JP2022098240A - Shock absorbing sheet - Google Patents

Abstract

To provide a shock absorbing sheet having excellent peeling resistance and bending resistance at a low temperature.SOLUTION: A shock absorbing sheet includes a silicone-containing layer containing a silicone resin and an adhesive layer that overlaps the silicone-containing layer. A thickness of the silicone-containing layer is 60% or more and 95% or less of a thickness of the shock absorbing sheet. A storage elastic modulus (G1) at -20°C and a storage elastic modulus (G2) at 25°C of the silicone-containing layer are both 1×104 Pa or more and 1×105 Pa or less. The adhesive layer contains a resin (A) having a peak temperature of tangent loss of 0°C or lower.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a shock absorbing sheet, and more particularly to a shock absorbing sheet including a silicone-containing layer and an adhesive layer.

In display devices used in various electronic devices such as smartphones, tablet terminals, and notebook computers, a shock absorbing sheet for absorbing shock and vibration is provided on the back side of the display. In recent years, these electronic devices have been rapidly reduced in size and thickness, and in response to this, shock absorbing sheets that can exhibit excellent shock absorption even if the shock absorbing layer is thinned have been studied (in response to this). See Patent Document 1, Patent Document 2 and Patent Document 3).

Japanese Unexamined Patent Publication No. 2016-03394 International Publication No. 2018/131219 Japanese Unexamined Patent Publication No. 2012-102878

Recently, flexible displays such as organic EL have come to be used in foldable terminals, electronic paper, and the like. Since the shock absorbing sheet used in the display device including such a flexible display is loaded each time it is bent, defects such as interface peeling and structural deformation may occur. Since this defect becomes particularly remarkable in a low temperature environment of 0 ° C. or lower, it is necessary for the shock absorbing sheet to improve both peeling resistance and bending resistance at low temperature.

An object of the present disclosure is to provide a shock absorbing sheet having excellent peeling resistance and bending resistance at low temperatures.

The shock absorbing sheet according to one aspect of the present disclosure includes a silicone-containing layer containing a silicone resin and an adhesive layer overlapping the silicone-containing layer. The thickness of the silicone-containing layer is 60% or more and 95% or less of the thickness of the shock absorbing sheet. The storage elastic modulus (G1) at −20 ° C. and the storage elastic modulus (G2) at 25 ° C. of the silicone-containing layer are both 1 × 10 ⁴ Pa or more and 1 × 10 ⁵ Pa or less. The adhesive layer contains a resin (A) having a peak temperature of tangent loss of 0 ° C. or lower.

According to the present disclosure, it is possible to provide a shock absorbing sheet having excellent peeling resistance and bending resistance at low temperatures.

FIG. 1 is a schematic cross-sectional view of a shock absorbing sheet according to an embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional view of a shock absorbing sheet according to another embodiment of the present disclosure.

<Shock absorption sheet>
The shock absorbing sheet according to the present embodiment (hereinafter, also referred to as shock absorbing sheet 1) includes a silicone-containing layer containing a silicone resin and an adhesive layer overlapping the silicone-containing layer. The thickness of the silicone-containing layer is 60% or more and 95% or less of the thickness of the shock absorbing sheet 1. The storage elastic modulus (G1) at −20 ° C. and the storage elastic modulus (G2) at 25 ° C. of the silicone-containing layer are both 1 × 10 ⁴ Pa or more and 1 × 10 ⁵ Pa or less. The adhesive layer contains a resin (A) having a peak temperature of tangent loss of 0 ° C. or lower. In addition, "overlapping" means that the silicone-containing layer and the adhesive layer overlap in a plan view.

The shock absorbing sheet 1 has a low temperature because both G1 and G2 are 1 × 10 ⁴ Pa or more and 1 × 10 ⁵ Pa or less, and the peak temperature of the loss tangent of the resin (A) constituting the adhesive layer is 0 ° C. or less. The adhesive strength between the silicone-containing layer and the adhesive layer underneath is increased, and the peeling resistance is excellent, and the bending resistance at low temperature evaluated in the bending test is also excellent. The reason can be inferred as follows. When both G1 and G2 of the silicone-containing layer are in the specific range and the peak temperature of the loss tangent (tan δ) of the resin (A) is equal to or lower than the specific temperature, the shock absorbing sheet 1 is flexible at a low temperature. It is considered that the property becomes appropriate, and the bending resistance can be improved. Further, it is considered that the wettability of the interface between the silicone-containing layer and the adhesive layer at low temperature can be improved, the adhesive strength between the layers is increased, and the peeling resistance at low temperature is improved. When at least one of G1 and G2 is less than 1 × 10 ⁴ Pa or more than 1 × 10 ⁵ Pa, or when the peak temperature of the loss tangent of the resin (A) is more than 0 ° C., the adhesive strength between the layers is small at low temperature. As a result, the peeling resistance is lowered, the flexibility of the shock absorbing sheet 1 at low temperature or normal temperature is not appropriate, and the bending resistance is lowered. Further, in order to make the shock absorbing sheet 1 excellent in both peeling resistance and bending resistance at low temperature, in addition to these, the thickness of the silicone-containing layer is 60% or more of the thickness of the shock absorbing sheet 1. We found that it was necessary to be 90% or less. If this thickness is less than 60%, the flexibility of the shock absorbing sheet 1 becomes unsuitable, and the bending resistance at low temperatures is lowered. Further, when this thickness exceeds 95%, the strength of the adhesive layer is weakened, and the peeling resistance between the silicone-containing layer and the adhesive layer at a low temperature is lowered.

FIG. 1 shows an example of a shock absorbing sheet according to the present embodiment. The shock absorbing sheet 1 of FIG. 1 includes a silicone-containing layer 2 and an adhesive layer 3 that directly overlaps the silicone-containing layer 2.

[Silicone-containing layer]
The silicone-containing layer 2 contains a silicone resin. The silicone-containing layer 2 preferably contains a silicone resin as a main component. The "main component" refers to a component having the largest mass ratio, preferably 50% by mass or more, more preferably 70% by mass or more, and further preferably 90% or more.

The shock absorbing sheet 1 may have one silicone-containing layer 2 or two or more layers, but is usually one layer. The shape of the silicone-containing layer 2 is, for example, a film shape, a sheet shape, a plate shape, or the like.

The thickness of the silicone-containing layer 2 is 60% or more and 95% or less of the thickness of the shock absorbing sheet 1. The thickness of the silicone-containing layer 2 is preferably 63% or more, more preferably 66% or more, further preferably 70% or more, and particularly preferably 73% or more. The thickness of the silicone-containing layer 2 is preferably 92% or less, more preferably 90% or less, further preferably 87% or less, and particularly preferably 85% or less. By setting the thickness of the silicone-containing layer 2 within the above range, peeling resistance and bending resistance at low temperatures can be further improved.

The thickness of the silicone-containing layer 2 is preferably 80 μm or more. In this case, the impact absorption rate of the impact absorption sheet 1 can be further improved. This thickness is more preferably 100 μm or more, further preferably 150 μm or more, and particularly preferably 200 μm or more. Further, the thickness of the silicone-containing layer 2 is preferably 700 μm or less. In this case, the bending resistance at low temperature can be further improved. This thickness is more preferably 600 μm or less, further preferably 500 μm or less, and particularly preferably 400 μm or less.

The storage elastic modulus (G1) at −20 ° C. and the storage elastic modulus (G2) at 25 ° C. of the silicone-containing layer 2 are both 1 × 10 ⁴ Pa or more and 1 × 10 ⁵ Pa or less. At least one of G1 and G2 is preferably 1.5 × 10 ⁴ or more and 7 × 10 ⁴ or less, more preferably 1.8 × 10 ⁴ or more and 5 × 10 ⁴ or less, and 2 × 10 ⁴ or more. It is more preferably 3 × 10 ⁴ or less, and particularly preferably 2.2 × 10 ⁴ or more and 2.7 × 10 ⁴ or less. Further, it is most preferable that both G1 and G2 are in the above range. By setting G1 and G2 in the above range, peeling resistance and bending resistance at low temperatures can be further improved.

(Silicone resin)
The "silicone resin" refers to a compound containing a polysiloxane chain (-Si-O-Si-O-) composed of a siloxane bond as a main skeleton. The silicone resin preferably contains a silicone gel from the viewpoint of shock absorption performance, and more preferably contains an addition reaction type silicone gel from the viewpoint that G1 and G2 can be easily adjusted in the above range. The addition reaction type silicone gel is obtained, for example, by using organohydrogenpolysiloxane and alkenylpolysiloxane, which will be described later, as raw materials, and subjecting both to a hydrosilylation reaction (addition reaction) in the presence of a catalyst. The organohydrogenpolysiloxane is represented by, for example, the following formula (1).

In formula (1), R ¹ represents the same or different substituted or unsubstituted monovalent hydrocarbon group. ^{R2 ,} R3 and ^R4 represent ^R1 or —H, and at least two of ^{R2 ,} R3 and ^R4 represent —H. x and y indicate the number of each unit, and are independently integers of 0 or more. x + y is an integer of 5 or more and 300 or less.

x is preferably 10 or more and 30 or less. y is preferably 1 or more and 10 or less. x + y is preferably 30 or more and 200 or less. y / (x + y) is preferably 0.1 or less. If y / (x + y) exceeds 0.1, the number of cross-linking points may increase and the impact absorption may decrease.

The arrangement of each unit in the equation (1) may be random or block, but random is preferable.

A hydrogen atom (Si—H) directly bonded to a silicon atom is required for an addition reaction (hydrosilylation reaction) with an alkenyl group directly or indirectly bonded to the silicon atom, and is contained in an organohydrogenpolysiloxane molecule. It is preferable to have at least two hydrogen atoms.

The alkenylpolysiloxane is represented by, for example, the following formula (2).

In formula (2), R ¹ represents the same or different substituted or unsubstituted monovalent hydrocarbon group, R ⁵ , R ⁶ and R ⁷ represent R ¹ or an alkenyl group, and R ⁵ , R. At least two of ⁶ and R ⁷ represent an alkenyl group. s and t indicate the number of each unit, and are independently integers of 0 or more. s + t is an integer of 10 or more and 600 or less.

s is preferably 10 or more and 30 or less. t is preferably 1 or more and 10 or less. t / (s + t) is preferably 0.1 or less. If t / (s + t) exceeds 0.1, the number of cross-linking points may increase and the impact absorption may decrease.

An alkenyl group (vinyl group, allyl group, etc.) directly or indirectly bonded to the silicon atom is necessary for carrying out an addition reaction (hydrosilylation reaction) with the hydrogen atom (Si—H) directly bonded to the silicon atom. , It is preferable to have at least two in the alkenylpolysiloxane molecule.

Examples of R ¹ in the formula (1) and the formula (2) include an alkyl group such as a methyl group, an ethyl group, a propyl group and a butyl group; a cycloalkyl group such as a cyclopentyl group and a cyclohexyl group; a phenyl group and a trill group. Examples thereof include an aryl group; an aralkyl group such as a benzyl group and a phenethyl group; a halogenated hydrocarbon group in which a part or all of the hydrogen atom of these groups is substituted with a chlorine atom, a fluorine atom or the like.

The hydrosilylation reaction can be carried out using known techniques. Examples of the catalyst for the hydrosilylation reaction include platinum chloride acid, a complex obtained from platinum chloride acid and alcohol, a platinum-olefin complex, a platinum-vinylsiloxane complex, and a platinum-phosphorus complex. The amount of the catalyst used is usually 1 ppm or more and 500 ppm or less, and preferably 3 ppm or more and 200 ppm or less as a platinum atom with respect to the alkenylpolysiloxane.

In addition to the silicone resin, the silicone-containing layer 2 may contain components other than the silicone resin, such as resins, pigments, heat-dissipating fine particles, flame-retardant agents, and heat stabilizers, as long as the effects of the present disclosure are not impaired.

The method for forming the silicone-containing layer 2 is not particularly limited, but for example, a composition containing a precursor of a silicone resin is molded by a molding method such as an extrusion molding method, and then a curing reaction such as a hydrosilylation reaction is performed to carry out a curing reaction such as a hydroxysilylation reaction to carry out a silicone resin. The method of forming the above is mentioned.

The adhesive strength of the silicone-containing layer 2 to the polyethylene terephthalate film at −20 ° C. is preferably 5 N / 25 mm or more. In this case, the peel resistance at low temperature can be further improved. This adhesive strength is more preferably 7 N / 25 mm or more, and further preferably 10 N / 25 mm or more. The upper limit of this adhesive strength is not particularly limited, but is, for example, 30 N / 25 mm.

[Adhesive layer]
The adhesive layer 3 is arranged so as to be overlapped with the silicone-containing layer 2. The adhesive layer 3 contains a resin (A) having a peak temperature of tangent loss of 0 ° C. or lower. The shock absorbing sheet 1 may be provided with one adhesive layer 3, two layers, or three or more layers.

The shape of the adhesive layer 3 is, for example, a film shape, a sheet shape, a plate shape, or the like.

The thickness of the adhesive layer 3 is preferably 5 μm or more. In this case, the peel resistance at low temperature can be further improved. This thickness is more preferably 10 μm or more, and further preferably 20 μm or more. Further, this thickness is preferably 100 μm or less. In this case, the bending resistance at low temperature can be further improved. This thickness is more preferably 90 μm or less, and further preferably 80 μm or less.

(Resin (A))
The resin (A) has a peak temperature of tangent loss of 0 ° C. or lower. The peak temperature is preferably −5 ° C. or lower, more preferably −10 ° C. or lower, and even more preferably −15 ° C. or lower. In this case, peeling resistance and bending resistance at low temperatures can be further improved. The lower limit of the peak temperature of the tangent loss is not particularly limited, but is, for example, −50 ° C.

The resin (A) is not particularly limited as long as it is a resin in which the peak temperature of the tangent loss is in the above range. Examples of the resin (A) include (meth) acrylic resin, polyester resin, urethane resin, polyvinyl resin (polyvinyl alcohol, vinyl chloride-vinyl acetate copolymer, etc.) and the like. The (meth) acrylic resin comprises both acrylic and methacrylic resins and contains structural units derived from (meth) acrylic acid esters.

The resin (A) preferably contains a (meth) acrylic resin from the viewpoint of further improving the peeling resistance at low temperatures.

Examples of the (meth) acrylic acid ester that gives the (meth) acrylic resin include a (meth) acrylic acid ester having a substituted or unsubstituted monovalent hydrocarbon group.

Examples of the monovalent hydrocarbon group include an alkyl group having 1 or more and 20 or less carbon atoms such as a methyl group, an ethyl group, a propyl group, a butyl group and a 2-ethylhexyl group; and a cyclopentyl group and a cyclohexyl group having 3 or more and 20 carbon atoms. Examples thereof include the following cycloalkyl groups; aryl groups having 6 or more and 20 or less carbon atoms such as phenyl groups and trill groups; and aralkyl groups having 7 or more and 20 or less carbon atoms such as benzyl groups and phenethyl groups.

The number of carbon atoms of the monovalent hydrocarbon group is preferably 2 or more, more preferably 3 or more, further preferably 4 or more, and particularly preferably 5 or more. The carbon number is preferably 15 or less, more preferably 12 or less, further preferably 9 or less, and particularly preferably 8 or less.

Examples of the substituent of the hydrocarbon group include a polar group and the like. "Polar group" means a group containing at least one heteroatom. Examples of the hetero atom include an oxygen atom, a nitrogen atom, a sulfur atom, a phosphorus atom, a halogen atom and the like. Examples of the polar group include a carboxy group, a hydroxy group, an oxygen atom (—O—, an epoxy group), an alkoxy group, an alkoxyalkylalkoxy group, an amino group, a substituted amino group, a sulfanyl group, an alkylsulfanyl group; a fluorine atom and a chlorine atom. , Bromine atom, halogen atom such as iodine atom and the like.

The (meth) acrylic acid ester preferably contains an unsubstituted hydrocarbon group, more preferably contains an unsubstituted alkyl group, and further preferably contains an unsubstituted alkyl group having 4 or more and 9 or less carbon atoms. ..

Examples of the (meth) acrylic acid ester having an unsubstituted alkyl group having 4 or more and 9 or less carbon atoms include n-butyl (meth) acrylate, isobutyl (meth) acrylate, and sec-butyl (meth) acrylate. (Meta) acrylic acid butyl ester such as t-butyl acrylate; (meth) acrylic acid pentyl ester, (meth) acrylic acid hexyl ester, (meth) acrylic acid heptyl ester; (meth) acrylic acid n-octyl , (Meta) acrylic acid octyl ester such as 2-ethylhexyl (meth) acrylic acid; (meth) acrylic acid nonyl ester and the like. Of these, acrylic acid esters are preferred.

When the resin (A) has a structural unit derived from a (meth) acrylic acid ester having an unsubstituted hydrocarbon group, the proportion of the structural unit derived from the (meth) acrylic acid ester having an unsubstituted hydrocarbon group is , 50% by mass or more, more preferably 90% by mass or more, further preferably 97% by mass or more, and 98% by mass, based on all the structural units constituting the resin (A). The above is particularly preferable. This ratio is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, further preferably 99.3% by mass or less, and 99.0% by mass or less. Is particularly preferred.

When the resin (A) has a structural unit derived from a (meth) acrylic acid ester having an unsubstituted hydrocarbon group, it is preferable that the resin (A) further has a structural unit containing a polar group. In this case, the peak temperature of the loss tangent can be adjusted more appropriately. Examples of the structural unit containing a polar group include a structural unit derived from (meth) acrylic acid, a structural unit derived from a (meth) acrylic acid ester having a hydrocarbon group to which a polar group is bonded, and the like.

Examples of the (meth) acrylic acid ester having a hydrocarbon group to which a polar group is bonded include (meth) hydroxybutyl acrylate, (meth) hydroxypentyl acrylate, (meth) hydroxyhexyl acrylate, and (meth) acrylic. Hydroxy group-containing (meth) acrylic acid esters such as hydroxyoctyl acid, hydroxycyclohexyl (meth) acrylic acid, hydroxyphenyl (meth) acrylic acid, polyethylene glycol ester (meth) acrylic acid; carboxypentyl (meth) acrylic acid, (meth). ) Carboxyl carboxy octyl acrylate, (meth) carboxycyclohexyl acrylate, carboxy group-containing (meth) acrylic acid esters such as (meth) carboxyphenyl acrylate; ethoxybutyl (meth) acrylate, methoxyhexyl (meth) acrylate, ( (Meta) Acrylic acid ester containing an alkoxy group such as methoxycyclohexyl acrylate and ethoxyphenyl (meth) acrylate; (meth) epoxy ethyl acrylate, epoxy butyl (meth) acrylate, epoxy cyclohexyl (meth) acrylate and the like. Epoxy group-containing (meth) acrylic acid ester; containing amino groups such as (meth) aminobutyl acrylate, (meth) dimethylaminobutyl acrylate, (meth) aminocyclohexyl acrylate, and (meth) methylaminophenyl acrylate. Meta) Acrylic acid ester and the like can be mentioned.

The structural unit containing a polar group preferably contains a structural unit derived from (meth) acrylic acid, and more preferably contains a structural unit derived from acrylic acid.

In the resin (A), the ratio of the structural units containing the polar group is preferably 0.1% by mass or more with respect to all the structural units constituting the resin (A). In this case, the adhesive force between the adhesive layer 3 and the silicone-containing layer 2 can be further increased, and as a result, the peeling resistance and bending resistance at low temperatures can be further improved. This ratio is more preferably 0.5% by mass or more, further preferably 0.7% by mass or more, and particularly preferably 1.0% by mass or more. This ratio is preferably 10% by mass or less, more preferably 3% by mass or less, further preferably 2.5% by mass or less, and particularly preferably 2% by mass or less.

The resin (A) preferably has a structural unit derived from a (meth) acrylic acid ester having an unsubstituted hydrocarbon group and a structural unit containing a polar group, and has 4 or more and 9 or less carbon atoms. It is more preferable to have a structural unit derived from a (meth) acrylic acid ester having an alkyl group and a structural unit derived from a structural unit derived from (meth) acrylic acid, and the number of carbon atoms is 4 or more and 9 or less. It contains 97% by mass or more and 99.9% by mass or less of structural units derived from (meth) acrylic acid ester having an alkyl group, and 0.1% by mass or more and 3% by mass or less of structural units derived from (meth) acrylic acid. It is more preferable to include it.

The pressure-sensitive adhesive layer 3 can be formed by using, for example, a pressure-sensitive adhesive containing the resin (A). The method for forming the adhesive layer 3 is not particularly limited, and for example, a method of applying a pressure-sensitive adhesive containing a resin (A) to the surface of the silicone-containing layer 2 and drying the adhesive layer 3 to form the adhesive layer 3 and a material constituting the silicone-containing layer 2. Examples thereof include a method of forming by coextruding with a pressure-sensitive adhesive containing the resin (A).

The adhesive strength between the silicone-containing layer 2 and the adhesive layer 3 at −20 ° C. is preferably 3N / 25 mm or more. In this case, the peel resistance and bending resistance at low temperature can be further improved. This adhesive strength is more preferably 6 N / 25 mm or more, and further preferably 8 N / 25 mm or more.

The adhesive strength of the adhesive layer 3 to SUS at 25 ° C. is preferably 10 N / 25 mm or more, more preferably 13 N / 25 mm or more, and further preferably 16 N / 25 mm or more.

[Other layers]
The shock absorbing sheet 1 may include other layers in addition to the silicone-containing layer 2 and the adhesive layer 3. The shape of the other layer is, for example, a film shape, a sheet shape, a plate shape, or the like.

Examples of the other layer include a heat-diffusing layer having a heat-diffusing property, a shield layer having an electromagnetic wave shielding property, a protective layer such as a separator, and the like.

[Layer structure]
Examples of the layer structure of the shock absorbing sheet 1 according to the present embodiment include the following (a) to (p). In the following, the notation of A / B / C indicates that, for example, A, B, and C are stacked in this order from the back side of the display.
(A) Adhesive layer / Silicone-containing layer (b) Adhesive layer / Silicone-containing layer / Adhesive layer (c) Adhesive layer / Silicone-containing layer / Heat diffusion layer (d) Adhesive layer / Silicone-containing layer / Heat diffusion layer / Adhesive layer (E) Adhesive layer / Silicone-containing layer / Heat diffusion layer / Adhesive layer / Shield layer (f) Adhesive layer / Silicone-containing layer / Heat diffusion layer / Adhesive layer / Shield layer / Adhesive layer (g) Adhesive layer / Silicone-containing layer / Adhesive layer / Heat diffusion layer / Adhesive layer / Shield layer (h) Adhesive layer / Silicone-containing layer / Adhesive layer / Heat diffusion layer / Adhesive layer / Shield layer / Adhesive layer (i) Separator / Adhesive layer / Silicone-containing layer ( j) Separator / Adhesive layer / Silicone-containing layer / Adhesive layer / Separator (k) Separator / Adhesive layer / Silicone-containing layer / Heat diffusion layer (l) Separator / Adhesive layer / Silicone-containing layer / Heat diffusion layer / Adhesive layer / Separator (M) Separator / Adhesive layer / Silicone-containing layer / Heat diffusion layer / Adhesive layer / Shield layer (n) Separator / Adhesive layer / Silicone-containing layer / Heat diffusion layer / Adhesive layer / Shield layer / Adhesive layer / Separator (o) Separator / Adhesive layer / Silicone-containing layer / Adhesive layer / Heat diffusion layer / Adhesive layer / Shield layer (p) Separator / Adhesive layer / Silicone-containing layer / Adhesive layer / Heat diffusion layer / Adhesive layer / Shield layer / Adhesive layer / Separator

FIG. 2 shows a shock absorbing sheet having the layer structure of (j). The shock absorbing sheet 1 of FIG. 2 has a silicone-containing layer 2, two adhesive layers 3 and 3 directly laminated on both surfaces of the silicone-containing layer 2, and two separators directly laminated on these adhesive layers 3 and 3. It has 4 and 4.

The total thickness of the silicone-containing layer 2 and the adhesive layer 3 in the shock absorbing sheet 1 is preferably 100 μm or more. In this case, the impact absorption rate of the impact absorption sheet 1 can be further improved. This thickness is more preferably 200 μm or more, and further preferably 300 μm or more. The total thickness is preferably 1000 μm or less. In this case, the bending resistance at low temperature can be further improved. This thickness is more preferably 900 μm or less, and further preferably 800 μm or less.

The thickness of the shock absorbing sheet 1 is preferably 100 μm or more. In this case, the strength of the shock absorbing sheet 1 can be further improved. This thickness is more preferably 200 μm or more, and further preferably 300 μm or more. The thickness of the shock absorbing sheet 1 is preferably 1000 μm or less. In this case, it is possible to further reduce the thickness of the display device including the display. This thickness is more preferably 900 μm or less, and further preferably 800 μm or less.

The shock absorption rate of the shock absorbing sheet 1 is preferably 10% or more, more preferably 20% or more, further preferably 30% or more, and particularly preferably 50% or more. The upper limit of this shock absorption rate may be 100%.

The impact absorption rate of the impact absorption sheet 1 is a value calculated from the impact acceleration measured by measuring the impact acceleration in accordance with, for example, JIS-C6000068-2-27. The method for measuring the shock absorption rate will be described in the column of Examples described later.

The shock absorbing sheet 1 according to the present embodiment can be suitably used for a flexible display. The shock absorbing sheet 1 is preferably used by being arranged on the back surface side of a flexible display such as an organic EL, and more preferably used by being directly laminated on the back surface of the flexible display. By using the shock absorbing sheet 1 according to the present embodiment in a display device including a flexible display, it is possible to suppress the occurrence of breakage due to interface peeling or bending in the shock absorbing sheet 1 even when used at a low temperature. It can protect the flexible display from shocks and vibrations.

Hereinafter, the present disclosure will be described in more detail by way of examples, but the present disclosure is not limited to these examples.

1. 1. Preparation of Shock Absorption Sheet-Materials for Silicone-Containing Layer and Adhesive Layer (a) As a silicone resin for providing the silicone-containing layer, a two-component addition reaction type silicone gel (manufactured by Shin-Etsu Chemical Co., Ltd., product number: X32-3443, main agent (A)) And the curing agent (B)) were used. An addition reaction type silicone polymer (manufactured by Shin-Etsu Chemical Co., Ltd., product number: X-40-3240) was used as the silicone resin for providing the silicone-containing layer in Comparative Example 2.
(B) As the pressure-sensitive adhesive for providing the pressure-sensitive adhesive layer, a copolymer of an acrylic pressure-sensitive adhesive (manufactured by Nippon Shokubai Co., Ltd., product number: HS51E, 2-ethylhexyl acrylate, n-butyl acrylate and a monomer component containing acrylic acid is contained. ) Was used.
-Preparation of shock absorbing sheet (i) The two-component addition reaction type silicone gel was formed into a sheet by extrusion molding, and then dried and cured to form a silicone-containing layer having the thickness shown in Table 1.
(Ii) Next, an acrylic pressure-sensitive adhesive was applied to one surface of the silicone-containing layer and dried to form a pressure-sensitive adhesive layer (1) having the thickness shown in Table 1. Next, an acrylic pressure-sensitive adhesive was applied to the surface of the silicone-containing layer opposite to the pressure-sensitive adhesive layer (1) and dried to form the pressure-sensitive adhesive layer (2) having the thickness shown in Table 1. In this way, a shock absorbing sheet was produced.

2. 2. Evaluation [shock absorption rate]
A shock absorbing sheet was attached to a polycarbonate plate (PC plate) having a thickness of 1.0 mm, and a metal cylinder having a diameter of 20 mm and a thickness of 4 mm was attached thereto to prepare a test piece. The impact acceleration of this test piece was measured according to JIS-C6000068-2-27 using a pendulum type impact test device (manufactured by Shinyei Testing Machinery Co., Ltd., model number PST-300). The shock absorption rate (%) was calculated by the following formula.
Impact absorption rate (%) = (1- (impact acceleration of test piece)) x 100 / (impact acceleration of PC plate alone)

[Adhesive strength between silicone-containing layer and adhesive layer (-20 ° C)]
For the adhesive strength between the silicone-containing layer and the adhesive layer at -20 ° C, a laminate of the silicone-containing layer and the adhesive layer was obtained from the shock absorbing sheet and cut into dimensions of 25 mm in width and 125 mm in length, and the silicone-containing layer was obtained. A PET film (manufactured by Toray Co., Ltd., product number S10) having a width of 30 mm, a length of 200 mm, and a thickness of 25 μm was bonded to a SUS plate using double-sided tape to prepare a test piece, and JIS-Z0237 " The measurement was performed in an environment of −20 ° C. by a method according to the “Adhesive Tape / Adhesive Sheet Test Method” (bonding conditions: 2 kg roller 1 reciprocation, peeling speed: 300 mm / min, peeling angle: 180 °).

[Bending resistance (-20 ° C)]
The bending resistance of the shock absorbing sheet at −20 ° C. was evaluated by performing the bending test shown below in an environment of −20 ° C. The shock absorbing sheet was cut into 20 cm squares to prepare test pieces. This test piece was fixed in a self-standing endurance tester (manufactured by Yuasa System Equipment Co., Ltd., model number TCD-BTFB) so that the core metal having a diameter of 20 mm and the center line of the test piece were aligned with each other. The bending test was carried out for 30 hours by repeating the operation of winding the shock absorbing sheet and the operation of returning the shock absorbing sheet at a speed of 30 times per minute. The bending resistance was evaluated as "OK" when the impact absorbing sheet after the bending test did not break or delaminate, and as "NG" when the breaking or delamination occurred.

[Adhesive strength of the adhesive layer against polyethylene terephthalate film (-20 ° C)]
The adhesive strength of the adhesive layer to the polyethylene terephthalate film at -20 ° C is such that the polyethylene terephthalate film (thickness 25 μm, manufactured by Toray Co., Ltd., product number S10) is bonded to the adhesive layer (1) in the shock absorbing sheet, and the width is 25 mm. × A test piece with a length of 125 mm was prepared and conformed to JIS-Z0237 “Adhesive Tape / Adhesive Sheet Test Method” (bonding conditions: 2 kg roller 1 reciprocation, peeling speed: 300 mm / min, peeling angle: 180 °). The measurement was carried out in an environment of −20 ° C.

[Adhesive strength of the adhesive layer against SUS (25 ° C)]
The adhesive strength of the shock absorbing sheet to SUS was determined by an adhesive strength test based on JIS-Z0237 "Adhesive Tape / Adhesive Sheet Test Method" under the condition of a tensile speed of 300 mm / min with a 90 degree peel tester under an environment of 25 ° C. Measured at.

1 Shock absorbing sheet 2 Silicone-containing layer 3 Adhesive layer 4 Separator

Claims (6)

A silicone-containing layer containing a silicone resin and
A shock absorbing sheet provided with an adhesive layer that overlaps the silicone-containing layer.
The thickness of the silicone-containing layer is 60% or more and 95% or less of the thickness of the shock absorbing sheet.
The storage elastic modulus (G1) at −20 ° C. and the storage elastic modulus (G2) at 25 ° C. of the silicone-containing layer are both 1 × 10 ⁴ Pa or more and 1 × 10 ⁵ Pa or less.
A shock absorbing sheet in which the adhesive layer contains a resin (A) having a peak temperature at which the loss tangent is 0 ° C. or lower. The shock absorbing sheet according to claim 1, wherein the silicone-containing layer has an adhesive force with respect to a polyethylene terephthalate film at −20 ° C. of 5 N / 25 mm or more. The resin (A) contains 97% by mass or more and 99.9% by mass or less of structural units derived from a (meth) acrylic acid ester having an alkyl group having 4 or more and 9 or less carbon atoms, and is derived from (meth) acrylic acid. The shock absorbing sheet according to claim 1 or 2, which contains 0.1% by mass or more and 3% by mass or less of the structural unit. The shock absorbing sheet according to any one of claims 1 to 3, wherein the thickness of the silicone-containing layer is 80 μm or more and 700 μm or less. The shock absorbing sheet according to any one of claims 1 to 4, wherein the thickness is 100 μm or more and 1000 μm or less. The shock absorbing sheet according to any one of claims 1 to 5, which is for a flexible display.

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