JP6357947B2 - Multilayer substrate and image display device - Google Patents

Description

  The present invention relates to a multilayer base material and an image display device including the multilayer base material.

In recent years, mobile information terminal devices equipped with a transparent touch panel for information display and information input, which have bidirectional communication functions such as tablet PCs and smartphones, have begun to spread widely not only in Japan but around the world. Came.
From the viewpoint of miniaturization and weight reduction of mobile information terminal devices, thinning is also required for touch panels and image display elements mounted thereon. As a method for reducing the thickness of the touch panel and the image display element, a method for reducing the number of various functional films as these constituent members, a method for reducing the thickness of the functional film, and the like have been studied.
Various functional films include protective films provided for the purpose of protecting the electrodes (sensors) used in touch panels, as well as films with optical or electrical performance such as antireflection, antistatic properties, and conductivity. And so on.

  In order to reduce the thickness of these functional films, there is a method of using an extremely thin base film (for example, a thickness of 40 μm or less) as a base material constituting the functional film. However, when a functional layer is formed on a thin base film, the problem that the film is easily curled due to stress generated in the forming process becomes more remarkable. A curled film (ie, low flatness) is not only difficult to handle in the manufacturing process, but also protects the sensor particularly in an image display device equipped with a touch panel (hereinafter also referred to as “touch panel image display device”). If it is used for an air gap part or a bonding part for the purpose, the thickness unevenness occurs in the air gap part or the bonding part, and there arises a problem that the appearance of the touch panel is deteriorated due to the Newton ring being seen due to the interference action of light. . It is also expected that the touch panel sensor sensitivity will be reduced.

  As a film having a functional layer and less curling, for example, Patent Document 1 discloses a curl after curing having a cured resin layer obtained by applying and curing a curable composition on a substrate. Fewer hard coat films are disclosed.

JP 2003-147017 A

However, the hard coat film described in Patent Document 1 is assumed to be used on the outermost surface of the display for the purpose of protecting the surface of the image display device. For example, in the air gap portion or the bonding portion of the touch panel image display device. There is no disclosure or suggestion about its use. The base material of the hard coat film used in the example of Patent Document 1 is as thick as 188 μm (see paragraph 00099), and is not suitable for touch panel applications that require thinning.
In addition, the functional film used in the image display device is required to be less colored from the viewpoint of appearance and not to yellow even when stored for a long period of time, particularly under high temperature and high humidity conditions. However, Patent Document 1 does not disclose or suggest the suppression of coloring of the hard coat film.

On the other hand, since the strength decreases when the base film is thinned, it is also required to impart hardness while maintaining the flexibility of the base film in order to improve the handleability during the manufacturing process. However, for example, a film for protecting a sensor or the like used in an air gap part or a bonding part of a touch panel image display device has a surface protection performance that can prevent the sensor or the like from being damaged during the manufacturing process. It ’s enough. In addition, since there is little permanent deformation due to external stress and it is required to have toughness that can withstand repeated pressing during touch panel operation, excessive rigidity is required in the air gap part or bonding part of the touch panel image display device. The use of the film it has may not be suitable.
Especially in mobile devices with touch panels such as tablet PCs and smartphones, for example, they may be bent when they are carried in jackets or pants pockets, or the display surface may be heavy. . Therefore, the film used for the mobile touch panel image display device is required to have a flexibility that does not break even when the above-described force is applied. Therefore, as in conventional hard coat films, merely having hardness and not curling is insufficient as performance.

  An object of the present invention is to provide a multilayer base material having a protective layer on at least one surface of a base material film. An object of the present invention is to provide a multilayer base material that has little yellowing even when stored under the surface, has excellent flexibility, and has a sufficient surface protection performance, and an image display device including the multilayer base material.

As a result of intensive studies to solve the above problems, the present inventors have a protective layer on at least one surface of the base film, and the thickness of the base film is 40 μm or less. It has been found that the above problem can be solved by using a cured product of a curable resin composition having a composition and setting b * to a predetermined value or less.
That is, the present invention provides the following multilayer substrates and image display devices [1] and [2].
[1] A multilayer substrate having a protective layer on at least one surface of the substrate film, wherein the thickness of the substrate film is 40 μm or less, and the protective layer comprises a cationically polymerizable resin and a radically polymerizable resin. A multilayer substrate, which is a cured product of an ionizing radiation curable resin composition, and has b * of 2.0 or less in the CIE1976-L * a * b * color system.
[2] An image display device comprising the multilayer substrate according to [1].

  The multilayer base material of the present invention has little curling, little coloration, little yellowing due to long-term storage under high temperature and high humidity conditions, excellent flexibility, and sufficient surface protection performance. Thus, for example, by using it as a protective member inside the image display device, it is possible to prevent damage that may occur during the manufacturing process of the image display device, and to facilitate thinning without impairing the appearance of the image display device. .

It is sectional drawing which shows an example of the touchscreen image display apparatus which has an air gap part. It is sectional drawing which shows an example of the touchscreen image display apparatus which has a bonding part.

Embodiments of the present invention will be described below.
[Multilayer substrate]
The multilayer substrate of the present invention has a protective layer on at least one surface of the substrate film, the thickness of the substrate film is 40 μm or less, and the protective layer comprises a cationic polymerizable resin and a radical polymerizable resin. It is a cured product of the ionizing radiation curable resin composition to be included. The multilayer base material of the present invention is characterized in that b * is 2.0 or less in the CIE1976-L * a * b * color system. The protective layer may be provided on either one side or both sides of the base film, but the multilayer base material of the present invention has an effect of suppressing curling even if the protective layer is provided only on one side of the base film. It is.

(Base film)
As a base film used for the multilayer base material of the present invention, it is preferable that the base film has light transmittance, smoothness and heat resistance and is excellent in mechanical strength. Such base films include polyester, triacetyl cellulose (TAC), cellulose diacetate, cellulose acetate butyrate, polyamide, polyimide, polyether sulfone, polysulfone, polypropylene, polymethylpentene, polyvinyl chloride, polyvinyl acetal. , Polyether ketone, polymethyl methacrylate, polycarbonate, polyurethane, and amorphous olefin (Cyclo-Olefin-Polymer: COP). The base film may be a laminate of two or more plastic films.
Among the above, a base film selected from a triacetyl cellulose film, a polyester film, and an acrylic film is preferable. From the viewpoints of mechanical strength and dimensional stability, polyester (polyethylene terephthalate, polyethylene naphthalate) that has been stretched, particularly uniaxially or biaxially stretched, is preferable. It is preferable from the viewpoint.
COP and polyester are preferable in terms of easy retardation control. In addition, a plastic film having a retardation value of 3000 to 30000 nm or a plastic film having a quarter wavelength retardation is preferable in that unevenness of different colors can be prevented from being observed on the display screen when an image is observed through polarized sunglasses. It is.

The thickness of the base film is 40 μm or less from the viewpoint of thinning the image display device, preferably 5 μm or more, more preferably 15 μm or more from the viewpoint of strength.
In order to improve the adhesion, the surface of the base film may be preliminarily coated with a coating called an anchor agent or a primer in addition to physical treatment such as corona discharge treatment and oxidation treatment.

(Protective layer)
The multilayer base material of the present invention is at least one surface of the base film from the viewpoint of reinforcing the strength of the thin base film and providing sufficient surface protection performance during the manufacturing process of the image display device. Has a protective layer. The protective layer is a cationically polymerizable resin and a radically polymerizable resin from the viewpoint of suppressing curling even when a thin base film is used, and from suppressing coloring and yellowing under storage at high temperature and high humidity conditions. And a cured product of an ionizing radiation curable resin composition.

Conventionally, the hard coat layer of a hard coat film used on the outermost surface of an image display device uses a curable resin composition mainly composed of a polyfunctional radical polymerizable resin from the viewpoint of imparting high hardness. It has been. However, since the radical polymerizable resin has a high cure shrinkage rate, curling due to cure shrinkage is likely to occur when the radical polymerizable resin composition is applied to a substrate film and cured by irradiation with ionizing radiation. In particular, when an extremely thin base film having a thickness of 40 μm or less is used, curling on the resin composition side becomes remarkable.
On the other hand, cationically polymerizable resins are characterized by having a relatively low curing shrinkage even if they are cured and expanded to curl to the base film side or cure and shrink. However, it is inferior to the radical polymerizable resin in terms of the hardness of the cured product. Moreover, in addition to being easy to color, the hardened | cured material of the resin composition containing a cationic polymerization initiator tends to generate | occur | produce yellowing especially when preserve | saved on high temperature, high humidity conditions.
However, the present inventors have disclosed a cationic polymerizable resin and a radical as a protective member used in the image display device (for example, a protective member used in an air gap portion or a bonding portion provided in the touch panel image display device). By using an ionizing radiation curable resin composition containing a polymerizable resin, it is possible to prevent scratches that may occur in the manufacturing process of the image display device, and curl generation is suppressed even when a base film having a thickness of 40 μm or less is used. Furthermore, when stored under high-temperature and high-humidity conditions or under external light such as sunlight, yellowing is small, and flexibility is excellent, and b * in the CIE 1976-L * a * b * color system is 2. It has been found that it can be made 0 or less.

<Ionizing radiation curable resin composition>
The ionizing radiation curable resin composition used in the present invention is preferably a resin composition containing a photopolymerization initiator, various additives, and a solvent in addition to the cationic polymerizable resin and the radical polymerizable resin.
The ionizing radiation means an electromagnetic wave or a charged particle beam having an energy quantum capable of polymerizing or cross-linking molecules, and usually ultraviolet (UV) or electron beam (EB) is used. Electromagnetic waves such as X-rays and γ-rays, and charged particle beams such as α-rays and ion beams can also be used. In the present invention, the radical polymerizable resin and the cationic polymerizable resin are preferably ultraviolet curable resins that are cured by irradiation with ultraviolet rays.

[Cationically polymerizable resin]
Examples of the ionizing radiation curable cationic polymerizable resin include compounds having a cationic polymerizable functional group in the molecule and no radical polymerizable functional group. Examples of the cationic polymerizable functional group include an epoxy group, an oxetanyl group, a vinyl ether group, an episulfide group, and an ethyleneimine group, and at least one selected from an epoxy group and an oxetanyl group is preferable. Among these, from the viewpoint of the strength of the protective layer obtained and the curability, the cationic polymerizable resin is preferably a compound having two or more cationic polymerizable functional groups in the molecule, and a compound having two or more epoxy groups in the molecule. It is more preferable to contain.
The cationic polymerizable resin may have only one type of cationic polymerizable functional group, or may have two or more types.

Any of a monomer, an oligomer, and a polymer can be used for the cationic polymerizable resin used in the present invention.
Examples of the cationic polymerizable monomer used as the cationic polymerizable resin include vinyl ethers such as ethyl vinyl ether, n-butyl vinyl ether, cyclohexyl vinyl ether, butanediol vinyl ether, and diethylene glycol divinyl ether; phenyl glycidyl ether, p-t-butylphenyl glycidyl ether Butyl glycidyl ether, 2-ethylhexyl glycidyl ether, allyl glycidyl ether, 1,2-butylene oxide, 1,3-butadiene monooxide, 1,2-dodecylene oxide, epichlorohydrin, 1,2-epoxydecane Glycidyl ethers such as styrene oxide; 3-ethyl-3-hydroxyethyl oxetane, 1,4-bis [(3-ethyl-3-oxetanyl Toxi) methyl] benzene, 3,3-dimethyloxetane, 3,3-bis (chloromethyl) oxetane, 2-hydroxymethyloxetane, 3-methyl-3-oxetanemethanol, 3-methyl-3-methoxymethyloxetane, 3 -Ethyl-3-phenoxymethyloxetane, 3-ethyl-3 {[(3-ethyloxetane-3-yl) methoxy] methyl} oxetane, resorcinol bis (3-methyl-3-oxetanylethyl) ether, xylylene bisoxetane , Oxetanes such as m-xylylene bis (3-ethyl-3-oxetanyl ethyl ether); cyclohexene oxide, 1,13-tetradecadiene dioxide, limonene dioxide, (3,4,3 ′, 4′-diepoxy) Bicyclohexyl, 3,4-epoxy Alicyclic epoxies such as cyclohexylmethyl (3 ′, 4′-epoxy) cyclohexanecarboxylate, bis (3,4-epoxycyclohexyl) adipate, and bis (3,4-epoxycyclohexyl) sebacate; .
Of the above, 3-ethyl-3 {[(3-ethyloxetane-3-yl) methoxy] methyl} oxetane, (3,3 ', 4,4'-diepoxy) bicyclohexyl and 3,4-epoxycyclohexylmethyl One or more selected from (3 ′, 4′-epoxy) cyclohexanecarboxylate is preferred.

The cationic polymerizable oligomer used as the cationic polymerizable resin preferably has two or more cationic polymerizable functional groups in the molecule. Further, those having a weight average molecular weight of less than 4,000 are preferred, more preferably more than 1,000 and less than 4,000. In addition, a weight average molecular weight is a value calculated | required by gel permeation chromatography (GPC) and calculated | required by standard polystyrene conversion.
Examples of the oligomer include compounds represented by the following formulas (1) to (2).

In said formula (1), a, b, and c are the average repeating number of a structural unit, respectively, and show a number of 1 or more. The average of a + b + c is in the range of 10-25. In said formula (2), d is an average repeating number of a structural unit, and shows the number of 1-15.
When the cationic polymerizable oligomer is a compound represented by the above formula (1), the weight average molecular weight (polystyrene equivalent weight average molecular weight measured by GPC method) is preferably 2,000 to 3,800. When the cationically polymerizable oligomer is a compound represented by the above formula (2), the weight average molecular weight is preferably 1,200 to 2,000. Especially, the compound shown by the said Formula (1) is preferable.
As a commercial item containing the compound shown by the said Formula (1), "EHPE3150" (a brand name, Daicel Corporation make) etc. can be mentioned.

The polymer-type cationic polymerizable resin preferably has a weight average molecular weight (polystyrene equivalent weight average molecular weight measured by GPC method) of 4,000 or more from the viewpoint of curling suppression, coloring and yellowing suppression, and surface protection performance. Is 4,000 to 100,000, more preferably 5,000 to 50,000, and still more preferably 10,000 to 50,000.
Although there is no restriction | limiting in particular about the glass transition temperature of a polymer type cationic polymerizable resin, The higher one is preferable and it is 40 degreeC or more normally.
The number of functional groups of the polymer-type cationic polymerizable resin is not particularly limited, but from the viewpoint of curability, it is preferable that the number of functional groups per molecule is large (that is, the functional group equivalent is low). The functional group equivalent of the polymer-type cationic polymerizable resin is preferably 400 g / equivalent or less, more preferably 300 g / equivalent or less, and further preferably 250 g / equivalent or less.

  Specific examples of the polymer type cationic polymerizable resin include those having a structural unit represented by the following general formula (3).

In general formula (3), R ¹ represents a hydrogen atom or a methyl group, and R ² represents an organic group containing at least one cationically polymerizable functional group.
Examples of the structural unit represented by the general formula (3) include structural units represented by the following (3-1) to (3-26).

  Among the above structural units, from the viewpoint of curability, the polymer type cationic polymerizable resin preferably has at least one structural unit selected from the above formulas (3-1) to (3-7). It is more preferable to have at least one structural unit selected from (3-1), (3-5), (3-6) and (3-7).

  From the viewpoint of curability and curling, the polymer type cationic polymerizable resin preferably contains 50% by mole or more, more preferably 75 to 100% by mole, and still more preferably 90 to 90% by mole of the structural unit represented by the general formula (3). It is preferable to contain 100 mol%.

The polymer type cationic polymerizable resin may contain other structural units other than the structural unit represented by the general formula (3). The other structural unit may be a structural unit derived from a compound copolymerizable with a compound capable of forming the structural unit represented by the general formula (3). Examples of the compound include an alkyl (meth) acrylate having an alkyl group having 1 to 12 carbon atoms and a cycloalkyl (meth) acrylate having a cycloalkyl group having 3 to 12 carbon atoms. A (meth) acrylate having 6 alkyl groups is preferred. In addition, the said alkyl group, a cycloalkyl group, etc. may have a substituent, respectively.
The polymer type cationic polymerizable resin may contain only one kind of the other structural unit, or may contain two or more kinds.

Specific examples of such a polymer type cationic polymerizable resin are selected from 3,4-epoxycyclohexylmethyl (meth) acrylate, glycidyl (meth) acrylate, and 3- (meth) acryloxymethyl-3-ethyloxetane. Homopolymers of compounds; two or more copolymers of these compounds; and copolymers with other (meth) acrylates copolymerizable with these compounds.
As a commercial product of a polymer containing glycidyl methacrylate as a structural unit, “Malproof G-01100 (weight average molecular weight 12,000, Tg 47 ° C., epoxy equivalent 170 g / equivalent)”, “Malproof G-0150M (weight average) Molecular weight 10,000, Tg 71 ° C., epoxy equivalent 310 g / equivalent) ”,“ Malproof G-0250SP (weight average molecular weight 20,000, Tg 74 ° C., epoxy equivalent 310 g / equivalent) ”(trade name, both Co., Ltd.) Oil)).

The above cationic polymerizable resins can be used singly or in combination of two or more.
Among the above, the cationic polymerizable resin used in the present invention preferably includes a cationic polymerizable resin having a weight average molecular weight (polystyrene equivalent weight average molecular weight measured by GPC method) of 3,000 or more. By containing a cationically polymerizable resin having a weight average molecular weight of 3,000 or more, curling is less likely to occur, coloration and yellowing when stored under high temperature and high humidity conditions, excellent flexibility, and the inside of the image display device A multilayer base material having sufficient surface protection performance as a protective member used in the above is obtained. The reason for this is not clear, but is presumed as follows.
Of the cationic polymerizable resin and the radical polymerizable resin, the radical polymerizable resin has a faster curing rate. Therefore, when the ionizing radiation curable resin composition containing the cationic polymerizable resin and the radical polymerizable resin is cured, first, the radical polymerization reaction proceeds first and the crosslinking proceeds. Here, the cation polymerization reaction is performed between the cation polymerizable resins, but due to the thickening due to the progress of the radical polymerization reaction, the progress of the cation polymerization reaction is suppressed. For this reason, when only a monomer is used as the cationic polymerizable resin, it is expected that an unreacted monomer remains in the cured film. It is considered that this unreacted monomer falls off from the cured film during storage under high-temperature and high-humidity conditions, or undergoes decomposition due to oxidation, hydrolysis, ultraviolet ray degradation, etc., which causes yellowing.
However, since the cationic polymerizable resin having a weight average molecular weight of 3,000 or more is less likely to fall off from the cured film and is not easily decomposed as described above, if a cationic polymerizable resin having a weight average molecular weight of 3,000 or more is used, coloring or It is inferred that yellowing will be reduced. A cationically polymerizable resin having a weight average molecular weight of 3,000 or more is also preferable in that it generates little heat during curing, and therefore has little heat damage to the base film and hardly causes wrinkles on the cured surface.

  The content of the cationic polymerizable resin having a weight average molecular weight of 3,000 or more in the cationic polymerizable resin is preferably 65% by mass or more, more preferably 75 to 100% by mass, and further preferably 85 to 100% by mass. It is. When the content is 65% by mass or more, it is possible to obtain a multilayer base material with less curling, little yellowing when stored under initial coloring and high temperature and high humidity conditions, and excellent surface protection performance. it can.

[Radical polymerizable resin]
In the present invention, the ionizing radiation curable radical polymerizable resin means a compound having a radical polymerizable functional group in the molecule and not having the above-mentioned cationic polymerizable functional group. Examples of the radical polymerizable functional group include ethylenically unsaturated bond-containing groups such as a (meth) acryloyl group, a vinyl group, and an allyl group. Among these, from the viewpoint of the strength and curability of the protective layer to be obtained, the radical polymerizable resin is preferably a compound having two or more ethylenically unsaturated bond-containing groups in the molecule, and a (meth) acryloyl group in the molecule. A polyfunctional (meth) acrylate compound having two or more is more preferable. As the polyfunctional (meth) acrylate compound, any of a monomer, an oligomer and a polymer can be used, but it is preferable that at least a polyfunctional (meth) acrylate monomer is included from the viewpoint of the strength and curability of the protective layer.

Among polyfunctional (meth) acrylate compounds, bifunctional (meth) acrylate monomers include ethylene glycol di (meth) acrylate, bisphenol A tetraethoxydiacrylate, bisphenol A tetrapropoxy diacrylate, and 1,6-hexanediol diacrylate. Etc.
Examples of the tri- or higher functional (meth) acrylate monomer include trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, dipenta Examples include erythritol tetra (meth) acrylate and isocyanuric acid-modified tri (meth) acrylate.
In addition, the (meth) acrylate monomer may be modified with a part of the molecular skeleton, and has been modified with ethylene oxide, propylene oxide, caprolactone, isocyanuric acid, alkyl, cyclic alkyl, aromatic, bisphenol and the like. Things can also be used.

The polyfunctional (meth) acrylate oligomer is not particularly limited as long as it is a bifunctional or higher functional (meth) acrylate oligomer. For example, urethane (meth) acrylate oligomer, epoxy (meth) acrylate oligomer, polyester (meth) Examples include various (meth) acrylate oligomers such as acrylate oligomers and polyether (meth) acrylate oligomers.
A urethane (meth) acrylate oligomer is obtained by reaction of a polyhydric alcohol and organic diisocyanate and hydroxy (meth) acrylate, for example.
Preferred epoxy (meth) acrylate oligomers are (meth) acrylates obtained by reacting tri- or higher functional aromatic epoxy resins, alicyclic epoxy resins, aliphatic epoxy resins and the like with (meth) acrylic acid, 2 A functional or higher aromatic epoxy resin, an alicyclic epoxy resin, an aliphatic epoxy resin or the like, a (meth) acrylate obtained by reacting a polybasic acid and (meth) acrylic acid, and a bifunctional or higher aromatic epoxy resin , (Meth) acrylates obtained by reacting alicyclic epoxy resins, aliphatic epoxy resins, etc. with phenols and (meth) acrylic acid.

The polyfunctional (meth) acrylate oligomer preferably has a weight average molecular weight (polystyrene converted weight average molecular weight measured by GPC method) of less than 4,000, more preferably more than 1,000 and less than 3,000.
Moreover, the polyfunctional (meth) acrylate oligomer is more preferably 3 to 12 functional, and further preferably 3 to 10 functional. When the number of functional groups is within the above range, a protective layer having excellent strength can be obtained.

  The polyfunctional (meth) acrylate polymer is not particularly limited as long as it is a bifunctional or higher functional (meth) acrylate polymer. For example, urethane (meth) acrylate polymer, epoxy (meth) acrylate polymer, polyester (meth) acrylate polymer Various (meth) acrylate polymers such as polyether (meth) acrylate polymers can be used.

From the viewpoint of obtaining the above effects, the polyfunctional (meth) acrylate polymer preferably has a weight average molecular weight (polystyrene equivalent weight average molecular weight measured by GPC method) of 4,000 or more, preferably 10,000 to 100, 000, more preferably 10,000 to 50,000. When the weight average molecular weight is 100,000 or less, the curability and the coating property are good.
The number of functional groups in the polyfunctional (meth) acrylate polymer is not particularly limited, but from the viewpoint of curability, it is preferable that the number of functional groups per molecule is large (that is, the functional group equivalent is low). The functional group equivalent of the polyfunctional (meth) acrylate polymer is preferably 400 g / equivalent or less, more preferably 300 g / equivalent or less, and still more preferably 250 g / equivalent or less.

The above radical polymerizable resins can be used singly or in combination of two or more.
Especially, it is preferable that the radically polymerizable resin used for this invention has the above-mentioned polyfunctional (meth) acrylate monomer as a main component from a viewpoint of sclerosis | hardenability and the mechanical strength of a protective layer. The content is preferably 50% by mass or more, more preferably 70 to 100% by mass, and still more preferably 85 to 100% by mass with respect to the total amount of the radical polymerizable resin.

The radical polymerizable resin preferably includes a radical polymerizable resin having a hydroxyl group. The radical polymerizable resin having a hydroxyl group may be any of a monomer, an oligomer, and a polymer, but is preferably a monomer, and more preferably the aforementioned polyfunctional (meth) acrylate monomer. By including a radically polymerizable resin having a hydroxyl group, the balance of strength and curl suppression of the protective layer obtained is improved. The reason why such an effect is obtained is that the hydroxyl group in the radical polymerizable resin increases the rate of cation polymerization by a chain transfer reaction to the cation polymerization active terminal and is incorporated into the polymerization network to become a crosslinking point. It is considered that the strength of the cured product is improved because the bond becomes strong.
In addition, when the radical polymerizable resin has a hydroxyl group, the water contact angle on the surface of the cured product is likely to be lowered, which is preferable when the multilayer base material is used for a bonding portion described later.
Preferable polyfunctional (meth) acrylate monomers having a hydroxyl group include pentaerythritol tri (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate and the like. These can be used alone or in combination of two or more.

As the radical polymerizable resin, a mixture of a radical polymerizable resin having a hydroxyl group and a radical polymerizable resin having no hydroxyl group may be used. For example, a mixture of pentaerythritol tri (meth) acrylate and pentaerythritol tetra (meth) acrylate, dipentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, and a mixture of dipentaerythritol hexa (meth) acrylate Etc.
In the above mixture, the proportion of the radical polymerizable resin having a hydroxyl group is preferably 25% by mass or more, more preferably 50% by mass or more, and further preferably 65% by mass or more, from the viewpoint of the balance between the strength of the protective layer and curl suppression. And preferably less than 100% by mass.

The content ratio of the cationic polymerizable resin to the radical polymerizable resin in the ionizing radiation curable resin composition is preferably 5:95 to 30:70 by mass ratio, and is preferably 5:95 to 20:80. It is more preferable that the ratio is 5:95 to 15:85. If the mass ratio of the cationic polymerizable resin is 5 or more, the occurrence of curling can be sufficiently suppressed, and a protective layer excellent in flexibility can be formed. Moreover, if the above-mentioned mass ratio of the cationic polymerizable resin is 30 or less, initial coloration is small, yellowing when stored under high-temperature and high-humidity conditions is small, and a protective layer with good surface protection performance can be formed. it can.
In addition, the total content of the cationic polymerizable resin and the radical polymerizable resin in the ionizing radiation curable resin composition is preferably 50% by mass or more, more preferably 70%, based on the total amount of the resin components in the composition. -100 mass%, More preferably, it is 85-100 mass%. A total content of 50% by mass or more is preferable in terms of strength and curability.

  The ionizing radiation curable resin composition may contain a resin component other than the cationic polymerizable resin and the radical polymerizable resin as long as the performance of the present invention is not impaired. Examples of the resin component include thermoplastic resins, thermosetting resins, and compounds having a cationic polymerizable functional group and a radical polymerizable functional group. When the ionizing radiation curable resin composition contains a thermosetting resin, a curing agent is added as necessary.

From the viewpoint of curability, the ionizing radiation curable resin composition preferably includes at least a photocationic polymerization initiator, and more preferably includes a photocationic polymerization initiator and a photoradical polymerization initiator. There is no restriction | limiting in particular as these photoinitiators, A conventionally well-known thing can be used.
Examples of the cationic photopolymerization initiator include aryl diazonium salts such as p-methoxybenzenediazonium hexafluorophosphate, diaryliodonium salts such as diphenyliodonium hexafluorophosphate, diphenyliodonium hexafluoroantimonate; triphenylsulfonium hexafluorophosphate, triphenylsulfone Phenylsulfonium hexafluoroantimonate, diphenyl [4- (phenylthio) phenyl] sulfonium hexafluorophosphate, diphenyl [4- (phenylthio) phenyl] sulfonium hexafluoroantimonate, diphenyl [4- (phenylthio) phenyl] sulfonium pentafluorohydroxy Antimonate, diphenyl [4- (phenylthio) phenyl] Triarylsulfonium salts such as rufonium tris (pentafluoroethyl) trifluorophosphate and 4,4-bis (thiantrenium-9-yl) -diphenyl ether dihexafluorophosphate (compound represented by the following structure); triphenylselenonium Triarylselenonium salts such as hexafluorophosphate, triphenylselenonium tetrafluoroborate, triphenylselenonium hexafluoroantimonate; dialkylphenacyl such as dimethylphenacylsulfonium hexafluoroantimonate, diethylphenacylsulfonium hexafluoroantimonate Sulfonium salt; 4-hydroxyphenyldimethylsulfonium hexafluoroantimonate, 4-hydroxyphenylbenzene Dialkyl-4-hydroxy salts such as dimethylsulfonium hexafluoroantimonate; sulfonic acid esters such as α-hydroxymethylbenzoin sulfonate, N-hydroxyimide sulfonate, α-sulfonyloxyketone, β-sulfonyloxyketone, etc. Is mentioned.

Commercially available triarylsulfonium salts include “AT-6922” and “AT-6976” (trade names, both manufactured by ACETO); “Adekaoptomer SP-150”, “Adekaoptomer SP-170”, “ Adekaoptomer SP-171 "(trade name, all manufactured by ADEKA Corporation);" CPI-100P "," CPI-110P "," CPI-110A "," CPI-210S "(trade names, both are Sun Apro) "TS-91", "TS-01" (trade names, both manufactured by Sanwa Chemical Co., Ltd.); "Esacure 1187", "Esacure 1188" (trade names, both manufactured by Lamberti), “Omnicat 550”, “Omnicat 650” (trade names, both manufactured by IGM RESIN) and the like.
Among these, from the viewpoints of curability and transparency, the photocationic polymerization initiator is preferably a triarylsulfonium salt, such as diphenyl [4- (phenylthio) phenyl] sulfonium hexafluorophosphate, diphenyl [4- (phenylthio) phenyl. ] At least one selected from sulfonium tris (pentafluoroethyl) trifluorophosphate and 4,4-bis (thiantrenium-9-yl) -diphenyl ether dihexafluorophosphate is more preferable, and diphenyl [4- (phenylthio) More preferred is phenyl] sulfonium hexafluorophosphate.

  The above cationic photopolymerization initiators can be used alone or in combination of two or more. Furthermore, it can also be used in combination with an appropriate sensitizer.

Examples of the photoradical polymerization initiator include one or more selected from acetophenone, benzophenone, α-hydroxyalkylphenone, Michler's ketone, benzoin, benzylmethyl ketal, benzoylbenzoate, α-acyloxime ester, thioxanthones and the like. Among these, α-hydroxyalkylphenone is preferable from the viewpoint of curability and transparency.
The said photoradical polymerization initiator can be used individually or in combination of 2 or more types.

The content of the photopolymerization initiator in the ionizing radiation curable resin composition is preferably 1 to 20 parts by mass, more preferably 2 to 10 parts by mass with respect to 100 parts by mass of the ionizing radiation curable resin from the viewpoint of curability. Part. The content is the total amount of the photocationic polymerization initiator and the photoradical polymerization initiator.
Of these, the content ratio of the cationic photopolymerization initiator to the radical photopolymerization initiator is preferably 1: 0.5 to 1:10 by mass ratio, more preferably 1: 1 to 1: 8. Preferably, it is 1: 1-1: 4. If the content ratio is in the above range, sufficient strength and curability can be imparted, and there is little coloration, and when it is stored under high-temperature and high-humidity conditions, it suppresses yellowing under external light such as sunlight. Can do.

The ionizing radiation curable resin composition preferably contains at least one inorganic fine particle selected from silica and alumina from the viewpoint of improving the strength of the protective layer and reducing curling shrinkage to suppress curling. From the viewpoint of imparting hydrophilicity to the protective layer and reducing the water contact angle on the surface of the protective layer, silica fine particles are more preferable. The inorganic fine particles can be used alone or in combination of two or more.
Examples of the silica fine particles include solid fine particles and hollow fine particles. From the viewpoint of improving the strength of the protective layer, solid fine particles are preferable. In the present invention, solid fine particles mean fine particles having no voids. Since the solid fine particles are neither porous nor hollow, the solid fine particles are not easily crushed by pressure (external pressure) applied to the particles from the outside, and are excellent in pressure resistance.

The shape of the solid silica fine particles is not particularly limited, and may be any of a substantially spherical shape, a chain shape, a needle shape, a plate shape, a piece shape, a rod shape, and a fiber shape. From the viewpoint of improving the strength of the protective layer, it is preferably substantially spherical or chain-like, and more preferably elliptical spherical silica particles or chain-like silica fine particles.
From the viewpoint of improving the strength of the protective layer, the solid silica fine particles are irregularly shaped silica fine particles in which 3 to 20 substantially spherical silica fine particles having an average particle diameter of 1 to 100 nm are bonded by an inorganic chemical bond. Is more preferable.

The silica fine particles may be surface-treated with a silane coupling agent, a titanate coupling agent, a fatty acid, a surfactant, or the like. For example, silica fine particles whose surface is treated with a silane coupling agent are preferably used. The silane coupling agent can be used without any particular limitation, but as a functional group in terms of imparting hardness to the protective layer and improving the compatibility with the ionizing radiation curable resin to obtain transparency ( A silane coupling agent having at least one selected from a (meth) acryloyl group and an epoxy group is preferred. By surface treatment with these silane coupling agents, the silica fine particles become reactive silica fine particles having at least one reactive group selected from a (meth) acryloyl group and an epoxy group.
Examples of the silane coupling agent having a (meth) acryloyl group include “KBM-502”, “KBM-503”, “KBE-503”, and “KBM-5103” (trade names, all of which are trade names). (Made by Co., Ltd.) etc. are mentioned preferably. Examples of the silane coupling agent having an epoxy group include commercially available “KBM-303”, “KBM-402”, “KBM-403”, “KBE-402”, “KBE-403” (trade names, both Preferred is Shin-Etsu Chemical Co., Ltd.).

Examples of the form of the inorganic fine particles include a solid form or a colloid form dispersed in a solvent, but those dispersed in a solvent are preferable in terms of dispersibility in the protective layer. The average primary particle diameter of the inorganic fine particles is usually about 1 to 300 nm, preferably 1 to 150 nm, and more preferably 5 to 75 nm from the viewpoint of the transparency of the protective layer.
In the present invention, the average particle size of the particles can be calculated by the following operations (1) to (3) when the particles are primary particles that are not in the form of aggregated particles.
(1) Taking a surface image of a scanning transmission electron microscope (TEM, STEM) of the particle itself or a particle dispersion liquid coated and dried on a transparent substrate (observation conditions: acceleration voltage 10 to 30 kV, observation) (Magnification 50,000 to 300,000 times).
(2) Ten arbitrary particles are extracted from the surface image, the major axis and minor axis of each particle are measured, and the particle diameter of each particle is calculated from the average of the major axis and minor axis.
(3) The same operation is performed five times in the imaging of another screen of the same sample, and the value obtained from the number average of the particle diameters of a total of 50 primary particles is defined as the average primary particle diameter.
Further, when the particles take the form of aggregated particles, the particle diameter of each aggregated particle can be calculated from the average of the major axis and the minor axis of the aggregated particle, and the average can be calculated. Specifically, two arbitrary aggregated particles are extracted from the surface image or cross-sectional image of the multilayer substrate by a scanning transmission electron microscope (TEM, STEM) (in the case of a surface image, two can be selected at random). In the case of a cross section, it is unclear where the particles are cut, so select two particles that are as large as possible.) Measure the major axis and minor axis of each agglomerated particle to determine the particle size of each agglomerated particle The same operation is performed 9 times in another screen imaging of the same sample, and the value obtained from the number average of the particle diameters of the aggregated particles for a total of 20 particles is set as the average particle diameter of the aggregated particles (observation conditions) : Acceleration voltage 10 to 30 kV, observation magnification 50,000 to 300,000 times). The major axis is the longest diameter on the aggregated particle screen. The minor axis is a distance between two points where a line segment perpendicular to the midpoint of the line segment constituting the major axis is drawn and the perpendicular line segment intersects with the aggregated particles.

  The content of the inorganic fine particles in the ionizing radiation curable resin composition is preferably 10 to 70% by mass and more preferably 15 to 60% by mass with respect to the total amount of the ionizing radiation curable resin and the inorganic fine particles. When the content of the inorganic fine particles is 10% by mass or more, the effect of improving the strength of the protective layer and the effect of suppressing the curling due to the reduction of curing shrinkage can be obtained. Moreover, if it is 70 mass% or less, sclerosis | hardenability and film forming property will not be impaired.

If necessary, the ionizing radiation curable resin composition further contains additives such as a photopolymerization accelerator, a refractive index adjusting agent, an antiglare agent, an antifouling agent, an antistatic agent, a leveling agent, and a lubricant. You can also
The photopolymerization accelerator is one that can reduce polymerization inhibition by air during curing and accelerate curability, and is selected from, for example, p-dimethylaminobenzoic acid isoamyl ester, p-dimethylaminobenzoic acid ethyl ester, and the like. 1 type or more is mentioned.

  The antistatic agent is not particularly limited, and examples thereof include cationic antistatic agents such as quaternary ammonium salts and pyridinium salts; anionic charging agents such as sulfonates, sulfates, phosphates, and phosphonates. Inhibitors; zwitterionic antistatic agents such as alkylbetaines and derivatives thereof, imidazolines and derivatives thereof, alanine and derivatives thereof; nonionic antistatic agents such as amino alcohols and derivatives thereof, glycerin and derivatives thereof, polyethylene glycol and derivatives thereof Preferred examples include organometallic compounds such as tin and titanium alkoxides; metal chelate compounds such as acetylacetonate salts of the organometallic compounds. An ion conductive polymer obtained by polymerizing or copolymerizing monomers having various ion conductive groups such as the above cationic, anionic and zwitterionic groups can also be used.

As the antistatic agent, at least one selected from alkali metal salts and ionic liquids is also preferably used. Examples of the alkali metal salt include alkali metal ions such as Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ and Cs ⁺ , halogen ions such as Cl ⁻ , Br ⁻ and I ⁻ , SO ₄ ²⁻ , NO ₃ ⁻ and ClO. Examples of the salt include a combination of ₄ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , various sulfonate ions, acid group ions such as COO ⁻ , or anions such as perchlorate ions. Of the alkali metal salts, lithium salts are preferred.

An ionic liquid refers to a molten salt that is liquid at room temperature (25 ° C.). Examples of the ionic liquid include imidazolium-based, pyridinium-based, quaternary ammonium-based, quaternary phosphonium-based cationic substances, counter ions such as Cl ⁻ , Br ⁻ and I ⁻ halogen ions, SO ₄ ^2- , NO ₃ ⁻ , ClO ₄ ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , acid group ions such as various sulfonate ions and COO ^−, and salts (liquids) bonded to anions such as perchlorate ions. .

  Furthermore, as an antistatic agent, conductive polymers such as polyaniline, polyacetylene, polypyrrole, polythiophene, and polyvinylcarbazole; carbon-based materials such as fullerene and carbon nanotubes; indium oxide, zinc oxide, tin oxide, potassium titanate, titanium oxide, tin Metal oxide materials such as antimony oxide, indium-tin oxide, and antimony-tin oxide can also be used.

An antistatic agent can be used individually by 1 type or in combination of 2 or more types. Among the antistatic agents, from the antistatic effect and compatibility with the ionizing radiation curable resin, from cationic antistatic agents such as quaternary ammonium salts and pyridinium salts or polymers thereof, and alkali metal salts. At least one selected is preferable, and at least one selected from a quaternary ammonium salt or a polymer thereof and a lithium salt is more preferable.
The content of the antistatic agent in the ionizing radiation curable resin composition can be appropriately selected according to the purpose and is not particularly limited, but is preferably 1 to 15 with respect to 100 parts by mass of the ionizing radiation curable resin. It is 2 mass parts, More preferably, it is 2-10 mass parts, More preferably, it is 3-8 mass parts. When the content is 1 part by mass or more, sufficient antistatic properties are imparted. Moreover, if it is 15 mass parts or less, precipitation and bleeding out of an antistatic agent can be avoided.

Furthermore, the ionizing radiation curable resin composition can contain a solvent. As the solvent, any solvent that can dissolve each component contained in the resin composition can be used without particular limitation, but ketones or esters are preferable, and at least one selected from methyl ethyl ketone and methyl isobutyl ketone is used. More preferred. The said solvent can be used individually or in combination of 2 or more types.
The content of the solvent in the ionizing radiation curable resin composition is usually 20 to 90% by mass, preferably 30 to 85% by mass, and more preferably 40 to 80% by mass. When the content of the solvent is within the above range, the coating suitability is excellent.

The protective layer can be formed by applying an ionizing radiation curable resin composition on a base film to form a coating layer, and performing a drying step as necessary, followed by curing.
The coating layer can be formed by applying an ionizing radiation curable resin composition prepared by mixing other components such as a cationic polymerizable resin, a radical polymerizable resin, and a photopolymerization initiator.
Moreover, you may form by the method of preparing separately the resin composition containing a cationic polymerizable resin, and the resin composition containing a radical polymerizable resin, and apply | coating it sequentially on a base film. In this case, the order of application is not particularly limited, but from the viewpoint of imparting strength to the surface of the protective layer and reducing curling, the radically polymerizable resin is applied after applying the resin composition containing the cationic polymerizable resin. It is more preferable to apply a resin composition containing the same. In addition, after forming the coating layer of the resin composition containing the cationic polymerizable resin, and then forming the coating layer of the resin composition containing the radical polymerizable resin, the coating layers are simultaneously cured by irradiation with ionizing radiation. Is preferable in terms of adhesion between the layers.

  The method of applying the ionizing radiation curable resin composition may be any method that can be applied uniformly to a desired thickness, and may be appropriately selected from conventionally known methods. For example, gravure coating, knife coating, dip coating, spray coating, air knife coating, spin coating, roll coating, curtain coating, die coating, casting, bar coating, and extrusion coating Can be mentioned.

Subsequently, after performing a drying process as needed, the said coating layer is irradiated with ionizing radiations, such as an electron beam and an ultraviolet-ray, and the said coating layer is hardened. When an electron beam is used as the ionizing radiation, the acceleration voltage can be appropriately selected according to the resin used and the thickness of the layer, but it is usually preferable to cure the coating layer at an acceleration voltage of about 70 to 300 kV.
When ultraviolet rays are used as the ionizing radiation, those containing ultraviolet rays having a wavelength of 190 to 380 nm are usually emitted. There is no restriction | limiting in particular as an ultraviolet-ray source, For example, a high pressure mercury lamp, a low pressure mercury lamp, a metal halide lamp, a carbon arc lamp, etc. are used. The ultraviolet irradiation is preferably performed in a nitrogen atmosphere having an oxygen concentration of 1000 ppm or less.
Ultraviolet irradiation may be performed in a lump, and in order to prevent wrinkles from being generated on the surface of the cured product due to heat generated during the ultraviolet irradiation, the ultraviolet irradiation may be performed in a plurality of steps.

The thickness of the protective layer (at the time of curing) can be appropriately selected according to the thickness of the substrate film, but preferably 2 μm or more and 20 μm from the viewpoint of imparting sufficient strength and suppressing curling. More preferably, it is 2-15 micrometers, More preferably, it is 3-15 micrometers, More preferably, it is the range of 3-12 micrometers. If the thickness of the protective layer is 2 μm or more, surface protection performance and flexibility are good, and if it is less than 20 μm, curling can be suppressed while maintaining flexibility.
The thickness of the protective layer can be calculated, for example, by measuring the thickness of 20 locations from a cross-sectional image taken using a transmission electron microscope (TEM) and calculating the average value of the 20 locations.

  Moreover, the thickness ratio of the protective layer to the base film (the thickness of the protective layer / the thickness of the base film) is preferably 0.04 to 5 from the viewpoint of imparting sufficient strength and suppressing the occurrence of curling. Preferably it is 0.05-2, More preferably, it is the range of 0.05-0.5.

(Other layers)
The multilayer base material of the present invention may further have other functional layers such as an antireflection layer, an antistatic layer, a refractive index adjusting layer, and an antifouling layer on any surface of the base film. Among these, from the viewpoint of reducing reflection on the display surface, the multilayer base material preferably further has an antireflection layer. In this case, the multilayer base material has a structure having a base film, a protective layer, and an antireflection layer in this order, and a structure having an antireflection layer on the outermost surface of the multilayer base material is preferable.

  The antireflection layer may have a single layer structure composed of a layer having a lower refractive index than that of the protective layer. Further, a multilayer structure having a high refractive index layer and a low refractive index layer in order from the protective layer side, the outermost layer being a low refractive index layer, and the thickness d of each layer satisfying d = mλ / 4n may be employed. Here, m represents a positive odd number, n represents the refractive index of the low refractive index layer, and λ represents the wavelength. m is preferably 1. λ is preferably 450 to 700 nm, and more preferably 500 to 600 nm.

The low-refractive index layer and the high-refractive index layer can also be formed by a method such as vacuum deposition or sputtering using, for example, low-refractive index fine particles or high-refractive index fine particles. Examples of the low refractive index fine particles include SiO ₂ (refractive index n = 1.45), MgF ₂ (refractive index n = 1.38), LiF (refractive index n = 1.36), NaF (refractive index n = 1). .33), CaF ₂ (refractive index n = 1.44), 3NaF · AlF ₃ (refractive index n = 1.4), AlF ₃ (refractive index n = 1.37), Na ₃ AlF ₆ (refractive index n). = 1.33) and the like, and the hollow particles. As the high refractive index fine particles, Al ₂ O ₃ (refractive index n = 1.63), La ₂ O ₃ (refractive index n = 1.95), ZrO ₂ (refractive index n = 2.05), Y ₂ Examples thereof include fine particles of metal oxide such as O ₃ (refractive index n = 1.87).
From the viewpoint of forming a layer more easily, it is preferable to form these fine particles by a known method using, for example, a resin composition dispersed in an ionizing radiation curable resin used for the protective layer. Further, for example, the low refractive index layer has two or more reactive functional groups in one molecule, such as the above-mentioned low refractive index fine particles, fluorine-containing compounds such as vinylidene fluoride copolymer and silicone-containing vinylidene fluoride copolymer. For example, it may be formed using a curable resin composition preferably containing a fluorine-containing monomer having a pentaerythritol skeleton, an ionizing radiation curable resin, and the like.

  The multilayer substrate of the present invention may have a structure having an antistatic layer. The antistatic layer is preferably provided at a position in contact with at least one surface of the protective layer. For example, a configuration having a base film, an antistatic layer, and a protective layer in order; a configuration having a base film, a protective layer, and an antistatic layer in order; a base film, an antistatic layer, a protective layer, and an antistatic layer The structure which has in order; etc. are mentioned.

As an antistatic layer, the layer formed using the resin composition containing the antistatic agent mentioned above, for example is mentioned. The resin contained in the resin composition is not particularly limited as long as it is a transparent resin that can contain the antistatic agent. For example, a thermoplastic resin, a thermosetting resin, or an ionizing radiation curable resin. Etc.
There is no restriction | limiting in particular in the formation method of an antistatic layer, A normal coating method can be used. The thickness of the antistatic layer is not particularly limited as long as desired antistatic performance can be imparted.

  The multilayer base material of the present invention, when used in an image display device, for example, an air gap part or a bonding part of a touch panel image display device, exhibits sufficient surface protection performance in the manufacturing process, and the image display device is thin. The total thickness is preferably from 23 to 70 μm, more preferably from 25 to 50 μm, from the viewpoint of conversion to a low temperature.

(Properties of multilayer substrate)
The multilayer base material of the present invention is characterized by little coloring and little yellowing even when stored for a long time under high temperature and high humidity conditions. Regarding the coloring of the multilayer substrate, specifically, in the CIE1976-L * a * b * color system, b * is 2.0 or less, preferably 1.0 or less, more preferably 0.50 or less. It is. When b * of the multilayer substrate exceeds 2.0, the appearance is deteriorated when used in an image display device.
For yellowing under high temperature and high humidity conditions, the multilayer substrate of the present invention was subjected to a temperature of 80 ° C. and 90% R.P. H. The Δb * before and after storage for 500 hours is preferably less than 0.70, more preferably 0.40 or less, and still more preferably 0.20 or less.
Specifically, the value of b * can be measured by the method described in Examples.

  The multilayer base material of the present invention is characterized by less curling. As for the degree of curling, it is preferable that the shortest distance between the edges of the multilayer base material when the multilayer base material of the present invention is cut to 100 mm × 100 mm and placed on a horizontal surface is 60 to 100 mm, and 30 to 100 mm. It is more preferable that “The shortest distance between the edges of a multilayer substrate” means the shortest distance between opposite sides of the multilayer substrate where the curl has occurred, the shortest distance between diagonals of the multilayer substrate where the curl has occurred, or the occurrence of curl It means the shortest distance among the shortest distances between one side of the multilayer base material and the corners facing it. When no curling occurs, the shortest distance is 100 mm, and when curled in a cylindrical shape, the shortest distance is 0 mm. Specifically, the curl evaluation can be performed by the method described in Examples.

  In addition, the multilayer base material of the present invention, when used in an image display device, for example, an air gap part or a bonding part of a touch panel image display device, has a protective layer surface from the viewpoint of exhibiting sufficient surface protection performance in the production process. The pencil hardness is preferably H or higher, more preferably 2H or higher, and still more preferably 3H or higher. In particular, when used for an air gap portion, a pencil hardness of H or higher is preferable from the viewpoint of preventing deformation when an external force is applied. Moreover, when using for a bonding part, since the multilayer base material and the bonding layer mentioned later contact, the pencil hardness of the surface of a protective layer has preferable 2H or more. The pencil hardness can be evaluated according to JIS K5600-5-4, and can be specifically measured by the method described in Examples.

  The multilayer substrate of the present invention is suitably used for an image display device. In particular, it can be used in an air gap part or a bonding part of a touch panel image display device for the purpose of preventing damage to a protective member inside the image display device, for example, a sensor part mainly in a touch panel manufacturing process.

Here, although there is no restriction | limiting in particular about the water contact angle of the outermost surface of the multilayer base material of this invention, When using for the bonding part of a touchscreen image display apparatus, the temperature of the outermost surface of a multilayer base material is 25 degreeC, and humidity is 50. The water contact angle in% is preferably 80 ° or less, more preferably 70 ° or less. When the water contact angle is 80 ° or less, the adhesiveness with the bonding layer of the touch panel image display device is good, and bubbles are less likely to enter even when bonded to the bonding layer. The water contact angle is preferably 40 ° or more from the viewpoint of facilitating re-peeling from the bonding layer when a product defect occurs.
From the same viewpoint as described above, when the multilayer base material of the present invention is used for a bonding part of a touch panel image display device, the contact angle of hexadecane at a temperature of 25 ° C. and a humidity of 50% of the outermost surface of the multilayer base material is preferably Is 25 ° or less, more preferably 20 ° or less, and preferably 2 ° or more.
The contact angle can be measured according to JIS R3257 (1999) “Test method for wettability of substrate glass surface”.

When using the multilayer base material of this invention for an air gap part, it is preferable that the surface reflectance is 1.1% or less. This is because when the surface reflectance of the multilayer base material is high, a decrease in luminance due to this reflection and a decrease in visibility due to the occurrence of Newton rings occur. From this viewpoint, the surface reflectance of the multilayer base material is more preferably 0.5% or less, and further preferably 0.35% or less. A surface reflectance is calculated | required by bonding the surface by the side of the base film of a multilayer base material to a black acrylic board through an adhesive, for example, and measuring a 5 degree regular reflectance with a spectrometer.
As a method for lowering the surface reflectance of the multilayer base material, the above-described antireflection layer may be provided on the outermost surface.

[Image display device]
The image display device of the present invention comprises the multilayer substrate of the present invention. The image display device is not particularly limited, and examples thereof include a liquid crystal display device (LCD), a plasma display device (PDP), an inorganic and organic EL display device, an electronic paper display, and a touch panel image display device. A touch panel image display device is preferable from the viewpoint of satisfying the demand for thinning and from the viewpoint of providing various effects by providing the multilayer base material of the present invention. For example, by providing the multilayer base material of the present invention in the air gap part or bonding part of the touch panel image display device, the appearance deteriorates due to uneven thickness of the air gap part or bonding part due to low flatness of the multilayer base material, A decrease in sensor sensitivity can be avoided. Examples of the touch panel include a capacitive touch panel, a resistive touch panel, an optical touch panel, an ultrasonic touch panel, and an electromagnetic induction touch panel. The touch panel image display device may be an on-cell type or an in-cell type.
Here, the air gap portion of the touch panel image display device refers to a portion in contact with a gap (air gap) of about 0.5 to 1 mm provided via a spacer between the touch panel and the display element. By having the air gap, even when a surface protective material such as glass provided on the outermost surface of the touch panel is broken by an external impact, the display element is not affected.

FIG. 1 is a cross-sectional view illustrating an example of a touch panel image display device having an air gap portion. In FIG. 1, 10 is a touch panel, 20 is an air layer forming an air gap, 22 is a spacer, and 30 is a display element.
The touch panel 10 includes a surface protective material 11, a sensor 12, and a multilayer base material 13 in order. The multilayer base material 13 has at least a base film and a protective layer as described above. From the viewpoint of protecting the sensor, the multilayer base material 13 is preferably provided so that the surface on the protective layer side faces the air gap side.
In the touch panel image display device having the configuration of FIG. 1, the multilayer base material 13 includes a base material film, a protective layer, and antireflection from the viewpoint of reducing interface reflection resulting from a difference in refractive index between the touch panel 10 and the air layer 20. A structure having layers in order is preferable. In this case, the multilayer base material 13 is preferably provided so that the surface on the antireflection layer side faces the air gap side.
As the surface protective material 11, glass, a plastic substrate, or the like is used.

In FIG. 1, the sensor 12 is bonded to the surface protective material 11 via the adhesive layer 14. However, in the touch panel image display device of the present invention, the sensor 12 may be directly formed on the surface protective material 11. .
The display element 30 may have a protective material 31 on the surface on the air gap side. As the protective material 31, the multilayer substrate of the present invention can also be used. The multilayer substrate is also preferably provided so that the surface on the protective layer side faces the air gap side. In addition, from the viewpoint of reducing interfacial reflection derived from the refractive index difference between the air layer 20 and the display element 30, the multilayer base material is preferably configured to have a base film, a protective layer, and an antireflection layer in order. It is preferable that the surface on the antireflection layer side is provided so as to face the air gap side.

On the other hand, in the touch panel image display device 101 having the configuration shown in FIG. 1, the display element 30 (or the protective material 31), the air layer 20, and the touch panel 10 have different refractive indexes as described above. Reflection of light occurs at the interface with the air layer, the interface between the air layer and the touch panel, and the interface between the touch panel and the external atmosphere), which may cause a decrease in luminance.
Therefore, a touch panel image display device having a configuration in which a transparent resin (bonding layer) having a refractive index close to that of the touch panel 10 is enclosed in the air layer 20 has also been proposed. In this specification, a portion in contact with the bonding layer in the touch panel image display device is referred to as a bonding portion.

FIG. 2 is a cross-sectional view illustrating an example of a touch panel image display device having a bonding portion.
In the touch panel image display apparatus 102 of FIG. 2, 10 is a touch panel, 24 is a bonding layer, and 30 is a display element. Since the bonding layer 24 has a refractive index close to that of the touch panel 10, the light reflection at each interface between the layers in the touch panel image display device 101 in FIG.
Also in the touch panel image display device 102, the configuration of the touch panel 10 includes a surface protective material 11, a sensor 12, and a multilayer base material 13 in the same manner as in the case of FIG. 1. However, since the refractive index of the bonding layer 24 is close to that of the touch panel 10, an antireflection layer is not necessary in the multilayer base material 13. The display element 30 may further have a protective material (not shown) on the surface on the bonding layer side.

The resin used for the bonding layer 24 is not particularly limited as long as the resin has a refractive index close to that of the touch panel 10 and is less colored and highly transparent. From the viewpoint of weather resistance, mechanical strength, and visibility (blackness and presence / absence of Newton's ring), the bonding layer 24 can be a transparent optical adhesive (OCA) film or curable by irradiation with heat or ionizing radiation. It is preferable to use a cured product of the resin composition.
As the ionizing radiation curable resin composition, the same resin composition as described in the formation of the protective layer can be used, and any of cationic polymerizable resins and radical polymerizable resins can be used.

Examples of the display element 30 include a liquid crystal display element, an in-cell touch panel liquid crystal display element, an EL display element, and a plasma display element.
The in-cell touch panel liquid crystal element is a liquid crystal element in which a liquid crystal is sandwiched between two glass substrates, and a touch panel function such as a resistive film type, a capacitance type, and an optical type is incorporated therein. Examples of the liquid crystal display method of the in-cell touch panel liquid crystal element include an IPS method, a VA method, a multi-domain method, an OCB method, an STN method, and a TSTN method. In-cell touch panel liquid crystal elements are described in, for example, Japanese Patent Application Laid-Open Nos. 2011-76602 and 2011-222009.

  EXAMPLES Next, although an Example demonstrates this invention further in detail, this invention is not limited at all by these examples. “Part” and “%” are based on mass unless otherwise specified.

Synthesis Example 1 Synthesis of 3,4-epoxycyclohexylmethyl methacrylate homopolymer A 4-necked flask equipped with a nitrogen inlet, a stirrer, a condenser and a thermometer was charged with 48 parts of 3,4-epoxycyclohexylmethyl methacrylate, methyl 50 parts of isobutyl ketone (MIBK), 0.48 part of azobisisobutyronitrile (AIBN) and 0.49 part of dodecyl mercaptan were added and heated to 85 ° C. with stirring under a nitrogen atmosphere for 3 hours. . The obtained polymer solution had a solid content of 50%. When analyzed by GPC, the polymer weight average molecular weight (in terms of polystyrene) was 15,000.

Synthesis Example 2 Synthesis of 3,4-epoxycyclohexylmethyl methacrylate / methyl methacrylate / n-butyl methacrylate copolymer In a four-necked flask equipped with a nitrogen inlet, a stirrer, a condenser and a thermometer, 3,4-epoxycyclohexyl was added. Add 43.2 parts of methyl methacrylate, 2.4 parts of methyl methacrylate, 2.4 parts of n-butyl methacrylate, 50 parts of MIBK, 0.48 part of AIBN, and 0.25 part of dodecyl mercaptan, and stir in a nitrogen atmosphere at 85 ° C. The reaction was performed by heating for 3 hours. The solid part of the obtained polymer solution was 50%, and analysis by GPC revealed that the polymer weight average molecular weight (polystyrene conversion) was 26,000.

(Evaluation method)
(1) Measurement of thickness of protective layer The thickness of the protective layer in the multilayer substrates obtained in Examples and Comparative Examples was measured at 20 locations from cross-sectional images taken using a transmission electron microscope (TEM). And it computed from the average value of the value of 20 places.

(2) Curl evaluation The multilayer base material obtained by the Example and the comparative example was cut into 100 mm x 100 mm, and was mounted in the horizontal surface. The shortest distance between the edges of the multilayer substrate (the shortest distance between opposite sides of the multilayer substrate, the shortest distance between diagonals of the multilayer substrate, or the shortest distance between one side of the multilayer substrate and the opposite corner) The shortest distance) was measured with a ruler and evaluated according to the following criteria.
◎; 30-100mm
○: More than 0 mm, less than 30 mm ×: 0 mm (tubular shape)

(3) Coloring evaluation (initial coloring b *)
The initial coloration of the multilayer base materials obtained in Examples and Comparative Examples was calculated from the average value of b * measured at five locations using a spectroscope (“UVPC2450” manufactured by Shimadzu Corporation).
(Δb * when stored under high temperature and high humidity conditions)
After measuring the initial coloration (b *) of the multilayer substrate, the multilayer substrate was subjected to a temperature of 80 ° C. and 90% R.D. H. The sample was stored for 500 hours under the above conditions, and b * was measured by the same method as described above to determine Δb * before and after storage. The smaller the value of b * after storage and the smaller Δb *, the better the result.

(4) Pencil hardness About the multilayer base material obtained by the Example and the comparative example, the pencil hardness of the protective layer surface was measured by the method based on JISK5600-5-4 (1999) with the load of 500g.

(5) Flexibility evaluation (mandrel test)
About the multilayer base material obtained by the Example and the comparative example, the mandrel test was done based on the cylindrical mandrel method prescribed | regulated by JISK5600-5-1. The value (mmφ) shown in Table 1 indicates the minimum mandrel diameter at which the protective layer is not peeled or cracked when wound around a mandrel rod with the protective layer side facing outward, and the smaller this value, the more flexible It is excellent in.

Example 1
An ionizing radiation curable resin composition having the composition shown in Table 1 was applied on a base film (triacetylcellulose (TAC) film, thickness: 25 μm, manufactured by Konica Minolta Co., Ltd.) and dried at 70 ° C. for 40 seconds. . Next, the ionizing radiation curable resin composition was cured by irradiating ultraviolet rays so that the integrated light quantity was 250 mJ / cm ² to form a protective layer to obtain a multilayer substrate. The thickness of the protective layer was 7 μm.
Said evaluation was performed about the obtained multilayer base material. The evaluation results are shown in Table 1.

Examples 2-16, Comparative Examples 1-3
A multilayer base material was obtained in the same manner as in Example 1 except that the base film, the protective layer thickness, and the composition of the ionizing radiation curable resin composition for forming the protective layer were changed as shown in Table 1. The evaluation results are shown in Table 1.

The components shown in Table 1 are as follows. In addition, the mass part in a table | surface shows the mass part of solid content conversion except a solvent.
<Cationically polymerizable resin>
Polymer 1: 3,4-epoxycyclohexylmethyl methacrylate homopolymer solution synthesized in Synthesis Example 1 (50 mass% MIBK solution, Mw 15,000)

Polymer 2; 3,4-epoxycyclohexylmethyl methacrylate / methyl methacrylate / n-butyl methacrylate (mass ratio 90/5/5) copolymer solution synthesized in Synthesis Example 2 (50 mass% MIBK solution, Mw 26,000)

-Polymer 3: Glycidyl methacrylate unit-containing polymer (manufactured by NOF Corporation "Malproof G-01100", Mw 12,000, epoxy equivalent 170 g / equivalent)
Oligomer: Cationic polymerizable polyfunctional oligomer represented by the above formula (1) ("EHPE3150" manufactured by Daicel Corporation, Mw 3,200, epoxy equivalent 179 g / equivalent)
Cationic polymerizable monomer; bifunctional cationic polymerizable monomer represented by the following structural formula ((3,4,3 ′, 4′-diepoxy) bicyclohexyl)

<Radically polymerizable resin>
Radical polymerizable monomer 1; mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (“KAYARAD PET-30” manufactured by Nippon Kayaku Co., Ltd.)
・ Radical polymerizable monomer 2; Mixture of dipentaerythritol hexaacrylate and dipentaerythritol pentaacrylate (“KAYARAD DPHA” manufactured by Nippon Kayaku Co., Ltd.)
Radical polymerizable monomer 3; mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (“Aronix M-306” manufactured by Toagosei Co., Ltd., content of pentaerythritol triacrylate; 65 to 70 mass%)
Radical polymerizable monomer 4; mixture of dipentaerythritol hexaacrylate and dipentaerythritol pentaacrylate (“Aronix M-403” manufactured by Toagosei Co., Ltd., content of dipentaerythritol pentaacrylate; 50 to 60% by mass)
-Radical polymerizable oligomer: Polyfunctional urethane acrylate oligomer (Nippon Synthetic Chemical Industry Co., Ltd. "UV-1700B", Mw 2,000, functional group number 10)
-Radical polymerizable polymer: polyfunctional polymer acrylate (Arakawa Chemical Industries "beam set 371", Mw 40,000, acrylic equivalent 400 g / equivalent)

<Photocationic polymerization initiator>
CPI-100P: Triarylsulfonium salt-based photocationic polymerization initiator having the following structure (diphenyl [4- (phenylthio) phenyl] sulfonium hexafluorophosphate 50 mass% propylene carbonate solution, manufactured by San Apro Co., Ltd.)

<Radical radical polymerization initiator>
Irgacure 184; 1-hydroxycyclohexyl phenyl ketone (manufactured by BASF)

<Additives>
・ Leveling agent: Fluorine-based leveling agent (“F477” manufactured by DIC Corporation)
Antistatic agent: quaternary ammonium salt type antistatic polymer (“1SX-1055F” manufactured by Taisei Fine Chemical Co., Ltd.)
Silica fine particles: “MIBK-SD” manufactured by Nissan Chemical Industries, Ltd., silica dispersion, solvent MIBK, silica content 30%, average primary particle size 12 nm

<Solvent>
・ MIBK: Methyl butyl ketone ・ MEK: Methyl ethyl ketone

  As is clear from the results in Table 1, the multilayer substrate of the present example had little curling, initial coloring and yellowing due to high temperature and high humidity storage, high pencil hardness, and sufficient surface protection performance. On the other hand, the multilayer base material of Comparative Example 1 is curled because the curable resin composition forming the protective layer does not contain a cationic polymerizable resin, and the multilayer base material of Comparative Example 2 is further inferior in flexibility. became. In the multilayer base material of Comparative Example 3, the curable resin composition forming the protective layer does not contain a radical polymerizable resin. Therefore, when it is stored under high temperature and high humidity conditions, yellowing occurs and the hardness of the surface of the protective layer is low. Therefore, the surface protection performance was also low.

  The multilayer base material of the present invention has little curling, little coloration, little yellowing due to long-term storage under high temperature and high humidity conditions, excellent flexibility, and sufficient surface protection performance. Therefore, for example, by using it as a protective member inside the image display device, it is possible to prevent damage that may occur during the manufacturing process of the image display device, and to easily reduce the thickness without deteriorating the appearance of the image display device.

DESCRIPTION OF SYMBOLS 101,102 Touch panel image display apparatus 10 Touch panel 11 Surface protective material 12 Sensor 13 Multilayer base material 14 Adhesive layer 20 Air layer 22 forming air gap 22 Spacer 30 Display element 31 Protective material

Claims (10)

An ionizing radiation comprising a multilayer substrate having a protective layer on at least one surface of the substrate film, wherein the thickness of the substrate film is 40 μm or less, and the protective layer comprises a cationic polymerizable resin and a radical polymerizable resin It is a cured product of a curable resin composition, and the cationic polymerizable resin includes a cationic polymerizable resin having a weight average molecular weight of 3,000 or more , and b * is 2.0 in the CIE1976-L * a * b * color system. A multilayer substrate that is: The multilayer base material according to claim 1 , wherein a content ratio of the cationic polymerizable resin and the radical polymerizable resin in the ionizing radiation curable resin composition is 5:95 to 30:70 by mass ratio. . The ionizing radiation curable resin composition comprises a cationic photopolymerization initiator and a photo-radical polymerization initiator, the content ratio, in mass ratio 1: 0.5 to 1: 10, claim 1 or 3. The multilayer substrate according to 2. The multilayer substrate according to any one of claims 1 to 3 , wherein the cationic polymerizable resin has at least one cationic curable functional group selected from an epoxy group and an oxetanyl group. The multilayer substrate according to any one of claims 1 to 4 , wherein the radical polymerizable resin contains a polyfunctional (meth) acrylate monomer having a hydroxyl group. The thickness of the protective layer is 2μm or more and less than 20 [mu] m, a multilayer substrate according to any one of claims 1-5. The multilayer substrate according to any one of claims 1 to 6 , wherein a thickness ratio of the protective layer to the substrate film is 0.04 to 5 . The multilayer substrate according to any one of claims 1 to 7 , wherein the total thickness is 23 to 70 µm. The multilayer substrate according to any one of claims 1 to 8 , wherein the substrate film is selected from a triacetyl cellulose film, a polyester film, and an acrylic film. An image display device having a multi-layer substrate according to any one of claims 1-9.