JPH07261139A - Production of optical element - Google Patents

Abstract

PURPOSE:To provide a production method of an optical element using a light- diffusing compsn. comprising at least a high-molecular liquid crystal so that optical characteristics such as display characteristics and light controlling characteristics, reproducibility of recording and erasing, and uniformity of display are largely improved. CONSTITUTION:This optical element is produced by heat treating a high- molecular liquid crystal compsn. to control the multidomain structure and crosslinking the compsn. while the multidomain structure is maintained. In this method, heat treatment is preferably performed at a temp. at which the high-molecular liquid crystal compsn. shows a liquid crystal phase. Crosslinking is preferably performed at a temp. lower than the liquid crystal phase-isotropic phase transition temp. of the high-molecular liquid compsn. The max. domain diameter in the domain distribution of the multidomain structure of the obtd. optical element is preferably <=3mum, and especially 200-1500nm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an optical element capable of controlling the light scattering property by an external action, and more particularly to a method of manufacturing an optical element made of at least a polymer liquid crystal.

[0002]

2. Description of the Related Art Polymer liquid crystals are a new functional material.
Applications to recording materials and display materials are being studied. For example, regarding recording materials, JP-A-59-10930 and JP-A-63-223066, and regarding display materials, JP-A-62-14114 and JP-A-2 can be used.
-2513 gazette, and Polym. Commun.
Vol. 24, 364 (1983), Japan Di
It is disclosed in spray, 260 (1986) and the like. In addition, the technology for cross-linking polymer liquid crystals is described in Makro
mol. Chem. Rapid Commun. , Vo
l. 2,317 (1981), Makromol. Ch
em. , Vol. 667,188 (1987), Ang
ew. Chem. Adv. Mater. , Vol. 10
1,1437 (1989), Makromol. Che
m. , Vol. 187, 1915 (1989) and the like, and is expected to be applied as an elastomer, a novel light modulation element or a display element. Further, a technique relating to a display element in which main chain type polymer liquid crystal is crosslinked to reduce damage by a thermal head is disclosed in JP-A-2-42415.

[0003]

DISCLOSURE OF INVENTION Problems to be Solved by the Invention In an optical element or medium using a conventional polymer liquid crystal as a light scattering layer,
Not only the display characteristics (optical characteristics) are low, but in the case of recording / display and erasing using heat, the reproducibility of the display characteristics often deteriorates due to uneven temperature and cooling rate. . That is, in an optical element using polymer liquid crystal, the light scattering property (whiteness) greatly depends on the cooling rate after heating. Therefore, precise cooling rate control is required to obtain uniform and large light scattering property. In addition, when the optical element has a large area, there is a problem that precise temperature control over a large area is required so that uneven whiteness does not occur. Therefore,
The present invention has been made for the purpose of solving the above problems in the conventional art. That is, an object of the present invention is to use a light-scattering composition composed of at least a polymer liquid crystal, which has greatly improved optical characteristics such as display characteristics and dimming characteristics, reproducibility of recording / erasing, and display uniformity. Another object of the present invention is to provide a manufacturing method of the optical element.

[0004]

The method for producing an optical element of the present invention comprises subjecting a polymer liquid crystal composition to a heat treatment,
It is characterized by controlling a multi-domain structure and crosslinking the composition while maintaining the multi-domain structure. That is, the optical element of the present invention, by heat-treating a light-scattering composition comprising at least a polymer liquid crystal, the internal structure of the composition is made into a multi-domain structure having a desired domain diameter distribution, and this multi-domain structure is The composition is characterized in that the composition is crosslinked in the state of being held, and the domain diameter is controlled by heat treatment, and the composition containing the polymer liquid crystal is crosslinked in the state of holding the multi-domain structure. is there.

The "light-scattering composition comprising at least a polymer liquid crystal" which is a polymer liquid crystal composition in the present invention is
A multi-domain structure is formed in the temperature range where the composition exhibits a liquid crystal phase. The “multi-domain structure” in the present invention means a structure composed of a plurality of phases having different properties. Each "domain" constituting this "multi-domain" is mainly formed by the difference in the orientation of the side chain liquid crystal molecules inside the domain. In other words, the liquid crystal molecules are aligned in substantially the same direction inside one domain, and as a result of the alignment, one domain has optical anisotropy and can be optically distinguished from other domains. . The “multi-domain structure” is an aggregate of domains exhibiting such optical anisotropy. In order to improve the light scattering property, it is desirable that the orientation direction of each domain is random.

In the present invention, the multi-domain structure is
In order to be used as a light scattering layer, it is desirable that the size of each domain is a set having a size of about the wavelength of visible light. The specific preferred size of the domain diameter is such that the maximum value of the number distribution of domains is 3 μm or less, and more preferably 2
It is in the range of 00 nm to 1500 nm. Also, the domain diameter distribution range is substantially uniform such that the difference between the minimum domain diameter and the maximum domain diameter is 5 μm or less, preferably 3 μm or less, and more preferably about 1 μm. A multi-domain structure having domains of such a size and distribution range is preferable because it strongly scatters visible light wavelengths and has a high white turbidity.

In the polymer liquid crystal composition of the present invention, the multi-domain structure can change the size and density of the domain by external temperature before crosslinking. That is, by performing heat treatment, a multi-domain structure having domains of a desired order can be formed, and a light scattering layer having a higher light scattering property can be obtained.

Next, the polymer liquid crystal used in the polymer liquid crystal composition will be described. Generally, polymer liquid crystals are classified into main chain type polymer liquid crystals and side chain type polymer liquid crystals, but side chain type polymer liquid crystals are preferably used in the present invention. Further, in the present invention, a polymer liquid crystal containing a reactive group for crosslinking as one component of the main chain or the side chain is preferable. As a reactive group, a vinyl group, an acrylate group,
Polymerizable groups such as methacrylate groups, heterocyclic groups such as epoxy groups, isocyanate groups, hydroxyl groups, amino groups, acid amide groups, thiol groups, carboxyl groups, sulfonic acid groups, phosphoric acid groups, metal alcoholate groups, magnesium halides (Grignard). ) Groups or other reactive groups can be used as preferred ones.

Next, a method for producing such a polymer liquid crystal will be described. Usually, the side chain type high molecular weight liquid crystal can be produced by polymerizing a polymerizable mesogenic compound or by adding a mesogenic compound capable of addition reaction to a reactive polymer such as hydrogenated polysilicone. Such techniques are described in Makromol. Chem. , P2
73, 179 (1978), Eur, Polym.
J. , P651, 18, (1982) and Mol. C
ryst. Liq. Cryst. , P167,169
(1989) and the like. The polymer liquid crystal used in the present invention can also be manufactured by the same method as disclosed in these. That is, a polymerizable mesogenic compound (mesogenic monomer) is copolymerized with a polymerizable compound having a reactive group (reactive monomer), or a mesogenic compound and a reactive compound capable of addition reaction are added to a reactive polymer. Can be manufactured. Examples of the polymerizable mesogen compound and the addition mesogenic compound that can be used in the present invention include biphenyl-based, phenylbenzoate-based, cyclohexylbenzene-based, azoxybenzene-based, azobenzene-based, azomethine-based, phenylpyrimidine-based, diphenyl A variety of rigid molecules (mesogens) such as acetylene, biphenylbenzoate, cyclohexylbiphenyl, terphenyl, etc., to which acrylic acid ester, methacrylic acid ester group or vinyl group is bonded via an alkyl spacer of a specified length. Typical examples are compounds and the like.

Representative structural examples of these compounds are shown below. _{CH 2 = C (R) -COO-} (CH 2) k -O-A CH 2 = CH- (CH 2) in _k -O-A [wherein, R represents a hydrogen atom or a methyl group, k is 1 ~
An integer selected from 30, and A represents a mesogen having the following structure.

[Chemical 1] (In the formula, X and Y are each a single bond, -N = N-,
-N (→ O) = N-, -CH = N-, -N = CH-,-
COO -, - O (C = O) - and represents a group selected from an ethynylene group, p is an integer selected from among 1 to 5, R ¹ represents an alkoxy group, a halogen atom, a cyano group, a carboxyl Represents a group selected from a group and an alkyl group, and when p is 2 or more, each R ¹ may be different. )]

The polymer liquid crystal used in the present invention can be produced by copolymerizing or co-adding the above-mentioned compound having a reactive group (reactive monomer) in addition to the above mesogenic compound. Specific examples of the compound having a reactive group used in that case include (meth) acrylic acid,
ω-carboxy-polycaprolactone-mono (meth) acrylate, vinyl sulfonate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 2- (meth) acryloxyethyl acid phosphate, 2-hydroxy-3-phenoxy. Propyl (meth) acrylate, 2- (meth) acryloxyethyl succinate, phthalic acid mono (meth) acrylate,
2- (meth) acryloxyethyl (2-hydroxyethyl) phthalate, 4- (meth) acryloxyalkyloxy-benzoic acid, glyceryl (meth) acrylate, hydroxy group-substituted styrene, (meth) acrylamide, N, N- Examples thereof include dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate, glycidyl (meth) acrylate, 2-propen-1-ol, and 5-hexen-1-ol. In addition, after reacting these compounds by copolymerization or co-addition, another reactive group may be introduced to convert the reactive group. For example, (meth) acrylic acid or the like can be added to the hydroxyl group introduced by copolymerizing hydroxyethyl (meth) acrylate to introduce a polymerizable group into the polymer side chain. Furthermore, it is also possible to use various mesogenic compounds capable of polymerization or addition having the above-mentioned reactive groups. For example, in the structural example of the mesogen compound described above, a compound having a hydroxyl group, a carboxyl group or an amino group as the substituent R ¹ can be used. What is illustrated here is an example, and there is no particular limitation.

Further, in order to produce the polymer liquid crystal used in the present invention, in addition to the above-mentioned two kinds of mesogenic compound and non-mesogenic compound having a reactive group, a reactive group is contained as a third component. Various compounds that are not present can be copolymerized or co-added. Examples of the compound that can be used as the third component include alkyl (meth) acrylate and its derivatives, styrene and its derivatives, (meth) acrylonitrile, vinyl chloride, vinylidene chloride, vinylpyrrolidone, vinyl acetate, 1-hexene, 1- Examples include non-mesogenic monomers such as octene. These non-mesogenic compounds are useful for controlling the multi-domain structure and thermal properties and are preferably used. The co-weight ratio or co-addition amount of these third components is in the range of 0.01 to 20% by weight. It should be noted that each of the above compounds may be used in plural kinds.

The copolymerization ratio of the above two or three components is
The content of the polymerizable mesogenic compound (mesogen monomer) is preferably in the range of 40 to 99% by weight, more preferably 60 to 99% by weight, based on the polymer liquid crystal, although the content may be varied depending on the desired characteristics. The form of copolymerization may be any of various known forms such as random, graft, and alternating, and is not particularly limited. Also,
The amount of the above-mentioned compound having a reactive group copolymerized or co-added to the polymer liquid crystal is 0.1 mol% as a monomer unit.
The range of ˜70 mol% is preferred. The weight average molecular weight of the polymer liquid crystal is in the range of 1,000 to 1,000,000, particularly preferably 10,000 to 500,000.

Next, the characteristics of the polymer liquid crystal composition of the present invention and the method for producing the same will be described. It is preferable to use the above-mentioned polymer liquid crystal as a composition to which various catalysts and polyfunctional reactive compounds are added for the purpose of crosslinking. As the catalyst, various UV polymerization initiators, thermal polymerization initiators and the like, and as the polyfunctional reactive compound, a polyfunctional isocyanate compound, a polyfunctional epoxy compound, a polyfunctional melamine compound, a polyfunctional aldehyde compound, a polyfunctional amine compound and a polyfunctional amine compound. Functional carboxyl compounds and the like are preferably used. Regarding the catalyst and the polyfunctional reactive compound, for example, as the catalyst, an azo-based polymerization initiator such as azobisisobutyronitrile (ABIN), a peroxide-based polymerization initiator such as benzoyl peroxide, or a phenyl ketone-based Examples of the polyfunctional reactive compound include toluene diisocyanate (TDI), 4,4′-diphenylmethane diisocyanate, 3,4-dichlorophenyl diisocyanate, polymethylene polyphenyl isocyanate, and hexamethylene diisocyanate ( HDI), TDI or an adduct of HDI and a polyol such as trimethylolpropane, bisphenol A-diglycidyl, melamine, ethylenediamine, hexamethylenediamine, phenylenediamine, glutaraldehyde, terephthalaldehyde, Acid, succinic acid, glutaric acid, maleic acid, terephthalic acid, pyromellitic acid, pyromellitic anhydride and the like. The addition amount of the catalyst or polyfunctional reactive compound is preferably in the range of 0.01% by weight to 20% by weight with respect to the polymer liquid crystal.

Various components other than the above may be added to the polymer liquid crystal composition of the present invention for the purpose of improving the characteristics. For example, various antioxidants such as hindered amines and hindered phenols may be added for the purpose of improving weather resistance, and anthraquinone-based, styryl-based, azomethine-based and azo-based compounds may be added for the purpose of improving display contrast. You may add various dichroic dyes, such as. Further, various fluorescent dyes may be added for the purpose of improving the light scattering property. Furthermore, in order to efficiently perform thermal writing with laser light, various laser light absorbing dyes (78
When a general semiconductor laser having a wavelength of 0 to 830 nm is used, it is also preferable to add a near infrared absorbing dye such as phthalocyanine, squarylium or azurenium). The addition amount of the various components listed above is preferably in the range of 0.01 to 5% by weight in the polymer liquid crystal composition. A low molecular weight liquid crystal compound may be added to the polymer liquid crystal composition within the range of 1 to 20% by weight.

In the present invention, the heat treatment method is as follows:
Control of the cooling rate from a predetermined temperature or annealing treatment at a predetermined temperature can be applied as a preferable method. In particular, the method of performing the annealing treatment in the temperature range in which the main chain movement of the polymer liquid crystal is allowed and the liquid crystal phase in which the light scattering property can be confirmed is performed is most effective. The temperature range in which the liquid crystal phase of the polymer liquid crystal composition shows varies depending on the composition of the polymer liquid crystal to be used and the like.
It is desirable to carry out at a temperature in the range of 300 ° C, preferably 20 ° C to 200 ° C. The annealing time also varies depending on the composition of the polymer liquid crystal composition, but 5 seconds to 200 hours is suitable. By performing the heat treatment as described above,
After forming a high "multi-domain structure" of the light scattering layer to control the domain diameter of the multi-domain structure, the polymer liquid crystal composition is cross-linked. As a method for crosslinking the above-mentioned polymer liquid crystal composition, a heat-treated polymer liquid crystal composition is heated,
It is performed by applying light, an electron beam or the like. Also,
From the viewpoint of process efficiency, it is preferable to carry out the crosslinking at the same time as the process of controlling the domain diameter by the heat treatment. The temperature at the time of crosslinking is not particularly limited as long as it is a temperature range in which the multi-domain structure is retained, but a temperature range of the liquid crystal phase-isotropic phase transition point of the composition or lower and the glass transition point or higher are preferable. By crosslinking in this way,
It is possible to stabilize the multi-domain structure and obtain a light-scattering layer which does not change in structure due to external temperature and always exhibits a high light-scattering property.

In the present invention, it is preferable to heat-treat and crosslink after processing into a desired form using a solution or a heated solution of the above-mentioned polymer liquid crystal or a composition in which a catalyst or the like is mixed. The polymer liquid crystal composition layer thus produced (hereinafter referred to as "polymer liquid crystal layer")
Can be used as an optical element in the form of a film, a block, a fiber, etc., as it is, as it is, as a self-supporting substance, but preferably, a polymer liquid crystal layer is formed on a substrate or two sheets are used. It is used as an optical element in a laminated form between base materials. 1 to 4 show configuration examples of the optical element produced by the present invention. 1 to 3 show a structure in which a polymer liquid crystal layer (recording layer) 2 is laminated on a substrate 1 and a protective layer 3 is provided for the purpose of improving surface strength and heat resistance. Further, FIG. 4 shows a structure in which a polymer liquid crystal layer (recording layer) 2 is laminated between two base materials 1 and 1 with a transparent electrode 6 interposed therebetween. In the figure, 4 is a colored layer and 5 is a light reflection layer.

As the base material, various polymer films such as polyvinyl chloride, polypropylene, polyester (PET, etc.) and polyimide, paper, metal, ceramic, glass and the like can be used. Also, as a base material, a coloring film in which a pigment is dispersed in a PET (polyethylene terephthalate) film or the like or a coloring layer is provided in a PET film or the like, or a vapor deposition film in which a metal having a high reflectance is deposited on the surface of the base material is used. It may also be used as a light absorbing layer, a coloring layer, or a light reflecting layer (FIGS. 2 and 3). The thickness of the light absorption layer and the light reflection layer is 0.00
It is selected from the range of 1 to 100 μm. It is also preferable to use a substrate with an electrode as the substrate. The polymer liquid crystal layer can be formed on the surface of the base material by a general method such as a coating method using a solvent or a hot melt coating method. The thickness of the polymer liquid crystal layer is not particularly limited, but can be variously changed depending on the desired contrast, and is preferably in the range of 1 to 100 μm, particularly preferably 5 to 50.
It is selected from the range of μm. Although a widely used overcoat material can be used for the protective layer, particularly preferable ones having high heat resistance are fluorine-based polymers, silicone-based polymers, thermosetting polymers, UV-curing polymers and electron beam curing. A polymer or the like can be used. A plurality of protective layers may be laminated, and the thickness thereof is selected from the range of 0.1 to 20 μm. These protective layers can be formed by a coating method using a solvent.

Next, a method for controlling the light-scattering property of an optical element using the above-mentioned polymer liquid crystal composition will be described by taking as an example the one having the constitution shown in FIGS. In the configurations of FIGS. 1 to 3, the light scattering property can be controlled using only heat. The polymer liquid crystal layer produced by the production method of the present invention exhibits a light scattering state (white turbid state) derived from the multi-domain structure. Here, the polymer liquid crystal composition is brought into an isotropic state by partial heating using a thermal head, laser light, etc., and the heated portion is fixed in an isotropic state by quenching, and the area is light-scattering. It becomes a small transparent state. In this way, information can be recorded by controlling the light scattering property. On the other hand, in the case of increasing the light scattering property and erasing the recorded information, it is possible to return to the initial state of large light scattering by cooling after heating after heating slowly. That is, the light scattering state can be reversibly changed many times, and information can be recorded / erased. When a thermal head or a laser beam is used as the heating means for controlling the light scattering property, the light reflectivity can be controlled by controlling the pulse width and energy applied.

[0020]

In the present invention, when an optical element using a polymer liquid crystal composition is produced, the optical liquid crystal composition is heat-treated to make the internal structure of the composition a multi-domain structure having a desired domain diameter, The polymer liquid crystal composition is crosslinked while maintaining the multi-domain structure.
As a result, the multi-domain structure is effectively controlled to a form in which visible light is scattered, and the composition is stabilized while maintaining the form. That is, the production method of the present invention has an effect of stabilizing the multi-domain structure in a state of high light scattering and making it a memory. The size of light scattering of the light-scattering composition depends on the domain diameter and density in the multi-domain structure. However, in the conventional technique, not only the optical characteristics are low, but also the domain is increased during repeated heating / cooling (recording / erasing). Although the diameter and density were changed from the initial state, or were partially nonuniform due to heat unevenness, the optical properties and the like were deteriorated. However, according to the present invention, the domain diameter is controlled to a predetermined size and crosslinking is performed. Stabilized multi-domain structure can be obtained by the action of the stabilized multi-domain structure, and excellent optical properties can be obtained, and at the same time, excellent reproduction in the process of repeated heating / cooling (recording / erasing). It becomes possible to express the sex.

[0021]

【Example】

Example 1 1.9 g of 4-acryloxyhexyloxy-4′-cyano-biphenyl as a mesogenic monomer and 0.1 g of 2-hydroxyethyl acrylate as a reactive non-mesogenic monomer were combined with azobisisobutyronitrile (ABI).
N) was used as an initiator, and tetrahydrofuran was used as a solvent for copolymerization, followed by precipitation and purification with ethyl alcohol three times to obtain 1.9 g of a polymer liquid crystal represented by the following structural formula (I).

[Chemical 2] To 1.0 g of the above-mentioned polymer liquid crystal, 0.05 g of a polyfunctional isocyanate compound (Coronate HX, manufactured by Nippon Polyurethane Company) as a cross-linking agent, and methyl ethyl ketone (ME
A solution containing 3.0 g of K) was applied onto a 100 μm thick aluminum vapor-deposited PET film using a blade coater and dried to form a polymer liquid crystal layer with a thickness of about 6 μm. The polymer liquid crystal layer after coating and drying was cloudy and formed a light scattering control film. T of the composition before crosslinking
i (liquid crystal phase-isotropic phase transition point) was about 90 ° C. Next, after heating for 10 minutes in an oven at 60 ° C. to perform an annealing treatment, reaction was carried out in an open at 30 ° C. for 72 hours to crosslink. Further, an ultraviolet curable composition (Aronix UV, manufactured by Toagosei Co., Ltd.) is applied as a protective layer and cured by using a high pressure mercury lamp to form a protective layer of about 2 μm on the polymer liquid crystal layer to form an optical element. It was made.
At this time, the domain diameter at the maximum of the number of distributed domains in the multi-domain structure was 300 nm. The difference between the maximum domain diameter and the minimum domain diameter is 0.9μ.
It was m.

Example 2 1.8 g of the same mesogenic monomer as in Example 1, 0.1 g of reactive non-mesogenic monomer and 0.1 g of butyl acrylate.
g was polymerized in the same manner as in Example 1 to synthesize a polymer liquid crystal represented by the following structural formula (II).

[Chemical 3] To 1.0 g of this polymer liquid crystal, 0.05 g of a polyfunctional isocyanate compound (Coronate HX, manufactured by Nippon Polyurethane Co., Ltd.) as a crosslinking agent, and methyl ethyl ketone (ME
A solution containing 3.0 g of K) was applied onto a 100 μm thick aluminum vapor-deposited PET film using a blade coater and dried to form a polymer liquid crystal layer with a thickness of about 6 μm. The polymer liquid crystal layer after coating and drying was cloudy and formed a light scattering control film. The Ti (liquid crystal phase-isotropic phase transition point) of the composition before cross-linking was about 85 ° C. Next, heat in an oven at 70 ° C for 24 hours,
The annealing treatment and the crosslinking reaction were performed at the same time. Further Example 1
A protective layer was formed in the same manner as in 1. to produce an optical element.
At this time, the domain diameter at the maximum of the number of distributed domains in the multi-domain structure was 330 nm. The difference between the maximum domain diameter and the minimum domain diameter is 0.8μ
It was m.

Example 3 1.8 g of the same mesogenic monomer as in Example 1, 0.1 g of glycidyl acrylate as a reactive non-mesogenic monomer,
Butyl methacrylate 0.1 as non-mesogenic monomer
g was polymerized in the same manner as in Example 1 to synthesize a polymer liquid crystal represented by the following structural formula (III).

[Chemical 4] A solution prepared by adding 0.02 g of hexamethylene diamine, which is a polyfunctional amine compound as a cross-linking agent, and 3.0 g of methyl ethyl ketone (MEK) as a solvent, to 1.0 g of this liquid crystal polymer was placed on a 100 μm thick aluminum vapor-deposited PET film using a blade coater. Apply and dry
A polymer liquid crystal layer having a thickness of about 6 μm was formed. The polymer liquid crystal layer after coating and drying was cloudy and formed a light scattering control film. The Ti (liquid crystal phase-isotropic phase transition point) of the composition before crosslinking was about 90 ° C. Next, heat in an oven at 60 ° C. for 10 minutes to anneal, then
The reaction was carried out in an oven at 0 ° C. for 24 hours for crosslinking. Further, a protective layer was formed in the same manner as in Example 1 to fabricate an optical element. At this time, the domain diameter at the maximum of the number of distributed domains in the multi-domain structure is 280 nm.
Met. The difference between the maximum domain diameter and the minimum domain diameter was 1.0 μm.

Comparative Example 1 An optical element was produced by the same procedure as in Example 1 except that the polymer liquid crystal (structural formula (I)) synthesized in Example 1 was used and the crosslinking reaction was not performed with an isocyanate compound. The polymer liquid crystal layer after production was cloudy. Comparative Example 2 An optical element was produced by the same operation as in Example 1 except that the polymer liquid crystal (Structural Formula I) synthesized in Example 1 was used and no annealing treatment was performed. The polymer liquid crystal layer after production was cloudy.

(Evaluation Result) Reproducibility Evaluation of Light Scattering Control A thermal printer (8
An area (transparent state) having a reduced light scattering property was provided by using dots / mm, 0.3 mJ / dot). Hot stamping (130 ° C) is also used to erase information on optical elements.
Was used to return to a state where the light scattering property was large (light scattering state). Further, the reflection optical density before and after the annealing treatment and after repeating recording / erasing once and 100 times were measured using X-rite968 (manufactured by X-rite), and the reproducibility and display quality were repeatedly measured. Was evaluated for stability. The evaluation results are shown in Table 1. The optical density in Table 1 means the reflection optical density.

[0026]

[Table 1]

As is clear from Table 1, in Examples 1 and 2, there was almost no change in the light scattering state (reflection optical density) before recording, after the first erasing, and after 100 times of erasing, which was excellent. There is reproducibility of whiteness. On the other hand, in Comparative Example 1,
Since the crosslinking reaction is not performed, the effect of annealing is not reflected in the repeatable optical density. Further, in the case of Comparative Example 2, since there is no effect of the annealing treatment, the reflection optical density is not optimized even in the initial state, and
There is no difference in the reflection optical density between before recording and after erasing, and the display (white turbidity) characteristic remains poor. From the above, it is clear that this optical element manufactured by the manufacturing method of the present invention is excellent in reproducibility of recording / erasing and display characteristics.

[0028]

According to the present invention, a multi-domain structure is controlled by heat-treating a polymer liquid crystal composition,
Since the composition is cross-linked while maintaining the multi-domain structure, in the obtained optical element, the domain diameter in the multi-domain structure of the polymer liquid crystal composition is controlled to a predetermined size and is effectively visible. The light is stabilized while being held in a scattered form. Therefore, the optical element manufactured by the method of the present invention has excellent optical characteristics due to the action of the stabilized multi-domain structure, and at the same time, it is repeatedly heated / cooled (recording / erasing).
In the above process, excellent reproducibility can be exhibited, and it is useful as an optical element such as a light control element, an optical recording medium, an optical modulation element, and a reversible display recording element.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an example of a light modulation element manufactured according to the present invention.

FIG. 2 is a schematic cross-sectional view of another example of the light modulation element manufactured by the present invention.

FIG. 3 is a schematic cross-sectional view of another example of the light modulation element manufactured according to the present invention.

FIG. 4 is a schematic cross-sectional view of still another example of the light modulation element manufactured according to the present invention.

[Explanation of symbols]

1 ... Substrate, 2 ... Polymer liquid crystal layer, 3 ... Protective layer, 4 ... Colored layer, 5 ... Light reflecting layer, 6 ... Transparent electrode.

Claims (7)

[Claims] 1. A method for producing an optical element, which comprises subjecting a polymer liquid crystal composition to a heat treatment to control a multi-domain structure and crosslinking the composition while maintaining the multi-domain structure. 2. The method of manufacturing an optical element according to claim 1, wherein the domain diameter at the maximum of the number of domain distributions in the multi-domain structure is 3 μm or less. 3. The domain diameter at the maximum of the number of distributed domains in the multi-domain structure is 200 nm to 1500.
The optical element manufacturing method according to claim 2, wherein the optical element has a thickness of nm. 4. The method of manufacturing an optical element according to claim 1, wherein the difference between the maximum domain diameter and the minimum domain diameter in the multi-domain structure is 5 μm or less. 5. The method for producing an optical element according to claim 1, wherein the polymer liquid crystal composition comprises a copolymer containing a liquid crystal monomer and a non-liquid crystal monomer. 6. The method for producing an optical element according to claim 1, wherein the polymer liquid crystal composition is heat-treated at a temperature at which the polymer liquid crystal composition exhibits a liquid crystal phase. 7. The method for producing an optical element according to claim 1, wherein the crosslinking is carried out at a temperature not higher than the liquid crystal phase-isotropic phase transition temperature of the polymer liquid crystal composition.