阅读说明：本技术 液晶表示元件 (Liquid crystal display element ) 是由 保坂和义 片山雅章 于 2019-03-18 设计创作，主要内容包括：提供表现出良好的光学特性、液晶表示元件的驱动电压降低的液晶表示元件。一种液晶表示元件,其特征在于,其具有液晶层,所述液晶表示元件在没有施加电压时成为散射状态、在施加电压时成为透明状态,所述液晶层是对于配置于具备电极的一对基板之间的含有液晶和聚合性化合物的液晶组合物照射紫外线进行固化而成的,前述液晶具有正的介电各向异性,并且前述液晶组合物含有下述式[1]所示的化合物。(式中的各记号的定义如说明书中记载所述。)<Image he="82" wi="700" file="DDA0002684769560000011.GIF" imgContent="drawing" imgFormat="GIF" orientation="portrait" inline="no"></Image>(A liquid crystal display element exhibiting excellent optical characteristics and having a reduced driving voltage is provided. A liquid crystal display element having a liquid crystal layer which is in a scattering state when no voltage is applied and is in a transparent state when a voltage is applied, the liquid crystal layer being obtained by curing a liquid crystal composition containing a liquid crystal and a polymerizable compound, the liquid crystal composition being disposed between a pair of substrates having electrodes, the liquid crystal having a positive polarityAnd the liquid crystal composition contains the following formula [1 ]]The compounds shown. (wherein each symbol is as defined in the description.))

1. A liquid crystal display element having a liquid crystal layer which is in a scattering state when no voltage is applied and is in a transparent state when a voltage is applied, the liquid crystal layer being obtained by curing a liquid crystal composition containing a liquid crystal and a polymerizable compound, which is arranged between a pair of substrates having electrodes, by irradiating ultraviolet rays,

the liquid crystal has positive dielectric anisotropy, and

the liquid crystal composition contains a compound represented by the following formula [1],

formula [1]In, X¹Represents the following formula [1-a]-formula [1-j]，X²Represents a single bond, -O-, -NH-, -N (CH)₃)-、-CH₂O-、-CONH-、-NHCO-、-CON(CH₃)-、-N(CH₃) CO-, -COO-or-OCO-, X³Represents a single bond or- (CH)₂)_a-, wherein a is an integer of 1 to 15, X⁴Represents a single bond, -O-, -OCH₂-, -COO-or-OCO-, X⁵Represents a 2-valent cyclic group selected from the group consisting of a benzene ring, a cyclohexane ring and a heterocycle, or a 2-valent organic group having a steroid skeleton and having 17 to 51 carbon atoms, wherein any hydrogen atom in the cyclic group is optionally substituted by an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluoroalkyl group having 1 to 3 carbon atoms, a fluoroalkoxy group having 1 to 3 carbon atoms or a fluorine atom, and X is a group represented by⁶Represents a single bond, -O-, -CH₂-、-OCH₂-、-CH₂O-, -COO-or-OCO-, X ⁷Represents a cyclic group selected from the group consisting of a benzene ring, a cyclohexane ring and a heterocycle, any hydrogen atom in these cyclic groups is optionally substituted by an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluoroalkyl group having 1 to 3 carbon atoms, a fluoroalkoxy group having 1 to 3 carbon atoms or a fluorine atom, and X is⁸Represents an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, a fluorine-containing alkyl group having 1 to 18 carbon atoms, an alkoxy group having 1 to 18 carbon atoms or a fluorine-containing alkoxy group having 1 to 18 carbon atoms, Xm represents an integer of 0 to 4,

wherein, X^ARepresents a hydrogen atom or a benzene ring.

2. The liquid crystal display element according to claim 1, wherein the amount of the compound represented by the formula [1] introduced is 0.5 to 20 parts by mass per 100 parts by mass of the liquid crystal.

3. Liquid crystal cell according to claim 1 or 2Wherein said formula [1]]X in (1)¹Is represented by the formula [1-a]Formula [1-b ]]Formula [1-c ]]Formula [1-d]Formula [1-e]Or formula [1-f]。

4. The liquid crystal display element according to claim 1 or 2, wherein the compound represented by the formula [1] is at least one selected from the group consisting of the following formulae [1a-1] to [1a-11],

formula [1a-1]-formula [1a-4]In, X^arepresents-O-or-COO-, X^bRepresents an alkyl group having 1 to 12 carbon atoms, p1 represents an integer of 1 to 10, p2 represents an integer of 1 or 2,

Formula [1a-5]-formula [1a-8]In, X^cRepresents a single bond, -COO-or-OCO-, X^dRepresents an alkyl group or an alkoxy group having 1 to 12 carbon atoms, p3 represents an integer of 1 to 10, p4 represents an integer of 1 or 2,

formula [1a-9]-formula [1a-11]In, X^erepresents-O-or-COO-, X^fRepresents a C17-51 2-valent organic group having a steroid skeleton, X^gRepresents an alkyl group having 1 to 12 carbon atoms or an alkenyl group having 2 to 18 carbon atoms, and p5 represents an integer of 1 to 10.

5. The liquid crystal display element according to any one of claims 1 to 4, wherein the substrate of the liquid crystal display element is a glass substrate or a plastic substrate.

6. A liquid crystal display element according to any one of claims 1 to 5, wherein the liquid crystal display element is a light modulating window or shutter element.

Technical Field

The present invention relates to a transmission/scattering type liquid crystal display element which is brought into a transmission state when a voltage is applied.

Background

As a liquid crystal display element, a Twisted Nematic (TN, Twisted Nematic) mode has been put to practical use. In this mode, since light is switched by utilizing the optical rotation characteristics of liquid crystal, a polarizing plate needs to be used. When the polarizing plate is used, the light use efficiency is lowered.

As a liquid crystal display element not using a polarizing plate, there is an element that switches between a transmission state (also referred to as a transparent state) and a scattering state of liquid crystal. It is generally known to use polymer dispersed Liquid crystal (also referred to as pdlc (polymer dispersed Liquid crystal)) and polymer Network Liquid crystal (also referred to as pnlc (polymer Network Liquid crystal)).

In these liquid crystal display devices, a liquid crystal composition containing a polymerizable compound that is polymerized by ultraviolet light is disposed between a pair of substrates having electrodes, and the liquid crystal composition is cured by irradiation of ultraviolet light to form a composite of the liquid crystal and a cured product (e.g., a polymer network) of the polymerizable compound. In the liquid crystal display element, the scattering state and the transmission state of the liquid crystal are controlled by applying a voltage.

Liquid crystal display elements using PDLC and PNLC are in a state of white turbidity (scattering) because liquid crystals are oriented in random directions when no voltage is applied, and are in a state of transmitting light when the liquid crystals are aligned in the direction of an electric field when a voltage is applied (also referred to as a normal type element). In this case, since the liquid crystal is random when no voltage is applied, a liquid crystal alignment film or an alignment treatment for aligning the liquid crystal in one direction is not necessary. Therefore, in this liquid crystal display device, the electrode and the liquid crystal layer (the composite of the liquid crystal and the cured product of the polymerizable compound) are directly connected (see patent documents 1 and 2).

Disclosure of Invention

Problems to be solved by the invention

The polymerizable compound in the liquid crystal composition has an action of forming a polymer network to obtain desired optical characteristics and an action of improving adhesion between the liquid crystal layer and the electrode. However, in order to realize them, a tight polymer network needs to be formed, and thus driving of liquid crystal molecules for voltage application is hindered. Therefore, the driving voltage of the present cell is higher than that of a liquid crystal display cell such as a TN mode.

In view of the above, an object of the present invention is to provide a liquid crystal display element exhibiting excellent optical characteristics and reduced driving voltage of the liquid crystal display element.

Means for solving the problems

The present inventors have conducted extensive studies to achieve the above object, and as a result, have completed the present invention having the following gist.

That is, the liquid crystal display element of the present invention is characterized by comprising a liquid crystal layer which is in a scattering state when no voltage is applied and is in a transparent state when a voltage is applied, wherein the liquid crystal layer is obtained by irradiating a liquid crystal composition containing a liquid crystal and a polymerizable compound, which is disposed between a pair of substrates provided with electrodes, with ultraviolet light and is cured, wherein the liquid crystal has positive dielectric anisotropy, and the liquid crystal composition contains a compound represented by the following formula [1 ].

(X¹Represents the following formula [1-a]-formula [1-j]。X²Represents a single bond, -O-, -NH-, -N (CH)₃)-、-CH₂O-、-CONH-、-NHCO-、-CON(CH₃)-、-N(CH₃) CO-, -COO-or-OCO-. X³Represents a single bond or- (CH)₂)_a- (a is an integer of 1 to 15). X⁴Represents a single bond, -O-, -OCH₂-, -COO-or-OCO-. X⁵Represents a 2-valent cyclic group selected from the group consisting of a benzene ring, a cyclohexane ring and a heterocycle, or a 2-valent organic group having a steroid skeleton and having 17 to 51 carbon atoms, wherein any hydrogen atom in the cyclic group is optionally substituted by an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluorine-containing alkyl group having 1 to 3 carbon atoms, a fluorine-containing alkoxy group having 1 to 3 carbon atoms or a fluorine atom. X⁶Represents a single bond, -O-, -CH₂-、-OCH₂-、-CH₂O-, -COO-or-OCO-. X⁷Represents a cyclic group selected from the group consisting of a benzene ring, a cyclohexane ring and a heterocycle, and any hydrogen atom in these cyclic groups is optionally substituted by an alkyl group having 1 to 3 carbon atoms, an alkoxy group having 1 to 3 carbon atoms, a fluorine-containing alkyl group having 1 to 3 carbon atoms, a fluorine-containing alkoxy group having 1 to 3 carbon atoms or a fluorine atom. X⁸Represents an alkyl group having 1 to 18 carbon atoms, an alkenyl group having 2 to 18 carbon atoms, a fluoroalkyl group having 1 to 18 carbon atoms, an alkoxy group having 1 to 18 carbon atoms or a fluoroalkoxy group having 1 to 18 carbon atoms. Xm represents an integer of 0 to 4. )

(X^ARepresents a hydrogen atom or a benzene ring. )

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a liquid crystal display element having excellent optical characteristics and a reduced driving voltage of the liquid crystal display element is obtained. Therefore, the element of the present invention can be used as a standard type element for a liquid crystal display for the purpose, a light control window for controlling transmission and blocking of light, a shutter element, and the like.

The mechanism why the liquid crystal display element having the above-described excellent characteristics is obtained by the present invention is not necessarily clear, but is estimated as follows.

The liquid crystal composition used in the present invention contains a liquid crystal having positive dielectric anisotropy, a polymerizable compound, and the formula[1]The compounds shown (also referred to as specific compounds). The specific compound has a site having a rigid structure such as a benzene ring or a cyclohexane ring, and the formula [1 ]]X in (1)¹The sites shown are those where polymerization reaction proceeds by ultraviolet light. Therefore, when the specific compound is contained in the liquid crystal composition, the vertical alignment property of the liquid crystal is improved at the site of the rigid structure of the specific compound, and the driving of the liquid crystal with the application of voltage is promoted, so that the driving voltage of the liquid crystal display element can be reduced. In addition, the general formula [1 ]]X in (1)¹The site (b) reacts with the polymerizable compound to maintain the polymer network in a compact state.

From the above, it is understood that the liquid crystal display element using the liquid crystal composition of the present invention is a standard type element having good optical characteristics and a reduced driving voltage of the liquid crystal display element.

Detailed Description

< liquid crystal composition >

The liquid crystal composition of the present invention comprises a liquid crystal, a polymerizable compound and a specific compound represented by the formula [1 ].

As the liquid crystal, nematic liquid crystal, smectic liquid crystal, or cholesteric liquid crystal can be used. Among them, in the present invention, it preferably has positive dielectric anisotropy. In addition, from the viewpoint of low voltage driving and scattering characteristics, it is preferable that the anisotropy of dielectric constant is large and the anisotropy of refractive index is large. In addition, 2 or more kinds of liquid crystals can be mixed and used according to the above-described respective physical property values of the phase transition temperature, the dielectric anisotropy, and the refractive index anisotropy.

In order to drive a liquid crystal display element as an active element such as a Thin Film Transistor (TFT) or the like, the liquid crystal is required to have high resistance and high voltage holding ratio (also referred to as VHR). Therefore, fluorine-based or chlorine-based liquid crystals having high resistance and free from VHR degradation by active energy rays such as ultraviolet rays are preferably used as the liquid crystals.

Further, the liquid crystal display element may be a host-guest type element formed by dissolving the dichroic dye in the liquid crystal composition. In this case, an element which absorbs (scatters) when no voltage is applied and becomes transparent when a voltage is applied is obtained. In this liquid crystal display element, the direction of the director (direction of alignment) of the liquid crystal changes by 90 degrees depending on the presence or absence of voltage application. Therefore, the liquid crystal display element utilizes the difference in light absorption characteristics of the dichroic dye, and thus achieves a higher contrast ratio than a conventional host-guest type element in which random alignment and vertical alignment are switched. In a host-guest type element in which a dichroic dye is dissolved, the element becomes colored when the liquid crystal is aligned in the horizontal direction, and becomes opaque only in a scattering state. Therefore, an element which changes from colored opaque when no voltage is applied to colored transparent to colorless transparent state with voltage application can be obtained.

The polymerizable compound in the liquid crystal composition is used for forming a curable resin by polymerization reaction by ultraviolet irradiation at the time of manufacturing the liquid crystal display element. Therefore, a polymer obtained by previously polymerizing a polymerizable compound may be introduced into the liquid crystal composition. However, even when a polymer is formed, it is necessary to have a site where a polymerization reaction proceeds by irradiation of ultraviolet rays. The polymerizable compound is preferably used from the viewpoint of handling of the liquid crystal composition, that is, suppression of an increase in viscosity of the liquid crystal composition, and solubility in a liquid crystal.

The polymerizable compound is not particularly limited as long as it is dissolved in the liquid crystal, and when the polymerizable compound is dissolved in the liquid crystal, a temperature at which a liquid crystal phase is expressed needs to be present in part or all of the liquid crystal composition. Even when a part of the liquid crystal composition exhibits a liquid crystal phase, the scattering properties and transparency substantially the same as those of the entire device can be obtained if the liquid crystal display device is visually confirmed.

The polymerizable compound may be a compound that is polymerized by ultraviolet rays, and in this case, the polymerizable compound may be polymerized in any reaction form to form a curable resin. Specific reaction forms include radical polymerization, cationic polymerization, anionic polymerization, and addition polymerization.

Among them, the reaction form of the polymerizable compound is preferably radical polymerization from the viewpoint of optical characteristics of the liquid crystal display element. In this case, the following radical type polymerizable compound or oligomer thereof can be used as the polymerizable compound. As described above, a polymer obtained by polymerizing these polymerizable compounds may be used.

Specific examples of the radical polymerizable compound or oligomer thereof include radical polymerizable compounds described on pages 69 to 71 of International publication No. 2015/146987 (publication No. 2015.10.1).

The amount of the radical polymerizable compound or oligomer thereof is preferably 70 to 150 parts by mass, more preferably 80 to 110 parts by mass, based on 100 parts by mass of the liquid crystal in the liquid crystal composition, from the viewpoint of adhesion between the liquid crystal layer of the liquid crystal display element and the electrode. The radical polymerizable compound may be used in a mixture of 1 or 2 or more depending on the characteristics.

In order to promote the formation of the curable resin, it is preferable to introduce a radical initiator (also referred to as a polymerization initiator) that generates radicals by ultraviolet rays into the liquid crystal composition in order to promote radical polymerization of the polymerizable compound.

Specifically, the radical initiator is described in International publication No. 2015/146987, pages 71 to 72.

The ratio of the radical initiator is preferably 0.01 to 20 parts by mass, more preferably 0.05 to 10 parts by mass, per 100 parts by mass of the liquid crystal in the liquid crystal composition, from the viewpoint of adhesion between the liquid crystal layer of the liquid crystal display element and the electrode. The radical initiator may be used in a mixture of 1 or 2 or more species depending on the characteristics.

The specific compound is a compound represented by the formula [1 ].

Formula [1]In, X¹～X⁸And Xm are as defined above, but the following examples are preferred among them, respectively.

X¹Preferably the aforementioned formula [1-a]Formula [1-b ]]Formula [1-c ]]Formula [1-d]Formula [1-e]Or formula [1-f]More preferably the formula [1-a]Formula [1-b ]]Formula [1-c ]]Or formula [1-e]At the mostPreferably of the formula [1-a]Or formula [1-b]。

X²Preferably a single bond, -O-, -CH₂O-, -CONH-, -COO-or-OCO-, more preferably a single bond, -O-, -COO-or-OCO-.

X³Preferably a single bond or- (CH)₂)_a- (a is an integer of 1 to 10), more preferably- (CH)₂)_a- (a is an integer of 1 to 10).

X⁴Preferably a single bond, -O-or-COO-, more preferably-O-.

X⁵Preferably a benzene ring or a cyclohexane ring, or a C17-51 2-valent organic group having a steroid skeleton, and more preferably a benzene ring or a C17-51 2-valent organic group having a steroid skeleton.

X⁶Preferably a single bond, -O-, -COO-or-OCO-, more preferably a single bond, -COO-or-OCO-.

X⁷Preferably a benzene ring or a cyclohexane ring.

X⁸Preferably an alkyl group or an alkoxy group having 1 to 18 carbon atoms or an alkenyl group having 2 to 18 carbon atoms, more preferably an alkyl group or an alkoxy group having 1 to 12 carbon atoms. Xm is preferably an integer of 0 to 2.

Formula [1]Preferred X in (1)¹～X⁸The combinations of Xm and Xm are shown in tables 1 to 9 below.

[ Table 1]

[ Table 2]

[ Table 3]

[ Table 4]

[ Table 5]

[ Table 6]

[ Table 7]

[ Table 8]

[ Table 9]

Of these, (1-3a) - (1-8a), (1-11a) - (1-24a), (1-27a) - (1-36a), (1-39a), (1-40a), (1-43a) - (1-48a), (1-51a) - (1-64a), (1-67a) - (1-76a), (1-79a), (1-80a), (1-83a) - (1-88a), (1-91a) - (1-104a), (1-107a) - (1-116a), (1-119a), (1-120a), (1-123a), (1-124a), (1-129a), (1-130a), (1-133a), (1-134a), (1-137a), (1-138a), (1-141a), (1-142a), (1-145a), (1-146a), or (1-149a) to (1-172 a).

More preferably (1-3a) - (1-8a), (1-11a), (1-12a), (1-15a) - (1-18a), (1-21a), (1-22a), (1-27a) - (1-30a), (1-33a), (1-34a), (1-39a), (1-40a), (1-43a) - (1-48a), (1-51a), (1-52a), (1-55a) - (1-58a), (1-61a), (1-62a), (1-67a) - (1-70a), (1-73a), (1-74a), (1-79a), (1-80a), (1-83a) - (1-88a), (1-91a), (1-92a), (1-95a) - (1-98a), (1-101a), (1-102a), (1-107a) - (1-110a), (1-113a), (1-114a), (1-119a), (1-120a), (1-123a), (1-124a), (1-129a), (1-130a), (1-133a), (1-134a), (1-137a), (1-138a), (1-141a), (1-142a), (1-145a), (1-146a) or (1-149a) - (1-172 a).

Most preferably (1-3a) - (1-8a), (1-15a) - (1-18a), (1-29a), (1-30a), (1-43a) - (1-48a), (1-55a) - (1-58a), (1-69a), (1-70a), (1-83a) - (1-88a), (1-95a) - (1-98a), (1-109a), (1-110a), (1-123a), (1-124a), (1-133a), (1-134a), (1-141a), (1-142a), (1-149a) to (1-152a), or (1-161a) to (1-172 a).

More specific compounds include compounds selected from the group consisting of the following formulas [1a-1] to [1a-11], and these compounds are preferably used.

(X^arepresents-O-or-COO-. X^bRepresents an alkyl group having 1 to 12 carbon atoms. p1 represents an integer of 1 to 10.

p2 represents an integer of 1 or 2. )

(X^cRepresents a single bond, -COO-or-OCO-. X^dRepresents an alkyl group or an alkoxy group having 1 to 12 carbon atoms. p3 represents an integer of 1 to 10. p4 represents an integer of 1 or 2. )

(X^erepresents-O-or-COO-. X^fRepresents a C17-51 organic group having a steroid skeleton and a valence of 2. X^gRepresents an alkyl group having 1 to 12 carbon atoms or an alkenyl group having 2 to 18 carbon atoms. p5 represents an integer of 1 to 10. )

The content ratio of the specific compound is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 20 parts by mass, and most preferably 1 to 10 parts by mass, relative to 100 parts by mass of the liquid crystal in the liquid crystal composition, from the viewpoint of adhesion between the liquid crystal layer of the liquid crystal display element and the electrode. The specific compound may be used in a mixture of 1 or 2 or more depending on the characteristics.

Examples of the method for producing the liquid crystal composition include a method in which a liquid crystal is added with a single or a mixture of a plurality of polymerizable compounds and a specific compound; a method of adding a specific compound to a liquid crystal in advance to prepare a mixture, and adding a single or plural kinds of polymerizable compounds to the mixture.

When a plurality of polymerizable compounds are used, heating may be performed depending on the solubility of the polymerizable compounds when they are mixed. The temperature at this time is preferably less than 100 ℃. The same applies to the case where the polymerizable compound and the specific compound are mixed, and the case where the liquid crystal and the specific compound are mixed.

< method for manufacturing liquid crystal display element >

The substrate used for the liquid crystal display element is not particularly limited as long as it is a substrate having high transparency, and a plastic substrate such as an acrylic substrate, a polycarbonate substrate, a PET (polyethylene terephthalate) substrate, or the like, and a film thereof may be used in addition to the glass substrate. In particular, when used for a light control window or the like, a plastic substrate or a film is preferable. In view of process simplification, it is preferable to use a substrate on which an ITO electrode, an Indium Zinc Oxide (IZO) electrode, an Indium Gallium Zinc Oxide (IGZO) electrode, an organic conductive film, and the like are formed for driving a liquid crystal. In the case of forming a reflective liquid crystal display element, a substrate formed with a silicon wafer, a metal such as aluminum, or a dielectric multilayer film may be used as long as the substrate is a single-sided substrate.

The liquid crystal composition used for the liquid crystal display element is the liquid crystal composition described above, and a spacer for controlling an electrode gap (also referred to as a void) of the liquid crystal display element may be introduced.

The method of injecting the liquid crystal composition is not particularly limited, and the following methods may be mentioned. That is, when a glass substrate is used as the substrate, a pair of substrates is prepared, a sealant is applied to 4 substrates on one side except a part thereof, and then the other substrate is bonded with the electrode surface facing the inside to form an empty cell. And then injecting the liquid crystal composition under reduced pressure from a portion where the sealant is not applied to obtain a cell into which the liquid crystal composition is injected. Further, when a plastic substrate or a film is used as the substrate, a method may be mentioned in which a pair of substrates are prepared, a liquid crystal composition is dropped on one substrate by an odf (one Drop filling) method, an ink jet method, or the like, and then the other substrate is bonded to obtain a unit into which the liquid crystal composition is injected. In the liquid crystal display element of the present invention, since the liquid crystal layer has high adhesion to the electrodes, the 4 substrates need not be coated with the sealant.

The gap of the liquid crystal display element can be controlled by the aforementioned spacer or the like. As described above, this method includes a method of introducing spacers having a target size into a liquid crystal composition, a method of using a substrate having pillar spacers having a target size, and the like. In addition, when the substrates are laminated using a plastic or film substrate, the gap may be controlled without introducing a spacer.

The size of the gap of the liquid crystal display element is preferably 1 to 100 μm, more preferably 1 to 50 μm, and particularly preferably 2 to 30 μm. If the gap is too small, the contrast of the liquid crystal display element decreases, and if it is too large, the driving voltage of the element increases.

The liquid crystal display element is obtained by curing a liquid crystal composition to form a liquid crystal layer. The liquid crystal composition is cured by irradiating a cell into which the liquid crystal composition is injected with ultraviolet rays. Examples of the light source of the ultraviolet irradiation device used in this case include a metal halide lamp and a high-pressure mercury lamp. In this case, the wavelength of the ultraviolet ray is preferably 250 to 400nm, more preferably 310 to 370 nm. After the irradiation with ultraviolet rays, heat treatment may be performed. The temperature at this time is preferably 20 to 120 ℃, more preferably 30 to 100 ℃.