JPWO2020008912A1 - Photocurable ink for optical sheets - Google Patents

Abstract

To provide a photocurable ink that has excellent adhesion to a polyethylene terephthalate film that has not been easily adhered and that suppresses yellowing of a cured product in a high temperature and high humidity (65 ° C., 95% RH) atmosphere. A photocurable ink containing a polymer (A) obtained by polymerizing at least one (meth) acrylate having a ring structure, a polyfunctional (meth) acrylate (B), and a photopolymerization initiator (D). A cured film made of a cured product of a photocurable ink, an optical sheet having the cured film, a backlight unit having the optical sheet, and a liquid crystal display element equipped with the backlight unit.

Description

INDUSTRIAL APPLICABILITY The present invention can form a cured product having excellent adhesion to a plastic such as a polyethylene terephthalate (PET) film that has not been particularly easily adhered, and the cured product in a high temperature and high humidity (65 ° C., 95% RH) atmosphere. The present invention relates to a photocurable ink in which yellowing is suppressed, a cured film formed from the ink, and an optical sheet containing the cured film.

In recent years, the applications of liquid crystal displays such as televisions, personal computers, smartphones, and mobile phones have expanded, and brighter liquid crystal displays are required. In order to improve the brightness of this liquid crystal display, it is important to improve the light diffusivity and light transmission in the light diffusing sheet of the backlight unit, and about 90% of the light diffusing sheet is made of polyethylene terephthalate (PET) film. The actual base film is further enhanced in light diffusivity by applying an ink containing a filler such as fine particles to the PET film using an acrylic resin as a binder. However, due to the pursuit of cost reduction by liquid crystal display manufacturers, there is a shift to PET (untreated PET) films that have not been subjected to easy-adhesion treatment, and therefore, further improvement in adhesion is required.

Patent Document 1 is an optical sheet for a liquid crystal display device provided with a transparent base material layer and a sticking prevention layer laminated on the back surface side of the base material layer and containing beads and a binder, which is a main component of the beads. An optical sheet for a liquid crystal display device is disclosed, wherein the component is a polyamide resin, and the binder is a resin composition containing an acrylic polymer as a main component.

As a transmissive liquid crystal display device, a backlight method that illuminates the liquid crystal layer from the back is widespread, and a backlight unit such as an edge light type (side light type) or a direct type is equipped on the lower surface side of the liquid crystal layer. There is. Generally, as shown in FIG. 1A (FIG. 3 of Patent Document 1), the edge light type backlight unit 40 is arranged with a light source 41 and an end portion along the light source 41. A square plate-shaped light guide plate 42 and a plurality of optical sheets 43 arranged so as to be stacked on the surface side of the light guide plate 42 are provided. The optical sheet 43 has optical functions such as diffusion and refraction with respect to transmitted light rays. (1) A light diffusion sheet 44 arranged on the surface side of a light guide plate 42 and mainly having a light diffusion function. , (2) A prism sheet 45 or the like, which is arranged on the surface side of the light diffusion sheet 44 and has a refraction function in the normal direction, is used.

Explaining the function of the backlight unit 40, first, the light rays incident on the light guide plate 42 from the light source 41 are reflected by the reflection dots or reflection sheets (not shown) on the back surface of the light guide plate 42 and each side surface, and are reflected from the surface of the light guide plate 42. It is emitted. The light rays emitted from the light guide plate 42 enter the light diffusing sheet 44, are diffused, and are emitted from the surface. The light rays emitted from the surface of the light diffusion sheet 44 enter the prism sheet 45, are refracted in the normal direction by the prism portions of a plurality of ridges formed on the surface, and are emitted further. Illuminates the entire surface of the liquid crystal layer.

The light diffusing sheet 44 disperses transmitted light rays substantially uniformly, and is used for the purpose of making the brightness uniform due to its light diffusing property, increasing the brightness in the front direction, and the like. As the light diffusion sheet 44, as shown in FIG. 1B, the base material layer 46 made of synthetic resin, the light diffusion layer 47 laminated on the surface of the base material layer 46, and the base material layer 46. It is provided with a sticking prevention layer 48 laminated on the back surface. The anti-sticking layer 48 prevents the inconvenience that the back surface of the light diffusion sheet 44 sticks (closely adheres) to the front surface of the light guide plate 42 to cause interference fringes. The anti-sticking layer 48 generally has spherical beads and a binder made of a thermosetting or photocurable resin that coats the beads, and the light guide plate is provided by a convex portion that protrudes toward the back surface side due to the beads. Prevents sticking with. Such anti-sticking performance is called anti-blocking property.

As described above, Patent Document 1 discloses an anti-sticking layer containing a binder composed of beads and a resin composition containing an ultraviolet curable resin as a main polymer. However, when a general ultraviolet curable resin is used, the light diffusion layer and the anti-sticking layer may be peeled off from the base material layer, and particularly when PET (untreated PET) which has not been easily adhered is used as the base material. , There is a problem that the adhesion with the base material is not sufficient.

Patent Document 2, which discloses that the adhesion is enhanced by containing a specific polyester resin in the ultraviolet curable ink in order to improve the lack of adhesion due to shrinkage of the cured product, styrene or styrene as a polymer or copolymer. Patent Document 3, which discloses that adhesion can be improved by adding a polymer component containing at least one derivative, acrylic acid ester, and acrylic acid, and addition of a partially polymerized photocurable resin. Although Patent Document 4 is known which discloses that the adhesion can be improved by reducing the volume shrinkage, no mention is made of the effect of improving the adhesion to untreated PET.

Patent Document 5 discloses an inkjet ink containing a monofunctional polymerizable monomer (A) having a hydroxyl having a specific structure, a bifunctional (meth) acrylate (B), and a photopolymerization initiator (C). The technique relates to an inkjet ink suitable for forming a high-definition pattern on a circuit board by an inkjet method, and does not describe any adhesion to an untreated PET film. Further, when the adhesion to the untreated PET film was confirmed using the ink obtained by this method, it was found that the adhesion was insufficient.

Patent Document 6 contains a trifunctional (meth) acrylate (A), a monofunctional (meth) acrylate (B), a photopolymerization initiator (C), and a surfactant (D) having a photocrosslinkable functional group. Inkjet ink with a contact angle of water of 90 ° or more measured at 25 ° C. on the surface of the cured film obtained by applying the composition on a substrate ^{and irradiating it with ultraviolet rays at an exposure amount of 2000 mJ / cm 2.} There is disclosed an ink jet ink having a viscosity at 25 ° C. of 1 to 200 mPa · s. The technique relates to the manufacture of display elements for liquid crystals or EL, and electronic circuit boards such as printed wiring boards and flexible wiring boards, and does not describe any adhesion to untreated PET film. Further, when the adhesion to the untreated PET film was confirmed using the ink obtained by this method, it was found that the adhesion was insufficient.

Patent Document 7 describes a (meth) acrylic acid ester (A) having a specific ring structure, a photopolymerization initiator (B), and a radically polymerizable double bond other than the (meth) acrylic acid ester (A). A photocurable inkjet ink containing the compound (C) having the above is disclosed. The technique relates to a photocurable inkjet ink preferably used for manufacturing an optical device such as a liquid crystal display element, and does not describe any adhesion to an untreated PET film. Further, when the adhesion to the untreated PET film was confirmed using the ink obtained by this method, it was found that the adhesion was insufficient.

Patent Document 8 discloses a method for producing an aqueous dispersion containing a microencapsulating colorant, and a polymer using (meth) acrylate having a ring structure for microencapsulation in an ink composition using the dispersion. ing. The technique relates to an inkjet ink having excellent dispersion stability and ejection stability, and does not describe any adhesion to an untreated PET film.

Further, the above resin composition does not describe any yellowing of the cured film in a high temperature and high humidity atmosphere. That is, the cured film formed of the conventional resin composition could not satisfy both the adhesion to the untreated PET film and the suppression of yellowing in a high temperature and high humidity atmosphere.

Japanese Unexamined Patent Publication No. 2014-130234 Japanese Unexamined Patent Publication No. 2011-225751 Japanese Unexamined Patent Publication No. 2013-249357 Japanese Unexamined Patent Publication No. 2015-196703 Japanese Unexamined Patent Publication No. 2008-063556 Japanese Unexamined Patent Publication No. 2011-231248 Japanese Unexamined Patent Publication No. 2013-014740 International Patent Publication WO2014 / 091923

Under the above circumstances, an object of the present invention is to form a cured product having excellent adhesion to an untreated PET film and suppressing yellowing of the cured product in a high temperature and high humidity (65 ° C., 95% RH) atmosphere. The purpose is to provide a photocurable ink that makes it possible.

The present inventors contain a polymer (A) obtained by polymerizing at least one (meth) acrylate having a ring structure, a polyfunctional (meth) acrylate (B), and a photopolymerization initiator (D). It was found that a photocurable ink provides a cured product in which the ink has excellent adhesion to an untreated PET film and yellowing is suppressed in a high temperature and high humidity (65 ° C., 95% RH) atmosphere. The present invention was completed based on the above.

That is, the present invention includes the following items.
[1] Photocurability containing a polymer (A), a polyfunctional (meth) acrylate (B), and a photopolymerization initiator (D) obtained by polymerizing at least one (meth) acrylate having a ring structure. ink.

[2] The photocurable ink according to [1], wherein the (meth) acrylate having a ring structure is a compound represented by the following formula (3).

（式中、Ｒ^１１は水素またはメチルであり、Ｒ^１２は、シクロヘキサン、シクロペンタン、ビシクロ［２.２.１］ヘプタン、５員環以上の環状エーテル、５員環以上のラクトン、ジシクロペンタン、ジシクロペンテン、アダマンタンおよび環状ホルマールからなる環構造より選ばれる少なくとも１種を有する有機基であり、ｂは０または１であり、Ｚは下記式（３−１）または式（３−２）で表される二価の基である。）

(In the formula, R ¹¹ is hydrogen or methyl, and R ¹² is cyclohexane, cyclopentane, bicyclo [2.2.1] heptane, a cyclic ether having a 5-membered ring or more, a lactone having a 5-membered ring or more, and dicyclopentane. , Dicyclopentene, adamantan and cyclic formal, which is an organic group having at least one selected from the ring structure, b is 0 or 1, and Z is the following formula (3-1) or formula (3-2). It is a divalent group represented.)

（式中、ｃおよびｄは０〜１０の整数である。）

(In the formula, c and d are integers from 0 to 10.)

[3] The photocurable ink according to [1] or [2], wherein the (meth) acrylate having a ring structure contains at least one selected from dicyclopentanyl methacrylate and dicyclopentenyloxyethyl methacrylate.

[4] The weight average molecular weight of the polymer (A) obtained by polymerizing at least one kind of (meth) acrylate having a ring structure is 10,000 or less in terms of polystyrene obtained by the GPC method. The photocurable ink according to any one of [1] to [3].

[5] Polyfunctional (meth) acrylate (B) is pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, trimethylol. Propanetri (meth) acrylate, ditrimethylolpropanetetra (meth) acrylate, glycerintri (meth) acrylate, bisphenol A ethyleneoxide-added di (meth) acrylate having 2 to 6 repeating units of ethylene oxide in the structure, ε-caprolactone addition [1] to [4] comprising at least one selected from tris (meth (acryloyloxyethyl) isocyanurate, di ((meth) acryloyloxyethyl) isocyanurate, and tri ((meth) acryloyloxyethyl) isocyanurate). ] The photocurable ink according to any one of.

[6] Polyfunctional (meth) acrylate (B) is pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, trimethylolpropane tri (meth) acrylate, di ((meth) acryloyloxyethyl) isocyanurate. The photocurable ink according to any one of [1] to [4], which comprises at least one selected from (meth) acryloyloxyethyl) isocyanurate.

[7] The photocurable ink according to any one of [1] to [6], which further contains a monofunctional (meth) acrylate (C).

[8] The photocurable ink according to any one of [1] to [7], wherein the photopolymerization initiator (D) is an α-hydroxyalkylphenone-based photopolymerization initiator.

[9] A cured film made of a cured product of the photocurable ink according to any one of [1] to [8].

[10] The cured film according to [9], which is used for an optical sheet.

[11] The cured film for an optical sheet according to [10], wherein the cured film is formed on the surface of a transparent base material sheet.

[12] The cured film for an optical sheet according to [11], wherein the transparent base sheet is a polyethylene terephthalate film that has not been easily adhered.

[13] An optical sheet having the cured film for the optical sheet according to [12].

[14] A backlight unit having the optical sheet according to [13].

[15] A liquid crystal display element equipped with the backlight unit according to [14].

In the photocurable ink of the present invention, since the cured film obtained from this has excellent adhesion to the untreated PET film, the cured film can be formed on the untreated PET film. Further, since yellowing of the cured product in a high temperature and high humidity (65 ° C., 95% RH) atmosphere is suppressed, when the photocurable ink of the present invention is used, a high-quality optical sheet is produced by a simple and inexpensive manufacturing process. Can be suitably produced.

The schematic diagram of the edge light type backlight unit is shown.

Hereinafter, the present invention will be specifically described.
<1. Photocurable ink>
The present invention is photocurable containing a polymer (A), a polyfunctional (meth) acrylate (B), and a photopolymerization initiator (D) obtained by polymerizing at least one (meth) acrylate having a ring structure. Regarding sex ink.

Since the photocurable ink of the present invention is used for an optical sheet, it is preferably colorless and transparent. However, the obtained cured film may not be colorless and transparent as long as the original optical function of the optical sheet is not significantly impaired or the mounted optical sheet does not adversely affect the liquid crystal display device.

Further, the photocurable ink of the present invention can be used as necessary for other compounds having a radically polymerizable double bond, a solvent, a polymerization inhibitor, a flame retardant, an ultraviolet absorber, a light stabilizer, an antioxidant, and a charge. It can contain inhibitors, curing aids, surfactants, fine particles and the like. Here, the "compound having another radically polymerizable double bond" refers to a radically polymerizable double bond other than the polyfunctional (meth) acrylate (B) and monofunctional (meth) acrylate (C) shown below. It is a compound having a radically polymerizable double bond other than the compound having.

1.1. (Meta) Acrylate In the present specification, "(meth) acrylate" is used to indicate both acrylate and methacrylate, or one of them.
In the curing reaction of (meth) acrylate, the double bond of the (meth) acryloyl group is radically polymerized, so that the "functional" portion is the (meth) acryloyl group, and the "monofunctional" is the (meth) acryloyl group. One, "polyfunctional" means one having two or more (meth) acryloyl groups.
Hereinafter, each of the above components will be described.

1.2. Polymer (A) obtained by polymerizing at least one (meth) acrylate having a ring structure.
The polymer (A) obtained by polymerizing at least one kind of (meth) acrylate having a ring structure used in the present invention may be one kind or two or more kinds. The content of the polymer (A) in the photocurable ink of the present invention is 30 to 80% by weight of the total weight of the resin component of the photocurable ink of the present invention from the viewpoint of obtaining a cured film having excellent adhesion. It is preferable to have.

1.2.1. (Meta) Acrylate Having a Ring Structure As the (meth) acrylate having a ring structure used in the present invention, a (meth) acrylate represented by the following formula (3) is exemplified.

（式中、Ｒ^１１は水素またはメチルであり、Ｒ^１２は、シクロヘキサン、シクロペンタン、ビシクロ［２.２.１］ヘプタン、５員環以上の環状エーテル、５員環以上のラクトン、ジシクロペンタン、ジシクロペンテン、アダマンタンおよび環状ホルマールからなる環構造より選ばれる少なくとも１種を有する有機基であり、ｂは０または１であり、Ｚは下記式（３−１）または式（３−２）で表される二価の基である。）

(In the formula, R ¹¹ is hydrogen or methyl, and R ¹² is cyclohexane, cyclopentane, bicyclo [2.2.1] heptane, a cyclic ether having a 5-membered ring or more, a lactone having a 5-membered ring or more, and dicyclopentane. , Dicyclopentene, adamantan and cyclic formal, which is an organic group having at least one selected from the ring structure, b is 0 or 1, and Z is the following formula (3-1) or formula (3-2). It is a divalent group represented.)

（式中、ｃおよびｄは０〜１０の整数である。）

(In the formula, c and d are integers from 0 to 10.)

Specific examples of the (meth) acrylate having a ring structure include cyclohexyl (meth) acrylate, 4-butylcyclohexyl (meth) acrylate, cyclopentyl (meth) acrylate, isobornyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, and caprolactone addition. Tetrahydrofurfuryl (meth) acrylate, tetrahydrofurfuryl alcohol acrylic acid multimeric ester, γ-butyrolactone (meth) acrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) ) Acrylate, 2-methyl-2-adamantyl (meth) acrylate, 2-ethyl-2-adamantyl (meth) acrylate, 3,5-dimethyl-7-hydroxyadamantyl (meth) acrylate, 3-hydroxy-1-adamantyl () Examples thereof include meta) acrylates, methacryloyloxynorbornane (meth) acrylates, and cyclic trimethylolpropanformal (meth) acrylates.

Further, from the viewpoint of obtaining the polymer (A) having high heat resistance, it is preferable that the (meth) acrylate having a ring structure has a glass transition temperature (Tg) of a homopolymer composed of this monomer of 50 ° C. or higher. Specific examples of such (meth) acrylates include cyclohexyl methacrylate, isobornyl (meth) acrylate, tetrahydrofurfuryl methacrylate, dicyclopentanyl (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl methacrylate, and the like. And cyclic trimethylolpropane formal methacrylate can be mentioned.
The glass transition temperature of these homopolymers can be known from known literature. For example, it is described in the acrylic ester catalog (2016 degree version) of Mitsubishi Chemical Corporation, Kyozo Kitaoka, "New Polymer Bunko 7 Introduction to Synthetic Resins for Paints", Polymer Publishing Association, p168 to p169.

From the above, dicyclopentanyl methacrylate and dicyclopentenyloxyethyl methacrylate are particularly preferable from the viewpoint of obtaining a cured film having high adhesion and heat resistance.

The (meth) acrylate having a ring structure used in the present invention may be one kind or two or more kinds.
The content of the (meth) acrylate having a ring structure in the polymer (A) is preferably 30 to 80% by weight from the viewpoint of obtaining a cured film having high heat resistance.

1.2.2. Other Compounds Having Radical Polymerizable Double Bonds To the polymer (A) of the present invention, other compounds having radically polymerizable double bonds may be added in order to improve compatibility. Other compounds having a radically polymerizable double bond include compounds having a radically polymerizable double bond other than (meth) acrylate and (meth) acrylate.

Specific examples of other compounds having a radically polymerizable double bond include (meth) acrylates such as (meth) acrylic acid, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and butyl (meth). ) Acrylate, Pentyl (meth) acrylate, Hexyl (meth) acrylate, Octyl (meth) acrylate, Decyl (meth) acrylate, Tridecyl (meth) acrylate, Lauryl (meth) acrylate, Stearyl (meth) acrylate, Isooctyl (meth) acrylate , Isodecyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, phenoxydiethylene glycol (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, glycidyl (meth) acrylate, ethoxydiethylene glycol acrylate, 2- (2-) Ethoxyethoxy) ethyl acrylate, methoxypolyethylene glycol acrylate, methoxypolyethylene glycol acrylate, polyalkylene glycol acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 1 , 4-Cyclohexanedimethanol mono (meth) acrylate and the like, and specific examples of compounds having a radically polymerizable double bond other than (meth) acrylate include crotonic acid, α-chloroacrylic acid, silicic acid and malein. Acid, fumaric acid, N-vinylformamide, methyl 2-allyloxymethylacrylic acid, polymethylmethacrylate macromonomer, N-cyclohexylmaleimide, N-phenylmaleimide, styrene, (meth) acrylamide, N, N-dimethyl (meth) Acrylate, N, N-diethyl (meth) acrylamide, N, N-dimethylaminopropyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, acryloylmorpholine, and N-vinylimidazole. Can be mentioned.

The weight average molecular weight of the polymer (A) obtained by polymerizing at least one kind of (meth) acrylate having a ring structure is preferably 10,000 or less from the viewpoint of adhesion and compatibility.

The weight average molecular weight in the present specification is a polystyrene-equivalent value obtained by the GPC method (column temperature: 35 ° C., flow velocity: 1 mL / min). Standard polystyrene is polystyrene with a molecular weight of 645-132,900 (for example, Agilent SM2-10 polystyrene calibration kit PL2010-0102 (trade name; Agilent Technologies, Inc.)), and column is PLgel MIXED-D (commodity). Name: Agilent Technologies, Inc.) and can be measured using THF as the mobile phase.

1.3. Polyfunctional (meth) acrylate (B)
Any aspect of the polyfunctional (meth) acrylate (B) used in the present invention can be adopted as long as it has two or more (meth) acryloyl groups in the structure.

Specific examples of the polyfunctional (meth) acrylate (B) used in the present invention include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, and the like. Butylene glycol di (meth) acrylate, hexanediol di (meth) acrylate, cyclohexanedimethanol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, poly Tetramethylene glycol diacrylate, neopentyl glycol diacrylate, tricyclodecanedimethanol diacrylate, bisphenol A alkylene oxide-added di (meth) acrylate, bisphenol Falkylene oxide-added di (meth) acrylate, trimethylolpropane tri (meth) acrylate , Ditrimethylolpropane tetra (meth) acrylate, glycerintri (meth) acrylate, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate , Ethethyleneoxide-added trimethylolpropane tri (meth) acrylate, ethylene oxide-added trimethylolpropane tetra (meth) acrylate, ethylene oxide-added pentaerythritol tetra (meth) acrylate, ethylene oxide-added dipentaerythritol hexa (meth) acrylate, propylene oxide-added trimethylolpropane Tri (meth) acrylate, propylene oxide-added trimethylolpropane tetra (meth) acrylate, propylene oxide-added pentaerythritol tetra (meth) acrylate, propylene oxide-added dipentaerythritol hexa (meth) acrylate, ε-caprolactone-added trimethylolpropane tri (meth) acrylate Meta) acrylate, ε-caprolactone-added ditrimethylolpropane tetra (meth) acrylate, ε-caprolactone-added pentaerythritol tetra (meth) acrylate, ε-caprolactone-added dipentaerythritol hexa (meth) acrylate, ε-caprolactone-added tris ((meth) ) Acryloxyethyl) isocyanurate, di ((meth) acryloyloxye) Chill) isocyanurate, tri ((meth) acryloyloxyethyl) isocyanurate, alkylene oxide-added tri (acryloyloxyethyl) isocyanurate, alkylene oxide-added tri (methacryloyloxyethyl) isocyanurate and tolylene diisocyanate, isophorone diisocyanate, xylylene A polyfunctional urethane (meth) acrylate obtained by reacting a polyfunctional isocyanate such as isocyanate with a hydroxyl group-containing (meth) acrylic acid ester such as 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate. be.

Among them, pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, and dipentaerythritol penta (meth) acrylate are obtained from the viewpoint of obtaining a cured film having a good balance of adhesion and strength to the untreated PET film. Pentaerythritol hexa (meth) acrylate, trimethylol propanetri (meth) acrylate, ditrimethylol propanetetra (meth) acrylate, glycerin tri (meth) acrylate, bisphenol A ethylene oxide addition having 2 to 6 repeating units of ethylene oxide in the structure. Di (meth) acrylate, ε-caprolactone-added tris (meth (acryloxyethyl) isocyanurate, di ((meth) acryloyloxyethyl) isocyanurate, tri ((meth) acryloyloxyethyl) isocyanurate, preferably pentaerythritol tri () Meta) acrylates, pentaerythritol tetra (meth) acrylates, trimethylpropantri (meth) acrylates, di ((meth) acryloyloxyethyl) isocyanurates and tri ((meth) acryloyloxyethyl) isocyanurates are preferred, especially at high temperatures. Pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, trimethylpropantri (meth) acrylate, di ((meth) acryloyloxy) from the viewpoint of obtaining a cured film in which yellowing is suppressed in a high humidity atmosphere. Ethyl) isocyanurate and tri ((meth) acryloyloxyethyl) isocyanurate are more preferred.

The polyfunctional (meth) acrylate (B) used in the present invention may be one kind or two or more kinds.
When the content of the polyfunctional (meth) acrylate (B) is 30 to 70% by weight of the total weight of the resin component of the photocurable ink of the present invention, a cured film having a good balance between adhesion and strength can be obtained. It is preferable because it can be used.

1.4. Monofunctional (meth) acrylate (C)
Any aspect of the monofunctional (meth) acrylate (C) can be adopted as long as it has one (meth) acryloyl group in the structure. By adding the monofunctional (meth) acrylate (C), a cured film having good adhesion to the untreated PET film can be obtained.

Specific examples of the monofunctional (meth) acrylate (C) used in the present invention include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, pentyl (meth) acrylate, and hexyl. (Meta) acrylate, octyl (meth) acrylate, decyl (meth) acrylate, tridecyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, isooctyl (meth) acrylate, isodecyl (meth) acrylate, ethoxydiethylene glycol acrylate , 2- (2-ethoxyethoxy) ethyl acrylate, methoxypolyethylene glycol acrylate, methoxypolyethylene glycol acrylate, polyalkylene glycol acrylate, cyclohexyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, alkoxylated tetrahydrofurfuryl acrylate, caprolactone addition Tetrahydrofurfuryl (meth) acrylate, tetrahydrofurfuryl alcohol acrylic acid multimeric ester, 2-phenoxyethyl acrylate, 3,3,5-trimethylcyclohixanol (meth) acrylate, isobornyl (meth) acrylate, benzyl (meth) Acrylate, phenoxydiethylene glycol (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, cyclohexyl (meth) acrylate, 4-butylcyclohexyl (meth) acrylate, cyclopentyl (meth) acrylate, γ-butyrolactone (meth) acrylate, dicyclopentanyl (Meta) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, 2-methyl-2-adamantyl (meth) acrylate, 2-ethyl-2-adamantyl (meth) acrylate, 3,5 -Dimethyl-7-hydroxyadamantyl (meth) acrylate, 3-hydroxy-1-adamantyl (meth) acrylate, methacryloyloxynorbornane (meth) acrylate, tetramethylpiperidinyl (meth) acrylate, pentamethylpiperidinyl (meth) Acrylate, (meth) acrylate having an imide ring, cyclic trimethylolpropaneformal (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl ( Meta) acrylate, 4-hydroxybutyl (meth) acrylate, and 1,4-cyclohexanedimethanol mono (meth) acrylate.

Of these, tetrahydrofurfuryl (meth) acrylate and tetrahydrofurfuryl alcohol acrylic acid multimer ester are preferable from the viewpoint of obtaining a cured film having good adhesion to the untreated PET film.

The monofunctional (meth) acrylate (C) used in the present invention may be one kind or two or more kinds.
The content of the monofunctional (meth) acrylate (C) is preferably 5 to 30% by weight based on the total amount of the photocurable ink of the present invention, because a cured film having a good balance between adhesion and strength can be obtained.

1.5. Other Compounds with Radical Polymerizable Double Bonds The photocurable ink of the present invention contains compounds with other radically polymerizable double bonds as long as the photocurability, adhesion, transmittance and strength are not impaired. It may be added. Further, other compounds having a radically polymerizable double bond may be polymerized to form a resin.

Other compounds having a radically polymerizable double bond include compounds having a radically polymerizable double bond other than (meth) acrylate, and examples of the resin include unsaturated polyester resin, polyester (meth) acrylate resin, and epoxy. A resin having an unsaturated bond capable of radical polymerization, such as a (meth) acrylate resin and a urethane (meth) acrylate resin, is included.

Specific examples of compounds having a radically polymerizable double bond other than (meth) acrylate include crotonic acid, α-chloroacrylic acid, silicic acid, maleic acid, fumaric acid, N-vinylformamide, and 2-allyloxymethylacrylic acid. Methyl acid, polymethylmethacrylate macromonomer, N-cyclohexylmaleimide, N-phenylmaleimide, styrene, (meth) acrylamide, N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N, N- Included are dimethylaminopropyl (meth) acrylamide, N-isopropyl (meth) acrylamide, N-hydroxyethyl (meth) acrylamide, acrylic morpholine, and N-vinylimidazole.

As the unsaturated polyester resin, a condensation product (unsaturated polyester) obtained by an esterification reaction of a polyhydric alcohol and an unsaturated polybasic acid (and, if necessary, a saturated polybasic acid) is dissolved in a polymerizable monomer. Can be mentioned.

Unsaturated polyester can be produced by polycondensing an unsaturated acid such as maleic anhydride with a diol such as ethylene glycol. Specifically, a polybasic acid having a polymerizable unsaturated bond such as phthalic acid, maleic acid, and itaconic acid or an anhydride thereof is used as an acid component, and this and ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, 1, 2 -Butandiol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, cyclohexane Polyhydric alcohols such as -1,4-dimethanol, ethylene oxide adduct of bisphenol A, and propylene oxide adduct of bisphenol A are reacted as alcohol components, and if necessary, phthalic acid, isophthalic acid, terephthalic acid, etc. Examples thereof include polybasic acids having no polymerizable unsaturated bond such as tetrahydrophthalic acid, adipic acid, and sebacic acid, or those produced by adding an anhydride thereof as an acid component.

As the polyester (meth) acrylate resin, (1) a polyester having a terminal carboxyl group obtained from a saturated polybasic acid and / or an unsaturated polybasic acid and a polyhydric alcohol contains an α, β-unsaturated carboxylic acid ester group. (Meta) acrylate obtained by reacting the epoxy compound to be used, (2) obtained by reacting a hydroxyl group-containing acrylate with a polyester having a terminal carboxyl group obtained from saturated polybasic acid and / or unsaturated polybasic acid and polyhydric alcohol. Examples of the (meth) acrylate obtained are (3) saturated polybasic acid and / or (meth) acrylate obtained by reacting (meth) acrylic acid with polyester having a terminal hydroxyl group obtained from unsaturated polybasic acid and polyhydric alcohol. Be done.

Saturated polybasic acids used as raw materials for polyester (meth) acrylate include polybasic acids that do not have polymerizable unsaturated bonds, such as phthalic acid, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, adipic acid, and sebatic acid. Examples thereof include an acid or an anhydride thereof and a polymerizable unsaturated polybasic acid such as fumaric acid, maleic acid, and itaconic acid or an anhydride thereof. Further, the polyhydric alcohol component is the same as that of the unsaturated polyester.

The epoxy (meth) acrylate resin is polymerizable unsaturated produced by a ring-opening reaction between a compound having a glycidyl group (epoxide group) and a carboxyl group of a carboxyl compound having a polymerizable unsaturated bond such as (meth) acrylic acid. It is a compound having a bond (vinyl ester). Usually, one dissolved in a polymerizable monomer is used.

Examples of the compound having a glycidyl group (epoxide group) include bisphenol A diglycidyl ether, its high-molecular-weight homologue, and novolak-type glycidyl ethers. In addition to (meth) acrylic acid, it may contain a reaction product of bisphenol (for example, type A) or a dibasic acid such as adipic acid, sebacic acid, and dimer acid (Haridimer 270S: Harima Chemicals, Inc.).

As the urethane (meth) acrylate resin, for example, a polyisocyanate is reacted with a polyhydroxy compound or a polyhydric alcohol, and then a hydroxyl group-containing (meth) acrylic compound and, if necessary, a hydroxyl group-containing allyl ether compound are further reacted. Examples thereof include radically polymerizable unsaturated group-containing oligomers that can be obtained.

Specific examples of the polyisocyanate include 2,4-tolylene diisocyanate and its isomers, diphenylmethane diisocyanate, hexamethylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, dicyclohexylmethane diisocyanate, naphthaline diisocyanate, and triisocyanate. Phenylmethane triisocyanate, Vernock D-750, Chrisbon NK (trade name: manufactured by DIC Co., Ltd.), Death Module L (trade name: manufactured by Sumika Cobestrourethane Co., Ltd.), Coronate L (trade name: manufactured by Toso Co., Ltd.) ), Takenate D102 (trade name; manufactured by Mitsui Chemicals Co., Ltd.), and isocyanate 143L (trade name; manufactured by Dow Chemical Japan Co., Ltd.).

Examples of the polyhydroxy compound include polyester polyols and polyether polyols, and specific examples thereof include glycerin-ethylene oxide adducts, glycerin-propylene oxide adducts, glycerin- tetrahydrofuran adducts, and glycerin-ethylene oxide propylene oxide adducts. , Trimethylol Propane-Ethylene Oxide Adduct, Trimethylol Propane-Ethylene Oxide Adduct, Trimethylol Propane- tetrahydrofuran Adduct, Trimethylol Propane-Ethylene Oxide Propylene Oxide Adduct, Dipentaesritol-Ethylene Oxide Adduct, Di Included are pentaesritol-propylene oxide adducts, dipentaesritol- tetrahydrofuran adducts, and dipentaesritol-ethylene oxide propylene oxide adducts. Of these, polyester diols and polyether diols, which can easily induce urethane (meth) acrylate resins having excellent adhesion to untreated PET, are preferable.

Specific examples of the polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 2-methyl-1,3-propanediol, and 1,3-. Butanediol, an adduct of bisphenol A with propylene oxide or ethylene oxide, 1,2,3,4-tetrahydroxybutane, glycerin, trimethylolpropane, 1,3-butanediol, 1,2-cyclohexaneglycol, 1, Examples thereof include 3-cyclohexaneglycol, 1,4-cyclohexaneglycol, paraxylene glycol, bicyclohexyl-4,4-diol, 2,6-decalin glycol and 2,7-decalin glycol.

The hydroxyl group-containing (meth) acrylic compound is not particularly limited, but a hydroxyl group-containing (meth) acrylic acid ester is preferable, and specifically, for example, 2-hydroxyethyl (meth) acrylate and 2-hydroxy. Propyl (meth) acrylate, 3-hydroxybutyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, tris (hydroxyethyl) isocyanulsannodi (meth) acrylate, and pentaeslitortri ( Meta) acrylate can be mentioned.

The other compound having a radically polymerizable double bond may be one kind or two or more kinds.
When the content of the other compound having a radically polymerizable double bond is 5 to 30% by weight based on the total weight of the resin component of the photocurable ink of the present invention, the photocurability is obtained with respect to the substrate of the obtained cured film. Good balance of adhesion, transmittance and strength.

1.5. Photopolymerization initiator (D)
The photocurable ink of the present invention contains a photopolymerization initiator (D). The photopolymerization initiator (D) is not particularly limited as long as it is a compound capable of generating radicals by irradiation with ultraviolet rays or visible light, but an α-hydroxylalkylphenone type is preferable.

Specific examples of the photopolymerization initiator (D) include benzophenylone, Michler's ketone, 4,4'-bis (diethylamino) benzophenone, xanthone, thioxanthone, isopropylxanthone, 2,4-diethylthioxanthone, 2-ethylanthraquinone, acetophenone, 2-. Hydroxy-2-methylpropiophenone, 2-hydroxy-1-{4- [4- (2-hydroxy-2-methylpropionyl) benzyl] phenyl} -2-methylpropan-1-one, 2-hydroxy-2 -Methyl-4'-Isopropylpropiophenone, 1-hydroxycyclohexylphenylketone, isopropylbenzoin ether, isobutylbenzoin ether, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-dimethoxy -1,2-diphenylethane-1-one, phenylquinone, benzanthron, 2-hirodoxy-1- [4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] phenyl] -2-methyl -Propane-1-one, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propane-1-one, 2-hydroxy-2-methyl-1-phenyl- Propane-1-one, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholino-1-propanone, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -1- Butanone, 2-dimethylamino-2- (4-methylbenzyl) -1- (4-morpholinophenyl) -1-butanone, oxy-phenyl-acetic acid 2- (2-oxo-2-phenyl-acetoxy-) Ethoxy) -Ethyl ester, Oxy-Phenyl-Acetic acid 2- (2-Hydroxy-ethoxy) -Ethyl ester, Oxy-Phenyl-Acetic acid 2- (2-Oxo-2-phenyl-acetoxy-ethoxy) -Ethyl A mixture of ester and oxy-phenyl-acetylid 2- (2-hydroxy-ethoxy) -ethyl ester, phenylglycoxyacid methyl ester, ethyl 4-dimethylaminobenzoate, isoamyl 4-dimethylaminobenzoate, 4 , 4'-di (t-butylperoxycarbonyl) benzophenone, 3,4,4'-tri (t-butylperoxycarbonyl) benzophenone, 3,3', 4,4'-tetra (t-butylpero) Xycarbonyl) benzophenone, 3,3', 4,4'-tetra (t-hexylperoxycarbonyl) benzophenone, 3,3'-di (methoxycarbonyl) -4,4'-di (t-butylperoxycarbonyl) benzophenone , 3,4'-di (methoxycarbonyl) -4,3'-di (t-butylperoxycarbonyl) benzophenone, 4,4'-di (methoxycarbonyl) -3,3'-di (t-butylperoxycarbonyl) ) Benzophenone, 2- (4'-methoxystyryl) -4,6-bis (trichloromethyl) -s-triazine, 2- (3', 4'-dimethoxystyryl) -4,6-bis (trichloromethyl)- s-triazine, 2- (2', 4'-dimethoxystyryl) -4,6-bis (trichloromethyl) -s-triazine, 2- (2'-methoxystyryl) -4,6-bis (trichloromethyl) -S-triazine, 2- (4'-pentyloxystyryl) -4,6-bis (trichloromethyl) -s-triazine, 4- [pn, N-di (ethoxycarbonylmethyl)]-2,6 -Di (trichloromethyl) -s-triazine, 1,3-bis (trichloromethyl) -5- (2'-chlorophenyl) -s-triazine, 1,3-bis (trichloromethyl) -5- (4'- Methylphenyl) -s-triazine, 2- (p-dimethylaminostyryl) benzoxazole, 2- (p-dimethylaminostyryl) benzthiazole, 2-mercaptobenzothiazole, 3,3'-carbonylbis (7-diethylaminocoumarin) ), 2- (o-Chlorophenyl) -4,4', 5,5'-tetraphenyl-1,2'-biimidazole, 2,2'-bis (2-chlorophenyl) -4,4', 5, 5'-tetrakis (4-ethoxycarbonylphenyl) -1,2'-biimidazole, 2,2'-bis (2,4-dichlorophenyl) -4,4', 5,5'-tetraphenyl-1,2 '-Biimidazole, 2,2'-bis (2,4-dibromophenyl) -4,4', 5,5'-tetraphenyl-1,2'-biimidazole, 2,2'-bis (2, 4,6-Trichlorophenyl) -4,4', 5,5'-tetraphenyl-1,2'-biimidazole, 3- (2-methyl-2-dimethylaminopropionyl) carbazole, 3,6-bis ( 2-Methyl-2-morpholinopropionyl) -9-n-dodecylcarbazole, 1-hydrochi Shi phenyl ketone, bis (eta ^{5-2,4-cyclopentadiene-1-yl)} - bis (2,6-difluoro-3-(1H-pyrrol-1-yl) - phenyl) titanium, bis (2, 4,6-trimethylbenzoyl) phenylphosphine oxide, and 2,4,6-trimethylbenzoyldiphenylphosphine oxide can be mentioned.

Among them, 2-hydroxy-1- {4- [4- (2-hydroxy-2-methylpropionyl) benzyl] phenyl} -2-methylpropan-1-one or 1-hydroxy because the cured film is less colored. Cyclohexylphenyl ketone is preferred.

The photopolymerization initiator (D) may be one kind or a mixture of two or more kinds.
The content of the photopolymerization initiator (D) is preferably 1 to 20% by weight based on the total weight of the resin component of the photocurable ink of the present invention because it is excellent in photocurability against ultraviolet rays, and more preferably 2 to 20% by weight. It is 15% by weight, more preferably 3 to 10% by weight.

1.6. Fine Particles The photocurable ink of the present invention may contain fine particles. By containing the fine particles, it is possible to impart a light diffusion function and a sticking prevention function to the obtained cured film.

The fine particles are not particularly limited as long as the object of the present invention is not impaired, and glass, silica, titanium dioxide, indium oxide, tin oxide, zirconium oxide, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfide, and magnesium silicate are used. Inorganic fine particles such as, organic fine particles made of synthetic resin, and the like can be used. It is preferably an organic fine particle made of a synthetic resin, and specific examples of the organic fine particle include acrylic resin, acrylonitrile resin, epoxy resin, nylon resin, polyurethane, polyvinyl chloride, polystyrene, polyamide and polyacrylonitrile. Among these, highly transparent acrylic resin is preferable, and polymethylmethacrylate (PMMA) is more preferable.

The shape of the fine particles is not particularly limited, and is, for example, spherical, cubic, needle-shaped, or rod-shaped. Spindle shape, plate shape, scale shape, fibrous shape and the like can be mentioned, and among them, a spherical shape having excellent light diffusivity and anti-sticking function is preferable.

The fine particles may be monodisperse or polydisperse, and the fine particles used in the photocurable ink of the present invention may be one kind or a mixture of two or more kinds.
When imparting a light diffusing function to the cured film, it is preferable to use polydisperse as the fine particles, and the average particle size of the fine particles is not particularly limited, but is preferably 1 to 50 μm, more preferably 2 to 20 μm. , 5 to 15 μm is more preferable. When the average particle size is 1 μm or more, the unevenness of the surface of the light diffusing layer formed by the light diffusing agent becomes an appropriate state, and the light diffusing property of the light diffusing sheet becomes sufficient. When the average particle size is 50 μm or less, the thickness of the light diffusion sheet does not increase more than necessary, and the diffusion becomes uniform. Due to the polydisperse, the particles are preferably not uniform in size, and the CV value (coefficient of variation) is preferably in the range of 15 to 60%, preferably 20 to 50%.

"Average particle size" refers to the average particle size of 30 particles randomly selected from particles observed with an electron microscope at a magnification of 1000 times, and the particle size is the ferret diameter (parallel lines in a certain direction). It is defined by the interval when the projected image is sandwiched).

The "CV value (coefficient of variation)" of the particle size distribution of the fine particles is a value indicating the variation state of the particle size distribution of the fine particles, and is a percentage of the value obtained by dividing the standard deviation of the particle size distribution by the average particle size.
Coefficient of variation = (square root of unbiased variance) / (arithmetic mean) x 100%

When the light diffusing function is imparted, the content of the fine particles is not particularly limited, but the content of the fine particles with respect to 100 parts by weight of the resin component of the photocurable ink of the present invention is preferably 10 to 500 parts by weight, preferably 20 to 300 parts by weight. Parts are more preferable, and 50 to 200 parts by weight are even more preferable. When the content of the fine particles is 10 parts by weight or more, sufficient light diffusivity can be obtained. When the content of the fine particles is 500 parts by weight or less, the fine particles are sufficiently fixed. When the optical sheet is used as a so-called upper light diffusing sheet arranged on the surface side of the prism sheet, high light diffusing property is not required, so that the blending amount of the light diffusing agent is 5 to 40 parts by weight. Preferably, 10 to 30 parts by weight is more preferable. The resin component is a component that polymerizes and cures in the composition, and the solvent and the polymerization initiator are excluded.

When the anti-sticking function is imparted, the average particle size of the fine particles is not particularly limited, but is preferably 2 to 20 μm, more preferably 3 to 10 μm, and even more preferably 4 to 6 μm. By setting the average particle size of the fine particles within the above range, it is possible to meet the demand for thinning the optical sheet for the liquid crystal display device, effectively prevent damage to the optical member on the back surface side, and prevent sticking. Can be played sufficiently.

When a sticking prevention function is imparted to the cured film, the content of the fine particles is not particularly limited, but the content of the fine particles with respect to 100 parts by weight of the resin component of the photocurable ink of the present invention is preferably 0.1 to 5 parts by weight. , 0.3 to 4 parts by weight is more preferable, and 0.5 to 3 parts by weight is further preferable. When the content of the fine particles is at least the above lower limit, the abundance ratio of the fine particles in the sticking prevention layer is sufficient, and the sticking prevention function with the light guide plate is sufficiently maintained. On the other hand, if the content is not more than the upper limit, there is no concern that the optical function of the light diffusion sheet will be impaired.

1.7. Solvent The photocurable ink of the present invention may contain a solvent.
The solvents that can be used in the present invention are methanol, ethanol, propanol, isopropanol, butanol, t-butyl alcohol, tetrahydrofuran, methyl ethyl ketone, methyl isobutyl ketone, acetonitrile, propionitrile, benzonitrile, ethyl acetate, isobutyl acetate, butyl acetate. , Butyl propionate, ethyl lactate, methyl oxyacetate, ethyl oxyacetate, butyl oxyacetate, methyl methoxyacetate, ethyl methoxyacetate, butyl methoxyacetate, methyl ethoxyacetate, ethyl ethoxyacetate, methyl 3-oxypropionate, 3-oxy Ethyl propionate, methyl 3-methoxypropionate, ethyl 3-methoxypropionate, methyl 3-ethoxypropionate, ethyl 3-ethoxypropionate, methyl 2-hydroxyisobutyrate, methyl 2-oxypropionate, 2-oxypropion Ethyl acid, propyl 2-oxypropionate, methyl 2-methoxypropionate, ethyl 2-methoxypropionate, propyl 2-methoxypropionate, methyl 2-ethoxypropionate, ethyl 2-ethoxypropionate, 2-oxy-2 -Methyl methylpropionate, ethyl 2-oxy-2-methylpropionate, methyl 2-methoxy-2-methylpropionate, ethyl 2-ethoxy-2-methylpropionate, methyl pyruvate, ethyl pyruvate, propylpyruvate , Methyl acetoacetate, ethyl acetoacetate, methyl 2-oxobutate, ethyl 2-oxobutate, methyl xisobutyrate, dioxane, ethylene glycol, diethyl ether, diethylene glycol, propylene glycol, dipropylene glycol, propylene glycol monomethyl ether, propylene glycol mono Ethyl ether, propylene glycol monopropyl ether, propylene glycol monobutyl ether, propylene glycol monophenyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether , Diethylene glycol monobutyl ether, diethylene glycol monophenyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether Dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, dipropylene glycol monophenyl ether, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, glycerin, benzyl alcohol, cyclohexanol, 1,4-butanediol, tri Ethylene glycol, tripropylene glycol, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, propylene glycol monopropyl ether acetate, dipropylene glycol monoethyl ether acetate, dipropylene glycol monobutyl ether acetate, ethylene glycol monobutyl ether acetate, cyclohexanone, Cyclopentanone, diethylene glycol monomethyl ether acetate, diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol ethyl methyl ether, tetraethylene glycol dimethyl ether, toluene, xylene, anisole, γ-butyrolactone, N, N Included are -dimethylacetamide, N, N-dimethylformamide, N-methyl-2-pyrrolidone, and dimethylimidazolidinone.

Among them, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, isobutyl acetate, butyl acetate, methyl 3-methoxypropionate, methyl 2-hydroxyisobutyrate and propylene because the polymer (A) has high solubility and can shorten the drying time. Glycol monoethyl ether and is preferred.

The solvent used in the photocurable ink of the present invention may be one kind or a mixture of two or more kinds.
In the photocurable ink of the present invention, when the content of the solvent is 0 to 60% by weight with respect to 100% by weight of the total amount of the ink (solid content + solvent), the ink jet is applied when the ink is applied by the inkjet method. This is preferable because the discharge hole of the head is less likely to be blocked. Considering the balance with other characteristics, it is more preferably 0 to 40% by weight, and further preferably 0 to 20% by weight.

1.8. Polymerization inhibitor The photocurable ink of the present invention may contain a polymerization inhibitor in order to improve storage stability. Specific examples of the polymerization inhibitor include 4-methoxyphenol, hydroquinone and phenothiazine. Among these, phenothiazine is preferable because the increase in viscosity is small even during long-term storage.
The polymerization inhibitor used in the photocurable ink of the present invention may be one kind or a mixture of two or more kinds.

1.9. Flame Retardant The photocurable ink of the present invention may contain a flame retardant. It is preferable to contain a flame retardant because the obtained cured film has high flame retardancy. The flame retardant is not particularly limited as long as it is a compound capable of imparting flame retardancy, but it is preferable to use an organic phosphorus flame retardant from the viewpoint of low toxicity, low pollution and safety.

Organophosphorus flame retardants include triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, cresylphenyl phosphate, 2-ethylhexyldiphenyl phosphate, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10. Oxide, 10- (2,5-dihydroxyphenyl) -10H-9-oxa-10-phosphaphenanthrene-10-oxide and condensed 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10 oxide, etc. Can be mentioned.

1.10. Ultraviolet absorber and light stabilizer The photocurable ink of the present invention contains an ultraviolet absorber and a light stabilizer (HALS) in order to prevent the obtained cured film and the like from being deteriorated by light such as a backlight. You may.

Examples of the ultraviolet absorber include 2- (5-methyl-2-hydroxyphenyl) benzotriazole, 2- (3,5-di-t-butyl-2-hydroxyphenyl) benzotriazole, and 2- (3,5-di). Benzotriazole compounds such as -t-butyl-2-hydroxyphenyl) -5-chlorobenzotriazole, 2- (3,5-di-t-amyl-2-hydroxyphenyl) benzotriazole, 2- (4,6-- Triazine compounds such as diphenyl-1,3,5-triazine-2-yl) -5-[(hexyl) oxy] -phenol, benzophenone compounds such as 2-hydroxy-4-n-octyloxybenzophenone, and 2-ethoxy- Examples thereof include oxalic acid anilide compounds such as 2'-ethyloxalic acid bisanilide.

Examples of the light stabilizer (HALS) include TINUVIN (registered trademark) 5100, TINUVIN292 (compound name: bis (1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate, methyl (1,2,2,6). , 6-Pentamethyl-4-piperidinyl) sevacate), TINUVIN152 (Compound name: 2,4-bis [N-butyl-N- (1-cyclohexyloxy-2,2,6,6-tetramethylpiperidin-4-yl) ) Amino] -6- (2-hydroxyethylamine) -1,3,5-triazine), TINUVIN144 (Compound name: bis (1,2,2,6,6-pentamethyl-4-piperidinyl)-[[3, 5-Bis (1,1-dimethylethyl) -4-hydroxyphenyl] methyl] butylmalonate), TINUVIN123 (Compound name: decanedic acid, bis (2,2,6,6-tetramethyl-1- (octyl)) Reaction product of oxy) -4 piperidinyl) ester (in the presence of 1,1-dimethylethylhydroperoxide and octane)), TINUVIN111FDL (approximately 50%, TINUVIN622, compound name: (butane diic acid polymer (4-hydroxy-)) 2,2,6,6-tetramethylpiperidinyl-yl) in the presence of ethanol), about 50%, CHIMASSORB119, compound name: NN'-N''-N'''-tetrakis (4,6-bis (4,6-bis) Butyl- (N-methyl-2,2,6,6-tetramethylpiperidin-4-yl) amino) triazine-2-yl) -4,7-diazadecan-1,10-diamine), (both from BASF) (Manufactured by) and Adecaster LA series (manufactured by Adeca Co., Ltd.), specifically, LA-52, LA-57, LA-62, LA-67 and the like can be mentioned.
The ultraviolet absorber and the light stabilizer that can be used in the photocurable ink of the present invention may be one kind or two or more kinds.

1.11. Antioxidant The photocurable ink of the present invention may contain an antioxidant in order to prevent oxidation of the obtained cured film or the like.

Antioxidants are pentaerythritol tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, triethylene glycol-bis- [3- (3-t-butyl-5-methyl-4). -Hydroxyphenyl) propionate], 1,6-hexanediol-bis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate], octadecyl-3- (3,5-di-t-) Hindered phenol compounds such as butyl-4-hydroxyphenyl) propionate, 3,5-di-t-butyl-4-hydroxybenzylphosphonate diethyl ester, amine compounds such as n-butylamine, triethylamine and diethylaminomethylmethacrylate, (dilauryl- Sulfur compounds such as 3,3'-thiodipropionate, dimyristyl-3,3'-thiodipropionate, distearyllu-3,3'-thiodipropionate, etc.), Riphenylphosphite, diphenylisodecylphos Phenyl Diisodecyl phosphite, Tris (nonylphenyl) phosphite, Diisodecylpentaerythritol phosphite, Tris (2,4-di-t-butylphenyl) phosphite, Cyclic neopentanetetraylbis (octadecyl) phosphite, Cyclic neopentanetetraylbi (2,4-di-t-butylphenyl) phosphite, cyclic neopentanetetraylbi (2,4-di-t-butyl-4-methylphenyl) phosphite, bis [2- t-Butyl-6-methyl-4- {2- (octadecyloxycarbonyl) ethyl} phenyl] hydrogen phosphite, etc.), and oxaphosphaphenanthrene oxides (9,10-dihydro-9-oxa-10-phos) Phenyl-10-oxide, 10- (3,5-di-t-butyl-4-hydroxybenzyl) -9,10-dihydro-9-oxa-10-phosphenylanthrene-10-oxide, and 10-decyloxy Examples thereof include phosphorus compounds such as -9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide.
The antioxidant that can be used in the photocurable ink of the present invention may be one kind of compound or a mixture of two or more kinds of compounds.

1.12. Antistatic agent The photocurable ink of the present invention may contain an antistatic agent. The antistatic agent prevents the surface of the obtained cured film from being charged by static electricity and suppresses the adhesion of dust and the like to the surface.

The antistatic agent is not particularly limited, and is ethoxyglycerin fatty acid ester, quaternary amine compound, lithium salt compound, aliphatic amine derivative, alkyl sulfonate compound, polyoxyalkylene ether sulfate compound, polyethylene oxide. Any charge known to those skilled in the art can be exemplified such as epoxy resins, siloxanes, silicone oligomers, ionic liquids and other alcohol derivatives such as poly (ethylene glycol) esters, poly (ethylene glycol) ethers. It may be an inhibitor.

Specific examples of the antistatic agent include Colcoat 200, Colcoat 515, Colcoat 1000, Colcoat WAS-15X (all manufactured by Colcoat Co., Ltd.), Electrostripper AC, Electrostripper QN, and Electrostripper ME-2 (all are Kao (all). (Manufactured by Co., Ltd.), FC-4400 (manufactured by 3M), AC-ILA (manufactured by Kaken Sangyo Co., Ltd.), AS100, AS300, AS400 (all manufactured by Nippon Emulsifier Co., Ltd.), IL-A2, IL-AP3 , IL-MA3, IL-P14 (all manufactured by Koei Chemical Industry Co., Ltd.), PEL-20A, PEL-25, PEL-46, PEL-100, CIL- 312, CIL-313 (all are Nippon Carlit (all) (Manufactured by Taisei Co., Ltd.), Akrit 1SX-1055, Akrit 1SX-1060, Akrit 1SX-1090, Akrit 1SX-3000 (all manufactured by Taisei Fine Chemical Co., Ltd.), DISPARLON1121 (manufactured by Kusumoto Kasei Co., Ltd.), PC-3662, PC -6862, PC-6905, PC-9102, PC-9106, PC-9107 (all manufactured by Maruhishi Yuka Kogyo Co., Ltd.), Sanconol A600-50R, Sanconol MEK-50R, Sanconol PETA-20R, Sanconol AD2300- 20R, Sanconol AD2600-50R, Sanconol BUAC-20R and Sanconol EAC-20R (all manufactured by Sanko Chemical Industry Co., Ltd.), and X-40-2450 (manufactured by Shinetsu Chemical Industry Co., Ltd.) can be mentioned.
The antistatic agent used in the photocurable ink of the present invention may be one kind or two or more kinds.

1.13. Curing Aid The photocurable ink of the present invention may contain a curing aid for the purpose of improving sensitivity. Examples of the curing aid include compounds having two or more thiols in one molecule. More specifically, hexanedithiol, decandithiol, 1,4-dimethylmercaptobenzene, butanediol bisglycolate, ethylene glycol bisthioglycolate, trimethylpropanthritol glycolate, butanediol bisthiopropionate, tri. Methylolpropantristhiopropionate, trimethylpropanetristhiopropionate, pentaerythritol tetrakisthiopropionate, pentaerythritol tetrakisthioglyconate, trishydroxyethyltristhiopropionate, 1,4-bis (3-mercaptobutane) Liloxy) butane (trade name: Karenz MT BD1, manufactured by Showa Denko Co., Ltd.), pentaerythritol tetrakis (3-mercaptobutylate) (trade name: Karenz MT PE1, manufactured by Showa Denko Co., Ltd.), and 1,3,5 -Tris (3-mercaptobutyloxyethyl) -1,3,5-triazine-2,4,6 (1H, 3H, 5H) -trion (trade name: Karenz MT NR1, manufactured by Showa Denko Co., Ltd.) can be mentioned. ..
These curing aids can be used alone or in combination of two or more.

1.14. Surfactant The photocurable ink of the present invention may further contain a surfactant, if necessary, for the purpose of controlling the coatability on the substrate.

Specific examples of the surfactant include Polyflow No. 45, Polyflow KL-245, Polyflow No. 75, Polyflow No. 90, Polyflow No. 95 (trade name, manufactured by Kyoeisha Chemical Industry Co., Ltd.), Disperbak 161, Disperbake 162, Disperbake 163, Disperbake 164, Disperbake 166, Disperbake 170, Disperbake 180, Disperbake 181 and Disperbake. Bake 182, BYK300, BYK306, BYK310, BYK320, BYK330, BYK342, BYK344, BYK346 (trade name, manufactured by Big Chemie Japan Co., Ltd.), KP-341, KP-358, KP-368, KF-96-50CS, KF -50-100CS (trade name, manufactured by Shin-Etsu Chemical Industry Co., Ltd.), Surflon SC-101, Surflon KH-40 (trade name, manufactured by Seimi Chemical Co., Ltd.), Futergent 222F, Futergent 251 and FTX-218 (trade name) Product name, Neos Co., Ltd.), TEGO Rad2100, 2200N, 2250, 2500, 2600, 2700 (Product name, Ebonic Japan Co., Ltd.) EFTOP EF-351, EFTOP EF-352, EFTOP EF-601, EFTOP EF -801, EFTOP EF-802 (trade name, manufactured by Mitsubishi Materials Co., Ltd.), Megafuck F-171, Megafuck F-177, Megafuck F-475, Megafuck F-477, Megafuck F-556, Mega Fuck R-08, Megafuck R-30 (trade name, manufactured by DIC Co., Ltd.), fluoroalkylbenzene sulfonate, fluoralkylcarboxylate, fluoroalkylpolyoxyethylene ether, fluoroalkylammonium iodide, fluoroalkylbetaine , Fluoroalkyl sulfonate, diglycerin tetrakis (fluoroalkyl polyoxyethylene ether), fluoroalkyltrimethylammonium salt, fluoroalkylaminosulfonate, polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene lauryl Ether, polyoxyethylene oleyl ether, polyoxyethylene tridecyl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene laurate, polyoxyethylene oleate, polyoxyethylene stearate, polyoxyethylene laurylamine , Solbitan Laurate, Solbitan Palmitate, So Rubitan stearate, sorbitan oleate, sorbitan fatty acid ester, polyoxyethylene sorbitan laurate, polyoxyethylene sorbitan palmitate, polyoxyethylene sorbitan stearate, polyoxyethylene sorbitan oleate, polyoxyethylene naphthyl ether, alkylbenzene sulfonic acid Salts and alkyldiphenyl ether disulfonates can be mentioned.

The surfactant used in the photocurable ink of the present invention may be one kind or two or more kinds.

The photocurable ink of the present invention can be prepared by mixing each of the above materials in a predetermined amount ratio using a known means, and dissolving or dispersing them.

The cured film of the present invention is made of the cured product of the above photocurable ink and is formed on the surface of the base material.

<2. Curing method of photocurable ink>
The method for forming a cured film of the present invention includes the following steps.
(Step 1) A step of applying the photocurable ink of the present invention to a substrate by various printing methods to form a coating film on the substrate, and (Step 2) a step of irradiating the coating film obtained in Step 1 with ultraviolet rays.

2.1. (Step 1) A step of applying a photocurable ink to a substrate by a printing method to form a coating film on the substrate An untreated PET film can be used as the substrate to which the photocurable ink of the present invention is applied. However, the present invention is not limited to this, and any substrate known to those skilled in the art such as glass or plastic may be used as long as the desired optical function can be obtained, and the shape thereof is a flat plate. The shape is not limited to the shape, and may be a curved shape.

The material of the substrate is not particularly limited, but for example, polyester resins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and polybutylene terephthalate (PBT), polyolefin resins such as polyethylene and polypropylene, and polymethyl methacrylate (PMMA). Such as acrylic resin, polystyrene resin, polycycloolefin resin, polyurethane resin, triacetyl cellulose (TAC), polyvinyl chloride, fluororesin, polyamide, polycarbonate and plastic film such as polyimide, cellophane, acetate, metal foil, polyimide and Examples thereof include laminated films with metal foils, glassin papers and parchment papers having a sealing effect, and papers and glasses sealed with polyethylene, clay binders, polyvinyl alcohols, starches or carboxymethyl cellulose (CMC) and the like.

The substances constituting these substrates include antioxidants, deterioration inhibitors, fillers, ultraviolet absorbers, antistatic agents and / or electromagnetic wave inhibitors, as long as they do not adversely affect the effects of the present invention. Additives may be included. In addition, at least a part of the surface of the substrate is subjected to an easy-adhesion treatment such as water-repellent treatment, corona treatment, plasma treatment, or blast treatment, if necessary, and at least a part of the surface is protected for an easy-adhesion layer or a color filter. A film or a hard coat film may be provided.

The thickness of the substrate is not particularly limited, but is usually 10 μm to 10 mm, and is appropriately adjusted depending on the purpose of use.
The photocurable ink of the present invention can be applied to a substrate by using a known printing method. The printing method is not particularly limited, but is an inkjet method, a spin coating method, a roll coating method, a slit coating method, a dipping method, a spray coating method, a gravure coating method, a reverse coating method, a rod coating method, a bar coating method, and a die coating method. , Kiss coat method, reverse kiss coat method, air knife coat method, curtain coat method, etc.

2.2. (Step 2) Step of irradiating the composition with ultraviolet rays to the coating film obtained in Step 1 The cured film of the present invention was obtained by applying the photocurable ink of the present invention to the substrate surface by a desired printing method. It is obtained by irradiating the coating film with light such as ultraviolet rays or visible light to cure it after undergoing a drying step as necessary.

The photocurable ink containing a solvent may be subjected to a drying step for the purpose of removing the solvent before curing. For example, by heating at 50 to 200 ° C. for 1 to 5 minutes, the solvent is removed and the film adheres. The sex can be further enhanced.

The amount of light (exposure) to be emitted when irradiating ultraviolet rays or visible light depends on the composition of the photocurable ink, but is an illuminometer (UVPF-A1 / PD-365, manufactured by Iwasaki Electric Co., Ltd.). 100 to 5,000 mJ / cm ² is preferable, 100 to 4,000 ^{mJ / cm 2} is more preferable, and 100 to 3,000 ^{mJ / cm 2} is even more preferable. The wavelength of ultraviolet rays and visible rays to be irradiated is preferably 200 to 500 nm, more preferably 300 to 450 nm.

The exposure machine is particularly limited as long as it is equipped with a high-pressure mercury lamp, an ultra-high pressure mercury lamp, a metal halide lamp, a halogen lamp, an LED lamp, etc., and irradiates ultraviolet rays or visible light in the range of 250 to 500 nm. Not done.

Further, if necessary, the cured film cured by irradiation with light may be further heated, and the strength of the cured film can be further increased by heating at, for example, 80 to 250 ° C. for 10 to 60 minutes.

<3. Applications of cured film>
The application of the cured film of the present invention is not particularly limited, but since the cured film of the present invention has excellent adhesion to the untreated PET film, an optical sheet using the untreated PET film as a substrate, particularly a backlight of a liquid crystal display element. It is preferably used for the optical sheet for light diffusion used in the unit.

3.1. Optical sheet for light diffusion The optical sheet for light diffusion includes a base sheet, a light diffusion layer laminated on the surface of the base sheet, and the like.
It is composed of a sticking prevention layer arranged on the back surface of the base sheet. The photocurable ink of the present invention may be used for forming a light diffusing layer, for forming an anti-sticking layer, or for both. The composition is appropriately adjusted according to the composition of the target layer, and the cured film does not necessarily have to be formed from inks having the same composition.

3.1.1. Base sheet The base sheet is formed of a transparent, particularly colorless and transparent synthetic resin as a main component because it is necessary to transmit light rays. The synthetic resin used for the base sheet is not particularly limited, and examples thereof include polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, and weather-resistant vinyl chloride. Among them, polyethylene terephthalate having excellent transparency and high strength is preferable, and polyethylene terephthalate having improved bending performance is particularly preferable. Since the photocurable ink of the present invention has excellent adhesion to untreated PET, it is more preferable to use untreated PET as the base sheet.

The lower limit of the average thickness of the base sheet is preferably 10 μm, more preferably 35 μm, and even more preferably 50 μm. On the other hand, the upper limit of the average thickness of the base sheet is preferably 500 μm, more preferably 250 μm, and even more preferably 188 μm. When the average thickness of the base sheet is 10 μm or more, it is possible to suppress the occurrence of curls and wrinkles when the light diffusion layer and the anti-sticking layer are formed by coating. When the average thickness of the base sheet is 500 μm or less, the decrease in the brightness of the liquid crystal display device can be suppressed, and the thickness of the backlight unit can be kept small, which is advantageous for reducing the thickness of the liquid crystal display device.

3.1.2. Light-diffusing layer The light-diffusing layer is laminated on the surface of the base sheet. The light diffusing layer has a light diffusing agent and a binder thereof. The light diffusing layer contains the light diffusing agent dispersedly at substantially equal densities. The light diffusing agent is surrounded by a binder. By dispersing and containing the light diffusing agent, the light diffusing layer diffuses the light transmitted from the back surface side to the front surface side substantially uniformly. Further, in the light diffusing layer, fine irregularities are formed substantially uniformly on the surface by the light diffusing agent, and each concave portion and convex portion of the fine irregularities are formed in a lens shape. The light diffusing layer exerts an excellent light diffusing function due to the lens-like action of such fine irregularities, and due to this light diffusing function, the refracting function of refracting the transmitted light rays toward the normal direction and the transmitted light in the normal direction. It has a light-collecting function that causes the light to be focused macroscopically.

The light diffusing agent is particles having a property of diffusing light rays, and corresponds to the above-mentioned fine particles in the photocurable ink of the present invention.
The binder is formed by curing (crosslinking, etc.) a polymer composition containing a base polymer. The light diffusing agent is arranged and fixed at substantially equal densities on the entire surface of the base sheet by the binder. The cured product of the resin component of the photocurable ink of the present invention functions as the binder, and the photocurable ink includes, for example, a fine inorganic filler, a curing agent, a plasticizer, a dispersant, and various types in addition to the resin component and fine particles. A leveling agent, an antistatic agent, an ultraviolet absorber, an antioxidant, a viscosity modifier, a lubricant, a light stabilizer and the like may be appropriately blended.

The method of laminating the light diffusion layer on the base sheet is not particularly limited, and various known methods are adopted. As a specific laminating means, for example, coating using a gravure coating method, a roll coating method, a bar coating method, a blade coating method, a spray coating method, or the like is adopted. Of these, the gravure coating method, which can coat a binder containing a light diffusing agent thinly and evenly, is most preferable.

3.1.3. Anti-sticking layer The anti-sticking layer is disposed on the surface opposite to the light diffusing layer via the base sheet. In the anti-sticking layer, for example, when an optical sheet having a light diffusion layer is arranged on a light guide plate, a part of the back surface of the optical sheet sticks (partially adheres) to the front surface of the light guide plate to generate interference fringes. Although it prevents inconvenience, the best way to prevent sticking is to form protrusions so that they do not structurally stick together.
When the photocurable ink of the present invention is used for the anti-sticking layer, a method of dispersing fine particles can be adopted in the same manner as the light diffusing layer.

Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited to these Examples.

The names of the reaction raw materials and solvents used in the synthesis examples are indicated by abbreviations. This abbreviation is used in the following description.
FA513M: Dicyclopentanyl methacrylate (manufactured by Hitachi Kasei Co., Ltd.)
CHMI: N-Cyclohexylmaleimide MAA: FA512M Methacrylic Acid: Dicyclopentenyloxyethyl methacrylate (manufactured by Hitachi Chemical Co., Ltd.)
BzMA: Benzyl methacrylate GMA: Glycidyl methacrylate FA400M: Methoxypolyethylene glycol methacrylate, ethylene oxide repeating unit = 9 (manufactured by Hitachi Kasei Co., Ltd.)
PME1000: Repeating unit of methoxypolyethylene glycol methacrylate and ethylene oxide = 23 (manufactured by NOF CORPORATION)
V601: 2,2'-azobis (methyl isobutyrate) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)
PGMEA: Propylene glycol monomethyl ether acetate

The names of the reaction raw materials and the solvents used in Examples and Comparative Examples are indicated by abbreviations. This abbreviation is used in the following description.
Ingredient (B)
M305: Mixture of pentaerythritol tetraacrylate and pentaerythritol triacrylate (manufactured by Toagosei Co., Ltd.)
M327: ε-caprolactone-added tris (acryloxyethyl) isocyanurate SR602: Bisphenol A ethylene oxide-added diacrylate, ethylene oxide repeating unit = 10 (manufactured by Sartmer Japan Co., Ltd.)
Ingredient (C)
THFA: Tetrahydrofurfuryl Acrylate
Ingredient (D)
IC127: 2-Hirodoxy-1- {4- [4- (2-hydroxy-2-methyl-propionyl) -benzyl] phenyl] -2-methyl-propan-1-one (manufactured by BASF)
Antistatic agent X-40-2450: Ionic group-containing silicone oligomer (manufactured by Shin-Etsu Chemical Co., Ltd.)
Solvent MEK: Methyl ethyl ketone

[Synthesis Example 1] A four-necked flask equipped with a synthetic stirrer for a polymer (A1) solution is charged with FA513M, CHMI, MAA, FA512M, V-601 and PGMEA under the following weights, and is charged at 110 ° C. under a dry nitrogen stream for 2 hours. The mixture was heated and stirred to obtain a polymer (A1).
FA513M 9.400g
CHMI 4.600g
MAA 5.000g
FA512M 1,000g
V601 3.000g
PGMEA 46.67g

The polymerization solution was cooled to room temperature to obtain a 30% by weight solution of the pale yellow transparent polymer (A1). A part of the solution was sampled and the weight average molecular weight was measured by GPC analysis (polystyrene standard). As a result, the weight average molecular weight Mw of the obtained polymer (A1) was 4,000.

[Synthesis Examples 2 to 4] Synthesis of Polymer (A2) to (A4) Solutions According to the method of Synthesis Example 1, each component is reacted at the temperature, time and ratio (unit: g) shown in Table 1. Polymer (A2)-(A4) solutions were obtained.

[Comparative Synthesis Example 1] Synthesis of Polymer (A'1) Solution According to the method of Synthesis Example 1, each component is reacted at the temperature, time and ratio (unit: g) shown in Table 1 to obtain a polymer (A'1) solution. A'1) A solution was obtained.

[Example 1]
<Preparation of photocurable ink 1>
The materials shown below were mixed and dissolved, and then filtered through a UPE membrane filter (0.2 μm) to obtain a photocurable ink 1.
(A) A1 5.00g
(B) M305 1.50g
(D) IC127 0.11 g
(Solvent) MEK 1.16g

<Preparation of cured film>
The obtained photocurable ink 1 is applied onto a PET film (thickness: 50 μm, brand name: Lumirror T60, manufactured by Toray Industries, Inc.) using a coating rod (# 10, manufactured by R.D. Specialties). did.
The obtained coating film was dried in a high-temperature chamber at 80 ° C. for 1 minute, and used with a conveyor-type UV irradiation device equipped with a high-pressure mercury lamp (H08-L41, rated 160 W / cm, manufactured by Iwasaki Electric Co., Ltd.). Ultraviolet rays were irradiated at an illuminance of 300 mW / cm ² and an exposure of 300 mJ / cm ² to obtain a transparent cured film. The film thickness of the cured film measured using a digital length measuring machine (DIGIMICRO MF-501, manufactured by Nikon Corporation) was 14 μm.
<Evaluation of cured film>
The adhesion and color change of the obtained cured film were evaluated.
The above results are shown in Tables 2 and 3.
Each physical property in the example was measured under the following conditions.

(I) Adhesion After the coating film is cured, four vertical and horizontal cuts are made on the surface of the cured film at 5 mm intervals to make nine squares, and commercially available cellophane tape (cellotape (registered trademark), CT24, Nichiban Co., Ltd.) was brought into close contact with the product, and when the cured film was rapidly peeled off 180 degrees toward the front, the grid remaining without peeling was evaluated as follows.
⊚: No peeling of any grid ○: The area where the cured film was peeled off clearly did not exceed 5% (small peeling of the cured film at the intersection of cuts)
Δ: The area where the cured film was peeled off was 5% or more and less than 35% (the cured film was partially or completely peeled off along the cut line).
×: 35% or more is peeled off

(Ii) Color change After the coating film is cured, the color of the cured film is measured with an ultraviolet-visible near-infrared spectrophotometer (trade name; V-670, JASCO Corporation) for the PET film with a cured film. ^{The b *} value in the CIELAB color system was measured with the light source setting D65 and the viewing angle of 2 °, and was set to ^{b1 *.} Then, the measured PET film with a cured film was left to stand in an atmosphere of 65 ° C. and a relative humidity of 95% for 500 hours, and then the color of the cured film was measured again with an ultraviolet-visible near-infrared spectrophotometer to measure ^{the b * value.} , B2 ^* values. Then, ^{the Δb *} value was obtained by calculating the ^{b2 *} value −b1 ^{* value.} The obtained Δb ^* value was evaluated as follows.
⊚: <0.1
◯: 0.1 to 0.3
Δ: 0.3 to 0.5
×: 0.5 <
If it is "◎ to ○", the change in color is small and the optical characteristics can be maintained even in a high temperature and high humidity environment.

[Examples 2 to 9]
Photocurable inks 2 to 9 were prepared in the same manner as in Example 1 except that the materials shown in Tables 2 to 3 were used. Using the photocurable inks 2 to 9, a cured film was prepared in the same manner as in Example 1, and the adhesion and the change in color were evaluated.

[Comparative Examples 1 to 3]
Photocurable inks R1 to R3 were prepared in the same manner as in Example 1 except that the materials shown in Tables 2 to 3 were used. Using the photocurable inks R1 to R3, a cured film was prepared in the same manner as in Example 1, and the adhesion and the change in color were evaluated. The results are shown in Tables 2-3.

As shown in Tables 2 and 3, Examples 1 to 9 are suitable for photocurable inks for optical sheets because they are excellent in adhesion to untreated PET and color change.
Comparative Examples 1 and 3 have insufficient adhesion to untreated PET. In Comparative Example 2, since the color change is large, the optical characteristics are not sufficiently maintained in a high temperature and high humidity environment.

As described above, the photocurable ink of the present invention can provide a photocurable ink in which the cured film has excellent adhesion to an untreated PET film and can maintain optical characteristics even in a high temperature and high humidity environment. Is. Further, since the cured film of the present invention is formed by irradiating the photocurable ink of the present invention with ultraviolet rays, the use of heat that causes distortion of the substrate can be minimized. Therefore, the photocurable ink of the present invention is useful for suitably producing a high-quality optical sheet by a simple and inexpensive manufacturing process. Since such a cured film of the present invention can be formed on an optical sheet using an untreated PET film as a substrate, it can be particularly suitably used for a backlight unit of a liquid crystal display element.

40: Backlight unit 41: Light source 42: Light guide plate 43: Optical sheet 44: Light diffusion sheet 45: Prism sheet 46: Base material layer 47: Light diffusion layer 48: Sticking prevention layer

Claims (15)

A photocurable ink containing a polymer (A), a polyfunctional (meth) acrylate (B), and a photopolymerization initiator (D) obtained by polymerizing at least one (meth) acrylate having a ring structure. The photocurable ink according to claim 1, wherein the (meth) acrylate having a ring structure is a compound represented by the following formula (3).

(In the formula, R ¹¹ is hydrogen or methyl, and R ¹² is cyclohexane, cyclopentane, bicyclo [2.2.1] heptane, a cyclic ether having a 5-membered ring or more, a lactone having a 5-membered ring or more, and dicyclopentane. , Dicyclopentene, adamantan and cyclic formal, which is an organic group having at least one selected from the ring structure, b is 0 or 1, and Z is the following formula (3-1) or formula (3-2). It is a divalent group represented.)

(In the formula, c and d are integers from 0 to 10.) The photocurable ink according to claim 1 or 2, wherein the (meth) acrylate having a ring structure contains at least one selected from dicyclopentanyl methacrylate and dicyclopentenyloxyethyl methacrylate. Claim 1 that the weight average molecular weight of the polymer (A) obtained by polymerizing at least one kind of (meth) acrylate having a ring structure is 10,000 or less in terms of polystyrene obtained by the GPC method. The photocurable ink according to any one of 3 to 3. Polyfunctional (meth) acrylate (B) is pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, trimethyl propantri ( Meta) acrylate, ditrimethylolpropanetetra (meth) acrylate, glycerintri (meth) acrylate, bisphenol A ethylene oxide-added di (meth) acrylate having 2 to 6 repeating units of ethylene oxide in the structure, ε-caprolactone-added tris (meth) Any one of claims 1 to 4, comprising at least one selected from (acryloxyethyl) isocyanurate, di ((meth) acryloyloxyethyl) isocyanurate, and tri ((meth) acryloyloxyethyl) isocyanurate. The photocurable ink described in the section. The polyfunctional (meth) acrylate (B) is pentaerythritol tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, trimethylolpropane tri (meth) acrylate, di ((meth) acryloyloxyethyl) isocyanurate, and tri. The photocurable ink according to any one of claims 1 to 4, which comprises at least one selected from ((meth) acryloyloxyethyl) isocyanurate. The photocurable ink according to any one of claims 1 to 6, further comprising a monofunctional (meth) acrylate (C). The photocurable ink according to any one of claims 1 to 7, wherein the photopolymerization initiator (D) is an α-hydroxyalkylphenone-based photopolymerization initiator. A cured film made of a cured product of the photocurable ink according to any one of claims 1 to 8. The cured film according to claim 9, which is for an optical sheet. The cured film for an optical sheet according to claim 10, wherein the cured film is formed on the surface of a transparent base material sheet. The cured film for an optical sheet according to claim 11, wherein the transparent base sheet is a polyethylene terephthalate film that has not been easily adhered. An optical sheet having a cured film for an optical sheet according to claim 12. A backlight unit having the optical sheet according to claim 13. A liquid crystal display element equipped with the backlight unit according to claim 14.

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