JP2017116782A - Flexible display and method for using the display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flexible display that can maintain a deformed state and can restore the deformed state to the initial state before deformation.SOLUTION: A flexible display 1 includes a shape memory resin substrate 2 with a Ttrans higher than room temperatures and an electric heat converter 4. The flexible display 1 heats the shape memory resin substrate 2 by applying a voltage to the electric heat converter 4. The shape of the shape memory resin substrate 2 is deformed by a heat not lower than Ttrans and is maintained under a heat lower than Ttrans.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a flexible display and a method of using the same.

  In recent years, among various displays such as liquid crystal displays and organic EL displays, attention has been focused on flexible displays that are thin, light, flexible, and deformable. As such a flexible display, a flexible display using a plastic film formed of polyethylene terephthalate, polyethylene naphthalate, or the like as a substrate has been known (for example, Patent Document 1).

JP 2006-73636 A

The flexible display may be used in a deformed state (for example, a curved surface shape) or may be transported or transported after being deformed into a compact state, so that the deformed state can be maintained. There is a demand for flexible displays.
However, the conventional flexible display is deformed by applying an external force, and can be almost restored to its original shape (for example, a flat shape) by removing the external force, but is deformed if no external force is applied. There is a problem that the state cannot be maintained.

  The present invention has been made to solve the above problems, and provides a flexible display capable of maintaining a deformed state and recovering the original shape before the deformation and a method of using the same. The purpose is to do.

As a result of continual research, the present inventors have used a shape memory resin having a temperature at which solidification-softening transition occurs (Ttrans) higher than room temperature as a substrate, and combining this substrate with an electrothermal conversion element, the above-mentioned The present inventors have found that the problem can be solved and have completed the present invention.
That is, the present invention comprises a shape memory resin substrate having a Ttrans higher than room temperature and an electrothermal conversion element, and the shape memory resin substrate is heated by applying a voltage to the electrothermal conversion element. It is a display.
In addition, the present invention is characterized in that the flexible display heats the shape memory resin substrate to a temperature equal to or higher than Ttrans by applying a voltage to the electrothermal conversion element, and recovers the original shape stored. This is a method of using a flexible display.

  ADVANTAGE OF THE INVENTION According to this invention, while maintaining the deformed state, the flexible display which can be recovered to the original shape before a deformation | transformation, and its usage method can be provided.

It is a cross-sectional schematic diagram of the flexible display of this invention.

  The flexible display of the present invention includes a shape memory resin substrate having a Ttrans higher than room temperature and an electrothermal conversion element, and the shape memory resin substrate is heated by applying a voltage to the electrothermal conversion element.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of a flexible display and a method of using the flexible display according to the invention will be described with reference to the drawings.
FIG. 1 is a schematic cross-sectional view of the flexible display of the present invention. In FIG. 1, a flexible display 1 includes a shape memory resin substrate 2, an electrothermal conversion element 4 provided on the shape memory resin substrate 2, and a display element 3 provided on the electrothermal conversion element 4. .
Here, in the present specification, the “shape memory resin substrate 2” means a substrate formed from a shape memory resin. Shape memory resin can be deformed and fixed from its original shape (permanent shape) to another temporary shape, and usually retains its temporary shape, but spontaneously changes to a permanent shape by stimuli such as heat. It means a resin having the property of recovering automatically. The permanent shape of the shape memory resin is imparted by crosslinking the polymer chain. The cross-linked structure is not necessarily a chemical cross-link, and may be a pseudo cross-link by physical interaction as long as the relaxation time is sufficiently long. The resin having such a crosslinked structure is applied with an external force at a temperature higher than Ttrans, that is, a temperature capable of performing segmental movement of the molecular chain, deformed, and then cooled to a temperature lower than Ttrans to freeze the segmental movement. Thus, the temporary shape is fixed. When the shape memory resin is heated to a temperature equal to or higher than Ttrans and segment motion is enabled again, it spontaneously recovers to its original permanent shape. The temperature at which the shape memory resin is solidified and softened (Ttrans) is the temperature at which the cross-linked chain is solidified, and corresponds to the glass transition temperature (Tg) for glassy polymers and the melting temperature (Tm) for crystalline polymers. The shape memory resin is also referred to as a shape memory polymer.

The shape memory resin substrate 2 has Ttrans higher than room temperature, preferably 40 ° C to 80 ° C.
Here, in this specification, “room temperature” generally means 25 ° C.
Further, in this specification, “Ttrans” means a value measured by differential scanning calorimetry (DSC) based on “Measurement method of plastic transition temperature” of JIS K7121.
The shape memory resin substrate 2 is deformed into a desired shape by heating the shape memory resin substrate 2 to a temperature higher than Ttrans and deforming it into a desired shape and then cooling it to a temperature lower than Ttrans. Can be maintained. In addition, the characteristic in which the shape is maintained by cooling to a temperature lower than Ttrans while maintaining the shape given at a temperature higher than Ttrans is hereinafter referred to as “shape fixability”.
In addition, the shape memory resin substrate 2 fixed in a deformed state can be recovered to a memorized shape (original shape before deformation) by heating to a temperature higher than Ttrans. In addition, the characteristic which returns to the memorize | stored shape by heating to such temperature higher than Ttrans is called "shape recovery property" below.

  The thickness of the shape memory resin substrate 2 is not particularly limited as long as the flexibility is not impaired, but is generally 20 μm to 2000 μm, preferably 30 μm to 1500 μm, and more preferably 40 μm to 1000 μm.

The type of the shape memory resin used for the shape memory resin substrate 2 is not particularly limited as long as Ttrans is higher than room temperature, but polynorbornene, trans polyisoprene, styrene-butadiene copolymer, polyurethane, an acrylic crosslinked material, or the like is used. be able to. Among these, the acrylic crosslinked product is excellent in shape memory characteristics and transparency, and can be said to be a material suitable for the use of the present invention. The acrylic crosslinked product may be produced by a method known in the technical field, or a commercially available product may be used.
The acrylic crosslinked product is generally a homopolymer or copolymer of an alkyl (meth) acrylate.
Here, “(meth) acrylic acid alkyl ester” in this specification means both acrylic acid alkyl ester and methacrylic acid alkyl ester.

  As alkyl acrylates, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, n-pentyl acrylate, n-hexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, n-decyl acrylate, n-dodecyl acrylate , N-lauryl acrylate, n-octadecyl acrylate and the like. These can be used alone or in combination of two or more.

  Examples of methacrylic acid alkyl esters include methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-pentyl methacrylate, n-hexyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, n-decyl methacrylate, and n-dodecyl methacrylate. , N-lauryl methacrylate, n-octadecyl methacrylate and the like. These can be used alone or in combination of two or more.

Among homopolymers or copolymers of (meth) acrylic acid alkyl ester, from the viewpoint of stably obtaining Ttrans (= Tg) higher than room temperature, it is a homopolymer or copolymer of methacrylic acid alkyl ester. Is preferred.
In the case of a copolymer of (meth) acrylic acid alkyl ester, the type is not particularly limited, and may be a random copolymer, an alternating copolymer, a block copolymer, or a graft copolymer.

The shape memory resin substrate 2 is preferably transparent when the shape memory resin substrate 2 is disposed on the display surface side of the display element 3 or when applied to a transparent display.
As used herein, “transparent” means transparent to visible light.

A homopolymer or copolymer of (meth) acrylic acid alkyl ester, together with (meth) acrylic acid alkyl ester, using a crosslinking agent and a polymerization initiator as raw materials, emulsion polymerization, suspension polymerization, solution polymerization, bulk polymerization, etc. It can manufacture by the well-known method of these. For example, after mixing (meth) acrylic acid alkyl ester, a crosslinking agent and a polymerization initiator, the mixture may be poured into a predetermined mold or coated on a support to form a film and polymerized and crosslinked. .
The polymerization conditions are not particularly limited as long as they are appropriately adjusted according to the type of raw material used, but the polymerization temperature is generally 50 ° C. to 200 ° C., preferably 60 ° C. to 150 ° C., and the polymerization time is generally 0.5 hours to 48 hours, preferably 1 to 24 hours.
Further, the crosslinking of the polymer is performed after the polymerization or simultaneously with the polymerization. What is necessary is just to heat to predetermined temperature when bridge | crosslinking is performed after superposition | polymerization. The crosslinking time and the crosslinking temperature are not particularly limited as long as they are appropriately adjusted according to the type of the crosslinking agent to be used, but the crosslinking temperature is generally 100 ° C. to 250 ° C. and the crosslinking time is generally 0.5 hours to 5 hours.

  As the crosslinking agent, ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, neo Examples include pentyl glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and the like. These can be used alone or in combination of two or more. The blending ratio of the crosslinking agent is not particularly limited as long as it is appropriately adjusted according to the type of the (meth) acrylic acid alkyl ester to be used. % To 20 mol%, preferably 0.3 mol% to 15 mol%, more preferably 0.5 mol% to 10 mol%.

  As polymerization initiators, benzoyl peroxide, methylcyclohexanone peroxide, cumene hydroperoxide, diisopropylbenzene peroxide, di-t-butyl peroxide, t-butylperoxybenzoate, diisopropylperoxycarbonate, t-butylperoxy Examples thereof include radical polymerization initiators such as organic peroxides such as isopropyl monocarbonate and azo compounds such as 2,2′-azobisisobutyronitrile (AIBN). These can be used alone or in combination of two or more. The blending ratio of the polymerization initiator is not particularly limited as long as it is appropriately adjusted according to the type of the (meth) acrylic acid alkyl ester and the crosslinking agent to be used, but with respect to the total of the (meth) acrylic acid alkyl ester and the crosslinking agent. Generally, it is 0.01 mol% to 10 mol%, preferably 0.03 mol% to 5 mol%, more preferably 0.05 mol% to 3 mol%.

  In the case of producing a copolymer of (meth) acrylic acid alkyl ester, the blending ratio of each (meth) acrylic acid alkyl ester is such that Ttrans (= Tg) of the copolymer is higher than room temperature. There is no particular limitation.

  The display element 3 is not particularly limited, and those known in the technical field can be used. Examples of the display element 3 include an organic EL display element, a liquid crystal display element, and electronic paper.

The electrothermal conversion element 4 is a member for heating the shape memory resin substrate 2 to a temperature higher than Ttrans. The electrothermal conversion element 4 is not particularly limited as long as it can generate heat upon application of a voltage. The shape of the electrothermal conversion element 4 is not particularly limited, but is preferably a flexible film from the viewpoint of uniformly heating the shape memory resin substrate 2. Such an electrothermal conversion element 4 is generally marketed under the names of a film heater, a sheet heater, a panel heater, and the like, and these commercial products can be used.
The electrothermal conversion element 4 is preferably transparent when the electrothermal conversion element 4 is arranged on the display surface side of the display element 3 or when applied to a transparent display. Examples of the transparent electrothermal conversion element 4 include a transparent resin film such as PET or PEN and an ITO film formed on the transparent resin film.

Since the flexible display 1 of the present invention has the shape memory resin substrate 2 having both shape fixability and shape recoverability, the deformed state is maintained and restored to the original shape before the deformation. Is possible.
1 shows an example in which one shape memory resin substrate 2 is provided. However, when the shape fixability and shape recoverability of the shape memory resin substrate 2 are insufficient, the shape memory resin substrate 2 is used. The number of is not particularly limited, and there may be a plurality of sheets. Moreover, in the flexible display 1 of FIG. 1, although the example which provided the electrothermal conversion element 4 adjacent to the shape memory resin substrate 2 was shown, if the heat from the electrothermal conversion element 4 can be transmitted to the shape memory resin substrate 2, it will be shown. The electrothermal conversion element 4 and the shape memory resin substrate 2 may not be adjacent to each other. In the flexible display 1 of FIG. 1, the example in which the shape memory resin substrate 2 is provided as a member separate from the display element 3 is shown, but the shape memory resin substrate 2 may be used as the substrate of the display element 3. .

In the flexible display 1 of the present invention, the shape memory resin substrate 2 is heated to a temperature higher than Ttrans by applying a voltage to the electrothermal conversion element 4 and then deformed, and the shape memory is maintained while the deformed state is maintained. The shape of the resin substrate 2 can be fixed by cooling the resin substrate 2 to a temperature lower than Ttrans. Therefore, the flexible display 1 of the present invention can be used in a deformed state, and can be transported or transported.
Moreover, the flexible display 1 of this invention can heat the shape memory resin board | substrate 2 to temperature higher than Ttrans by applying a voltage to the electrothermal conversion element 4, and can make it memorize | store in the memorize | stored original shape. Therefore, the flexible display 1 of the present invention can be restored to the original shape even if it is deformed into various shapes.

Although the following experiment demonstrates the detail of this invention, this invention is not limited by these.
(1) Sample A: Preparation of polybutyl methacrylate (PBMA) Butyl methacrylate (BMA) was placed in a flask, and ethylene glycol dimethacrylate (EGDMA) was added as a crosslinking agent. The blending ratio of the cross-linking agent was 1.0% by mole with respect to BMA. Next, 2,2-azobisisobutyronitrile (AIBN) was added as a polymerization initiator. Here, the blending ratio of the polymerization initiator was set to 0.1 mol% as an outer ratio with respect to the total of butyl methacrylate and EGDMA. Next, after nitrogen was bubbled through the flask for 10 minutes to remove oxygen, the flask was poured into a mold and placed in a 85 ° C. constant temperature bath for polymerization for 24 hours. Thereafter, the temperature was raised to 120 ° C. and cross-linking was performed for 1 hour to obtain a plate-like polybutyl methacrylate having a thickness of 1 mm. It was 36 degreeC when Tg of the obtained polybutylmethacrylate was measured by said method.

(2) Sample B: Preparation of random copolymer of butyl methacrylate (BMA) and methyl methacrylate (MMA) BMA and MMA were placed in a flask, and ethylene glycol dimethacrylate (EGDMA) was added as a crosslinking agent. Here, the blending ratio of MMA is 9 mole% of the molar ratio of MMA with respect to the sum of BMA and MMA, and the blending ratio of the cross-linking agent is 1.0 mole% of the total of BMA and MMA. . Next, after nitrogen was bubbled through the flask for 10 minutes to remove oxygen, the flask was poured into a mold and placed in a 85 ° C. constant temperature bath for polymerization for 24 hours. Thereafter, the temperature was raised to 120 ° C. and crosslinked for 1 hour to obtain a plate-like random copolymer having a thickness of 1 mm. It was 47 degreeC when Tg of the obtained copolymer was measured by said method.

(3) Sample C: Preparation of random copolymer of butyl methacrylate (BMA) and methyl methacrylate (MMA) Regarding the blending ratio of MMA, except that the molar ratio of MMA to the total of BMA and MMA was changed to 17 mol% Obtained a plate-like random copolymer having a thickness of 1 mm in the same manner as Sample B. It was 53 degreeC when Tg of the obtained copolymer was measured by said method.
(4) Sample D: Preparation of random copolymer of butyl methacrylate (BMA) and methyl methacrylate (MMA) The blending ratio of the cross-linking agent was changed to 3.0 mol% as an external ratio with respect to the total of BMA and MMA. Except that, a plate-like random copolymer having a thickness of 1 mm was obtained in the same manner as Sample C. It was 59 degreeC when Tg of the obtained copolymer was measured by said method.

(5) Sample E: Preparation of random copolymer of butyl methacrylate (BMA) and methyl methacrylate (MMA) The blending ratio of the cross-linking agent was changed to 5.0 mol% as an external ratio with respect to the total of BMA and MMA. Except that, a plate-like random copolymer having a thickness of 1 mm was obtained in the same manner as Sample C. It was 66 degreeC when Tg of the obtained copolymer was measured by said method.
(6) Sample F: Preparation of random copolymer of butyl methacrylate (BMA) and methyl methacrylate (MMA) Regarding the blending ratio of MMA, except that the molar ratio of MMA to the total of BMA and MMA was changed to 33 mol% Obtained a plate-like random copolymer having a thickness of 1 mm in the same manner as Sample B. It was 64 degreeC when Tg of the obtained copolymer was measured by said method.

About each sample obtained above, shape fixability and shape recoverability were evaluated. Evaluation was performed according to the following procedure.
(I) A test piece of 50 mm × 3 mm × 1 mm was cut out from each sample.
(Ii) mounting the specimen in a uniaxial stretching machine to measure the length L ₀ of the beginning of the test piece.
(Iii) The test piece was put into a thermostat set to each deformation temperature (T _def ) and heated for 10 minutes. T _def was set to Tg + 10 ° C. for each sample.
(Iv) Grant 45 mm / min elongation deformation at a strain rate of the specimen to measure the length L ₁ at this time.
(V) The test piece was cooled for 30 minutes at a fixed temperature (T _fix ) with the stress (iv) applied.
(Vi) except stress, the test piece was placed in a Teflon (registered trademark) petri _dish, allowed to stand for 30 minutes at _{T fix,} to measure the length _{L 2} of the test piece.
(Vii) It was put in a thermostatic bath set to T _fix and heated at a constant rate of temperature increase. Taken out of the test piece every time the temperature of the thermostatic chamber is raised 5 ° C., it was measured length L _3.

The shape fixing rate (R _f ), which is an evaluation index of shape fixability, and the shape recovery rate (R _r ), which is an evaluation index of shape recoverability, were calculated by the following equations.
R _f (%) = (L ₂ −L ₀ ) / (L ₁ −L ₀ ) × 100
R _r (%) = (L ₁ −L ₃ ) / (L ₁ −L ₀ ) × 100
In this evaluation, the shape fixing rate (R _f ) needs to be 85% or more from the viewpoint of practicality, preferably 90%%, more preferably 92% or more. Further, the shape recovery rate (R _r ) needs to be 90% or more from the viewpoint of practicality, preferably 92%, and more preferably 93%. The evaluation results are shown in Table 1.

As shown in Table 1, each sample had a high shape fixing rate (R _f ) and a shape recovery rate (R _r ).
As can be seen from the above results, according to the present invention, it is possible to provide a flexible display capable of maintaining a deformed state and recovering the original shape before the deformation and a method of using the flexible display.

  1 flexible display, 2 shape memory resin substrate, 3 display element, 4 electrothermal conversion element.

Claims (9)

  A flexible display comprising a shape memory resin substrate and an electrothermal conversion element having a Ttrans higher than room temperature, and the shape memory resin substrate is heated by applying a voltage to the electrothermal conversion element.   2. The flexible display according to claim 1, wherein the shape memory resin substrate has a Ttrans of 40 ° C. to 80 ° C. 3.   The flexible display according to claim 1, wherein the shape memory resin substrate and the electrothermal conversion element are transparent.   The flexible display according to claim 1, wherein the shape memory resin substrate is an acrylic cross-linked body.   The flexible display according to claim 4, wherein the acrylic crosslinked product is a homopolymer or a copolymer of an alkyl (meth) acrylate.   The flexible display according to claim 4 or 5, wherein the acrylic crosslinked product is a homopolymer of butyl methacrylate or a copolymer of butyl methacrylate and methyl (meth) acrylate.   The flexible display according to claim 1, wherein the electrothermal conversion element includes a transparent resin film and an ITO film formed on the transparent resin film.   It is a usage method of the flexible display as described in any one of Claims 1-7, Comprising: By applying a voltage to the said electrothermal conversion element, the said shape memory resin substrate is heated to temperature higher than Ttrans, and the said flexible display Use of a flexible display characterized by fixing the shape of the flexible display by cooling the shape memory resin substrate to a temperature higher than Ttrans while keeping the deformed state after the display is deformed Method.   It is a usage method of the flexible display as described in any one of Claims 1-7, Comprising: The said shape memory resin substrate is heated to temperature higher than Ttrans by applying a voltage to the said electrothermal conversion element, and is memorize | stored. A method of using a flexible display, characterized by restoring the original shape.

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