WO2014033932A1

WO2014033932A1 - Optical sheet

Info

Publication number: WO2014033932A1
Application number: PCT/JP2012/072251
Authority: WO
Inventors: 浩一梅本; 綾横山
Original assignee: 株式会社ダイセル
Priority date: 2012-08-31
Filing date: 2012-08-31
Publication date: 2014-03-06

Abstract

Provided is an optical sheet having high transparency, suitable elasticity, and excellent toughness, moldability, and productivity. An optical sheet is composed of a curing material for a polymerizable composition containing a bifunctional urethane (meth)acrylate having a number-average molecular weight of 2000 to 50000, a monofunctional vinyl monomer, and a trifucntional vinyl monomer. A polymerizable component having an α,β-ethylenically unsaturated double bond in the polymerizable composition, wherein the number-average molecular weight is 1000 or more in terms of the weighted average per α,β-ethylenically unsaturated double bond. The curing material may be a photo-curing material obtained by the irradiation of an electron beam, or may be a curing material that contains essentially no polymerization initiator. The urethane (meth)acrylate may be an aliphatic urethane (meth)acrylate. This optical sheet is suitable as a key sheet, a light-guide sheet, a reflective sheet, an OCA tape substrate, or the like.

Description

Optical sheet

The present invention relates to an optical sheet used for a key sheet (key top sheet, key mat sheet, etc.), a light guide sheet, a reflective sheet, an optical transparent adhesive tape base material, etc. for electrical / electronic devices or optical devices.

With recent miniaturization and sophistication of optical and electronic devices, optical sheets such as light guide sheets or films (or light guide plates) are required to have various characteristics depending on the application. The light guide sheet used is required to have elasticity and flexibility to be bent by being pressed by a hand or the like. Furthermore, an illumination type key for using a terminal at night or in a dark place is adopted in a mobile device such as a mobile phone.

For example, as shown in FIG. 1, an illumination key switch structure of a cellular phone that has been thinned in recent years has been developed to illuminate with an LED light source 6 or the like from the side portion of the operation surface. . In this switch structure, a click dome 4 that is a spring member made of metal or the like is formed on the flexible printed wiring board 5, and the light from the light source 6 is guided on the click dome 4. For this purpose, a light guide sheet 3 is formed. Further, an embossed key top sheet 1 and a key mat sheet 2 are laminated on the light guide sheet 3 as an operation panel (operation surface) of an illumination type key. By clicking, the key mat sheet 2 laminated on the back surface of the key top sheet 1 comes into contact with the light guide sheet 3 and the click dome 4 is pressed. That is, in this switch structure, the key top sheet 1, the key mat sheet 2, and the light guide sheet 3 need to be bent by clicking. Furthermore, since the light from the light source 6 is guided by the light guide sheet 3 and passes through the key mat sheet 2 and the key top sheet 1, these sheets are required to have transparency.

As an optical sheet used for such applications, Japanese Patent Application Laid-Open No. 8-111822 (Patent Document 1) describes a thin part and a base part made of drawn polyethylene terephthalate (PET), and a Shore D hardness. A cover member for a push button switch is disclosed in which a key top portion made of a high-hardness resin of 40 degrees or more is integrated. This document describes that the high-hardness resin may be selected from general resins such as silicone resin, urethane resin, epoxy resin, acrylic resin, and PET.

Japanese Patent Laid-Open No. 10-172379 (Patent Document 2) integrally forms a film in which a display portion curved in the same shape is printed on the upper surface side of a key top body made of a thermoplastic material molded by a mold. In the sheet-like key top of the push button switch thus formed, the film is a multilayer elastic film having two or more layers, and the display portion is printed on the key top body side of the multilayer elastic film to form the display portion printed layer. A sheet-like key top structure is disclosed. This document discloses a multilayer elastic film in which an elastic film composed of various thermoplastic elastomers and a base material composed of various hard thermoplastic resins are laminated. A key top sheet in which nylon is laminated on both sides of an elastomer film is described.

However, in these sheets, it is difficult to achieve both mechanical properties such as flexibility and toughness, transparency, durability (heat resistance, weather resistance, water resistance, etc.) and formability. For example, a sheet made of a silicone resin has low moldability and transparency, and a sheet made of a urethane resin has insufficient heat resistance, water resistance, hydrolysis resistance, and moldability. Furthermore, since thermoplastic resins or elastomers are not sufficient in heat resistance and transparency and are molded by extrusion, it is difficult to produce a thin film or a film having a smooth surface.

On the other hand, as a sheet composed of a thermosetting resin, Japanese Patent Application Laid-Open No. 2008-62217 (Patent Document 3) applies a radiation curable paint containing a radiation curable silicone compound on a substrate to form a coating film. A step of forming, a step of covering the surface of the coating film with a release substrate having a silicone-treated surface so that the silicone-treated surface is in contact with the coating film, and irradiating the coating film covered with the release substrate with radiation. There is disclosed a method for forming a cured coating film comprising a step of curing the film and a step of peeling the release substrate from the cured coating film. This document describes silicone-modified urethane (meth) acrylate as a radiation-curable silicone compound. Furthermore, the obtained cured film is an article requiring stain resistance, abrasion resistance and transparency, for example, wallpaper; furniture, bathroom, kitchen, decorative sheet or decorative material for home appliances; automotive interior material; It is described that it is used as a protective film for an optical disk or the like; a protective film for a display. However, while the cured resin has high heat resistance and rigidity, thermal shrinkage easily occurs due to crosslinking. Moreover, when such a sheet | seat is applied to a keytop sheet | seat, it will be easy to tear when peeling a base material in a manufacturing process.

JP 2010-27153 A (Patent Document 4) discloses an optical sheet composed of a cured product of a polymerizable composition containing urethane (meth) acrylate. This document describes that the urethane (meth) acrylate may contain a bifunctional or trifunctional polyester type urethane (meth) acrylate from the viewpoint of improving the flexibility of the optical sheet. In addition, this document describes that a polymerizable vinyl component may be further included, and examples of the polymerizable vinyl component include a monofunctional vinyl monomer, a bifunctional vinyl monomer, and a trifunctional or higher polyfunctional vinyl monomer. Has been. In the examples of this document, an example in which an optical sheet is produced by curing a polymerizable composition containing a bifunctional urethane acrylate and a bifunctional vinyl monomer (polypropylene glycol diacrylate) is described. However, this optical sheet has a high heat shrinkage rate and insufficient dimensional stability. In addition, this optical sheet cannot secure flexibility at low temperatures, and becomes hard when used as a key top sheet or a light guide sheet for a key sheet in a cold region, so that sufficient softness and touch cannot be ensured.

JP-A-8-112822 (Claim 1, paragraph [0012]) JP-A-10-172379 (claims 1 to 3, paragraph [0012], examples) JP 2008-62217 A (claims, paragraphs [0029] [0058]) JP 2010-27153 A (claims, paragraphs [0017] [0041], examples)

Therefore, an object of the present invention is to provide an optical sheet having high transparency, high flexibility, and excellent toughness and dimensional stability.

Another object of the present invention is to provide an optical sheet that is excellent in flexibility even in a crosslinked structure and excellent in heat resistance and weather resistance.

Still another object of the present invention is to provide an optical sheet that can ensure sufficient softness and touch even when used in cold regions.

Another object of the present invention is to provide an optical sheet excellent in moldability and workability.

As a result of intensive studies to achieve the above-mentioned problems, the present inventors have found that an optical sheet is made of a polymerizable composition containing a bifunctional urethane (meth) acrylate having a specific molecular weight, a monofunctional vinyl monomer, and a trifunctional vinyl monomer. It has been found that when it is composed of a cured product, it is excellent in transparency and flexibility, and because the entanglement between molecular chains is increased, the toughness can be improved and the dimensional stability is excellent, and the present invention has been completed.

That is, the optical sheet of the present invention has a bifunctional urethane (meth) acrylate having a number average molecular weight of 2,000 to 50,000 [for example, a bifunctional aliphatic urethane as a polymerizable component having an α, β-ethylenically unsaturated double bond. (Meth) acrylate], a monofunctional vinyl monomer [e.g., monofunctional (meth) acrylate] and a trifunctional vinyl monomer [e.g., trifunctional (meth) acrylate]. ing. In the polymerizable component having an α, β-ethylenically unsaturated double bond in the polymerizable composition, the number average molecular weight (hereinafter simply referred to as a weighted average) per α, β-ethylenically unsaturated double bond ( The “weighted average double bond equivalent” may be 1000 or more.

The glass transition temperature of bifunctional urethane (meth) acrylate may be about −80 ° C. to −30 ° C. The number average molecular weight per α, β-ethylenically unsaturated double bond of the bifunctional urethane (meth) acrylate (hereinafter sometimes simply referred to as “double bond equivalent”) may be about 1000 to 20000. .

The monofunctional vinyl monomer may contain at least one monofunctional (meth) acrylate selected from a heterocyclic (meth) acrylate containing a nitrogen atom as a heterocyclic atom and a bridged cyclic (meth) acrylate. The trifunctional vinyl monomer may be a tri (meth) acrylate of an alkanetri to hexaol C _2-4 alkylene oxide adduct.

The proportion of the monofunctional vinyl monomer may be about 1 to 200 parts by weight with respect to 100 parts by weight of the bifunctional urethane (meth) acrylate, and the proportion of the trifunctional vinyl monomer may be about 1 to 100 parts by weight. Good.

The cured product of the polymerizable composition may be a photocured product (in particular, a photocured product obtained by irradiating an electron beam and substantially free of a polymerization initiator). The elongation at break of the optical sheet of the present invention may be about 100 to 300%. The optical sheet of the present invention was selected from a key sheet (key top sheet, key mat sheet, etc.), a light guide sheet, a reflective sheet, and an optical transparent adhesive tape substrate (OpticalOptClear Adhesive (OCA) tape substrate). It can be suitably used as a kind of sheet.

In this specification, “number average molecular weight in weighted average per α, β-ethylenically unsaturated double bond” means the total amount of polymerizable components having α, β-ethylenically unsaturated double bonds. The double bond equivalent of the weighted average of For example, a polymerizable component having an α, β-ethylenically unsaturated double bond is a component A (having three ethylenically unsaturated double bonds in one molecule and having a number average molecular weight of Ma), a B component ( 2 ethylenically unsaturated double bonds per molecule, number average molecular weight Mb), C component (one ethylenically unsaturated double bond per molecule, number average molecular weight Mc) In the polymerizable composition containing the A component as Wa parts by weight, the B component as Wb parts by weight, and the C component as Wc parts by weight, the number average as the weighted average per α, β-ethylenically unsaturated double bond The molecular weight can be calculated by the following formula (1).

The number average molecular weight of the low molecular weight polymerizable component may be a value calculated from the chemical formula and atomic weight.

In this specification, acrylic (or acrylate) and methacryl (or methacrylate) are collectively referred to as (meth) acrylic (or (meth) acrylate).

In the present invention, the optical sheet is composed of a cured product of a polymerizable composition containing a bifunctional urethane (meth) acrylate having a specific molecular weight, a monofunctional vinyl monomer, and a trifunctional vinyl monomer as a polymerizable component. High transparency, high flexibility, and excellent toughness and dimensional stability. In particular, in the present invention, even a crosslinked structure has high flexibility and is excellent in durability such as heat resistance and weather resistance. In the present invention, sufficient softness and tactile sensation can be secured even when used in a cold region. Furthermore, in this invention, it is excellent also in the moldability and workability. The optical sheet of the present invention is suitable for a key top sheet and the like, and can be effectively prevented from being broken when it is peeled off from a substrate after printing in the key top sheet manufacturing process.

FIG. 1 is a schematic diagram showing a switch structure of a lighted key of a thin cellular phone.

[Optical sheet]
The optical sheet of the present invention is composed of a cured product of a polymerizable composition containing a bifunctional urethane (meth) acrylate having a specific molecular weight, a monofunctional vinyl monomer, and a trifunctional vinyl monomer. In the present invention, since urethane (meth) acrylate having a specific molecular weight is included, the entanglement points between the molecular chains are increased, or toughness can be improved, and even if the elastic limit is exceeded, it does not break easily. In the present invention, since bifunctional urethane (meth) acrylate, trifunctional vinyl monomer, and monofunctional vinyl monomer are combined, the flexibility (glass transition temperature) of the polymerizable composition can be controlled and the thermal shrinkage rate can be reduced. , Dimensional stability can be improved.

(Bifunctional urethane (meth) acrylate)
The bifunctional urethane (meth) acrylate is a polyisocyanate [or a (meth) acrylate having an active hydrogen atom in a urethane prepolymer having a free isocyanate group produced by a reaction between a polyisocyanate and a polyol] [for example, It may be a urethane (meth) acrylate obtained by reacting a hydroxyalkyl (meth) acrylate or the like].

The polyisocyanate is not particularly limited as long as it has two or more isocyanate groups in the molecule. For example, it may be a heterocyclic polyisocyanate or a derivative thereof, but usually an aliphatic polyisocyanate or an alicyclic group. Polyisocyanates, aromatic polyisocyanates, and derivatives thereof.

Aliphatic polyisocyanates include diisocyanates [for example, C _2-16 alkane diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate (HDI), 2,4,4- or 2,2,4-trimethylhexamethylene diisocyanate (TMDI). , 2,6-diisocyanatomethylcaproate, lysine diisocyanate (LDI), etc.], polyisocyanates having 3 or more isocyanate groups in the molecule (for example, lysine ester triisocyanate, 1,3,6-hexamethylene tris) Isocyanate, C _6-20 alkane triisocyanate such as 1,6,11-undecane triisocyanate methyl octane) and the like.

Alicyclic polyisocyanates include diisocyanates (eg, 1,4-cyclohexane diisocyanate, isophorone diisocyanate (IPDI), 4,4′-methylene bis (cyclohexyl isocyanate), hydrogenated xylylene diisocyanate, hydrogenated bis (isocyanatophenyl). Methane, norbornane diisocyanate, etc.), polyisocyanates having 3 or more isocyanate groups in the molecule (for example, 1,3,5-trimethylisocyanatocyclohexane, 2- (3-isocyanatopropyl) -2,5-di ( Isocyanatomethyl) -bicyclo [2.2.1] heptane, 5- (2-isocyanatoethyl) -2-isocyanatomethyl-3- (3-isocyanatopropyl) -bicyclo [2.2.1] heptane Triisocyanate such as Theft, etc.), and the like.

Aromatic polyisocyanates include diisocyanates (eg, phenylene diisocyanate, 1,5-naphthylene diisocyanate (NDI), xylylene diisocyanate (XDI), tetramethylxylylene diisocyanate (TMXDI), diphenylmethane diisocyanate (MDI), tolylene diisocyanate. (TDI), 4,4′-toluidine diisocyanate (TODI), 4,4′-diphenyl ether diisocyanate, 1,3-bis (isocyanatophenyl) propane, etc.), polyisocyanate having three or more isocyanate groups in the molecule (For example, triisocyanates such as 1,3,5-triisocyanatomethylbenzene, triphenylmethane-4,4 ′, 4 ″ -triisocyanate, 4,4′-diph Nirumetan 2,2 ', like tetraisocyanates such as 5,5'-tetra isocyanate) and the like.

Examples of the polyisocyanate derivatives include dimers, trimers, biurets, allophanates of the above polyisocyanates, polyisocyanates having a 2,4,6-oxadiazine trione ring which is a polymer of carbon dioxide and the above polyisocyanate monomer. Isocyanates, carbodiimides, uretdiones and the like.

Polyisocyanates can be used alone or in combination of two or more. Among polyisocyanates, aliphatic diisocyanates such as HDI, alicyclic diisocyanates such as IPDI and hydrogenated XDI, and aromatic diisocyanates such as XDI, TDI, MDI and NDI are widely used, and high weather resistance is required. Non-aromatic polyisocyanates, for example, non-yellowing type diisocyanates (aliphatic diisocyanates such as HDI, alicyclic diisocyanates such as IPDI and hydrogenated XDI) or derivatives thereof (trimers having an isocyanurate ring). It may be used.

Examples of polyols include aliphatic diol [alkanediol (ethylene glycol, propylene glycol, trimethylene glycol, tetramethylene ether glycol, 1,3-butylene glycol, 1,5-pentanediol, neopentyl glycol, 1,6 -C _2-10 alkanediols such as hexanediol), diethylene glycol, triethylene glycol, dipropylene glycol, etc.], cycloaliphatic diols (1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, etc.) , hydrogenated bisphenols, such as hydrogenated bisphenol a, or an C _2-4 alkylene oxide adduct thereof), aromatic aliphatic diols and aromatic diols (xylylene glycol, Bisufe Lumpur A, bisphenol S, bisphenol such as bisphenol F, or a diol such as these C _2-4 alkylene oxide adduct thereof), triols (glycerol, trimethylolethane, trimethylolpropane, 1,2,6 -Hexanetriol, triethanolamine, etc.), tetraols (pentaerythritol, sorbitan or derivatives thereof, etc.), hexaols (dipentaerythritol, etc.), polymer polyols and the like.

The polymer polyols include polyester polyols, polyether polyols, polyether ester polyols, polycarbonate polyols, polyester amide polyols, acrylic polymer polyols, and the like.

The polyester polyol may be, for example, a reaction product of polycarboxylic acid (or its anhydride) and polyol, or a reaction product obtained by ring-opening addition polymerization of a lactone with respect to an initiator.

Polycarboxylic acids include dicarboxylic acids [for example, aromatic dicarboxylic acids or anhydrides thereof (terephthalic acid, isophthalic acid, phthalic anhydride, etc.), alicyclic dicarboxylic acids or anhydrides thereof (tetrahydrophthalic anhydride, het anhydride, etc. , Hymic anhydride, etc.), aliphatic dicarboxylic acid or its anhydride (succinic acid, succinic anhydride, adipic acid, azelaic acid, sebacic acid and other C _4-20 alkanedicarboxylic acid, maleic anhydride, fumaric acid, etc. Saturated dicarboxylic acid etc.)], polyvalent carboxylic acids (for example, trimellitic acid, trimellitic anhydride, pyromellitic anhydride, etc.) or alkyl esters of these carboxylic acids. Of these polycarboxylic acids, aliphatic dicarboxylic acids or anhydrides thereof (C _6-20 alkane dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, etc.) are preferred. These polycarboxylic acids can be used alone or in combination of two or more. Examples of the polyol include the aliphatic diol, the alicyclic diol, and the aromatic diol. These polyols can be used alone or in combination of two or more.

Examples of lactones include C such as γ-butyrolactone (GBL), γ-valerolactone, δ-valerolactone, β-methyl-δ-valerolactone, γ-caprolactone, and enanthlactone (7-hydroxyheptanoic acid lactone). _{And 3-10} lactone. These lactones can be used alone or in combination of two or more. Of these lactones, C _4-8 lactones such as valerolactone and caprolactone are preferred.

Initiators for lactones include, for example, water, oxirane compounds (eg, C _2-6 alkylene oxides such as ethylene oxide, propylene oxide, butylene oxide, tetrahydrofuran, etc.) or copolymers [eg, polyethylene glycol (PEG) , Polypropylene glycol (PPG), polytetramethylene ether glycol (PTMG), etc.], low molecular weight polyols (ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexamethylene glycol, trimethylolpropane, glycerin, penta Erythritol, bisphenol A, etc.), compounds having an amino group (for example, ethylenediamine, hexamethylenediamine, hydrazine, xylylenediamine, isophoronediamine). Which diamine compounds, polyamine compounds such as diethylenetriamine, etc.). These initiators can be used alone or in combination of two or more.

Examples of the polyether polyol include a ring-opening polymer of the oxirane compound (for example, poly C _2-4 alkylene glycol such as polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, etc.).

Examples of the polyether ester polyol include a polyether ester which is a polymer of the dicarboxylic acid (aromatic dicarboxylic acid, alicyclic dicarboxylic acid, aliphatic dicarboxylic acid, etc.) or a dialkyl ester thereof and the polyether polyol. A polyol etc. are mentioned.

Polycarbonate polyols include, for example, glycols (ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol and other alkane diols; diethylene glycol, dipropylene glycol, etc. (Poly) oxyalkylene glycols; alicyclic diols such as 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydrogenated bisphenol A; bisphenols such as bisphenol A, alkylene oxide adducts of bisphenols, etc. One or more glycols selected from aromatic diols) and carbonates (dimethyl carbonate, ethylene carbonate, diphenyl carbonate, etc.) or phosgene Etc. etc. polymers and the like with.

As the polyesteramide polyol, in the reaction of the polyester polyol (polymerization of dicarboxylic acid and diol, etc.), a terminal carboxyl group-containing polyester and a diamine (for example, an aliphatic diamine having an amino group such as ethylenediamine, propylenediamine, hexamethylenediamine, etc.) Etc.) as a reaction component.

Acrylic polyols include hydroxyl group-containing polymerizable monomers (for example, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, etc.), and (meth) acrylic that does not contain hydroxyl groups. Examples thereof include acrylic polyol which is a polymer with a monomer (for example, (meth) acrylic acid or an ester thereof).

Polyols can be used alone or in combination of two or more. Of the polyols, polyester polyols, polyether polyols, polycarbonate polyols, and acrylic polyols are preferable from the viewpoint of flexibility and versatility. Of these, polyester polyols and polyether polyols are preferable from the viewpoint of flexibility and the like, and polyester polyols are particularly preferable from the viewpoint of excellent moisture absorption stability.

Examples of the urethane prepolymer include multimers of the polyisocyanates, burette-modified multimers of the polyisocyanates, adducts of the polyisocyanates and the polyols, and an excess of the polyisocyanate relative to the polyols. Examples thereof include urethane prepolymers obtained by reacting isocyanates. These prepolymers can be used alone or in combination of two or more.

Preferred urethane prepolymers include, for example, multimers (trimers, pentamers, heptamers, etc.) of the polyisocyanates, burette multimers (burette-modified products) of the polyisocyanates, the polyisocyanates and polyols. Adducts with diols (triols such as glycerin and trimethylolpropane), urethane prepolymers of the diisocyanates and polyester polyols, urethane prepolymers of the diisocyanates and polyether polyols, especially the diisocyanates and polyether polyols or polyesters A urethane prepolymer with a polyol is preferred.

Examples of the (meth) acrylate having an active hydrogen atom include hydroxy C _2-6 alkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate; 2-hydroxy-3- Hydroxyalkoxy C _2-6 alkyl (meth) acrylates such as methoxypropyl (meth) acrylate; hydroxyalkanedi (such as glycerin di (meth) acrylate, trimethylolpropane di (meth) acrylate, trimethylolethane di (meth) acrylate) Meth) acrylates; hydroxyglycans tri (meth) acrylates such as diglycerin tri (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol tri (meth) acrylate Dipentaerythritol tetra or penta (meth) acrylate can be exemplified.

Urethane (meth) acrylate is a ratio of polyisocyanate and (meth) acrylate having an active hydrogen atom, which is generally equivalent to an isocyanate group and an active hydrogen atom (isocyanate group / active hydrogen atom = 0.8 / 1). To about 1.2 / 1). JP-A-2008-74891 and the like can be referred to for the method for producing these urethane (meth) acrylates.

The bifunctional urethane (meth) acrylate can be used alone or in combination of two or more. Among the bifunctional urethane (meth) acrylates, a bifunctional polyether type urethane (meth) acrylate and a bifunctional polyester type urethane (meth) acrylate are widely used. Of the bifunctional urethane (meth) acrylates, bifunctional aliphatic urethane (meth) acrylates are preferable from the viewpoint of improving the flexibility of the optical sheet.

The number average molecular weight of the bifunctional urethane (meth) acrylate can be selected from a range of about 2000 or more (for example, 2000 to 50000) in terms of polystyrene in gel permeation chromatography (GPC), for example, and 2500 to 45000 (for example, 3000 to 40000), preferably 3500 to 35000 (for example, 4000 to 30000), more preferably about 4500 to 25000 (for example, 4500 to 20000), and may be about 10,000 or more (for example, 15000 to 20000). . If the molecular weight of the bifunctional urethane (meth) acrylate is too large, the cross-linking density is reduced and the heat resistance is lowered. If the molecular weight is too small, the entanglement of molecules is reduced or the toughness is lowered.

The double bond equivalent ((meth) acryloyl group equivalent) (g / mol) of the bifunctional urethane (meth) acrylate can be selected from the range of about 1000 or more (for example, 1000 to 20000), for example, 1200 to 18000 (for example, 1400-16000), preferably 1500-15000 (for example, 1800-14000), more preferably about 2000-12000 (for example, 2200-10000), and even about 5000 or more (for example, 6000-10000). Good. If the double bond equivalent of the bifunctional urethane (meth) acrylate is increased, the weighted average double bond equivalent in the total amount of the polymerizable component can be increased, the crosslinking density can be reduced, and the entanglement by the molecular chain can be improved. The thermal shrinkage rate can be reduced and the dimensional stability can be improved.

The glass transition temperature of the bifunctional urethane (meth) acrylate (the glass transition temperature of the homopolymer, Tg) can be selected from the range of −20 ° C. or less, for example, −80 ° C. to −20 ° C., preferably −75 ° C. to − It may be about 20 ° C. (for example, −70 ° C. to −25 ° C.), more preferably about −65 ° C. to −25 ° C. (for example, −60 ° C. to −30 ° C.). It is about ℃. When the Tg of the bifunctional urethane (meth) acrylate is too large, flexibility (particularly flexibility at low temperature) is lowered, and it becomes difficult to ensure sufficient flexibility and tactile sensation when used in cold regions. . Tg can be measured using a differential scanning thermometer.

(Monofunctional vinyl monomer)
Examples of the monofunctional vinyl monomer include (meth) acrylic acid; methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) ) Acrylate, t-butyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, decyl (meth) acrylate, lauryl (meth) acrylate, stearyl C _1-24 alkyl (meth) acrylates such as (meth) acrylate; cycloalkyl (meth) acrylates such as cyclohexyl (meth) acrylate; dicyclopentanyl (meth) acrylate, dicyclope Bridged cyclic (meth) acrylates such as tertenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, bornyl (meth) acrylate, isobornyl (meth) acrylate, tricyclodecanyl (meth) acrylate; phenyl (meta ) Acrylate, aryl (meth) acrylates such as nonylphenyl (meth) acrylate; aralkyl (meth) acrylates such as benzyl (meth) acrylate; hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate hydroxy _{C 2-10} alkyl (meth) acrylate or _{C 2-10} alkanediol mono (meth) acrylate and the like; trifluoroethyl (meth) acrylate, Tetorafuruo Propyl (meth) acrylate, fluoroalkyl C _1-10 alkyl (meth) acrylates such as hexafluoroisopropyl (meth) acrylate; alkoxyalkyl such as methoxyethyl (meth) acrylate (meth) acrylate; phenoxyethyl (meth) acrylate, phenoxypropyl Aryloxyalkyl (meth) acrylates such as (meth) acrylate; aryloxy (poly) alkoxyalkyl (meta) such as phenyl carbitol (meth) acrylate, nonylphenyl carbitol (meth) acrylate, nonylphenoxypolyethylene glycol (meth) acrylate ) Acrylate; polyalkylene glycol mono (meth) acrylate such as polyethylene glycol mono (meth) acrylate; 2-methoxy (Poly) alkylene glycol mono (meta) having substituents (alkyl group etc.) such as ethyl (meth) acrylate, methyltriethylene glycol (meth) acrylate, ethyl carbitol (meth) acrylate, 2-ethylhexyldiethylene glycol (meth) acrylate ) Acrylate [eg linear or branched C _1-10 alkyl poly C _2-4 alkylene glycol (meth) acrylate etc.]; alkane polyol mono (meth) acrylate such as glycerin mono (meth) acrylate; 2-dimethyl (Meth) acrylates having amino groups such as aminoethyl (meth) acrylate, 2-diethylaminoethyl (meth) acrylate, and 2-t-butylaminoethyl (meth) acrylate; glycidyl (meth) acrylate G: Heterocyclic (meth) such as piperidinyl (meth) acrylate, alkylpiperidinyl (meth) acrylate (pentamethylpiperidinyl (meth) acrylate, etc.), morpholino (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, etc. Examples include acrylates; N-vinyl heterocyclic compounds such as N-vinyl pyrrolidone, N-vinyl pyridine and N-vinyl caprolactam; N-vinyl acetamide, N-vinyl formamide and the like.

A monofunctional vinyl monomer can be used individually or in combination of 2 or more types. A monofunctional vinyl monomer is a (meth) acrylate having a ring structure, for example, a heterocyclic (meth) acrylate containing a nitrogen atom (N) as a heterocyclic atom, because the thermal shrinkage can be reduced and the dimensional stability can be improved. [For example, (meth) acryloylmorpholine, 5- to 6-membered N-containing heterocyclic (meth) acrylates such as N-vinylpyrrolidone, etc.] and bridged cyclic (meth) acrylates [eg, isobornyl (meth) acrylate, etc. Preferably, it contains at least one monofunctional (meth) acrylate selected from C _6-10 bridged cyclic (meth) acrylate and the like]. Furthermore, the monofunctional vinyl monomer is a (meth) acrylate having a chain aliphatic skeleton, such as an alkyl (poly) alkylene glycol, from the viewpoints of adjusting the viscosity of the polymerizable composition, adjusting the Tg of the cured product, and imparting flexibility. (Meth) acrylate [for example, linear or branched C _1-10 alkyl (poly) C _2-4 alkylene glycol (meth) acrylate such as 2-ethylhexyldiethylene glycol (meth) acrylate) may be included. In the alkyl (poly) alkylene glycol (meth) acrylate, the average added mole number of alkylene oxide (C _2-4 alkylene oxide and the like) is, for example, 1 to 10 moles, preferably 1 to 5 moles, more preferably 1 to 5 moles. About 3 mol may be sufficient.

The double bond equivalent (eg (meth) acryloyl group equivalent) (g / mol) of the monofunctional vinyl monomer can be selected from the range of, for example, about 50 to 1000 (eg, 80 to 500), preferably 100 to 300, preferably Is about 120 to 280, more preferably about 130 to 270 (for example, 140 to 260).

The proportion of the monofunctional vinyl monomer is, for example, 1 to 200 parts by weight, preferably 5 to 180 parts by weight, and more preferably about 10 to 150 parts by weight with respect to 100 parts by weight of the bifunctional urethane (meth) acrylate. In particular, the proportion of the monofunctional vinyl monomer having a ring structure is 1 to 100 parts by weight (for example, 5 to 80 parts by weight, preferably 10 to 50 parts by weight) with respect to 100 parts by weight of the bifunctional urethane (meth) acrylate. It may be about 20 to 200 parts by weight (for example, 50 to 150 parts by weight, preferably 80 to 120 parts by weight). The proportion of the (meth) acrylate having a chain aliphatic skeleton is, for example, 50 parts by weight or less, preferably 30 parts by weight or less, and more preferably 20 parts by weight with respect to 100 parts by weight of the bifunctional urethane (meth) acrylate. Part or less (for example, 1 to 20 parts by weight).

(Trifunctional vinyl monomer)
Examples of the trifunctional vinyl monomer include alkanetri to hexaol (for example, C _3-10 alkanetri to hexaol such as trimethylolethane, trimethylolpropane, glycerin, pentaerythritol, sorbitol, etc.) or alkylene oxide adducts thereof. Examples include tri (meth) acrylates; tri (meth) acrylates having a triazine ring such as tris (2-hydroxyethyl) isocyanurate tri (meth) acrylate.

A trifunctional vinyl monomer can be used individually or in combination of 2 or more types. Trifunctional vinyl monomers include alkanetri to hexaol alkylene oxides such as trimethylolpropane and glycerol (for example, C _2-4 alkylene such as ethylene oxide and propylene oxide) from the viewpoint of improving flexibility even in a crosslinked structure. Oxide) adduct tri (meth) acrylate is preferred. In this tri (meth) acrylate, the average number of added moles of alkylene oxide (for example, C _2-4 alkylene oxide) is, for example, 1 to 10 moles, preferably 1 to 5 moles, more preferably 1 to 3 moles (for example, 1 or 2 mol).

The double bond equivalent (for example, (meth) acryloyl group equivalent) (g / mol) of the trifunctional vinyl monomer can be selected from the range of, for example, about 50 to 1000 (for example, 50 to 500), preferably 60 to 400, Is about 80 to 300, more preferably about 100 to 200 (for example, 120 to 180). If it exists in the said range, even if it is a crosslinked structure, a high softness | flexibility and tack-free property can be provided.

The ratio of the trifunctional vinyl monomer is, for example, 1 to 100 parts by weight, preferably 5 to 80 parts by weight, and more preferably about 10 to 50 parts by weight with respect to 100 parts by weight of the bifunctional urethane (meth) acrylate. The proportion of the trifunctional vinyl monomer is, for example, 1 to 150 parts by weight, preferably 5 to 100 parts by weight (for example, 8 to 50 parts by weight), more preferably 10 to 100 parts by weight of the monofunctional vinyl monomer. About 40 parts by weight (for example, 12 to 30 parts by weight).

(Other polymerizable components)
The polymerizable composition may further contain other polymerizable components as long as the effects of the present invention are not impaired. Other polymerizable components include bifunctional vinyl monomers [for example, allyl (meth) acrylate; (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, glycerin di (meth) acrylate, etc.] (Poly) alkane polyol di (meth) acrylates; di (meth) acrylates of bisphenols (bisphenol A, S, etc.) or C _2-4 alkylene oxide adducts thereof; diacids of acid-modified alkane polyols such as fatty acid-modified pentaerythritol (Meth) acrylates; bridged cyclic di (meth) acrylates such as tricyclodecane dimethanol di (meth) acrylate], polyfunctional vinyl monomers having 4 or more functionalities [for example, pentaerythritol tetra (meth) acrylate, tetramethyl Roll methane tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) acrylate, etc.], vinyl oligomer having a polymerizable group [for example, polyester (meth) acrylate, epoxy (meth) acrylate, Examples thereof include polyacryl (meth) acrylate, polyether (meth) acrylate, polybutadiene (meth) acrylate, melamine (meth) acrylate, polyacetal (meth) acrylate, and the like. Other polymerizable components can be used alone or in combination of two or more.

In the polymerization composition, each molecule of the polymerizable component having an α, β-ethylenically unsaturated double bond has a π-electron cloud of carbon-carbon double bonds overlapping each other, and interacts by van der Waals force. It is exerting. When this polymerizable composition is cured (crosslinked), a covalent bond is formed between the molecules, so that the intermolecular distance is reduced and volume shrinkage occurs. In order to suppress this volume shrinkage, it is advantageous to reduce the number of α, β-ethylenically unsaturated double bonds and increase the molecular weight of the polymerizable component.

In the polymerization composition having an α, β-ethylenically unsaturated double bond in the polymerizable composition, the number average molecular weight of the weighted average per α, β-ethylenically unsaturated double bond [eg, weighted average (meta)] The acryloyl group equivalent] (g / mol) is, for example, about 1000 or more (for example, 1000 to 10000), preferably about 1100 to 8000 (for example, 1200 to 6000), more preferably about 1300 to 5000 (for example, 1500 to 4500). It may be. If the number average molecular weight in the weighted average per α, β-ethylenically unsaturated double bond is too small, the thermal shrinkage rate increases and the dimensional stability decreases, and if it is too large, the crosslinking density decreases and the heat resistance Solvent resistance (ink adhesion, etc.) and mechanical strength are reduced.

(Polymerization initiator)
The polymerizable composition may contain a polymerization initiator. The polymerization initiator may be a thermal polymerization initiator (thermal radical generator such as a peroxide such as benzoyl peroxide) or a photopolymerization initiator (photo radical generator). A preferred polymerization initiator is a photopolymerization initiator. Examples of the photopolymerization initiator include benzoins (benzoin alkyl ethers such as benzoin, benzoin methyl ether, benzoin ethyl ether, and benzoin isopropyl ether), phenyl ketones [for example, acetophenones (for example, acetophenone, 2-hydroxy -2-methyl-1-phenylpropan-1-one, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone, etc.), 2-hydroxy-2 -Alkyl phenyl ketones such as methylpropiophenone; cycloalkyl phenyl ketones such as 1-hydroxycyclohexyl phenyl ketone], aminoacetophenones {2-methyl-1- [4- (methylthio) phene ] -2-morpholinoaminopropanone-1, 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1}, anthraquinones (anthraquinone, 2-methylanthraquinone, 2-ethylanthraquinone) 2-t-butylanthraquinone, 1-chloroanthraquinone, etc.), thioxanthones (2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, 2,4-diisopropylthioxanthone, etc.), ketals (acetophenone) Dimethyl ketal, benzyl dimethyl ketal, etc.), benzophenones (benzophenone, etc.), xanthones, phosphine oxides (eg 2,4,6-trimethylbenzoyldiphenylphosphine oxide, etc.) It can be shown. These photopolymerization initiators can be used alone or in combination of two or more.

The ratio of the polymerization initiator is 0.1 to 20 parts by weight, preferably 0.5 to 15 parts by weight, more preferably 1 to 10 parts by weight (particularly 3 to 8 parts by weight) with respect to 100 parts by weight of the polymerizable component. Part) degree.

The photopolymerization initiator may be combined with a photosensitizer. Examples of the photosensitizer include conventional components such as tertiary amines [for example, trialkylamine, trialkanolamine (such as triethanolamine), ethyl N, N-dimethylaminobenzoate, N, N-dimethyl. Dialkylaminobenzoic acid alkyl esters such as amyl aminobenzoic acid, bis (dialkylamino) benzophenone such as 4,4-bis (dimethylamino) benzophenone (Michler's ketone), 4,4'-diethylaminobenzophenone], triphenylphosphine, etc. Phosphines, toluidines such as N, N-dimethyltoluidine, anthracene such as 9,10-dimethoxyanthracene, 2-ethyl-9,10-dimethoxyanthracene, 2-ethyl-9,10-diethoxyanthracene, etc. It is done. The photosensitizers may be used alone or in combination of two or more.

The ratio of the photosensitizer is, for example, about 0.1 to 100 parts by weight, preferably 0.5 to 80 parts by weight, and more preferably about 1 to 50 parts by weight with respect to 100 parts by weight of the photopolymerization initiator. May be.

A polymerization initiator (particularly a photopolymerization initiator and a photosensitizer) is preferably not substantially contained when the polymerizable composition is cured by irradiation with an electron beam. When it does not contain a polymerization initiator, weather resistance, in particular, difficult yellowing for long-term use is improved.

In addition to the polymerization initiator, the polymerizable composition is a conventional additive such as an antioxidant, a stabilizer such as a heat stabilizer, a plasticizer, and an antistatic agent, as long as flexibility and transparency are not impaired. Further, it may contain a flame retardant, an ultraviolet absorber and the like.

Furthermore, the polymerizable composition may be a solvent such as ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, etc.), ethers (dioxane, tetrahydrofuran, etc.), aliphatic hydrocarbons (hexane, etc.), alicyclic carbonization. Hydrogen (such as cyclohexane), aromatic hydrocarbons (such as benzene), halogenated carbons (such as dichloromethane and dichloroethane), esters (such as methyl acetate and ethyl acetate), water, alcohols (ethanol, isopropanol, butanol, Cyclohexanol, etc.), cellosolves (methyl cellosolve, ethyl cellosolve, etc.), cellosolve acetates, amides (dimethylformamide, dimethylacetamide, etc.) and the like may be contained. These solvents can be used alone or as a mixed solvent.

(Characteristics and manufacturing method of optical sheet)
The optical sheet of the present invention includes a coating step of applying the polymerizable composition on a substrate, a curing step of irradiating the applied polymerizable composition with active energy rays and curing, and curing of the polymerizable composition. It is manufactured through a peeling process for peeling an object from the substrate.

In the coating step, the substrate is not particularly limited as long as the surface of the cured product can be formed smoothly, and a sheet having a smooth surface and high peelability, such as a plastic sheet (for example, polyethylene terephthalate or polyethylene naphthalate). Polyester sheets such as polyethylene and polypropylene, polystyrene sheets, polyamide sheets such as polyamide 6 and polyamide 66, polycarbonate sheets such as bisphenol A type polycarbonate), release paper (for example, release agents such as silicone compounds) It may be a surface-treated paper or the plastic sheet). Among these base materials, polyester sheets such as polyethylene terephthalate and polyethylene naphthalate, polyolefin sheets such as polyethylene and polypropylene, and the like are widely used because the surface smoothness of the optical sheet can be easily improved.

As a coating method of the polymerizable composition, conventional methods such as roll coater, air knife coater, blade coater, rod coater, reverse coater, bar coater, comma coater, dip squeeze coater, die coater, gravure coater, microgravure coater Examples include coater, silk screen coater method, dip method, spray method, spinner method and the like. Of these methods, the bar coater method and the gravure coater method are widely used.

If the polymerizable composition contains a solvent, it may be dried as necessary after coating. Drying may be performed at a temperature of, for example, about 50 to 150 ° C., preferably 60 to 140 ° C., and more preferably about 70 to 130 ° C.

In the curing step, the polymerizable composition may be cured by heating depending on the type of the polymerization initiator, but it can usually be cured by irradiation with active energy rays. As active energy rays, heat and / or light energy rays can be used, and it is particularly useful to use light energy rays. As light energy rays, radiation (gamma rays, X-rays, etc.), ultraviolet rays, visible rays, electron beams (EB), etc. can be used, and usually ultraviolet rays and electron beams are often used. In particular, when producing a sheet that can be polymerized without using a polymerization initiator and has high weather resistance, it may be irradiated with an electron beam.

As the light source, for example, in the case of ultraviolet rays, a Deep UV lamp, a low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high pressure mercury lamp, a halogen lamp, a laser light source (light source such as helium-cadmium laser or excimer laser), etc. may be used. it can. Irradiation light amount (irradiation energy) varies depending on the thickness of the coating film, for example, 50 ~ 10000mJ / cm ^2, preferably 70 ~ 7000mJ / cm ^2, more preferably may be 100 ~ 5000mJ / cm ² approximately.

In the case of an electron beam, a method of irradiating an electron beam with an exposure source such as an electron beam irradiation apparatus can be used. The irradiation amount (dose) varies depending on the thickness of the coating film, but is, for example, about 1 to 200 kGy (gray), preferably 5 to 150 kGy, more preferably 10 to 100 kGy (particularly 20 to 80 kGy). The acceleration voltage is, for example, about 10 to 1000 kV, preferably about 50 to 500 kV, and more preferably about 100 to 300 kV.

In addition, you may perform irradiation of an active energy ray (especially electron beam) in inert gas (for example, nitrogen gas, argon gas, helium gas, etc.) atmosphere if necessary.

In the peeling step, the cured product of the polymerizable composition is peeled from the base material, but by using a sheet having a smooth surface as the base material, a cured product having a smooth surface can be easily obtained. In this invention, since it is excellent in toughness, it can prevent effectively that an optical sheet tears when peeling from a base material.

The glass transition temperature (Tg) of the cured product (optical sheet) of the polymerizable composition obtained is, for example, −80 ° C. to 100 ° C., preferably −50 ° C. to 80 ° C., more preferably −20 ° C. to 70 ° C. About 20 ° C. to 100 ° C. (for example, 40 ° C. to 80 ° C.). In addition, when the glass transition temperature is in the vicinity of 20 ° C., that is, in the vicinity of the temperature to be used, the flexibility becomes softer in the use temperature range and the film becomes tough and firm.

The tensile elastic modulus of the optical sheet is, for example, about 1 to 150 MPa, preferably 5 to 120 MPa, more preferably 10 to 100 MPa (for example, 10 to 50 MPa) in accordance with JIS K7161.

The elongation at break of the optical sheet can be selected from a range of, for example, about 50 to 500% (for example, 55 to 450%) in accordance with JIS K7161, 60 to 400%, preferably 65 to 350%, Preferably, it may be about 70 to 300% (for example, 100 to 300%).

The optical sheet has high transparency, and the total light transmittance measured according to JIS K7361-1 is, for example, 80% or more (for example, 80 to 100%), preferably 85% or more (for example, 85 to 99%), more preferably about 90% or more (for example, 90 to 98%). The haze measured according to JIS K7361-1 is, for example, 5% or less (for example, 0.1 to 5%), preferably 3% or less (for example, 0.2 to 3%), and more preferably 2. It is about 5% or less (for example, 0.5 to 2.5%).

The optical sheet has a small heat shrinkage, and when heated at 80 ° C. for 30 minutes (for example, drying conditions in a general key sheet manufacturing process), the heat shrinkage is, for example, 0.001 to 0.5%. It is preferably about 0.005 to 0.4%, more preferably about 0.1 to 0.3% (for example, 0.05 to 0.2%). Thus, when the thermal contraction rate of the optical sheet is small, for example, in the key sheet manufacturing process in which the pitch between the keys is narrow, it is possible to prevent the keys from being fused by heat treatment in the drying step after printing. The heat shrinkage rate can be measured by the method described in the examples.

The thickness of the optical sheet can be selected according to the application, for example, can be selected from the range of about 1 to 500 μm, for example, about 3 to 300 μm, preferably about 5 to 200 μm, more preferably about 10 to 100 μm (particularly about 20 to 100 μm). It is.

The optical sheet of the present invention may be subjected to a surface treatment. In addition to surface coating for imparting various properties such as heat resistance, the surface treatment includes printing treatment (printing treatment using heat or active energy rays such as screen printing and spray printing). Furthermore, the optical sheet of the present invention may be secondarily formed by punching or cutting, or may be laminated with another plastic sheet (via an adhesive layer as necessary).

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In addition, the tension test of the obtained optical sheet, the total light transmittance, the measuring method of thermal contraction rate, and the content of each component are as follows.

(Tensile test)
The obtained sheet was punched into a No. 7 dumbbell shape, and in accordance with JIS K7161, in a test environment with a temperature of 25 ° C. and a humidity of 50% RH, a tensile / compression tester (Orientec Co., Ltd., Tensilon UCT-5T) Was used to obtain a stress-strain curve measured at a tensile speed of 20 mm / min. From the obtained stress-strain curve, the elastic modulus and elongation at break were determined.

(Total light transmittance)
The total light transmittance (TT) of the obtained sheet was measured using a haze meter (NDH-5000W, manufactured by Nippon Denshoku Industries Co., Ltd.) according to JIS K7361-1.

(Heat shrinkage)
About the obtained sheet | seat, it cuts out to 12 cm square, and marks 10 cm each in the MD and TD directions, and describes three places. First, the distance between marked lines before heating was read with a digital scale (manufactured by Sony Magnescale Co., Ltd., LF-100). Further, the sheet was heated at 80 ° C. for 30 minutes, the distance between marked lines after heating was read in the same manner, and the contraction length was divided by the length before heating to calculate the heat shrinkage rate.

Thermal contraction rate = (length before heating−length after heating) / length before heating × 100 (%)
(Content of each component)
KRM7735 (Daicel Cytec Co., Ltd., aliphatic urethane acrylate, bifunctional, number average molecular weight 5000, acryloyl group equivalent 2500, homopolymer Tg: −30 ° C.)
PU2300T (manufactured by Bigen Specialty Chemical Co., Ltd., aliphatic urethane acrylate, bifunctional, number average molecular weight 16000, acryloyl group equivalent 8000, homopolymer Tg: −40 ° C.)
EB230 (manufactured by Daicel Cytec Co., Ltd., “EBECRYL-230”, aliphatic urethane acrylate, bifunctional, number average molecular weight 5000, acryloyl group equivalent 2500, homopolymer Tg: −55 ° C.)
EB270 (manufactured by Daicel Cytec Co., Ltd., “EBECRYL-270”, aliphatic urethane acrylate, bifunctional, number average molecular weight 1500, acryloyl group equivalent 750, homopolymer Tg: −27 ° C.)
OTA480 (Daicel Cytec Co., Ltd., glycerin propoxytriacrylate, trifunctional, molecular weight 428, acryloyl group equivalent 143)
M-120 (manufactured by Toagosei Co., Ltd., 2-ethylhexyl ethylene oxide modified acrylate, ethylene oxide addition mole number: about 2 moles, monofunctional, molecular weight 260, acryloyl group equivalent 260, Tg of homopolymer: −65 ° C.)
ACMO (manufactured by Kojin Co., Ltd., N-acryloylmorpholine, monofunctional, molecular weight 141, acryloyl group equivalent 141)
IBOA (Daicel Cytec Co., Ltd., isobornyl acrylate, monofunctional, molecular weight 210, acryloyl group equivalent 210, homopolymer Tg: 94 ° C.).

Example 1
60 parts by weight of urethane acrylate (KRM7735), 5 parts by weight of acrylic monomer (OTA480), 10 parts by weight of acrylic monomer (M-120), 25 parts by weight of acrylic monomer (ACMO), photopolymerization initiator (manufactured by Ciba Japan Co., Ltd.) 2 parts by weight of “Irgacure 184” were weighed and mixed in a light-shielding bottle. This solution was heated to 60 ° C. and cast on a base film (release PET film, T-789, manufactured by Daicel Value Coating Co., Ltd., thickness 50 μm) using wire bar # 55, and then nitrogen. A cured product with a thickness of 76 μm is irradiated with ultraviolet rays at an output of 4 kW and a conveying speed of 4 m / min using an ultraviolet irradiation device (“ECS-4011GX”, high-pressure mercury lamp) manufactured by Eye Graphics Co., Ltd. in an atmosphere. Got. The obtained cured product was peeled from the substrate film to obtain an optical sheet.

Example 2
60 parts by weight of urethane acrylate (KRM7735), 5 parts by weight of acrylic monomer (OTA480), 10 parts by weight of acrylic monomer (M-120) and 25 parts by weight of acrylic monomer (ACMO) were weighed and mixed in a light shielding bottle. This solution was heated to 60 ° C. and cast on a base film (T-789) using a wire bar # 55, and then an electron beam irradiation device (manufactured by NHV Corporation, “ EBC300-60 ") was irradiated with an electron beam under the conditions of an acceleration voltage of 200 kV and a dose of 100 kGy to obtain a cured product having a thickness of 75 μm. The obtained cured product was peeled from the substrate film to obtain an optical sheet.

Example 3
50 parts by weight of urethane acrylate (PU2300T), 10 parts by weight of acrylic monomer (OTA480), 40 parts by weight of acrylic monomer (ACMO), and 2 parts by weight of photopolymerization initiator (Irgacure 184) were weighed and mixed in a light-shielding bottle. This solution was heated to 60 ° C., cast on a base film (T-789) using a wire bar # 55, and then subjected to a lamp using a UV irradiation device (ECS-4011GX) under a nitrogen atmosphere. Output: UV was irradiated at 4 kW and a conveyance speed of 4 m / min to obtain a cured product having a thickness of 72 μm. The obtained cured product was peeled from the substrate film to obtain an optical sheet.

Example 4
50 parts by weight of urethane acrylate (PU2300T), 10 parts by weight of acrylic monomer (OTA480), and 40 parts by weight of acrylic monomer (ACMO) were weighed and mixed in a light shielding bottle. This solution was heated to 60 ° C. and cast on a base film (T-789) using a wire bar # 55, and then using an electron beam irradiation apparatus (EBC300-60) in a nitrogen atmosphere, An electron beam was irradiated under conditions of an acceleration voltage of 200 kV and a dose of 100 kGy to obtain a cured product having a thickness of 70 μm. The obtained cured product was peeled from the substrate film to obtain an optical sheet.

Example 5
50 parts by weight of urethane acrylate (EB230), 25 parts by weight of acrylic monomer (OTA480), 25 parts by weight of acrylic monomer (IBOA) and 2 parts by weight of photopolymerization initiator (Irgacure 184) were weighed and mixed in a light-shielding bottle. This solution was heated to 60 ° C., cast on a base film (T-789) using a wire bar # 55, and then subjected to a lamp using a UV irradiation device (ECS-4011GX) under a nitrogen atmosphere. Output: UV was irradiated at 4 kW and a conveyance speed of 4 m / min to obtain a cured product having a thickness of 76 μm. The obtained cured product was peeled from the substrate film to obtain an optical sheet.

Example 6
60 parts by weight of urethane acrylate (EB230), 20 parts by weight of acrylic monomer (OTA480), 20 parts by weight of acrylic monomer (IBOA) and 2 parts by weight of photopolymerization initiator (Irgacure 184) were weighed and mixed in a light-shielding bottle. This solution was heated to 60 ° C., cast on a base film (T-789) using a wire bar # 55, and then subjected to a lamp using a UV irradiation device (ECS-4011GX) under a nitrogen atmosphere. Output: UV was irradiated at 4 kW and a conveyance speed of 4 m / min to obtain a cured product having a thickness of 78 μm. The obtained cured product was peeled from the substrate film to obtain an optical sheet.

Example 7
80 parts by weight of urethane acrylate (EB230), 10 parts by weight of acrylic monomer (OTA480), 10 parts by weight of acrylic monomer (IBOA), and 2 parts by weight of photopolymerization initiator (Irgacure 184) were weighed and mixed in a light-shielding bottle. This solution was heated to 60 ° C., cast on a base film (T-789) using a wire bar # 55, and then subjected to a lamp using a UV irradiation device (ECS-4011GX) under a nitrogen atmosphere. Output: UV was irradiated at 4 kW and a conveyance speed of 4 m / min to obtain a cured product having a thickness of 78 μm. The obtained cured product was peeled from the substrate film to obtain an optical sheet.

Comparative Example 1
50 parts by weight of urethane acrylate (EB270), 25 parts by weight of acrylic monomer (OTA480), 25 parts by weight of acrylic monomer (IBOA) and 2 parts by weight of photopolymerization initiator (Irgacure 184) were weighed and mixed in a light-shielding bottle. This solution was heated to 60 ° C., cast on a base film (T-789) using a wire bar # 55, and then subjected to a lamp using a UV irradiation device (ECS-4011GX) under a nitrogen atmosphere. Output: UV was irradiated at 4 kW and a conveyance speed of 4 m / min to obtain a cured product having a thickness of 76 μm. The obtained cured product was peeled from the substrate film to obtain an optical sheet.

Comparative Example 2
60 parts by weight of urethane acrylate (EB270), 20 parts by weight of acrylic monomer (OTA480), 20 parts by weight of acrylic monomer (IBOA) and 2 parts by weight of photopolymerization initiator (Irgacure 184) were weighed and mixed in a light-shielding bottle. This solution was heated to 60 ° C., cast on a base film (T-789) using a wire bar # 55, and then subjected to a lamp using a UV irradiation device (ECS-4011GX) under a nitrogen atmosphere. Output: UV was irradiated at 4 kW and a conveyance speed of 4 m / min to obtain a cured product having a thickness of 78 μm. The obtained cured product was peeled from the substrate film to obtain an optical sheet.

Comparative Example 3
80 parts by weight of urethane acrylate (EB270), 10 parts by weight of acrylic monomer (OTA480), 10 parts by weight of acrylic monomer (IBOA) and 2 parts by weight of photopolymerization initiator (Irgacure 184) were weighed and mixed in a light-shielding bottle. This solution was heated to 60 ° C., cast on a base film (T-789) using a wire bar # 55, and then subjected to a lamp using a UV irradiation device (ECS-4011GX) under a nitrogen atmosphere. Output: UV was irradiated at 4 kW and a conveyance speed of 4 m / min to obtain a cured product having a thickness of 78 μm. The obtained cured product was peeled from the substrate film to obtain an optical sheet.

Comparative Example 4
30 parts by weight of urethane acrylate (EB230), 35 parts by weight of acrylic monomer (OTA480), 35 parts by weight of acrylic monomer (IBOA), and 2 parts by weight of a photopolymerization initiator (Irgacure 184) were weighed and mixed in a light-shielding bottle. This solution was heated to 60 ° C., cast on a base film (T-789) using a wire bar # 55, and then subjected to a lamp using a UV irradiation device (ECS-4011GX) under a nitrogen atmosphere. Output: UV was irradiated at 4 kW and a conveyance speed of 4 m / min to obtain a cured product having a thickness of 68 μm. The obtained cured product was peeled from the substrate film to obtain an optical sheet.

Table 1 shows the evaluation results of the optical sheets obtained in Examples and Comparative Examples.

As is clear from Table 1, in the examples, the thermal shrinkage is small, the elasticity is appropriate, and the elongation at break is large compared to the comparative example.

The optical sheet of the present invention can be used as an optical sheet used in various electrical / electronic devices or optical devices such as portable devices, home appliances, and control devices. Specifically, push button switches (or operation panels) for applications requiring high transparency and flexibility, such as mobile phones, gaming devices, mobile devices, car navigation systems, watches, calculators, televisions, personal computers, etc. ), A sheet-like member such as a membrane switch, a sensor switch or a touch panel, and an optical adhesive tape substrate (for example, an OCA tape substrate). Such a sheet-like member includes a key top sheet, a key mat sheet, a light guide plate, a reflection plate, a retardation plate, a polarizing plate, a viewing angle expansion plate, a diffusion plate, an alignment film, and a luminance for constituting a switch or an operation panel. An improvement board etc. may be sufficient. Among these, a light guide sheet or a reflective sheet used for an operation panel of a mobile phone, a game machine, a mobile device, a touch panel, etc., for example, a back surface of a key top sheet by clicking on the back side of a key top sheet of a mobile phone. And a sheet for guiding or reflecting light from a light source such as an LED light source to the key top surface (operation surface).

DESCRIPTION OF SYMBOLS 1 ... Key top sheet 2 ... Key mat sheet 3 ... Light guide sheet 4 ... Click dome 5 ... Flexible printed wiring board 6 ... Light source

Claims

A polymerizable composition comprising a bifunctional urethane (meth) acrylate having a number average molecular weight of 2000 to 50000, a monofunctional vinyl monomer, and a trifunctional vinyl monomer as a polymerizable component having an α, β-ethylenically unsaturated double bond An optical sheet composed of a cured product of
The polymerizable component having an α, β-ethylenically unsaturated double bond in the polymerizable composition has a weighted average number average molecular weight per α, β-ethylenically unsaturated double bond of 1000 or more. Optical sheet.
The optical sheet according to claim 1, wherein the bifunctional urethane (meth) acrylate is a bifunctional aliphatic urethane (meth) acrylate.
The optical sheet according to claim 1 or 2, wherein the bifunctional urethane (meth) acrylate has a glass transition temperature of -80 ° C to -30 ° C.
The optical sheet according to any one of claims 1 to 3, wherein the bifunctional urethane (meth) acrylate has a number average molecular weight per α, β-ethylenically unsaturated double bond of 1,000 to 20,000.
The monofunctional vinyl monomer contains at least one monofunctional (meth) acrylate selected from a heterocyclic (meth) acrylate containing a nitrogen atom as a heterocyclic atom and a bridged cyclic (meth) acrylate. An optical sheet according to any one of the above.
The optical sheet according to any one of claims 1 to 5, wherein the trifunctional vinyl monomer is a tri (meth) acrylate of a C 2-4 alkylene oxide adduct of alkanetri to hexaol.
7. The proportion of monofunctional vinyl monomer is 1 to 200 parts by weight and the proportion of trifunctional vinyl monomer is 1 to 100 parts by weight with respect to 100 parts by weight of bifunctional urethane (meth) acrylate. An optical sheet according to crab.
The optical sheet according to any one of claims 1 to 7, wherein the cured product of the polymerizable composition is a photocured product obtained by irradiating an electron beam and substantially does not contain a polymerization initiator.
The optical sheet according to any one of claims 1 to 8, which has an elongation at break of 100 to 300%.
10. The optical sheet according to claim 1, wherein the optical sheet is a kind selected from a key sheet, a light guide sheet, a reflective sheet, and an optical transparent adhesive tape substrate.