Impact absorption sheet

Abstract

To provide an impact absorption sheet that is excellent in both peeling resistance and flex resistance under low temperature.SOLUTION: An impact absorption sheet 1 comprises a silicone-containing layer 2 containing silicone resin, and an adhesive layer 3 overlapped on the silicone-containing layer. The thickness of the silicone-containing layer is 80 μm or more and 400 μm or less. The thickness of adhesive layer is 5 μm or more and 90 μm or less. The thickness of the silicone-containing layer is 60% or more and 95% or less the thickness of the impact absorption sheet. The silicone resin contains addition reaction type silicone gel which is an addition reaction product of organohydrogenpolysiloxane and alkenyl polysiloxane. The adhesive layer contains resin (A) including a structural unit derived from (meth)acrylic acid ester by 97 mass% or more and 99.9 mass% or less and a structural unit derived from (meth)acrylic acid by 0.1 mass% or more and 3 mass% or less. The impact absorption ratio of the impact absorption sheet is 20% or more and 100% or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] 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.

Background Art

[0002] In display devices used in various electronic devices such as smartphones, tablet terminals, and notebook computers, a shock-absorbing sheet for absorbing shocks and vibrations is provided on the back side of the display. In recent years, these electronic devices have been rapidly miniaturized and thinned, and in response, shock-absorbing sheets that can exhibit excellent shock-absorbing properties even when the shock-absorbing layer is made thin have been studied (see Patent Document 1, Patent Document 2, and Patent Document 3).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0004] Recently, in foldable terminals, electronic papers, etc., flexible displays such as organic ELs have come to be used. In a shock-absorbing sheet used for a display device including such a flexible display, since a load is applied every time it is bent, problems such as interfacial peeling and structural deformation may occur. Since this problem becomes particularly prominent in a low-temperature environment of 0°C or lower, it is necessary for the shock-absorbing sheet to improve both peel resistance and bend resistance at low temperatures.

[0005] An object of the present disclosure is to provide a shock-absorbing sheet that is excellent in both peel resistance and bend resistance at low temperatures.

Means for Solving the Problems

[0006] 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 80 μm or more and 400 μm or less. The thickness of the adhesive layer is 5 μm or more and 90 μm or less. The thickness of the silicone-containing layer is 60% or more and 95% or less of the thickness of the shock-absorbing sheet. The silicone resin includes an addition reaction type silicone gel. The addition reaction type silicone gel is an addition reaction product of an organohydrogenpolysiloxane represented by the following formula (1) and an alkenylpolysiloxane represented by the following formula (2). The adhesive layer contains a resin (A). The resin (A) contains 97% by mass or more and 99.9% by mass or less of a structural unit derived from a (meth)acrylate having an alkyl group having 4 to 9 carbon atoms, and 0.1% by mass or more and 3% by mass or less of a structural unit derived from (meth)acrylic acid. The shock absorption rate calculated from the shock acceleration measured in accordance with JIS-C60068-2-27 of the shock-absorbing sheet is 20% or more and 100% or less.

Chemical formula

Chemical formula

Advantages of the Invention

[0007] According to the present disclosure, it is possible to provide a shock-absorbing sheet that is excellent in both peel resistance and bend resistance at low temperatures.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0009] <Shock-Absorbing 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 loss tangent of 0°C or less. Note that "overlapping" means that the silicone-containing layer and the adhesive layer overlap in a plan view.

[0010] The shock-absorbing sheet 1 has G1 and G2 both being 1×10 41×10 or more Pa 5 equal to or less than 1×10 Pa, and the peak temperature of the loss tangent of the resin (A) constituting the pressure-sensitive adhesive layer is 0°C or lower, so that the adhesive force between the silicone-containing layer and the pressure-sensitive adhesive layer at low temperatures becomes high, excellent peel resistance is achieved, and excellent flex resistance at low temperatures as evaluated by a bending test is also achieved. The reason can be inferred as follows. When both G1 and G2 of the silicone-containing layer are within the specific range, and the peak temperature of the loss tangent (tanδ) of the resin (A) is equal to or lower than the specific temperature, the shock-absorbing sheet 1 is considered to have appropriate flexibility at low temperatures, and the flex resistance can be improved. Also, it is considered that the wettability of the interface between the silicone-containing layer and the pressure-sensitive adhesive layer at low temperatures can be improved, the adhesive force between the layers becomes high, and the peel resistance at low temperatures 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 higher than 0°C, the adhesive force between the layers becomes small at low temperatures, the peel resistance decreases, and the flexibility of the shock-absorbing sheet 1 at low or normal temperatures becomes inappropriate, and the flex resistance decreases. Also, in order to make both the peel resistance and flex resistance of the shock-absorbing sheet 1 at low temperatures excellent, in addition to these, it has been found that the thickness of the silicone-containing layer needs to be 60% or more and 90% or less of the thickness of the shock-absorbing sheet 1. When this thickness is less than 60%, the flexibility of the shock-absorbing sheet 1 becomes inappropriate, and the flex resistance at low temperatures decreases. Also, when this thickness exceeds 95%, the strength of the pressure-sensitive adhesive layer becomes weak, and the peel resistance at low temperatures between the silicone-containing layer and the pressure-sensitive adhesive layer decreases.

[0011] FIG. 1 shows an example of a shock-absorbing sheet according to the present embodiment. The shock-absorbing sheet 1 in FIG. 1 includes a silicone-containing layer 2 and a pressure-sensitive adhesive layer 3 that directly overlaps the silicone-containing layer 2.

[0012] [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 the component with the largest mass ratio, preferably a component containing 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% or more.

[0013] The shock-absorbing sheet 1 may have one layer or two or more layers of the silicone-containing layer 2, but usually has one layer. The shape of the silicone-containing layer 2 is, for example, film-like, sheet-like, plate-like, etc.

[0014] 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, even more 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, even more preferably 87% or less, and particularly preferably 85% or less. By setting the thickness of the silicone-containing layer 2 within the above range, the peel resistance and flex resistance at low temperatures can be further improved.

[0015] The thickness of the silicone-containing layer 2 is preferably 80 μm or more. In this case, the shock absorption rate of the shock-absorbing sheet 1 can be further improved. This thickness is more preferably 100 μm or more, even more preferably 150 μm or more, and particularly preferably 200 μm or more. Also, the thickness of the silicone-containing layer 2 is preferably 700 μm or less. In this case, the flex resistance at low temperatures can be further improved. This thickness is more preferably 600 μm or less, even more preferably 500 μm or less, and particularly preferably 400 μm or less.

[0016] The storage elastic modulus (G1) of the silicone-containing layer 2 at -20°C and the storage elastic modulus (G2) at 25°C are both 1×10 4 Pa or more and 1×10 5is less than Pa. At least one of G1 and G2 is 1.5×10 4 or more and 7×10 4 or less, preferably 1.8×10 4 or more and 5×10 4 or less, more preferably 2×10 4 or more and 3×10 4 or less, even more preferably 2.2×10 4 or more and 2.7×10 4 or less, particularly preferably. Most preferably, both G1 and G2 are within the above range. By setting G1 and G2 within the above range, the peel resistance and flex resistance at low temperatures can be further improved.

[0017] (Silicone resin) The "silicone resin" refers to a compound containing a polysiloxane chain (-Si-O-Si-O-) composed of siloxane bonds as the main skeleton. From the perspective of impact absorption performance, it is preferable to contain a silicone gel, and from the perspective of easier adjustment of G1 and G2 within the above range, it is more preferable to contain an addition reaction type silicone gel. The addition reaction type silicone gel can be obtained, for example, by using an organohydrogenpolysiloxane and an alkenylpolysiloxane described below as raw materials and subjecting both to a hydrosilylation reaction (addition reaction) in the presence of a catalyst. The organohydrogenpolysiloxane is represented, for example, by the following formula (1).

[0018] [Chemical formula]

[0019] In formula (1), R 1 represents the same or different substituted or unsubstituted monovalent hydrocarbon group. R 2 , R 3 and R 4 represent R 1 or -H, and R 2 , R 3 and R 4At least two of them represent -H. x and y represent the number of each unit and are each independently an integer of 0 or more. x + y is an integer of 5 or more and 300 or less.

[0020] 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. When y / (x + y) exceeds 0.1, the number of crosslinking points may increase and the shock absorbency may decrease.

[0021] The arrangement of each unit in formula (1) may be random or block, but random is preferred.

[0022] The hydrogen atom directly bonded to the silicon atom (Si-H) is necessary for performing an addition reaction (hydrosilylation reaction) with an alkenyl group directly or indirectly bonded to the silicon atom, and preferably has at least 2 in the organohydrogenpolysiloxane molecule.

[0023] The alkenylpolysiloxane is represented by, for example, the following formula (2).

[0024]

Chemical formula

[0025] In formula (2), R 1 represents the same or different substituted or unsubstituted monovalent hydrocarbon group, and R 5 , R 6 and R 7 represent R 1 or an alkenyl group, and at least two of R 5 , R 6 and R 7 represent an alkenyl group. s and t represent the number of each unit and are each independently an integer of 0 or more. s + t is an integer of 10 or more and 600 or less.

[0026] 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. When t / (s + t) exceeds 0.1, the number of crosslinking points increases, and the impact absorbency may decrease.

[0027] The alkenyl group (vinyl group, allyl group, etc.) directly or indirectly bonded to the silicon atom is necessary for performing an addition reaction (hydrosilylation reaction) with the hydrogen atom (Si-H) directly bonded to the silicon atom, and it is preferably contained in at least 2 in the alkenyl polysiloxane molecule.

[0028] R in formula (1) and formula (2) 1 Examples include alkyl groups such as methyl group, ethyl group, propyl group, and butyl group; cycloalkyl groups such as cyclopentyl group and cyclohexyl group; aryl groups such as phenyl group and tolyl group; aralkyl groups such as benzyl group and phenethyl group; and halogenated hydrocarbon groups in which some or all of the hydrogen atoms of these groups are substituted with chlorine atoms, fluorine atoms, etc.

[0029] The hydrosilylation reaction can be carried out using known techniques. Examples of the catalyst for the hydrosilylation reaction include chloroplatinic acid, a complex obtained from chloroplatinic acid and alcohol, a platinum-olefin complex, a platinum-vinylsiloxane complex, a platinum-phosphorus complex, etc. The amount of the catalyst used is usually 1 ppm or more and 500 ppm or less, preferably 3 ppm or more and 200 ppm or less, in terms of platinum atoms, based on the alkenyl polysiloxane.

[0030] In addition to the silicone resin, the silicone-containing layer 2 may contain components such as other resins, pigments, heat-dissipating fine particles, flame retardants, and heat stabilizers as long as the effects of the present disclosure are not impaired.

[0031] The method for forming the silicone-containing layer 2 is not particularly limited. Examples include a method in which 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 carried out to form a silicone resin.

[0032] The adhesive force 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 temperatures can be further improved. This adhesive force is more preferably 7 N / 25 mm or more, and even more preferably 10 N / 25 mm or more. The upper limit value of this adhesive force is not particularly limited, but is, for example, 30 N / 25 mm.

[0033] [Adhesive layer] The adhesive layer 3 is disposed so as to overlap the silicone-containing layer 2. The adhesive layer 3 contains a resin (A) having a peak temperature of loss tangent of 0°C or less. The shock-absorbing sheet 1 may include one layer of the adhesive layer 3, two layers, or three or more layers.

[0034] The shape of the adhesive layer 3 is, for example, film-like, sheet-like, plate-like, or the like.

[0035] The thickness of the adhesive layer 3 is preferably 5 μm or more. In this case, the peel resistance at low temperatures can be further improved. This thickness is more preferably 10 μm or more, and even more preferably 20 μm or more. Also, this thickness is preferably 100 μm or less. In this case, the flex resistance at low temperatures can be further improved. This thickness is more preferably 90 μm or less, and even more preferably 80 μm or less.

[0036] (Resin (A)) The resin (A) has a peak temperature of loss tangent of 0°C or less. This peak temperature is preferably -5°C or less, more preferably -10°C or less, and even more preferably -15°C or less. In this case, the peel resistance and flex resistance at low temperatures can be further improved. The lower limit value of the peak temperature of loss tangent is not particularly limited, but is, for example, -50°C.

[0037] The resin (A) is not particularly limited as long as it is a resin whose peak temperature of loss tangent is within the above range. Examples of the resin (A) include (meth)acrylic resins, polyester resins, urethane resins, polyvinyl resins (such as polyvinyl alcohol, vinyl chloride-vinyl acetate copolymers, etc.). The (meth)acrylic resin includes both acrylic resins and methacrylic resins and contains structural units derived from (meth)acrylic acid esters.

[0038] From the viewpoint of further improving the peel resistance at low temperatures, the resin (A) preferably contains a (meth)acrylic resin.

[0039] Examples of the (meth)acrylic acid ester that gives the (meth)acrylic resin include (meth)acrylic acid esters having a substituted or unsubstituted monovalent hydrocarbon group.

[0040] Examples of the monovalent hydrocarbon group include alkyl groups having 1 to 20 carbon atoms such as methyl group, ethyl group, propyl group, butyl group, 2-ethylhexyl group; cycloalkyl groups having 3 to 20 carbon atoms such as cyclopentyl group, cyclohexyl group; aryl groups having 6 to 20 carbon atoms such as phenyl group, tolyl group; aralkyl groups having 7 to 20 carbon atoms such as benzyl group, phenethyl group, etc.

[0041] The number of carbon atoms of the monovalent hydrocarbon group is preferably 2 or more, more preferably 3 or more, still more preferably 4 or more, and particularly preferably 5 or more. The number of carbon atoms is preferably 15 or less, more preferably 12 or less, still more preferably 9 or less, and particularly preferably 8 or less.

[0042] Examples of the substituent of the hydrocarbon group include a polar group and the like. The "polar group" refers to a group containing at least one heteroatom. Examples of the heteroatom 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-, epoxy group), an alkoxy group, an alkoxyalkylalkoxy group, an amino group, a substituted amino group, a sulfanyl group, an alkylsulfanyl group; a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, and the like.

[0043] (Meth)acrylic acid ester preferably contains an unsubstituted hydrocarbon group, more preferably contains an unsubstituted alkyl group, and even more preferably contains an unsubstituted alkyl group having 4 to 9 carbon atoms.

[0044] Examples of the (meth)acrylic acid ester having an unsubstituted alkyl group having 4 to 9 carbon atoms include butyl (meth)acrylate such as n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, t-butyl (meth)acrylate; pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate; octyl (meth)acrylate such as n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate; nonyl (meth)acrylate and the like. Among these, acrylic acid ester is preferable.

[0045] When the resin (A) has a structural unit derived from a (meth)acrylate having an unsubstituted hydrocarbon group, the proportion of the structural unit derived from the (meth)acrylate having an unsubstituted hydrocarbon group is preferably 50% by mass or more, more preferably 90% by mass or more, still more preferably 97% by mass or more, and particularly preferably 98% by mass or more, based on all the structural units constituting the resin (A). This proportion is preferably 99.9% by mass or less, more preferably 99.5% by mass or less, still more preferably 99.3% by mass or less, and particularly preferably 99.0% by mass or less.

[0046] When the resin (A) has a structural unit derived from a (meth)acrylate having an unsubstituted hydrocarbon group, it preferably 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 and a structural unit derived from a (meth)acrylate having a hydrocarbon group to which a polar group is bonded.

[0047] Examples of the (meth)acrylic acid ester having a hydrocarbon group to which a polar group is bonded include hydroxy group-containing (meth)acrylic acid esters such as hydroxybutyl (meth)acrylate, hydroxypentyl (meth)acrylate, hydroxyhexyl (meth)acrylate, hydroxyoctyl (meth)acrylate, hydroxycyclohexyl (meth)acrylate, hydroxyphenyl (meth)acrylate, and polyethylene glycol (meth)acrylate; carboxy group-containing (meth)acrylic acid esters such as carboxypentyl (meth)acrylate, carboxyoctyl (meth)acrylate, carboxycyclohexyl (meth)acrylate, and carboxyphenyl (meth)acrylate; alkoxy group-containing (meth)acrylic acid esters such as ethoxybutyl (meth)acrylate, methoxyhexyl (meth)acrylate, methoxycyclohexyl (meth)acrylate, and ethoxyphenyl (meth)acrylate; epoxy group-containing (meth)acrylic acid esters such as epoxyethyl (meth)acrylate, epoxybutyl (meth)acrylate, and epoxycyclohexyl (meth)acrylate; and amino group-containing (meth)acrylic acid esters such as aminobutyl (meth)acrylate, dimethylaminobutyl (meth)acrylate, aminocyclohexyl (meth)acrylate, and methylaminophenyl (meth)acrylate.

[0048] 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.

[0049] In the resin (A), the proportion of the structural unit containing a polar group is preferably 0.1% by mass or more based on 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 increased, and as a result, the peel resistance and bend resistance at low temperatures can be further improved. This proportion is more preferably 0.5% by mass or more, still more preferably 0.7% by mass or more, and particularly preferably 1.0% by mass or more. This proportion is preferably 10% by mass or less, more preferably 3% by mass or less, still more preferably 2.5% by mass or less, and particularly preferably 2% by mass or less.

[0050] 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 more preferably has a structural unit derived from a (meth)acrylic acid ester having an alkyl group having 4 to 9 carbon atoms and a structural unit derived from (meth)acrylic acid. It is still more preferable to contain 97% by mass or more and 99.9% by mass or less of the structural unit derived from the (meth)acrylic acid ester having an alkyl group having 4 to 9 carbon atoms and 0.1% by mass or more and 3% by mass or less of the structural unit derived from (meth)acrylic acid.

[0051] The adhesive layer 3 can be formed using, for example, an adhesive containing the resin (A). The method for forming the adhesive layer 3 is not particularly limited, and examples thereof include a method of applying an adhesive containing the resin (A) to the surface of the silicone-containing layer 2 and drying it, and a method of co-extruding the material constituting the silicone-containing layer 2 and the adhesive containing the resin (A).

[0052] The adhesive force between the silicone-containing layer 2 and the adhesive layer 3 at -20°C is preferably 3 N / 25 mm or more. In this case, the peel resistance and bend resistance at low temperatures can be further improved. This adhesive force is more preferably 6 N / 25 mm or more, and still more preferably 8 N / 25 mm or more.

[0053] The adhesive force 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 even more preferably 16 N / 25 mm or more.

[0054] [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 layers is, for example, film-like, sheet-like, plate-like, or the like.

[0055] Examples of the other layers include a heat diffusion layer having heat diffusivity, a shield layer having electromagnetic wave shielding properties, and a protective layer such as a separator.

[0056] [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 A / B / C indicates that they are laminated in the order of A, B, and C from the back side of the display, for example. (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 / Thermal diffusion layer / Adhesive layer / Shield layer (n) Separator / Adhesive layer / Silicone-containing layer / Thermal diffusion layer / Adhesive layer / Shield layer / Adhesive layer / Separator (o) Separator / Adhesive layer / Silicone-containing layer / Adhesive layer / Thermal diffusion layer / Adhesive layer / Shield layer (p) Separator / Adhesive layer / Silicone-containing layer / Adhesive layer / Thermal diffusion layer / Adhesive layer / Shield layer / Adhesive layer / Separator

[0057] FIG. 2 shows a shock-absorbing sheet having the layer structure of the above (j). The shock-absorbing sheet 1 in FIG. 2 includes a silicone-containing layer 2, two adhesive layers 3, 3 directly laminated on both sides of the silicone-containing layer 2, and two separators 4, 4 directly laminated on these adhesive layers 3, 3.

[0058] 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 shock absorption rate of the shock-absorbing sheet 1 can be further improved. This thickness is more preferably 200 μm or more, and even more preferably 300 μm or more. Also, the total thickness is preferably 1000 μm or less. In this case, the bending resistance at low temperatures can be further improved. This thickness is more preferably 900 μm or less, and even more preferably 800 μm or less.

[0059] 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 even more preferably 300 μm or more. The thickness of the shock-absorbing sheet 1 is preferably 1000 μm or less. In this case, the thinning of the display device including the display can be further achieved. This thickness is more preferably 900 μm or less, and even more preferably 800 μm or less.

[0060] The impact absorption rate of the impact absorption sheet 1 is preferably 10% or more, more preferably 20% or more, still more preferably 30% or more, and particularly preferably 50% or more. The upper limit value of this impact absorption rate may be 100%.

[0061] The impact absorption rate of the impact absorption sheet 1 is, for example, a value calculated from the impact acceleration measured in accordance with JIS-C60068-2-27. The measurement method of the impact absorption rate will be described in the column of Examples below.

[0062] The impact absorption sheet 1 according to the present embodiment can be suitably used for a flexible display. The impact absorption sheet 1 is preferably disposed on the back side of a flexible display such as an organic EL, and more preferably directly laminated on the back of the flexible display. By using the impact absorption sheet 1 according to the present embodiment in a display device including a flexible display, even when used at a low temperature, the occurrence of interface peeling and breakage due to bending in the impact absorption sheet 1 can be suppressed, and the flexible display can be protected from impacts and vibrations.

Examples

[0063] Hereinafter, the present disclosure will be described in more detail by way of examples, but the present disclosure is not limited to these examples in any way.

[0064] 1. Fabrication of Impact Absorption Sheet - Materials for the silicone-containing layer and the adhesive layer (a) As the 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, having a main agent (A) and a curing agent (B)) was used. As the silicone resin for providing the silicone-containing layer in Comparative Example 2, an addition reaction type silicone polymer (manufactured by Shin-Etsu Chemical Co., Ltd., product number: X-40-3240) was used. (b) As the adhesive for providing the adhesive layer, an acrylic adhesive (manufactured by Nippon Shokubai Co., Ltd., product number: HS51E, containing a copolymer of monomer components including 2-ethylhexyl acrylate, n-butyl acrylate, and acrylic acid) was used. - Preparation of Impact Absorbing Sheet (i) A two-component addition reaction type silicone gel was formed into a sheet shape by extrusion molding, and then dried and cured to form a silicone-containing layer with the thickness shown in Table 1. (ii) Next, an acrylic adhesive was applied to one surface of this silicone-containing layer and dried to form an adhesive layer (1) with the thickness shown in Table 1. Then, an acrylic adhesive was similarly applied and dried to the surface of the silicone-containing layer opposite to the adhesive layer (1) to form an adhesive layer (2) with the thickness shown in Table 1. In this way, an impact absorbing sheet was prepared.

[0065] 2. Evaluation [Impact Absorption Rate] The impact absorbing sheet was bonded to a polycarbonate plate (PC plate) with a thickness of 1.0 mm, and further, a metal cylinder with a diameter of 20 mm and a thickness of 4 mm was bonded on it to prepare a test piece. For this test piece, an impact acceleration was measured using a pendulum type impact test apparatus (manufactured by Shinei Test Machinery Co., Ltd., model number PST-300) in accordance with JIS-C60068-2-27. The impact absorption rate (%) was calculated by the following formula. Impact Absorption Rate (%) = (1 - (impact acceleration of the test piece)) × 100 / (impact acceleration of the PC plate alone)

[0066] [Adhesion Force between Silicone-Containing Layer and Adhesive Layer (-20°C)] The adhesive force between the silicone-containing layer and the adhesive layer at -20°C was obtained by taking a laminate of the silicone-containing layer and the adhesive layer from the shock-absorbing sheet, cutting it into dimensions of 25 mm in width and 125 mm in length. The silicone-containing layer was bonded to a SUS plate using double-sided tape, and a PET film (manufactured by Toray Industries, Inc., product number S10) with a width of 30 mm, a length of 200 mm, and a thickness of 25 μm was bonded to the adhesive layer to prepare a test piece. It was measured in an environment of -20°C by a method conforming to JIS-Z0237 "Test Methods for Adhesive Tapes and Adhesive Sheets" (laminating condition: 1 reciprocation with a 2 kg roller, peeling speed: 300 mm / min, peeling angle: 180°).

[0067] [Flexural Resistance (-20°C)] Regarding the flexural resistance of the shock-absorbing sheet at -20°C, it was evaluated by conducting the following bending test in an environment of -20°C. The shock-absorbing sheet was cut into a 20 cm square to prepare a test piece. This test piece was fixed in a self-standing durability tester (manufactured by Yuasa System Devices Co., Ltd., model number TCD-BTFB) so that the center line of the test piece aligned with a mandrel having a diameter of 20 mm. The bending test was repeated at a speed of 30 times per minute for the operations of winding and unwinding the shock-absorbing sheet, and was performed for 30 hours. The flexural resistance was evaluated as "OK" when no breakage or delamination occurred in the shock-absorbing sheet after the bending test, and as "NG" when breakage or delamination occurred.

[0068] [Adhesive Force of the Adhesive Layer to the Polyethylene Terephthalate Film (-20°C)] The adhesive force of the adhesive layer to the polyethylene terephthalate film at -20°C was obtained by bonding a polyethylene terephthalate film (thickness 25 μm, manufactured by Toray Industries, Inc., product number S10) to the adhesive layer (1) in the shock-absorbing sheet, preparing a test piece with a width of 25 mm × a length of 125 mm, and using a method conforming to JIS-Z0237 "Test Methods for Adhesive Tapes and Adhesive Sheets" (laminating condition : 1 reciprocation with a 2 kg roller, peeling speed: 300 mm / min, peeling angle: 180°), and measuring it in an environment of -20°C.

[0069] [Adhesive Force of the Adhesive Layer to SUS (25°C)] The adhesion of the shock-absorbing sheet to SUS was measured under the environment of 25°C by a 90-degree peel tester at a tensile speed of 300 mm / min according to the adhesion test in accordance with JIS-Z0237 "Test Methods for Adhesive Tapes and Adhesive Sheets".

[0070]

Table 1

Explanation of Signs

[0071] 1 Shock-absorbing sheet 2 Silicon-containing layer 3 Adhesive layer 4 Separator

Claims

1. a silicone-containing layer containing a silicone resin; an adhesive layer overlying the silicone-containing layer; An impact absorbing sheet comprising: The thickness of the silicone-containing layer is 80 μm or more and 400 μm or less, The thickness of the adhesive layer is 5 μm or more and 90 μm or less, the thickness of the silicone-containing layer is 60% or more and 95% or less of the thickness of the impact absorbing sheet, The silicone resin includes an addition reaction type silicone gel, The addition reaction type silicone gel is An organohydrogenpolysiloxane represented by the following formula (1); An alkenylpolysiloxane represented by the following formula (2): is an addition reaction product of The adhesive layer contains a resin (A), 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 to 9 carbon atoms, and contains 0.1% by mass or more and 3% by mass or less of structural units derived from (meth)acrylic acid, The impact absorbing sheet has an impact absorption rate of 20% or more and 100% or less, calculated from impact acceleration measured in accordance with JIS-C60068-2-27. 【Chemistry 1】 In formula (1), R １ R represents the same or different substituted or unsubstituted monovalent hydrocarbon groups. ２ , R ３ and R ４ is R １ or -H, R ２ , R ３ and R ４ At least two of the groups represent -H. x and y represent the number of each unit and are each independently an integer of 0 or more. x+y is an integer between 5 and 300. 【Chemistry 2】 In formula (2), R １ R represents the same or different substituted or unsubstituted monovalent hydrocarbon groups; ５ , R ６ and R ７ is R １ or an alkenyl group; R ５ , R ６ and R ７ At least two of the groups represent an alkenyl group. s and t represent the number of each unit and are each independently an integer of 0 or more. s+t is an integer of 10 or more and 600 or less.

2. 2. The impact absorbing sheet according to claim 1, wherein the adhesive strength of the silicone-containing layer to a polyethylene terephthalate film at −20° C. is 5 N / 25 mm or more.

3. 3. The impact absorbing sheet according to claim 1, having a thickness of 100 μm or more and 1000 μm or less.

4. The impact absorbing sheet according to any one of claims 1 to 3, which is for a flexible display.

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