JP5675862B2 - Photocurable elastomer composition, gasket for hard disk drive and hard disk drive - Google Patents

Description

  The present invention relates to a photocurable elastomer composition, a gasket for a hard disk drive, and a hard disk drive.

2. Description of the Related Art In recent years, gaskets are used in hard disk drives (hereinafter sometimes simply referred to as “HDDs”) used in computers and video recording equipment to prevent dust and water vapor from entering.
In order to improve the water vapor barrier property (hereinafter simply referred to as “barrier property”) in a gasket, it is the easiest method to harden the gasket, but the gasket depends on the member to be bonded or sealed. Since it is used after being compressed, flexibility is required from the viewpoint of durability.

  Examples of the ultraviolet curable gasket material include epoxy acrylate and urethane acrylate (for example, Patent Documents 1 to 3). Epoxy acrylate is hard and has good barrier properties, but there is room for improvement in terms of flexibility. Some urethane acrylates have good flexibility, but there is room for further improvement in terms of barrier properties.

JP 2010-260918 A JP 2009-43295 A JP 2009-221329 A

Further, in the HDD gasket, the adherends (also referred to as adherends) are sealed, and then the adhesion of the adherends is released (peeled), and then the adherends are again connected using the same HDD gasket. The property that can be sealed, so-called reworkability is also required.
According to the present inventor, when the compression set is large (bad), when the adhesive is released and the same HDD gasket is used and the cover for sandwiching the HDD gasket is closed and reattached, It has been found that the HDD gasket does not recover to a predetermined size (height), and a gap is formed, resulting in insufficient adhesion or sealing, and sufficient reworkability may not be obtained. Therefore, a small (good) compression set is necessary to ensure sufficient reworkability.

  The present invention has been made in order to solve the above-described problems. When the photocurable elastomer composition is cured, the light is excellent in flexibility and barrier properties and can exhibit a small compression set. An object is to provide a curable elastomer composition.

The photocurable elastomer composition according to the present invention comprises a liquid polymer mainly composed of (A)-[CH ₂ C (CH ₃ ) ₂ ] -units, (B) a number average molecular weight of 3,000 or more, ) A polymer having at least two reactive functional groups in one molecule selected from the group consisting of an acrylic group, a vinyl group, a vinylidene group, and a maleimide group; and (C) a (meth) acrylate monomer; , (D) a photopolymerization initiator, and the mass ratio of the component (A) to the component (B) ((A) :( B)) is 7:93 to 75:25, and Content of the said (C) component is 25-55 mass% with respect to the total amount of three components of the said (A) component, (B) component, and (C) component, It is characterized by the above-mentioned.
The said specific liquid polymer which is (A) component can provide the softness | flexibility and barrier property which were excellent in the hardened | cured material of the photocurable elastomer composition which concerns on this invention.
Moreover, the said photocurable elastomer composition was hardened because the mass ratio ((A) :( B)) of the said (A) component and the said (B) component is 7: 93-75: 25. Sometimes a small compression set is obtained while ensuring excellent flexibility and barrier properties.
Furthermore, when the content of the component (C) is 25 to 55% by mass with respect to the total amount of the three components (A), (B), and (C), the photocurability The elastomer composition can exhibit excellent moldability, flexibility and barrier properties.

In this specification, “light” in “photocurability” and “photopolymerization” means ultraviolet rays, visible rays, charged particle rays such as α rays, β rays, electron rays, electromagnetic waves such as γ rays, and high energy particles. In particular, ultraviolet rays are preferably included.
In the present specification, the “number average molecular weight” means a number average molecular weight represented by a standard polystyrene equivalent value measured by a gel permeation chromatography (GPC) method unless otherwise specified.
In the present specification, the proportion of — [CH ₂ C (CH ₃ ) ₂ ] — units in the liquid polymer of component (A), the unit derived from polyisoprene, the unit derived from polybutadiene in the polymer of component (B), styrene -The ratio of the unit derived from a butadiene copolymer, the unit derived from an ethylene-propylene copolymer, and the unit derived from these hydrogenated products can be determined using the peak ratio of NMR.
In this specification, “liquid” means having fluidity at a molding temperature, for example, room temperature (25 ° C.).
In this specification, (meth) acrylate means at least one of acrylate and methacrylate. (Meth) acryl means at least one of acrylic and methacrylic.
In this specification, a vinyl group means (CH ₂ ═CH—), an acrylic group means (CH ₂ ═CHCO—), and a methacryl group means (CH ₂ ═C (CH ₃ ) CO—). Means.
In this specification, a gasket is synonymous with a sealing material, a sealing material, a sealing material, or packing. In this specification, the gasket includes both a fixing seal (static seal) and a motion seal unless otherwise specified.

In the photocurable elastomer composition according to the present invention, the component (B) is derived from a polyisoprene-derived unit, a polybutadiene-derived unit, a styrene-butadiene copolymer-derived unit, and an ethylene-propylene copolymer-derived unit. The polymer is preferably a polymer mainly comprising any one selected from the group consisting of units and units derived from these hydrogenated products.
By using such a component (B), a smaller compression set is obtained and a barrier property is further improved with respect to the cured product of the photocurable elastomer composition.

  In the photocurable elastomer composition according to the present invention, the component (C) is a (meth) acrylate derived from a hydrocarbon (meth) acrylate having 6 or more carbon atoms, isobornyl (meth) acrylate, and dicyclopentadiene. Preferably, it is at least one monofunctional (meth) acrylate selected from the group consisting of: By using such a component (C), higher flexibility and barrier properties can be obtained. It is also excellent in compatibility and toughness.

  The photocurable elastomer composition according to the present invention preferably further contains at least one selected from an inorganic filler and an organic filler as the component (E). By using such component (E), pseudoplasticity is imparted to the photocurable elastomer composition, and the moldability of the photocurable elastomer composition is enhanced.

  In the photocurable elastomer composition according to the present invention, the component (E) is preferably fumed silica. By using fumed silica as the component (E), there is an advantage of having excellent pseudoplasticity.

  The photocurable elastomer composition according to the present invention is suitably used for a hard disk drive gasket.

  The gasket for a hard disk drive according to the present invention is characterized in that the photocurable elastomer composition is used at least in part. The gasket for a hard disk drive according to the present invention is excellent in flexibility and barrier properties and has a small compression set by using the photocurable elastomer composition at least in part.

  The hard disk drive according to the present invention is characterized by having at least a part of the hard disk drive gasket. The hard disk drive according to the present invention is excellent in durability and barrier properties and has sufficient reworkability by having the hard disk drive gasket at least in part.

  ADVANTAGE OF THE INVENTION According to this invention, when a photocurable elastomer composition is hardened, the photocurable elastomer composition which is excellent in a softness | flexibility and barrier property, and can exhibit a small compression set can be provided. Further, according to the present invention, it is possible to provide a hard disk drive gasket which is excellent in flexibility and barrier properties and has a small compression set. Furthermore, according to the present invention, it is possible to provide a hard disk drive that is excellent in durability and barrier properties and has sufficient reworkability.

(Photocurable elastomer composition)
Hereinafter, an example of a preferred embodiment of the photocurable elastomer composition according to the present invention will be described in detail.
The photocurable elastomer composition according to the present invention comprises a liquid polymer mainly composed of (A)-[CH ₂ C (CH ₃ ) ₂ ] -units, (B) a number average molecular weight of 3,000 or more, ) A polymer having at least two reactive functional groups in one molecule selected from the group consisting of an acrylic group, a vinyl group, a vinylidene group, and a maleimide group; and (C) a (meth) acrylate monomer; , (D) a photopolymerization initiator, and the mass ratio of the component (A) to the component (B) ((A) :( B)) is 7:93 to 75:25, and Content of the said (C) component is 25-55 mass% with respect to the total amount of three components of the said (A) component, (B) component, and (C) component, It is characterized by the above-mentioned.
The said specific liquid polymer which is (A) component can provide the softness | flexibility and barrier property which were excellent in the hardened | cured material of the photocurable elastomer composition which concerns on this invention.
Moreover, the said photocurable elastomer composition was hardened because the mass ratio ((A) :( B)) of the said (A) component and the said (B) component is 7: 93-75: 25. Sometimes a small compression set is obtained while ensuring excellent flexibility and barrier properties.
Furthermore, when the content of the component (C) is 25 to 55% by mass with respect to the total amount of the three components (A), (B), and (C), the photocurability The elastomer composition can exhibit excellent moldability, flexibility and barrier properties.
Hereinafter, the components (A) to (C) of the photocurable elastomer composition according to the present invention and other components that may be appropriately included will be described.

<(A) component>
The component (A) is a liquid polymer mainly containing — [CH ₂ C (CH ₃ ) ₂ ] — units (units derived from polyisobutylene).
In the molecule of the component (A), in addition to the — [CH ₂ C (CH ₃ ) ₂ ] — unit, a component such as a modifier used in the synthesis of the component (A) may be contained. . (A) component, _{- [CH 2 C (CH 3} ) 2] - unit may be the mainly terminally modified polymer and _{- [CH 2 C (CH 3} ) 2] - other than the unit of other The polymer (for example, block copolymer) containing a structural unit or a repeating unit may be sufficient. The component (A) exhibits an excellent flexibility and barrier property when the photocurable elastomer composition is cured, and therefore 80 mass of — [CH ₂ C (CH ₃ ) ₂ ] — unit in the molecule. % Or more is preferable.
The component (A) is mainly a non-reactive (non-crosslinkable) liquid polymer because it mainly contains — [CH ₂ C (CH ₃ ) ₂ ] — units. As described above, since the component (A) has an effect of exhibiting excellent flexibility, it is preferable that the component (A) does not contain a reactive functional group such as a (meth) acryl group. A reactive functional group such as a (meth) acryl group may be contained in the component (A) without departing from the spirit of the invention.
As described above, the component (A) is liquid. When the component (A) is solid, mixing with other components becomes difficult.

  The number average molecular weight of the component (A) is not particularly limited as long as it is in a range that can exhibit the above flexibility and barrier properties, but the component (A) on the cured product surface of the cured product of the photocurable elastomer composition is not limited. From the viewpoint of suppressing bleed out (migration), the number average molecular weight of the component (A) is preferably 20,000 or more, and from the viewpoint that the viscosity of the photocurable elastomer composition is moderate and productivity is increased. Since the average molecular weight is preferably 50,000 or less, 20,000 to 50,000 is more preferable.

  Examples of such commercially available products of component (A) include, for example, trade names manufactured by Kaneka Corporation, EPION (registered trademark) 200A (number average molecular weight 5,000), 400A (number average molecular weight 10,000), 600A (several Average molecular weight 15,000), trade names Tetrax (registered trademark) 3T (number average molecular weight 30,000), 4T (number average molecular weight 40,000), 5T (number average molecular weight 50) manufactured by JX Nippon Mining & Energy Corporation , 000) and 6T (number average molecular weight 60,000).

  (A) A component may be used individually by 1 type and may be used in combination of 2 or more type.

In the photocurable elastomer composition according to the present invention, the mass ratio ((A) :( B)) of the component (A) to the component (B) described later is 7:93 to 75:25. Thereby, when the photocurable elastomer composition is cured, a small compression set is obtained while ensuring excellent flexibility and barrier properties.
The component (A) has both hydrophobicity due to the hydrocarbon-based skeleton and a bulky (bulky) skeleton of — [CH ₂ C (CH ₃ ) ₂ ] — unit, so that both amorphousness and increase in excluded volume are achieved. In addition, it exhibits excellent barrier properties due to a decrease in the diffusion rate of water vapor (however, when only the component (A) exists independently, it tends to flow as a result of stress and remain as a permanent strain). On the other hand, when the component (B) is cross-linked and the stress is unloaded, the shape is restored to a certain degree according to the entropy elasticity of the component (B) itself, thereby exhibiting a small compression set. And since the mass ratio of this (A) component and (B) component is the said specific range, a crosslinking density and the non-uniformity of bridge | crosslinking become moderate (In the clearance gap of the crosslinked structure of (B) component, ( Even if the A) component is incorporated, the (A) component does not adversely affect the restoration due to the entropy elasticity of the (B) component), thereby obtaining a small compression set while ensuring excellent flexibility and barrier properties. It is done.
The mass ratio ((A) :( B)) is preferably 8:92 to 50:50, and more preferably 8:92 to 30:70, from the viewpoint of obtaining a small compression set.

<(B) component>
The component (B) has a number average molecular weight of 3,000 or more and contains at least one reactive functional group selected from the group consisting of a (meth) acryl group, a vinyl group, a vinylidene group, and a maleimide group in one molecule. 2 or more. As described above, the component (B) contributes to exerting a small compression set by the cured product of the photocurable elastomer composition.

  The component (B) has two or more reactive functional groups selected from the group consisting of a (meth) acryl group, a vinyl group, a vinylidene group, and a maleimide group in one molecule. These reactive functional groups improve the photoactivity including ultraviolet rays. Further, by having two or more of these reactive functional groups in one molecule, there is an advantage that a three-dimensional crosslinking is formed and the compression set is reduced. The number of reactive functional groups in one molecule of the component (B) is 2 or more, but 2 to 6 is more preferable.

  (B) The number average molecular weight of a component is 3,000 or more. By setting the number average molecular weight to 3,000 or more, it becomes easy to increase the flexibility of the cured product of the photocurable elastomer composition, and it becomes easy to ensure the sealing property. In particular, the HDD gasket is required to have a sealing property of (i) preventing intrusion of dust and water vapor from the outside, and (ii) preventing outflow of an inert gas sealed inside the apparatus. The HDD gasket is an elastic body and is sandwiched between two covers to exhibit such a sealing property. However, at this time, if the HDD gasket is not sufficiently flexible, it cannot follow the cover, cannot prevent intrusion of dust and water vapor, and the enclosed inert gas also flows out. A sufficient sealing performance cannot be obtained. On the other hand, as described above, when the number average molecular weight of the component (B) is 3,000 or more, flexibility is increased, sealing performance is ensured, and sufficient reworkability is easily obtained. The number average molecular weight of the component (B) is more preferably 20,000 or less. By being this range, the viscosity of a photocurable elastomer composition can be kept low, and productivity increases.

  As the component (B), for example, trade name UC-102 manufactured by Kuraray Co., Ltd. (methacryl-modified polyisoprene, number average molecular weight 17,000, having two reactive functional groups in the side chain), UC-203 (methacryl Modified polyisoprene, number average molecular weight 35,000, having 3 reactive functional groups in the side chain), product name CN-307 (polybutadiene diacrylate, number average molecular weight 3,500, reactive functional group, manufactured by Arkema) 2) and the like. (B) A component may be used individually by 1 type and may be used in combination of 2 or more type.

In the photocurable elastomer composition according to the present invention, the component (B) is derived from a polyisoprene-derived unit, a polybutadiene-derived unit, a styrene-butadiene copolymer-derived unit, and an ethylene-propylene copolymer-derived unit. The polymer is preferably a polymer mainly comprising any one selected from the group consisting of units and units derived from these hydrogenated products.
By using such a component (B), a smaller compression set is obtained and a barrier property is further improved with respect to the cured product of the photocurable elastomer composition.
In this case, the component (B) may be a polymer mainly composed of the above structural unit, and may contain components such as a modifier used in the synthesis of the component (B), and the terminal is modified. It may be a polymer (for example, a block copolymer) containing a structural unit other than the above structural unit and a repeating unit or a repeating unit. (B) It is preferable that a component contains the said structural unit 80 mass% or more.

  Examples of such component (B) include trade names UC-102 and UC-203 manufactured by Kuraray Co., Ltd., and trade names CN-307 manufactured by Arkema.

  Furthermore, among these, the component (B) is not a hydrogenated product (having a carbon-carbon unsaturated bond), a unit derived from polyisoprene, a unit derived from polybutadiene, a unit derived from a styrene-butadiene copolymer, and It is preferably a polymer mainly composed of any one selected from the group consisting of units derived from an ethylene-propylene copolymer (EP). Such non-hydrogenated polymers have the advantages of being inexpensive, readily available, low viscosity, and capable of shortening the synthesis process. Examples of the component (B) having such a carbon-carbon unsaturated bond include trade names UC-102 and UC-203 manufactured by Kuraray Co., Ltd., and trade names CN-307 manufactured by Arkema.

  The content of the component (B) may be appropriately adjusted in accordance with the application, use state, required performance, and the like within the range of the mass ratio with the component (A) described above.

<(C) component>
The (meth) acrylate monomer as the component (C) has a function of adjusting viscosity in addition to a function of imparting photocurability (moldability) to the photocurable elastomer composition according to the present invention. As the component (C), a (meth) acrylate monomer used in a conventionally known photocurable composition can be used. (C) A component may be used individually by 1 type and may be used in combination of 2 or more type. The (C) component (meth) acrylate monomer may be a monomer having at least one (meth) acryl group, and more preferably has only one (meth) acryl group. The molecular weight of the component (C) (meth) acrylate monomer may be appropriately selected according to the use, use state, required performance, etc. of the photocurable elastomer composition according to the present invention, but is less than 1000. Is preferred. Thereby, the effect which reduces the viscosity of the photocurable elastomer composition which concerns on this invention increases.

Examples of the (meth) acrylate monomer having a molecular weight of less than 1000 include n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, dicyclopentanyl (meth) acrylate, and dicyclohexane. Pentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, diethylene glycol monoethyl ether (meth) acrylate, dimethylaminoethyl (meth) acrylate, dipropylene glycol mono (meth) acrylate, ethoxydiethylene glycol (meth) acrylate, ethoxy Phenyl (meth) acrylate, ethyl (meth) acrylate, isoamyl (meth) acrylate, isobornyl (meth) acrylate, isobutyl (meth) acrylate , Isodecyl (meth) acrylate, isooctyl (meth) acrylate, isomyristyl (meth) acrylate, isostearyl (meth) acrylate, n-octadecyl (meth) acrylate, lauroxy polyethylene glycol (meth) acrylate, lauryl (meth) Examples include acrylate, methoxydipropylene glycol (meth) acrylate, methoxytripropylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, and methoxytriethylene glycol (meth) acrylate.
In addition, for example, (meth) acrylic monomers described in Patent Documents 1 and 2 and acrylic monomers described in Patent Document 3 can be mentioned.

  In the photocurable elastomer composition according to the present invention, the component (C) is derived from a hydrocarbon (meth) acrylate having 6 or more carbon atoms, isobornyl (meth) acrylate, and dicyclopentadiene. And at least one monofunctional (meth) acrylate selected from the group consisting of: Thereby, higher flexibility and barrier properties can be obtained. It is also excellent in compatibility and toughness.

As for carbon number of C6 or more hydrocarbon (meth) acrylate, 6-24 are more preferable.
The hydrocarbon portion of the hydrocarbon (meth) acrylate having 6 or more carbon atoms may be linear, branched or cyclic. Examples of the hydrocarbon (meth) acrylate having 6 or more carbon atoms include n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, isomyristyl (meth) acrylate, and isostearyl (meth). Examples include acrylate, n-octadecyl (meth) acrylate, and esters of (meth) acrylic acid and polyhydric alcohols.
Examples of (meth) acrylates derived from dicyclopentadiene include dicyclopentanyl (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, and norbornyl (meth) acrylate. Can be mentioned.

  Content of (C) component in a photocurable elastomer composition should just be 25-55 mass% with respect to the total amount of three components of said (A) component, (B) component, and (C) component, Within this range, it may be appropriately adjusted according to the application, use state, required performance, and the like. The content of the component (C) is more preferably 30 to 40% by mass with respect to the total amount of the three components (A), (B) and (C).

<(D) component>
The photopolymerization initiator of component (D) has a function of initiating or accelerating photopolymerization or curing of a photocurable component (for example, the above components (A) to (C)).
As a photoinitiator, what is used for a conventionally well-known photocurable composition, such as the thing of patent documents 1-3, for example, can be selected suitably, and can be used.
Examples of the component (D) include benzoin alkyl ether photopolymerization initiators such as benzoin ethyl ether, benzoin isobutyl ether, and benzoin isopropyl ether; 2,2-diethoxyacetophenone, 4′-phenoxy-2,2-dichloroacetophenone Acetophenone-based photopolymerization initiators such as 2-hydroxy-2-methylpropiophenone, 4′-isopropyl-2-hydroxy-2-methylpropiophenone, 4′-dodecyl-2-hydroxy-2-methylpropio Propiophenone photopolymerization initiators such as phenone; benzyldimethyl ketal, 1-hydroxycyclohexyl phenyl ketone, 1- [4- (2-hydroxyethoxy) -phenyl] -2-hydroxy-2-methyl-1-propane- Alkylphenone series such as 1-one Polymerization initiator; 2-ethylanthraquinone, 2-chloro-anthraquinone photoinitiator anthraquinone; photoinitiator intramolecular cleavage type such as acylphosphine oxide-based photopolymerization initiators. Among these, anthraquinone photopolymerization initiators such as 1-hydroxycyclohexyl phenyl ketone and propiophenone photopolymerization initiators such as 2-hydroxy-2-methylpropiophenone are preferable.
Other examples of the component (D) include hydrogen abstraction type photopolymerization initiators such as benzophenone / amine photopolymerization initiators, Michler ketone / benzophenone photopolymerization initiators, and thioxanthone / amine photopolymerization initiators. it can.
Of the photopolymerization initiators, 1-hydroxycyclohexyl phenyl ketone (trade name Irgacure (registered trademark) 184 manufactured by BASF) is particularly preferable.

  (D) The photoinitiator of a component may be used individually by 1 type, and may be used in combination of 2 or more type. What is necessary is just to adjust suitably content of a photoinitiator according to the kind, content, etc. of a photocurable component in a photocurable elastomer composition. Content of a photoinitiator is 0.1-10 mass parts normally with respect to 100 mass parts of total amounts of the said photocurable component (for example, said (A)-(C) component), for example. Preferably it is 0.5-5 mass parts, More preferably, it is 0.5-3 mass parts. Moreover, you may use together a well-known photosensitizer with the said photoinitiator.

<Optional component>
The photo-curable elastomer composition according to the present invention includes, as necessary, component (E) (inorganic filler, organic thixotropic agent (thixotropic agent)); cup, without departing from the spirit of the present invention. Ring agent; antioxidant (anti-aging agent); light stabilizer; carbodiimides (moisture and heat resistant anti-aging agent); other fatty acids such as stearic acid (lubricant); fatty acid metal salts such as calcium stearate (lubricant); stearic acid Fatty acid amide (thickening agent) such as amide; Fatty acid ester (plasticizer); Internal mold release agent such as polyolefin wax and paraffin wax; Softener such as process oil; Colorant; Leveling agent; Can do. Examples of the coupling agent, antioxidant (anti-aging agent), and light stabilizer include those described in Patent Documents 1 and 2.
Hereinafter, the component (E) will be described.

<(E) component>
The photocurable elastomer composition according to the present invention preferably further contains at least one selected from an inorganic filler and an organic filler as the component (E).
By using such a component (E), thixotropy (pseudoplasticity) is imparted to the photocurable elastomer composition, and the moldability of the photocurable elastomer composition is enhanced.
Examples of the inorganic filler include silica (SiO ₂ ), alumina, titania and their composite oxides, layered oxides; and clay minerals. Among these, silica is more preferable. More specifically, silica fine powder (for example, product name: Aerosil 300 manufactured by Nippon Aerosil Co., Ltd.) that has been micronized by a dry method can be used. In the photocurable elastomer composition according to the present invention, the component (E) is preferably fumed silica. By using fumed silica, there is an advantage of having excellent pseudoplasticity. As the fumed silica, for example, trade name HDK (registered trademark) N20 manufactured by Asahi Kasei Wacker Silicone Co., Ltd. is preferable.

  The average particle diameter of the inorganic filler is more preferably 5 to 50 μm, and further preferably 5 to 12 μm, from the viewpoint of imparting thickening and pseudoplasticity. The average particle size of the inorganic filler can be determined by a method such as BET adsorption or SEM, for example. When the photocurable elastomer composition contains an inorganic filler, the content thereof may be adjusted as appropriate, and is preferably 0.1 to 30 parts by mass with respect to 100 parts by mass of the total amount of the photocurable elastomer composition. More preferably, it is 1-15 mass parts.

  As the organic filler (organic thixotropic agent), conventionally known ones may be used, and examples thereof include hydrogenated castor oil, amide wax, or a mixture thereof. Specific examples include those described in JP 2012-72204 A.

<Viscosity of photocurable elastomer composition>
The photocurable elastomer composition according to the present invention preferably has a viscosity of 1 to 10,000 Pa · s at a temperature of 50 ° C. and a shear rate of 1.0 / second. When the viscosity is within such a range, the photocurable elastomer composition has appropriate fluidity and good handling properties, and is also photocurable according to the shape of a desired sealing material such as a gasket. The shape of the elastomer composition can be maintained, whereby the shape of the sealing material can be maintained. The viscosity of the photocurable elastomer composition is more preferably 10 to 2,000 Pa · s, and further preferably 30 to 1,000 Pa · s.
<< Viscosity Measurement Method >>
It is measured using a rheometer “RS-600” (manufactured by Harke). The photocurable elastomer composition was adjusted to 50 ° C., the shear stress was measured while changing the shear rate in the range of ¹ to 10 s ⁻¹ with a gap of 0.2 mm, and the shear rate and the 1/2 power of the plot were plotted. A viscosity line at 1 s ⁻¹ is calculated by drawing an approximate line by the least square method from the Cason plot.

<Method for Preparing Photocurable Elastomer Composition>
There is no restriction | limiting in particular in the preparation method of the photocurable elastomer composition of this invention, A well-known method can be used. For example, a kneader (for example, a single screw extruder, a twin screw extruder, a planetary mixer, a twin screw mixer, a high shear mixer, etc.) capable of adjusting the temperature of the components (A) to (D) and the optional component. It can be prepared by using and kneading.

<Use of photocurable elastomer composition>
The photocurable elastomer composition according to the present invention includes, for example, HDD gaskets; ink tank sealing materials; desktop computers, notebook computers, tablet computers and other various computers, mobile phones, liquid crystal display devices, organic EL displays, and electronic papers. And various display devices such as plasma displays, and sealing materials for various electronic parts such as cameras; sealing materials for automobile parts, water purification devices, air purification devices, agitators, speakers, pumps, etc .; anti-vibration devices, waterproof devices, It can be used for sealing materials for structures such as dampers, civil engineering, and buildings; packing such as O-rings.

  The photocurable elastomer composition according to the present invention is suitably used for a hard disk drive gasket. As described above, the photocurable elastomer composition according to the present invention is excellent in flexibility and barrier properties, and can exhibit a small compression set.

(Hard disk drive gasket)
The gasket for a hard disk drive according to the present invention is characterized in that the photocurable elastomer composition is used at least in part. That is, the gasket for a hard disk drive according to the present invention is a gasket for a hard disk drive including at least a part of a cured product obtained by irradiating the photocurable elastomer composition with light such as ultraviolet rays.
The gasket for a hard disk drive according to the present invention is excellent in flexibility and barrier properties and has a small compression set by using the photocurable elastomer composition at least in part.
Although the thickness of a gasket can be suitably adjusted with a use, it is about 0.1-2 mm normally.

  The HDD gasket according to the present invention preferably has a JIS-A hardness of 80 or less, which is described later, preferably 25 to 70, from the viewpoint of achieving both flexibility and barrier properties of the HDD gasket. Is more preferable, and 30 to 60 is even more preferable.

  The barrier property of the HDD gasket according to the present invention can be appropriately adjusted according to the application. As for the barrier property of the HDD gasket according to the present invention, the moisture permeability described later is preferably 10 or less.

  The compression set of the HDD gasket according to the present invention is preferably 50% or less, more preferably 30% or less, and still more preferably 20% or less.

<Method for manufacturing gasket for hard disk drive>
A hard disk drive gasket can be produced by applying the photocurable elastomer composition to an adherend and curing it by irradiating light.
The adherend can be appropriately selected depending on the application. For example, the adherend may be a metal or a hard resin. A metal adherend is preferred from the viewpoint of workability.
The metal as the adherend is not particularly limited, and a conventionally known adherend can be used. For example, a cold rolled steel plate, a galvanized steel plate, an aluminum / zinc alloy plated steel plate, a stainless steel plate, an aluminum plate, an aluminum alloy plate, a magnesium plate, a magnesium alloy plate, and the like can be given. Moreover, what injection-molded magnesium can also be used.

  The method for applying the photocurable elastomer composition to the adherend is not particularly limited, and a conventionally known method can be appropriately selected and used. Application is, for example, adjusting the temperature of the photocurable elastomer composition as necessary, adjusting to a desired viscosity, gravure coat, roll coat, spin coat, reverse coat, bar coat, screen coat, blade coat, air It can be performed by knife coating, dipping, dispensing, or the like. After applying a photocurable elastomer composition to a to-be-adhered body and shape | molding as needed, a photocurable elastomer composition can be hardened by irradiating light and the gasket for hard disk drives can be obtained.

Light for curing the photocurable elastomer composition may be appropriately selected from ultraviolet rays, charged particle beams such as α rays and β rays, electromagnetic waves such as γ rays and ionizing radiation including high energy particles. Such light is preferably ultraviolet rays from the viewpoints of operability, productivity, economy, and the like.
As the ultraviolet ray source, a conventionally known one can be used, and examples thereof include a xenon lamp, a low-pressure mercury lamp, a high-pressure mercury lamp, a metal halide lamp, and a microwave excimer lamp.
The atmosphere for irradiating ultraviolet rays may be an air atmosphere, an inert gas atmosphere such as nitrogen gas or carbon dioxide gas, or an atmosphere with a reduced oxygen concentration. As such an atmosphere, an inert gas atmosphere or an atmosphere with a reduced oxygen concentration is preferable. The irradiation atmosphere temperature may be adjusted as appropriate, and can usually be 10 to 200 ° C.
The irradiation time may be appropriately adjusted and is usually preferably 10 seconds to 60 minutes. The integrated light amount may be adjusted as appropriate, and is usually preferably 1,000 to 20,000 mJ / cm ² .

(Hard disk drive)
The hard disk drive according to the present invention is characterized by having at least a part of the hard disk drive gasket.
The apparatus according to the present invention has excellent durability and barrier properties and has sufficient reworkability by having the hard disk drive gasket at least in part.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples.

(Examples 1-18 and Comparative Examples 1-10)
Each component was mix | blended with the prescription shown in Table 1 and 2 (The value in each component represents a mass part), and the photocurable elastomer composition was prepared. Then, the hardness (flexibility), moisture permeability (barrier property) and compression set were measured and evaluated by the following methods. The results are shown in Tables 1 and 2.

Each component used in this study is shown below.
Polyisobutylene A (component (A)): manufactured by Kaneka Corporation, EPION (registered trademark) 200A (number average molecular weight 5,000)
Polyisobutylene B (component (A)): manufactured by Kaneka Corporation, EPION (registered trademark) 400A (number average molecular weight 10,000)
Polyisobutylene C (component (A)): manufactured by Kaneka Corporation, EPION (registered trademark) 600A (number average molecular weight 15,000)
Polyisobutylene D (component (A)): Tetrax (registered trademark) 3T (number average molecular weight 30,000) manufactured by JX Nippon Mining & Energy Corporation
Polyisobutylene E (component (A)): Tetrax (registered trademark) 4T (number average molecular weight 40,000) manufactured by JX Nippon Mining & Energy Corporation
Incidentally, polyisobutylene _{A~E - [CH 2 C (CH} 3) 2] - the proportion of units 99% or more.
Methacryl-modified polyisoprene (component (B)): UC-102 manufactured by Kuraray Co., Ltd. (number average molecular weight 17,000, having two reactive functional groups in the side chain)
Acrylic modified polybutadiene (component (B)): CN-307 (number average molecular weight 3,500, having two reactive functional groups) manufactured by Arkema
Monomer A (component (C)): IBXA (isobornyl acrylate, monofunctional acrylate monomer) manufactured by Osaka Organic Chemical Industry Co., Ltd.
Monomer B (component (C)): Light acrylate LA (lauryl acrylate, monofunctional acrylate monomer) manufactured by Kyoeisha Chemical Co., Ltd.
Monomer C (component (C)): FA-513AS (dicyclopentanyl acrylate, monofunctional acrylate monomer) manufactured by Hitachi Chemical Co., Ltd.
Monomer D (component (C)): Light acrylate 1.9ND-A (1,9-nonanediol diacrylate, bifunctional acrylate monomer) manufactured by Kyoeisha Chemical Co., Ltd.
Photopolymerization initiator (component (D)): Irgacure (registered trademark) 184 manufactured by BASF
Fumed silica (component (E)): Asahi Kasei Wacker Silicone Co., Ltd. HDK (registered trademark) N20
Urethane acrylate: Kyoeisha Chemical Co., Ltd. light tack PUA-KH32M
Bisphenol A type epoxy acrylate: CN104LC manufactured by Arkema

<Flexibility (hardness)>
A photocurable elastomer composition was formed to a thickness of about 2 mm, and this was cured by light irradiation using a metal halide lamp to obtain a sheet. The light irradiation was performed under the conditions of an illuminance of about 150 mW / cm ² and an integrated light amount of about 9000 mJ / cm ^{2 in} an air atmosphere. This sheet was further baked at 120 ° C. for 4 hours in an air atmosphere. The hardness of this sheet was measured with a type A durometer in accordance with JIS K 6253. A specimen having a thickness of about 6 mm obtained by laminating three sheets having a thickness of about 2 mm was used. In addition, A hardness shows that 80 or less is favorable.

<Barrier properties (moisture permeability)>
A sheet having a thickness of about 1 mm was measured under the conditions of 50 ° C. and 90% relative humidity in accordance with JIS Z 0208 using a method A moisture permeable cup described in JIS L 1099. The moisture permeability is preferably smaller, and 10 [g / m ² · day] or less is preferable.

<Compression set>
In accordance with JIS K 6262, 5 sheets each having a thickness of 2 mm cut into 2 cm squares were stacked to form a measurement sample, and compression set was measured at a test temperature of 70 ° C. The compression set is preferably as small as possible, and is preferably 50% or less.

From Table 1, in the examples, cured products having excellent hardness (flexibility) and flexibility and small compression set were obtained.
On the other hand, in Comparative Examples 1 and 2 in which the mass ratio of the component (A) is small in the mass ratio of (A) :( B), the barrier property was inferior due to the lack of the component (A) relative to the component (B). In Comparative Example 3 in which the mass ratio of the component (B) was small in the mass ratio of (A) :( B), the compression set was inferior due to the shortage of the component (B) relative to the component (A).
In Comparative Example 4 in which the component (A) was not included, the barrier property was inferior.
In Comparative Example 5 in which the component (A) was not included, the barrier properties and compression set were inferior. Furthermore, in Comparative Example 5, since the flexibility is low, the sealing property is also poor.
In Comparative Example 6 in which the component (B) was not included, the compression set was inferior.
In Comparative Example 7 using a conventional urethane acrylate instead of the component (A) and the component (B), the barrier property was inferior.
In Comparative Example 8 using a conventional epoxy acrylate instead of the component (A) and the component (B), the compression set was inferior. Furthermore, since Comparative Example 8 has low flexibility, the sealing performance is also poor.
In Comparative Example 9 in which the content of the component (C) is small relative to the total amount of the component (A), the component (B) and the component (C), these components are separated without being compatible with each other, and the moldability is poor. The performance could not be measured.
In Comparative Example 10 in which the content of the component (C) was large with respect to the total amount of the components (A), (B) and (C), the compression set was inferior. Furthermore, since Comparative Example 10 has low flexibility, the sealing performance is also poor.

Claims (8)

_{(A) - [CH 2 C} (CH 3) 2] - a liquid polymer consisting mainly of units,
(B) Two or more reactive functional groups selected from the group consisting of a (meth) acryl group, a vinyl group, a vinylidene group, and a maleimide group with a number average molecular weight of 3,000 or more in one molecule A polymer having
(C) a (meth) acrylate monomer;
(D) a photopolymerization initiator,
The mass ratio ((A) :( B)) of the component (A) and the component (B) is 7:93 to 75:25, and
The content of the component (C) is 25 to 55% by mass with respect to the total amount of the three components (A), (B), and (C), and is photocured Elastomeric composition.   The component (B) is a unit derived from polyisoprene, a unit derived from polybutadiene, a unit derived from a styrene-butadiene copolymer, a unit derived from an ethylene-propylene copolymer, and a unit derived from a hydrogenated product thereof. The photocurable elastomer composition according to claim 1, which is a polymer mainly comprising any one selected from the group consisting of:   The component (C) is at least one selected from the group consisting of a hydrocarbon (meth) acrylate having 6 or more carbon atoms, isobornyl (meth) acrylate, and (meth) acrylate derived from dicyclopentadiene. The photocurable elastomer composition according to claim 1, which is a monofunctional (meth) acrylate.   The photocurable elastomer composition according to claim 1, further comprising at least one selected from an inorganic filler and an organic filler as the component (E).   The photocurable elastomer composition according to claim 4, wherein the component (E) is fumed silica.   The photocurable elastomer composition according to claim 1, wherein the photocurable elastomer composition is used for a gasket for a hard disk drive.   A hard disk drive gasket comprising at least a part of the photocurable elastomer composition according to any one of claims 1 to 6. A hard disk drive comprising at least a part of the gasket for a hard disk drive according to claim 7.