KR20230041697A - shock absorber sheet - Google Patents

Abstract

The shock-absorbing sheet 1 includes a silicon-containing layer 2 made of a silicone resin, and an elastic layer 3 overlapping the silicon-containing layer 2 . The thickness of the silicon-containing layer 2 is 50% or more and 98% or less of the thickness of the shock-absorbing sheet 1. The penetration of the silicon-containing layer 2 at 25°C in accordance with JIS K 2207 is 80 or more and 160 or less. The elastic layer 3 has a tensile modulus of elasticity of 1×10 ⁶ Pa or more and 1×10 ⁹ Pa or less, and the elastic layer 3 has an elongation at break of 100% or more.

Description

shock absorber sheet

The present disclosure relates to an impact-absorbing sheet, and more particularly, to an impact-absorbing sheet comprising a silicon-containing layer and an elastic layer.

BACKGROUND ART A shock absorbing sheet for absorbing shock or vibration generated when a display device is dropped is provided in a display of a display device used in various electronic devices such as a smartphone, a tablet terminal, and a notebook computer. In recent years, miniaturization and thinning of these electronic devices are rapidly progressing, and in response to this, shock-absorbing sheets capable of exhibiting excellent shock-absorbing properties even when the shock-absorbing layer is thin have been studied (Patent Document 1, Patent Document 2, and Patent Document 3). reference).

In recent years, displays having flexibility such as organic EL have been used in foldable terminals, electronic paper, and the like. A shock absorbing sheet used in a display device including such a flexible display may have problems such as deformation, such as unevenness, due to collision with an object caused by a drop or the like.

Japanese Unexamined Patent Publication No. 2016-030394 International Publication No. 2018/131619 Japanese Unexamined Patent Publication No. 2012-102878

An object of the present disclosure is to provide an impact absorbing sheet excellent in both shock absorbing properties and recovery properties against uneven deformation.

An impact absorbing sheet according to one aspect of the present disclosure includes a silicon-containing layer containing a silicone resin and an elastic layer overlapping the silicon-containing layer. The thickness of the silicon-containing layer is 50% or more and 98% or less of the thickness of the shock-absorbing sheet. The penetration of the silicon-containing layer at 25°C in accordance with JIS K 2207 is 60 or more and 160 or less. The elastic layer has a tensile modulus of elasticity of 1×10 ⁶ Pa or more and 1×10 ⁹ Pa or less, and the elastic layer has an elongation at break of 100% or more.

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

<Shock Absorption Sheet>

An impact-absorbing sheet (hereinafter, also referred to as impact-absorbing sheet 1) according to the present embodiment includes a silicone-containing layer containing a silicone resin and an elastic layer overlapping the silicone-containing layer. The thickness of the silicon-containing layer is 50% or more and 98% or less of the thickness of the shock-absorbing sheet 1. The penetration of the silicon-containing layer at 25°C in accordance with JIS K 2207 is 60 or more and 160 or less. The elastic layer has a tensile modulus of elasticity of 1×10 ⁶ Pa or more and 1×10 ⁹ Pa or less, and the elastic layer has an elongation at break of 100% or more. On the other hand, "overlapping" means that the silicon-containing layer and the elastic layer overlap in plan view.

The inventors of the present invention have found that, in an impact absorbing sheet 1 comprising a silicon-containing layer and an elastic layer, the efficiency of absorbing energy due to impact and the ability to recover to its original state when uneven deformation occurs, the penetration of the silicon-containing layer, and the tensile modulus of elasticity and the elongation at break of the elastic layer. That is, when the penetration of the silicon-containing layer is within the above-mentioned specific range, the elastic layer has a tensile modulus of elasticity of 1×10 ⁶ Pa or more and 1×10 ⁹ Pa or less, and the elongation at break is 100% or more, the shock-absorbing sheet 1 can be obtained. , it was found that, without impairing shock absorbency, recovery against uneven deformation can be improved. As described above, according to the present disclosure, it is possible to provide an impact absorbing sheet excellent in both shock absorbing properties and recovery against concave-convex deformation. When the penetration degree of the silicon-containing layer is outside the above range, the tensile modulus of the elastic layer is outside the above range, or the elongation at break is less than the above value, the flexibility of the silicon-containing layer or the elastic layer is not suitable, etc., resulting in uneven deformation. recovery is reduced. Further, in order to make the shock-absorbing sheet 1 excellent in both the shock-absorbing property and the recovery property against uneven deformation, in addition to these, the thickness of the silicon-containing layer is 50% or more and 98% or less of the thickness of the shock-absorbing sheet 1. found what was needed. If this thickness is less than 50%, the shock-absorbing property is lowered because the softness of the shock-absorbing sheet 1 is not appropriate. In addition, when this thickness is more than 98%, the resilience to concavo-convex deformation is lowered due to, for example, the thickness of the elastic layer being reduced.

1 shows an example of an impact absorbing sheet according to the present embodiment. The shock-absorbing sheet 1 in FIG. 1 includes a silicon-containing layer 2 and an elastic layer 3 directly overlapping the silicon-containing layer 2 .

[Silicone-containing layer]

The silicon-containing layer 2 contains a silicone resin. The silicon-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 even more preferably 90% by mass or more.

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

The thickness of the silicon-containing layer 2 is 50% or more and 98% or less of the thickness of the shock-absorbing sheet 1. The thickness of the silicon-containing layer 2 is preferably 63% or more, more preferably 70% or more, still more preferably 80% or more, and particularly preferably 83% or more. The thickness of the silicon-containing layer 2 is preferably 96% or less, more preferably 94% or less, still more preferably 92% or less, and particularly preferably 90% or less. By setting the thickness of the silicon-containing layer 2 within the above range, the shock absorption property and the recovery property against concavo-convex deformation can be further improved.

The thickness of the silicon-containing layer 2 is preferably 50 μm or more. In this case, the shock absorbing property of the shock absorbing sheet 1 can be further improved. As for this thickness, it is more preferable that it is 100 micrometers or more, it is still more preferable that it is 150 micrometers or more, and it is especially preferable that it is 200 micrometers or more. Moreover, it is preferable that the thickness of the silicon-containing layer 2 is 500 micrometers or less. In this case, the shock-absorbing sheet 1 can further improve its bending resistance. As for this thickness, it is more preferable that it is 400 micrometers or less, it is still more preferable that it is 350 micrometers or less, and it is especially preferable that it is 300 micrometers or less.

The penetration of the silicon-containing layer 2 is 60 or more and 160 or less. This penetration was measured in accordance with JIS K 2207 by using a penetration tester RPM-201 manufactured by Rigo Co., Ltd., vertically penetrating the sample at 25 ° C. under the condition that the total weight of the needle holder and needle is 50 g, It is a value multiplied by 10 times the penetration depth (mm) of the needle in seconds. The penetration is preferably 70 or more, more preferably 80 or more, still more preferably 90 or more, and particularly preferably 100 or more. In this case, shock absorbency can be further improved. Moreover, the penetration is preferably 150 or less, more preferably 140 or less, still more preferably 130 or less, and particularly preferably 120 or less. In this case, recovery against uneven deformation can be further improved.

The storage elastic modulus (G1) at -20°C and the storage elastic modulus (G2) at 25°C of the silicon-containing layer 2 are preferably 1×10 ⁴ Pa or more and less than 1×10 ⁶ Pa. In this case, a decrease in the adhesive force between the silicon-containing layer 2 and the elastic layer 3 at low temperatures can be reduced, and the peeling resistance of the shock-absorbing sheet 1 can be further improved. Further, in this case, it is considered that the wettability of the silicon-containing layer 2 and the elastic layer 3 can be maintained at low temperatures, the adhesive force between the layers does not significantly decrease, and the peeling resistance at low temperatures is further improved. When at least one of G1 and G2 is less than 1 × 10 ⁴ Pa or more than 1 × 10 ⁶ Pa, the adhesive force between the layers is reduced at low temperatures, and peeling resistance is lowered, as well as impact resistance and recovery from uneven deformation. There may be cases At least one of G1 and G2 is more preferably 1.5 × 10 ⁴ or more and 1 × 10 ⁵ or less, more preferably 1.8 × 10 ⁴ or more and 5 × 10 ⁴ or less, and particularly preferably 2 × 10 ⁴ or more and 3 × 10 ^{4 or} less. It is preferable, and it is particularly more preferable that it is 2.2×10 ⁴ or more and 2.7×10 ⁴ or less. Further, it is most preferable that both G1 and G2 are within the above ranges. By making G1 and G2 into the said range, peeling resistance and bending resistance in low temperature can be further improved.

(silicone resin)

A "silicone resin" refers to a compound containing a polysiloxane print (-Si-O-Si-O-) composed of siloxane bonds as a main skeleton. The silicone resin preferably contains silicone gel from the viewpoint of shock absorption performance, and more preferably contains addition reaction type silicone gel from the viewpoint of more easily adjusting the penetration of the silicon-containing layer 2 within the above range. do. The addition reaction type silicone gel is obtained, for example, by subjecting organohydrogenpolysiloxane and alkenylpolysiloxane to be described later as raw materials to a hydrosilylation reaction (addition reaction) of both in the presence of a catalyst. Organohydrogenpolysiloxane is represented by following formula (1), for example.

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 at least two of R ² , R ³ and R ⁴ represent -H. x and y represent the number of each unit, and are each independently an integer greater than or equal to 0. x+y is an integer of 5 or more and 300 or less.

It is preferable that x is 10 or more and 30 or less. It is preferable that y is 1 or more and 10 or less. It is preferable that x+y is 30 or more and 200 or less. It is preferable that y/(x+y) is 0.1 or less. When y/(x+y) exceeds 0.1, the number of crosslinking points increases, and impact absorption may decrease.

Arrangement of each unit in Formula (1) may be random or block, but random is preferable.

A hydrogen atom (Si-H) bonded directly to a silicon atom is necessary for carrying out an addition reaction (hydrosilylation reaction) with an alkenyl group bonded directly or indirectly to a silicon atom, and is present in the organohydrogenpolysiloxane molecule. It is desirable to have at least two.

Alkenyl polysiloxane is represented by following formula (2), for example.

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. 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 greater than or equal to 0. s+t is an integer of 10 or more and 600 or less.

It is preferable that s is 10 or more and 30 or less. It is preferable that t is 1 or more and 10 or less. It is preferable that t/(s+t) is 0.1 or less. When t/(s+t) exceeds 0.1, the number of crosslinking points may increase and the shock absorbency may decrease.

An alkenyl group (vinyl group, allyl group, etc.) bonded directly or indirectly to a silicon atom is required for carrying out an addition reaction (hydrosilylation reaction) with a hydrogen atom (Si-H) directly bonded to a silicon atom, It is preferable to have at least 2 in an alkenyl polysiloxane molecule.

Examples of R ¹ in Formulas (1) and (2) include alkyl groups such as a methyl group, an ethyl group, a propyl group, and a butyl group; Cycloalkyl groups, such as a cyclopentyl group and a cyclohexyl group; Aryl groups, such as a phenyl group and a tolyl group; Aralkyl groups, such as a benzyl group and a phenethyl group; and halogenated hydrocarbon groups in which some or all of the hydrogen atoms in these groups are substituted with chlorine atoms, fluorine atoms, or the like.

The hydrosilylation reaction can be performed using a known technique. 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, and a platinum-phosphorus complex. 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, as platinum atoms, relative to the alkenylpolysiloxane.

The silicone-containing layer 2 may contain components other than the silicone resin, such as resins other than the silicone resin, pigments, heat dissipating fine particles, flame retardants, and thermal stabilizers, within a range not impairing the effects of the present disclosure.

The method for forming the silicone-containing layer 2 is not particularly limited, but is, for example, a method of applying a silicone resin to the surface of the elastic layer 3 or a molding method such as extrusion molding of a composition containing a precursor of the silicone resin. and then performing a curing reaction such as a hydrosilylation reaction to form a silicone resin.

[elastic layer]

The elastic layer (3) is disposed overlapping the silicon-containing layer (2). The elastic layer 3 has a tensile modulus of elasticity of 1×10 ⁶ Pa or more and 1×10 ⁹ Pa or less, and an elongation at break of 100% or more. The shock-absorbing sheet 1 may include one layer of the elastic layer 3, may include two layers, or may include three or more layers.

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

It is preferable that the thickness of the elastic layer 3 is 5 micrometers or more. In this case, shock absorbency can be further improved. As for this thickness, it is more preferable that it is 10 micrometers or more, and it is still more preferable that it is 20 micrometers or more. Moreover, it is preferable that this thickness is 100 micrometers or less. In this case, bending resistance can be further improved. As for this thickness, it is more preferable that it is 70 micrometers or less, and it is more preferable that it is 50 micrometers or less.

The tensile modulus of elasticity of the elastic layer 3 is preferably 2.5 × 10 ⁶ or more and 5.0 × 10 ⁸ or less, more preferably 5.0 × 10 ⁶ or more and 2.5 × 10 ⁸ or less, and 1.0 × 10 ⁷ or more and 1.0 × 10 ⁸ or less. More preferably, it is 2.5×10 ⁷ or more and 7.5×10 ⁷ or less is particularly preferable. In this case, it is possible to further improve recovery against uneven deformation without impairing shock absorption.

The material that can be used for the elastic layer 3 is not particularly limited as long as it is a resin having a tensile elastic modulus and an elongation at break in the above ranges. Examples of the resin include (meth)acrylic resin, polyester resin, urethane resin, polyvinyl resin (polyvinyl alcohol, vinyl chloride-vinyl acetate copolymer, etc.), epoxy resin and the like. A (meth)acrylic resin includes both an acrylic resin and a methacrylic resin, and contains a structural unit derived from a (meth)acrylic acid ester.

The elastic layer 3 preferably contains a stretchable elastomer resin from the viewpoint of further improving the recovery property against uneven deformation.

Examples of the stretchable elastomer resin include acrylic elastomers, urethane elastomers, olefin elastomers, amide elastomers, styrene elastomers, and ester elastomers.

Examples of the acrylic elastomer include copolymers in which the hard segment contains a (meth)acrylic acid ester unit and the soft segment contains an acrylonitrile unit, an ethylene unit, and a (meth)acrylic acid ester unit.

Examples of the urethane-based elastomer include copolymers in which the hard segment contains a polyurethane structure and the soft segment contains a polyester structure, a polyether structure, a polycaprolactone structure, and the like.

As the olefinic elastomer, for example, olefinic rubber such as ethylene/propylene rubber or ethylene/propylene/diene terpolymer is finely dispersed in a matrix of olefinic resin such as polypropylene and polyethylene. polymer alloy; and copolymers in which the hard segment contains a polybutadiene structure and the soft segment contains a polyether structure, a polyester structure, and the like.

Examples of the amide-based elastomer include copolymers in which the hard segment contains a polyamide structure and the soft segment contains a polyether structure or a polyester structure.

Examples of the styrenic elastomer include copolymers in which the hard segment contains styrene units and the soft segment contains butadiene units or hydrogenated butadiene units, or isoprene units or hydrogenated isoprene units. can

Examples of the ester-based elastomer include copolymers in which the hard segment contains a polyester structure and the soft segment contains a polyether structure, a polyester structure, and the like.

The elastic layer 3 preferably contains at least one of a (meth)acrylic resin and an acrylic elastomer from the viewpoints of adhesiveness, transparency and weather resistance.

Examples of (meth)acrylic acid esters that give (meth)acrylic resins and acrylic elastomers include (meth)acrylic acid monomers such as (meth)acrylic acid esters having a substituted or unsubstituted monovalent hydrocarbon group.

As a monovalent hydrocarbon group, For example, C1-C20 alkyl groups, such as a methyl group, an ethyl group, a propyl group, and a butyl group; cycloalkyl groups having 3 or more and 20 or less carbon atoms, such as a cyclopentyl group and a cyclohexyl group; aryl groups having 6 or more and 20 or less carbon atoms, such as a phenyl group and a tolyl group; Aralkyl groups having 7 or more and 20 or less carbon atoms, such as a benzyl group and a phenethyl group; and the like.

(Meth)acrylic resins and acrylic elastomers are (meth)acrylic monomers having a homopolymer glass transition temperature (Tg) of -10°C or lower (hereinafter also referred to as monomer A) from the viewpoint of further improving recovery properties against uneven deformation. and a (meth)acrylic monomer (hereinafter also referred to as monomer B) having a homopolymer Tg of 60°C or higher.

Examples of the monomer A include n-butyl acrylate, 2-ethylhexyl (meth)acrylate, isooctyl (meth)acrylate, n-octyl (meth)acrylate, isononyl (meth)acrylate, Lauryl methacrylate etc. are mentioned. Examples of the monomer B include methyl methacrylate, benzyl methacrylate, cyclohexyl methacrylate, and isobornyl (meth)acrylate.

In the (meth)acrylic resin and the acrylic elastomer, the proportion of structural units derived from the monomer A is preferably 45% by mass or more with respect to all the structural units constituting the (meth)acrylic resin and the acrylic elastomer. In this case, the adhesive force between the elastic layer 3 and the silicon-containing layer 2 can be increased, and as a result, peeling resistance and bending resistance can be further improved. As for this ratio, it is more preferable that it is 50 mass % or more, it is still more preferable that it is 55 mass % or more, and it is especially preferable that it is 60 mass % or more. Further, the proportion of structural units derived from the monomer A is preferably 95% by mass or less, more preferably 80% by mass or less, and even more preferably 70% by mass or less.

The elastic layer 3 preferably contains a (meth)acryl block copolymer elastomer having a block composed of structural units derived from monomer A and a block composed of structural units derived from monomer B, and a butyl acrylate unit. and a (meth)acrylic block copolymer elastomer having a methyl methacrylate unit.

Examples of the epoxy resin include bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, aralkyl epoxy resin, phenol novolak type epoxy resin, alkylphenol novolak type epoxy resin, and biphenol type epoxy resin. , naphthalene-type epoxy resins, dicyclopentadiene-type epoxy resins, epoxides of condensates of phenols and aromatic aldehydes having phenolic hydroxyl groups, triglycidyl isocyanurates, alicyclic epoxy resins, and the like. These may be used individually by 1 type, and may be used in combination of 2 or more type.

As the epoxy resin, more preferably, a stretchable epoxy elastomer containing two or more epoxy groups and three methyl groups in one molecule and having a molecular weight of 500 or more is preferably exemplified. The epoxy resin may be cured using additives such as a curing agent and a curing accelerator.

The elastic layer 3 preferably contains at least one of a (meth)acryl block copolymer elastomer and an epoxy resin, and a (meth)acryl block copolymer elastomer and epoxy having a butyl acrylate unit and a methyl methacrylate unit It is more preferable to include at least one of resins.

The method of forming the elastic layer 3 is not particularly limited, but examples include a method of applying a material constituting the elastic layer 3 to the surface of the silicon-containing layer 2, and a method of applying a material constituting the elastic layer 3 to the surface of the elastic layer 3. , a method of applying the material constituting the silicon-containing layer 2, a method of co-extruding the material constituting the silicon-containing layer 2 and the material constituting the elastic layer 3, etc., the elastic layer 3 and the silicone A method of separately forming the containing layer 2 and bonding them together, and the like are exemplified.

It is preferable that the adhesive strength of the silicon-containing layer 2 to the elastic layer 3 at room temperature is 2 N/25 mm or more. In this case, peeling resistance and bending resistance can be further improved. As for this adhesive force, it is more preferable that it is 3 N/25 mm or more, it is still more preferable that it is 5 N/25 mm or more, and it is especially preferable that it is 7 N/25 mm or more.

[other floors]

The shock-absorbing sheet 1 may include other layers in addition to the silicon-containing layer 2 and the elastic layer 3. The shape of another layer is, for example, film, sheet, or plate, and may include an adhesive layer.

Examples of other layers include a thermal diffusion layer having thermal diffusion properties, a shield layer having electromagnetic wave shielding properties, and protective layers such as separators.

[Layer composition]

Examples of the layer structure of the shock-absorbing sheet 1 according to the present embodiment include the following (a) to (p) and the like. In the following, notation of A/B/C indicates that, for example, A, B, and C are laminated in order from the rear side of the display.

(a) elastic layer/silicon-containing layer

(b) elastic layer/silicon-containing layer/elastic layer

(c) elastic layer/silicon-containing layer/thermal diffusion layer

(d) elastic layer/silicon-containing layer/thermal diffusion layer/adhesive layer

(e) elastic layer/silicon-containing layer/thermal diffusion layer/adhesive layer/shield layer

(f) Elastic layer/Silicone-containing layer/Heat diffusion layer/Adhesive layer/Shield layer/Adhesive layer

(g) elastic layer/silicon-containing layer/adhesive layer/thermal diffusion layer/adhesive layer/shield layer

(h) elastic layer/silicon-containing layer/adhesive layer/thermal diffusion layer/adhesive layer/shield layer/adhesive layer

(i) Separator/adhesive layer/elastic layer/silicon-containing layer

(j) Separator/adhesive layer/elastic layer/silicon-containing layer/elastic layer/adhesive layer/separator

(k) Separator/adhesive layer/elastic layer/silicon-containing layer/thermal diffusion layer

(l) Separator/adhesive layer/elastic layer/silicon-containing layer/thermal diffusion layer/adhesive layer/separator

(m) Separator / adhesive layer / elastic layer / silicon-containing layer / thermal diffusion layer / adhesive layer / shield layer

(n) Separator/adhesive layer/elastic layer/silicon-containing layer/thermal diffusion layer/adhesive layer/shield layer/adhesive layer/separator

(o) Separator/adhesive layer/elastic layer/silicon-containing layer/adhesive layer/thermal diffusion layer/adhesive layer/shield layer

(p) Separator/adhesive layer/elastic layer/silicon-containing layer/adhesive layer/thermal diffusion layer/adhesive layer/shield layer/adhesive layer/separator

Fig. 2 shows an impact-absorbing sheet having the layer configuration of (j) above. The shock-absorbing sheet 1 in FIG. 2 includes a silicon-containing layer 2, two elastic layers 3 and 3 directly laminated on both surfaces of the silicon-containing layer 2, and these elastic layers 3 and 3 directly. Two adhesive layers 4 and 4 to be laminated, and separators 5 and 5 to be directly laminated on these adhesive layers 4 and 4 are provided.

The total of the thickness of the silicon-containing layer 2 and the thickness of the elastic layer 3 in the shock-absorbing sheet 1 is preferably 50 μm or more. In this case, the shock absorbing property of the shock absorbing sheet 1 can be further improved. As for this thickness, it is more preferable that it is 100 micrometers or more, and it is more preferable that it is 200 micrometers or more. Moreover, it is preferable that the total of this thickness is 500 micrometers or less. In this case, bending resistance can be further improved. As for this thickness, it is more preferable that it is 400 micrometers or less, and it is more preferable that it is 350 micrometers or less.

The thickness of the shock-absorbing sheet 1 is preferably 50 μm or more. In this case, the strength of the shock-absorbing sheet 1 can be further improved. As for this thickness, it is more preferable that it is 100 micrometers or more, and it is more preferable that it is 200 micrometers or more. The thickness of the shock-absorbing sheet 1 is preferably 500 µm or less. In this case, it is possible to further reduce the thickness of the display device including the display. As for this thickness, it is more preferable that it is 400 micrometers or less, and it is more preferable that it is 350 micrometers or less.

The impact absorption rate of the shock-absorbing sheet 1 is preferably 10% or more, more preferably 20% or more, still more preferably 30% or more, and particularly preferably 40% or more. The upper limit of this shock absorption rate may be 100%. The shock absorption rate of the shock-absorbing sheet 1 is a value measured by, for example, a steel ball drop method. The measuring method of shock absorption rate is demonstrated in the column of the Example posted later.

The shock-absorbing sheet 1 according to the present embodiment can be suitably used for flexible displays. The shock absorbing sheet 1 is preferably disposed on the rear side or surface side of a flexible display such as organic EL and used, more preferably disposed on the rear side and used, and is directly laminated on the rear surface of the flexible display. It is more preferable to use A flexible display can be effectively protected from shock or vibration by using the shock-absorbing sheet 1 excellent in both shock absorption and uneven deformation recovery according to the present embodiment in a display device including a flexible display. can

Example

Hereinafter, the present disclosure will be described in more detail with examples, but the present disclosure is not limited to these examples at all.

1. Fabrication of shock absorbing sheet

- silicone resin to give a silicone-containing layer

Resin A: Two-component addition reaction type silicone gel (manufactured by Shin-Etsu Chemical Co., Ltd., part number: KE-104, having a main agent (A) and a curing agent (B))

Resin B: 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))

Resin C: addition curing type silicone adhesive (manufactured by Shin-Etsu Chemical Co., Ltd., product number: X-40-3240, having a main agent (A) and a curing agent (B))

For the resins A to C, the main agent (A) and the curing agent (B) were mixed and used in the compounding ratio shown in Table 1.

- Elastomer resin that gives an elastic layer

・Acrylic elastomer (block copolymer of butyl acrylate (BA) and methyl methacrylate (MMA), manufactured by Kuraray Co., Ltd., product number: LA4285), and acrylic elastomer (butyl acrylate (BA) and methyl methacrylate (MMA)) A block copolymer of Kuraray Co., Ltd., product number: LA2270) was used in combination, and the ratio (mass ratio) of BA/MMA was 55/45 (Example 1, Example 2, Example 4, Example 8 and Example 12) Alternatively, they were mixed and used so as to become 52/48 (Example 3 and Comparative Example 4). In addition, LA4285 and an acrylic elastomer (a block copolymer of butyl acrylate (BA) and methyl methacrylate (MMA), manufactured by Kuraray Co., Ltd., product number: LA2250) were used in combination, and the ratio of BA/MMA was 65/35 (Example 5 , Examples 13 and 14) were mixed and used. In addition, LA4285 and an acrylic elastomer (a block copolymer of butyl acrylate (BA) and methyl methacrylate (MMA), manufactured by Kuraray Co., Ltd., product number: LK9243) were used in combination, and the ratio of BA/MMA was 80/20 (Comparative Example 2 ) were mixed and used.

As the stretchable epoxy elastomer, an epoxy resin (manufactured by Mitsubishi Chemical, product number JER1003) and polyrotaxane (manufactured by ASM, product number SH3400P) were used in combination, and mixed so that the ratio of JER1003/SH3400P was as shown in Table 1. With respect to 100 parts by mass of the stretchable epoxy elastomer, as a curing agent, an acid anhydride (“YH-307” manufactured by Mitsubishi Chemical Corporation, monofunctional acid anhydride, functional group equivalent: 231) 1 part by mass, and an imidazole-based curing accelerator as a curing accelerator ( "2E4MZ" manufactured by Shikoku Chemical Industries, Ltd., 2-ethyl-4-methylimidazole) 0.5 parts by mass was mixed and used.

- Manufacture of shock absorbing sheet

(i) A silicone-containing layer having a thickness shown in Table 1 was formed by molding the two-component addition reaction type silicone gel into a sheet shape by extrusion molding, followed by drying and curing.

(ii) Next, the synthesized elastomer resin was applied to the release treated surface of the release polyethylene terephthalate film and dried to form elastic layers 1 and 2 of the types and thicknesses of the resins shown in Table 1.

(iii) Subsequently, the elastic layers 1 and 2 formed above were bonded to both surfaces of the silicon-containing layer. In this way, a shock absorbing sheet was produced.

"-" in elastic layer 1 and elastic layer 2 in Table 1 indicates that the corresponding elastic layer was not used.

2. Measurement of physical properties

[Storage modulus of silicon-containing layer]

The silicon-containing layer was cut into a size of 10 mm in width and 20 mm in length to prepare a test piece. For this test piece, using a dynamic viscoelasticity measuring device (DVA-200, manufactured by Haiti Metrology Co., Ltd.), the storage modulus (Pa) at -20 ° C and 25 ° C under conditions of a frequency of 10 Hz and a heating rate of 5 ° C / min. was measured.

[Tensile modulus of elasticity of elastic layer]

The elastic layer was cut into a size of 10 mm in width and 20 mm in length to prepare a test piece. With respect to this test piece, the tensile modulus (Pa) at 25 ° C. was measured using a dynamic viscoelasticity measuring device (DVA-200, manufactured by Haiti Metrology Co., Ltd.) under conditions of a frequency of 10 Hz and a heating rate of 5 ° C./min.

[Elongation at Break of Elastic Layer]

(Production of test piece)

A No. 6 dumbbell test piece of JIS K 6251 regulation was punched out to make a test piece.

(Measurement of elongation at break)

Using the obtained test piece, a tensile test was conducted under the conditions shown below with an Autograph (AGS-X) manufactured by Shimadzu Corporation.

Temperature: 25℃

Load cell: 50N

Distance between initial grippers: 35 mm

Tensile speed: 25mm/min

(Calculation of elongation at break)

Elongation at break (%) is calculated by the following equation using the gripper travel distance at break.

Elongation at break (%)=(L-Lo)×100/Lo

Lo: sample length before test, L: sample length at break

[Adhesion of Silicon-Containing Layer to Elastic Layer]

The silicon-containing layer was cut into a size of 25 mm in width and 100 mm in length, laminated on the elastic layer, and the laminate was made to reciprocate once using a rubber roller of 2.0 kg at a speed of 300 mm/min, thereby forming the silicon-containing layer. and an elastic layer were bonded together. Next, it was left to stand for 20 minutes under conditions of 25°C to prepare a test piece. This test piece was tested at room temperature (23°C) by a method based on JIS-Z0237 "Testing methods for adhesive tapes and adhesive sheets" (bonding conditions: 2 kg roller 1 reciprocation, peeling speed: 300 mm/min, peeling angle: 180°). ) was measured under the environment of

3. Evaluation

[Shock absorption rate] (steel ball drop test)

(sample production)

The shock-absorbing sheet was cut into a size of 5 cm x 5 cm to prepare a sample for a steel ball drop test.

(Assessment Methods)

An acceleration sensor element of a digital accelerometer (modeled by Showa Soki Co., Ltd., MODEL-1340B) was fixed to one side of a 10 cm square aluminum plate with a thickness of 2 mm using a general-purpose adhesive tape with a thickness of 25 μm. Next, the aluminum plate was fixed to the mount with the acceleration sensor facing down. Next, the cut sample was placed on the aluminum plate, and a steel ball drop test was conducted using a SUS ball having a diameter of 20 mm and a weight of 14 g under the condition of a drop height of 10 cm.

(Calculation of shock absorption rate)

The impact absorption rate (%) was calculated by the following formula.

Impact absorption rate (%) = (Peak acceleration in aluminum alone - Peak acceleration in case of using test piece) × 100 / (Peak acceleration in aluminum alone)

[Irregular deformation recovery test] (steel ball drop test)

(sample production)

The shock-absorbing sheet was cut into a size of 5 cm x 5 cm to prepare a sample for a steel ball drop test.

(Assessment Methods)

The cut sample was placed on a 10 cm square aluminum plate with a thickness of 2 mm, and a steel ball drop test was conducted using a SUS ball with a diameter of 20 mm and a weight of 14 g under the condition of a drop height of 10 cm.

(Roughness evaluation)

The depression of the test sample immediately after the steel ball was dropped was observed with the naked eye, and the recovery of the impact-absorbing sheet against uneven deformation was evaluated according to the following criteria.

A: no dent

B: The depression disappears within 2 hours

C: The depression is not lost

[bending test]

The bending resistance of the impact-absorbing sheet was evaluated by conducting a bending test described below.

The impact-absorbing sheet was cut into a 2×10 cm spherical shape to prepare a test piece. This test piece was fixed so that the bending radius was 5 mm in a planar unloaded U-shaped extension tester (manufactured by Yuasa System Equipment, model number: body: DMLHB, jig: planar unloaded U-shaped extension test jig). The bending test was performed 10,000 times by repeating the operation of bending and returning the shock-absorbing sheet at a rate of 30 times per minute. The test piece after the bending test was visually observed, and the bending resistance of the shock-absorbing sheet was evaluated according to the following criteria.

A: No change in appearance or wrinkles

B: Wrinkles disappear within 24 hours

C: No loss of wrinkles

1 shock absorbing seat
2 Silicon-containing layer
3 elastic layer
4 adhesive layer
5 separator

Claims (5)

A silicon-containing layer comprising a silicone resin;
An elastic layer overlapping the silicon-containing layer
As a shock absorbing sheet having a,
The thickness of the silicon-containing layer is 50% or more and 98% or less of the thickness of the shock absorbing sheet,
The silicon-containing layer has a penetration of 60 or more and 160 or less at 25 ° C in accordance with JIS K 2207,
The impact-absorbing sheet according to claim 1 , wherein the elastic layer has a tensile modulus of elasticity of 1×10 ⁶ Pa or more and 1×10 ⁹ Pa or less, and the elastic layer has an elongation at break of 100% or more. According to claim 1,
A shock-absorbing sheet having a shock absorption rate of 20% or more as measured by the steel ball drop method. According to claim 1 or 2,
An impact-absorbing sheet wherein the adhesive force of the silicon-containing layer to the elastic layer is 2 N/25 mm or more. According to any one of claims 1 to 3,
A shock-absorbing sheet with a thickness of 50 μm or more and 500 μm or less. According to any one of claims 1 to 4,
An impact-absorbing sheet in which the elastic layer includes at least one of a (meth)acrylic block copolymer elastomer having a butyl acrylate unit and a methyl methacrylate unit, and an epoxy resin.

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