Reinforcement plate for flexible display

Abstract

To provide a reinforcement plate for a flexible display which is not separated from an adhesive on the plate if the plate is repeatedly bent in a twisting direction.SOLUTION: The reinforcement plate for a flexible display includes a reinforcement plate body; and a first adhesive layer on a first surface of the reinforcement plate body. The aspect ratio (Str) of the surface property determined according to ISO 25178-6:2010 in the first surface of the reinforcement plate body is at least 0.3.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a reinforcing plate for a flexible display.

Background Art

[0002] In recent years, display devices represented by personal computers, tablets, and smartphones have been accelerating the development of foldable (foldable) and rollable devices in order to achieve both miniaturization and an increase in the display area. Flexible displays incorporated into such devices are also required to have performance that can withstand the repeated bending and rolling loads.

[0003] For example, in Patent Document 1, many flexible displays are composed of two flat display portions and a bending portion connecting them. In the flat portion and the bending portion, a reinforcing plate made of a thin plate such as stainless steel is used to ensure strength, and components such as a display portion and a signal circuit are adhered via an adhesive. And an invention is disclosed in which a cavity portion is formed in the bending portion to suppress adhesive failure in the bending portion of the reinforcing plate.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, forming cavities only in the bent portions complicates the lamination process and increases costs. On the other hand, if an adhesive layer is formed on the entire flat portion and the bent portion to reduce costs, a problem occurs in that peeling easily occurs between the adhesive and the reinforcing plate when bending is repeated. In particular, when repeating bending with torsional shear different from bending in a certain direction such as rollable, peeling easily occurs between the reinforcing plate and the adhesive laminated thereon, and a flexible display that does not peel from the reinforcing plate over a long period of time is required.

[0006] An object of the present disclosure is to realize a reinforcing plate for a flexible display that has good bendability in the torsional direction and does not cause peeling between the reinforcing plate and the adhesive layer even when the above bending is repeated.

Means for Solving the Problems

[0007] The present disclosure includes a reinforcing plate body, a first adhesive layer provided on a first surface of the reinforcing plate body, and relates to a reinforcing plate for a flexible display, wherein an aspect ratio (Str) of surface properties obtained in accordance with ISO 25178-6:2010 on the first surface of the reinforcing plate body is 0.3 or more.

[0008] The present disclosure relates to the reinforcing plate for a flexible display, wherein an arithmetic mean height (Sa) on the first surface of the reinforcing plate body is 0.01 μm or more.

[0009] The present disclosure relates to the reinforcing plate for a flexible display, wherein a minimum autocorrelation length (Sal) obtained in accordance with ISO 25178-6:2010 on the first surface of the reinforcing plate body is 17 μm or less.

[0010] The present disclosure relates to the reinforcing plate for a flexible display, wherein the material of the reinforcing plate body is stainless steel.

[0011] The present disclosure relates to a reinforcing plate for a flexible display, wherein the thickness of the reinforcing plate body is 15 μm to 160 μm.

Effects of the Invention

[0012] According to the reinforcing plate for a flexible display of the present disclosure, even when repeated bending in the torsional direction is performed, peeling between the reinforcing plate and the adhesive layer does not occur.

Brief Description of the Drawings

[0013]

Figure 1

Modes for Carrying Out the Invention

[0014] Hereinafter, the present disclosure will be described in detail. As long as it conforms to the gist of the present disclosure, other embodiments are also included in the scope of the present disclosure. In addition, the numerical range specified using "~" in this specification includes the numerical values described before and after "~" as the range of the lower limit value and the upper limit value. In addition, in this specification, "film" and "sheet" are synonymous and are not distinguished by thickness. In addition, various components appearing in this specification may be used alone or in combination of two or more, unless otherwise noted. The numerical values described in this specification refer to the values obtained by the method described in [Examples] described later.

[0015] As shown in FIG. 1, in a laminate 1 for a flexible display, an adhesive layer 11 is laminated on one surface of a reinforcing plate body 10, and a display portion 12 is laminated via this. The laminate of the reinforcing plate body 10 and the adhesive layer 11 is a reinforcing plate 20 for a flexible display.

[0016] The reinforcing plate body 10 has an aspect ratio (Str) of the surface property on the first surface 10A in contact with the adhesive layer 11 of 0.3 or more. By setting the Str of the first surface 10A to 0.3 or more, the adhesive layer is less likely to peel even when repeated bending or torsion is performed.

[0017] Str is a parameter representing the direction dependence of the surface properties and takes a value from 0 to 1.0. As the value approaches 1.0, the direction dependence of the surface properties decreases. In the case where linear unevenness is provided in one direction like hairline processing, even on a surface with a large arithmetic mean height (Sa), Str becomes almost 0. When the value of Str is small, the adhesive layer is likely to peel off after repeated bending and twisting. On the other hand, the inventors of the present application have found that when the value of Str is 0.3 or more, preferably 0.4 or more, more preferably 0.5 or more, peeling of the adhesive layer is suppressed after repeated bending and twisting. When the value of Str is 0.3 or more, the direction dependence of the surface unevenness becomes small, and the direction dependence of the anchoring effect of the adhesive layer adhered to the surface also decreases, so it is considered that a strong adhesive force can be maintained against deformation from any angle. It is preferable that the value of Str is large, and being closer to 1.0 can further reduce peeling. From the viewpoint of the productivity of the reinforcing plate for flexible displays, the maximum value is preferably less than 1.0, more preferably 0.99 or less. Str can be measured in accordance with ISO25178-6:2010 as described in the examples.

[0018] If Str is larger than a predetermined value, the value of Sa on the first surface 13A in contact with the adhesive layer 11 of the reinforcing plate 10 does not matter, but by setting the value of Sa to preferably 0.01 μm or more, more preferably 0.04 μm or more, the anchoring effect of the adhesive layer is enhanced and peeling of the adhesive layer after repeated bending and twisting can be reduced. Sa can be measured in accordance with ISO25178-6:2010 as described in the examples.

[0019] The material used for the reinforcing plate body 10 is preferably a resin film or a metal plate, and a metal plate is preferable from the viewpoint of durability against bending and twisting. As the metal plate, for example, materials including stainless steel, nickel, copper, silver, tin, gold, palladium, aluminum, chromium, titanium, and zinc can be used, and stainless steel is preferable from the viewpoint of corrosion resistance.

[0020] The resin film is not particularly limited, and for example, a resin film formed of polyethylene terephthalate, polypropylene, crosslinked polyethylene, polyester, polybenzimidazole, polyimide, polyimide amide, polyether imide, or polyphenylene sulfide can be used.

[0021] The thickness of the reinforcing plate body 10 is not particularly limited, but from the viewpoint of reinforcing the members constituting the flexible display, it is preferably 15 μm or more, more preferably 30 μm or more, and from the viewpoint of flexibility such as bendability and winding property, it is preferably 160 μm or less, more preferably 140 μm or less, and even more preferably 100 μm or less.

[0022] The Str of the reinforcing plate can be adjusted by performing surface roughening treatment in at least two directions. In the case of the commonly performed roll-to-roll hairline processing, it is roughening in one direction, and even if Sa can be increased, it is difficult to increase Str. On the other hand, for example, Str can be increased by processing using both a roll provided with irregularities extending in a first direction and a roll provided with irregularities extending in a second direction intersecting the first direction.

[0023] Furthermore, it is preferable that the minimum autocorrelation length (Sal) of the surface on the first surface 10A in contact with the adhesive layer 11 of the reinforcing plate body 10 is 17 μm or less. The minimum autocorrelation length Sal of the reinforcing plate surface is a value defined in accordance with ISO 25178-6:2010 and is an evaluation index representing the fineness. Specifically, it is a quantification of the density of the uneven state of the reinforcing plate surface in units of length, and it can be said that the smaller the value of the minimum autocorrelation length Sal, the finer the appearance. The minimum autocorrelation length Sal of the surface of the reinforcing plate is more preferably 1 to 15 μm, and even more preferably 2 to 11 μm. When Sal is 17 μm or less, the surface of the reinforcing plate becomes finer, and since the adhesive layer adheres following the fine irregularities, it is possible to further reduce the peeling of the adhesive layer after repeated bending and twisting.

[0024] The Sal of the reinforcing plate can be adjusted by roughening treatment such as etching and physical polishing.

[0025] The adhesive layer 11 only needs to contain an adhesive. The adhesive is not particularly limited as long as it is a resin having adhesiveness, and examples thereof include those composed of acrylic resins, urethane resins, silicone resins, etc., and acrylic resins or urethane resins are preferred. Usually, the adhesive layer 11 can be formed on a release film.

[0026] The adhesive layer 11 may further contain additives such as tackifying resins, fillers, crosslinking agents, crosslinking accelerators, anti-aging agents, antioxidants, plasticizers, softeners, surfactants, antistatic agents, surface lubricants, leveling agents, light stabilizers, ultraviolet absorbers, polymerization inhibitors, foil-like substances, rust preventives, colorants (pigments and dyes), etc., within a range that does not impair the effects of the present invention. Each of the above additives may be used alone or in combination of two or more.

[0027] The reinforcing plate 20 for a flexible display can be manufactured, for example, as follows. First, an adhesive is coated on a release substrate (separate film) to form the adhesive layer 11. Next, by laminating and adhering the adhesive layer 11 and the reinforcing plate 10, a reinforcing plate 20 for a flexible display with a release substrate having a structure of reinforcing plate body 10 / adhesive layer 11 / release substrate can be obtained.

[0028] As the release substrate, one having a silicone-based or non-silicone-based release agent applied on the surface on the side where the adhesive layer 11 of a base film such as polyethylene terephthalate or polyethylene naphthalate is formed can be used. The thickness of the release substrate is not particularly limited and can be determined as appropriate considering ease of use.

[0029] The thickness of the adhesive layer 11 is preferably 15 μm to 100 μm. By setting it to 15 μm or more, sufficient adhesive force can be ensured and sufficient adhesion to the reinforcing plate body can be obtained. Also, by setting it to 100 μm or less, it is possible to meet the requirements of bendability and thinning, which is also advantageous in terms of cost.

[0030] The bonding of the flexible display reinforcing plate 20 to the display portion 12 can be performed, for example, as follows. Peel off the release substrate from the reinforced laminate 20 with a release substrate having a structure of the reinforcing plate body 10 / adhesive layer 11 / release substrate manufactured by the above method, and laminate and adhere the exposed adhesive layer 11 and the display portion 12. Then, it is preferably cured. Curing is preferably performed at 23°C and a relative humidity of 50% (hereinafter 50% RH) for 7 days.

[0031] Examples of the display portion include an acrylic plate having a transparent conductive film, a polycarbonate plate, a cycloolefin film, glass, or polyethylene terephthalate, etc. Also, examples include a polarizing film, a retardation film, an elliptical polarizing film, an antireflection film, a brightness enhancement film, etc.

Example

[0032] Hereinafter, the flexible display reinforcing plate of the present disclosure will be described in more detail using examples. The following examples are illustrative and are not intended to limit the present invention.

[0033] (Preparation of Adhesive) 100 parts by weight of an acrylic adhesive (manufactured by Toyochem Co., Ltd., product name: Olivine BPS5762K, solid content concentration: 45.5% by weight), 1.4 parts by weight of a crosslinking agent (manufactured by Toyochem Co., Ltd., product name: BXX5627, solid content concentration: 50% by weight), and 30.6 parts by weight of MEK were mixed to prepare an adhesive coating solution with a solid content concentration of 35%.

[0034] The above-mentioned adhesive was coated on a release sheet (made of polyethylene terephthalate) with a thickness of 38 μm using a comma coater so that the thickness after drying would be 25 μm, and dried at 100 °C for 2 minutes to form an adhesive layer. Next, a release sheet (made of polyethylene terephthalate) with a thickness of 50 μm was laminated on this adhesive layer, and cured for 1 week under the conditions of a temperature of 23 °C and 50% RH to obtain an adhesive sheet having a structure of "release sheet / adhesive layer / release sheet".

[0035] (Example 1) As the reinforcing plate body, a SUS304 plate with a surface roughening treatment and a thickness of 30 μm was used. Str was 0.3, Sa was 0.01 μm, and Sal was 18 μm.

[0036] <Measurement of surface properties> Str, Sa, and Sal on the surface of the reinforcing plate body were measured using a confocal microscope (OPTELICS HYBRID manufactured by Lasertec), and then the surface inclination correction was performed using data analysis software (LMeye7), and Str, Sa, and Sal were determined in accordance with ISO 25178-6:2010. The measured values were obtained at three arbitrary locations on the surface of the reinforcing plate body, and the average was calculated.

[0037] <Bending suitability> The release sheet with a thickness of 38 μm was peeled off from the prepared adhesive sheet, and the exposed adhesive layer was adhered to the surface-treated surface of the reinforcing plate body using a laminator in an atmosphere of 25°C and 50% RH. Then, the other release sheet was peeled off and laminated to a PET film with a thickness of 188 μm using a laminator to obtain a test laminate composed of a PET film / adhesive layer / reinforcing plate body. Next, the test laminate was subjected to a bending test using a bending tester (manufactured by Yuasa System Equipment Co., Ltd.) at 25°C and 50% RH as a normal test, and the inner diameter (diameter) at the time of bending was set to 3 mm. Bending and 180° opening were repeated 300,000 cycles as one cycle. The lifting and peeling of the adhesive layer at the bent portion after the test were visually confirmed and evaluated according to the following criteria. Appearance: The presence or absence of bubbles and the presence or absence of lifting and peeling of the adhesive layer of the test laminate were visually evaluated under the following conditions. A: There is no lifting, peeling, or whitening at the bent portion. Excellent. B: There is no lifting or peeling at the bent portion, but there is slight whitening. Good. NG: Lifting or peeling occurs at the bent portion, or there is significant whitening. There is a problem in practical use.

[0038] <Torsion suitability> In the same procedure as the bending test, a test laminate was created. The test laminate was twisted left and right using a flat body unloaded torsion tester (manufactured by Yuasa System Equipment Co., Ltd.) in an atmosphere of 25°C and 50% RH, and then repeated 200,000 cycles as one cycle until it returned to the state before twisting. The test was conducted with N = 5, and the appearance after the test was evaluated. The evaluation criteria are as follows. A: No generation of bubbles, lifting, or peeling was observed in all 5 times. Excellent. B: Generation of bubbles, lifting, or peeling was slightly observed only once. Good. C: Generation of bubbles, lifting, or peeling was slightly observed at a frequency of 2 or 3 times. There is no problem in practical use. NG: Generation of bubbles, lifting, or peeling was slightly observed at a frequency of 4 or more times, or generation of bubbles, lifting, or peeling was significantly observed even once. There is a problem in practical use.

[0039] (Examples 2 to 10, Comparative Example 1) As shown in Table 1, reinforcing plates with various Str, Sal, and Sa materials were prepared, and the bending suitability and torsional suitability were measured in the same manner as in Example 1.

[0040] The characteristics and measured values for each example and comparative example are summarized in Table 1.

[0041]

Table 1

Industrial Applicability

[0042] The reinforcing plate for a flexible display of the present disclosure has good adhesion to the adhesive layer even at bent or twisted portions, and is useful for reinforcing flexible displays such as foldable and rollable displays.

Explanation of Reference Numerals

[0043] 1 Laminated body for flexible display 10 Reinforcing plate body 10A First surface 11 Adhesive layer 12 Display portion 20 Reinforcing plate for flexible display

Claims

1. a reinforcing plate body, and a first adhesive layer provided on the first surface of the reinforcing plate body, A reinforcing plate for a flexible display, wherein the aspect ratio (Str) of the surface texture determined in accordance with ISO 25178-6:2010 on the first surface of the reinforcing plate body is 0.3 or more.

2. The reinforcing plate for a flexible display according to claim 1, wherein the arithmetic mean height (Sa) on the first surface of the reinforcing plate body is 0.01 μm or more.

3. The reinforcing plate for a flexible display according to claim 2, wherein the minimum autocorrelation length (Sal) determined in accordance with ISO 25178-6:2010 on the first surface of the reinforcing plate body is 17 μm or less.

4. The reinforcing plate for a flexible display according to claim 3, wherein the material of the reinforcing plate body is stainless steel.

5. The reinforcing plate for a flexible display according to any one of claims 1 to 4, wherein the thickness of the reinforcing plate body is 15 μm to 160 μm.

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