Shock absorber

Abstract

The present invention provides an impact absorber having adhesiveness and light-shielding properties. The impact absorber (1) comprises an insulating inorganic black pigment (3) contained in an organic silicone composition (2) having adhesiveness and stress relaxation properties. The impact absorber (1) has an adhesive force of 2 N / 20 mm or more to a glass plate. The impact absorber (1) has a transmittance of 0.6% or less for light having a wavelength of 300 nm or more and 850 nm or less. The impact absorber (1) has a needle penetration of 90 or more and 160 or less at 25°C according to JIS K 2207. The impact absorption rate of the impact absorber (1) is 20% or more.

Description

Technical Field

[0001] The present invention generally relates to an impact absorber, and more particularly to an impact absorber obtained by imparting light-shielding properties to an adhesive silicone composition. Background Art

[0002] Patent Document 1 describes an impact-absorbing film comprising a laminate. This laminate comprises a first stretchable film and a foam. The first stretchable film has a 10% modulus of tensile strength of 0.15 to 0.5 N / 10 mm and exhibits stretchability, returning to its original length upon release of the tensile force. The foam has a thickness of 0.05 mm to 0.5 mm. When multiple sheets composed solely of this foam are stacked to a thickness of 1 cm and compressed to 50% of the thickness, the rebound stress of the sheet is measured to be 0.02 MPa to 3.0 MPa.

[0003] Such impact-absorbing films are particularly used to protect the display panels, electronic circuits, batteries, and other components of products such as smartphones, tablets, and laptop computers. Specifically, these impact-absorbing films are used as shock-absorbing materials to prevent damage to the display panels of smartphones, tablets, and other products when they are subjected to impacts such as being dropped.

[0004] The impact-absorbing film of Patent Document 1 has difficulty imparting light-shielding properties to the impact-absorbing film itself, requiring the light-shielding film to be attached to the impact-absorbing film via an adhesive layer. Specifically, since the impact-absorbing film comprises a foam, surface pores on its surface cause surface scattering, making it difficult to impart light-shielding properties to the foam itself, requiring the light-shielding film to be attached separately to the impact-absorbing film.

[0005] Furthermore, when attaching the impact-absorbing film of Patent Document 1 to a display panel, etc., an adhesive layer is required to bond the impact-absorbing film to the display panel, etc. Furthermore, when the aforementioned light-shielding film is required, an adhesive layer is also required to bond the light-shielding film to the impact-absorbing film. Consequently, the display panel, etc., to which the light-shielding film and impact-absorbing film are attached, becomes rigid as a laminate, which can hinder the display panel, etc. from exhibiting its required functions of being able to bend and stretch freely.

[0006] Urethane, acrylic, or silicone foam or rubber-like shock absorbers are commonly used. However, silicone is advantageous for display applications, where performance stability is often required despite repeated use. Furthermore, shock absorbers work by contacting the object being protected, so they must exhibit adhesion to prevent separation from the object under repeated impact. Furthermore, displays, which require expensive components, require reworkability, making it crucial to control the adhesion of shock absorbers.

[0007] Patent Document 2 describes an adhesive sheet made of an addition-curable silicone composition with light-shielding properties. This adhesive sheet is used to shield and protect electrodes. However, the sheet is pressed against the object being protected in a semi-cured (A-stage) state and then cured by heat to achieve adhesion, making the production process complex. Furthermore, to maintain the semi-cured sheet, it must be stored at low temperatures, making production management difficult.

[0008] Patent Document 3 describes a material that is an addition-curable silicone composition and can be formed into a sheet. This material can be given light-shielding properties, thermal conductivity, and vibration absorption properties by adding materials, but there is no description regarding the adhesive strength of the material.

[0009] Patent Documents 4 and 5 describe adhesive silicone compositions. These silicone compositions adhere to the object being protected through heat upon contact. Patent Document 4 does not mention light-shielding properties. Such silicone compositions are not particularly useful due to the high likelihood of damage to displays during reprocessing.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-30394

[0013] Patent Document 2: Japanese Patent Application Laid-Open No. 2010-90363

[0014] Patent Document 3: Japanese Patent Application Laid-Open No. 2010-144133

[0015] Patent Document 4: Japanese Patent Application Laid-Open No. 2002-173661

[0016] Patent Document 5: Japanese Patent Application Laid-Open No. 62-240361 Summary of the Invention

[0017] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an impact absorber having adhesiveness and light-shielding properties.

[0018] Another object of the present invention is to provide a shock absorber that can be stored at room temperature and does not require post-curing.

[0019] An impact absorber according to one embodiment of the present invention comprises an insulating inorganic black pigment in a silicone composition having adhesive and stress-relieving properties. The impact absorber exhibits adhesion to a glass plate of 2 N / 20 mm or greater. Furthermore, the impact absorber exhibits a transmittance of 0.6% or less for light with a wavelength of 300 nm to 850 nm. Furthermore, the impact absorber exhibits a needle penetration of 90 to 160 at 25°C in accordance with JIS K 2207. Furthermore, the impact absorption rate of the impact absorber is 20% or greater. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A is a schematic diagram showing a shock absorber according to one embodiment of the present invention. Figure 1 B is an explanatory diagram showing a shock-absorbing laminate according to a comparative example.

[0021] Figure 2 This is a schematic diagram showing a test for measuring the adhesive strength of the impact absorber according to one embodiment of the present invention.

[0022] Figure 3 This is a schematic diagram showing a test for measuring the impact acceleration of the impact absorber according to one embodiment of the present invention. DETAILED DESCRIPTION

[0023] (Overview of shock absorbers)

[0024] Figure 1 A represents the impact absorber 1 of this embodiment. The impact absorber 1 comprises an insulating inorganic black pigment 3 contained in a silicone composition 2. The silicone composition 2 is a reaction product of an organosilicon compound and has adhesiveness and stress relaxation properties.

[0025] Figure 1B represents an impact-absorbing laminate 100 designed to achieve the same level of impact absorption, light-shielding properties, and adhesion as the impact-absorbing material 1. The impact-absorbing laminate 100 includes a porous structural layer 101 to achieve impact absorption. The porous structural layer 101 is formed from a foam such as polypropylene, polyethylene, polyacrylic acid, or polyurethane, and has a thickness of 50 to 1000 μm. Furthermore, the impact-absorbing laminate 100 includes a light-shielding substrate 102 with low light transmittance to achieve light-shielding properties. The light-shielding substrate 102 is formed to a thickness of 5 to 50 μm and is adhered to one surface of the porous structural layer 101 using an adhesive layer 103 having a thickness of 3 to 50 μm. Furthermore, the impact-absorbing laminate 100 includes two adhesive layers 104 and 105 having a thickness of 3 to 50 μm to achieve adhesion. Adhesion refers to the ability to adhere the impact-absorbing laminate 100 to other components. Therefore, one adhesive layer 104 is provided on the other side of the porous structure layer 101 (the side without the light-shielding substrate 102 ), and another adhesive layer 105 is provided on one side of the light-shielding substrate 102 (the side without the adhesive layer 103 ).

[0026] Thus, the impact-absorbing laminate 100 is composed of a porous structure layer 101 for achieving impact absorption, a light-shielding substrate 102 for achieving light-shielding properties, two adhesive layers 104 and 105 for achieving adhesion, and an adhesive layer 103 for bonding (adhering) the light-shielding substrate 102 to the porous structure layer 101. Consequently, its thickness is significantly increased. Meanwhile, the impact absorber 1 of this embodiment incorporates an insulating inorganic black pigment 3 within a silicone composition 2 having adhesive and stress-relieving properties. Thus, the silicone composition 2 provides impact absorption and adhesion, while the insulating inorganic black pigment 3 provides light-shielding properties. Therefore, even without the light-shielding substrate 102 and the three adhesive layers 103, 104, and 105, the impact absorber 1 has the same degree of impact absorption, light-shielding, and adhesion as the impact-absorbing laminate 100. Thus, the impact absorber 1 of this embodiment has impact absorption, light-shielding, and adhesion, while being thinner than the impact-absorbing laminate 100 (achieving a thinner profile). Specifically, the impact absorber 1 of this embodiment can be formed to have a thickness equivalent to that of the porous structure layer 101, or a thickness thinner than that of 80 μm to 500 μm. The thickness of the impact absorber 1 is preferably 100 μm to 450 μm. More preferably, the thickness of the impact absorber 1 is 150 μm to 300 μm.

[0027] The impact absorber 1 of this embodiment is preferably used, for example, for light shielding and shock absorption in display panels. Thus, the display panel is easily protected from the effects of impact by the impact absorber 1. Furthermore, the display panel is shielded from light by the impact absorber 1, which facilitates a clearer display. The display panel may be a liquid crystal panel, an organic EL panel, or the like.

[0028] The impact absorber 1 of this embodiment is preferably composed of a single layer. That is, the impact absorber 1 is preferably not laminated with other layers, but rather has adhesiveness, light-shielding properties, and impact-absorbing properties in one layer. As a result, the impact absorber 1 of this embodiment can be easily formed thinner. Adhesion refers to the function of being able to adhere to other components. The adhesiveness of the impact absorber 1 of this embodiment is determined by the adhesion to the glass plate. In addition, light-shielding properties refer to the function of being able to block light. The light-shielding properties of the impact absorber 1 of this embodiment are determined by the transmittance of light with a wavelength of 300 nm or more and 850 nm or less. Impact absorption refers to the function of being able to absorb impact. The impact absorption of the impact absorber 1 of this embodiment is determined by the impact absorption rate.

[0029] The impact absorber 1 of this embodiment is used in a state where it is arranged on the back side of a display panel. That is, the impact absorber 1 is used by being laminated on the back side of a display panel such as a liquid crystal panel used in a flat panel display. The impact absorber 1 of this embodiment does not require post-curing using heat and ultraviolet rays when it is arranged on the back side of a display panel. Here, post-curing refers to the curing process in the final stage of the manufacturing process. Therefore, the impact absorber 1 of this embodiment does not require a process for finally curing it using heat and ultraviolet rays when it is arranged on the back side of a display panel. That is, the impact absorber 1 of this embodiment can be bonded to the back side of a display panel even without post-curing based on heat and ultraviolet rays. Therefore, the impact absorber 1 of this embodiment can be bonded while reducing the adverse effects of heat and ultraviolet rays on the display panel.

[0030] The impact absorber 1 of this embodiment can be stored at room temperature. Specifically, the impact absorber 1 can be stored for long periods of time without experiencing significant changes in properties, without being exposed to low temperatures. Here, room temperature refers to 25°C. Furthermore, the impact absorber 1 can be stored at room temperature for six months with minimal changes in adhesiveness, light-shielding properties, penetration, and impact absorption.

[0031] (Silicone composition)

[0032] Silicone composition 2, a reaction product of organosilicon compounds, constitutes the main body of impact absorber 1. Specifically, silicone composition 2 functions as a matrix that inherently holds insulating inorganic black pigment 3. Furthermore, impact absorber 1 can physically mitigate impact energy primarily through silicone composition 2, without employing a porous structure.

[0033] In the impact absorber 1 of this embodiment, the silicone composition 2 has a sheet, plate, or film form. The thickness of the silicone composition 2 in these forms is 80 μm to 500 μm. That is, the thickness of the silicone composition 2 corresponds to the thickness of the impact absorber 1.

[0034] Silicone composition 2 has adhesive properties. Adhesion, as used herein, refers to the ability to bond (adhere) the silicone composition 2 to other components. Specifically, it is determined by the force required to peel the soda glass in the 90-degree peel mode of the adhesion test according to JIS Z0237. In this case, the adhesive strength of silicone composition 2 is preferably 2N / 20mm or greater. It should be noted that the adhesion test method used in the present invention uses a tensile speed of 300mm / min and a test piece in the form of a strip with a width of 20mm, a length of 100mm, and a thickness of 150μm. Furthermore, the test piece is bonded to the soda glass using a 2kg roller, followed by one reciprocating motion and then stabilization at 23°C for 24 hours.

[0035] The silicone composition 2 has stress relaxation properties. Here, stress relaxation properties refer to the ability to absorb the impact energy generated by stress by deformation or conversion into heat energy when stress is applied to the silicone composition 2, making it difficult for the stress to be transmitted. Specifically, the stress relaxation properties of the silicone composition 2 are defined as a complex elastic modulus of 10 in a dynamic viscoelasticity measurement (torsion shear mode) between 0°C and 200°C. 3 Pa and above 10 5 Pa range, and tanδ is 10 -2 The complex elastic modulus and tan δ were measured using a 25 mm (25 mm diameter) and 2 mm thick disk-shaped test piece under conditions of 1% strain and 10 Hz vibration frequency.

[0036] Dynamic elastic modulus includes storage modulus G' (Pa) and loss modulus G" (Pa). Storage modulus G' (Pa) is the component of energy generated by external force and strain in an object that is stored inside the object, while loss modulus G" (Pa) is the component that diffuses to the outside. Complex elastic modulus (Pa) by = (G' 2 +G” 2 ) 1 / 2 It represents the hardness of an object. Tanδ is the loss coefficient, which is the ratio of G” to G' (tanδ = G” / G' = loss modulus / storage modulus).

[0037] By making the complex elastic modulus (Pa) is 10 between 0℃ and 200℃ 3 Pa and above 10 5 Pa or less, and tanδ is 10 -2When the silicone composition 2 is within the range of 1 or above and 1 or below, the silicone composition 2 can exhibit the property of storing energy within the silicone composition 2 and then gradually dissipating it to the outside as heat when external force, strain, etc. is applied, thereby exhibiting shock absorption properties. When the silicone composition 2 is within the range outside the range above, the energy generated by external force, strain, etc. is not stored within the silicone composition 2, but instead generates elastic rebound force toward the outside or undergoes plastic deformation, making it difficult for the shock absorber 1 to maintain its original shape.

[0038] The silicone composition 2 more preferably has a complex elastic modulus of (Pa) is in the range of 20,000 Pa to 80,000 Pa both inclusive between 0°C and 200°C, and tan δ is in the range of 0.1 to 0.9 both inclusive.

[0039] It should be noted that as the complex elastic modulus As a measuring device for (Pa), for example, “ARES G2” manufactured by TA Instruments, Inc. is used.

[0040] The silicone composition used in this embodiment can be any known silicone composition having rubber elasticity or viscoelasticity, as long as it can achieve the desired cushioning and absorption properties. From the perspective of cushioning and absorption properties, silicone gel is preferably used as the silicone composition, and from the perspective of curability, addition-reaction-type (or cross-linking) silicone gel is particularly preferred. Addition-reaction-type silicone gels are not particularly limited. Typically, as an example of an organosilicon compound, they are obtained by using organohydrogenpolysiloxane and alkenylpolysiloxane as raw materials and subjecting them to a hydrosilylation reaction (addition reaction) in the presence of a catalyst. That is, in this embodiment, the organosilicon compound that can serve as the raw material for silicone gel generally refers to organohydrogenpolysiloxane and alkenylpolysiloxane. The organohydrogenpolysiloxane used as one of the raw materials is preferably represented by the following general formula (1).

[0041] [Chemical Formula 1]

[0042]

[0043] Where R 1 represents the same or different substituted or unsubstituted monovalent hydrocarbon groups, R 2 、R 3 and R 4 Represents R 1 or -H,R 2 、R 3 and R 4At least two of the units represent -H, x and y are integers representing the number of units, and the units are arranged in blocks or randomly, preferably randomly. x is an integer greater than or equal to 0, preferably 10 to 30, and y is an integer greater than or equal to 0, preferably 1 to 10. x + y is an integer from 5 to 300, preferably 30 to 200. Furthermore, the range of y / (x + y) ≤ 0.1 is preferred. Exceeding this range may result in increased crosslinking points and reduced impact cushioning properties.

[0044] As R 1 Examples include alkyl groups such as methyl, ethyl, propyl and butyl groups, cycloalkyl groups such as cyclopentyl and cyclohexyl groups, aryl groups such as phenyl and tolyl groups, aralkyl groups such as benzyl and phenylethyl groups, or halogenated hydrocarbons in which some of their hydrogen atoms are substituted with chlorine atoms, fluorine atoms or the like.

[0045] Hydrogen (Si—H) directly bonded to a silicon atom is necessary for an addition reaction (hydrosilylation reaction) with an alkenyl group directly or indirectly bonded to a silicon atom, and preferably at least two of these are present in the organohydrogenpolysiloxane molecule.

[0046] Furthermore, alkenyl polysiloxane, which is another raw material used in producing the cross-linked silicone gel used in this embodiment, is preferably represented by the following general formula (2).

[0047] [Chemical Formula 2]

[0048]

[0049] Where R 1 represents the same or different substituted or unsubstituted monovalent hydrocarbon groups, R 5 、R 6 and R 7 Represents R 1 or alkenyl, R 5 、R 6 and R 7 At least two of the units represent alkenyl groups, s and t are integers representing the number of units, and the units are arranged in blocks or randomly, preferably randomly. s represents an integer greater than 0, t represents an integer greater than 0, s + t is an integer from 10 to 600, and t / (s + t) ≤ 0.1. Furthermore, t / (s + t) ≤ 0.1 is preferably within a range. Exceeding this range may increase the number of crosslinking points and reduce impact cushioning properties.

[0050] As R 1Examples include alkyl groups such as methyl, ethyl, propyl, and butyl; cycloalkyl groups such as cyclopentyl and cyclohexyl; aryl groups such as phenyl and tolyl; aralkyl groups such as benzyl and phenylethyl; and halogenated hydrocarbons in which some of their hydrogen atoms are substituted with chlorine atoms, fluorine atoms, or the like. Alkenyl groups (such as vinyl and allyl) directly or indirectly bonded to silicon atoms are necessary for an addition reaction (hydrosilylation reaction) with hydrogen (Si—H) directly bonded to silicon atoms, and preferably at least two of these alkenyl groups are present in the polysiloxane molecule.

[0051] In this embodiment, the hydrogen polysiloxane represented by general formula (1) has a -H (hydrogen group) directly bonded to a silicon atom, and the alkenyl polysiloxane represented by general formula (2) has a carbon-carbon double bond. Therefore, the carbon-carbon double bond and the -H (hydrogen group) undergo an addition reaction, which is called a hydrosilylation reaction. Furthermore, by adjusting the equivalent ratio of the -H (hydrogen group) directly bonded to a silicon atom of the hydrogen polysiloxane represented by general formula (1) to the alkenyl group of the alkenyl polysiloxane represented by general formula (2), the hardness and cushioning properties of the silicone composition 2 can be adjusted. The hydrosilylation reaction can be carried out using known techniques, and can be carried out using a catalyst such as chloroplatinic acid, a complex obtained from chloroplatinic acid and an alcohol, a platinum-olefin complex, a platinum-vinylsiloxane complex, or a platinum-phosphorus complex. The amount of the catalyst used is generally 1 ppm to 500 ppm based on platinum atoms relative to the alkenyl polysiloxane, and is preferably 3 ppm to 250 ppm in consideration of curability and the physical properties of the cured product.

[0052] (Insulating inorganic black pigment)

[0053] The insulating inorganic black pigment 3 is contained in the silicone composition 2 mainly to impart light-shielding properties to the impact absorber 1. That is, the impact absorber 1 obtains the desired light-shielding properties due to the insulating inorganic black pigment 3.

[0054] The insulating inorganic black pigment 3 has electrical insulation. In the present invention, electrical insulation refers to a function that has a large resistance value and is difficult to conduct electricity. The resistivity of the insulating inorganic black pigment 3 is preferably set to 1×10 5 Ω·cm or more and 1×10 19 The electrical resistivity of the insulating inorganic black pigment 3 is more preferably set to 1×10 11 Ω·cm or more and 1×10 19 The range is less than Ω·cm, and more preferably 1×10 15 Ω·cm or more and 1×10 19 The range is below Ω·cm.

[0055] The insulating inorganic black pigment 3 comprises an inorganic material. In the present invention, examples of such inorganic materials include insulating metals, metal oxides, metal nitrides, and ceramics. Specifically, the insulating inorganic black pigment 3 can be a single element or alloy of a metal containing at least one element selected from titanium, iron, zinc, titanium oxide, titanium nitride, and aluminum oxide, or an oxide, nitride, or ceramic. The insulating inorganic black pigment 3 composed of an inorganic material is resistant to discoloration and has stable properties, thereby minimizing degradation of the light-shielding properties of the impact absorber 1.

[0056] The insulating inorganic black pigment 3 is black. In the present invention, black refers to the color code using CIE1976 In the coordinates of the color space (measurement light source C: color temperature 6774K), 0≤ ≤14, 6≤ ≤8, -10≤ ≤-5 range, the most preferred is 1.26, is 6.9, is -8.12. The insulating inorganic black pigment 3 is, for example, jet black with a color code of #0d0015. If the insulating inorganic black pigment 3 is black, the desired light-shielding property of the impact absorber 1 can be obtained. The insulating inorganic black pigment 3 is a particle. The insulating inorganic black pigment 3 is roughly spherical, but has various shapes. The average primary particle size of the insulating inorganic black pigment 3 is preferably in the range of 10 nm to 300 nm. As a result, the insulating inorganic black pigment 3 is easily uniformly dispersed in the organosilicon compound and the organosilicon composition 2. Here, uniform means that the composition of the impact absorber 1 per unit volume is roughly the same. The average primary particle size of the insulating inorganic black pigment 3 is more preferably in the range of 20 nm to 150 nm.

[0057] In the present invention, the average primary particle size is determined by the following method. Pigment particles contained in silicone composition 2 are observed at a magnification of 5000x or greater using a transmission electron microscope (TEM), a scanning transmission electron microscope (STEM), or a scanning electron microscope (SEM). In the TEM or STEM image or the multiple particles observed by SEM, pigment particles that have not formed aggregates are considered primary particles. The major axis of these primary particles is considered the primary particle size. The primary particle size is measured for one hundred primary particles. The result, calculated as the arithmetic mean of the primary particle sizes based on the number of particles, is used as the average primary particle size.

[0058] The content of the insulating inorganic black pigment 3 in the impact absorber 1 is in the range of 5 parts by mass to 40 parts by mass per 100 parts by mass of the silicone composition 2. When the content of the insulating inorganic black pigment 3 is within this range, the light-shielding properties of the impact absorber 1 are easily achieved without impairing the adhesiveness and stress relaxation properties of the silicone composition 2. The content of the insulating inorganic black pigment 3 is more preferably in the range of 7 parts by mass to 35 parts by mass per 100 parts by mass of the silicone composition 2, and even more preferably in the range of 10 parts by mass to 30 parts by mass.

[0059] Furthermore, in order to improve dispersibility in the organosilicon compound and the organosilicon composition 2 , the insulating inorganic black pigment 3 is preferably surface-treated with an organosilicon-based treatment agent.

[0060] Examples of insulating inorganic black pigments 3 include titanium oxynitride (titanium oxynitride). Titanium oxynitride has a high nitrogen content and is x N y The composition has x = 0.05 to 0.50, and y = 0.6 to 1.0. If the oxygen content x is less than 0.05, the insulation properties tend to be insufficient, while if it is greater than 0.50, the light-shielding properties tend to decrease, which is not preferred. If the nitrogen content y is less than 0.60, the light-shielding properties tend to decrease, while if it is greater than 1.0, the insulation properties tend to be insufficient, which is not preferred.

[0061] Furthermore, the impact absorbing material 1 may contain components such as heat dissipating fine particles, a flame retardant, and a heat stabilizer, within a range that does not inhibit the effects of the present invention.

[0062] (Heat dissipation particles)

[0063] The heat dissipation particles 4 are mainly included to impart heat dissipation properties to the shock absorbing material 1 , and inorganic materials such as aluminum hydroxide, magnesium oxide, anhydrous magnesium carbonate, aluminum oxide, silicon dioxide, aluminum nitride, and boron nitride can be used.

[0064] The addition of the heat dissipating particles 4 changes the hardness and viscoelastic properties of the impact absorbing material 1 . Therefore, the particle size and content of the heat dissipating particles 4 may be appropriately set within a range that allows the desired light shielding and impact cushioning properties of the impact absorbing material 1 to be obtained.

[0065] (Method for manufacturing shock absorbing material)

[0066] The impact absorber 1 is produced by mixing and kneading an organosilicon compound and an insulating inorganic black pigment 3, forming the mixture by extrusion or other molding method, and then drying, reacting, and curing the organosilicon compound to form an organosilicon composition.

[0067] (Physical properties of shock absorbers)

[0068] The adhesive strength of the impact absorber 1 to the glass plate is 2N / 20mm or more. This adhesive strength is measured as follows. The adhesive strength is measured using a 90-degree peel tester at a tensile speed of 300mm / min, using the peel strength at 90 degrees in the adhesive strength test according to JIS Z0237 "Testing methods for adhesive tapes and sheets" as the adhesive strength. The test specimens used for adhesive strength evaluation are as follows: Figure 2 As shown schematically, the impact absorber 1 is produced by laminating a glass plate 300 to one surface, followed by laminating a resin film (PET, Emblet, manufactured by Unitika) 301 to the other surface (the back surface) via a primer (Primer A manufactured by Shin-Etsu Chemical Co., Ltd.) 302. The lamination conditions are one reciprocating motion with a 2 kg roller, followed by a 24-hour temperature change at 23°C. The glass plate 300 is a 1 mm thick soda glass plate (manufactured by Hiraoka Glass Co., Ltd.).

[0069] The impact absorber 1 has an adhesive strength of 2 N / 20 mm or greater to the glass plate. Therefore, it is easily attached to the glass plate that constitutes a display panel such as a liquid crystal panel or an organic EL panel, achieving adhesion (bonding) and resisting detachment. Furthermore, from the perspective of workability, such as reattachment (reprocessing) to the display panel, the adhesive strength of the impact absorber 1 to the glass plate is preferably 6.5 N / 20 mm or less, and more preferably 5 N / 20 mm or less.

[0070] The impact absorber 1 has a transmittance of light having a wavelength of 300 nm to 850 nm of 0.6% or less. The transmittance is measured in accordance with JIS K 7136.

[0071] The lower the light transmittance of the impact absorbing material 1 , the better. Therefore, the lower limit is 0%.

[0072] The impact absorber 1 has a needle penetration of 90 or more and 160 or less at 25°C. This penetration is determined by multiplying the depth (mm) of needle penetration in 5 seconds by 10, using a penetration tester RPM-201 manufactured by RIGO Corporation, with the combined weight of the needle holder and needle being 50g, into a 25°C specimen in accordance with JIS K 2207. If the impact absorber 1 has a penetration of less than 90, the material is too rigid, making it difficult to bend or stretch, and thus unable to cope with flexible deformation. If the impact absorber 1 has a penetration of more than 160, the material is too soft, making it difficult to attach to other components and reducing its workability. The penetration of the impact absorber 1 under these conditions is preferably between 100 and 135, and more preferably between 110 and 135.

[0073] The impact absorption rate of the impact absorbing material 1 is 20% or greater. The impact absorption rate is measured as follows: using a pendulum impact tester PST-300 manufactured by SHINYEITESTING MACHINERY, the impact acceleration at a pendulum angle of 18° is measured in accordance with JISC 60068-2-27, and the impact absorption rate is calculated using the following formula.

[0074] Shock absorption rate (%) = (1-(shock acceleration of the test piece with shock absorber) / (shock acceleration of the PC board alone)) × 100

[0075] The test piece for measuring impact acceleration is made by laminating the impact absorber 1 on a 1.0 mm thick polycarbonate plate (PC plate) 400, and further laminating a 16 mm Φ (= 16 mm diameter) and 4 mm thick metal cylinder 401 on top of the plate. Figure 3 .

[0076] The shock absorption rate of the shock absorber 1 is preferably 25% or higher. The higher the shock absorption rate of the shock absorber 1, the better. Therefore, the upper limit is 100%. However, the upper limit of the shock absorption rate of the shock absorber 1 currently available is 85%.

[0077] (filler)

[0078] The impact absorber 1 preferably contains 0.5 parts by mass or more and 50 parts by mass or less of a resin filler 5 per 100 parts by mass of the silicone composition 2. The inclusion of the filler 5 allows the impact absorber 1 to have a needle penetration of 90 or more, improves its flexibility, and minimizes degradation in shape retention and handling. If the filler 5 content is less than 0.5 parts by mass per 100 parts by mass of the silicone composition 2, the impact absorber 1 may have difficulty maintaining its shape. If the filler 5 content exceeds 50 parts by mass, the light transmittance of the impact absorber 1 may increase. The filler 5 content is preferably 10 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the silicone composition 2.

[0079] The filler 5 is preferably in a particulate form, and has a major diameter of preferably 5 μm to 25 μm, more preferably 10 μm to 20 μm. In the present invention, the “major diameter” refers to the diameter of the longest portion of the cross section of the particulate filler 5 .

[0080] The filler 5 may be, for example, silicone microparticles or acrylic microparticles. In this case, the filler 5 comprises a silicone resin or an acrylic resin. The filler 5 may be formed from a resin alone. In other words, the filler 5 may be formed from the resin alone or contain other inorganic materials.

[0081] (Use of shock-absorbing materials)

[0082] The impact absorber 1 of this embodiment is used by being attached to another component. In this case, since the impact absorber 1 has adhesive properties, it can be attached by contacting the surface of the impact absorber 1 with the surface of the other component. However, if it is desired to firmly attach the impact absorber 1 to the other component, an adhesive or pressure-sensitive adhesive may also be used.

[0083] Other components that are susceptible to damage when impacted include display panels such as liquid crystal panels and organic EL panels. Impact absorber 1 is attached to the back surface of the display panel (the surface opposite to the side displaying text or images). Examples of display panels include flexible organic liquid crystal displays (OLCDs), electronic paper (E-paper), organic EL displays (OLEDs), quantum dot displays (QLEDs), and micro LED displays (μLEDs).

[0084] The impact absorber 1 of this embodiment can be appropriately used for flexible displays such as foldable terminals. A flexible display is provided with a sheet-like impact absorber on its back. If the impact characteristics of the impact absorber are low, the display may be damaged by the impact when it falls. Smartphone manufacturers, etc., have studied making the structure of the display simpler and thinner in order to evolve the foldable function. Therefore, in such applications, the level of impact characteristics required of the impact absorber becomes higher. Among them, in order to achieve further softening in the impact absorber using a silicone composition, the improvement of the cohesion of the bulk of fillers and pigments becomes a problem, but in the impact absorber 1 of this embodiment, when it falls, it is possible to suppress the uneven deformation to the surface and absorb the impact energy when falling, so that it can be made into an impact absorber with high impact absorption. In addition, in the impact absorber 1 of this embodiment, in order to prevent the illumination of the display from leaking from the back, it has a light-shielding property.

[0085] Compared to conventional technologies, the impact absorber 1 of this embodiment is thinner, more flexible, lighter, and has foldable features. It also has light-shielding properties. Therefore, when attached to a display panel such as a liquid crystal panel or an organic EL panel, an optical display unit can be obtained that has a large screen when in use and can be folded down to a smaller size for transportation.

[0086] For example, acrylic foams, such as those previously used as impact absorbers, are foams with closed cells, making it difficult to impart light-shielding properties. Furthermore, impact absorbers using conventional silicone compositions sometimes exhibit both light-shielding and impact resistance, but softening can sometimes cause problems with shape retention and handling, placing an upper limit on penetration. This means that further softening of the impact absorber is difficult, and therefore there is a limit to improving impact absorption. Therefore, in this embodiment, for example, the impact absorption is improved by improving penetration (softening) through a balance between the main agent and curing agent in the silicone composition. Furthermore, in the impact absorber of this embodiment, a filler with a major diameter of 5 to 25 μm is added to the silicone composition at a rate of 0.5 to 50% by mass, thereby preventing the impact absorber from becoming excessively soft.

[0087] Example

[0088] (Example 1)

[0089] Shin-Etsu Chemical Co., Ltd.'s two-component addition-reaction silicone gel (model number: X32-3443) was used as the silicone composition. The silicone compound used as the raw material for this silicone composition includes a base (A) and a curing agent (B). The lower the proportion of curing agent (B) relative to base (A), the greater the needle penetration (i.e., the softer) of the resulting silicone composition.

[0090] As the insulating inorganic black pigment, product number 13M-C manufactured by Mitsubishi Materials Corporation was used.

[0091] As fillers, product numbers AFX-8 (average particle size 8 μm), AFX-15 (average particle size 15 μm), and AFX-30 (average particle size 30 μm) manufactured by Sekisui Chemicals Co., Ltd. were used. The resin contained in these fillers was a cross-linked polyacrylate.

[0092] These materials were mixed and kneaded according to the amounts shown in Table 1, and formed into a sheet by extrusion. Thereafter, the sheet was dried and cured to form a silicone composition, thereby forming an impact absorber having a thickness of 200 μm.

[0093] (Examples 2 to 8, Comparative Examples 1 to 4)

[0094] As shown in Table 1, in Example 1, the blending amounts of the materials used were changed to form a variety of impact absorbers having different physical properties.

[0095] (physical properties)

[0096] For each of the above Examples and Comparative Examples, the adhesive strength to the glass plate, the transmittance of light with a wavelength of 300 nm to 850 nm, the needle penetration at 25°C according to JIS K 2207, and the impact absorption rate were measured. The transmittance was measured using a spectrophotometer V-650 manufactured by JASCO Corporation.

[0097] The impact absorbers of the present invention were evaluated for ease of processing in the Examples and Comparative Examples, from the perspective of cutting, laminating, and other processing. Workability was evaluated by visually observing the appearance of the impact absorbers when cut into 15 cm x 15 cm pieces and bonded to a 20 cm x 20 cm glass plate.

[0098] OK: The shock absorber is not broken at all, and the end portion of the shock absorber is in contact with the glass without deformation of 1 cm or more.

[0099] NG: A portion of the shock absorber is broken, or the end portion of the shock absorber is in a state of being attached to the glass with a deformation of 1 cm or more.

[0100] Furthermore, the room temperature storage stability of the impact absorber of the present invention was evaluated as follows.

[0101] OK: After being stored at room temperature for 6 months, the properties are almost unchanged compared to before storage.

[0102] NG: After 6 months of storage at room temperature, the product has changed in properties to such an extent that it may cause problems in use compared to before storage.

[0103] [Table 1]

[0104]

[0105] Description of Reference Numerals

[0106] 1. Impact absorbing material

[0107] 2 Silicone composition

[0108] 3 Insulating inorganic black pigment

Claims

1. An impact absorber comprising an insulating inorganic black pigment in a silicone composition having adhesiveness and stress relaxation properties. The impact absorbing material has an adhesive strength of 2N / 20mm or more to the glass plate. The impact absorbing material has a transmittance of 0.6% or less for light with a wavelength of 300 nm to 850 nm. The impact absorbing material has a needle penetration at 25°C in accordance with JIS K 2207 of 90 or more and 160 or less, The shock absorption rate of the shock absorbing material is greater than 20%. The silicone composition contains a filler comprising a resin in an amount of 0.5 parts by mass or more and 50 parts by mass or less based on 100 parts by mass of the silicone composition.

2. The shock absorber according to claim 1, wherein: The major diameter of the filler is 5 μm or more and 25 μm or less.

3. The shock absorber according to claim 1, wherein: The thickness is 80 μm or more and 500 μm or less.

4. The shock absorber according to claim 1, wherein The content of the insulating inorganic black pigment is 5 parts by mass or more and 40 parts by mass or less relative to 100 parts by mass of the silicone composition. The impact absorber according to claim 1 , which is used for light shielding and impact absorption of a display panel.

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