WO2017170793A1 - Closed-cell foam sheet, and display device - Google Patents

Abstract

This closed-cell foam sheet is provided with at least nine regions each having, provided in at least one place, a recess having a depth of 1-99% of the thickness, each of said regions being divided into 25, and having an area in a 1cm ×1cm square region which decreases. Furthermore, this display device is provided with the aforementioned closed-cell foam sheet, and a display panel. According to the present invention, a foam sheet exhibiting high shock absorption, and a display device which uses said foam sheet can be provided.

Description

Closed cell foam sheet and display device

The present invention relates to a closed cell foam sheet and a display device.

Demands for thinner and lighter mobile devices such as notebook personal computers, mobile phones, smart phones, and tablets are desired. In particular, the demand for thinner and lighter smartphones is increasing year by year. Along with the reduction in thickness and weight of portable devices, the front plate composed of a glass plate, an acrylic plate or the like disposed on the front side of the display device, and the display panel are also reduced in thickness. However, when the front plate and the display panel are thinned, the front plate and the display panel are easily broken.

2. Description of the Related Art Conventionally, in a portable device, an impact absorbing sheet is disposed over the entire rear surface of the display panel or on the periphery in order to prevent damage and failure of the display device due to impact repeatedly applied in everyday life. It has been known. The impact-absorbing sheet is required to have high flexibility in order to obtain impact-absorbing properties against repeated impacts, and foamed sheets are widely used. As a foamed sheet, for example, as described in Patent Document 1, a polyethylene-based crosslinked foamed sheet containing a large number of closed cells is known. In addition, urethane foam sheets, rubber foam sheets, and the like are also used.

JP 2014-214205 A

When the shock absorbing sheet is disposed on the entire rear surface side of the display panel or on the periphery, a very thin one having a thickness of less than 1 mm is usually used for portable devices. However, in the foam sheet described in Patent Document 1, if such an extremely thin sheet is used, it may not be said that the shock absorbing performance against the impact repeatedly applied in daily life may be excellent. In some cases, cracking could not be sufficiently prevented.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a foam sheet having high impact absorption and a display device including the same.

As a result of intensive studies to solve the above problems, the present inventor has found that the following invention can be solved by the following invention. That is, this invention provides the following foam sheet and a display apparatus provided with the same.

[1] A region having at least one concave portion having a depth of 1 to 99% with respect to the thickness, which is any region in which the area of a region divided into 25 and a 1 cm × 1 cm square region is reduced. A closed cell foam sheet having 9 or more.
[2] A display device comprising the closed-cell foamed sheet according to [1] and a display panel.

In the present invention, a closed cell foam sheet having high shock absorption and a display device including the same are provided.

It is a conceptual diagram for demonstrating the area | region divided | segmented into 25. FIG. It is a schematic diagram which shows the one aspect | mode of the closed cell foam sheet of this invention. It is a schematic diagram which shows the one aspect | mode of the closed cell foam sheet of this invention. It is typical sectional drawing which shows the display apparatus of this invention. It is typical sectional drawing which shows the laminated body for measuring glass crack height.

Hereinafter, the closed cell foam sheet of the present invention will be described. In the present specification, the numerical values “above” and “below” related to the description of numerical ranges are numerical values that can be arbitrarily combined. Further, in this specification, the numerical range indicated by using “to” indicates a range including the numerical values described before and after “to” as the minimum value and the maximum value, respectively, The value and the maximum value may be arbitrarily combined.

[Closed cell foam sheet]
The closed-cell foamed sheet of the present invention (hereinafter sometimes simply referred to as “foamed sheet”) is any region in which the area of a region divided into 25 and a square region of 1 cm × 1 cm is reduced, It has 9 or more regions having at least one recess having a depth of 1 to 99% of the thickness. In the present invention, by having 9 or more regions where the recesses are present, the 25% compressive strength is reduced to obtain high shock absorption, and excellent pooling resistance is also obtained. More specifically, by adopting a configuration in which the recesses are present to some extent uniformly on the sheet, the 25% compressive strength of the foamed sheet itself is reduced and becomes moderately soft, and high impact absorption is obtained. In addition, the moderate softness relieves the stress generated during the operation of the display device, and a secondary excellent pooling resistance can be obtained. In addition, pooling property means the bleeding of the liquid crystal by press.

The area divided into 25 (hereinafter, simply referred to as “25 divided areas”) is an area that is set by dividing the vertical direction and the horizontal direction of the closed cell foam sheet into 5 equal parts. For example, when the closed cell foam sheet is a square having four angles of 90 °, such as a square or a rectangle, the vertical and horizontal sides are divided into five equal parts as shown in FIG. These 25 areas are defined as 25 divided areas. If the sheet has a shape other than a square or a rectangle, for example, a parallelogram shown in FIG. 1-b, the vertical and horizontal sides of the circumscribed square or rectangle are divided into five equal parts and set. The area is defined as a 25-divided area. Also, in the case of a substantially circular shape such as the ellipse shown in 1-c of FIG. 1, the circumscribed rectangle is set by dividing the vertical and horizontal sides into five equal parts as in 1-b of FIG. These 25 areas are defined as 25 divided areas.
In the case of a shape other than a square or a rectangle, such as a parallelogram shown by 1-d in FIG. Although it exists (in the case of 1-d, two in the upper left and two in the lower right, a total of four), including these, the area is divided into 25 areas.

Also, for example, in 1-a of FIG. 1, when the sheet size is a square of 20 cm × 20 cm, when divided into 25 areas, one area becomes a square of 4 cm × 4 cm. In such a case, since the area of a 1 cm × 1 cm square area (hereinafter sometimes simply referred to as “square area”) is smaller than the 25 divided area, the square area is defined as the area in the present invention. To do. The method for setting the square area is the same as the method for setting the 25-divided area except that the 25-divided area is divided into 1 cm by dividing the vertical and horizontal sides into five equal parts.

In the present invention, the area is selected from the 25 divided areas and the square area in which the area becomes smaller in consideration of the area where a human finger touches the touch panel when operating the touch panel. For example, even if there is at least one recess in a square area of 4 cm × 4 cm, the pooling resistance may not be reliably obtained unless there is a recess at or near the location where the finger touches. Therefore, according to the present invention, the area of the region is 1 cm ² of 1 cm × 1 cm at the maximum, and the presence of a recess in the region can improve the pooling resistance obtained as a secondary.

From the viewpoint of improving impact absorption and pooling resistance, the number of regions having recesses is preferably 10 or more, more preferably 12 or more, and still more preferably 14 or more.
In addition, when the region is a square region, the 25 divided region is larger than a 1 cm × 1 cm square area of 1 cm ² , that is, the total area of the sheet is larger than 25 cm ² , so that there are 25 or more square regions. There is. In this case, the ratio of the region having a recess having a depth of 1 to 99%, preferably 1 to 90% with respect to the thickness is preferably 40% or more, more preferably 50% or more, and 60%. The above is more preferable. When the ratio of the area having the recesses to the entire area is within the above range, the impact absorption and the pooling resistance are improved.

The recess has a depth of 1 to 99% with respect to the thickness of the foam sheet. When the depth of the recess is 1 to 99% with respect to the thickness of the sheet, the impact absorbability and the pooling resistance are improved. In consideration of the same viewpoint and ease of processing, the depth of the recess is preferably 5 to 95%, more preferably 10 to 90%, and still more preferably 20 to 80% with respect to the thickness of the sheet.

The shape of the concave portion as viewed from above the sheet (hereinafter sometimes simply referred to as “shape”) is not particularly limited, but is linear such as a straight line or a curve, circular, elliptical, and similar shapes. In general circles, squares, rectangles, parallelograms, trapezoids, and similar shapes, etc. A substantially polygonal shape such as a similar shape, or a combination of these can be selected as appropriate. Moreover, as a kind of shape, you may use independently and may use it in combination of multiple types. For example, a linear concave portion may exist alone, a linear concave portion and a circular concave portion may exist at the same time, or linear shapes having different shapes such as a linear concave portion and a curved concave portion. It may exist at the same time.

The shape of the concave sheet viewed from the cross section (hereinafter, sometimes simply referred to as “cross-sectional shape”) is not particularly limited, and is generally V-shaped, square, rectangular, trapezoidal, or the like, semicircular, semielliptical, etc. Any of the substantially semicircular shapes may be used.

The shape of the recess is due to the method of forming the recess. For example, when a concave portion is formed by cutting with a cutter, the shape of the concave portion is linear, and the cross-sectional shape is V-shaped. When the concave portion is formed using an embossing roll, the shape of the concave portion is substantially square. When the concave portion is formed by using a needle roll, the shape of the concave portion is substantially circular and the cross-sectional shape is V-shaped.
In view of improving impact absorption and pooling resistance, and taking into account the ease of processing the recess, it is preferable to form the recess by cutting using a cutter. That is, in this invention, it is preferable that it is a linear recessed part.

When the shape of the concave portion is linear, the width of the concave portion is preferably 0.1 to 2 mm, more preferably 0.3 to 1.5 mm, and still more preferably 0.4 to 1 mm. When the width is within the above range, impact absorbability and pooling resistance are improved, and the recesses can be easily processed.
Moreover, when the shape of a recessed part exhibits linear form, it is preferable that this linear recessed part exists over at least 2 area | region from a viewpoint which shock absorption property and pooling resistance improve more.

When the shape of the concave portion is substantially square, the length of one side is preferably 0.1 to 4.5 mm, more preferably 0.2 to 3 mm, still more preferably 0.3 to 2 mm, and more preferably 0.5 to 1.5 mm. Particularly preferred. Further, the length of one side is preferably 2 to 90% as a ratio with respect to the length of one side of the entire sheet (the length of one side of the circumscribed rectangle when the sheet shape is not a square). A length of 60% is more preferred, and a length of 15-40% is even more preferred.
Further, when the shape of the concave portion is a line shape or a shape other than a substantially square shape, that is, a substantially circular shape, a substantially triangular shape, a substantially polygonal shape, or the like, the size is preferably inscribed in the substantially square shape.

The area ratio of the recesses on the entire surface of the sheet is preferably 1 to 90%. When the area ratio is 1 to 90%, the impact absorption and pooling resistance are further improved. Further, from the same viewpoint, when the shape of the recess is linear, the area ratio of the recess is more preferably 3 to 50%, and further preferably 5 to 30%. When the shape of the recess is other than linear, the area ratio of the recess is more preferably 10 to 90%, further preferably 20 to 85%.

(Various aspects of closed cell foam sheet)
More specifically, the embodiment of the foam sheet of the present invention will be described with reference to the drawings. 2 and 3 show an example of the embodiment of the foam sheet of the present invention. The embodiment shown in FIGS. 2 and 3 is merely an example, and the foamed sheet of the present invention is not limited to the embodiment shown in FIGS.

Each mode shown in FIG. 2 has a 25-divided area and has various patterns of recesses.
The sheet 2-a has a plurality of straight concave portions. Of the 25 divided regions, there are no recesses in the five rightmost regions, but there are linear recesses in the other 20 regions. Even if it has a region where there is no recess, such as the sheet 2-a, if there are 9 or more regions having a recess, the presence of recesses in other regions Therefore, high impact absorption as a whole sheet and excellent pooling resistance can be obtained. Moreover, in one area | region, you may have several linear recessed part.

The sheet 2-b also has a plurality of linear recesses, and there are not only vertical but also vertical straight recesses and horizontal straight recesses as in 2-a. In the case of the 2-b sheet, it is shown that all the regions have recesses, and that one region may have a plurality of vertical and horizontal straight recesses. The sheet 2-c has a plurality of curved concave portions, and there are no concave portions in a total of four areas, two in the upper left and two in the lower right, but the other 21 areas are curved concave It is the area which has.

The 2-d sheet has a plurality of rectangular recesses. This sheet has a recess in the entire region, for example, there is one recess in the upper left region, two recesses in the lower region, and a recess in the right region. There are four places.

The sheet 2-e has a plurality of circular recesses. In this case, there are no recesses in the five regions of the bottom row, but the other 20 regions are regions having at least one circular recess. As shown in 2-e, the shape of the recess may be a shape cut off in the middle. Further, the arrangement of the recesses may be regular as in the 2-d sheet, or may be irregular as in the 2-e sheet.
The 2-f sheet also has a plurality of circular recesses. The number of recesses is smaller than that of 2-e sheet, and the number of regions having recesses is as small as 9. However, even in such an aspect, the structure of the present invention is provided, and high shock absorption and excellent pooling resistance are achieved. It can be a sheet having the properties.

The 2-g sheet has one rectangular recess in the sheet. This sheet has a recess in the entire region. As shown in the 2-g sheet, the entire surface of one region may be a recess, but from the viewpoint of improving shock absorption and pooling resistance, the number of regions where the entire surface is a recess is 12 or less. Preferably, 10 or less is more preferable, and 8 or less is still more preferable. Further, when the region is a square region, the number of the square regions is preferably 50% or less, more preferably 40% or less, and still more preferably 35% or less with respect to the total number of regions.
In the case of 25 divided regions, when the number of regions whose entire surface is a recess is 25, the entire surface becomes a recess, that is, the sheet does not have a recess as a result over the entire surface of the sheet. Needless to say, no effect can be obtained. In the case of a square region, the same applies when the entire surface of all the square regions is a recess.

The 2-h sheet has a square opening in the sheet, and vertical and horizontal straight concave portions exist on the peripheral edge of the frame-shaped sheet. This sheet has a plurality of recesses in 16 regions at the peripheral edge.
As shown by the 2-h sheet, the foamed sheet of the present invention may have an opening. In this case, the shape of the opening is not particularly limited, and examples include the shape exemplified as the shape of the recess, for example, a linear shape, a substantially circular shape, a substantially quadrangular shape, a substantially triangular shape, a substantially polygonal shape, and a combination thereof. Further, the opening may be provided at one place as shown by the 2-h sheet, or may be provided at a plurality of places.

In the case of having openings, the area ratio of the openings to the entire sheet surface is preferably 1 to 90%, more preferably 10 to 85%, and still more preferably 20 to 85%. When the area ratio of the opening is within the above range, the recess can be sufficiently formed, and the impact absorption and the pooling resistance are improved.

Each mode shown in FIG. 3 has a square area and has various patterns of recesses. Although only two examples are shown in FIG. 3, for example, a sheet having concave portions having the same pattern as the concave portions having various patterns shown in FIG. Can be.
The 3-a sheet has concave portions having the same pattern as that of the 2-a sheet. However, since the area is 1 cm ² or more in the 25 divided areas, a square area is applied as the area. This sheet has no recess in the left end, the right end, and the region of the sixth row from the left, but has a recess in the other regions. The number of regions having recesses is 54, and the ratio of regions having recesses to the entire region (81) is 66.7%.

The 3-b sheet, like the 3-a sheet, has a plurality of straight concave portions, and the regions having the concave portions are the second row from the top, the second row from the bottom, and the third row from the left. In addition, there are recesses in a total of 35 regions surrounded by the region in the third row from the right. The ratio of the region (35) having the recesses to the entire region (81) is 43.2%. When the region is a square region, if there are 9 or more regions having recesses, high shock absorption and excellent pooling resistance can be obtained, but if 40% or more regions have recesses as described above, impact absorption and Pooling resistance is improved.

(Performance of closed cell foam sheet)
The foamed sheet of the present invention is a closed cell foamed sheet composed of closed cells. The closed cell means that the closed cell rate is 70% or more. That is, the bubbles included in the foam sheet are generally closed cells. From the viewpoint of improving impact absorption and pooling resistance, the closed cell ratio is preferably 90 to 100%, more preferably 95 to 100%.

The closed cell ratio can be measured as follows.
First, a flat square test piece having a side of 5 cm is cut out from the foam sheet. Then, by measuring the thickness of the test piece to calculate the apparent volume V ₁ of the test piece, measuring the mass W ₁ of the specimen. Next, the volume V ₂ occupied by the bubbles is calculated based on the following formula. The density of the resin material constituting the test piece is ρ (g / cm ³ ).
Volume occupied by bubbles V ₂ = V ₁ −W ₁ / ρ
Subsequently, the test piece is immersed in distilled water at 23 ° C. to a depth of 100 mm from the water surface, and a pressure of 15 kPa is applied to the test piece for 3 minutes. Then, after releasing from pressurization in water and allowing to stand for 1 minute, the test piece was taken out of water, the water adhering to the surface of the test piece was removed, and the mass W _{2 of the} test piece was measured. Te to calculate the open cell ratio F ₁ and the closed cell ratio F _2.
Open cell ratio F ₁ (%) = 100 × (W ₂ −W ₁ ) / V ₂
Closed cell ratio F ₂ (%) = 100−F ₁

If the bubbles in the foam sheet are closed cells, the repulsive force against the pressure is large, so that it is generally effective for the expression of pooling resistance. On the other hand, if the repulsive force is too large, the impact absorbability may decrease, and it can be said that the impact absorbability and the pooling resistance are contradictory. In the present invention, it has been found that by providing a recess in this closed cell foam sheet, the repulsive force indicated by 25% compressive strength or the like is reduced, and the repulsive force is small despite being a closed cell foam sheet. By making it possible, it was possible to improve impact absorption and pooling resistance.

The 25% compressive strength of the foamed sheet is preferably 40 to 200 kPa, more preferably 50 to 180 kPa, and still more preferably 60 to 170 kPa for the foamed sheet before the recess is provided. The 25% compressive strength of the foamed sheet of the present invention after providing the recesses is preferably 3 to 90 kPa. Furthermore, 15 to 90 kPa is preferable, 20 to 80 kPa is more preferable, and 30 to 70 kPa is still more preferable. Further, the reduction rate of the 25% compressive strength before and after providing the recesses is preferably 15 to 80%, more preferably 30 to 75%, and still more preferably 50 to 70%.
As described above, the foamed sheet of the present invention is provided with the recesses, so that the compressive strength is reduced by 25% in spite of being closed cells, and the impact absorption and the pooling resistance are improved. In this specification, the 25% compressive strength is a value measured according to JIS K 6767. The reduction rate of 25% compressive strength is a numerical value represented by the following formula.
f _Δ = (f ₀ −f ₁ ) / f ₀ × 100
_fΔ : Reduction rate of 25% compression strength (%)
f ₀ : 25% compressive strength (kPa) of the foamed sheet before providing the recesses
f ₁ : 25% compressive strength (kPa) of the foamed sheet after providing the recesses

The thickness of the foam sheet is preferably 0.03 to 0.6 mm, considering the thickness desired for use in a display device, the ease of obtaining shock absorption and pooling resistance, and the like, preferably 0.05 to 0 mm. 0.5 mm is more preferable, and 0.06 to 0.3 mm is even more preferable.

The density of foam sheet, shock absorption, in view of improving the resistance to pooling resistance, preferably 60 ~ 600kg / ^{m 3,} preferably 60 ~ 400kg / ^{m 3,} more preferably ^{150 ~ 600kg / m 3, 180} ~ 480kg / M ³ is more preferable.

The average cell diameter of the bubbles in the foam sheet is preferably 25 to 300 μm, more preferably 30 to 300 μm, still more preferably 35 to 230 μm, and most preferably 50 to 180 μm in MD. In TD, 30 to 330 μm is preferable, 50 to 300 μm is more preferable, and 60 to 250 μm is still more preferable. Further, ZD is preferably 10 to 80 μm, more preferably 15 to 75 μm, still more preferably 20 to 70 μm. When the average bubble diameter of the bubbles is within the above range, impact absorbability and pooling resistance can be improved.

The foam sheet is obtained by crosslinking and foaming a resin sheet of a resin material described later. The degree of crosslinking of the foamed sheet is usually about 5 to 60% by mass, preferably 10 to 40% by mass.
The degree of crosslinking is measured by the following measuring method. A 100 mg test piece is collected from the foamed sheet, and the mass A (mg) of the test piece is precisely weighed. Next, this test piece was immersed in 30 cm ³ of xylene at 120 ° C. and allowed to stand for 24 hours, and then filtered through a 200-mesh wire mesh to collect the insoluble matter on the wire mesh, vacuum dried, and the mass of the insoluble matter. Weigh B (mg) precisely. From the obtained value, the degree of crosslinking (mass%) is calculated by the following formula.
Crosslinking degree (% by mass) = 100 × (B / A)

(Raw resin)
The raw material resin constituting the closed-cell foamed sheet of the present invention may be, for example, any of polyolefin resin, acrylic resin, silicone resin, urethane resin, rubber resin, and shock absorption and anti-pooling Considering the properties, it is preferable to use a polyolefin resin.

The polyolefin resin, which is a preferable material in the present invention, will be described.
Examples of the polyolefin resin used to form the foamed sheet include a polyethylene resin, a polypropylene resin, or a mixture thereof. Among these, polyethylene is a polyethylene resin from the viewpoint of improving impact absorption and pooling resistance. Based resins are preferred. More specifically, examples thereof include polyethylene resins, polypropylene resins, or mixtures thereof polymerized with a polymerization catalyst such as a Ziegler-Natta compound, a metallocene compound, and a chromium oxide compound. Among these, polymerization of a metallocene compound is included. A polyethylene resin polymerized with a catalyst is preferred.

The polyethylene resin may be an ethylene homopolymer, but by copolymerizing ethylene with a small amount (for example, 30% by mass or less of the total monomers, preferably 1 to 10% by mass) of α-olefin as necessary. Polyethylene resins obtained are preferred, and among them, linear low density polyethylene is preferred.

By using a polyethylene-based resin, particularly a linear low density polyethylene, obtained by a polymerization catalyst of a metallocene compound, it becomes easy to obtain a foamed sheet having improved flexibility, mechanical strength, and pooling resistance. Moreover, as will be described later, it is easy to maintain high performance even if the foam sheet is thin.

Specific examples of the α-olefin constituting the polyethylene resin include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. . Of these, α-olefins having 4 to 10 carbon atoms are preferred.
As the polyethylene resin, an ethylene-vinyl acetate copolymer is also preferably used. The ethylene-vinyl acetate copolymer is usually a copolymer containing 50% by mass or more of ethylene units.

The polyethylene resin, the ethylene-vinyl acetate copolymer, or a mixture thereof obtained by the polymerization catalyst of the metallocene compound is preferably contained in the foamed sheet in an amount of 50% by mass or more, more preferably 60% by mass. As described above, it is most preferably contained by 100% by mass.

Examples of the polypropylene resin include a propylene homopolymer, a propylene-α-olefin copolymer containing 50% by mass or more of a propylene unit, and the like. These may be used alone or in combination of two or more.
Specific examples of the α-olefin constituting the propylene-α-olefin copolymer include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1- Among these, α-olefins having 6 to 12 carbon atoms are preferable.

Suitable metallocene compounds include compounds such as bis (cyclopentadienyl) metal complexes having a structure in which a transition metal is sandwiched between π-electron unsaturated compounds. More specifically, tetravalent transition metals such as titanium, zirconium, nickel, palladium, hafnium, and platinum have one or more cyclopentadienyl rings or their analogs as ligands (ligands). The compound to be mentioned is mentioned.
Such metallocene compounds have uniform active site properties and each active site has the same activity. A polymer synthesized using a metallocene compound has high uniformity such as molecular weight, molecular weight distribution, composition, and composition distribution. Therefore, when a sheet containing a polymer synthesized using a metallocene compound is crosslinked, crosslinking occurs. Progress evenly. Since the uniformly crosslinked sheet is easily stretched uniformly, the thickness of the crosslinked polyolefin resin foamed sheet is easily uniformed, and high performance is easily maintained even when the sheet is thin.

Examples of the ligand include a cyclopentadienyl ring and an indenyl ring. These cyclic compounds may be substituted with a hydrocarbon group, a substituted hydrocarbon group or a hydrocarbon-substituted metalloid group. Examples of the hydrocarbon group include a methyl group, an ethyl group, various propyl groups, various butyl groups, various amyl groups, various hexyl groups, 2-ethylhexyl groups, various heptyl groups, various octyl groups, various nonyl groups, and various decyl groups. , Various cetyl groups, phenyl groups and the like. The “various” means various isomers including n-, sec-, tert-, and iso-.
Moreover, what polymerized the cyclic compound as an oligomer may be used as a ligand.
In addition to π-electron unsaturated compounds, monovalent anion ligands such as chlorine and bromine or divalent anion chelate ligands, hydrocarbons, alkoxides, arylamides, aryloxides, amides, arylamides, phosphides, aryls Phosphide or the like may be used.

Examples of metallocene compounds containing tetravalent transition metals and ligands include, for example, cyclopentadienyl titanium tris (dimethylamide), methylcyclopentadienyl titanium tris (dimethylamide), bis (cyclopentadienyl) titanium dichloride, dimethyl And silyltetramethylcyclopentadienyl-t-butylamidozirconium dichloride.
The metallocene compound exhibits an action as a catalyst in the polymerization of various olefins by combining with a specific cocatalyst (co-catalyst). Specific examples of the cocatalyst include methylaluminoxane (MAO) and boron compounds. The proportion of the cocatalyst used with respect to the metallocene compound is preferably 100,000 to 1,000,000 mole times, more preferably 50 to 5,000 mole times.

The Ziegler-Natta compound is a triethylaluminum-titanium tetrachloride solid composite, which is obtained by reducing titanium tetrachloride with an organoaluminum compound and then treating with various electron donors and electron acceptors. A method of combining a composition, an organoaluminum compound, and an aromatic carboxylic acid ester (see JP-A 56-1000080, JP-A 56-120712, JP-A 58-104907), halogens Method of supported catalyst in which magnesium tetrachloride is brought into contact with magnesium tetrachloride and various electron donors (see JP-A-57-63310, JP-A-63-43915, JP-A-63-83116), etc. What was manufactured by is preferable.

The polyethylene resin preferably has a low density in order to increase the flexibility, mechanical strength, and recovery rate of the foam sheet. Specifically, the density of the polyethylene resin is preferably 0.920 g / cm ³ or less, more preferably 0.880 to 0.915 g / cm ³ , still more preferably 0.885 to 0.910 g / cm ^3. It is. The density is measured according to ASTM D792.

In addition, as polyolefin resin, resin other than the above-mentioned polyolefin resin can also be used, and resin other than polyethylene resin and polypropylene resin may be used by further mixing with polyethylene resin and polypropylene resin. Good.
Furthermore, the polyolefin resin may be mixed with various additives and other components described later, and the foamed sheet is obtained by crosslinking and foaming a polyolefin resin containing additives and other components. Is preferred.
Examples of other components contained in the foamed sheet include resins and rubbers other than polyolefin-based resins, and these are total and less in content than polyolefin-based resins, and are usually based on 100 parts by mass of polyolefin-based resin. It is about 50 parts by mass or less, preferably about 30 parts by mass or less.

(Method for producing foam sheet)
The method for producing the foamed sheet of the present invention is not particularly limited, and examples thereof include a method including the following steps (1) to (5).
Step (1): Melting resin materials such as raw resin, additives such as pyrolytic foaming agent, and other additives added as necessary, at a temperature lower than the decomposition temperature of the pyrolytic foaming agent, Step of kneading and molding into a resin sheet by a known molding method Step (2): Step of crosslinking the resin sheet obtained in step (1) Step (3): Decomposition temperature of the thermally decomposable foaming agent Step of heating and foaming Step (4): Step of stretching the resin sheet Step (5): Step of forming a recess in the foamed sheet obtained by stretching The above steps (1) to (5) are: Although you may perform in order of this process, it does not necessarily need to perform in order of this process, for example, you may perform a process (3) after a process (4). Moreover, two processes may be performed simultaneously, for example, you may perform process (3) and (4) simultaneously.

(Process (1))
In the step (1), a raw material resin, additives such as a pyrolytic foaming agent, and resin materials such as other additives are supplied to an extruder such as a single screw extruder or a twin screw extruder, etc. The resin material is made into a sheet-like resin sheet by melting and kneading at a temperature lower than the decomposition temperature of the decomposable foaming agent and extruding by extrusion molding or the like.
Here, examples of the additive other than the thermal decomposition type foaming agent include a decomposition temperature adjusting agent, a crosslinking aid, an antioxidant, a cell nucleating agent, a colorant, a flame retardant, an antistatic agent, a filler, and the like. . The raw material resin may be a polyolefin resin as described above, but may be a mixture of a polyolefin resin and a resin component other than the polyolefin resin, or may be a resin component other than the polyolefin resin.

As the thermally decomposable foaming agent, for example, one having a decomposition temperature higher than the melting temperature of the raw material resin can be used. For example, an organic or inorganic chemical foaming agent having a decomposition temperature of 160 to 270 ° C. can be used.

Examples of the organic foaming agent include azo compounds such as azodicarbonamide, metal salts of azodicarboxylic acid (such as barium azodicarboxylate) and azobisisobutyronitrile; nitroso compounds such as N, N′-dinitrosopentamethylenetetramine; And hydrazine derivatives such as hydrazodicarbonamide, 4,4′-oxybis (benzenesulfonylhydrazide) and toluenesulfonylhydrazide; and semicarbazide compounds such as toluenesulfonyl semicarbazide.
Examples of the inorganic foaming agent include ammonium acid, sodium carbonate, ammonium hydrogen carbonate, sodium hydrogen carbonate, ammonium nitrite, sodium borohydride, anhydrous monosodium citrate, and the like.
Among these, azo compounds and nitroso compounds are preferable from the viewpoint of obtaining fine bubbles, and from the viewpoints of economy and safety, and azodicarbonamide, azobisisobutyronitrile, N, N′-dinitrosopentamethylene. Tetramine is more preferred, and azodicarbonamide is still more preferred. These pyrolytic foaming agents can be used alone or in combination of two or more.

The amount of the pyrolytic foaming agent added is preferably 1 to 10 parts by weight, more preferably 1.5 to 5 parts by weight, and more preferably 1.5 to 3 parts by weight with respect to 100 parts by weight of the raw material resin (for example, polyolefin resin). Part is more preferred.

The decomposition temperature adjusting agent that can be used as another additive is blended to lower the decomposition temperature of the pyrolytic foaming agent, or to increase or adjust the decomposition rate. Specific examples of the compound include zinc oxide, zinc stearate, urea and the like. For example, 0.01 to 5 parts by mass of the decomposition temperature regulator is blended with respect to 100 parts by mass of the raw material resin in order to adjust the surface state of the foam sheet.

Examples of the crosslinking aid include polyfunctional monomers. By adding a crosslinking aid to the polyolefin-based resin, the ionizing radiation dose irradiated in the step (2) described later is reduced, and the resin molecules are prevented from being cut and deteriorated due to the irradiation of the ionizing radiation.

Specific examples of the crosslinking aid include trimethylolpropane trimethacrylate, trimethylolpropane triacrylate, trimellitic acid triallyl ester, 1,2,4-benzenetricarboxylic acid triallyl ester, triallyl isocyanurate, and the like. Compounds having three functional groups in the molecule; two compounds in one molecule such as 1,6-hexanediol dimethacrylate, 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, divinylbenzene, etc. Compounds having a functional group; diallyl phthalate, diallyl terephthalate, diallyl isophthalate, ethyl vinyl benzene, neopentyl glycol dimethacrylate, lauryl methacrylate, stearyl methacrylate and the like. These crosslinking aids are used alone or in combination of two or more.

The addition amount of the crosslinking aid is preferably 0.2 to 10 parts by mass, more preferably 0.3 to 5 parts by mass, and still more preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the raw material resin. When the addition amount is 0.2 parts by mass or more, it is possible to stably obtain the desired degree of crosslinking of the foam sheet, and when it is 10 parts by mass or less, the degree of crosslinking of the foam sheet is easily controlled.

Examples of the antioxidant include phenolic antioxidants such as 2,6-di-t-butyl-p-cresol.

(Process (2))
In step (2), the resin sheet obtained in step (1) is crosslinked. Crosslinking in the step (2) is preferably performed by irradiating the resin sheet with ionizing radiation. Examples of the ionizing radiation include α-rays, β-rays, γ-rays, and electron beams, and electron beams are more preferable. The amount of ionizing radiation applied to the resin sheet is preferably 1 to 10 Mrad, more preferably 1.5 to 8 Mrad. In the case of using a crosslinking aid, the irradiation amount of ionizing radiation is preferably 0.3 to 8 Mrad, more preferably 0.5 to 5.5 Mrad.
By setting the irradiation amount of ionizing radiation to the above lower limit value or more, it becomes easy to impart a shear viscosity necessary for foaming the resin sheet. Moreover, by setting it as the said upper limit or less, the shear viscosity of a resin sheet does not become high too much, but foamability becomes favorable. Therefore, it becomes easy to obtain the above-described density foam sheet, and the appearance of the foam sheet is also improved.
However, since the degree of progress of crosslinking is usually influenced by the raw material resin, the type of additives, etc., the irradiation dose of ionizing radiation is usually adjusted while measuring the degree of crosslinking so that the degree of crosslinking described above is obtained. To.

(Process (3))
In step (3), the resin sheet is heated to a temperature equal to or higher than the decomposition temperature of the thermally decomposable foaming agent and foamed. Usually, this process (3) is implemented after the said process (2).
The temperature at which foaming is carried out depends on the decomposition temperature of the pyrolytic foaming agent, but is usually from 140 to 300 ° C, preferably from 160 to 260 ° C. The method for foaming the resin sheet is not particularly limited, and examples thereof include a method of heating with hot air, a method of heating with infrared rays, a method using a salt bath, a method using an oil bath, and the like. Good.

(Process (4))
In step (4), the resin sheet is stretched. By stretching, the average cell diameter, the number of cells, the thickness of the foam sheet, and the like of the foam sheet can be adjusted. Stretching may be performed after foaming the resin sheet, or may be performed while foaming the resin sheet. The stretching may be performed with a known apparatus such as a uniaxial stretching machine or a biaxial stretching machine.
In addition, when extending | stretching after making a resin sheet foam, it is better to continue extending | stretching, maintaining the molten state at the time of foaming, without cooling a resin sheet, but after cooling a resin sheet, it heats again. Then, it may be stretched after being in a molten or softened state.

Moreover, although the example which performs bridge | crosslinking using ionizing radiation was demonstrated above, crosslinking agents, such as an organic peroxide, are mix | blended with polyolefin resin as an additive, polyolefin resin is heated, and organic You may carry out by the method of decomposing | disassembling a peroxide. Examples of such organic peroxides include 1,1-bis (t-butylperoxy) 3,3,5-trimethylcyclohexane, 1,1-bis (t-butylperoxy) cyclohexane, and the like. .

The addition amount of the organic peroxide is preferably 0.01 to 5 parts by mass, more preferably 0.1 to 3 parts by mass with respect to 100 parts by mass of the raw material resin. When the addition amount of the organic peroxide is within the above range, crosslinking of the resin material is likely to proceed, and the amount of decomposition residue of the organic peroxide in the foamed sheet is suppressed.
Further, the resin material may be foamed by gas foaming typified by carbon dioxide gas or butane gas instead of using the foaming agent, or may be foamed by a mechanical floss method.

(Process (5))
Step (5) is a step of forming a recess in the foamed sheet obtained by stretching. The method of forming the recess is not particularly limited, and examples thereof include a method of forming a recess using an embossing roll, a method of forming a recess using a needle roll, and a method of forming a recess using a cutter. it can.

(Usage and use of foam sheet)
The foamed sheet of the present invention can be used as it is, but may be used by providing a pressure-sensitive adhesive layer on any one or both sides. The thickness of the pressure-sensitive adhesive layer is preferably 5 to 200 μm, more preferably 7 to 150 μm.
There is no restriction | limiting in particular as an adhesive which comprises the adhesive layer provided in one side or both surfaces of a foam sheet, For example, an acrylic adhesive, a urethane type adhesive, a rubber-type adhesive, etc. are mentioned.

As a method of providing the pressure-sensitive adhesive layer on the foamed sheet, for example, a method of applying the pressure-sensitive adhesive using a coating machine such as a coater on at least one surface of the foamed sheet, or using a spray on at least one surface of the foamed sheet Examples thereof include a method of spraying and applying an adhesive, and a method of applying an adhesive using a brush on one surface of a foam sheet.

The foamed sheet of the present invention can be used as an adhesive for bonding a front plate such as an acrylic plate or a glass plate, or a touch panel provided on the front plate and the main body of the display device. In this case, the foam sheet can be used by providing an opening so as to have a frame shape, or cut into a desired shape, for example, a strip shape. When the foamed sheet of the present invention is used as an adhesive, since the foamed sheet is a closed cell body and the bubbles are not in communication, a gap generated between the frame and the front plate when stress is applied to the frame. It is also possible to suppress entry of dust, moisture, etc. from Moreover, the effect which suppresses the failure | damage of a front plate is also acquired by shock absorption.

Moreover, the foam sheet of this invention can be used as an impact-absorbing material of display panels, such as a liquid crystal panel, for example. The shock absorber of the display panel is disposed on the back side of the display panel, and absorbs the shock applied to the display panel to prevent the display panel from being damaged or broken. Since the foamed sheet of the present invention has a shock absorbing property and a pooling resistance, it is arranged as a shock absorbing material on the back side of the display panel, so that the occurrence of pooling caused by pressing the surface of the display panel is prevented. Can also be prevented.
Note that terms such as a front plate, a touch panel, a display device, an adhesive, a frame, a display panel, and a shock absorber that constitute the display device will be described later.

[Display device]
The display device of the present invention includes the closed-cell foamed sheet of the present invention and a display panel, and the foamed sheet of the present invention is used for at least one of an impact absorbing material 13 and an adhesive 16 described later. . An example of the display device of the present invention will be described with reference to FIG.
4 includes a display panel 11, a front plate 12 provided on the front side of the display panel 11, an adhesive 16 for bonding the front plate 12 and the frame 15, and a back side of the display panel 11. The shock absorbing material 13 and the like are provided.

The display panel 11 is a unit that is disposed on the shock absorber 13 and includes at least a display element such as a liquid crystal display element or an organic EL display element in which a liquid crystal layer is disposed between two glass substrates. However, in addition to the display element, a protective film, a polarizing element, a retardation film, or the like may be laminated. The display panel 11 further includes a backlight unit provided on the back side of the display element when the display element is a liquid crystal display element. The display panel 11 preferably includes a liquid crystal display element.

The front plate 12 includes a cover plate material for protecting the display panel 11 and the like. Although a cover board | plate material will not be specifically limited if it has a light transmittance, An acrylic board, a glass plate, etc. are mentioned. The front plate 12 may further include a member other than the cover plate material. For example, when the display device 10 is a touch panel type, a touch panel unit (not shown) is laminated on the lower surface side of the cover plate material. It may be.

The impact absorbing material 13 is provided to absorb the impact when the impact is applied to the display panel 11 and the front plate 12, and a foam sheet is usually used. As this foamed sheet, the closed cell foamed sheet of the present invention having high impact absorbability is preferably used. In addition, since the foamed sheet of the present invention is excellent in pooling resistance, the use of the foamed sheet as the shock absorbing material 13 can also prevent the occurrence of pooling caused by pressing the display panel 11 through the front plate 12. .

The front plate 12 is supported by the frame 15. The frame 15 has a quadrangular frame shape and is provided with a fitting portion 15 </ b> A having a lower inner peripheral side height. The front plate 12 is disposed so as to be fitted to the fitting portion 15A. The front plate 12 is fixed to the frame 15 by being bonded to the fitting portion 15A by the adhesive 16 arranged in the fitting portion 15A. As the adhesive 16, a double-sided tape or the like in which a pressure-sensitive adhesive layer is provided on both surfaces of a base material is used. As the base material of the double-sided tape, the foamed sheet of the present invention is suitably used. Since the foamed sheet of the present invention is excellent in impact absorption, it is possible to reduce the impact on the front plate 12 and to prevent the front surface 12 from being damaged. In addition, since the foam sheet of the present invention is a closed-cell body, and bubbles are not communicated, when stress is applied to the frame during use, dust from a gap generated between the frame and the front plate, There is also an effect that it is possible to suppress intrusion of moisture and the like.

The display panel 11 is bonded to the back surface of the front plate 12 through the adhesive layer 17, and thereby is integrated with the front plate 12 and supported by the frame 15. The adhesive layer 17 is composed of an adhesive layer having optical transparency called OCA (Optically Clear Adhesive) or an adhesive layer.

Further, on the back side of the display panel 11, a plate 18 arranged with a certain distance from the display panel 11 is provided. The plate 18 is fixed to the frame 15. A clearance may be provided between the shock absorber 13 disposed on the surface of the plate 18 and the display panel 11.

The display device of the present invention is suitably provided in a portable device such as a notebook personal computer, a mobile phone, a smartphone, or a tablet.
The display device of the present invention may be a touch panel type including a touch panel unit. Although the surface of the touch panel is repeatedly pressed at a high speed, when the foam sheet of the present invention is used as the shock absorber 13, the occurrence of pooling is suppressed, so that the display performance of the display device is improved.

Although the display device of the present invention has been described with reference to FIG. 4, the display device shown in FIG. 4 shows an example of the display device of the present invention, and various modifications can be made. For example, the display panel 11 and the front plate 12 may be supported by a member other than the frame 15, and the shock absorber 13 may be disposed on a member other than the plate 18. Moreover, the material used for each member is only an example, and materials made of materials usually used for these members can be used.

Examples The present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
Various physical properties and evaluation methods in this specification are as follows.
<Thickness>
It measured according to the method of JIS K6767.
<Density>
It measured according to the method of JIS K6767.
<25% compressive strength>
The 25% compressive strength of the foamed sheet was measured three times repeatedly according to the method of JIS K6767, specifically, using a measuring device (manufactured by ORIENTEC, product name “TENSILON RTG-1250”). Was 25% compressive strength.

<Average bubble diameter>
The foamed sheet is cut into a 50mm square, immersed in liquid nitrogen for 1 minute, then cut in the thickness direction along each of MD and TD, and a digital microscope (manufactured by Keyence Corporation, product name "VHX-900") is used. Take a 200x magnified photograph, measure the bubble diameter of MD, ZD, and the bubble diameter of TD, ZD and the bubble diameter of TD, ZD for all the bubbles present on the cut surface of 2 mm in length in each of MD and TD. Repeated times. The average value of the bubble diameters of all the bubbles MD and TD is taken as the average bubble diameter of the MD and TD, and the average value of the bubble diameters of all ZDs measured by the above operation is taken as the average bubble diameter of the ZD. It was.

<Closed cell ratio>
The closed cell ratio of the foamed sheet is measured by the method described in the specification.

[Evaluation of shock absorption (glass crack height)]
As shown in FIG. 5, on a glass plate (100 mm × 100 mm square, thickness: 0.55 mm, manufactured by Corning, trade name “Gorilla Glass 3”), double-sided PET tape (Stock of Century Water Chemicals Co., Ltd.) A foam sheet (100 mm x 100 mm) with a product name "Double-sided tape 3801X for fixing LCD members" affixed to both ends of a glass plate and an acrylic plate (thickness 10 mm: manufactured by Mitsubishi Rayon Co., Ltd.) through the foam sheet , Product name “Acrylite”) was produced, and the laminate was dropped with the glass surface down.If it was dropped 10 times from a height of 10 cm and not broken, it was further 10 cm above (20 cm). The glass break height is taken as the glass break height, and it was used as an index of shock absorption. The better the impact absorption against an impact applied returned.

[Pooling resistance evaluation]
A 4.7-inch liquid crystal panel was placed on a 50 mm × 70 mm foam sheet, a load was applied to the surface of the liquid crystal panel using a push rod, and evaluation was performed according to the following criteria. Here, the push bar has a diameter of 15 mm, rubber (hardness: 30) is provided at the tip, and the push bar is assumed to be pushed by a human finger.
A: When the load was 6N or more, pooling did not occur.
B: Slight pooling occurred at a load of 3N or more and less than 5N.
C: Pooling occurred when the load was less than 3N.

[Example 1]
100 parts by mass of linear low-density polyethylene (trade name “EXACT3027” manufactured by Exxon Chemical Co., Ltd.) obtained using a metallocene compound as a polyethylene resin, 2 parts by mass of azodicarbonamide as a foaming agent, , 6-di-t-butyl-p-cresol 0.3 parts by mass and 1 part by mass of zinc oxide are supplied to an extruder and melt-kneaded at 130 ° C., and then a resin sheet having a thickness of about 0.2 mm is obtained. Extruded.
Next, the resin sheet is cross-linked by irradiating an electron beam with an acceleration voltage of 800 kV on both surfaces by 5 Mrad, and then continuously fed into a foaming furnace maintained at 250 ° C. by hot air and an infrared heater to be heated and foamed. At the same time, it was stretched at a stretch ratio of MD of 1.3 times and a stretch ratio of TD of 2.0 times while foaming to obtain a foam sheet having a thickness of 0.06 mm. The resulting foamed sheet had a degree of crosslinking of 25% and a 25% compressive strength of 118 kPa. This foamed sheet is cut into a 5 cm × 5 cm square, and 8 linear recesses (width: 0) are vertically used by using an embossing roll so that a pattern shown by 2-b in FIG. 2 is obtained. 5 mm, length: 40 mm, distance between lines: 5 mm, depth: 20%, number of regions having recesses: 25, recess area ratio: 12%) to obtain a foam sheet of Example 1. For the foamed sheet of Example 1, the thickness, density, compressive strength, average cell diameter (MD, TD, ZD), and closed cell ratio were measured by the above methods. The measured values are shown in Table 1. Moreover, the impact absorbability and pooling resistance were evaluated by the above methods. The results are shown in Table 1.

[Examples 2 to 6]
It implemented like Example 1 except the point which adjusted the mass part of the foaming agent, the draw ratio of MD, and the draw ratio of TD so that it might become the cell diameter of density of Table 1, MD, TD, and ZD. However, in Example 6, the irradiated electron beam was further changed to 7 Mrad.

[Comparative Examples 1 and 2]
Except for the point of adjusting the mass part of the foaming agent, the draw ratio of MD and the draw ratio of TD, and the point of not providing the recess so as to obtain the density, MD, TD, and ZD cell diameter in Table 1. A foamed sheet was prepared in the same manner as in No. 1, and each property was measured by the above method to evaluate impact absorption and anti-pooling.

[Comparative Examples 3 and 4]
In Comparative Examples 3 and 4, the properties of SCF400 (manufactured by Nitto Denko Corporation) and Poron (manufactured by Roger Sinoac Co., Ltd.), which are commercially available foamed sheets, were measured and evaluated by the above methods.

[Comparative Example 5]
A foamed sheet was prepared in the same manner as in Example 1 except that no recess was provided in Example 1, and each property was measured and evaluated.

[Comparative Example 6]
In Example 1, a foamed sheet was prepared in the same manner as in Example 1 except that Poron (manufactured by Roger Sinoac Co., Ltd.), which is a commercial product, was used as the foamed sheet, and each property was measured and evaluated.

 

As is clear from Examples 1 to 6 above, it was confirmed that the foamed sheet of the present invention has high impact absorbability and excellent pooling resistance. On the other hand, the foamed sheets of Comparative Examples 1 and 2 that do not have recesses are insufficient in shock absorption and pooling resistance compared to the foamed sheets of the examples. It was confirmed that Comparative Example 5 using a foam sheet having no slag was insufficient in impact absorption and pooling resistance. In Comparative Examples 3 and 4 using an open-cell foam sheet, both the shock absorption and the pooling resistance were insufficient to reach the foam sheet of the example, and the open-cell foam sheet was also used to provide a recess. Also in Comparative Example 6 using the foamed sheet, it was confirmed that both the pooling resistance and the foamed sheet of the examples were not sufficient. Further, from the results of Comparative Example 6, even when the open-celled foam sheet is provided with a recess, the 25% compressive strength is hardly reduced, and the effect of reducing the 25% compressive strength is a phenomenon peculiar to the closed-cell foamed sheet. It was confirmed that there was.

DESCRIPTION OF SYMBOLS 10 Display apparatus 11 Display panel 12 Front plate 13 Shock absorber 15 Frame 16 Adhesive material 17 Adhesive layer 18 Plate

Claims (11)

1. There are 9 or more regions having at least one recess having a depth of 1 to 99% of the thickness, which is any region in which the area of the region divided into 25 and a square region of 1 cm × 1 cm is reduced. Closed cell foam sheet.
2. The closed-cell foamed sheet according to claim 1, wherein the area ratio of the recess to the entire sheet is 1 to 90%.
3. The closed-cell foamed sheet according to claim 1 or 2, wherein the recess is linear.
4. The closed-cell foamed sheet according to claim 3, wherein the width of the recess is 0.1 to 2 mm.
5. The closed-cell foamed sheet according to any one of claims 1 to 4, wherein the concave portion exists over at least two regions.
6. 6. The closed-cell foamed sheet according to any one of claims 1 to 5, which has bubbles having an average cell diameter in MD of 25 to 300 μm and an average cell diameter in TD of 30 to 330 μm.
7. The closed-cell foamed sheet according to any one of claims 1 to 6, wherein the density is 60 to 600 kg / m ³ .
8. The closed cell foam sheet according to any one of claims 1 to 7, wherein the closed cell ratio is 90 to 100%.
9. The closed-cell foamed sheet according to any one of claims 1 to 8, wherein the 25% compressive strength is 3 to 90 kPa.
10. A display device comprising the closed cell foam sheet according to any one of claims 1 to 9 and a display panel.
11. The display device according to claim 10, wherein the display panel is disposed on the closed cell foam sheet.

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