R ⁸ are each independently preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, more preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and the hydrogen atoms contained in R ¹ to R ⁸ may each independently be substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. R ¹ to R ⁸ are each independently more preferably a hydrogen atom, a methyl group, a fluoro group, a chloro group, or a trifluoromethyl group, from the viewpoint of the surface hardness, transparency, and bending resistance of the laminate, and particularly preferably R ¹ , R ³ , R ⁴ , R ⁵ , R ⁶ , and R ⁸ are hydrogen atoms, and R ² and R ⁷ are hydrogen atoms, methyl groups, fluoro groups, chloro groups, or trifluoromethyl groups, and particularly preferably R ² and R ⁷ are methyl groups or trifluoromethyl groups. However, the fluorine content of the polyimide as a whole must be 25% by mass or less.

In a preferred embodiment of the present invention, the structural unit represented by the formula (2) is a structural unit represented by the formula (3). That is, at least a part of the multiple Xs is a structural unit represented by the formula (3). In this case, the fluorine-containing skeleton increases the solubility of the polyimide in a solvent, and the storage stability of the polyimide-containing varnish is easily improved, and the viscosity of the varnish is easily reduced, and the coating property when the polyimide is made into a dry film is easily improved. In addition, the fluorine-containing skeleton improves the optical properties of the polyimide (total light transmittance, YI value, haze, etc.). However, from the viewpoint of adhesion to a glass substrate, the fluorine content of the polyimide as a whole needs to be 25% by mass or less.

In one embodiment of the present invention, X in the polyimide is preferably 30 mol% or more, more preferably 50 mol% or more, and even more preferably 70 mol% or more is represented by formula (2), particularly formula (3). When X in the polyimide within the above range is represented by formula (2), particularly formula (3), the solubility in a solvent is easily improved by the skeleton containing fluorine element, and the storage stability of the varnish containing the polyimide is easily improved, and the viscosity of the varnish is easily reduced, improving the coatability. In addition, the skeleton containing fluorine element also improves optical properties such as total light transmittance, YI value, and haze. The proportion of the structural unit represented by formula (2) or (3) of X in the polyimide can be measured using, for example, ¹ H-NMR, but it can also be calculated from the charging ratio of the raw materials.

In the above formula (1), Y represents a tetravalent organic group, preferably a tetravalent organic group having 4 to 40 carbon atoms, more preferably a tetravalent organic group having 4 to 40 carbon atoms and a cyclic structure. Examples of the cyclic structure include an alicyclic ring, an aromatic ring, and a heterocyclic structure. The organic group is an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group, and in that case, the number of carbon atoms in the hydrocarbon group and the fluorine-substituted hydrocarbon group is preferably 1 to 8.

In one embodiment of the present invention, the polyimide may contain multiple types of Y, which may be the same or different from one another. Y is preferably a group represented by the following formula. Examples of these exemplified groups include groups in which a hydrogen atom is substituted with a methyl group, a fluoro group, a chloro group, or a trifluoromethyl group; and tetravalent chain hydrocarbon groups having 6 or less carbon atoms.

In the above formula, * represents a bond, and ^B1 represents a single bond, -O-, -CH2-, _-CH2 -CH2-, -CH( _{CH3 )} -, -C(CH3) _2- , -C( _CF3 ) _2- , -Ar-, -SO2-, -CO-, _-O- Ar-O-, -Ar-O-Ar-, -Ar-CH2-Ar-, -Ar-C( _CH3 ) ₂ -Ar- or Ar _- SO2 _-Ar- . Ar represents an arylene _group having 6 to 20 carbon atoms in which a hydrogen atom may be substituted with a fluorine atom, and _a specific example is a phenylene group.

Among the above groups, from the viewpoint of the surface hardness and flex resistance of the laminate, groups represented by the following formulas are preferred: From the viewpoint of easily increasing the surface hardness and flex resistance of the laminate and easily reducing yellowness, they are preferably each independently a single bond, -O-, -CH ₂ -, -CH ₂ -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ - or C(CF ₃ ) ₂ -, more preferably a single bond, -O-, -CH ₂ -, -CH(CH ₃ )-, -C(CH ₃ ) ₂ - or C(CF ₃ ) ₂ -, and even more preferably a single bond, -C(CH ³ ) ₂ - or C(CF ₃ ) ₂ -.

In one embodiment of the present invention, at least a part of the Y's in formula (1) are structural units represented by the following formula (4). When at least a part of the Y's in formula (1) are groups represented by formula (4), the solubility of the polyimide in a solvent is increased, the viscosity of a varnish containing the polyimide is easily reduced, and the coatability is improved. In addition, the optical properties of the laminate are improved.

In formula (5), * represents a bond, R ⁹ to R ¹⁶ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or an aryl group having 6 to 12 carbon atoms, and the hydrogen atoms contained in R ⁹ to R ¹⁶ may each independently be substituted with a halogen atom. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.
From the viewpoint of easily improving the surface hardness, bending resistance, and optical properties of the laminate, R ⁹ to R ¹⁶ are more preferably each independently a hydrogen atom, a methyl group, a fluoro group, a chloro group, or a trifluoromethyl group, particularly preferably R ⁹ , R ¹⁰ , R ¹¹ , R ¹⁴ , R ¹⁵ , and R ¹⁶ are each a hydrogen atom, R ¹² and R ¹³ are each a hydrogen atom, a methyl group, a fluoro group, a chloro group, or a trifluoromethyl group, and particularly preferably R ¹² and R ¹³ are each a methyl group or a trifluoromethyl group.

In one embodiment of the present invention, the structural unit represented by the above formula (4) is preferably a group represented by the following formula (5). The fluorine-containing skeleton increases the solubility of the polyimide in a solvent, and the storage stability of the polyimide-containing varnish is easily improved, while the viscosity of the varnish is easily reduced, improving the coatability. In addition, the fluorine-containing skeleton improves the optical properties of the laminate.

In one embodiment of the present invention, preferably 50 mol % or more, more preferably 60 mol % or more, and even more preferably 70 mol % or more of Y in the polyimide is represented by formula (4), particularly formula (5). When Y in the polyimide within the above range is represented by formula (4), particularly formula (5), the solubility of the polyimide in a solvent is increased by the skeleton containing a fluorine element, the viscosity of a varnish containing a resin is easily reduced, and the processability of the resin layer is easily improved. In addition, the skeleton containing a fluorine element is easy to improve the optical properties of the laminate. It is preferable that 100 mol % or less of Y in the polyimide is represented by formula (4), particularly formula (5). Y in the polyimide may be formula (4), particularly formula (5). The ratio of the structural unit represented by formula (4) of Y in the polyimide can be measured using, for example, ¹ H-NMR, but it can also be calculated from the charging ratio of the raw materials.

The above-mentioned polyimide can contain, in addition to the constitutional unit represented by formula (1), a constitutional unit represented by formula (30) and/or a constitutional unit represented by formula (31).

In formula (30), Y1 is a tetravalent organic group, preferably an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Examples of ^Y1 include the above-mentioned preferred groups for Y. In one embodiment of the present invention, the polyimide may contain multiple types of ^Y1 , and the multiple types of ^Y1 may be the same or different from each other.

In formula (31), ^Y2 is a trivalent organic group, preferably an organic group in which a hydrogen atom in the organic group may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Examples of ^Y2 include a group in which one of the bonds of the above-mentioned preferred groups of Y is replaced with a hydrogen atom, and a trivalent chain hydrocarbon group having 6 or less carbon atoms. In one embodiment of the present invention, the polyimide may contain multiple types of ^Y2 , and the multiple types of ^Y2 may be the same or different from each other.

In formula (30) and formula (31), ^X1 and ^X2 are each independently a divalent organic group, preferably an organic group in which a hydrogen atom may be substituted with a hydrocarbon group or a fluorine-substituted hydrocarbon group. Examples of ^X1 and ^X2 include the preferred groups for X described above.

In one embodiment of the present invention, the polyimide comprises a constitutional unit represented by formula (1) and, optionally, a constitutional unit represented by formula (30) and/or formula (31). In addition, in terms of the optical properties, surface hardness and flex resistance of the laminate, the constitutional unit represented by formula (1) in the polyimide is preferably 80 mol% or more, more preferably 90 mol% or more, and even more preferably 95 mol% or more based on all constitutional units represented by formula (1) and, optionally, formula (30) and formula (31). In addition, in the polyimide, the constitutional unit represented by formula (1) is usually 100% or less based on all constitutional units represented by formula (1) and, optionally, formula (30) and/or formula (31). In addition, the above ratio can be measured, for example, using ¹ H-NMR, or can be calculated from the charging ratio of the raw materials.

In one embodiment of the present invention, from the viewpoint of adhesion between the resin layer and the glass substrate and the texture of the laminate, the polyimide may contain a structural unit represented by the following formula (40), in addition to the structural unit represented by formula (1) and, in some cases, the structural unit represented by formula (30) and/or formula (31).

In the above formula (40), * represents a bond, R ¹⁷ and R ¹⁸ are each independently a single bond, an alkylene group having 1 to 5 carbon atoms, or a divalent aromatic group having 6 or more carbon atoms, R ¹⁹ and R ²⁰ are each independently an alkyl group having 1 to 5 carbon atoms, R ²¹ and R ²² are each independently an aryl group having 4 to 10 carbon atoms, at least one of R ²³ and R ²⁴ is an alkenyl group having 2 to 10 carbon atoms, and m1, m2, and m3 are each independently an integer of 1 or more.

The repeating unit having the structure of the above formula (40) contains a repeating unit substituted with an alkyl group, a siloxane repeating unit substituted with an aryl group, and a siloxane repeating unit substituted with an alkenyl group, thereby improving the tensile modulus of the resin layer, improving the adhesion between the resin layer and the glass substrate, and improving the texture when formed into a laminate.

The order of the repeating units substituted with an alkyl group, the siloxane repeating units substituted with an aryl group, and the siloxane repeating units substituted with an alkenyl group can be changed as desired, and they may be positioned alternately.

In one embodiment of the present invention, in the structural unit represented by the above formula (40), R ¹⁷ and R ¹⁸ are each independently a single bond, an alkylene group having 1 to 5 carbon atoms, or a divalent aromatic group having 6 or more carbon atoms, preferably an alkylene group having 3 or more carbon atoms. In addition, R3 and R4 are each independently an alkyl group having 1 to 5 carbon atoms, preferably a methyl or ethyl group.
Furthermore, R ¹⁹ and R ²⁰ are each independently an aryl group having 4 to 10 carbon atoms, and preferably a phenyl group.
At least one of R ²¹ and R ²² is an alkenyl group having 2 to 10 carbon atoms, preferably an ethenyl or propenyl group, while the other one that is not an alkenyl group is an alkyl group having 1 to 5 carbon atoms.

In one embodiment of the present invention, in the structural unit represented by the above formula (40), m1, m2, and m3 are each independently an integer from 1 to 10; specifically, m1 is an integer from 3 to 9, m2 is an integer from 2 to 9, and m3 is an integer from 1 to 5.

In one embodiment of the present invention, the structural unit represented by the above formula (40) accounts for 5 mol % or more or 50 mol % or less, preferably 5 to 40 mol %, of the total units, from the viewpoint of the balance between heat resistance and adhesion.

The polyimide may contain halogen atoms such as fluorine atoms, which can be introduced, for example, by the above-mentioned fluorine-containing substituents, but the fluorine content of the polyimide must be 25 mass% or less. If the polyimide contains fluorine atoms, the optical properties (light transmittance, YI value, haze) of the resin layer are improved, but the adhesion to the glass substrate is reduced. The fluorine atom content in the polyimide is preferably 0 to 23 mass%, more preferably 0 to 20 mass%.

The imidization rate of the polyimide is preferably 90% or more, more preferably 93% or more, and even more preferably 96% or more. From the viewpoint of easily increasing the optical homogeneity of the laminate, it is preferable that the imidization rate is equal to or higher than the above lower limit. The upper limit of the imidization rate is 100% or less. The imidization rate indicates the ratio of the molar amount of imide bonds in the polyimide to twice the molar amount of the constituent units derived from the tetracarboxylic acid compound in the polyimide. In addition, when the polyimide contains a tricarboxylic acid compound, it indicates the ratio of the molar amount of imide bonds in the polyimide to the sum of twice the molar amount of the constituent units derived from the tetracarboxylic acid compound in the polyimide and the molar amount of the constituent units derived from the tricarboxylic acid compound. In addition, the imidization rate can be determined by IR method, NMR method, etc.

Polyimide can be produced, for example, using a tetracarboxylic acid compound and a diamine compound as the main raw materials. Note that a diisocyanate compound may be used instead of the diamine compound.

Examples of diamine compounds used in the production of polyimides include aliphatic diamines, aromatic diamines, diaminosiloxanes, and mixtures thereof. In this embodiment, "aromatic diamines" refers to diamines in which an amino group is directly bonded to an aromatic ring, and may contain an aliphatic group or other substituents in part of the structure. The aromatic ring may be a single ring or a condensed ring, and examples include a benzene ring, a naphthalene ring, an anthracene ring, and a fluorene ring, but are not limited to these. Of these, a benzene ring is preferable. Furthermore, "aliphatic diamines" refers to diamines in which an amino group is directly bonded to an aliphatic group, and may contain an aromatic ring or other substituents in part of the structure. Furthermore, "diaminosiloxanes" refers to compounds having an amino group at the end of a siloxane skeleton, and may be substituted in part of the structure with a hydrocarbon group.

Examples of aliphatic diamines include acyclic aliphatic diamines such as hexamethylenediamine, and cyclic aliphatic diamines such as 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)cyclohexane, norbornanediamine, and 4,4'-diaminodicyclohexylmethane. These can be used alone or in combination of two or more.

Examples of aromatic diamines include aromatic diamines having one aromatic ring, such as p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, m-xylylenediamine, p-xylylenediamine, 1,5-diaminonaphthalene, and 2,6-diaminonaphthalene, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, and 3,3'-diaminodiphenyl sulfone (sometimes abbreviated as 3,3'DDS), 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene (sometimes abbreviated as TPE-R), and 1,3-bis(3-aminophenoxy)benzene. Examples of aromatic diamines having two or more aromatic rings include aromatic diamines having two or more aromatic rings, such as bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2'-dimethylbenzidine, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl (sometimes referred to as TFMB), 4,4'-bis(4-aminophenoxy)biphenyl, 9,9-bis(4-aminophenyl)fluorene, 9,9-bis(4-amino-3-methylphenyl)fluorene, 9,9-bis(4-amino-3-chlorophenyl)fluorene, and 9,9-bis(4-amino-3-fluorophenyl)fluorene. These can be used alone or in combination of two or more.

The aromatic diamine is preferably 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenyl ether, 3,3'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone (3,3'DDS), 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene (TPE-R), 1,3-bis(3-aminophenoxy)benzene They are benzene (APB-N), bis[4-(4-aminophenoxy)phenyl]sulfone, bis[4-(3-aminophenoxy)phenyl]sulfone, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 2,2'-dimethylbenzidine, 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl (TFMB), and 4,4'-bis(4-aminophenoxy)biphenyl. These can be used alone or in combination of two or more.

Examples of diaminosiloxanes include 1,3-bis(3-aminopropyl)tetramethyldisiloxane, 1,3-bis(4-aminobutyl)tetramethyldisiloxane, α,ω-bis(2-aminoethyl)polydimethylsiloxane, α,ω-bis(3-aminopropyl)polydimethylsiloxane, α,ω-bis(4-aminobutyl)polydimethylsiloxane, α,ω-bis(5-aminopentyl)polydimethylsiloxane, α,ω-bis[3-(2-aminophenyl)propyl]polydimethylsiloxane, and α,ω-bis[3-(4-aminophenyl)propyl]polydimethylsiloxane. These can be used alone or in combination of two or more.

Among the above diamine compounds, from the viewpoint of the surface hardness, flexibility, and coloring degree (YI value) of the laminate, it is preferable to use one or more selected from the group consisting of aromatic diamines having a biphenyl structure, and among these, it is more preferable to use one or more selected from the group consisting of 2,2'-dimethylbenzidine, 2,2'-bis(trifluoromethyl)benzidine, 4,4'-bis(4-aminophenoxy)biphenyl, and 4,4'-diaminodiphenyl ether, and it is even more preferable to use 2,2'-bis(trifluoromethyl)-4,4'-diaminodiphenyl (TFMB).

From the viewpoint of flexibility of the laminate, it is preferable to use one or more selected from the group consisting of aromatic diamines having an ether bond, and among these, it is more preferable to use one or more selected from the group consisting of 4,4'-diaminodiphenyl ether, 1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene (TPE-R), and 1,3-bis(3-aminophenoxy)benzene (APB-N), and it is even more preferable to use 1,3-bis(4-aminophenoxy)benzene (TPE-R) and 1,3-bis(3-aminophenoxy)benzene (APB-N).

From the viewpoint of the transparency of the laminate, it is preferable to use one or more selected from the group consisting of aromatic diamines having sulfone bonds, and among these, it is more preferable to use one or more selected from the group consisting of 3,3'-diaminodiphenyl sulfone (3,3'DDS) and bis[4-(4-aminophenoxy)phenyl]sulfone, and it is even more preferable to use 3,3'-diaminodiphenyl sulfone (3,3'DDS).

Tetracarboxylic acid compounds used in the production of polyimides include aromatic tetracarboxylic acid compounds such as aromatic tetracarboxylic acid dianhydrides, and aliphatic tetracarboxylic acid compounds such as aliphatic tetracarboxylic acid dianhydrides. The tetracarboxylic acid compounds may be used alone or in combination of two or more. The tetracarboxylic acid compounds may be dianhydrides or tetracarboxylic acid compound analogs such as acid chloride compounds.

Specific examples of aromatic tetracarboxylic acid dianhydrides include non-condensed polycyclic aromatic tetracarboxylic acid dianhydrides, monocyclic aromatic tetracarboxylic acid dianhydrides, and condensed polycyclic aromatic tetracarboxylic acid dianhydrides. Examples of non-condensed polycyclic aromatic tetracarboxylic acid dianhydrides include 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride, 2,2',3,3'-benzophenone tetracarboxylic acid dianhydride, 3,3',4,4'-biphenyl tetracarboxylic acid dianhydride, 2,2',3,3'-biphenyl tetracarboxylic acid dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic acid dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, and 2,2-bis[4-(3,4-dicarboxyphenoxyphenyl)]propane dianhydride. (sometimes abbreviated as BisDA), 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (sometimes abbreviated as 6FDA), 1,2-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,2-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, 4,4'-(p-phenylenedioxy)diphthalic dianhydride, and 4,4'-(m-phenylenedioxy)diphthalic dianhydride. In addition, an example of a monocyclic aromatic tetracarboxylic dianhydride is 1,2,4,5-benzenetetracarboxylic dianhydride, and an example of a condensed polycyclic aromatic tetracarboxylic dianhydride is 2,3,6,7-naphthalenetetracarboxylic dianhydride.

Among the above, 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 2,2',3,3'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 2,2',3,3'-biphenyl tetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis(2,3-dicarboxyphenyl)propane dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxyphenyl)]propane dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA), 1,2-bis(2,3-dicarboxyphenyl)ethane dianhydride, 1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride, Examples of the dianhydride include 1,2-bis(3,4-dicarboxyphenyl)ethane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride, bis(3,4-dicarboxyphenyl)methane dianhydride, bis(2,3-dicarboxyphenyl)methane dianhydride, 4,4'-(p-phenylenedioxy)diphthalic dianhydride, and 4,4'-(m-phenylenedioxy)diphthalic dianhydride, and more preferably 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic dianhydride (6FDA), bis(3,4-dicarboxyphenyl)methane dianhydride, and 4,4'-(p-phenylenedioxy)diphthalic dianhydride. These can be used alone or in combination of two or more types.

Examples of aliphatic tetracarboxylic acid dianhydrides include cyclic or non-cyclic aliphatic tetracarboxylic acid dianhydrides. Cyclic aliphatic tetracarboxylic acid dianhydrides are tetracarboxylic acid dianhydrides having an alicyclic hydrocarbon structure, and specific examples thereof include cycloalkane tetracarboxylic acid dianhydrides such as 1,2,4,5-cyclohexane tetracarboxylic acid dianhydride, 1,2,3,4-cyclobutane tetracarboxylic acid dianhydride, and 1,2,3,4-cyclopentane tetracarboxylic acid dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride, 3,3',4,4'-dicyclohexyl tetracarboxylic acid dianhydride, and positional isomers thereof. These can be used alone or in combination of two or more. Specific examples of non-cyclic aliphatic tetracarboxylic acid dianhydrides include 1,2,3,4-butane tetracarboxylic acid dianhydride and 1,2,3,4-pentane tetracarboxylic acid dianhydride, and the like, and these can be used alone or in combination of two or more. Additionally, a combination of a cyclic aliphatic tetracarboxylic acid dianhydride and an acyclic aliphatic tetracarboxylic acid dianhydride may be used.

Among the above tetracarboxylic dianhydrides, from the viewpoints of high surface hardness, high transparency, high flexibility, high bending resistance, and low colorability of the laminate, 4,4'-oxydiphthalic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 2,2',3,3'-biphenyl tetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxyphenyl)]propane dianhydride, 3,3',4,4'-dicyclohexyl tetracarboxylic dianhydride, and mixtures thereof are preferred.

As the dicarboxylic acid compound used in the production of polyimide, terephthalic acid, 4,4'-oxybisbenzoic acid, or an acid chloride compound thereof is preferably used. In addition to terephthalic acid, 4,4'-oxybisbenzoic acid, or an acid chloride compound thereof, other dicarboxylic acid compounds may be used. Examples of other dicarboxylic acid compounds include aromatic dicarboxylic acids, aliphatic dicarboxylic acids, and acid chloride compounds and acid anhydrides related thereto, and two or more of them may be used in combination.
Specific examples include dicarboxylic acid compounds such as isophthalic acid, naphthalenedicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 3,3'-biphenyldicarboxylic acid, chain hydrocarbons having 8 or less carbon atoms, and compounds in which two benzoic acids are linked by a single bond, _-CH2- , -C( _CH3 ) _2- , _-SO2- or a phenylene group, as well as acid chloride compounds thereof. Specific examples are preferably 4,4'-oxybis(benzoyl chloride) and terephthaloyl chloride, and more preferably a combination of 4,4'-oxybis(benzoyl chloride) and terephthaloyl chloride.

The polyimide may be a product obtained by further reacting tetracarboxylic acid and tricarboxylic acid, as well as their anhydrides and derivatives, in addition to the tetracarboxylic acid compound, as long as the various physical properties of the laminate are not impaired. Examples of the tetracarboxylic acid include water adducts of the anhydrides of the tetracarboxylic acid compounds. Examples of the tricarboxylic acid compound include aromatic tricarboxylic acids, aliphatic tricarboxylic acids, and their related acid chloride compounds and acid anhydrides, and two or more of these may be used in combination. Specific examples include anhydrides of 1,2,4-benzenetricarboxylic acid; 2,3,6-naphthalenetricarboxylic-2,3-anhydride; and compounds in which phthalic anhydride and benzoic acid are linked by a single bond, -O-, -CH ₂ -, -C(CH ₃ ) ₂ -, -SO ₂ -, or a phenylene group.

In the production of polyimide, the amount of diamine compound, tetracarboxylic acid compound and/or dicarboxylic acid compound used can be appropriately selected according to the ratio of each of the desired structural units of the polyimide.

In the production of polyimide, the reaction temperature of the diamine compound, tetracarboxylic acid compound, and dicarboxylic acid compound is not particularly limited, but is, for example, 5 to 350°C, preferably 20 to 200°C, and more preferably 25 to 100°C. The reaction time is also not particularly limited, but is, for example, about 30 minutes to 10 hours. If necessary, the reaction may be carried out in an inert atmosphere or under reduced pressure. In a preferred embodiment, the reaction is carried out under normal pressure and/or an inert gas atmosphere with stirring. In addition, the reaction is preferably carried out in a solvent that is inert to the reaction.

The solvent is not particularly limited as long as it does not affect the reaction, but examples of the solvent include alcohol-based solvents such as water, methanol, ethanol, ethylene glycol, isopropyl alcohol, propylene glycol, ethylene glycol methyl ether, ethylene glycol butyl ether, 1-methoxy-2-propanol, 2-butoxyethanol, and propylene glycol monomethyl ether; ester-based solvents such as ethyl acetate, butyl acetate, ethylene glycol methyl ether acetate, γ-butyrolactone, γ-valerolactone, propylene glycol methyl ether acetate, and ethyl lactate; acetone, methyl ethyl ketone, cyclopentanone, cyclohexanone, 2-heptanone, Examples of suitable solvents include ketone-based solvents such as methyl isobutyl ketone and N-methyl-2-pyrrolidone; aliphatic hydrocarbon solvents such as pentane, hexane, and heptane; alicyclic hydrocarbon solvents such as ethylcyclohexane; aromatic hydrocarbon solvents such as toluene and xylene; nitrile-based solvents such as acetonitrile; ether-based solvents such as tetrahydrofuran and dimethoxyethane; chlorine-containing solvents such as chloroform and chlorobenzene; amide-based solvents such as N,N-dimethylacetamide and N,N-dimethylformamide; sulfur-containing solvents such as dimethylsulfone, dimethylsulfoxide, and sulfolane; carbonate-based solvents such as ethylene carbonate and propylene carbonate; and combinations (mixed solvents) thereof. Among these, amide-based solvents are preferably used from the viewpoint of solubility.

In the imidization step in the production of polyimide, imidization can be carried out in the presence of an imidization catalyst. Examples of the imidization catalyst include aliphatic amines such as tripropylamine, dibutylpropylamine, and ethyldibutylamine; alicyclic amines (monocyclic) such as N-ethylpiperidine, N-propylpiperidine, N-butylpyrrolidine, N-butylpiperidine, and N-propylhexahydroazepine; azabicyclo[2.2.1]heptane, azabicyclo[3.2.1]octane, azabicyclo[2.2.2]octane, and azabicyclo[3.2. 2] Alicyclic amines (polycyclic) such as nonane; and aromatic amines such as pyridine, 2-methylpyridine (2-picoline), 3-methylpyridine (3-picoline), 4-methylpyridine (4-picoline), 2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2,4-dimethylpyridine, 2,4,6-trimethylpyridine, 3,4-cyclopentenopyridine, 5,6,7,8-tetrahydroisoquinoline, and isoquinoline.

In addition, from the viewpoint of facilitating the imidization reaction, it is preferable to use an acid anhydride together with the imidization catalyst. Examples of the acid anhydride include conventional acid anhydrides used in imidization reactions, and specific examples thereof include aliphatic acid anhydrides such as acetic anhydride, propionic anhydride, and butyric anhydride, and aromatic acid anhydrides such as phthalic acid.

The polyimide may be isolated (separated and purified) by a conventional method, such as filtration, concentration, extraction, crystallization, recrystallization, column chromatography, or a combination of these. In a preferred embodiment, a large amount of alcohol such as methanol is added to a reaction solution containing a transparent polyamideimide resin to precipitate the resin, which is then isolated by concentration, filtration, drying, etc.

The weight average molecular weight (Mw) of the polyimide obtained as described above is preferably 30,000 to 1,000,000, more preferably 70,000 to 700,000, and even more preferably 100,000 to 500,000, from the viewpoints of solubility in a solvent when producing a dry film and surface hardness and flex resistance of the resin layer when using the dry film for optical applications. The weight average molecular weight (Mw) is a value measured by GPC (gel permeation chromatography) and calculated in terms of standard polystyrene.

When the polyimide used in the present invention is made into a single layer film having a thickness of 50 μm, the YI value of the single layer film is preferably 5.0 or less. By using a polyimide having a small YI value, a laminate produced using the dry film can be more suitably used as a cover window for a display for a flexible device. The YI value is more preferably 2.0 or less. In this specification, the YI value (yellowness index) means a value calculated based on the formula YI = 100 x (1.2769X - 1.0592Z) / Y by measuring the transmittance of light of 300 to 800 nm using an ultraviolet-visible-near infrared spectrophotometer in accordance with JIS K 7373:2006, determining the tristimulus values (X, Y, Z).

In addition, when the polyimide is made into a single layer film with a thickness of 50 μm, the haze of the single layer film is preferably 2.0 or less. In addition to the YI value, by using a polyimide with a small haze, a laminate produced using the dry film can be more suitably used as a cover window for a display for a flexible device. It is more preferable that the haze is 1.0 or less. In this specification, the haze means a value measured using a known turbidity meter in accordance with JIS K 7136:2000.

<Epoxy Compound>
The resin layer contains a specific epoxy compound in addition to the polyimide having a fluorine content of a certain value or less. The epoxy compound used in combination with the polyimide is an epoxy compound having an epoxy equivalent of 1000 g/eq or less and a molecular weight of 10,000 or less. By containing the specific epoxy compound in addition to the polyimide, the resin layer of the dry film can suppress the tack of the resin layer of the dry film at room temperature to improve the handling, while improving the adhesion to the adherend such as a glass substrate. The reason for this is not clear, but it is thought that the compatibility of the epoxy compound with the polyimide is good, and further, the epoxy compound reacts with a part of the amine or acid anhydride, which is the raw material of the polyimide, to show adhesion.

The epoxy equivalent refers to the total number of epoxy groups in an epoxy compound, and can be determined by the method described in JIS K7236.

Epoxy compounds that can be preferably used in the present invention are those that have an epoxy equivalent of 1000 g/eq or less and a molecular weight of 10,000 or less and can be used without particular limitation. For example, biphenyl type, bisphenol A type, bisphenol F type, dicyclopentadiene type, naphthalene type, and epoxy compounds having a triazine ring can be preferably used. Specifically, jER828, jER834, jER1001, and jER1004 manufactured by Mitsubishi Chemical Corporation, EPICLON840, EPICLON850, EPICLON860, and EPICLON1050 manufactured by DIC Corporation, Epotohto YD-011, YD-127, and YD-128 manufactured by Nippon Steel Sumitomo Chemical Co., Ltd., and A.E.R.330, A.E.R.331, and A.E.R. manufactured by Asahi Kasei Corporation. 661, A. E. R. bisphenol A type epoxy resins such as EPICLON 152 and EPICLON 165 manufactured by DIC Corporation, Epotohto YDB-400 and YDB-500 manufactured by Nippon Steel Sumitomo Chemical Co., Ltd., and Sumi-Epoxy ESB-400 and ESB-700 manufactured by Sumitomo Chemical Co., Ltd.; novolac type epoxy resins such as jER152 and jER154 manufactured by Mitsubishi Chemical Corporation, EPICLON N-730, EPICLON N-770, and EPICLON N-865 manufactured by DIC Corporation, YDCN-704 manufactured by Nippon Steel Sumitomo Chemical Co., Ltd., and EPPN-201, EOCN-1025, EOCN-1020, EOCN-104S, and NC-3000 manufactured by Nippon Kayaku Co., Ltd. epoxy resins; bisphenol F type epoxy resins such as EPICLON 830 manufactured by DIC Corporation, jER 807 manufactured by Mitsubishi Chemical Corporation, and Epotohto YDF-170 manufactured by Nippon Steel Sumitomo Chemical Co., Ltd. (all trade names); hydrogenated bisphenol A type epoxy resins such as Epotohto ST-2004, ST-2007, and ST-3000 (trade names) manufactured by Nippon Steel Sumitomo Chemical Co., Ltd.; glycidyl amine type epoxy resins such as jER 604 manufactured by Mitsubishi Chemical Corporation and Epotohto YH-434 manufactured by Nippon Steel Sumitomo Chemical Co., Ltd. (all trade names); alicyclic epoxy resins such as CELLOXIDE 2021P manufactured by Daicel Corporation (trade name); YL-933 manufactured by Mitsubishi Chemical Corporation, and T.E.N. manufactured by The Dow Chemical Company. trihydroxyphenylmethane type epoxy resins such as EPPN-501, EPPN-502 (all trade names); bixylenol type or biphenol type epoxy resins or mixtures thereof such as YX-4000 (all trade names) manufactured by Mitsubishi Chemical Corporation; bisphenol S type epoxy resins such as EBPS-200 manufactured by Nippon Kayaku Co., Ltd. and EXA-1514 (trade name) manufactured by DIC Corporation; bisphenol A novolac type epoxy resins such as jER157S (trade name) manufactured by Mitsubishi Chemical Corporation; tetrahydroxyphenylmethane type epoxy resins such as jERYL-931 (trade name) manufactured by Mitsubishi Chemical Corporation Phenylolethane type epoxy resins; heterocyclic epoxy resins such as TEPIC manufactured by Nissan Chemical Co., Ltd. (all trade names); tetraglycidyl xylenoylethane resins such as ZX-1063 manufactured by Nippon Steel Sumitomo Chemical Co., Ltd.; naphthalene group-containing epoxy resins such as ESN-190 and ESN-360 manufactured by Nippon Steel Chemical Co., Ltd. and HP-4032D and EXA-4710 manufactured by DIC Corporation; epoxy resins having a dicyclopentadiene skeleton such as HP-7200 and HP-7200H manufactured by DIC Corporation and XD-1000 manufactured by Nippon Kayaku Co., Ltd., but of course they are not limited to these. These epoxy resins can be used alone or in combination of two or more kinds.

Among the above epoxy compounds, those having a softening point of 150°C or less can be preferably used. As described later, when manufacturing a laminate using the dry film of the present invention, after forming a resin layer on a glass substrate, it is preferable to heat the resin layer at a predetermined temperature in order to improve the adhesion between the glass substrate and the resin layer, and the heating temperature at this time is preferably equal to or higher than the softening point temperature of the epoxy compound. Therefore, if the softening point temperature of the epoxy compound is too high, the components in the resin layer may be thermally deteriorated during the manufacturing of the laminate.

From the viewpoints of the transparency of the resin layer and adhesion to the adherend, the amount of the epoxy compound is preferably 1 to 50% by mass, and more preferably 3 to 40% by mass, of the non-volatile components in the resin composition used to form the resin layer.

<Solvent>
The resin composition preferably contains a solvent in consideration of the formability of the resin layer. The solvent may be any solvent capable of dissolving the polyimide and the epoxy compound, but from the viewpoints of the coatability of the varnish and the transparency of the resulting resin layer, a solvent containing at least one selected from the group consisting of an ester group, an ether group, a ketone group, a hydroxyl group, a sulfone group, and a sulfinyl group is preferred.

Examples of the solvent having an ester group include ester-based solvents such as methyl acetate, ethyl acetate, butyl acetate, and dimethyl carbonate.
Examples of the solvent having a cyclic ester group include lactone solvents such as γ-butyrolactone (GBL), δ-valerolactone, ε-caprolactone, γ-crotonolactone, γ-hexanolactone, α-methyl-γ-butyrolactone, γ-valerolactone, α-acetyl-γ-butyrolactone, and δ-hexanolactone.
Examples of the solvent having an ether group include tetrahydrofuran, dioxane, and dibutyl ether.
Examples of the solvent having a ketone group include ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone.
Examples of the solvent having a hydroxyl group include phenol-based solvents such as m-cresol.
Examples of the solvent having a sulfone group include methyl sulfone, ethyl phenyl sulfone, diethyl sulfone, diphenyl sulfone, sulfolane, bisphenol S, sorapsone, dapsone, bisphenol A polysulfone, and sulfolane.
Examples of solvents having a sulfinyl group include sulfoxide solvents, such as N,N-dimethylsulfoxide (DMSO).
In addition to the solvents listed above, amide solvents such as N-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), etc. can be used.

<Other ingredients>
The resin composition may contain any component other than those described above, such as a leveling agent for improving the coatability of the varnish when producing a dry film, a dispersant, a surfactant, a retardation regulator, an antioxidant, an ultraviolet inhibitor, a light stabilizer, a plasticizer, waxes, fillers, pigments, dyes, foaming agents, defoamers, dehydrating agents, antistatic agents, antibacterial agents, antifungal agents, etc. Among the above-mentioned colorants, the resin composition of the present invention preferably contains a bluing agent for improving the yellowish color derived from the polyimide.

Bluing agents are additives (dyes, pigments) that absorb light in the visible light range, for example, in the orange to yellow wavelength range, and adjust the hue. Examples include inorganic dyes and pigments such as ultramarine, Prussian blue, and cobalt blue, and organic dyes and pigments such as phthalocyanine-based bluing agents and condensed polycyclic bluing agents. The bluing agent is not particularly limited, but from the standpoint of heat resistance, light resistance, and solubility, condensed polycyclic bluing agents are preferred, and anthraquinone-based bluing agents are more preferred. The bluing agents may be used alone or in combination of two or more types.

Examples of condensed polycyclic bluing agents include anthraquinone-based bluing agents, indigo-based bluing agents, and phthalocyanine-based bluing agents. Among these, it is preferable to contain an anthraquinone-based bluing agent from the viewpoints of heat resistance, light resistance, and solubility.

From the viewpoint of maintaining a high total light transmittance of the resin layer when the resin layer is formed from the resin composition, it is preferable to keep the total amount (mixture amount) of the bluing agent used relatively small, and it is also preferable to use a small number of types of bluing agents. From the viewpoint of maintaining the total light transmittance while reducing the YI value, the content of the bluing agent is preferably 5 to 100 ppm, more preferably 10 to 70 ppm, based on the solid content of the resin composition.

<Resin Layer>
The resin layer can be formed by dissolving or dispersing the above-mentioned polyimide, epoxy compound, and any other component as required in a solvent to prepare a varnish, applying the varnish to a substrate to form a coating film, and then drying the coating film to remove the solvent. The coating process can be performed using various coating devices, and known coating methods such as spin coating, slit coating, slot die coating, and blade coating may be used.

There are no particular limitations on the drying process for the coating film as long as the temperature is such that the solvent evaporates, but from the perspective of obtaining a highly transparent resin layer, it is preferable to dry the coating film at 60 to 140°C for about 30 seconds to 30 minutes.

The thickness of the resin layer can be adjusted by the amount of varnish applied to the substrate, but in the present invention, from the viewpoint of achieving both adhesion to the glass substrate and surface hardness when formed into a laminate, it is preferably 5 to 25 μm, more preferably 10 to 20 μm. The total thickness of the glass substrate and the resin layer is preferably 30 to 135 μm, more preferably 30 to 100 μm.

When the resin layer is a single layer film having a thickness of 50 μm, the single layer film preferably has a total light transmittance of 88% or more. A total light transmittance of 88% or more allows the laminate to be suitably used as a cover window for a display for a flexible device. A total light transmittance of 90% or more is more preferable. In this specification, the total light transmittance means a value measured using a known turbidity meter in accordance with JIS K 7375:2008.

<Protective film>
In the dry film of the present invention, a protective film 30 may be further provided on the side of the resin layer 20 opposite to the side in contact with the substrate 10 as shown in FIG. 2 in order to prevent dust and the like from adhering to the surface of the resin layer and to improve handleability.

For example, polyester film, polyethylene film, polytetrafluoroethylene film, polypropylene film, surface-treated paper, etc. can be used as the protective film, but it is preferable to select a material such that the adhesive strength between the protective film and the resin layer is smaller than the adhesive strength between the substrate and the resin layer. In addition, in order to make it easier to peel off the protective film when using the dry film, the surface of the protective film that comes into contact with the resin layer may be subjected to a release treatment as described above.

The thickness of the protective film is not particularly limited, but is generally selected from the range of 10 to 150 μm depending on the application.

[Laminate]
The laminate according to the present invention will be described with reference to the drawings. FIGS. 3 to 5 are schematic cross-sectional views showing an embodiment of the laminate according to the present invention. As shown in FIG. 3, the laminate 2 according to the present invention includes a glass substrate 40 and a resin layer 20 provided on one of the main surfaces 40A of the glass substrate 40. According to an embodiment of the laminate according to the present invention, the laminate 2 may include a functional layer 50 on the outermost surface 20A of the resin layer as shown in FIG. 4. According to an embodiment of the laminate according to the present invention, the laminate 2 may include a support 60 on the other main surface 40B side of the glass substrate as shown in FIG. 5. Although not shown, in the embodiment shown in FIG. 5, the glass substrate 40 and the support 60 may be laminated via an adhesive. Hereinafter, each layer constituting the laminate according to the present invention will be described in detail.

<Glass substrate>
The glass substrate constituting the laminate of the present invention has a thickness of 25 to 100 μm. A glass substrate having a thickness of 25 to 100 μm can be used to form a laminate having bending resistance and impact resistance. The thickness of the glass substrate is preferably 30 to 70 μm from the viewpoint of achieving both manufacturing cost and bending resistance and impact resistance.

The glass substrate can be used without any particular restriction as long as it has the above thickness, but silicate glass or silica glass is preferred, and more preferably borosilicate glass, soda-lime glass, or aluminosilicate glass. Particularly preferred are chemically strengthened glass or alkali-free glass of these glasses. Chemically strengthened glass is a glass material obtained by chemically strengthening the above-mentioned glass material. The chemical strengthening treatment can be performed by a conventionally known method. For example, by immersing a glass substrate in a molten metal salt (e.g., potassium nitrate) containing a metal ion with a large ionic radius, the metal ion with a small ionic radius (typically Na ion or Li ion) in the glass substrate is replaced with a metal ion with a large ionic radius, and as a result, residual compressive stress can be generated on the surface of the glass substrate. Chemically strengthened glass has superior compressive strength, bending strength, and impact resistance compared to non-chemically strengthened glass. In addition, alkali-free glass refers to glass that does not substantially contain an alkali component (alkali metal oxide), specifically, glass with a weight ratio of the alkali component of 3000 ppm or less. The weight ratio of the alkali component is preferably 1000 ppm or less, more preferably 500 ppm or less, and most preferably 300 ppm or less.

The flexural modulus of the glass substrate is preferably 50 to 150 GPa, and more preferably 70 to 100 GPa. In this specification, the flexural modulus refers to the value measured at 25°C in accordance with JIS R 1602:1995.

The above-mentioned glass substrate may be a commercially available product, such as Dragontrail (registered trademark) (manufactured by AGC Inc.: material = aluminosilicate, containing silicon, thickness = 70 μm), SCHOTT AS 87 eco (manufactured by SCHOTT: material = aluminosilicate, thickness = 25 μm, 50 μm, 70 μm), SCHOTT Xensation (registered trademark) Up (manufactured by SCHOTT: material = aluminosilicate, thickness = 30 μm, 50 μm, 70 μm), D263 (registered trademark) Teco (manufactured by SCHOTT: material = borosilicate, thickness = 30 μm, 70 μm), G-Leaf (registered trademark) manufactured by Nippon Electric Glass Co., Ltd.: material = alkali-free glass, thickness = 50 μm, 100 μm), etc.

<Resin Layer>
The resin layer can be formed by using the above-mentioned dry film. Hereinafter, a method for forming a resin layer using the dry film of the present invention will be described. First, a dry film is attached to one of the main surfaces of a glass substrate so as to contact the resin layer of the dry film. If the dry film has a protective film, the protective film is peeled off from the dry film to expose the surface of the resin layer, and then the dry film is attached to the glass substrate.

The glass substrate and the dry film are preferably bonded under pressure and heat using a vacuum laminator or the like. By using such a vacuum laminator, the resin layer of the dry film and the glass substrate can be bonded together without air bubbles being trapped between them. The pressure conditions are preferably about 0.1 to 2.0 MPa, and the heating conditions are preferably 40 to 120°C.

After the dry film is laminated to the glass substrate, the substrate is peeled off from the dry film to form a resin layer on the glass substrate. The resin layer is then heated to a temperature equal to or higher than the softening point temperature of the epoxy compound, thereby improving the adhesion between the resin layer and the glass substrate.

<Functional layer>
The functional layer that is provided on the resin layer as desired will be described. The function of the functional layer is not particularly limited, and may be a general function adopted in the cover window of a flexible display element, such as a hard coat function, an antistatic function, an antiglare function, a low reflection function, an antireflection function, an antifouling function, a gas barrier function, a primer function, an electromagnetic wave shielding function, an undercoat function, an ultraviolet absorbing function, an adhesive function, a hue adjustment function, etc. The functional layer may be a layer having one type of function, or a layer having two or more types of functions. From the viewpoint of easy use as a cover window, at least one of the functional layers is preferably a layer having at least one function selected from the group consisting of a hard coat function, an antistatic function, an antiglare function, a low reflection function, an antireflection function, and an antifouling function. The functional layer may have multiple functions in one layer, or two or more layers having each function may be laminated. When two or more layers are laminated, the order of lamination is appropriately set according to the function.

The thickness of the functional layer may be set appropriately depending on the intended function, but from the viewpoint of making the laminate lighter and improving its optical homogeneity, it is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less.

(Hard coat function)
The hard coat function is a function of protecting the optical film by imparting scratch resistance, chemical resistance, etc. to the surface of the optical film. In the optical laminate of the present invention, the functional layer may be a layer having a hard coat function (hard coat layer). As the hard coat layer, a known one may be appropriately adopted, and examples thereof include known hard coat layers such as acrylic, epoxy, urethane, benzyl chloride, and vinyl. Among these, from the viewpoint of suppressing the decrease in visibility in the wide angle direction of the optical laminate and improving the bending resistance, acrylic, urethane, and combinations thereof are preferred. For example, the hard coat layer may be a cured product of a composition containing an active energy ray curable compound. The active energy ray curable compound is a compound having the property of being cured by irradiation with active energy rays such as electron beams and ultraviolet rays. Examples of such active energy ray curable compounds include, for example, electron beam curable compounds that are cured by irradiation with electron beams and ultraviolet ray curable compounds that are cured by irradiation with ultraviolet rays. These compounds are the same compounds as the main components of hard coat agents used in the formation of ordinary hard coat layers, and examples thereof include (meth)acrylic resins. In particular, among (meth)acrylic resins, those containing a polyfunctional (meth)acrylate compound as a main component are preferred. In this specification, (meth)acrylic means acrylic and/or methacrylic, and (meth)acrylate means acrylate and/or methacrylate.

A polyfunctional (meth)acrylate compound is a compound having at least two acryloyloxy groups and/or methacryloyloxy groups in the molecule, and specifically includes ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolethane tri(meth)acrylate, tetramethylolmethane tri(meth)acrylate, tetramethylolmethane tetra(meth)acrylate, pentaglycerol tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, glycerin tri(meth)acrylate, dipentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tris((meth)acryloyloxyethyl)isocyanurate, phosphazene-based acrylate compounds or phosphazene-based methacrylate compounds in which a (meth)acryloyloxy group has been introduced into the phosphazene ring of a phosphazene compound, urethane (meth)acrylate compounds obtained by reacting a polyisocyanate having at least two isocyanate groups in the molecule with a polyol compound having at least one (meth)acryloyloxy group and a hydroxyl group, polyester (meth)acrylate compounds obtained by reacting a polyol compound having at least two carboxylic acid halides in the molecule with at least one (meth)acryloyloxy group and a hydroxyl group, and oligomers such as dimers and trimers of the above compounds.

These compounds may be used alone or in a mixture of two or more. In addition to the above-mentioned polyfunctional (meth)acrylate compounds, at least one monofunctional (meth)acrylate may be used. Examples of monofunctional (meth)acrylates include hydroxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, and glycidyl (meth)acrylate. These compounds may be used alone or in a mixture of two or more. The content of the monofunctional (meth)acrylate compound is preferably 10% by mass or less based on the solid content of the compound contained in the composition for forming the functional layer (paint for the hard coat layer). In this specification, the solid content means all components contained in the curable composition except the solvent.

A polymerizable oligomer may be added to the functional layer, for example to adjust the hardness. Examples of such oligomers include macromonomers such as (meth)acrylate-terminated polymethyl methacrylate, styryl-terminated poly(meth)acrylate, (meth)acrylate-terminated polystyrene, (meth)acrylate-terminated polyethylene glycol, (meth)acrylate-terminated acrylonitrile-styrene copolymer, and (meth)acrylate-terminated styrene-methyl (meth)acrylate copolymer. When a polymerizable oligomer is added, the content is preferably 5 to 50 mass % based on the solid content of the functional layer-forming composition.

The active energy ray curable compound may be used in the form of a solution mixed with a solvent. The active energy ray curable compound or its solution may be commercially available as a hard coat agent. Specific examples of commercially available hard coat agents include NK Hard M101 (urethane acrylate compound, Shin-Nakamura Chemical Co., Ltd.), NK Ester A-TMM-3L (tetramethylolmethane triacrylate, Shin-Nakamura Chemical Co., Ltd.), NK Ester A-9530 (dipentaerythritol hexaacrylate, Shin-Nakamura Chemical Co., Ltd.), KAYARAD (registered trademark) DPCA series (derivatives of dipentaerythritol hexaacrylate compound, Nippon Kayaku Co., Ltd.), Aronix (registered trademark) M-8560 (polyester acrylate compound, Toa Gosei Co., Ltd.), New Frontier (registered trademark) TEICA (tris(acryloyloxyethyl) isocyanurate, Daiichi Kogyo Seiyaku Co., Ltd.), PPZ (phosphazene-based methacrylate compound, Kyoeisha Chemical Co., Ltd.), and the like.

When ultraviolet light or visible light is used as the active energy ray, a photopolymerization initiator is usually used as the polymerization initiator. Examples of photopolymerization initiators include acetophenone, acetophenone benzyl ketal, anthraquinone, 1-(4-isopropylphenyl-2-hydroxy-2-methylpropan-1-one, carbazole, xanthone, 4-chlorobenzophenone, 4,4'-diaminobenzophenone, 1,1-dimethoxydeoxybenzoin, 3,3'-dimethyl-4-methoxybenzophenone, thioxanthone, 2,2-dimethoxy-2-phenylacetophenone, 1-(4-dodecylphenyl)-2-hydroxy-2-methylpropan-1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, triphenylamine, 2 , 4,6-trimethylbenzoyldiphenylphosphine oxide, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, fluorenone, fluorene, benzaldehyde, benzoin ethyl ether, benzoisopropyl ether, benzophenone, Michler's ketone, 3-methylacetophenone, 3,3',4,4'-tetratert-butylperoxycarbonylbenzophenone (BTTB), 2-(dimethylamino)-1-[4-(morpholinyl)phenyl]-2-phenylmethyl)-1-butanone, 4-benzoyl-4'-methyldiphenyl sulfide, benzyl, etc.

The photopolymerization initiator may be used in combination with a dye sensitizer. Examples of dye sensitizers include xanthene, thioxanthene, coumarin, and ketocoumarin. Examples of combinations of photopolymerization initiators and dye sensitizers include a combination of BTTB and xanthene, a combination of BTTB and thioxanthene, a combination of BTTB and coumarin, and a combination of BTTB and ketocoumarin.

When a photopolymerization initiator is used, the amount used is preferably 0.1 parts by mass or more per 100 parts by mass of the active energy ray-curable compound. If the amount used is within the above range, a sufficient curing speed tends to be obtained. The amount of the photopolymerization initiator used is preferably 10 parts by mass or less per 100 parts by mass of the active energy ray-curable compound.

The thickness of the hard coat layer can be set as appropriate, but from the viewpoint of the bending resistance, surface hardness, and optical homogeneity of the laminate, it is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less.

A method for forming a hard coat layer on the surface of a resin layer may involve, for example, applying a composition for forming a hard coat layer containing an active energy ray curable compound (active energy ray curable resin) to the surface of the resin layer and irradiating the surface with active energy rays. Such a composition may be obtained by mixing the active energy ray curable compound with additives, etc., as necessary. The hard coat layer is formed from the cured product of the composition for forming a hard coat layer.

The composition for forming a hard coat layer preferably contains a solvent, and in the composition for forming a hard coat layer, the active energy ray curable compound is preferably diluted with a solvent. In this case, the composition may be produced by mixing the active energy ray curable compound with various additives (e.g., silicone oil, etc.) for imparting surface smoothness, etc., and then diluting the resulting mixture with a solvent, or by diluting the active energy ray curable compound with a solvent and then mixing the additives, or by mixing the active energy ray curable compound with an additive previously diluted with a solvent, or by mixing the active energy ray curable compound previously diluted with a solvent with an additive previously diluted with a solvent. The composition after mixing may be further stirred.

From the viewpoint of facilitating application, it is preferable that the composition for forming a hard coat layer contains a suitable solvent. The solvent can be appropriately selected from aliphatic hydrocarbons such as hexane and octane, aromatic hydrocarbons such as toluene and xylene, alcohols such as ethanol, 1-propanol, isopropanol, and 1-butanol, ketones such as methyl ethyl ketone and methyl isobutyl ketone, esters such as ethyl acetate and butyl acetate, cellosolves, and the like. These organic solvents may be mixed and used as necessary. From the viewpoint of easily evaporating the organic solvent by heating the composition for forming a hard coat layer after application, the boiling point of the solvent is preferably in the range of 70°C to 200°C. The type and amount of the solvent are appropriately selected depending on the type and amount of the active energy ray curable compound used, the material and shape of the resin layer, the application method, the desired thickness of the hard coat layer, and the like.

(Antistatic function)
The antistatic function is a function of preventing the surface of the laminate from being charged. In the laminate of the present invention, the functional layer may be a layer having an antistatic function (antistatic layer). As a method for forming an antistatic layer, in addition to the method of adding an antistatic agent to the composition for forming a hard coat layer to impart an antistatic function to the hard coat layer, a method of applying an antistatic layer forming composition obtained by diluting the antistatic agent with a solvent or the like onto the hard coat layer formed on the surface of the resin layer and drying it as necessary to form a single film can be mentioned. The antistatic agent may be included as a structural unit having an antistatic function in a part of the resin constituting the functional layer (for example, the cured product of the above-mentioned active energy ray curable compound), or may be added as an additive to the resin forming the functional layer. When the antistatic agent is added as an additive, the amount of the antistatic agent added is preferably 0.01 to 20% by mass, more preferably 0.05 to 10% by mass, and even more preferably 0.1 to 10% by mass, based on the solid content of the composition for forming the functional layer.

(Anti-glare function)
The antiglare function is a function of preventing reflection of external light by scattering and reflecting light. In the laminate of the present invention, the functional layer may be a layer having an antiglare function (antiglare layer). As the antiglare layer, a known material may be appropriately adopted. For example, the antiglare function may be imparted by forming a layer having a fine uneven shape on the surface using a resin composition containing one or more types of translucent fine particles in a translucent resin. More specifically, such an antiglare layer can be formed, for example, by applying a translucent resin solution in which translucent fine particles as a filler are dispersed on the surface of the resin layer, and adjusting the thickness of the application so that the translucent fine particles become the convex part on the surface of the antiglare layer. In this specification, "translucency" means that light can be almost transmitted regardless of the presence or absence of scattering inside the substance.

(Anti-reflection and low-reflection functions)
The anti-reflection function and the low reflection function are functions to prevent or reduce the reflection of external light. In the laminate of the present invention, the functional layer may be a layer having a function of preventing the reflection of external light (anti-reflection layer), or may be a layer having a function of reducing the reflection of external light (low reflection layer). The anti-reflection layer and the low reflection layer may be a single layer or a multilayer.

The anti-reflection layer may include a low refractive index layer. The anti-reflection layer may also be a layer having a multi-layer structure further including a low refractive index layer and a high refractive index layer and/or a medium refractive index layer laminated between the low refractive index layer and the resin layer. The above-mentioned hard coat layer may be provided between the anti-reflection layer and the resin layer.

The thickness of the anti-reflection layer is preferably 0.01 to 1 μm, more preferably 0.02 to 0.5 μm. Examples of the anti-reflection layer include a low refractive index layer having a smaller refractive index (e.g., a refractive index of 1.3 to 1.45) than the resin layer or other functional layer on which the anti-reflection layer is provided, and a layer in which multiple low refractive index layers made of thin films of inorganic compounds and high refractive index layers made of thin films of inorganic compounds are alternately laminated. Here, the refractive index of the high refractive index layer needs only to be larger than the refractive index of the low refractive index layer, but is preferably 1.60 or more.

The material forming the low refractive index layer is not particularly limited as long as it has a low refractive index. Examples include resin materials such as active energy ray curable resins (e.g., ultraviolet curable acrylic resins), hybrid materials in which inorganic particles such as colloidal silica are dispersed in a resin, and sol-gel materials using metal alkoxides such as tetraethoxysilane. These materials forming the low refractive index layer may be polymerized polymers, or may be precursor monomers or oligomers. In addition, the material constituting the antireflection layer preferably contains a fluorine-containing compound, since this can impart an antifouling function to the antireflection layer.

The high refractive index layer can be formed by applying a coating liquid containing a translucent resin such as a cured product of the above-mentioned active energy ray curable resin or a metal alkoxide polymer and inorganic and/or organic fine particles, and then curing the coating film as necessary. Examples of inorganic fine particles include zinc oxide, titanium oxide, cerium oxide, aluminum oxide, silane oxide, tantalum oxide, yttrium oxide, ytterbium oxide, zirconium oxide, antimony oxide, and indium tin oxide (ITO). The high refractive index layer containing these inorganic fine particles can also have an antistatic function.

The low-reflection layer is a layer formed of a low-refractive index material having a lower refractive index than the resin layer or other functional layers that are provided as required.The low-refractive index layer can be formed by applying a coating liquid containing a translucent resin such as the cured product of the above-mentioned active energy ray curable resin or a metal alkoxide polymer and inorganic fine particles, and then curing the coating film as necessary.Specific examples of such low-refractive index materials include inorganic low-refractive materials in which inorganic material fine particles such as lithium fluoride (LiF), magnesium fluoride (MgF ₂ ), aluminum fluoride (AlF ₃ ), and cryolite (3NaF·AlF ₃ or Na ₃ AlF ₆ ) are contained in acrylic resins or epoxy resins; organic low-refractive materials such as fluorine-based or silicone-based organic compounds, thermoplastic resins, thermosetting resins, and ultraviolet-curable resins.

<Touch sensor function>
A touch sensor function can be imparted to the laminate by forming a transparent electrode layer on the surface of the resin layer. For example, a transparent electrode layer can be formed on the surface of the resin layer or other functional layers that are provided as desired, using a sputtering device. This allows the laminate of the present invention to be used as a cover window to serve as a touch panel like a transparent electrode.

<Support>
The laminate of the present invention can improve the mechanical strength of the laminate by providing a support on the surface of the glass substrate opposite to the surface on which the resin layer is formed. Any material having optical transparency, mechanical strength, and flexibility can be used without particular limitation, and for example, transparent resin sheets such as polyimide, polyethylene terephthalate, polycarbonate, polyethersulfone, polyetheretherketone, polyvinyl fluoride, polyacrylate, polypropylene, polyethylene, amorphous polyolefin, and fluorine-based resin can be suitably used.

The thickness of the support may be appropriately determined depending on the application of the laminate. For example, when the laminate is used as a cover window for a flexible display element, the thickness is preferably 40 to 200 μm, and more preferably 50 to 100 μm.

<Applications of the laminate>
A flexible display element can be manufactured using the laminate of the present invention. The flexible display element can be an organic EL display, such as a bottom-emission type flexible organic EL display, a top-emission type flexible organic EL display, or a flexible liquid crystal display. When the laminate of the present embodiment is used as a cover window of a flexible display element, the flexible display element is preferably equipped with a light source, and the light of the light source is preferably output to the outside of the flexible display element through the laminate of the present embodiment. When the laminate of the present embodiment is used as a cover window of a flexible display element, the laminate is arranged so that the glass substrate is arranged closer to the light source than the resin layer.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Note that in the following, all "parts" and "%" are by weight unless otherwise specified.

<Preparation of polyimide>
The following polyimides 1 to 6 were prepared.
Polyimide 1:
Into a 500 ml separable flask equipped with a nitrogen inlet tube and a stirrer, 2.0 g (0.007 mol) of 1,3-bis(3-aminophenoxy)benzene (APB-N), 3.3 g (0.01 mol) of 1,3-bis(4-aminophenoxy)benzene (TPE-R), 2.8 g (0.01 mol) of 1,3-bis(3-aminopropyl)tetramethyldisiloxane (PAM-E), 15.9 g (0.03 mol) of 2,2-bis[4-(3,4-dicarboxyphenoxyphenyl)]propane dianhydride (BisDA), 56 g of ethyl benzoate, 0.47 g (0.006 mol) of pyridine, and 10 g of toluene were added, and the mixture was reacted under a nitrogen atmosphere at 180° C. for 4 hours while removing toluene from the system during the reaction, thereby obtaining a 30 wt % polyimide solution.
59.5 mL of DMAC and 59.5 mL of methanol were added to the obtained polyimide solution, and the mixture was stirred until it became uniform. The obtained solution was dropped into 300 mL of ion-exchanged water, and reprecipitation was performed to obtain solid polyimide 1. The weight average molecular weight (Mw) measured by gel permeation chromatography was 300,000, and the polydispersity expressed by weight average molecular weight (Mw)/number average molecular weight (Mn) was 4.2. The fluorine content in the polyimide was 0%.

Polyimide 2:
In a 200 mL glass vial, 60 g of the solvent N,N-dimethylacetamide (DMAC) and 3.8 g (0.012 mol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB) were added and stirred to dissolve TFMB in DMAC. Next, while stirring the contents in the vial, 3.7 g (0.012 mol) of 3,3',4,4'-dicyclohexyltetracarboxylic dianhydride (HBPDA) was added over about 5 minutes under a nitrogen stream, and the polymerization reaction was carried out by continuing to stir for 6 hours while adjusting the temperature to be in the range of 20 to 40 ° C., to obtain a viscous polyamic acid solution. The molar ratio of the tetracarboxylic dianhydride/aromatic diamine compound used was 1.00, and the concentration of the polyamic acid solution was 13.0 wt%.
Next, 5.9 g of pyridine was added as an imidization accelerator to the polyamic acid solution, and the solution was kept at a temperature of 30 to 40° C. with stirring. 7.1 g (0.07 mol) of acetic anhydride was slowly added dropwise thereto as an imidization agent over a period of about 10 minutes. Thereafter, the liquid temperature was further kept at 30 to 40° C. and stirring was continued for 12 hours to carry out a chemical imidization reaction, thereby obtaining a polyimide solution.
59.5 mL of DMAC and 59.5 mL of methanol were added to the obtained polyimide solution containing the imidization agent and the imidization accelerator, and the mixture was stirred until it became uniform. The obtained solution was dropped into 300 mL of ion-exchanged water, and reprecipitation was performed to obtain a solid polyimide 2. The weight average molecular weight (Mw) measured by gel permeation chromatography was 300,000, and the polydispersity expressed by weight average molecular weight (Mw)/number average molecular weight (Mn) was 4.0. The fluorine content in the polyimide was 21%.

Polyimide 3:
In a 200 mL glass vial, 60 g of the solvent N,N-dimethylacetamide (DMAC) and 3.8 g (0.012 mol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB) were added and stirred to dissolve TFMB in DMAC. Next, while stirring the contents in the vial, 3.7 g (0.012 mol) of diphenyl-3,3',4,4'-tetracarboxylic dianhydride (s-ODPA) was added over about 5 minutes under a nitrogen stream, and the polymerization reaction was carried out by continuing stirring for 6 hours while adjusting the temperature to be in the range of 20 to 40 ° C., to obtain a viscous polyamic acid solution. The molar ratio of the tetracarboxylic dianhydride/aromatic diamine compound used was 1.00, and the concentration of the polyamic acid solution was 10.0 wt%.
Next, 5.9 g of pyridine was added as an imidization accelerator to the polyamic acid solution, and the solution was kept at a temperature of 30 to 40° C. with stirring. 7.1 g (0.07 mol) of acetic anhydride was slowly added dropwise thereto as an imidization agent over a period of about 10 minutes. Thereafter, the liquid temperature was further kept at 30 to 40° C. and stirring was continued for 12 hours to carry out a chemical imidization reaction, thereby obtaining a polyimide solution.
59.5 mL of DMAC and 59.5 mL of methanol were added to the obtained polyimide solution containing the imidization agent and the imidization accelerator, and the mixture was stirred until it became uniform. The obtained solution was dropped into 300 mL of ion-exchanged water, and reprecipitation was performed to obtain solid polyimide 3. The weight average molecular weight (Mw) measured by gel permeation chromatography was 250,000, and the polydispersity expressed by weight average molecular weight (Mw)/number average molecular weight (Mn) was 4.3. The fluorine content in the polyimide was 20%.

Polyimide 4:
In a 200 mL glass vial, 59.5 g of the solvent N,N-dimethylacetamide (DMAC) and 4.7 g (0.188 mol) of 3,3'-diaminodiphenylsulfone (3,3'-DDS) were added and stirred to dissolve 33'-DDS in DMAC. Next, while stirring the contents in the vial, 5.8 g (0.188 mol) of tetracarboxylic dianhydride diphenyl-3,3',4,4'-tetracarboxylic dianhydride (s-ODPA) was added over about 5 minutes under a nitrogen stream, and the polymerization reaction was carried out by continuing to stir for 6 hours while adjusting the temperature to be in the range of 20 to 40 ° C., to obtain a viscous polyamic acid solution. The molar ratio of the tetracarboxylic dianhydride/aromatic diamine compound used was 1.00, and the concentration of the polyamic acid solution was 14.9 wt %.
Next, 5.9 g of pyridine was added as an imidization accelerator to the polyamic acid solution, and the solution was kept at a temperature of 30 to 40° C. with stirring. 7.1 g (0.07 mol) of acetic anhydride was slowly added dropwise thereto as an imidization agent over a period of about 10 minutes. Thereafter, the liquid temperature was further kept at 30 to 40° C. and stirring was continued for 12 hours to carry out a chemical imidization reaction, thereby obtaining a polyimide solution.
59.5 mL of DMAC and 59.5 mL of methanol were added to the obtained polyimide solution containing the imidization agent and the imidization accelerator, and the mixture was stirred until it became uniform. The obtained solution was dropped into 300 mL of ion-exchanged water, and reprecipitation was performed to obtain solid polyimide 4. The weight average molecular weight (Mw) measured by gel permeation chromatography was 210,000, and the polydispersity expressed by weight average molecular weight (Mw)/number average molecular weight (Mn) was 4.5. The fluorine content in the polyimide was 0%.

Polyimide 5:
In a 200 mL glass vial, 60 g of the solvent N,N-dimethylacetamide (DMAC) and 3.8 g (0.012 mol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB) were added and stirred to dissolve TFMB in DMAC. Next, while stirring the contents in the vial, 5.3 g (0.012 mol) of 4,4'-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)diphthalic dianhydride (6FDA) was added over about 5 minutes under a nitrogen stream, and the polymerization reaction was carried out by continuing stirring for 6 hours while adjusting the temperature to be in the range of 20 to 40 ° C., to obtain a viscous polyamic acid solution. The molar ratio of the tetracarboxylic dianhydride/aromatic diamine compound used was 1.00, and the concentration of the polyamic acid solution was 10.0 wt%.
Next, 5.9 g of pyridine was added as an imidization accelerator to the polyamic acid solution, and the solution was kept at a temperature of 30 to 40° C. with stirring. 7.1 g (0.07 mol) of acetic anhydride was slowly added dropwise thereto as an imidization agent over a period of about 10 minutes. Thereafter, the liquid temperature was further kept at 30 to 40° C. and stirring was continued for 12 hours to carry out a chemical imidization reaction, thereby obtaining a polyimide solution.
59.5 mL of DMAC and 59.5 mL of methanol were added to the obtained polyimide solution containing the imidization agent and the imidization accelerator, and the mixture was stirred until it became uniform. The obtained solution was dropped into 300 mL of ion-exchanged water, and reprecipitation was performed to obtain solid polyimide 5. The weight average molecular weight (Mw) measured by gel permeation chromatography was 210,000, and the polydispersity expressed by weight average molecular weight (Mw)/number average molecular weight (Mn) was 4.2. The fluorine content in the polyimide was 33%.

Polyimide 6:
Into a 200 mL glass vial were placed 59.5 g of a solvent, N,N-dimethylacetamide (DMAC), 3.819 g (0.012 mol) of 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl (TFMB), an aromatic diamine compound having a fluoro group, and 1.105 g (0.0003 mol) of X-22-1660B-3 (manufactured by Shin-Etsu Silicones), a silicone-modified diamine, and the mixture was stirred to dissolve the TFMB in the DMAC. Next, while stirring the contents of the vial, 5.576 g (0.013 moles) of 4,4'-(1,1,1,3,3,3-hexafluoropropane-2,2-diyl)diphthalic dianhydride (6FDA) was added under a nitrogen stream, and the polymerization reaction was carried out by continuing stirring for 6 hours while adjusting the temperature to be in the range of 20 to 40°C, thereby obtaining a viscous polyamic acid solution. The molar ratio of the tetracarboxylic dianhydride/aromatic diamine compound used was 1.03, and the concentration of the polyamic acid solution was 15% by weight.
Next, 3.9 g of pyridine was added as an imidization accelerator to the polyamic acid solution, and the solution was kept at a temperature of 30 to 40° C. with stirring. 5.1 g (0.05 mol) of acetic anhydride was slowly added dropwise thereto as an imidization agent. Thereafter, the liquid temperature was further kept at 30 to 40° C. and stirring was continued for 12 hours to carry out a chemical imidization reaction, thereby obtaining a polyimide solution.
59.5 mL of DMAC and 59.5 mL of methanol were added to the obtained polyimide solution containing the imidization agent and the imidization accelerator, and the mixture was stirred until it became uniform. The obtained solution was dropped into 300 mL of ion-exchanged water, and reprecipitation was performed to obtain solid polyimide 6. The weight average molecular weight (Mw) measured by gel permeation chromatography was 300,000, and the polydispersity expressed by weight average molecular weight (Mw)/number average molecular weight (Mn) was 4.2. The fluorine content in the polyimide was 28%.

<Epoxy Compound>
The following epoxy compounds 1 to 4 were prepared.
Epoxy 1: jER1001 (manufactured by Mitsubishi Chemical Corporation, epoxy equivalent 400 to 500 g/eq, molecular weight 900, softening temperature 64° C.)
Epoxy 2: XD1000 (manufactured by Nippon Kayaku Co., Ltd., epoxy equivalent 245 to 260 g/eq, molecular weight 990 to 1500, softening temperature 68 to 78° C.)
Epoxy 3: TEPIC-S (manufactured by Nissan Chemical Industries, Ltd., epoxy equivalent 100 g/eq or less, molecular weight 297, softening temperature 100 to 120° C.)
Epoxy 4: Epofriend AT501 (manufactured by Daicel Corporation, epoxy equivalent 850 to 1250 g/eq or less, molecular weight 180,000, softening temperature 100° C. or more)

<Other resins>
For comparison with the epoxy compound, the following three compounds were prepared.
Styrene-acrylic copolymer: ARUFON UC3900 (manufactured by Toagosei Co., Ltd.)
Polyvinyl butyral compound: S-LEC BL-1 (manufactured by Sekisui Chemical Co., Ltd.)
Polyester compound: Vylon 220 (manufactured by Toyobo Co., Ltd.)

[Examples 1 to 8, Comparative Examples 1 to 9]
<Preparation of dry film>
Each varnish was prepared by mixing each component with a solvent (dimethylacetamide) according to the composition shown in Table 1 below. The solvent was adjusted so that the amount of solvent was 333 parts by mass per 100 parts of polyimide. Next, the obtained varnish was applied to a polyester film (TN-200, manufactured by Toyobo Co., Ltd.) whose surface had been subjected to a release treatment so that the thickness after drying would be 15 μm, and the resin layer was formed by drying at 80° C. for 30 minutes, and each dry film was produced.
The blue dye in Table 1 is Plast Blue 8514 (manufactured by Arimoto Chemical Industry Co., Ltd.).

The resin layer surface of each dry film was laminated onto the surface of a glass substrate (DragonTrail (registered trademark), manufactured by AGC Inc.) measuring 15 cm in length × 11 cm in width × 70 μm in thickness, and the polyester film was peeled off from the dry film. The laminate was then subjected to a heat treatment at 150° C. for 30 minutes to obtain a laminate.
For the dry films of Examples 4 to 6, the resin layer surface of the dry film was laminated to a glass substrate using a vacuum pressure laminator (MVLP-500, manufactured by Meiki Seisakusho Co., Ltd.) at an upper and lower hot plate temperature of 90°C and a pressure of 0.5 MPa. After peeling the polyester film from the dry film, a heat treatment was performed at 200°C for 30 minutes to obtain a laminate.

[Comparative Examples 10 and 11]
Each varnish was prepared by mixing each component with a solvent (dimethylacetamide) according to the composition shown in Table 1 below. The solvent was prepared so that the solvent was 333 parts by mass per 100 parts of polyimide. Next, the obtained varnish was applied to a glass substrate (DragonTrail (registered trademark), manufactured by AGC Inc.) having a length of 15 cm, a width of 11 cm, and a thickness of 70 μm after drying to a thickness of 15 μm, and a resin layer was formed by drying at 150 ° C. for 30 minutes to obtain a laminate.

<Evaluation of Adhesion>
The surface of each of the obtained laminates was observed from the glass substrate side using a digital microscope (VHX-5000, manufactured by Keyence Corporation). The diameter of the confirmed air bubbles was evaluated at randomly selected arbitrary positions of the laminates, each of which was 1 cm square. The evaluation criteria were as follows:
◎: Bubble diameter 0 mm
○: Bubble diameter 0mm to 2mm
×: Air bubble diameter 2 mm or more The evaluation results are shown in the following Tables 1 and 2. In Table 1, the notation "-" means that no evaluation was performed.

<Cross-cut peel test evaluation>
Each of the resulting laminates was subjected to a cross-cut peel test evaluation in accordance with ASTM D 3559-B, and the evaluation results were as shown in Tables 1 and 2 below.

<Warpage evaluation of laminate>
Each laminate obtained by heating and drying was allowed to cool at room temperature for 1 hour, and then the laminate was placed on a flat desk with the glass substrate side facing downward, and the warpage values (distances from the desk to the glass substrate) of the four corners of the laminate were measured with a ruler, and the average of these values was taken as the warpage value. The evaluation criteria were as follows:
⊚: Less than 8 mm ◯: 8 mm or more and less than 10 mm ×: 10 mm or more XX: Unable to evaluate The evaluation results are shown in Tables 1 and 2 below.

<Evaluation of Hayes>
The haze (%) of each of the obtained laminates was measured in accordance with JIS K 7136: 2000 using a haze meter (NDH 7000 II, manufactured by Nippon Denshoku Industries Co., Ltd.) The evaluation criteria were as follows.
◯: Haze is 2.0% or less ×: Haze is more than 2.0% The evaluation results are shown in the following Tables 1 and 2. The haze value of the glass substrate itself used in the laminate was 0.35%.

<Impact resistance evaluation>
Each laminate obtained by heating and drying was allowed to cool at room temperature for 1 hour, and then the laminate was placed on a flat desk with the glass substrate side facing downward, and an iron ball with a diameter of 30 mm and a weight of 110 g was dropped onto the laminate. The glass after the iron ball was dropped was visually inspected, and the drop height at which cracks were observed was evaluated. The evaluation criteria were as follows.
⊚: 50 cm or more ◯: 40 cm or more and less than 50 cm Δ: 30 cm or more and less than 40 cm ×: less than 30 cm The impact resistance of the glass substrate used in the laminate was evaluated and rated as ×.

<Surface hardness evaluation>
The pencil hardness of the resin layer side of the laminate was measured in accordance with JIS-K5600-5-4:1999, and the highest pencil hardness that did not cause scratches on the coating film was recorded as the pencil hardness. The evaluation results are shown in Tables 1 and 2. The pencil hardness of the glass substrate used in the laminate was 9H.

1: Dry film 2: Laminate 10: Substrate 20: Resin layer 30: Protective film 40: Glass substrate 50: Functional layer 60: Support

Claims (10)

A dry film comprising a substrate and a resin layer releasably provided on the substrate,
The resin layer comprises a polyimide having a fluorine content of 25 mass% or less (excluding polyimide resins containing a phenolic hydroxyl group) and an epoxy compound having an epoxy equivalent of 1000 g/eq or less and a molecular weight of 10,000 or less. The dry film according to claim 1, wherein the polyimide has a YI value of 5.0 or less when made into a single layer film having a thickness of 50 μm. The dry film according to claim 1 or 2, wherein the polyimide has a haze of 2.0 or less when made into a single layer film having a thickness of 50 μm. The dry film according to any one of claims 1 to 3, wherein the epoxy compound has a softening point of 150°C or less. The dry film according to any one of claims 1 to 4, wherein the epoxy compound is contained in an amount of 1 to 50 mass% based on the total amount of solids in the resin layer. The dry film according to any one of claims 1 to 5, wherein the resin layer further contains a bluing agent. A laminate comprising a glass substrate and a resin layer provided on one of the main surfaces of the glass substrate so as to be in contact with the surface,
The resin layer is a resin layer of the dry film according to any one of claims 1 to 6. The laminate according to claim 7, wherein the glass substrate is chemically strengthened glass. The laminate according to claim 7 or 8, which is used as a cover window for a flexible display element. A method for producing a laminate including a glass substrate and a resin layer provided on one of the main surfaces of the glass substrate so as to be in contact with the resin layer, comprising the steps of:
The dry film according to any one of claims 1 to 6 is attached to one of the main surfaces of a glass substrate such that the resin layer of the dry film is in contact with the main surface of the glass substrate;
peeling the base material from the dry film to form a resin layer on the glass substrate;
The resin layer is heated to a temperature equal to or higher than the softening point temperature of the epoxy compound.
A method for producing a laminate, comprising: