JP5031436B2 - Low moisture permeability polyorganosiloxane composition - Google Patents

Description

  The present invention relates to a polyorganosiloxane composition that cures by an addition reaction, and particularly relates to a polyorganosiloxane composition that exhibits low moisture permeability.

  The curable polyorganosiloxane composition that exhibits fluidity in an uncured state and forms a rubbery elastic body upon curing includes a condensation reaction type and an addition reaction type depending on the curing mechanism. The former cures at room temperature and exhibits good adhesion, but it takes a long time to cure, and the curability is poor at sites where the supply of moisture in the air is insufficient, and by-products are generated during curing. As a result, shrinkage occurs and not only the dimensional stability is lost, but also there are problems such as contamination of processing objects and surrounding parts by by-products. On the other hand, the latter can be cured in a short time by heating, has excellent curability even in a region where the supply of moisture in the air is not sufficient, and does not generate by-products, so that it does not cause shrinkage or contamination, etc. It has the characteristics of.

  Such fluid curable polyorganosiloxane compositions are widely used in applications such as sealing materials, sealants, protective materials, and insulating materials for electronic components. However, polyorganosiloxane has a large moisture permeability due to the large molecular chain gap, and the polyorganosiloxane layer alone cannot prevent the effects of moisture permeation. It was necessary to take measures such as providing it, and improvements were required.

  In particular, the hard disk device is a device that stores a hard disk having a magnetic layer on a disk in a sealed container and reads information by a magnetic head, and since it is necessary to prevent intrusion of dust and moisture, between the container and the lid, It is necessary to provide a gasket with low moisture permeability.

  In response to such demand for moisture permeability, the condensation reaction type polyorganosiloxane composition has been proposed to suppress moisture permeability by mica (see Patent Documents 1 and 2), but the addition reaction type polyorganosiloxane composition. Attempts to apply the product to the product have not been successful because the base polymer has poor affinity for mica, and therefore it has failed to form a cured siloxane layer that is homogeneous and excellent in mechanical properties.

  The inventor previously added an addition reaction type polyorganosiloxane by blending mica having a specific average particle diameter and an organosilicon compound having a specific side chain in the addition reaction type polyorganosiloxane composition. It has been found that a silicone rubber having a low moisture permeability can be obtained by making use of the above characteristics (see Patent Document 3). However, further improvement in moisture permeability has been demanded.

JP-A-53-73251 JP-A-53-74560 JP-A-2005-008657

  The subject of this invention is providing the polyorganosiloxane composition which hardens | cures and gives the silicone rubber with low moisture permeability, making use of the characteristic of addition reaction type polyorganosiloxane. A further object of the present invention is to provide a hard disk and a display device having a protective layer exhibiting such low moisture permeability.

  As a result of repeated research to solve the above-mentioned problems, the present inventor, in addition reaction type polyorganosiloxane composition, by using a specific linear polyorganosiloxane as a base polymer in combination with mica powder, The present inventors have found that the problem can be solved and have completed the present invention.

（式中、
Ｒは、独立して、Ｒ^１又はＲ^２であり、Ｒのうち、少なくとも２個はＲ^１であり、
Ｒ^１は、独立して、Ｃ_２−Ｃ_６アルケニル基であり、
Ｒ^２は、独立して、Ｃ_１−Ｃ_６アルキル基又はフェニル基であり、Ｒ^２のうち、１５モル％以上はフェニル基であり、
ｎは、（Ａ）の２３℃における粘度を０．１〜１，０００Ｐａ・ｓとする数）で示される直鎖状ポリオルガノシロキサン １００重量部；
（Ｂ）ケイ素原子に結合した水素原子を分子中に２個を越える数で有するポリオルガノハイドロジェンシロキサン （Ａ）に存在するアルケニル基１個に対するケイ素原子に結合した水素原子の数が、０．５〜５．０になる量；
（Ｃ）白金族金属化合物 白金族金属原子を、（Ａ）の量に対して０．１〜１，０００重量ｐｐｍ含有する量；並びに
（Ｄ）マイカ粉 ２０〜２００重量部
を含む、ポリオルガノシロキサン組成物に関し、この組成物を硬化させて得られる保護層を有するハードディスク及び表示装置に関する。 That is, the present invention provides (A) Formula (I):

(Where
R is independently R ¹ or R ² , of which at least two are R ¹ ,
R ¹ is independently a C ₂ -C ₆ alkenyl group,
R ² is independently a C ₁ -C ₆ alkyl group or a phenyl group, and among R ² , 15 mol% or more is a phenyl group,
n is a number in which the viscosity of (A) at 23 ° C. is 0.1 to 1,000 Pa · s) 100 parts by weight of a linear polyorganosiloxane;
(B) Polyorganohydrogensiloxane having more than two hydrogen atoms bonded to silicon atoms in the molecule The number of hydrogen atoms bonded to silicon atoms for one alkenyl group present in (A) is 0.00. An amount of 5 to 5.0;
(C) Platinum group metal compound An amount containing 0.1 to 1,000 ppm by weight of a platinum group metal atom with respect to the amount of (A); and (D) a polyorgano containing 20 to 200 parts by weight of mica powder. The present invention relates to a siloxane composition, and relates to a hard disk and a display device having a protective layer obtained by curing the composition.

  According to the present invention, a polyorganosiloxane composition that cures by heating for a short time and gives a cured product with low moisture permeability while taking advantage of the characteristics of the addition reaction type polyorganosiloxane that there is no shrinkage or contamination of parts by by-products Can be provided. The composition of the present invention gives a cured product with lower moisture permeability, and can form an excellent protective layer on various devices and parts sensitive to moisture. Therefore, by using the composition of the present invention, it is possible to obtain a hard disk and a display device having a layer having a moisture permeability lower than that of a conventional product on the surface.

  The component (A) used in the present invention has the formula (I):

(Where
R is independently R ¹ or R ² , of which at least two are R ¹ ,
R ¹ is independently a C ₂ -C ₆ alkenyl group,
R ² is independently a C ₁ -C ₆ alkyl group or a phenyl group, and among R ² , 15 mol% or more is a phenyl group,
n is a linear polyorganosiloxane represented by (A) having a viscosity of 0.1 to 1,000 Pa · s at 23 ° C.).

This component (A) is a component which becomes a base polymer in the composition of the present invention, and forms a network structure by an addition reaction between R ¹ in formula (I) and the hydrosilyl group in component (B). A cured product can be formed.

In the formula (I), R ¹ is a C ₂ -C ₆ alkenyl group, which may be branched or linear, such as vinyl, allyl, 3-butenyl, 5-hexenyl, etc. Is exemplified. The vinyl group is most preferable because it is easy to synthesize and does not impair the fluidity of the composition before curing and the heat resistance of the composition after curing. There are at least two R ^{1 s} in formula (I). At this time, R ¹ may be present in any siloxane unit in the molecule, but in order to obtain good reactivity, at least a part of R ¹ is preferably present at the molecular end, and at each end, More preferably, there are two R ¹ , one by one.

In the formula (I), R ² is a C ₁ -C ₆ alkyl group or a phenyl group. The C ₁ -C ₆ alkyl group may be branched or linear, and examples thereof include methyl, ethyl, propyl, etc., which are easy to synthesize and handle, and have thermal and mechanical properties. A methyl group is particularly preferred because it provides an excellent cured product. Moreover, it is preferable that the siloxane unit which has two phenyl groups exists.

A feature of the present invention is that 15% by mole or more of R ² is a phenyl group in order to reduce moisture permeability. From the viewpoint of the moisture permeability reduction effect and handleability, 20 to 80 mol% of R ² is preferably a phenyl group, and more preferably 30 to 60 mol%.

  In the formula (I), n is a number that makes the viscosity of the component (A) at 23 ° C. 0.1 to 1,000 Pa · s. When the viscosity is in this range, the uncured composition exhibits good fluidity and excellent workability during casting and potting, while having excellent mechanical strength after curing, and Appropriate elasticity and hardness can be exhibited. n is preferably a number that makes the viscosity of component (A) at 23 ° C. 0.2 to 500 Pa · s.

In the polyorganohydrogensiloxane of the component (B) used in the present invention, the hydrosilyl group contained in the molecule undergoes an addition reaction with R ¹ in the component (A), thereby cross-linking the component (A). It functions as an agent. Such a component (B) functioning as a crosslinking agent has more than two hydrogen atoms bonded to silicon atoms involved in the addition reaction in order to reticulate the cured product, preferably Have 3 or more.

The component (B) is typically represented by the general formula (II):
(R ³ ) _c H _d SiO _{(4-cd) / 2} (II)
(Where
R ³ represents an unsubstituted or substituted monovalent hydrocarbon group not containing an aliphatic unsaturated carbon-carbon bond;
c is an integer from 0 to 2;
d is 1 or 2, provided that c + d is an integer of 1 to 3)
In the molecule, the number of units is more than 2, preferably 3 or more.

Examples of the organic group bonded to the silicon atom of R ³ and the other siloxane unit of component (B) are the same as those of R ^{2 in} component (A) described above, and among these, from the viewpoint of easy synthesis The methyl group is most preferred. Further, d is preferably 1 because synthesis is easy.

  The siloxane skeleton in the component (B) may be linear, branched or cyclic. Moreover, you may use these mixtures.

  The degree of polymerization of the component (B) is not particularly limited, but a polyorganohydrogensiloxane in which two or more hydrogen atoms are bonded to the same silicon atom is difficult to synthesize, and therefore preferably comprises three or more siloxane units. The number of siloxane units is more preferably 6 to 200, and particularly preferably 10 to 150, since it does not volatilize even when heated to the curing temperature, and is excellent in fluidity and easily mixed with the component (A).

The blending amount of the component (B) is such that sufficient adhesive force is obtained, and the silicone rubber obtained by curing has excellent mechanical properties, so the component (B) relative to the R ¹ group in the component (A) The amount (H / Vi) of hydrogen atoms bonded to silicon atoms in the amount is 0.5 to 5.0, preferably 1.0 to 3.0. If H / Vi is less than 0.5, a rubber-like elastic body having excellent mechanical strength cannot be obtained, and if it exceeds 5.0, foaming tends to occur during curing.

The platinum group metal compound of component (C) used in the present invention is a catalyst for promoting the addition reaction between R ^{1 in} component (A) and the hydrosilyl group in component (B). As the platinum group metal compound, a compound of a platinum group metal atom such as platinum, rhodium, palladium is used, and chloroplatinic acid, a reaction product of chloroplatinic acid and an alcohol, a platinum-olefin complex, a platinum-vinylsiloxane complex, Examples include platinum compounds such as platinum-ketone complexes and platinum-phosphine complexes; rhodium compounds such as rhodium-phosphine complexes and rhodium-sulfide complexes; and palladium compounds such as palladium-phosphine complexes.

  Of these, the reaction product of chloroplatinic acid and alcohol and a platinum-vinylsiloxane complex are preferred because of their good catalytic activity. When it is necessary to cure in a short time and develop adhesiveness, platinum- 1,3-divinyl-1,1,3,3-tetramethyldisiloxane complex and platinum-1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane are preferred. However, the necessary curing speed varies depending on the shape of the site where the cured product is provided and the required working time, and therefore can be arbitrarily selected depending on the combination of the component (C) and the curing retarder.

  (C) Since the compounding quantity of a component can obtain the outstanding hardening rate, it is 0.1-1,000 weight normally in conversion of a platinum group metal atom with respect to the total amount of (A) component and (B) component. ppm, preferably 0.5 to 200 ppm by weight. If it is less than 0.1 ppm by weight, the curing rate is slow, and even if it exceeds 1,000 ppm by weight, an increase in the curing rate commensurate with it cannot be obtained.

  (D) component used by this invention is a component which reduces the moisture permeability of the rubber-like elastic body obtained by hardening the composition of this invention with (A) component. The component (D) has an effect of reducing moisture permeability and a bead having a smooth surface by moldability, particularly extrusion, so that the average particle size is preferably 2.0 to 100 μm, more preferably 5.0 to 60 μm. preferable. Examples of the component (D) include natural mica such as muscovite, phlogopite, biotite, and synthetic mica. Mica is preferred because it has less impurities and gives the cured composition excellent mechanical properties. These mica are generally flat powders, where the particle size refers to the maximum diameter of the flat surface.

  (D) The compounding quantity of a component is 20-200 weight part with respect to 100 weight part of (A) component from the point which makes moisture permeability efficiently reduce and set it as appropriate hardness after hardening, and 40-100 Part by weight is preferred.

  The composition of the present invention may be of a type that does not exhibit adhesiveness to a substrate during curing, or a type that exhibits adhesiveness, depending on the purpose or form of use. In order to give the moisture proof property excellent in a process target, it is preferable that it is a type which exhibits adhesiveness with respect to a process target. In the adhesive type, an adhesiveness-imparting agent can be blended within a range that does not impair the catalytic ability of the component (C), depending on the purpose of moisture prevention and the type of substrate. Examples of the adhesion-imparting agent include 3-glycidoxypropyl group-containing alkoxy such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, and 3-glycidoxypropyl (methyl) dimethoxysilane. Silanes; 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltriethoxysilane, 2- (3,4-epoxycyclohexyl) ethyl (methyl) dimethoxysilane Such 2- (3,4-epoxycyclohexyl) ethyl group-containing alkoxysilanes; vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (2-methoxyethoxy) silane, methylvinyldimethoxysilane, allyltrimethoxysilane, allyltri Ethoxy Alkenylalkoxysilanes such as methyl and allyldimethoxysilane; 3-acryloxypropyltrimethoxysilane, 3-acryloxypropyltriethoxysilane, 3-acryloxypropyl (methyl) dimethoxysilane, 3-methacryloxypropyltrimethoxy (Meth) acryloxypropylalkoxysilanes such as silane, 3-methacryloxypropyltriethoxysilane, 3-methacryloxypropyl (methyl) dimethoxysilane; hydrogen atoms bonded to silicon atoms and the following general bonds bonded to silicon atoms Formula (III):

(Wherein Q ¹ represents a linear or branched alkylene group forming a carbon chain having two or more carbon atoms between a silicon atom and an ester bond; Q ² represents an oxygen atom and a side. Represents a linear or branched alkylene group which forms a carbon chain having 3 or more carbon atoms between silicon atoms in the chain; R ⁴ represents an unsubstituted or substituted alkyl group having 1 to 6 carbon atoms; An aluminum silicon alkoxide such as aluminum triethoxide, aluminum tripropoxide, aluminum tributoxide; titanium tetraethoxide, titanium tetrapropoxide, titanium tetraisopropoxide, Titanium alkoxides such as titanium tetrabutoxide, titanium tetraisobutoxide, titanium tetraisopropenyl oxide; Tetra isopropoxide, zirconium alkoxides such as zirconium tetrabutoxide; diallyl maleate, polar group-containing organic compounds such as triallyl isocyanate, and the like are exemplified.

In the side chain represented by the above general formula (III), Q ¹ is exemplified by an alkylene group such as ethylene, trimethylene, 2-methylethylene, tetramethylene, and the like. -A methylethylene group is preferred. Examples of Q ² include an alkylene group such as trimethylene, 2-methyltrimethylene, and tetramethylene, and a trimethylene group is preferable because synthesis and handling are easy. Examples of R ⁴ include alkyl groups such as methyl, ethyl, propyl, isopropyl, and butyl; and alkyl groups substituted with alkoxy such as 2-methoxyethyl, and alcohols that give good adhesion and are generated by hydrolysis Are easy to volatilize, methyl group and ethyl group are preferable, and methyl group is particularly preferable. As an organosilicon compound having such a side chain, formula (IV):

The cyclic siloxane compound shown by these is illustrated. The compounding amount of the adhesion-imparting agent varies depending on the kind of the adhesion-imparting agent and the substrate, but is usually in the range of 0.5 to 20 parts by weight with respect to 100 parts by weight of the component (A), and particularly to the substrate. 2-20 parts by weight is preferable, and 3-15 parts by weight is more preferable.

  In order to suppress the curing reaction and improve the storage stability and workability of the uncured composition, a curing inhibitor can be added to the composition of the present invention. The diallyl maleate is effective not only as an adhesion promoter but also as a curing inhibitor. In addition, as the curing inhibitor, 3-methyl-1-butyn-3-ol, 3-methyl-1-pentyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, 1-ethynyl- Acetylene alcohols such as 1-cyclohexane-1-ol are exemplified.

The composition of the present invention cures to form a cured product having low moisture permeability, but gives a suitable fluidity at the stage before curing, and a rubber-like elastic body obtained by curing depends on its use. In addition to the component (D), an inorganic filler can be added to give the required high mechanical strength. Examples of the inorganic filler include reinforcing fillers having an average particle size of less than 0.1 μm and a specific surface area of 30 mm ² / g or more; and non-reinforcing fillers having an average particle size of 0.1 to 50 μm. Examples of reinforcing fillers include dry silica such as fumed silica and arc silica; and wet silica such as precipitated silica. These may be used as they are, and hydrophobic such as hexamethyldisilazane. You may use it after surface-treating with an agent. Non-reinforcing fillers include diatomaceous earth, ground quartz, fused quartz, titanium oxide, aluminum oxide, zinc oxide, aluminosilicate, calcium carbonate, organic acid surface treated calcium carbonate, magnesium carbonate, zinc carbonate, calcium silicate, Examples include talc and ferric oxide, which are selected according to the extrusion workability and the physical properties required for the rubber-like elastic body obtained by curing. Further, a conductive filler such as carbon black may be blended depending on the purpose.

Furthermore, depending on the purpose, the composition of the present invention includes a pigment, a thixotropy imparting agent, a viscosity modifier for improving extrusion workability, an ultraviolet light inhibitor, a fungicide, a heat resistance improver, and a flame retardant. Various additives such as a chain extender may be added. As the chain extender, a linear hydrogen polyorganosiloxane having one hydrogen atom bonded to a silicon atom at each end (for example, both ends are ^MH units: (CH ₃ ) ₂ HSiO _1/2 -Blocked and the intermediate unit is D Unit: linear polymethylsiloxane composed of — (CH ₃ ) ₂ SiO—). Depending on the application, the composition of the present invention may be dissolved or dispersed in an organic solvent such as toluene or xylene.

  The composition of the present invention can be prepared by uniformly kneading the components (A) to (D), and other components blended as necessary, by a mixing means such as a universal kneader or a kneader. . In addition, in order to stably store for a long period of time, two pre-blends are appropriately prepared, stored and used so that component (B) and component (C) are contained in separate pre-blends. Immediately before, a composition may be prepared by mixing uniformly by a mixing means such as a mixing head of a quantitative mixer, defoamed under reduced pressure, and used for use.

  The polyorganosiloxane composition of the present invention is injected, dripped, casted, cast, extruded, or the like into a part where moisture should be blocked, for example, a part where a gasket is to be formed, or transfer molding or injection. Silicone rubber can be obtained by adhering to the object to be treated by heating and curing by integral molding by molding. Curing conditions can be arbitrarily set at a temperature between room temperature and 250 ° C. depending on the type and amount of the component (C) and reaction inhibitor, but are usually 130 to 170 ° C. and 5 to 30 minutes, as described above. Further, by selecting the composition, it is possible to develop adhesiveness to the substrate during curing. Moreover, in order to make a compression set small, it can also heat at 150-200 degreeC for 2 to 4 hours after hardening.

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In these examples, parts indicate parts by weight, and the viscosity indicates the viscosity at 23 ° C. The present invention is not limited by these examples.

In Examples and Comparative Examples, the following polysiloxanes were used as the components (A) and (B). Hereinafter, siloxane units are indicated by the following symbols. In the unit formula, the intermediate siloxane unit simply indicates the number of units. When a plurality of types of intermediate siloxane units are included, the intermediate siloxane units are randomly arranged.
^MH unit: (CH ₃ ) ₂ HSiO _1/2 −
M ^V _{unit: (CH 3) 2 (CH} 2 = CH) SiO 1/2 -
D Unit: - (CH _{3) 2} SiO-
D ^H units: - (CH ₃₎ HSiO-
D ^ff _{Unit: - (C 6 H 5)} 2 SiO-
^DE Unit:
_{- (CH 3) [(CH} 3 O) 3 Si (CH 2) 3 OC (O) C (CH 3) CH 2] SiO-
Q unit: SiO _4/2 (tetrafunctional)
A-1: both terminals blocked with M ^V unit, becomes the intermediate unit from D units, linear polymethylvinylsiloxane having a viscosity at 23 ° C. is at 3 Pa · s;
A-2: both terminals blocked with ^{M V} unit, consists 95 mol% intermediate units D units and ^{D ff} unit 5 mol%, the linear polymethyl vinyl siloxanes viscosity is 3 Pa · s;
A-3: both ends are blocked with ^{M V} unit, it consists of 80 mol% intermediate units D units and ^{D ff} unit 20 mol%, the linear polymethyl vinyl siloxanes viscosity is 3 Pa · s;
A-4: both terminals blocked with ^{M V} unit, consists of 70 mol% intermediate units D units and ^{D ff} unit 30 mol%, the linear polymethyl vinyl siloxanes viscosity is 3 Pa · s;
A-5: both terminals blocked with ^{M V} unit, consists 60 mol% intermediate units D units and ^{D ff} unit 40 mol%, the linear polymethyl vinyl siloxanes viscosity is 3 Pa · s;
B-1: Branched polymethylhydrogensiloxane represented by unit formula M ^H ₈ Q ₄ ;

In Examples and Comparative Examples, the following platinum complex was used as the component (C).
C-1: Complex obtained by heating chloroplatinic acid and octyl alcohol (4% by weight in terms of platinum atom).

The following were used as optional components: D-1: Cyclic polymethylhydrogensiloxane represented by unit formula DD ^H ₂ ^DE (two hydrogen atoms in the molecule).
D-2: 3-Glycidoxypropyltrimethoxysilane D-3: Diallyl maleate

The following fillers were used in Examples and Comparative Examples.
P-1: muscovite with an average particle size of 5 μm P-2: muscovite with an average particle size of 22 μm P-3: muscovite with an average particle size of 55 μm

Examples 1 and 2 and Comparative Examples 1 to 4
(Preparation of Preliminary Formula I)
As shown in Table 1, in a container equipped with a stirrer, 20 parts of P-1 to P-3 are added to 25 parts of A-1 to A-5, and then 0.03. A portion of C-1 was added and mixed until uniform to prepare Preformulation I.

(Preparation II preparation)
In the same apparatus, any 25 parts of A-1 to A-5, 20 parts of any of B-1 and P-1 to P-3 in amounts shown in Table 1, and 3.0 parts of D-1 , 1.0 part of D-2 and 0.3 part of D-3 were mixed and mixed until uniform to prepare Preliminary Formula II.

(Preparation of composition and production of silicone rubber sheet)
Preliminary formulation I and preliminary formulation II are charged in two containers of a quantitative mixer, respectively, and equal amounts of both preliminary formulations are supplied to the mixing head, mixed uniformly, and degassed under reduced pressure. Thus, a polyorganosiloxane composition was prepared. The composition was then poured into a stainless steel mold having a polytetrafluoroethylene treatment on the surface and cured by heating at 150 ° C. for 1 hour to produce a silicone rubber sheet having a thickness of 1.0 mm. .

  From the silicone rubber sheets obtained from the polyorganosiloxane compositions of Examples 1 to 5 and Comparative Examples 1 to 3, the moisture permeability for 24 hours was evaluated at a temperature of 40 ° C. and a humidity of 90% RH in accordance with JIS Z0208. .

Table 1 shows the composition ratios of the prepared examples and comparative examples, and the ratio (Ph / R ² ) of phenyl groups to the total of methyl groups and phenyl groups of polyorganosiloxanes A-1 to A-5. In addition, Table 1 shows the measurement results of moisture permeability.

  As shown in Table 1, the cured product of the present invention exhibited excellent low moisture permeability.

  The polyorganosiloxane composition of the present invention is useful for moisture-sensitive materials, particularly protective layers for electronic parts, hard disks, display devices, seals, gaskets, and the like. The hard disk and display device of the present invention are particularly useful for applications that require high stability against moisture.

Claims (6)

(A) Formula (I):

(In the formula,
R ¹ is independently a C ₂ -C ₆ alkenyl group,
R ² is independently a C ₁ -C ₆ alkyl group or a phenyl group, and 15 to 60 mol% of R ² is a phenyl group;
n is a number in which the viscosity of (A) at 23 ° C. is 0.1 to 1,000 Pa · s) 100 parts by weight of a linear polyorganosiloxane;
(B) Polyorganohydrogensiloxane having more than two hydrogen atoms bonded to silicon atoms in the molecule The number of hydrogen atoms bonded to silicon atoms for one alkenyl group present in (A) is 0.00. An amount of 5 to 5.0;
(C) Platinum group metal compound An amount containing 0.1 to 1,000 ppm by weight of a platinum group metal atom with respect to the amount of (A); and (D) a polyorgano containing 20 to 200 parts by weight of mica powder. Siloxane composition. The polyorganosiloxane composition according to claim 1, wherein R ¹ in (A) is a vinyl group. ^{R 2} is in the (A), a methyl group or a phenyl group, among ^{R 2,} 15 to 60 mol% are phenyl groups, according to claim 1 or 2 polyorganosiloxane composition.   The polyorganosiloxane composition according to any one of claims 1 to 3, wherein the average particle diameter of (D) is 2.0 to 100 µm.   A hard disk having a protective layer obtained by curing the polyorganosiloxane composition according to claim 1.   The display apparatus which has a protective layer obtained by hardening | curing the polyorganosiloxane composition of any one of Claims 1-4.