JP7128008B2 - Sealing material for electronic equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sheet material for an electronic device, which is sandwiched between members such as a housing and various parts inside the electronic device.

In recent years, there has been an increasing need for waterproof electronic devices such as smartphones, mobile phones, and tablet terminals. 2. Description of the Related Art A packing made of foam is sometimes used as a sealing material for waterproofing a connector, an electronic board, and various parts on the electronic board inside an electronic device.
Conventionally, as a foam used inside electronic devices, a crosslinked polyolefin resin foam sheet obtained by foaming and crosslinking an expandable polyolefin resin sheet containing a thermally decomposable foaming agent is known (for example, patent Reference 1).
Conventionally, as a sealing member for a vehicle, there is known a sealing member including an adsorption/releasing portion having an adsorption/releasing property to a wall surface of a vehicle body, and an elastic compression portion which is elastically compressible and laminated on the adsorption/releasing portion. (See Patent Document 2, for example).

WO 2005/007731 JP 2007-280632 A

By the way, waterproof sealing materials used in electronic devices are sometimes processed to have a thin thickness and a narrow width as the electronic devices are miniaturized. However, when a conventional sealing material made of foam used in electronic devices is processed to have a thin thickness or a narrow width, it may not be possible to sufficiently improve the waterproof performance of the electronic device. In particular, in recent years, even if electronic equipment is submerged in water, it is sometimes required that water does not enter inside the equipment, but it is difficult to satisfy such required performance with conventional foams.
On the other hand, the vehicle sealing member described in Patent Document 2 is formed thick and is not expected to be used with a narrow width, so it is used as it is as a sealing material for electronic devices. is difficult.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a sealing material for an electronic device that can improve the waterproof performance of the electronic device when used in the electronic device. and

As a result of intensive studies, the present inventors have found that, in the sealing material, a surface layer is provided on one side of the elastically compressible core layer, and the compressive strength of 25% of the sealing material for electronic devices and the micro-indentation of the surface layer The present inventors have found that the above problems can be solved by setting the hardness within a predetermined range, and completed the present invention described below.
That is, the present invention provides the following [1] to [13].
[1] An elastically compressible core layer and a surface layer laminated on one side of the core layer, wherein the surface layer has a microindentation hardness of 1.7 N/mm ² or less, A sealing material for electronic devices, having a 25% compressive strength of 5 to 2000 kPa.
[2] The sealing material for electronic devices according to [1] above, wherein the surface layer resin composition constituting the surface layer contains 70% by mass or more of a main agent selected from the group consisting of elastomers and soft resins.
[3] The electronic device seal according to [2] above, wherein the main agent is at least one selected from the group consisting of butyl rubber, ethylene propylene rubber, ethylene propylene diene rubber, acrylic resin, and styrenic thermoplastic elastomer. material.
[4] The group in which the surface layer resin composition comprises petroleum-based copolymers, ethylene-vinyl acetate copolymers, coumarone-indene-based resins, terpene-based resins, terpene-phenolic resins, rosin-based resins, and xylene-based resins. The sealing material for electronic devices according to the above [2] or [3], containing 0.5 to 20% by mass of at least one modified polymer selected from
[5] The main agent is at least one selected from the group consisting of butyl rubber, ethylene propylene rubber, ethylene propylene diene rubber, and styrenic thermoplastic elastomer, and the modified polymer is a petroleum-based copolymer and an ethylene- The electronic device sealing material according to the above [4], which is at least one selected from the group consisting of vinyl acetate copolymers.
[6] The main agent is an acrylic resin, and the modified polymer is selected from the group consisting of petroleum-based copolymers, coumarone-indene-based resins, terpene-based resins, terpene-phenolic resins, rosin-based resins, and xylene-based resins. The sealing material for electronic devices according to the above [4], which is at least one kind.
[7] The electronic device sealing material according to any one of [1] to [6] above, wherein the core layer is made of foam.
[8] The electronic device sealing material according to the above [7], wherein the resin constituting the foam is a polyolefin resin.
[9] The electronic device sealing material according to the above [7] or [8], wherein the foam has closed cells.
[10] The electronic device seal according to any one of [7] to [9] above, wherein the foam has an average cell diameter of 300 μm or less in the MD and TD directions and an average cell diameter of 150 μm or less in the ZD direction. material.
[11] The sealing material for electronic devices according to any one of [7] to [10] above, wherein the foam has an expansion ratio of 1.2 to 20 cm ³ /g.
[12] The sealing material for electronic devices according to any one of [1] to [11] above, which has a thickness of 0.05 to 2.5 mm.
[13] The sealing material for electronic devices according to any one of [1] to [12] above, which comprises an adhesive material on the other surface of the core layer.

By using the electronic device sealing material according to the present invention in an electronic device, it is possible to improve the waterproof performance of the electronic device.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic cross section which shows the sealing material for electronic devices which concerns on one Embodiment of this invention. FIG. 4 is a schematic cross-sectional view showing an electronic device sealing material according to another embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments according to the present invention will be described in detail.
[Sealant for electronic devices]
An electronic device sealing material 10 according to an embodiment of the present invention includes a core layer 11 and a surface layer 12 laminated on one surface of the core layer 11, as shown in FIG. Further, as shown in FIG. 2, an electronic device sealing material 20 according to another embodiment includes a core layer 11, a surface layer 12 laminated on one side of the core layer 11, and a surface layer 12 laminated on the other side of the core layer 11. and an adhesive material 13 laminated on the surface of the
The electronic device sealing materials 10 and 20 are sandwiched between two members 21 and 22 inside the electronic device.

In electronic device sealing materials 10 and 20, the core layer 11 is elastically compressible, and the surface layer 12 adheres to one member 21 of the above two members and re-applies to the member 21. It is peelable. In the electronic device sealing materials 10 and 20 having such a configuration, the surface layer 12 is pressed by the elastic force of the core layer 11 and adheres to the one member 21, so it is possible to exhibit high waterproof performance. become. Further, since the adsorbed surface layer 12 has a removability, the sealing materials 10 and 20 can be peeled off from the one member 21 even after the sealing material 10 has once been adsorbed to one member 21 in the electronic device. Then, it becomes possible to incorporate the sealing materials 10 and 20 into the electronic device again.
In addition, in the electronic device sealing material 20 including the adhesive 13, the surface layer 12 adheres to one member 21, and the adhesive 13 adheres to the other member 22. It becomes possible to make the water stoppage between 22 higher.

Inside the electronic device, the members 21 and 22 sandwiching the sealing materials 10 and 20 are electronic components inside the electronic device, a housing, a metal plate, a circuit board, and the like. The sealing material for electronic equipment enhances the waterproofness between the two members 21 and 22 and prevents water from entering a predetermined portion inside the electronic equipment. For example, the sealing material is arranged to surround various electronic components such as connectors or the entire electronic substrate to prevent the electronic components and the electronic substrate from getting wet.

In the present invention, the microindentation hardness H _IT of the surface layer of the sealing material for electronic devices is 1.7 N/mm ² or less. If the micro-indentation hardness is greater than 1.7 N/mm ² , the surface layer cannot be sufficiently adsorbed to the members inside the electronic device, making it difficult to achieve excellent waterproofing properties. Therefore, for example, it becomes difficult to realize IPX7 and IPX8 class waterproof performance. From the viewpoint of improving water stoppage, the micro-indentation hardness is more preferably 1.5 N/mm ² or less, and even more preferably 0.5 N/mm ² or less. The lower limit of the micro-indentation hardness is not particularly limited, but is preferably 0.15 N/mm ² or more, more preferably 0.2 N/mm ² or more. By setting the micro-indentation hardness to be equal to or higher than these lower limits, the sealing material for electronic devices is likely to have excellent removability.

Further, the sealing material for electronic devices of the present invention has a 25% compressive strength of 5 to 2000 kPa. If the 25% compressive strength is out of the above range, the elastic compression characteristics of the sealing material for electronic devices become inappropriate, making it difficult to sufficiently press the surface layer against the members inside the electronic device, making it difficult to achieve excellent water stopping performance. Become. Also, if the 25% compressive strength of the sealing material for electronic equipment exceeds 2000 kPa, it becomes difficult to easily incorporate it into a narrow space.
From these points of view, the 25% compressive strength is more preferably 50 to 800 kPa, even more preferably 60 to 750 kPa.
The micro indentation hardness and 25% compressive strength are measured according to the method described in Examples below.

The thickness of the sealing material for electronic devices is preferably 0.05 to 2.5 mm. By setting the thickness of the sealing material for electronic devices to 0.05 m or more, it becomes easier to secure water stoppage. Moreover, it can be suitably used for a miniaturized electronic device by making it 2.5 mm or less. From these points of view, the thickness of the sealing material for electronic devices is more preferably 0.1 to 2 mm, and even more preferably 0.15 to 1.5 mm. Even if the sealing material for electronic devices of the present invention is thin in this way, it is possible to exhibit sufficient waterproofing properties.
The thickness of the electronic device sealing material means the thickness of the entire electronic device sealing material. When the electronic device sealing material consists of two layers, a core layer and a surface layer, thickness. Moreover, when it consists of three layers of a core layer, a surface layer, and an adhesive material, it is the total thickness of these three layers.

The sealing material for electronic devices preferably has a narrow width, and more specifically, preferably has a fine wire shape. For example, the width of the sealing material for electronic devices may be 5 mm or less, preferably 3 mm or less, and more preferably 1 mm or less. Even if the width of the sealing material for electronic devices of the present invention is narrowed in this way, it is possible to exhibit water stopping properties. In addition, by narrowing the width of the sealing material for electronic devices, it can be suitably used inside miniaturized electronic devices.
Although the lower limit of the width of the sealing material for electronic devices is not particularly limited, it may be, for example, 0.1 mm or more, or 0.2 mm or more. The sealing material for electronic devices having a width equal to or greater than these lower limits facilitates increasing the water stoppage.
The planar shape of the electronic device sealing material is not particularly limited, but may be an elongated rectangular shape, a frame shape, an L shape, a U shape, or the like. However, other than these shapes, any other shape such as a normal square or circle may be used.

The electronic device sealing material can be used inside various electronic devices, and is preferably used inside various portable information devices. Portable information devices include mobile phones such as smart phones, tablet terminals, laptop personal computers, and the like. Since the sealing material for electronic devices of the present invention can appropriately exhibit its function even if it is thin and has a small width, it can be suitably used for portable information devices in which the space for arranging the sealing material for electronic devices is small. is.

Each member of the sealing material for electrical equipment will be described in more detail below.
(core layer)
The core layer is not particularly limited as long as it is elastically compressible, but specific examples thereof include rubber materials and foams, with foams being preferred. By using a foam, the core layer can be easily compressed in the thickness direction, so that it can be easily incorporated into miniaturized electronic devices and parts with irregular surfaces inside them.
The rubber material is made of a non-porous material, and various known rubber materials can be used.

(Closed cell rate)
Moreover, the core layer is preferably made of a non-water-permeable material from the viewpoint of enhancing the sealing performance of the sealing material for electronic devices. Therefore, the foam is preferably a foam having closed cells. A foam having closed cells means that the ratio of closed cells to all cells (referred to as "closed cell ratio") is 70% or more. The closed cell ratio is preferably 75% or more, more preferably 90% or more.
The closed cell content can be determined according to ASTM D2856 (1998). Commercially available measuring instruments include a dry automatic density meter Accupic 1330 and the like.

More specifically, the closed cell content is measured in the following manner. A test piece having a square shape with a side of 5 cm and a constant thickness is cut out from a sheet-like foam. _The thickness of the test piece is measured, the apparent volume V1 of the test piece is calculated, and the weight _W1 of the test piece is measured. Next, the apparent volume V2 occupied by the bubbles is calculated based on the following _formula . The density of the resin forming the test piece is 1 g/cm ³ .
Apparent volume occupied by bubbles V ₂ = V ₁ - W ₁
Subsequently, the test piece is submerged in distilled water at 23° C. to a depth of 100 mm from the water surface, and a pressure of 15 kPa is applied to the test piece for 3 minutes. After that, remove the test piece from the water, remove the moisture adhering to the surface of the test piece, measure the weight W2 of the test piece, and calculate the open cell rate _F1 and the closed cell rate F2 based _on the following _formula . do.
Open cell rate F ₁ (%) = 100 × (W ₂ - W ₁ )/V ₂
Closed cell rate F ₂ (%) = 100 - F ₁

(Average bubble diameter)
The cells of the foam used for the core layer are preferably so-called fine cells. Specifically, the foam preferably has an average cell diameter in the MD and TD directions of 300 μm or less, more preferably 250 μm or less, still more preferably 200 μm or less, and most preferably 100 μm or less. Also, the average cell diameter in the ZD direction is preferably 150 μm or less, more preferably 120 μm or less, still more preferably 80 μm or less, and most preferably 40 μm or less. By forming fine cells in this way, the number of cell walls per unit length is increased. Therefore, even when the width of the foam (sealing material for electronic devices) is narrowed, for example, a large number of cell walls exist between the narrow widths, resulting in good water stopping performance. It should be noted that fine cells can be easily formed by setting the degree of cross-linking and the expansion ratio of the foam to the suitable ranges described below.
Moreover, each of the average cell diameters in the MD and TD directions is preferably 10 μm or more, more preferably 20 μm or more, and still more preferably 25 μm or more from the viewpoint of ease of production. Also, the average cell diameter of ZD is preferably 5 μm or more, more preferably 10 μm or more, and still more preferably 15 μm or more.
In addition, the ratio of the average bubble diameter in the MD direction to the average bubble diameter in the ZD direction (hereinafter also referred to as “MD/ZD”) is 1 to 8, and the average bubble diameter in the TD direction to the average bubble diameter in the ZD direction The diameter ratio (hereinafter also referred to as “TD/ZD”) is preferably 1-8. More preferably, MD/ZD is 2-7 and TD/ZD is 2-7.

The average bubble diameter is measured in the following manner.
A foam sample for measurement was prepared by cutting a sheet-like foam into a 50 mm square. After immersing this in liquid nitrogen for 1 minute, it was cut in the thickness direction along the MD direction and the TD direction with a razor blade. Take a 200-fold enlarged photograph of this cross section using a digital microscope (manufactured by Keyence Corporation "VHX-900"), and take a 2 mm long cut surface in each of the MD direction, the TD direction, and the ZD direction. The diameter of the air bubbles was measured, and the operation was repeated 5 times. Then, the average value of all the bubbles was taken as the average bubble diameter in the MD direction, TD direction and ZD direction.
The MD direction means the machine direction and is a direction that coincides with the extrusion direction and the like, while the TD direction means the transverse direction and is a direction orthogonal to the MD direction. Also, the ZD direction is the thickness direction of the foam and is a direction perpendicular to both the MD direction and the TD direction.

(Degree of cross-linking)
The foam is preferably a cross-linked foam, and the degree of cross-linking is preferably 20 to 70% by mass. Moreover, the degree of cross-linking is more preferably 25 to 65% by mass, more preferably 30 to 60% by mass. By setting the degree of cross-linking to these lower limits or more, it becomes easier to obtain a foam having an average cell diameter within the above range. Further, by setting the degree of cross-linking within these ranges, it becomes easier to set the compressive strength of the sealing material for electronic devices within the above-described range.

(Expansion ratio)
The expansion ratio of the foam is preferably 1.2 to 20 cm ³ /g. By setting the expansion ratio within this range, the compressive strength of the sealing material for electronic devices can easily be within the above range, and the water stoppage can be easily improved. In addition, it is easy to improve the mechanical strength of the foam. From these points of view, the expansion ratio of the foam is more preferably 1.5 to 15 cm ³ /g, still more preferably 1.8 to 12 cm ³ /g. In the present invention, the density of the foam is obtained according to JISK7222, and the reciprocal thereof is used as the expansion ratio.

The foam is a resin foam made of resin. Examples of the resin constituting the foam include polyolefin resins, various elastomers, mixtures thereof, and the like, among which polyolefin resins are preferred. By using a polyolefin resin for the foam, it becomes easier to adjust the 25% compressive strength of the sealing material for electronic devices within the above range, and it becomes easier to mold a thin foam having a uniform thickness.
Elastomers used for foams include various thermoplastic elastomers such as styrene-based thermoplastic elastomers and ethylene-propylene-based thermoplastic elastomers such as EPDM. As the styrene-based thermoplastic elastomer, those listed as styrene-based thermoplastic elastomers that can be used in the surface layer described later can be appropriately selected and used.

[Polyolefin resin]
Polyolefin resins include polyethylene resins, polypropylene resins, ethylene-vinyl acetate copolymers, etc. Among these, polyethylene resins or mixtures of polyethylene resins and ethylene-vinyl acetate copolymers are preferred, and polyethylene resins are more preferred. preferable.
Examples of polyethylene resins include polyethylene resins polymerized with polymerization catalysts such as Ziegler-Natta compounds, metallocene compounds, and chromium oxide compounds. Preferably, polyethylene resins polymerized with a metallocene compound polymerization catalyst are used.

Moreover, as polyethylene resin, linear low-density polyethylene is preferable. By using linear low-density polyethylene, it is possible to impart good elastic compression properties to the foam and to make the foam thinner. From the viewpoint of thinning, the linear low-density polyethylene is more preferably obtained using a polymerization catalyst such as a metallocene compound. In addition, linear low-density polyethylene is obtained by copolymerizing ethylene (for example, 75% by mass or more, preferably 90% by mass or more with respect to the total amount of monomers) and a small amount of α-olefin if necessary. Linear low-density polyethylene is more preferred.
Specific examples of α-olefins include propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, and 1-octene. Of these, α-olefins having 4 to 10 carbon atoms are preferred.
The density of the polyethylene resin, for example, the linear low-density polyethylene described above, is preferably 0.870 to 0.910 g/cm 3 , more preferably 0.875 to 0.907 g/cm ³ , and more preferably 0.880 to 0.905 g/cm ³ . /cm ³ is more preferred. A plurality of polyethylene resins can be used as the polyethylene resin, and a polyethylene resin having a density other than the density range described above may be added.

(metallocene compound)
Examples of metallocene compounds include compounds such as bis(cyclopentadienyl) metal complexes having a structure in which a transition metal is sandwiched between π-electron unsaturated compounds. More specifically, tetravalent transition metals such as titanium, zirconium, nickel, palladium, hafnium, and platinum have one or more cyclopentadienyl rings or analogues thereof as ligands. can be mentioned.
Such a metallocene compound has uniform properties of active sites and each active site has the same degree of activity. Polymers synthesized using metallocene compounds have high uniformity in terms of molecular weight, molecular weight distribution, composition, and composition distribution. proceed to A uniformly cross-linked sheet is uniformly foamed, so it is easy to reduce variations in cell diameter. In addition, since the foam can be stretched uniformly, the thickness of the foam can be easily made thin and uniform.

Examples of ligands include cyclopentadienyl rings and indenyl rings. These cyclic compounds may be substituted with hydrocarbon groups, substituted hydrocarbon groups or hydrocarbon-substituted metalloid groups. Hydrocarbon groups include, for example, methyl group, ethyl group, various propyl groups, various butyl groups, various amyl groups, various hexyl groups, 2-ethylhexyl groups, various heptyl groups, various octyl groups, various nonyl groups, and various decyl groups. , various cetyl groups, and phenyl groups. The term "various" means various isomers including n-, sec-, tert- and iso-.
Moreover, you may use what polymerized the cyclic compound as an oligomer as a ligand.
Furthermore, in addition to π-electron unsaturated compounds, monovalent anion ligands such as chlorine and bromine or divalent anion chelate ligands, hydrocarbons, alkoxides, arylamides, aryloxides, amides, arylamides, phosphides, and aryls Phosphide or the like may also be used.

Examples of metallocene compounds containing tetravalent transition metals and ligands include cyclopentadienyltitanium tris(dimethylamide), methylcyclopentadienyltitanium tris(dimethylamide), bis(cyclopentadienyl)titanium dichloride, dimethyl and silyltetramethylcyclopentadienyl-t-butylamide zirconium dichloride.
A metallocene compound, in combination with a specific co-catalyst (co-catalyst), exhibits its action as a catalyst in the polymerization of various olefins. Specific co-catalysts include methylaluminoxane (MAO), boron-based compounds, and the like. The ratio of the cocatalyst used to the metallocene compound is preferably 100,000 to 1,000,000 mol times, more preferably 50 to 5,000 mol times.
When the linear low-density polyethylene described above is used as the polyolefin resin contained in the foam, the linear low-density polyethylene may be used alone, or may be used in combination with other polyolefin resins. For example, it may be used in combination with other polyolefin resins described below. When other polyolefin resin is contained, the ratio of other polyolefin resin to the total amount of linear low-density polyethylene and other polyolefin is preferably 80% by mass or less, more preferably 50% by mass or less, and 20% by mass or less. is more preferred.

Ethylene-vinyl acetate copolymers (EVA) used as polyolefin resins include, for example, ethylene-vinyl acetate copolymers containing 50% by mass or more of ethylene. When ethylene-vinyl acetate copolymer (EVA) is used, it is preferably used in combination with the polyethylene resin (PE) described above, and the mass ratio (EVA/PE) is preferably 10/90 to 90/10 20/80 to 80/20 is more preferred, and 50/50 to 80/20 is even more preferred.
Examples of polypropylene resins include polypropylene and propylene-α-olefin copolymers containing 50% by mass or more of propylene. These may be used individually by 1 type, and may use 2 or more types together.
Specific α-olefins constituting the propylene-α-olefin copolymer include ethylene, 1-butene, 1-pentene, 4-methyl-1-pentene, 1-hexene, 1-heptene, 1- Octene and the like can be mentioned, and among these, α-olefins having 6 to 12 carbon atoms are preferred.

Moreover, when a polyolefin resin is used as the resin for the foam, the resin contained in the foam may be the polyolefin resin alone, or may contain a resin other than the polyolefin resin. In the foam, the ratio of the polyolefin resin to the total amount of resin is preferably 50 to 100% by mass, more preferably 60 to 100% by mass, and even more preferably 70 to 100% by mass. Resins used in combination with polyolefin resins include elastomers such as the above-described styrene-based thermoplastic elastomers. The elastomer content is preferably 0 to 50% by mass, more preferably 0 to 40% by mass, still more preferably 0 to 30% by mass, based on the total amount of the resin.

(Pyrolytic foaming agent)
The foam is preferably obtained by foaming a foamable composition containing a thermally decomposable foaming agent in addition to the above resin.
Organic foaming agents and inorganic foaming agents can be used as thermal decomposition type foaming agents. Examples of organic foaming agents include azodicarbonamide, azodicarboxylic acid metal salts (barium azodicarboxylate, etc.), azo compounds such as azobisisobutyronitrile, nitroso compounds such as N,N'-dinitrosopentamethylenetetramine, Hydrazodicarbonamide, 4,4'-oxybis(benzenesulfonyl hydrazide), hydrazine derivatives such as toluenesulfonyl hydrazide, semicarbazide compounds such as toluenesulfonyl semicarbazide, and the like.
Examples of inorganic foaming agents include ammonium acid, sodium carbonate, ammonium hydrogencarbonate, sodium hydrogencarbonate, ammonium nitrite, sodium borohydride, and anhydrous monosoda citric acid.
Among these, azo compounds are preferable, and azodicarbonamide is particularly preferable, from the viewpoint of obtaining fine bubbles and from the viewpoints of economy and safety. These thermal decomposition type blowing agents can be used alone or in combination of two or more.
The content of the thermal decomposition type foaming agent in the foamable composition is preferably 0.5 to 10 parts by mass, more preferably 1 to 7 parts by mass, and even more preferably 1.5 to 5 parts by mass, relative to 100 parts by mass of the resin. part by mass.

Moreover, the foamable composition preferably contains a cell nucleus adjusting agent in addition to the resin and the thermally decomposable foaming agent. Examples of cell nucleus modifiers include zinc compounds such as zinc oxide and zinc stearate, and organic compounds such as citric acid and urea. Among these, zinc oxide is more preferable. By using a cell nucleus adjusting agent in addition to the foaming agent described above, it becomes easier to make the cell diameter smaller. The amount of the cell nucleus adjusting agent is preferably 0.4 to 8 parts by mass, more preferably 0.5 to 5 parts by mass, and still more preferably 0.8 to 2.5 parts by mass with respect to 100 parts by mass of the resin. is.
The foam (foamable composition), in addition to the above, is generally used for foams such as antioxidants, heat stabilizers, colorants, flame retardants, antistatic agents, fillers, etc. It may contain additives.

The thickness of the core layer is preferably 0.1-1.5 mm. By setting the thickness of the core layer to 0.1 mm or more, the elastic force of the core layer makes it easier to press the electronic device sealing material against the members inside the electronic device. Also, by setting the thickness to 1.5 mm or less, it can be suitably used for small portable electronic devices. From these viewpoints, the thickness of the core layer is more preferably 0.2 to 1.2 mm, more preferably 0.3 to 0.7 mm.

[Surface layer]
The surface layer is made of a material having a microindentation hardness within the above range. In addition, as described above, the surface layer is preferably one that adheres to one of the two members sandwiching the sealing material for electronic devices and that is releasable from that member. The surface layer is preferably composed of at least one of an elastomer and a soft resin. Here, the soft resin is a resin that can be used alone or in combination with a modified polymer to be described later so that the micro-indentation hardness can be adjusted to the range described above. By using an elastomer or a soft resin for the surface layer, it becomes easier to adjust the micro-indentation hardness within the above range, and to improve the adsorptivity and removability of the surface layer. In addition, the elastomer and the soft resin may be collectively referred to as the base material in this specification.
Also, the surface layer is preferably made of a water-impermeable material. The surface layer is made of at least one of an elastomer and a soft resin and is made of a non-porous material, so that it is impermeable to water.

Elastomers include acrylonitrile butadiene rubber, ethylene propylene diene rubber, ethylene propylene rubber, olefinic thermoplastic elastomer (TPO), natural rubber, butyl rubber, polybutadiene rubber, polyisoprene rubber, styrene thermoplastic elastomer, and the like. Styrene-based thermoplastic elastomers include styrene-butadiene block copolymers, styrene-butadiene-styrene block copolymers, styrene-isoprene block copolymers, styrene-isoprene-styrene block copolymers, and hydrogenated products thereof. etc. Among these, hydrogenated products are preferred, and hydrogenated styrene-isoprene-styrene block copolymers are more preferred. These elastomers may be used singly or in combination of two or more.

The elastomer forming the surface layer preferably has a Shore A hardness of 60 or less. By setting the Shore A hardness to 60 or less, the surface layer tends to have good adsorptivity and removability. In addition, it becomes easier to adjust the minute indentation hardness within a predetermined range. The Shore A hardness of the elastomer constituting the surface layer is more preferably 10-55, still more preferably 20-50, and even more preferably 30-45.

Moreover, as a soft resin, an acrylic resin is preferably used. Examples of acrylic resins include acrylic polymers obtained by polymerizing polymerizable monomers including (meth)acrylic acid alkyl ester monomers.
In this specification, the term "(meth)acrylic acid alkyl ester" refers to a concept including both acrylic acid alkyl ester and methacrylic acid alkyl ester, and the same applies to other similar terms. .
(Meth)acrylic acid alkyl ester-based monomer is an ester of (meth)acrylic acid and an aliphatic alcohol, wherein the alkyl group of the aliphatic alcohol has 1 to 18 carbon atoms, an alkyl ester derived from an aliphatic alcohol are preferred, and alkyl esters derived from aliphatic alcohols having 1 to 8 carbon atoms are more preferred.
Specific (meth)acrylic acid alkyl ester-based monomers (A) include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl ( meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate Acrylate, isooctyl (meth)acrylate, nonyl (meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, dodecyl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate and the like.
Further, among the (meth)acrylic acid alkyl ester-based monomers, it is preferable that the alkyl group contains an alkyl ester derived from an aliphatic alcohol having 4 to 8 carbon atoms, and the ratio is 70 based on the total amount of polymerizable monomers. % by mass or more is preferable, 80 to 100% by mass is more preferable, and 90 to 100% by mass is even more preferable. By containing a large amount of an alkyl ester derived from an aliphatic alcohol having an alkyl group of 4 to 8 carbon atoms, it becomes possible to impart good adsorbability and removability to the surface layer. In addition, it becomes easy to adjust the minute indentation hardness within a predetermined range.
The (meth)acrylic acid alkyl ester-based monomers may be used alone, or two or more of them may be used in combination.

The polymerizable monomer may consist of a (meth)acrylic acid alkyl ester-based monomer, but may contain a polar group-containing vinyl monomer in addition to the (meth)acrylic acid alkyl ester-based monomer. A polar group-containing vinyl monomer has a polar group and a vinyl group. Examples of polar group-containing vinyl monomers include carboxylic acid vinyl esters such as vinyl acetate, (meth)acrylic acid, carboxylic acids containing a vinyl group such as itaconic acid, and their anhydrides, 2-hydroxyethyl (meth) Vinyl monomers having hydroxyl groups such as acrylates, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, caprolactone-modified (meth)acrylates, polyoxyethylene (meth)acrylates, and polyoxypropylene (meth)acrylates , (meth)acrylonitrile, N-vinylpyrrolidone, N-vinylcaprolactam, N-vinyllauryllactam, (meth)acryloylmorpholine, (meth)acrylamide, dimethyl (meth)acrylamide, N-methylol (meth)acrylamide, N- Nitrogen-containing vinyl monomers such as butoxymethyl (meth)acrylamide and dimethylaminomethyl (meth)acrylate are included.
Moreover, the polymerizable monomer may contain other monomers than the (meth)acrylic acid alkyl ester-based monomer and the polar group-containing vinyl monomer described above. Other monomers include styrenic monomers and polyfunctional monomers. Styrenic monomers include, for example, styrene, α-methylstyrene, o-methylstyrene, and p-methylstyrene.
Examples of polyfunctional monomers include monomers having two or more vinyl groups, preferably polyfunctional (meth)acrylates having two or more (meth)acryloyl groups.
The type and content of the polymerizable monomer used in the acrylic polymer may be appropriately adjusted so that the surface layer has good adsorptivity and removability.

The weight average molecular weight of the acrylic polymer is preferably 100,000 to 1,500,000, more preferably 300,000 to 1,200,000, and still more preferably 500,000 to 1,000,000. In addition, a weight average molecular weight is measured using a gel permeation chromatography (GPC), and calculates it as a polystyrene conversion value.

As the main agent, it is more preferable to use butyl rubber, ethylene propylene rubber, ethylene propylene diene rubber, acrylic resin, styrenic thermoplastic elastomer, or a mixture of two or more selected from these. When these elastomers or acrylic resins are used, the adhesion to the core layer made of polyolefin resin foam, for example, can be easily increased.
The resin composition that constitutes the surface layer (hereinafter also referred to as the surface layer resin composition) preferably contains 70% by mass or more of the above-mentioned main agent, 80 to 99% by mass, based on the total amount of the surface layer resin composition. %, more preferably 85 to 97% by mass.

The main agent preferably contains butyl rubber, acrylic resin, and styrenic thermoplastic elastomer, and more preferably contains butyl rubber and acrylic resin, from the viewpoint of lowering micro-indentation hardness and improving adsorptivity.
It is also preferable to mix butylcom with other elastomers. For example, it is preferable to use a mixture of butyl rubber and ethylene propylene diene rubber (EPDM) as the main component. In this case, the mass ratio of butyl rubber to EPDM is preferably 5/95 to 80/20, more preferably 8/92 to 70/30. By setting such a mass ratio, it becomes easy to lower the micro-indentation hardness and improve the adsorptivity.
From the viewpoint of waterproofness, it is more preferable that the main agent contains a mixture of butyl rubber and ethylene propylene diene rubber (EPDM).

(modified polymer)
The surface layer resin composition may further contain a modifying polymer. By blending the modified polymer, it becomes easier to improve the adsorptivity. In addition, it becomes easy to adjust the minute indentation hardness within the above range. Examples of modified polymers include petroleum-based copolymers, ethylene-vinyl acetate copolymers, and the like. In addition, coumarone-indene resins, terpene resins, terpene phenol resins, polymerized rosin, rosin resins such as rosin esters, and xylene resins can also be used.
The modified polymer may be used singly, or two or more of them may be used in combination.
The content of the modifying polymer is preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, still more preferably 2 to 10% by mass, based on the total amount of the surface layer resin composition.

The ethylene-vinyl acetate copolymer used for the modified polymer includes, for example, an ethylene-vinyl acetate copolymer containing 50% by mass or more of ethylene, and may be appropriately modified.
Various petroleum resins can be used as petroleum-based copolymers, and examples thereof include C5-based petroleum resins, C9-based petroleum resins, C5C9-based petroleum resins, dicyclopentadiene resins, and hydrides thereof. Among these, hydrides are preferred. C5 petroleum resins are also preferred, and hydrides of C5 petroleum resins are more preferred.

Further, when the main agent constituting the surface layer is an elastomer selected from butyl rubber, ethylene propylene rubber, ethylene propylene diene rubber, styrenic thermoplastic elastomer, or a mixture thereof, the modified polymer may be a petroleum-based copolymer, It is preferred to use modified polymers selected from ethylene-vinyl acetate copolymers, more preferably petroleum-based copolymers. By using the petroleum-based copolymer together with the elastomer, it is possible to easily adjust the microindentation hardness within a predetermined range and to effectively improve the adsorptivity.

When the main agent constituting the surface layer is an acrylic resin, the modified polymer may be a petroleum-based copolymer, a coumarone-indene-based resin, a terpene-based resin, a terpene-phenolic resin, a rosin-based resin, or a xylene-based resin. are preferred, and rosin-based resins are particularly preferred. By using these modified polymers together with an acrylic resin, it is possible to easily adjust the microindentation hardness within a predetermined range and effectively improve the adsorptivity.

(Other additives)
When the surface layer resin composition contains an elastomer as a main component, the surface layer resin composition may further contain a vulcanizing agent. Vulcanizing agents include organic peroxides, sulfur, sulfur compounds, and the like. Examples of organic peroxides include diisopropylbenzene hydroperoxide, 2,4-dichlorobenzoyl peroxide, benzoyl peroxide, t-butyl perbenzoate, cumyl hydroperoxide, t-butyl hydroperoxide, 1,1 -di(t-butylperoxy)-3,3,5-trimethylhexane, n-butyl-4,4-di(t-butylperoxy)valerate, α,α'-bis(t-butylperoxyisopropyl) ) benzene, 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3, t-butylperoxycumene and the like. Examples of sulfur compounds include tetramethylthiuram disulfide, tetramethylthiuram monosulfide, zinc dimethyldithiocarbamate, 2-mercaptobenzothiazole, dibenzothiazyl disulfide, N-cyclohexyl-2-benzothiazolesulfenamide, Nt- Butyl-2-benzothiazolesulfenamide, sulfur monochloride, sulfur dichloride and the like.
Even when the resin composition for the surface layer contains an elastomer, it is preferable that the resin composition for the surface layer does not contain a vulcanizing agent and the surface layer is unvulcanized. When the surface layer is unvulcanized and contains the modified polymer described above, the surface layer tends to exhibit adsorptivity and removability, and the micro-indentation hardness can be easily adjusted within the range described above. .

On the other hand, when the resin composition for the surface layer contains an acrylic resin as a main component, the resin composition for the surface layer may further contain a cross-linking agent. The cross-linking agent is not particularly limited, and examples thereof include isocyanate-based cross-linking agents, epoxy-based cross-linking agents, melamine-based cross-linking agents, peroxide-based cross-linking agents, urea-based cross-linking agents, metal alkoxide-based cross-linking agents, and metal chelate-based cross-linking agents. , metal salt-based cross-linking agents, carbodiimide-based cross-linking agents, oxazoline-based cross-linking agents, aziridine-based cross-linking agents, amine-based cross-linking agents, polyfunctional acrylates, and the like. The above-mentioned cross-linking agents may be used alone or in combination. Among these, isocyanate-based cross-linking agents are preferred.
The content of the cross-linking agent is preferably 0.1 to 15% by mass, more preferably 0.5 to 10% by mass, still more preferably 0.8 to 5% by mass, based on the total amount of the surface layer resin composition.

In addition, other additives such as a plasticizer, a softening agent, a pigment, a dye, a reinforcing material, a flame retardant, and an antioxidant may be added to the surface layer resin composition constituting the surface layer. When the surface layer resin composition contains an elastomer, the surface layer resin composition preferably contains one or both of a reinforcing material and an antioxidant.
Carbon black is preferably used as the reinforcing material. Carbon black is contained in an amount of preferably 1 to 15% by mass, more preferably 2 to 10% by mass, still more preferably 2 to 8% by mass based on the total amount of the resin composition for the surface layer.
Examples of antioxidants include phenol antioxidants, sulfur antioxidants, phosphorus antioxidants, amine antioxidants, etc. Among these, sulfur antioxidants, phenol antioxidants, Antioxidants are preferred. The content of the antioxidant is preferably 0.1 to 8% by mass, preferably 0.2 to 5% by mass, more preferably 0.5 to 3% by mass, based on the total amount of the surface layer resin composition.

The thickness of the surface layer is preferably 0.05-0.5 mm. By setting the thickness of the surface layer to 0.05 mm or more, it becomes easy to develop the adsorptivity. Moreover, by making it 0.5 mm or less, it can be suitably used for a small-sized electronic device. From these viewpoints, the thickness of the surface layer is more preferably 0.07 to 0.3 mm, still more preferably 0.10 to 0.25 mm, and even more preferably 0.1 to 0.15 mm.

[Adhesive]
The adhesive material is laminated on the surface of the core layer opposite to the surface provided with the surface layer. The adhesive has at least an adhesive layer, and the adhesive layer adheres the electronic device sealing material to other members inside the electronic device. More specifically, the adhesive material may be a single adhesive layer laminated on the other surface of the core layer, or may be a double-sided adhesive tape attached to the surface of the core layer. A pressure-sensitive adhesive layer alone is preferred. The thickness of the sealing material for electronic devices can be easily reduced when the adhesive material consists of a single adhesive layer.

A double-sided adhesive tape comprises a substrate and adhesive layers provided on both sides of the substrate. It is to be adhered to.
The adhesive material is preferably laminated directly on the other surface of the core layer, but may be laminated on the core layer via a primer layer formed on the other surface of the core layer. The primer layer is, for example, a layer for enhancing adhesion between the core layer and the adhesive material, and may be formed by applying various primers to the core layer, for example.
The adhesive used for the adhesive layer is not particularly limited, and for example, an acrylic adhesive, a urethane adhesive, a rubber adhesive, or the like can be used.
The thickness of the adhesive material is preferably 5-200 μm, more preferably 10-100 μm. In addition, the thickness of the adhesive material means the thickness of the adhesive layer when the adhesive material consists of a single adhesive layer, and the total thickness of the double-sided adhesive tape when it is a double-sided adhesive tape. do.

[Method for producing sealing material for electronic device]
The method for producing the sealing material for electronic devices is not particularly limited, but examples thereof include a method of laminating a surface layer on one surface of a core layer. Here, when the core layer is a foam, the foam may be produced by the following method, and the surface layer may be laminated on one side of the foam.

(Method for producing foam)
The method for producing the foam is not particularly limited, but for example, the foam is produced by cross-linking a foamable composition containing a resin and a thermally decomposable foaming agent and heating to foam the thermally decomposable foaming agent. More specifically, the manufacturing method includes the following steps (1) to (4).
Step (1): A step of mixing a resin and an additive containing a thermally decomposable foaming agent to form a sheet-like foaming composition (resin sheet) Step (2): Forming a sheet-like foaming composition Step (3) of irradiating ionizing radiation to crosslink the foamable composition: Step of heating the crosslinked foamable composition to foam the thermally decomposable foaming agent to obtain a sheet-like foam. (4): A step of stretching the foam in one or both of the MD direction and the TD direction

In step (1), the method of forming the resin sheet is not particularly limited, but for example, the resin and additives are supplied to an extruder, melt-kneaded, and the foamable composition is extruded from the extruder into a sheet. The resin sheet may be molded by
As a method for cross-linking the foamable composition in step (2), a method of irradiating the resin sheet with ionizing radiation such as electron beams, α rays, β rays, and γ rays is used. The irradiation dose of the ionizing radiation may be adjusted so that the degree of cross-linking of the resulting foam falls within the above desired range, preferably 2 to 15 Mrad, more preferably 5 to 13 Mrad.
In step (3), the heating temperature when heating the foamable composition to foam the thermally decomposable foaming agent may be at least the foaming temperature of the thermally decomposable foaming agent. It is preferably 220 to 280°C.

The stretching of the foam in step (4) may be performed after foaming the resin sheet to obtain a sheet-like foam, or may be performed while foaming the resin sheet. In addition, when stretching the foam after foaming the resin sheet to obtain the foam, the foam may be stretched while maintaining the molten state at the time of foaming without cooling the foam. Alternatively, after cooling the foam, the foam may be heated again to be in a molten or softened state and then stretched. Stretching the foam makes it easier to make it thinner.
In step (4), the draw ratio of the foam in one or both of the MD and TD directions is preferably 1.1 to 5.0 times, more preferably 1.5 to 4.0 times.
When the draw ratio is equal to or higher than the above lower limit, the elastic compressive properties of the foam and the compressive strength of the sealing material for electronic devices tend to be improved. On the other hand, when it is below the upper limit, it is possible to prevent the foam from breaking during stretching, and from the foaming gas being released from the foam during foaming, to significantly reduce the expansion ratio. The strength is improved, and the quality becomes more uniform.
The foam may be heated to, for example, 100 to 280.degree. C., preferably 150 to 260.degree. C. during stretching.
However, the method for producing the foam is not limited to the above, and the foam may be produced by a method other than the above. For example, instead of irradiating ionizing radiation, cross-linking may be performed by adding an organic peroxide to the foamable composition in advance and heating the foamable composition to decompose the organic peroxide. good. Also, step (4), the stretching of the foam, may be omitted.

(Method for forming surface layer)
The method of forming the surface layer on one side of the core layer is not particularly limited, but the base material consisting of at least one of an elastomer and a soft resin is mixed with a modified polymer and other additives as necessary. The surface layer resin composition thus obtained may be processed into a sheet or layer and laminated on a core layer such as a foam. Alternatively, the surface layer may be formed by coating the surface layer resin composition on the core layer.

More specifically, the main agent, optionally modified polymer, and other additives are supplied to an extruder and melt-kneaded, and the resin composition for the surface layer is extruded from a die into a sheet to form a core such as a foam. Laminate on top of the layer. At this time, the resin composition for the surface layer extruded in the form of a sheet and the core layer may be heat-sealed by pressurization and heating between rolls. Alternatively, the surface layer resin composition that has been processed into a sheet in advance may be superimposed on a core layer such as a foam, and heat-sealed by heating or pressurization. When a vulcanizing agent and a cross-linking agent are added to the resin composition for the surface layer, the surface layer resin composition may be vulcanized or cross-linked by being superimposed on the core layer and heated in the laminated state.
Furthermore, the surface layer resin composition formed in a layer on the release-treated surface of the release sheet may be transferred onto the core layer. The resin composition for the surface layer may be formed in a layer by coating the resin composition for the surface layer on the release sheet. Examples of the release sheet include a paper substrate, a release paper obtained by releasing at least one side of a resin film, and a release film.

Application of the surface layer resin composition to the release sheet or core layer may be performed using various coaters, sprayers, brushes, and the like. Further, the resin composition for the surface layer may be diluted with an organic solvent as appropriate to obtain a diluted solution, and then applied. Moreover, after applying the surface layer resin composition or its diluted solution, heating, drying, etc. may be performed as necessary. The surface layer may be crosslinked by heating with a crosslinking agent or the like contained in the resin composition for the surface layer.

The surface layer is preferably laminated onto expanded foam when the core layer is foam. That is, the surface layer is preferably formed after step (3) or after step (4), and more preferably after step (4).
However, the foaming composition may be foamed after laminating a surface layer on the sheet-like foaming composition before foaming. In this case, the step of forming the surface layer may be performed, for example, between the steps (1) and (2) or between the steps (2) and (3).

(Method for forming adhesive material)
In the method of forming the adhesive on the other side of the core layer, when the adhesive consists of a single adhesive layer, the adhesive may be applied to the core layer, or may be formed on the release film. The formed pressure-sensitive adhesive layer may be transferred onto the other surface of the core layer. When the adhesive material is a double-sided adhesive tape, one adhesive layer of the double-sided adhesive tape may be attached to the other surface of the core layer.
The adhesive is not particularly limited, but is preferably formed on the other side of the core layer after forming a surface layer on one side of the core layer.
The electronic device sealing material obtained as described above may be cut into a desired shape by a known method such as punching.

The present invention will be described in more detail with reference to examples, but the present invention is not limited by these examples.

[Measuring method]
The measurement method and evaluation method of each physical property are as follows.
<Minor indentation hardness H _IT >
Using an ultra-microindentation hardness tester (“ENT-2100” manufactured by Elionix Co., Ltd.), the microindentation hardness was measured under the conditions of a test load of 1 mN and a load time of 10 seconds in a 23° C. environment.
<25% compression strength>
The 25% compressive strength of the sealing material for electronic devices was measured according to JIS K6767. The 25% compressive strength of the sealing material for electronic devices means the compressive strength of the laminate of the surface layer and the core layer (however, if there is a layer therebetween, that layer is also included). Therefore, when an adhesive material is provided on the other surface of the sealing material for electronic devices, the value is measured after removing the adhesive material.
<Shore A hardness>
It is a hardness measured at 23° C. with a type A durometer hardness tester according to JIS K 6253.

<Expansion ratio>
The apparent density of the foam was measured according to JISK7222, and the reciprocal thereof was taken as the expansion ratio.
<Degree of cross-linking>
A test piece of about 100 mg is taken from the foam, and the weight A (mg) of the test piece is precisely weighed. Next, this test piece was immersed in 30 cm ³ of xylene at 120° C. and allowed to stand for 24 hours, filtered through a 200-mesh wire mesh to collect the undissolved matter on the wire mesh, vacuum dried, and weighed the insoluble matter. Accurately weigh B (mg). From the obtained values, the degree of cross-linking (% by mass) was calculated according to the following formula.
Crosslinking degree (mass%) = 100 x (B/A)
<Closed cell rate>
Measured according to the method described in the specification.
<Average bubble diameter>
The average bubble diameter was measured by the method described in the specification.

<Waterproof>
The waterproof evaluation test is based on the IPX7 standard (JISC0920 and IEC60529), under the conditions of a temperature of 23 ° C. and a relative humidity of 50%, a test sample prepared by the following method is submerged in a water depth of 1 m and held for a predetermined time. The presence or absence of water intrusion was visually confirmed. "S" when there is no water immersion even after immersion for 3 hours or more, "A" when there is no water immersion after 30 minutes of immersion (meets IPX7 standards), "B" when there is water immersion after 30 minutes of immersion, Those that were submerged in water immediately after immersion were evaluated as "C".
In addition, the waterproof test was performed after curing for 30 minutes under conditions of a temperature of 23° C. and a relative humidity of 50% after preparation of the test sample.
(Preparation of test samples)
A double-sided adhesive tape ("3803BH" manufactured by Sekisui Chemical Co., Ltd.) is laminated on the core layer side of the sealing material, and a rectangular opening of 58 mm long x 38 mm wide is provided inside, and the opening is 60 mm long x 40 mm wide and 1.0 mm wide. A rectangular frame shape was punched out. However, all corners were rounded with R5 mm. The resulting sealing material was sandwiched between two 100 mm square acrylic plates with a thickness of 10 mm, and compressed by 20% of the thickness of the sealing material.

<Removability>
The sealing materials for electronic devices obtained in Examples and Comparative Examples were cut into 25 mm × 100 mm pieces, sandwiched between two acrylic plates, and compressed by 20% of the total thickness of the sealing material. It was cured for 30 minutes in an environment with a humidity of 50%. After that, the peelability was evaluated when the sealing material for electronic devices was peeled off from the acrylic plate by hand. Those that could be easily peeled off by hand were evaluated as "A", and those that could not be easily peeled off by hand or those in which the sealing material for electronic devices was damaged during peeling were evaluated as "B".

[Example 1]
(Production of foam)
100 parts by mass of a linear low-density polyethylene resin (manufactured by Dow Chemical Company, trade name “Affinity PL1850”, density: 0.902 g/cm ³ ) obtained by a polymerization catalyst of a metallocene compound; Extrusion of 9.5 parts by mass of dicarbonamide, 0.5 parts by mass of zinc oxide (manufactured by Sakai Chemical Industry Co., Ltd., trade name "OW-212F") as a cell nucleus regulator, and 1.0 part by mass of antioxidant. It was supplied to a machine, melt-kneaded at 130° C., and extruded into a long resin sheet having a thickness of 300 μm.
Next, both sides of the long resin sheet were irradiated with 4 Mrad of electron beams at an acceleration voltage of 500 kV to crosslink the resin sheet, and then the crosslinked resin sheet was placed in a foaming furnace maintained at 250°C by hot air and an infrared heater. , and heated to foam, thereby obtaining a sheet-like foam having a thickness of 1500 µm.
Next, after the obtained foam was continuously sent out from the foaming furnace, the foam was expanded three times in the TD direction while maintaining the temperature of both sides of the foam at 200 to 250 ° C. The foam was stretched at a draw ratio and also stretched in the MD direction by winding up the foam at a take-up speed higher than the feeding speed (supply speed) of the foam into the foaming furnace. Note that the winding speed of the foam was adjusted in consideration of the amount of expansion in the MD direction due to foaming of the resin sheet itself.

(Formation of surface layer)
Each component shown in Table 1 was put into an extruder and kneaded to obtain a surface layer resin composition, which was extruded into a sheet from a die and laminated on one side of a foam (core layer), and the pressure was 0. The mixture was pressurized at 3 MPa and heat-sealed at 70° C. to obtain a sealing material for electronic equipment consisting of a core layer and a surface layer.

[Example 2]
The same procedure as in Example 1 was carried out, except that the composition of the surface layer resin composition was changed as shown in Table 1.
[Example 3]
2.1 parts by mass of the thermal decomposition type foaming agent, the thickness of the resin sheet is 210 μm, the intensity of the irradiated electron beam is 7 Mrad, the thickness of the foam obtained by foaming (before stretching) is 300 μm, the foaming It was carried out in the same manner as in Example 1, except that the draw ratio in the TD direction of the body was changed to 2 times.
[Example 4]
11.0 parts by mass of the thermal decomposition type foaming agent, the thickness of the resin sheet is 300 μm, the intensity of the electron beam to be irradiated is 7 Mrad, the thickness of the foam obtained by foaming (before stretching) is 1600 μm, the foaming It was carried out in the same manner as in Example 1, except that the draw ratio in the TD direction of the body was changed to 2 times.
[Example 5]
The same procedure as in Example 1 was carried out, except that the composition of the surface layer resin composition was changed as shown in Table 1.
[Example 6]
The same procedure as in Example 1 was carried out, except that the composition of the surface layer resin composition was changed as shown in Table 1.

[Example 7]
(Production of foam)
3 parts by mass of thermally decomposable foaming agent, 250 μm thick resin sheet, 4 Mrad electron beam intensity, 500 μm thick foam (before stretching) obtained by foaming, TD of foam A foam was obtained in the same manner as in Example 1, except that the direction draw ratio was changed to 2.5 times.
(Adjustment of resin composition for surface layer)
A reactor equipped with a thermometer, a stirrer, and a cooling tube was charged with butyl acrylate and 2-ethylhexyl acrylate at a mass ratio of 50:40, added with 80% ethyl acetate, and purged with nitrogen. The reactor was then heated to initiate reflux. Subsequently, 0.1 part by weight of azobisisobutyronitrile was added as a polymerization initiator into the reactor, and refluxed at 70° C. for 5 hours to obtain an acrylic resin solution. A rosin ester-based modified polymer was added to the acrylic resin solution to obtain a diluted solution of the resin composition for the surface layer. Table 1 shows the solid content-based composition of the diluted solution of the surface layer resin composition.
(Formation of surface layer)
A release paper (thickness: 150 μm) is prepared, and a diluted solution of the resin composition for the surface layer is applied to the release-treated surface of the release paper and dried at 100° C. for 5 minutes to obtain a layered surface layer resin. A composition was formed. This layered resin composition for surface layer was attached to the surface of the foam to obtain a sealing material for electronic devices consisting of surface layer/foam. A release paper was attached to the surface of the surface layer, but it was removed before each evaluation.
[Example 8]
30 parts by mass of the linear low-density polyethylene resin "Affinity PL1850" and 70 parts by mass of ethylene-vinyl acetate copolymer (manufactured by Tosoh Corporation "Ultrasen 636") were added to the formulation of the resin used for the foam. It was implemented in the same manner as in Example 1 except that
[Example 9]
70 parts by mass of linear low-density polyethylene resin "Affinity PL1850" and 30 parts by mass of styrene-ethylene-butylene-styrene block copolymer (manufactured by JSR Corporation, "Dynaron 8600P") The procedure was carried out in the same manner as in Example 1, except that the number of parts was changed.
[Example 10]
The procedure was carried out in the same manner as in Example 7, except that the resin composition for the surface layer was changed to 97.7 parts of the acrylic resin and 2.2 parts of the modified polymer.

[Comparative Example 1]
A foam was produced in the same manner as in Example 1, except that the amount of azodicarbonamide as the thermal decomposition type foaming agent was changed to 7.0 parts by mass. The foam alone was used as a sealing material for electronic devices without laminating a surface layer on the foam.
[Comparative Example 2]
As the foam (core layer), commercially available urethane foam (trade name “PORON SR-S4
0P", manufactured by Rogers Inoac), and the foam alone was used as a sealing material for electronic devices without laminating a surface layer on the core layer.
[Comparative Example 3]
The procedure was carried out in the same manner as in Example 7, except that the resin composition for the surface layer was changed to 99 parts of the acrylic resin and 1 part of the modified polymer.

In Table 1, the Shore A hardness of the elastomer means the Shore A hardness of the elastomer obtained by mixing butyl rubber and EPDM in the proportions shown in Table 1 in Examples 1 to 5, 8 and 9. Example 6 means the Shore A hardness of TPS alone.

In addition, each component in the resin composition for surface layers is as follows.
Butyl rubber: trade name "BUTYL065", manufactured by JSR Corporation, Shore A hardness: 20
EPDM: Ethylene propylene diene rubber, trade name "EP21", manufactured by JSR Corporation, Shore A hardness: 73
TPS: Styrene-based thermoplastic elastomer (hydrogenated styrene-isoprene-styrene block copolymer) trade name "Hybler 7311", manufactured by Kuraray Co., Ltd., Shore A hardness: 41
Acrylic resin: weight average molecular weight of 700,000, modified copolymer of 55.6% by mass of butyl acrylate and 44.4% by mass of 2-ethylhexyl acrylate Polymer 1: petroleum-based polymer, trade name "Quintone A-100", Nippon Zeon Co., Ltd. modified polymer 2: rosin ester resin Carbon black: carbon black manufactured by Asahi Carbon Co., Ltd. Antioxidant: mixture of sulfur-based antioxidant and phenol-based antioxidant

The electronic device seal of each example has a core layer and a surface layer, and the micro-indentation hardness of the surface layer and the 25% compressive strength of the electronic device sealing material are within a predetermined range, so that waterproof performance was able to be superior. Moreover, even if it was once adhered to a part of an electronic device, it was possible to re-peel it from the part. In addition, for the structure shown in Example 4, after being adsorbed to the surface layer of the punched sample used for the waterproof evaluation, it was peeled off, and the waterproofness of the sample was measured by repeating this 10 times. cleared.
On the other hand, the electronic device seals of Comparative Examples 1 and 2 did not have a surface layer, and therefore could not sufficiently improve the waterproof performance. Further, in the electronic device seal of Comparative Example 3, the micro-indentation hardness of the surface layer was greater than 1.7 N/mm ² , so the waterproof performance could not be sufficiently improved.

REFERENCE SIGNS LIST 10 Sealing material for electronic device 11 Core layer 12 Surface layer 13 Adhesive material 21, 22 Components inside electronic device

Claims (11)

comprising an elastically compressible core layer and a surface layer laminated on one side of the core layer,
The micro-indentation hardness of the surface layer is 1.7 N/mm ² or less, and
25% compressive strength is 5 to 2000 kPa ,
the core layer is made of a foam,
The resin constituting the foam is polyethylene resin (PE) and ethylene-vinyl acetate copolymer (EVA), or polyolefin resin and elastomer,
When the resin constituting the foam is a polyethylene resin (PE) and an ethylene-vinyl acetate copolymer (EVA), the mass ratio (EVA/PE) of the polyethylene resin and the ethylene-vinyl acetate copolymer is 50. /50 to 80/20,
When the resin constituting the foam is a polyolefin resin and an elastomer, the ratio of the polyolefin resin to the total resin amount is 50 to 70% by mass, and the ratio of the elastomer to the total resin amount is 30 to 50% by mass . Sealing material for electronic devices. 2. The sealing material for electronic devices according to claim 1, wherein the surface layer resin composition constituting the surface layer contains 70% by mass or more of a main agent selected from the group consisting of elastomers and soft resins. 3. The electronic device sealing material according to claim 2, wherein the main agent is at least one selected from the group consisting of butyl rubber, ethylene propylene rubber, ethylene propylene diene rubber, acrylic resin, and styrenic thermoplastic elastomer. The surface layer resin composition is selected from the group consisting of petroleum-based copolymers, ethylene-vinyl acetate copolymers, coumarone-indene-based resins, terpene-based resins, terpene-phenolic resins, rosin-based resins, and xylene-based resins. The sealing material for electronic devices according to claim 2 or 3, containing 0.5 to 20% by mass of at least one modified polymer. The main agent is at least one selected from the group consisting of butyl rubber, ethylene propylene rubber, ethylene propylene diene rubber, and styrenic thermoplastic elastomer,
5. The electronic device sealing material according to claim 4, wherein the modified polymer is at least one selected from the group consisting of petroleum-based copolymers and ethylene-vinyl acetate copolymers. The main agent is an acrylic resin, and
5. The modified polymer according to claim 4, wherein the modified polymer is at least one selected from the group consisting of petroleum-based copolymers, coumarone-indene-based resins, terpene-based resins, terpene-phenolic-based resins, rosin-based resins, and xylene-based resins. Sealing material for electronic devices. The electronic device sealing material according to any one of claims 1 to 6 , wherein the foam has closed cells. The electronic device sealing material according to any one of claims 1 to 7 , wherein the foam has an average cell diameter of 300 µm or less in the MD and TD directions, and an average cell diameter of 150 µm or less in the ZD direction. The electronic device sealing material according to any one of claims 1 to 8 , wherein the foam has an expansion ratio of 1.2 to 20 cm ³ /g. The sealing material for electronic devices according to any one of claims 1 to 9 , which has a thickness of 0.05 to 2.5 mm. The electronic device sealing material according to any one of claims 1 to 10 , comprising an adhesive material on the other surface of the core layer.

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