Sealing agent for flexible GHLC element

Abstract

The objective of the present invention is to provide a sealing agent for a flexible GHLC element having excellent adhesiveness to a film with an alignment film, even immediately after light irradiation or under a high-temperature condition. The present invention is a sealing agent for a flexible GHLC element, the sealing agent containing a curable resin and a photopolymerization initiator, wherein a cured product has a glass transition temperature of 60 °C or less, the cured product has a storage modulus at 25 °C of 500 MPa or less, and the cured product has a storage modulus at 80 °C of 0.01 MPa or more.

Description

Sealant for flexible GHLC elements

[0001] The present invention relates to a sealant for flexible GHLC devices.

[0002] Liquid crystal light control devices using liquid crystal materials are widely used as light control devices whose light transmittance changes when a voltage is applied. Liquid crystal light control devices control the amount of light transmission by changing the orientation of liquid crystal molecules by changing the potential difference between transparent electrode layers, and have excellent responsiveness. Known examples of such liquid crystal light control devices include guest-host liquid crystal (GHLC) devices that use a GHLC containing a dichroic dye as a guest and liquid crystal molecules as a host. In particular, flexible GHLC devices manufactured by film bonding have recently attracted attention, replacing conventional GHLC devices manufactured by laminating glass panels. For example, Patent Document 1 discloses a guest-host liquid crystal light control device that includes a pair of substrates having transparent electrodes and a liquid crystal layer sandwiched between the pair of substrates and containing a host liquid crystal and a dichroic dye, in which the substrates are made of a transparent film material having a liquid crystal alignment film.

[0003] International Publication No. 2019 / 208765

[0004] The liquid crystal dropping method is the mainstream method for manufacturing liquid crystal devices. In this method, a sealant is first applied to a substrate to form a frame-shaped seal pattern. Next, while the sealant is still uncured, tiny droplets of liquid crystal are dropped into the frame of the seal pattern. Another substrate is then bonded to the substrate under vacuum, and the sealant is cured to produce a liquid crystal device. This liquid crystal dropping method requires an extremely small amount of sealant to bond the substrates. Therefore, flexible GHLC devices using alignment film-attached substrates, which are difficult-to-adhere materials, require a sealant with excellent adhesion to the alignment film. Typically, an alignment film-attached film is temporarily attached to a hard support layer with an adhesive, and then bonded to another alignment film. The film is then irradiated with light to cure the sealant before being peeled from the support layer. Conventional sealants exhibit little adhesiveness immediately after light irradiation, which can prevent the temporarily attached alignment film from peeling from the support layer immediately after light irradiation, resulting in peeling between the bonded alignment film-attached films. Furthermore, in the manufacture of liquid crystal elements, a lamination process is usually carried out under high temperature conditions after the process of curing the sealant, but conventional sealants sometimes fail to maintain adhesion during the lamination process and end up peeling off.

[0005] An object of the present invention is to provide a sealant for flexible GHLC elements that has excellent adhesion to alignment film-attached films even immediately after light irradiation or under high temperature conditions.

[0006] Disclosure 1 is a sealant for flexible GHLC elements comprising a curable resin and a photopolymerization initiator, wherein the cured product has a glass transition temperature of 60°C or lower, a storage modulus of 500 MPa or lower at 25°C, and a storage modulus of 0.01 MPa or higher at 80°C. Disclosure 2 is the sealant for flexible GHLC elements of Disclosure 1, wherein the curable resin comprises a monofunctional (meth)acrylic compound having one (meth)acryloyl group per molecule, and the content of the monofunctional (meth)acrylic compound per 100 parts by mass of the curable resin is 50 parts by mass or higher. Disclosure 3 is the sealant for flexible GHLC elements of Disclosure 2, wherein the curable resin comprises a monofunctional (meth)acrylic compound having a homopolymer glass transition temperature of 20°C or lower. Disclosure 4 is the sealant for flexible GHLC elements of Disclosure 2 or 3, wherein the curable resin comprises a monofunctional (meth)acrylic compound having a cyclic ether structure. Disclosure 5 relates to the flexible GHLC element sealant of Disclosure 1, 2, 3, or 4, wherein the curable resin comprises a polyfunctional (meth)acrylic compound having two or more (meth)acryloyl groups per molecule, and the content of the polyfunctional (meth)acrylic compound per 100 parts by mass of the curable resin is 0.1 parts by mass or more and 50 parts by mass or less. Disclosure 6 relates to the flexible GHLC element sealant of Disclosure 1, 2, 3, 4, or 5, further comprising a thermoplastic resin. Disclosure 7 relates to the flexible GHLC element sealant of Disclosure 1, 2, 3, 4, 5, or 6, wherein the cured product has a molecular weight between crosslinks of 100 g / mol or more and 20,000 g / mol or less. Disclosure 8 relates to the flexible GHLC element sealant of Disclosure 1, 2, 3, 4, 5, 6, or 7, wherein the viscosity measured at 25°C and 1 rpm using an E-type viscometer is 1 Pa s or more. The present invention is described in detail below.

[0007] The present inventors have investigated how to improve the adhesiveness of a sealant for flexible GHLC elements immediately after light irradiation by setting the glass transition temperature of the cured product at or below a specific temperature and the storage modulus at 25° C. to or below a specific value, and further how to maintain the adhesiveness even under high-temperature conditions by preventing the storage modulus at 80° C. from decreasing significantly from the storage modulus at 25° C. As a result, the present inventors have found that it is possible to obtain a sealant for flexible GHLC elements that has excellent adhesiveness to alignment film-attached films even immediately after light irradiation and under high-temperature conditions, and have thereby completed the present invention.

[0008] The sealant for flexible GHLC elements of the present invention has an upper limit of the glass transition temperature of 60°C for the cured product. Since the glass transition temperature of the cured product is 60°C or lower and the storage modulus at 25°C (described later) is 500 MPa or lower, the sealant for flexible GHLC elements of the present invention exhibits excellent adhesion to an alignment film-attached film even immediately after light irradiation. The upper limit of the glass transition temperature of the cured product is preferably 50°C, and more preferably 40°C. There is no particular preferred lower limit for the glass transition temperature of the cured product, but the substantial lower limit is -70°C. Note that, in this specification, the glass transition temperature of the cured product can be determined as the temperature at the maximum value of the loss tangent (tan δ) when the dynamic viscoelasticity of a 300 μm-thick cured product is measured using a dynamic viscoelasticity measuring device under the following conditions: test piece width: 5 mm, grip width: 25 mm, heating rate: 10°C / min, temperature range: -80°C to 200°C, and frequency: 10 Hz. As the dynamic viscoelasticity measuring device, for example, DVA-200 (manufactured by IT Measurement Control Co., Ltd.) can be used. The cured product for measuring the glass transition temperature and storage modulus described later can be obtained by light irradiation alone or by light irradiation and heating, depending on the curing type of the flexible GHLC element sealant. Specific curing methods include, for a photocurable sealant, light irradiation at a wavelength of 365 nm and an illuminance of 100 mW / cm. ２ For photothermal curing sealants, the wavelength is 365 nm and the illuminance is 100 mW / cm. ２ For example, the method involves irradiating the film with light for 30 seconds and then heating it at 80° C. for 60 minutes.

[0009] The sealant for flexible GHLC elements of the present invention has an upper limit of the storage modulus at 25°C of 500 MPa for the cured product. Since the storage modulus at 25°C of the cured product is 500 MPa or less and the glass transition temperature of the cured product is 60°C or less, the sealant for flexible GHLC elements of the present invention has excellent adhesion to an alignment film-attached film even immediately after light irradiation. The upper limit of the storage modulus at 25°C of the cured product is preferably 100 MPa, more preferably 50 MPa. Furthermore, from the viewpoint of moisture resistance, etc., the lower limit of the storage modulus at 25°C of the cured product is preferably 0.01 MPa, more preferably 0.05 MPa. The storage modulus at 25°C of the cured product and the storage modulus at 80°C of the cured product described below can be measured by performing dynamic viscoelasticity measurement on a 300 μm thick cured product in the same manner as for the glass transition temperature of the cured product described above.

[0010] The sealant for flexible GHLC elements of the present invention has a lower limit of the storage modulus of the cured product at 80°C of 0.01 MPa. When the storage modulus of the cured product at 80°C is 0.01 MPa or more, the sealant for flexible GHLC elements of the present invention can maintain adhesion to an alignment film-attached film even under high-temperature conditions. The lower limit of the storage modulus of the cured product at 80°C is preferably 0.02 MPa, and more preferably 0.04 MPa. Furthermore, it is preferable that the difference between the storage modulus of the cured product at 80°C and the storage modulus of the cured product at 25°C is small, and although there is no particularly preferred upper limit, the substantial upper limit is 500 MPa.

[0011] In the sealant for flexible GHLC elements of the present invention, the lower limit of the molecular weight between crosslinks of the cured product is preferably 100 g / mol, and the upper limit is preferably 20,000 g / mol. When the molecular weight between crosslinks of the cured product is within this range, the resulting sealant for flexible GHLC elements has better adhesion to films with alignment layers. A more preferred lower limit of the molecular weight between crosslinks of the cured product is 500 g / mol, and a more preferred upper limit is 1,000 g / mol. The molecular weight between crosslinks is determined by measuring the storage modulus of the cured product described above, where T (K) is the temperature at which the storage modulus is minimum above the glass transition temperature, E' (Pa) is the storage modulus at temperature T, and ρ (g / m ３ ), and the gas constant is R (J / (mol·K)), the molecular weight between crosslinks can be calculated by the following formula: Molecular weight between crosslinks=3ρRT / E′

[0012] The sealant for flexible GHLC elements of the present invention contains a curable resin. The curable resin preferably contains a (meth)acrylic compound. In a sealant for liquid crystal elements, liquid crystal contamination may occur when the sealant before curing comes into contact with liquid crystal. However, by including the (meth)acrylic compound as the curable resin, the resulting sealant for flexible GHLC elements has excellent low liquid crystal contamination properties. In this specification, the term "(meth)acrylic" means acrylic or methacrylic, the term "(meth)acrylic compound" means a compound having a (meth)acryloyl group, and the term "(meth)acryloyl" means acryloyl or methacryloyl.

[0013] The (meth)acrylic compound preferably contains a monofunctional (meth)acrylic compound having one (meth)acryloyl group per molecule. By containing the monofunctional (meth)acrylic compound, the resulting sealant for flexible GHLC elements has excellent wettability with respect to the film with an alignment film, and therefore has excellent adhesion to the film with an alignment film.

[0014] In particular, the curable resin preferably contains, as the monofunctional (meth)acrylic compound, a monofunctional (meth)acrylic compound whose homopolymer has a glass transition temperature of 20°C or lower. By containing the monofunctional (meth)acrylic compound whose homopolymer has a glass transition temperature of 20°C or lower, the resulting sealant for flexible GHLC elements has even better adhesion to alignment film-attached films. The glass transition temperature of the homopolymer is preferably 10°C or lower. There is no particular preferred lower limit for the glass transition temperature of the homopolymer, but the substantial lower limit is -70°C. The term "glass transition temperature of the homopolymer" means that there is a homopolymer exhibiting the specified glass transition temperature within a weight-average molecular weight range of 10,000 or more and 100,000 or less. In this specification, the "weight-average molecular weight" is a value determined by gel permeation chromatography (GPC) and converted into polystyrene equivalent. An example of a column used for measuring the weight average molecular weight in terms of polystyrene by GPC is Shodex LF-804 (manufactured by Showa Denko KK).

[0015] Examples of the monofunctional (meth)acrylic compound having a homopolymer glass transition temperature of 20° C. or less include butyl (meth)acrylate, 2-hydroxy-3-phenoxypropyl (meth)acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate, etc. In this specification, the term "(meth)acrylate" means acrylate or methacrylate.

[0016] In order to further improve the wettability of the resulting sealant for flexible GHLC elements to the film with an alignment layer, the curable resin preferably contains a monofunctional (meth)acrylic compound having a cyclic ether structure as the monofunctional (meth)acrylic compound. Examples of the cyclic ether structure include an oxirane ring, an oxetane ring, a dioxolane ring, a tetrahydrofuran ring, and a furan ring. Of these, a dioxolane ring is preferred.

[0017] Examples of the monofunctional (meth)acrylic compound having a cyclic ether structure include (2-methyl-2-ethyl-1,3-dioxolan-4-yl)methyl (meth)acrylate and (3,4-epoxycyclohexyl)methyl acrylate.

[0018] The curable resin may contain, as the monofunctional (meth)acrylic compound, another monofunctional (meth)acrylic compound having a homopolymer glass transition temperature of more than 20°C and not having a cyclic ether structure. As the other monofunctional (meth)acrylic compound, a monofunctional (meth)acrylimide compound is preferably used. Examples of the monofunctional (meth)acrylic compound include N-(meth)acryloyloxyethylhexahydrophthalimide.

[0019] A preferred lower limit of the content of the monofunctional (meth)acrylic compound in 100 parts by mass of the curable resin is 50 parts by mass. When the content of the monofunctional (meth)acrylic compound is 50 parts by mass or more, the resulting sealant for flexible GHLC elements has better adhesion to alignment film-attached films. A more preferred lower limit of the content of the monofunctional (meth)acrylic compound is 70 parts by mass. Furthermore, from the viewpoint of curability and the like, a preferred upper limit of the content of the monofunctional (meth)acrylic compound in 100 parts by mass of the curable resin is 99.9 parts by mass.

[0020] The curable resin preferably contains a polyfunctional (meth)acrylic compound having two or more (meth)acryloyl groups in one molecule, which allows the resulting sealant for flexible GHLC elements to have excellent curability and excellent adhesion to alignment film-attached films under high-temperature conditions.

[0021] Examples of the polyfunctional (meth)acrylic compound include epoxy (meth)acrylate, (meth)acrylic acid ester compounds, and urethane (meth)acrylates, which have two or more (meth)acryloyl groups in one molecule. Among these, the curable resin preferably contains the epoxy (meth)acrylate. In this specification, the term "epoxy (meth)acrylate" refers to a compound in which all epoxy groups in an epoxy compound have reacted with (meth)acrylic acid.

[0022] Examples of the epoxy (meth)acrylate include those obtained by reacting an epoxy compound having two or more epoxy groups in one molecule with (meth)acrylic acid in the presence of a basic catalyst according to a conventional method.

[0023] Examples of the epoxy compound that serves as a raw material for the epoxy (meth)acrylate include bisphenol A type epoxy compounds, bisphenol F type epoxy compounds, bisphenol E type epoxy compounds, bisphenol S type epoxy compounds, 2,2'-diallyl bisphenol A type epoxy compounds, hydrogenated bisphenol type epoxy compounds, propylene oxide-added bisphenol A type epoxy compounds, resorcinol type epoxy compounds, biphenyl type epoxy compounds, sulfide type epoxy compounds, diphenyl ether type epoxy compounds, dicyclopentadiene type epoxy compounds, naphthalene type epoxy compounds, phenol novolac type epoxy compounds, o-cresol novolac type epoxy compounds, dicyclopentadiene novolac type epoxy compounds, biphenyl novolac type epoxy compounds, naphthalene phenol novolac type epoxy compounds, glycidylamine type epoxy compounds, alkyl polyol type epoxy compounds, rubber-modified type epoxy compounds, and glycidyl ester compounds.

[0024] Examples of the bifunctional (meth)acrylic acid ester compounds include 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, 2-n-butyl-2-ethyl-1,3-propanediol di(meth)acrylate, dipropylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, and polypropylene glycol di(meth)acrylate. (meth)acrylate, neopentyl glycol di(meth)acrylate, ethylene oxide-added bisphenol A di(meth)acrylate, propylene oxide-added bisphenol A di(meth)acrylate, ethylene oxide-added bisphenol F di(meth)acrylate, dimethyloldicyclopentadienyl di(meth)acrylate, ethylene oxide-modified isocyanuric acid di(meth)acrylate, 2-hydroxy-3-(meth)acryloyloxypropyl (meth)acrylate, carbonate diol di(meth)acrylate, polyether diol di(meth)acrylate, polyester diol di(meth)acrylate, polycaprolactone diol di(meth)acrylate, polybutadiene diol di(meth)acrylate, and the like.

[0025] Examples of the tri- or higher functional (meth)acrylic acid ester compounds include ethylene oxide-added isocyanuric acid tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethylene oxide-added trimethylolpropane tri(meth)acrylate, propylene oxide-added trimethylolpropane tri(meth)acrylate, caprolactone-modified trimethylolpropane tri(meth)acrylate, glycerin tri(meth)acrylate, propylene oxide-added glycerin tri(meth)acrylate, pentaerythritol tri(meth)acrylate, tris(meth)acryloyloxyethyl phosphate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, and dipentaerythritol hexa(meth)acrylate.

[0026] The urethane (meth)acrylate can be obtained, for example, by reacting an isocyanate compound with a (meth)acrylic acid derivative having a hydroxyl group in the presence of a catalytic amount of a tin compound.

[0027] Examples of the isocyanate compound that can be used as a raw material for the urethane (meth)acrylate include isophorone diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, diphenylmethane-4,4'-diisocyanate (MDI), hydrogenated MDI, polymeric MDI, 1,5-naphthalene diisocyanate, norbornane diisocyanate, tolidine diisocyanate, xylylene diisocyanate (XDI), hydrogenated XDI, lysine diisocyanate, triphenylmethane triisocyanate, tris(isocyanatephenyl)thiophosphate, tetramethylxylylene diisocyanate, and 1,6,11-undecane triisocyanate.

[0028] Furthermore, as the isocyanate compound serving as a raw material for the urethane (meth)acrylate, a chain-extended isocyanate compound obtained by reacting a polyol with an excess of an isocyanate compound can also be used. Examples of the polyol include ethylene glycol, propylene glycol, glycerin, sorbitol, trimethylolpropane, carbonate diol, polyether diol, polyester diol, and polycaprolactone diol.

[0029] Examples of the (meth)acrylic acid derivatives having a hydroxyl group include hydroxyalkyl (meth)acrylates, mono(meth)acrylates of dihydric alcohols, mono(meth)acrylates or di(meth)acrylates of trihydric alcohols, and epoxy (meth)acrylates. Examples of the hydroxyalkyl (meth)acrylates include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. Examples of the dihydric alcohols include ethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, and polyethylene glycol. Examples of the trihydric alcohols include trimethylolethane, trimethylolpropane, and glycerin. Examples of the epoxy (meth)acrylates include bisphenol A-type epoxy (meth)acrylate.

[0030] The polyfunctional (meth)acrylic compound preferably has a flexible skeleton, from the viewpoint of further improving the adhesion of the resulting sealing agent for flexible GHLC elements to a film with an alignment layer. Examples of the flexible skeleton include a lactone ring-open structure, a polyalkylene oxide structure, a rubber structure derived from a conjugated diene, and a polysiloxane structure. Among these, a lactone ring-open structure is preferred. Examples of the lactone include γ-undecalactone, ε-caprolactone, γ-decalactone, σ-dodecalactone, γ-nonanolactone, γ-heptanolactone, γ-valerolactone, σ-valerolactone, β-butyrolactone, γ-butyrolactone, β-propiolactone, σ-hexanolactone, and 7-butyl-2-oxepanone.

[0031] The preferred lower limit of the content of the polyfunctional (meth)acrylic compound per 100 parts by mass of the curable resin is 0.1 parts by mass, and the preferred upper limit is 50 parts by mass. When the content of the polyfunctional (meth)acrylic compound is within this range, the resulting sealant for flexible GHLC elements will have better curability, adhesion to alignment film-attached films, and low liquid crystal contamination. The more preferred lower limit of the content of the polyfunctional (meth)acrylic compound is 0.5 parts by mass, and the more preferred upper limit is 5 parts by mass.

[0032] A preferred lower limit of the content of the (meth)acrylic compound per 100 parts by mass of the curable resin is 55 parts by mass. When the content of the (meth)acrylic compound is 55 parts by mass or more, the resulting sealant for flexible GHLC elements has better adhesion under high-temperature conditions. A more preferred lower limit of the content of the (meth)acrylic compound is 60 parts by mass. It is particularly preferred that the content of the (meth)acrylic compound per 100 parts by mass of the curable resin is 100 parts by mass, i.e., the curable resin is composed solely of the (meth)acrylic compound.

[0033] The preferred lower limit of the total content of the curable resins in 100 parts by mass of the sealant for flexible GHLC elements of the present invention is 90 parts by mass, and the preferred upper limit is 99 parts by mass. When the total content of the curable resins is within this range, the resulting sealant for flexible GHLC elements will have better curability and adhesiveness.

[0034] The sealing agent for flexible GHLC elements of the present invention contains a photopolymerization initiator, and a photoradical polymerization initiator is preferably used as the photopolymerization initiator.

[0035] Examples of the photoradical polymerization initiator include benzophenone compounds, acetophenone compounds, acylphosphine oxide compounds, titanocene compounds, oxime ester compounds, benzoin ether compounds, thioxanthone compounds, etc. Specific examples of the photoradical polymerization initiator include 1-hydroxycyclohexyl phenyl ketone, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-1-butanone, 2-(dimethylamino)-2-((4-methylphenyl)methyl)-1-(4-(4-morpholinyl)phenyl)-1-butanone, 2,2-dimethoxy-1,2-diphenylethan-1-one, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, 2-methyl-1-(4-methylthiophenyl) 2-morpholinopropan-1-one, 1-(4-(2-hydroxyethoxy)-phenyl)-2-hydroxy-2-methyl-1-propan-1-one, 1-(4-(phenylthio)phenyl)-1,2-octanedione 2-(O-benzoyloxime), 2-(acetoxyimino)-1-(4-(4-(2-hydroxyethoxy)phenylthio)phenyl)propan-1-one, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, 2,4-dimethylthioxanthen-9-one, and the like.

[0036] The content of the photopolymerization initiator is preferably 0.01 parts by mass at the lower limit and 10 parts by mass at the upper limit relative to 100 parts by mass of the curable resin. When the content of the photopolymerization initiator is within this range, the resulting sealant for flexible GHLC elements has better storage stability and photocurability. The more preferred lower limit of the content of the photopolymerization initiator is 0.1 parts by mass, and the more preferred upper limit is 5 parts by mass.

[0037] The sealing agent for flexible GHLC elements of the present invention may contain a thermal polymerization initiator within the range that does not impair the object of the present invention. As the thermal polymerization initiator, a thermal radical polymerization initiator is preferably used.

[0038] Examples of the thermal radical polymerization initiator include those composed of an azo compound, an organic peroxide, etc. Among them, from the viewpoint of suppressing contamination of the light-modulating material, an initiator composed of an azo compound (hereinafter also referred to as "azo initiator") is preferred. The thermal radical polymerization initiator may be used alone or in combination of two or more.

[0039] Specific examples of the azo compounds include those having a structure in which multiple units of polyalkylene oxide or polydimethylsiloxane are bonded via azo groups, 2,2'-azobis(2,4-dimethylvaleronitrile), 4,4'-azobis(4-cyanovaleric acid), polycondensates of 4,4'-azobis(4-cyanopentanoic acid) and polyalkylene glycol, polycondensates of 4,4'-azobis(4-cyanopentanoic acid) and polydimethylsiloxane having a terminal amino group, etc. Examples of the azo initiators include VPE-0201, VPE-0401, VPE-0601, VPS-0501, VPS-1001, V-65, and V-501 (all manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.).

[0040] Examples of the organic peroxide include ketone peroxides, peroxyketals, hydroperoxides, dialkyl peroxides, peroxyesters, diacyl peroxides, and peroxydicarbonates.

[0041] The content of the thermal polymerization initiator is preferably 0.01 parts by mass at the lower limit and 10 parts by mass at the upper limit relative to 100 parts by mass of the curable resin. By using the thermal polymerization initiator in this range, the resulting sealant for flexible GHLC elements has better storage stability and thermosetting properties. The more preferred lower limit of the content of the thermal polymerization initiator is 0.1 parts by mass, and the more preferred upper limit is 5 parts by mass.

[0042] The sealant for flexible GHLC elements of the present invention preferably further contains a thermoplastic resin from the viewpoints of adjusting the viscosity of the resulting sealant for flexible GHLC elements and further improving the adhesion to the alignment film-attached film.

[0043] The thermoplastic resin preferably has a glass transition temperature of 20°C or lower. When the thermoplastic resin has a glass transition temperature of 20°C or lower, the resulting sealant for flexible GHLC elements has superior adhesion to an alignment film-attached film. A more preferred upper limit of the glass transition temperature of the thermoplastic resin is 15°C. There is no particular preferred lower limit of the glass transition temperature of the thermoplastic resin, but the substantial lower limit is -125°C. In this specification, the glass transition temperature of the thermoplastic resin means a value measured by differential scanning calorimetry (DSC) in accordance with JIS K 7121.

[0044] The weight-average molecular weight of the thermoplastic resin preferably has a lower limit of 10,000 and an upper limit of 1,000,000. When the weight-average molecular weight of the thermoplastic resin is within this range, the resulting sealant for flexible GHLC elements has superior adhesion to alignment film-attached films. The weight-average molecular weight of the thermoplastic resin more preferably has a lower limit of 50,000 and an upper limit of 500,000.

[0045] Examples of the thermoplastic resin include styrene / (meth)acrylic copolymer, (meth)acrylic copolymer, polyolefin, polyester, polyamide, polyurethane, polystyrene, polycarbonate, polyphenylene oxide, ABS resin, AES resin, AAS resin, MBS resin, and phenoxy resin. Among these, the (meth)acrylic / styrene copolymer is preferred as the thermoplastic resin. Furthermore, the thermoplastic resin is preferably a block copolymer.

[0046] The content of the thermoplastic resin is preferably 10 parts by mass or less and 50 parts by mass or less per 100 parts by mass of the curable resin. By using the thermoplastic resin in this range, the resulting sealant for flexible GHLC elements has superior adhesion to the alignment film-attached film. The more preferred lower limit of the content of the thermoplastic resin is 20 parts by mass, and the more preferred upper limit is 40 parts by mass.

[0047] The sealing agent for flexible GHLC elements of the present invention may further contain additives such as a heat curing agent, a curing accelerator, a light-shielding agent, a filler, a silane coupling agent, a stress relaxation agent, a reactive diluent, a thixotropic agent, a spacer, an antifoaming agent, a leveling agent, and a polymerization inhibitor, as necessary.

[0048] The method for producing the sealing agent for flexible GHLC elements of the present invention includes, for example, a method of mixing a curable resin, a photopolymerization initiator, and a thermoplastic resin and additives used as needed using a mixer. Examples of the mixer include a homodisper, a homomixer, a universal mixer, a planetary mixer, a kneader, and a three-roll mill.

[0049] The flexible GHLC element sealant of the present invention has a viscosity of preferably 1 Pa s as measured at 25°C and 1 rpm using an E-type viscometer. When the viscosity is 1 Pa s or more, the resulting flexible GHLC element sealant has superior adhesion to an alignment film-attached film. A more preferred lower limit of the viscosity is 10 Pa s. From the viewpoint of coatability, a preferred upper limit of the viscosity is 500 Pa s, and a more preferred upper limit is 400 Pa s. As the E-type viscometer, for example, a DV-III (manufactured by BROOK FIELD) can be used.

[0050] The flexible GHLC element sealant of the present invention can be suitably used in the production of a GHLC element by a liquid crystal dropping method. Examples of methods for producing a GHLC element by the liquid crystal dropping method include the following. First, a process is performed in which the flexible GHLC element sealant of the present invention is applied to a film substrate by screen printing, dispenser application, or the like to form a frame-shaped seal pattern. Next, a process is performed in which, while the flexible GHLC element sealant of the present invention is still uncured, minute droplets of guest-host liquid crystal are dropwise applied to the entire frame of the seal pattern, and another film substrate is immediately superimposed on the film. A GHLC element can then be obtained by a method in which the seal pattern portion is irradiated with light such as ultraviolet light to cure the sealant. Alternatively, a process of heating and curing the sealant may be performed after the process of irradiating the seal pattern portion with light such as ultraviolet light to cure the sealant.

[0051] The sealant for flexible GHLC devices of the present invention is preferably used to seal a GHLC light control device having a film substrate.

[0052] According to the present invention, it is possible to provide a sealant for flexible GHLC elements that has excellent adhesion to an alignment film-attached film even immediately after light irradiation or under high temperature conditions.

[0053] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0054] (Examples 1 to 12, Comparative Examples 1 to 5) According to the blending ratios shown in Tables 1 and 2, each material was stirred with a planetary stirrer and then uniformly mixed with a ceramic triple roll to obtain sealing agents for flexible GHLC elements of Examples 1 to 12 and Comparative Examples 1 to 5. Awatori Mixer (manufactured by Thinky Corporation) was used as the planetary stirrer.

[0055] (Viscosity) The viscosity of the obtained sealing agent for flexible GHLC elements was measured using an E-type viscometer (manufactured by BROOK FIELD, "DV-III") at 25°C and 1 rpm. The results are shown in Tables 1 and 2.

[0056] (Glass transition temperature, storage modulus, and molecular weight between crosslinking points of the cured product) The sealants for flexible GHLC elements obtained in Examples 1 to 12 and Comparative Examples 1 to 4 were measured using a metal halide lamp at a wavelength of 365 nm and an illuminance of 100 mW / cm. ２ The sealant for flexible GHLC elements obtained in Comparative Example 5 was irradiated with light of wavelength 365 nm and illuminance 100 mW / cm using a metal halide lamp for 30 seconds to obtain a cured product of thickness 300 μm. ２ The cured product was irradiated with light for 30 seconds, followed by heating at 80°C for 60 minutes, yielding a cured product with a thickness of 300 μm. An MB1500T-3 (manufactured by Sen Special Light Sources Co., Ltd.) was used as the metal halide lamp. The dynamic viscoelasticity of the resulting cured product was measured using a dynamic viscoelasticity measuring device (manufactured by IT Measurement & Control Co., Ltd., "DVA-200") under the following conditions: test piece width 5 mm, grip width 25 mm, heating rate 10°C / min, temperature range -80°C to 200°C, and frequency 10 Hz, and the glass transition temperature, storage modulus at 25°C and 80°C, and molecular weight between crosslinks were determined. The results are shown in Tables 1 and 2.

[0057] <Evaluation> The obtained sealant for flexible GHLC elements was evaluated as follows. The results are shown in Tables 1 and 2.

[0058] (Adhesion to Films with Alignment Films) (1) Immediately after Light Irradiation An imide resin was spin-coated onto a PET film with an ITO thin film, prebaked at 80°C, and then baked at 230°C to produce a PET film with an alignment film (length 25 mm, width 45 mm). SE7492 (manufactured by Nissan Chemical Industries, Ltd.) was used as the imide resin. All PET films with alignment films used below were previously attached to a glass substrate (length 25 mm, width 45 mm) on the side opposite the alignment film using adhesive tape (Nichiban Co., Ltd., "Nicetack"). A small drop of the resulting sealant for flexible GHLC elements was applied to one of two PET films with alignment films. The other PET film with alignment film was then attached in a cross shape to this, and a metal halide lamp was used at a wavelength of 365 nm and an illuminance of 100 mW / cm. ２ A test piece was obtained by irradiating the test piece with light of 1000 kJ / cm or more for 30 seconds. The metal halide lamp used was an MB1500T-3 (manufactured by Sen Special Light Sources Co., Ltd.). For the test piece immediately after light irradiation, the edge of the lower alignment film-attached PET film was pressed into the test piece with a metal cylinder having a radius of 5 mm at a speed of 5 mm / min, and the strength at which the alignment film-attached PET film peeled off was measured. The obtained measured value (kgf) was divided by the diameter (cm) of the joint to determine the adhesive strength, and the adhesiveness was evaluated according to the following criteria: ◎: When the adhesive strength was 3.0 kgf / cm or more ○: When the adhesive strength was 1.5 kgf / cm or more and less than 3.0 kgf / cm ×: When the adhesive strength was less than 1.5 kgf / cm

[0059] (2) Under high temperature conditions For test pieces obtained in the same manner as in "(1) Immediately after light irradiation" above, the adhesive strength was measured in the same manner as in "(1) Immediately after light irradiation" above while kept at 80°C, and the adhesiveness was evaluated according to the following criteria: ◎: When the adhesive strength was 2.0 kgf / cm or more ○: When the adhesive strength was 1.0 kgf / cm or more and less than 2.0 kgf / cm ×: When the adhesive strength was less than 1.0 kgf / cm

[0060] (Low Liquid Crystal Contamination) One part by mass of spacer fine particles (Micropearl SI-H050, manufactured by Sekisui Chemical Co., Ltd.) having an average particle size of 7 μm was dispersed in 100 parts by mass of the obtained flexible GHLC element sealant, which was then filled into a syringe and degassed using a centrifugal degassing machine (Awatron AW-1, manufactured by Musashi Engineering Co., Ltd.). The degassed flexible GHLC element sealant was applied using a dispenser to one of two PET films with an alignment film obtained in the same manner as in the above "(Adhesion to Films with Alignment Films)" to form a frame-shaped seal pattern. At this time, the discharge pressure was adjusted so that the line width of the flexible GHLC element sealant was approximately 1.0 mm. Next, minute droplets of liquid crystal ("4-pentyl-4-biphenylcarbonitrile" manufactured by Tokyo Chemical Industry Co., Ltd.) were applied dropwise onto the entire surface within the frame of the seal pattern of the PET film with an alignment film to which the sealant for flexible GHLC elements had been applied, and the other PET film with an alignment film was attached under vacuum. After releasing the vacuum, the sealant for flexible GHLC elements in the seal pattern area was cured by the following method to obtain a test piece. The sealants for flexible GHLC elements obtained in Examples 1 to 12 and Comparative Examples 1 to 4 were irradiated with a metal halide lamp at a wavelength of 365 nm and an illuminance of 100 mW / cm. ２ The sealant for flexible GHLC elements obtained in Comparative Example 5 was cured by irradiating it with light of wavelength 365 nm and illuminance 100 mW / cm using a metal halide lamp. ２ After irradiating the film with light for 30 seconds, the film was cured by heating at 80°C for 60 minutes. The metal halide lamp used was an MB1500T-3 (manufactured by Sen Special Light Sources Co., Ltd.). The obtained test piece was observed using a polarizing microscope (manufactured by Keyence Corporation, "VHX-5000") to check for alignment disorder based on the presence or absence of color unevenness in the liquid crystal portion, and the low liquid crystal contamination property was evaluated according to the following criteria: ◎: When no alignment disorder was observed ○: When alignment disorder was observed only near the seal pattern (periphery) ×: When alignment disorder spread to the center

[0061]

[0062]

[0063] According to the present invention, it is possible to provide a sealant for flexible GHLC elements that has excellent adhesion to an alignment film-attached film even immediately after light irradiation or under high temperature conditions.

Claims

1. A sealant for flexible GHLC elements, comprising a curable resin and a photopolymerization initiator, wherein the cured product has a glass transition temperature of 60°C or less, a storage modulus of 500 MPa or less at 25°C, and a storage modulus of 0.01 MPa or more at 80°C.

2. A sealant for flexible GHLC elements according to claim 1, wherein the curable resin contains a monofunctional (meth)acrylic compound having one (meth)acryloyl group per molecule, and the content of the monofunctional (meth)acrylic compound per 100 parts by mass of the curable resin is 50 parts by mass or more.

3. The sealant for flexible GHLC elements according to claim 2, wherein the curable resin contains a monofunctional (meth)acrylic compound whose homopolymer has a glass transition temperature of 20°C or less.

4. A sealant for flexible GHLC elements according to claim 2 or 3, wherein the curable resin contains a monofunctional (meth)acrylic compound having a cyclic ether structure.

5. A sealant for flexible GHLC elements according to claim 1, 2, 3 or 4, wherein the curable resin contains a polyfunctional (meth)acrylic compound having two or more (meth)acryloyl groups in one molecule, and the content of the polyfunctional (meth)acrylic compound in 100 parts by mass of the curable resin is 0.1 parts by mass or more and 50 parts by mass or less.

6. The sealant for flexible GHLC elements according to claim 1, 2, 3, 4 or 5, further comprising a thermoplastic resin.

7. A sealant for flexible GHLC elements according to claim 1, 2, 3, 4, 5 or 6, wherein the molecular weight between crosslinks of the cured product is 100 g / mol or more and 20,000 g / mol or less.

8. A sealant for flexible GHLC elements according to any one of claims 1 to 7, which has a viscosity of 1 Pa·s or more measured at 25°C and 1 rpm using an E-type viscometer.

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