JP3360489B2 - Reversible display recording OHP sheet and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OHP (overhead projector) sheet capable of reversibly displaying, recording and erasing an image.

[0002]

2. Description of the Related Art Conventionally, a transparent or translucent plastic film is used for an OHP sheet, and an image is displayed and recorded on the OHP film by an electrophotographic system, an ink jet system, or the like. In recent years, there has been reported a display recording material capable of reversibly displaying and recording an image. For example, a composite membrane in which an organic low-molecular substance is dispersed in a polymer disclosed in JP-A-57-117140 and a plurality of polymers disclosed in JP-A-60-180887 are used. And a composite film using a leuco dye disclosed in JP-A-60-264285. These materials are all OH.
It can be used for a P-sheet, and can reversibly display / record / erase.

[0003]

However, when an image is displayed and recorded on a conventional OHP sheet by an electrophotographic method, an ink jet method, or the like, unless a special operation such as wiping off toner or ink using a solvent or the like is performed. It was difficult to erase the image, and it was difficult to rewrite the OHP sheet once used. For these reasons, OHP sheets on which images are displayed and recorded are often disposable, which is not preferable from the viewpoint of protecting the global environment and reusing resources. Further, Japanese Patent Application Laid-Open No.
No. 17140, JP-A-60-180887,
The reversible display recording material disclosed in JP-A-60-264285 and the like can be used as an OHP sheet and can rewrite an image.
The P sheet can be used repeatedly, and is preferable to the conventional OHP sheet from the viewpoint of protecting the global environment and reusing resources. However, in this case, the image density when projected by the overhead projector is insufficient, the image density is degraded due to repeated display recording / erasing of the image, or the image erasing performance is not sufficient and the image was recorded earlier. There is a problem that an image is projected.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems of the prior art. It is an object of the present invention to be able to repeatedly perform display recording / erasing of an image, to have a sufficient image density when projected by an overhead projector, and to reduce deterioration of the image density due to repeated display recording / erasing of an image. An object of the present invention is to provide a reversible display recording OHP sheet.

[0005]

The reversible display-recording OHP sheet of the present invention comprises a transparent or translucent film as a light-transmitting substrate and a high-density image capable of reversibly displaying and recording an image. It comprises a display recording layer made of molecular liquid crystal and a surface protective layer. In this configuration, a feature of the present invention is that the display recording layer is formed of a composition containing a polymer liquid crystal composed of a copolymer of at least two components of a mesogen monomer unit and a non-mesogen monomer unit, The composition has a multi-domain structure inside, and the composition is crosslinked.

First, a light-transmitting substrate used in the present invention for an image recording film will be described. As the transparent film material used for the translucent substrate in the present invention, a resin having good transparency and mechanically and thermally stable is preferable. Specifically, high molecular compounds such as polyester, acetate, polycarbonate, polysulfone, polyimide, polyethylene, polypropylene, polystyrene, and polyvinyl chloride are preferably used.

Next, the display recording layer according to the present invention will be described. The composition of the present invention is a composition containing a polymer liquid crystal composed of a copolymer of at least two components of a mesogen monomer unit and a non-mesogen monomer unit, and the composition has a multi-domain structure therein. And the composition is crosslinked. Here, the multi-domain structure is an aggregate of a plurality of minute domains, and various densities can be employed for the domain shown in a unit volume. In the present invention, it is preferable that such a domain has an optical anisotropy composed of an aggregate of mesogen molecules and aligned. Further, such a multi-domain structure is preferably formed by layer separation of at least two components of a liquid crystal component (mesogen component) and a non-liquid crystal component (non-mesogen component). Further, the direction of the optical anisotropy of each domain (the orientation direction of the liquid crystal molecules) is preferably random.

In the multi-domain structure, the preferred size of the domain diameter (liquid crystal domain diameter) formed by the liquid crystal component is such that the domain diameter at the maximum number of domain distributions is 0.2.
μm to 2.5 μm, more preferably 0.7 μm
The range is from μm to 2 μm, more preferably from 1 μm to 1.6 μm. In the multi-domain structure having the domain diameter distribution in the above range, since the visible light is highly scattered, the light shielding property is high when the light is collected at the expected angle of the OHP. Therefore, when projected as an OHP sheet, a sufficient image density can be obtained.

It is desirable that the average transmittance in the visible light range of the non-printed area is 10% or less, and the difference between the maximum transmittance and the minimum transmittance in the visible light range is 3% or less. If the average transmittance is larger than 10%, the contrast is small, and the visibility when projected as an OHP sheet is deteriorated. If the difference between the maximum transmittance and the minimum transmittance is more than 3%, the chromaticity of the non-printed portion becomes conspicuous, and the color when projected as an OHP sheet is significantly different from black. Further, in order to display black when projected by an overhead projector, the average transmittance in the visible light range of the OHP sheet is 4% or less, and the difference between the maximum transmittance and the minimum transmittance in the visible light range is 2% or less. It is desirable that

As the polymer liquid crystal used in the display recording layer, there are known a main chain type and a side chain type polymer liquid crystal in which a mesogen (molecule having liquid crystallinity) is bonded to a main chain or a side chain. In the present invention, a side chain type polymer liquid crystal is particularly preferably used. In the present invention, a polymer liquid crystal containing a reactive group as one component of the main chain or the side chain is preferably used. As the reactive group, a vinyl group, an acrylate group, a methacrylate group, a heterocyclic group such as an epoxy group, a polymerizable group such as an isocyanate group, a hydroxyl group, an amino group, an acid amide group, a thiol group, a carboxyl group, a sulfonic acid group, Phosphoric acid groups, metal alcoholate groups, magnesium halide (Grignard) groups and the like are preferred.

Next, a method for producing such a polymer liquid crystal will be described. Usually, the side chain type polymer liquid crystal can be produced by polymerizing a polymerizable mesogen compound or adding a mesogen compound capable of undergoing an addition reaction to a reactive polymer such as hydrogenated polysilicone. Such a technique is described in Makromol. Chem. , P273, 179 (1
978), Eur, Polym. J. , P651, 18
(1982), Mol. Cryst, Liq. Crys
t. , P167, 169 (1989). The polymer liquid crystal of the present invention can be produced by a similar method. Examples of the above-mentioned polymerizable mesogen monomer and mesogen compound capable of addition reaction include biphenyl, phenylbenzoate, cyclohexylbenzene, azoxybenzene, azobenzene, azomethine, phenylpyrimidine, diphenylacetylene, and biphenylbenzoate. , A rigid molecule (mesogen) such as cyclohexylbiphenyl, terphenyl, etc., through an alkyl spacer of a predetermined length, an acrylate ester,
Various compounds having a methacrylate group and a vinyl group bonded thereto can be mentioned as typical examples.

Representative structural examples of these compounds are shown below. These are typical examples of the structure, and the present invention is not limited thereto. CH ₂ ＣC (R _a ) -COO- (CH ₂ ) ₁ -OA CH ₂ ＣC (R _a ) -COO-A CH ₂ ＣＨCH- (CH ₂ ) ₁ -OA (wherein Ra represents _a hydrogen atom or a methyl group;
Represents an integer of from 30 to 30, and A represents a mesogen group of the following structural example. )

Embedded image (Wherein X and Y are each a single bond, -N = N-,
-N (→ O) = N-, -CH = N-, -N = CH-,-
COO -, - O (C = O) -, represents a group selected from an ethynylene group, R ¹ represents an alkoxy group, a halogen atom, a cyano group, a carboxyl group, a group selected from alkyl groups, p is 1 When p is 2 or more, each R ¹ may be different. )

The liquid crystal polymer according to the present invention can be produced by copolymerizing or co-adding a non-mesogenic compound containing at least the compound having a reactive group described above in addition to the mesogenic compound. Specific examples of the non-mesogenic compound having a reactive group used at this time 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-phenoxypropyl (meth) acrylate,
2- (meth) acryloxyethyl succinate, mono (meth) acrylate phthalate, 2- (meth) acryloxyethyl (2-hydroxyethyl) phthalate, 4-
(Meth) acryloxyalkyloxy-benzoic acid, glyceryl (meth) acrylate, hydroxy-substituted styrene, (meth) acrylamide, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate Glycidyl (meth) acrylate, 2-propen-1-ol, 5
-Hexen-1-ol and the like. After copolymerization or co-addition of these compounds, 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. What is illustrated here is an example, and there is no particular limitation.

Other non-mesogenic compounds other than the above include alkyl (meth) acrylates and derivatives thereof, styrene and derivatives thereof, (meth) acrylonitrile,
Examples thereof include vinyl chloride, vinylidene chloride, isoprene, vinylpyrrolidone, 1-hexane, and 1-octene.
These compounds are useful for controlling the multi-domain structure and thermal properties, and are preferably used. In addition, each of the above compounds may be used in a plural number.

The copolymerization or co addition amount of the polymer liquid crystal in a non meso Gen compounds described above, as the monomer units 0.1
Is preferably in the range of 20 mol%, the proportion of non-mesogenic compound having a reactive group of the non-meso Gen compound 100
The range of mol% to 1 mol% is preferred. The molecular weight of the polymer liquid crystal is in the range of 1,000 to 1,000,000 by weight average,
Particularly preferably, it is in the range of 10,000 to 500,000.

The composition for forming the display recording layer in the present invention needs to be crosslinked. Crosslinking is carried out by applying heat, ultraviolet rays, electron beams, etc. to a composition obtained by adding a catalyst or a polyfunctional reactive compound to the polymer liquid crystal obtained by the above-described production method, and the reaction in the polymer liquid crystal is performed. This is carried out by polymerizing a reactive group or by carrying out an addition reaction between a reactive group and a polyfunctional reactive compound. Various ultraviolet polymerization initiators, thermal polymerization initiators, etc. are used as catalysts, and polyfunctional isocyanate compounds, polyfunctional epoxy compounds, polyfunctional melamine compounds, polyfunctional aldehyde compounds, polyfunctional amino compounds, and polyfunctional are used as polyfunctional reactive compounds. Carboxy compounds and the like are preferably used. The addition amount of the catalyst and the polyfunctional reactive compound is from 0.01% by weight to 2% by weight based on the polymer liquid crystal.
A range of 0% by weight is preferred.

The thickness of the display recording layer is not particularly limited, but is preferably set in the range of 1 to 100 μm, particularly preferably in the range of 2 to 20 μm. The protective layer in the present invention desirably has high heat resistance, and a fluorine-based polymer, a silicone-based polymer, a thermosetting polymer, an ultraviolet-curable polymer, an electron beam-curable polymer, or the like can be used. The protective layer may be laminated in multiple layers,
The thickness of the protective layer is preferably selected from the range of 0.1 to 20 μm.

Next, a method for producing the reversible display recording OHP sheet of the present invention will be described. First, a polymer liquid crystal is formed on a transparent film substrate to form a display recording layer.
Next, by subjecting the polymer liquid crystal to a heat treatment, the size of the domain formed in the display recording layer is controlled to form a desired multi-domain structure. Thereafter, by applying heat, ultraviolet light, or the like, the reactive group in the polymer liquid crystal is polymerized, or the reactive group and the polyfunctional reactive compound are subjected to an addition reaction to crosslink the polymer liquid crystal. The cross-linking of the polymer liquid crystal is preferably performed after the above composition is applied on a translucent film substrate to form a film and the multi-domain structure is controlled. This is because, when the cross-linking of the polymer liquid crystal is completed, the control of the multi-domain structure becomes very difficult, and the desired optical characteristics cannot be obtained. According to the manufacturing method of the present invention, since the above-mentioned multi-domain structure can be controlled by a heat treatment, the domain diameter showing the maximum of the above-mentioned domain distribution is, for example, 0.7 μm to 2.0 μm.
A display recording layer having a multi-domain structure with excellent optical characteristics in the range of m can be easily produced. Next, a protective layer is formed on the display recording layer to form a reversible display record O.
An HP sheet is produced. The formation of the protective layer can be performed prior to the crosslinking of the polymer liquid crystal, that is, immediately after the heat treatment for controlling the multi-domain structure.

[0019]

The display recording layer of the reversible display recording OHP sheet of the present invention is formed of a composition containing a polymer liquid crystal comprising a copolymer of at least two components of a mesogen monomer unit and a non-mesogen monomer unit. When used as a material, the composition has a multi-domain structure showing excellent optical properties and the like inside. Reversible display record OHP of the present invention
The optical properties of the sheet are greatly affected by this multi-domain structure. Since this multi-domain structure can be controlled by a heat treatment, the heat treatment is performed and the domain diameter showing the maximum of the domain distribution in the multi-domain structure is 0.7 μm.
By controlling the thickness in the range of m to 2 μm, higher light shielding properties can be realized. In the present invention, since the polymer liquid phase composition is cross-linked after controlling the multi-domain structure, the controlled shape of the multi-domain structure is stably present. The curing by the cross-linking causes the image density of the reversible display recording OHP sheet to be lower than that of the image display / recording.
Deterioration does not occur even if erasure is repeated, so that stable image density reproducibility can be obtained. Further, high-speed and uniform erasing characteristics can be realized.

[0020]

The present invention will be specifically described below with reference to examples. Example 1 1.9 g of 4-acryloxyhexyloxy-4'-cyano-biphenyl as a mesogenic monomer and 0.2 g of 2-hydroxyethyl acrylate as a reactive monomer.
1 g was polymerized using AIBN as an initiator and tetrahydrofuran as a catalyst, and purified three times using ethyl alcohol to obtain 1.9 g of a polymer liquid crystal represented by the following structural formula (I).

Embedded image [Weight average molecular weight (polystyrene conversion by GPC):
150,000, Tg (glass transition point): 43 ° C., Ti
(Liquid crystal phase-isotropic phase transition point): 110 ° C.] To 1.0 g of the above polymer liquid crystal, 0.05 g of coronate HX (manufactured by Nippon Polyurethane), which is a polyfunctional isocyanate compound as a crosslinking agent, and methyl ethyl ketone as a solvent.
The solution obtained by adding 0 g was coated on a PET film having a thickness of 100 μm using a blade coater and dried to form a display recording layer having a thickness of about 6 μm. The obtained display recording layer was heated in an oven at 95 ° C. for 120 seconds to control the multi-domain structure. Next, the reaction was carried out in an oven at 60 ° C. for 72 hours for crosslinking. Further, an ultraviolet-curing composition (Aronix UV, manufactured by Toa Gosei Co., Ltd.) is applied and cured using a high-pressure mercury lamp to form a protective layer having a thickness of about 2 μm on the polymer liquid crystal layer, thereby displaying a reversible display. A recording OHP sheet was prepared. At this time, the domain diameter showing the maximum of the domain distribution in the multi-domain structure was 1.2 μm to 1.3 μm.

Example 2 As in Example 1, 1.8 g of the same mesogenic monomer as in Example 1, 0.1 g of 2-hydroxyethyl methacrylate as a reactive non-mesogenic monomer, and 0.1 g of butyl acrylate as a non-mesogenic monomer were used. By copolymerization, a polymer liquid crystal represented by the following structural formula (II) was synthesized.

Embedded image [Weight average molecular weight (polystyrene conversion by GPC):
100,000, Tg (glass transition point): 40 ° C, Ti
(Liquid crystal phase-isotropic phase transition point): 90 ° C.] 1.0 g of this polymer liquid crystal was mixed with 0.1 g of 4,4′-diphenylmethane diisocyanate, which is a polyfunctional cyanate compound, as a crosslinking agent.
03 g, methyl ethyl ketone (MEK) as a solvent3.
The solution obtained by adding 0 g was coated on a 100-μm-thick aluminum-evaporated PET film using a blade coater and dried to form a display recording layer having a thickness of about 6 μm. The obtained display recording layer was heated in an oven at 80 ° C. for 120 seconds to control the multi-domain structure. next,
The reaction was carried out in an oven at 60 ° C. for 72 hours for crosslinking. Further, a protective layer was formed in the same manner as in Example 1 to produce a reversible display recording OHP sheet. At this time, the domain diameter showing the maximum of the domain distribution in the multi-domain structure was 1.0 μm to 1.1 μm.

Example 3 As a process for preparing a reversible display recording OHP sheet, the applied display recording layer was reacted in a 60 ° C. oven for 72 hours to crosslink, and then heated in an 80 ° C. oven for 120 seconds. A reversible display recording OHP sheet was produced in the same manner as in Example 1 except that the multi-domain structure was controlled. At this time, the domain diameter showing the maximum of the domain distribution in the multi-domain structure is 0.4 μm to 0.5 μm.
Met.

Example 4 A reversible display recording OHP sheet was produced in the same manner as in Example 1 except that the control of the multi-domain structure was not performed. At this time, the domain diameter showing the maximum of the domain distribution in the multi-domain structure was 0.3 μm to 0.4 μm.

Comparative Example 1 Except that no polyfunctional isocyanate compound was added,
In the same manner as in Example 1, a reversible display recording OHP sheet was produced. At this time, the domain diameter showing the maximum of the domain distribution in the multi-domain structure is 1.2 μm to 1.3 μm.
Met.

(Evaluation Method) Recording was performed on a recording medium using a thermal printer (8 dots / mm, 0.3 mJ / dot) (the recording portion was transparent), and erasing was performed using a hot stamp (130 ° C.). . Before recording, after erasing,
The transmittance after repeating recording / erasing 100 times was measured using a spectrophotometer, and the reproducibility was evaluated repeatedly.
Table 1 shows the results.

[0026]

[Table 1] From the comparison between Examples 1 to 4 and Comparative Example 1, the effect of improving the reproducibility of transmittance due to crosslinking was confirmed, and particularly in the case of Examples 1 and 2, these effects are remarkable. In addition, it is confirmed that the transmittance is reduced when the multi-domain structure is controlled and the crosslinking is performed thereafter. Therefore, it can be seen that the reversible display recording OHP sheet produced by the production method of the present invention shows better optical characteristics.

[0027]

According to the reversible display recording OHP sheet of the present invention, the display recording layer contains a high-molecular liquid crystal composed of a copolymer of at least two components of a mesogen monomer unit and a non-mesogen monomer unit. Since it has a multi-domain structure and is formed of a cross-linked composition, it is possible to repeatedly perform display recording / erasing of an image, and has a sufficient image density when projected by an overhead projector, and Of the image density due to the repetition of the display recording / erasing of the image is small. In the present invention, since the display recording layer is heat-treated to control the multi-domain structure and then cross-linked, the domain diameter showing the maximum of the domain distribution in the multi-domain structure is in the range of 0.7 μm to 2 μm. It is possible to produce a reversible display recording OHP having a display recording layer exhibiting improved optical characteristics.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-187963 (JP, A) JP-A-8-160380 (JP, A) JP-A 8-160400 (JP, A) JP-A-8-160400 199167 (JP, A) JP-A-8-332778 (JP, A) JP-A-8-332779 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B41M 5/36 G02F 1 /13

Claims (5)

(57) [Claims] 1. A reversible display recording OHP sheet having a display recording layer provided on a light-transmitting substrate, wherein the display recording layer is formed of a mesogen monomer unit and a non-mesogen monomer unit. It is formed of a composition containing a polymer liquid crystal composed of a coalesced liquid, the composition has a multi-domain structure inside, and an image characterized by being cross-linked is reversibly displayed and recorded. Erasable reversible display recording OHP sheet. 2. The method according to claim 1, wherein the crosslinking is a polyfunctional isocyanate compound,
2. The reversible display recording OHP sheet according to claim 1, wherein the OHP sheet is formed by a reaction of a polyfunctional epoxy compound, a melamine compound or a polyfunctional amine compound. 3. The reversible display recording OHP sheet according to claim 1, wherein a domain diameter showing a maximum of a domain distribution in the multi-domain structure is in a range of 0.7 μm to 2 μm. 4. An average transmittance in a visible light range of 10%.
The reversible display recording OHP sheet according to claim 1, wherein the difference between the maximum transmittance and the minimum transmittance in the visible light range is 3% or less. 5. A layer formed on a substrate and comprising a composition comprising a polymer liquid crystal composed of a copolymer of at least two components of a mesogen monomer unit and a non-mesogen monomer unit, is subjected to a heat treatment. 2. The method for producing a reversible display recording OHP sheet according to claim 1, wherein the composition is crosslinked after controlling the domain structure.