WO2017170794A1 - Closed-cell foam sheet, and display device - Google Patents

Abstract

This closed-cell foam sheet is provided with: an opening; and cells which have an average cell diameter in MD and TD of 25-330 µm. The closed-cell foam sheet is provided with a section which is outside of the opening, and in which the minimum width is 1.5-60 times the average cell diameter. This display device is provided with the aforementioned closed-cell foam sheet, and a display panel. According to the present invention, a closed-cell foam sheet which exhibits not only high shock absorption, but also excellent pooling resistance, and a display device provided with said closed-cell 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 repeated impacts in everyday life. It is 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

By the way, as a display device of a portable device such as the above-mentioned smartphone, a touch panel type is often adopted. In the touch panel type liquid crystal panel, liquid crystal bleeding (pooling) may occur when the pressure during the operation becomes strong. In particular, in the case of smartphones, with the spread of mobile games, etc., the display device may be repeatedly pressed at a high speed with a strong force, and pooling may be conspicuous at that time, and there is an increasing demand for suppressing pooling. ing.
As described above, the foam sheet used in the display device is required not only to have a high impact absorbability against an impact repeatedly applied in daily life, but also to have a property of eliminating pooling at an early stage (that is, pooling resistance). It has become.

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 not only high shock absorption but also excellent pooling resistance, and a display device including the same. That is.

As a result of intensive studies to solve the above problems, the present inventor has found that the problem 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] An opening and bubbles having an average bubble diameter of 25 to 330 μm in MD and TD, and a minimum width of a portion other than the opening is an average bubble diameter in MD and an average bubble diameter in TD A closed-cell foamed sheet that is 1.5 to 60 times the larger average cell diameter.
[2] A display device comprising the closed-cell foamed sheet according to [1] and a display panel.

The present invention provides a foam sheet having not only high shock absorption but also excellent pooling resistance, and a display device including the same.

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 apparatus for measuring an impact absorption rate. It is a schematic diagram which shows the foam sheet used in the Example.

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 also simply referred to as “foamed sheet”) has an opening and a bubble having an average bubble diameter of 25 to 330 μm in MD and TD, and a portion other than the opening Is a foam sheet having a minimum width of 1.5 to 60 times the average bubble diameter of the larger average bubble diameter in MD and the average bubble diameter in TD. In addition, in this invention, an opening part means the through-hole penetrated from the one surface side of a foam sheet to the other surface side. In the present invention, there is provided a configuration in which the opening and the predetermined bubble are provided, and the portion other than the opening has a predetermined relationship between the minimum width and the average bubble diameter of the bubble. % Compressive strength can be reduced to obtain high shock absorption and excellent pooling resistance. More specifically, by providing an opening on the foamed sheet, the 25% compressive strength of the foamed sheet itself is reduced and softened moderately, and high impact absorption is obtained. By setting the minimum width in the portion and the average bubble diameter of the bubbles to have a predetermined relationship, the stress generated during the operation of the display device is relieved and excellent pooling resistance is obtained.

The shape of the opening viewed from the top of the sheet (sometimes simply referred to as “shape”) is not particularly limited, but is substantially square such as a square, a rectangle, a parallelogram, a trapezoid, and a similar shape, Circular, elliptical, and similar circular shapes, straight and curved lines, regular triangles, right-angled isosceles triangles, and similar triangular shapes, other pentagons, hexagons, and this It is possible to appropriately select and use a substantially polygonal shape such as a shape similar to the above and a combination of these. Moreover, as a kind of shape, you may use independently and may use it in combination of multiple types. For example, a substantially square opening may exist alone, a substantially square opening and a circular opening may exist simultaneously, or a square opening and a rectangular opening are different. A square opening may be present at the same time.

When the shape of the opening is linear, the width of the opening 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 absorption and pooling resistance are improved, and the opening is easily processed.
Moreover, when the shape of an opening part exhibits a linear form, it is preferable that this linear opening part exists over at least 2 area | region from a viewpoint which shock absorption and pooling resistance improve more.

When the shape of the opening 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 0.5 to 1. 5 mm is particularly preferable. 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.
In addition, when the shape of the opening is a linear 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, it is preferable that the size be inscribed in the substantially rectangular shape.

The area ratio of the openings on the entire surface of the sheet is preferably 1 to 90%, more preferably 1 to 85%. When the area ratio is 1 to 85%, the impact absorption and pooling resistance are further improved. Further, from the same viewpoint, when the shape of the opening is linear, the area ratio of the opening is more preferably 3 to 50%, and further preferably 5 to 30%. When the shape of the opening is not linear, the area ratio of the opening is more preferably 10 to 80%, further preferably 20 to 70%.

The minimum width in the portion other than the opening is the smallest length between the periphery of the opening and the periphery of the sheet when there is one opening (hereinafter referred to as “the length between the openings”). When there are two or more openings, the length between the opening sheets is the smallest, and between the periphery of one opening and the periphery of the other opening. Means the shortest one of the shortest lengths (hereinafter sometimes referred to as “length between openings”). When these lengths are the same, any length may be used.

In the present invention, the minimum width is 1.5 to 60 with respect to the average bubble diameter of the larger average bubble diameter in MD and the average bubble diameter in TD (hereinafter, sometimes simply referred to as “average bubble diameter”). It needs to be double. By providing the opening and setting the minimum width of the portion other than the opening within a predetermined range in relation to the average bubble diameter, high shock absorption and excellent pooling resistance can be obtained.
In the closed cell foam of the present invention, it is preferable to have at least two openings from the viewpoint of further improving shock absorption and pooling resistance. In this case, the width between the openings is an average in MD It is preferable to have a plurality of portions that are 1.5 to 60 times larger than the larger bubble diameter and the average bubble diameter in TD.
The width between the openings is synonymous with the length between the openings.
From the viewpoint of improving impact absorption and pooling resistance, the minimum width is preferably 2 to 50 times, more preferably 5 to 40 times, and even more preferably 10 to 30 times the average bubble diameter. The absolute value of the minimum width is not particularly limited as long as the above relationship with respect to the average bubble diameter is satisfied. For example, 0.1 to 250 mm is preferable, 0.5 to 200 mm is more preferable, and 1 to 150 mm is more preferable.

(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. FIG. 1 shows an example of an embodiment of the foam sheet of the present invention. The embodiment shown in FIG. 1 is merely an example, and the foam sheet of the present invention is not limited to the embodiment shown in FIG.

Each mode shown in FIG. 1 has various patterns of openings having various opening shapes, and assumes a square sheet having a side of 5 cm.
The sheet 1-a has a square opening in the sheet and has a frame shape. The opening is a square with a side of 4 cm, and the minimum width is the smallest length between the sheets of the opening, that is, the width of the frame portion is 0.5 cm.

In the 1-a sheet, the area of the opening is 16 cm ^2, and the area ratio of the opening to the entire sheet is 64%.
In the sheet 1-a, the opening is in the center of the sheet, but if the minimum width is in the range of 1.5 to 60 times the average bubble diameter, the opening It may be biased to either side.

The 1-b sheet has a plurality of (16) square openings in the sheet, which are evenly arranged vertically and horizontally in a lattice pattern. The opening is a square with a side of 1 cm, and the smallest length between the openings and the smallest length between the sheets between the openings are equal to each other, and both are 0.2 cm, so the minimum width is 0. .2cm. Further, the area ratio of the opening to the entire sheet surface is 64%.

As shown in the 1-b sheet, there are a plurality of portions having the same minimum width, that is, having openings in a regular pattern shape, which is equally high in shock absorption and excellent pooling resistance. From the viewpoint of obtaining Since the opening portion is square in the 1-b sheet, the portion that maintains the minimum width is continued. For example, like the 1-c sheet, the square opening portion in the 1-b sheet is formed. It may be replaced with an inscribed circular shape or an opening having another shape.
For example, when the openings are circular, a zigzag pattern or the like as shown in 1-c may be used. If the openings are 60 ° zigzag, the length between the openings of adjacent openings is the smallest. All are the same. The area ratio of the opening of the 1-c sheet to the entire sheet surface is 44%. Further, the arrangement in a zigzag pattern is not limited to the case where the openings are circular, but may be openings having other shapes.

The 1-d sheet has a plurality of circular openings. 1 and 2, 2 and 4, 6 and 7, 6 and 8 (number of each opening) are arranged so that the length between each opening is 2 mm. The opening is a circle having a diameter of 1 cm (a circle inscribed in a square having a side of 1 cm), and has eight circular openings and two semicircular openings. Thus, the opening may be a semicircle or may be irregularly arranged.
The minimum width of the 1-d sheet is 2 mm which is the length between the openings of 1 and 2, 2 and 4, 6 and 7, and 6 and 8. Also, for example, the length between the openings of 1 and 6, 2 and 3, 4 and 5, 4 and 7, or 1 and 4, 3 and 4, 3 and 5, 4 and 6, 5 and 7, and 7 and 8 Is not the minimum width, but depending on the average bubble diameter, the length may fall within the range of 1.5 to 60 times the average bubble diameter. In the present invention, even if it is not the minimum width, the portion where the length between the openings or the length between the sheets of the opening falls within the range of 1.5 to 60 times the average cell diameter is shock-absorbing. In addition, since it is possible to improve the pooling resistance, it is preferable that there are a plurality of portions in which the length between the openings is in the range of 1.5 to 60 times the average bubble diameter.

In the foam sheet of the present invention, not only the minimum width or the minimum width, but the length between the openings or the length between the openings is in the range of 1.5 to 60 times the average bubble diameter However, as shown in, for example, the above-mentioned sheets 1-a to d and 1-e to h described later, it is preferable that a plurality of them have a certain area. In this case, the area ratio of the portion to the entire sheet surface is preferably 5 to 70%, more preferably 5 to 60%, and still more preferably 10 to 50%.

The 1-e sheet has a plurality of linear openings so as to penetrate the sheet in the vertical direction. Although this sheet can also be said to be an assembly of strip-shaped sheets, the foamed sheet of the present invention includes such an embodiment in which the opening does not stay in the periphery of the sheet but reaches the periphery. More specifically, the 1-e sheets are strip-shaped sheets having a width of 9.2 mm and a length of 5 cm arranged at equal intervals of 1 mm.
In this case, the minimum width is the same as the length between the opening portions and the smallest length between the opening portion sheets, and is 9.2 mm which is the width of the strip-shaped sheet. The area ratio of the opening to the entire sheet surface is 8%.

The 1-e sheet is suitably used as an impact absorbing material disposed on the back side of the display panel, which will be described later. By arranging strip-shaped sheets as a single sheet, high shock absorption and excellent pooling resistance can be obtained. Since the foam sheet of such an aspect also has an opening and a predetermined minimum width in relation to the average cell diameter, high shock absorption and excellent pooling resistance are obtained. Yes.

The 1-f sheet has a plurality of straight openings. The left and right openings are arranged so that the length between the opening sheets is 5 mm, the length between the right opening and the middle opening is 1.5 cm, and the left opening The length between the openings of the middle opening is 2.1 cm. The width of each opening is 1 mm, the length is 3 cm, and the area ratio of the opening to the entire sheet surface is 3.6%.
The minimum width of the 1-f sheet is 5 mm, which is the length between the opening sheets of the left and right openings. In addition, although the width is not the minimum, the length between the opening of the right opening and the middle opening is 1.5 cm. Therefore, depending on the average bubble diameter, it is 1.5 to 60 times the average bubble diameter. May be in range. In this case, the portion that falls within the range of 1.5 to 60 times the average bubble diameter can improve the impact absorbability and the pooling resistance. Pooling resistance is further improved.

Further, since the length between the opening of the left opening and the middle opening is 2.1 cm, even when the average bubble diameter is 330 μm, which is the maximum value of 30 to 330 μm, the average bubble diameter of 60 μm. Since the length exceeds twice, high shock absorption and excellent pooling resistance cannot be obtained only by the portion sandwiched between these openings. However, the portion sandwiched between the left opening and the periphery of the seat, the portion sandwiched between the right opening and the periphery of the seat, and depending on the size of the average bubble diameter, the right opening and the middle opening The part sandwiched between the parts expresses shock absorption and pooling resistance. Therefore, even if there is a part where the shock absorption and pooling resistance cannot be obtained, if there is a part having these performances, the part that does not have these performances can be supplemented. High impact absorption and pooling resistance can be obtained. Here, the area ratio of the portion having these performances to the entire sheet surface is as described above.

1-g sheet has a plurality of S-shaped curved openings. The minimum width is 2 mm at the portion where the curves of the first opening and the second opening from the left are switched. Also, for example, the length between the opening sheets for the leftmost opening, the length between the openings of each other opening, and the length between the opening sheets for the rightmost opening also have a portion of 5 mm or less. Although these portions are not the minimum values, depending on the average bubble diameter, they may fall within the range of 1.5 to 60 times the average bubble diameter. The upper left and lower right of the 1-g sheet have a wide portion where there is no opening. However, depending on the average bubble diameter, the average bubble diameter of 1. Since it is compensated by the portion within the range of 5 to 60 times, the entire sheet can have high impact absorption and pooling resistance.

The 1-h sheet has a plurality of S-shaped curved openings and one circular opening. Thus, the foamed sheet of the present invention may have openings with different shapes.

(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 an opening in this closed cell foam sheet, the repulsive force indicated by the 25% compressive strength is reduced, and the repulsive force is small despite being a closed cell foam sheet. In particular, the shock absorption can be improved, and the anti-pooling property can be improved especially by making the predetermined relationship between the minimum width in the part other than the opening and the average bubble diameter. It was.

The 25% compressive strength of the foamed sheet is preferably 40 to 200 kPa, more preferably 50 to 180 kPa, and even more preferably 60 to 170 kPa for the foamed sheet before the opening is provided. The 25% compressive strength of the foamed sheet of the present invention after the opening is provided is preferably 3 to 90 kPa. Furthermore, 15 to 90 kPa is preferable, 3 to 70 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 an opening, whereby 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 the opening is provided
f ₁ : 25% compressive strength (kPa) of the foamed sheet after the opening is provided

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 bubbles in the foamed sheet is preferably 25 to 330 μm, more preferably 30 to 330 μm, in MD and TD. More specifically, MD is preferably 25 to 300 μm, more preferably 35 to 230 μm, and still more preferably 50 to 180 μm. 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 an opening in the stretched resin sheet The above steps (1) to (5) are performed in this step. Although it may be performed in order, it is not always necessary to perform in this order of the process. For example, the process (3) may be performed after the 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 pyrolyzable foaming agents are used alone or in combination. be able to

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))
In the step (5), an opening is formed in the foamed sheet obtained by stretching the resin sheet. The opening penetrates from one surface side of the foam sheet to the other surface side. The method for forming the opening is not particularly limited. For example, the opening can be formed by using a punching die or the like.

In addition to the above-described invention, the present invention also includes the following aspects of the invention.
[3] having two or more openings and bubbles having an average bubble diameter of 25 to 330 μm in MD and TD, and the length between the openings is large in average bubble diameter in MD and average bubble diameter in TD A closed cell foam sheet having a length 1.5 to 60 times the average cell diameter.

Such a closed-cell foamed sheet has excellent impact absorption and excellent pooling resistance. The foamed sheet preferably has 3 or more openings, more preferably 4 or more openings. The upper limit of the number of openings is not particularly limited, but is preferably 100 or less, more preferably 50 or less.
The length between the openings is preferably 2 to 50 times, more preferably 5 to 40 times, and more preferably 10 to 30 times the average bubble size of the larger average bubble size in MD and the average bubble size in TD. Is more preferable.

Furthermore, another aspect of the invention is the following invention [4].
[4] An opening and bubbles having an average bubble diameter of 25 to 330 μm in MD and TD, and a reduction rate (f _Δ ) of 25% compression strength defined by the following formula is 15 to 80% Closed cell foam sheet.
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 the opening is provided
f ₁ : 25% compressive strength (kPa) of the foamed sheet after the opening is provided

Such a closed-cell foamed sheet has excellent impact absorption and excellent pooling resistance.
From the viewpoint of excellent shock absorption and pooling resistance, the reduction rate of 25% compressive strength is preferably 30 to 75%, more preferably 50 to 70%.
The 25% compressive strength of the foamed sheet is preferably 40 to 200 kPa, more preferably 50 to 180 kPa, and even more preferably 60 to 170 kPa for the foamed sheet before the opening is provided. The 25% compressive strength of the foamed sheet of the present invention after the opening is provided is preferably 3 to 90 kPa. Furthermore, 15 to 90 kPa is preferable, 3 to 70 kPa is preferable, 20 to 80 kPa is more preferable, and 30 to 70 kPa is still more preferable.

(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 foam sheet of the present invention can be used, for example, as a shock absorber for a display panel such as a liquid crystal panel. 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.

The foam sheet of the present invention can also 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.
In addition, the display panel, the shock absorbing material, the front plate, the touch panel, and the adhesive constituting 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 suitably used for the impact absorbing material 13 described later. An example of the display device of the present invention will be described with reference to FIG.
A display device 10 shown in FIG. 2 includes a display panel 11, a front plate 12 provided on the front side of the display panel 11, an adhesive 16 that bonds the front plate 12 and the frame 15, and a rear 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 this double-sided tape, the foamed sheet of the present invention may be used.

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 20 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 foam sheet 13 is disposed on the surface of the plate 18. A clearance may be provided between the foam sheet 13 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. 2, the display device shown in FIG. 2 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. 3, a foam sheet (30 mm × 30 mm) is placed at the center of the other surface of an acrylic plate (10 cm × 10 cm, thickness: 1 cm) provided with an acceleration sensor on one surface, and weight 4 A steel ball (φ10 mm) of .5 g was naturally dropped from a height of 300 mm. After repeating this 10 times, the acceleration when the iron ball was naturally dropped was measured, and this was repeated 5 times, and the average value of acceleration for 5 times was used to calculate the impact absorption rate by the following formula. And evaluated according to the following criteria. It means that the larger the shock absorption rate, the better the shock absorption for repeated impacts.
Impact absorption rate (%) = (acceleration without foam sheet−acceleration when foam sheet is disposed) / (acceleration without foam sheet) × 100
Thickness A: The impact absorption rate was 12% or more.
B: The impact absorption rate was 7% or more and less than 12%.
C: The impact absorption rate was less than 7%.

[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 foam sheet is cut into 5 cm × 5 cm squares, and 25 square openings (vertical and horizontal 0.8 cm squares) are arranged in 5 rows and 5 rows using a punching die so that a pattern shown by 4-a in FIG. 4 is obtained. The foam sheet of Example 1 was prepared by providing 25 openings, a minimum width of 1.7 mm (length between openings: 1.7 mm), and an opening area ratio: 64%. With respect to the foamed sheet of Example 1, the thickness, density, 25% compressive strength before processing and after processing, closed cell ratio, and average cell diameter (MD, TD, ZD) 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]
For Examples 2 to 6, the mass part of the foaming agent, the MD stretching ratio, and the TD stretching ratio were adjusted so that the density, MD, TD, and ZD cell diameters shown in Table 1 were obtained, and The patterns are shown in FIG. 4 as 4-b (Example 2), 4-b (Example 3), 4-b (Example 4), 4-c (Example 5), and 4-d (Example 6), respectively. This was carried out in the same manner as in Example 1 except for the point. However, in Example 6, the irradiated electron beam was further changed to 7 Mrad. Note that 4-b in FIG. 4 shows 16 rectangular openings of 0.8 cm in length and breadth in four rows and rows, minimum width: 3.6 mm (length between openings: 3.6 mm), and area ratio of openings: 4-c is a sheet of 41%, 4-c is a square opening of 0.8 cm in diameter, 16 in 4 rows and 4 rows, minimum width: 3.6 mm (length between openings: 3.6 mm), opening area Ratio: 32% sheet, 4-d is 25 square openings with a diameter of 0.9 cm in 5 rows and 5 rows, minimum width: 0.8 mm (length between openings: 0.8 mm), opening Partial area ratio: 64% sheet.

[Comparative Examples 1 and 2]
Except for adjusting the mass part of the foaming agent, the stretching ratio of MD and the stretching ratio of TD, and the point of not providing the opening so as to be the density, MD, TD, and ZD cell diameter in Table 1. A foamed sheet was prepared in the same manner as in Example 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]
In Example 1, except that the opening was not provided, a foamed sheet was prepared in the same manner as 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 absorption and excellent pooling resistance. On the other hand, the foamed sheets of Comparative Examples 1 and 2 that do not have openings do not have sufficient performance in terms of impact absorption and pooling resistance compared to the foamed sheets of the Examples. It was confirmed that Comparative Example 5 using the foamed sheet that was used and did not have an opening did not have sufficient performance in terms of impact absorption and pooling resistance. In Comparative Examples 3 and 4 using an open-cell foam sheet, the shock absorption is insufficient. Similarly, in Comparative Example 6 using an open-cell foam sheet using an open-cell foam sheet, shock absorption is also achieved. It was confirmed that there was a lack of sex. Further, from the result of Comparative Example 6, even when an opening is provided in the open cell foam sheet, the 25% compressive strength is hardly reduced, and the effect of reducing the 25% compressive strength is a phenomenon peculiar to the closed cell foam sheet. It was confirmed that.

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 (10)

1. And the minimum width of the portion other than the opening is the larger of the average bubble diameter in MD and the average bubble diameter in TD. A closed cell foam sheet having a length of 1.5 to 60 times the average cell diameter.
2. The closed-cell foamed sheet according to claim 1, which has at least two openings.
3. 3. The closed-cell foaming according to claim 2, comprising a plurality of portions in which the width between the openings is 1.5 to 60 times the average bubble diameter of the larger average bubble diameter in MD and the average bubble diameter in TD. Sheet.
4. The closed-cell foamed sheet according to any one of claims 1 to 3, wherein the shape of the opening is at least one selected from a substantially rectangular shape, a substantially circular shape, and a linear shape.
5. The closed-cell foamed sheet according to any one of claims 1 to 4, wherein the area ratio of the opening to the entire sheet is 1 to 90%.
6. The closed-cell foamed sheet according to any one of claims 1 to 5, wherein the density is 60 to 600 kg / m ³ .
7. The closed cell foam sheet according to any one of claims 1 to 6, wherein the closed cell rate is 90 to 100%.
8. The closed-cell foamed sheet according to any one of claims 1 to 7, wherein the 25% compressive strength is 3 to 90 kPa.
9. A display device comprising the closed cell foam sheet according to any one of claims 1 to 8 and a display panel.
10. 10. The display device according to claim 9, wherein the display panel is disposed on the closed cell foam sheet.

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