JP2007154036A - Low-tackiness curable composition for coating electric/electronic part - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a curable composition for the coating of electric/electronic parts, having low tackiness and giving a cured product having remarkably reduced surface tackiness in spite of low hardness. <P>SOLUTION: The composition contains (A) a polyorganosiloxane having liquid or semisolid state at 25°C and expressed by average unit formula (SiO<SB>4/2</SB>)<SB>a</SB>(R<SP>1</SP>R<SP>2</SP><SB>2</SB>SiO<SB>1/2</SB>)<SB>b</SB>(R<SP>2</SP><SB>3</SB>Si<SB>1/2</SB>)<SB>c</SB>(R<SP>1</SP>is alkenyl; R<SP>2</SP>groups are each independently substituted or unsubstituted univalent hydrocarbon group excluding aliphatic unsaturated bond; a, b and c are each a positive number; a/(a+b+c) is 0.2-0.6; and b/(a+b+c) is 0.001-0.2), (B) a polyorganohydrogensiloxane containing R<SP>3</SP><SB>2</SB>HSiO<SB>1/2</SB>unit (R<SP>3</SP>groups are each independently substituted or unsubstituted univalent hydrocarbon group excluding aliphatic unsaturated bond) and having ≥2 SiH groups in one molecule and (C) a platinum-group catalyst. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention provides a cured product having a significantly reduced surface tack even with low hardness, and has low tack suitable for potting, sealing materials, coating materials, etc. of electric / electronic components. The present invention relates to a curable composition for coating.

  In addition to the function of protecting the light emitting element from the outside, the sealing composition such as the LED element in the electrical / electronic component, particularly the light emitting diode (LED), etc., is good with the supporting substrate such as the LED element or ceramic, In addition, stable adhesion is required.

  Conventionally, an epoxy resin or the like has been used as such a sealing composition. However, when an epoxy resin is used, cracks and yellowing have occurred due to an increase in the amount of heat generated with the recent increase in brightness of LEDs and the like, and the shortening of the wavelength of light, causing a decrease in brightness.

  Therefore, a silicone composition is used as a sealing composition having excellent heat resistance and ultraviolet resistance. In particular, addition reaction curable silicone rubber compositions are widely used because they cure in a short time by heating and thus have good productivity and do not generate by-products during curing (see, for example, Patent Document 1). ).

However, since the cured product of the silicone rubber composition is difficult to obtain sufficient adhesion to the supporting substrate as compared with the epoxy resin, it is required to reduce the hardness after curing. In the case of a cured product having low hardness (for example, JIS K 6253, durometer A hardness meter of 40 or less), the surface tends to exhibit tackiness (adhesiveness), tends to cause dirt due to adhesion of dust, and deteriorate the appearance. .
JP 2000-198930 A

  The object of the present invention is to cope with such a problem, and is a curing for coating electric and electronic parts having a low tack property that gives a cured product having a significantly reduced surface tack property even with a low hardness. It is to provide a sex composition.

As a result of intensive studies to achieve the above object, the present inventors have found that an addition reaction curable type silicone rubber containing a base polymer containing SiO _4/2 units, a crosslinking agent having a SiH group at the terminal, and a platinum-based catalyst. The present inventors have found that the composition gives a cured product having a remarkably reduced surface tack even when the hardness is low, and have reached the present invention.

That is, the curable composition for coating electrical and electronic parts having low tack of the present invention is
(A) Average unit formula:
(SiO _4/2 ) _a (R ¹ R ² ₂ SiO _1/2 ) _b (R ² ₃ SiO _1/2 ) _c
Wherein R ¹ is an alkenyl group, R ² is the same or different substituted or unsubstituted monovalent hydrocarbon group excluding an aliphatic unsaturated bond, a, b and c are each a positive number, and a / (A + b + c) is a number of 0.2 to 0.6, and b / (a + b + c) is a number of 0.001 to 0.2), and is a liquid or semi-solid polyorganosiloxane at 25 ° C., ( B) R ³ ₂ HSiO _1/2 units (R ³ is the same or different substituted or unsubstituted monovalent hydrocarbon group excluding aliphatic unsaturated bonds) and 2 or more per molecule Polyorganohydrogensiloxane having a SiH group of (A) The amount of SiH group to be 0.3 to 3.0 mol with respect to 1 mol of silicon atom-bonded alkenyl group of component (A), and (C) platinum-based catalyst catalyst amount It is characterized by containing.

  In the present invention, the low tackiness means that when the surface of the cured product is rubbed with a powder of silica, mica, silver or the like and sprayed with air, the residual powder that can be visually confirmed is less than 50% of the entire surface of the cured product. That is, it means a state having no effective tackiness.

  With the above configuration, it is possible to provide a curable composition for coating an electric / electronic component having a low tack property that gives a cured product having a significantly reduced surface tack even with a low hardness.

  Hereinafter, the curable composition for coating electric / electronic parts having low tack according to the present invention will be described.

[(A) component]
Component (A) is a base polymer and has an average unit formula:
(SiO _4/2 ) _a (R ¹ R ² ₂ SiO _1/2 ) _b (R ² ₃ SiO _1/2 ) _c
Is a polyorganosiloxane having a three-dimensional network structure (resin structure). One molecule has two or more silicon-bonded alkenyl groups.

In the above formula, R ¹ represents an alkenyl group. Examples of R ¹ include a vinyl group, an allyl group, a propenyl group, a butenyl group, a petenyl group, and a hexenyl group, and a vinyl group is particularly preferable.

R ² represents the same or different substituted or unsubstituted monovalent hydrocarbon group excluding an aliphatic unsaturated bond. Examples of R ² include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, hexyl, cyclohexyl, and octyl; aryl such as phenyl and tolyl A group; an aralkyl group such as a benzyl group or a phenylethyl group; and a group in which at least a part of hydrogen atoms bonded to carbon atoms of these groups are substituted with a halogen atom such as fluorine, chlorine or bromine or a cyano group, Examples include halogen-substituted alkyl groups such as chloromethyl group, 2-bromoethyl group, 3-chloropropyl group, chlorophenyl group, fluorophenyl group, and cyanoethyl group, cyano-substituted alkyl groups, and halogen-substituted aryl groups. In particular, a methyl group and a phenyl group are preferable.

  a, b and c are each a positive number, a / (a + b + c) is a number from 0.2 to 0.6, and b / (a + b + c) is a number from 0.001 to 0.2.

That is, the SiO _4/2 unit preferably has a ratio of 0.2 to 0.6, particularly 0.3 to 0.5 in the component (A). By setting it as such a range, the outstanding fluidity | liquidity can be provided to the obtained composition.

The R ¹ R ² ₂ SiO _1/2 unit is a cross-linking point of the resulting composition, and has a ratio of 0.001 to 0.2, particularly 0.001 to 0.1 in the component (A). preferable. If it is less than 0.001, moderate hardness cannot be imparted after curing, and it becomes difficult to synthesize a base polymer containing an alkenyl group with good yield. On the other hand, if it exceeds 0.2, the hardness after curing becomes too high, and a rubber-like elastic body cannot be obtained.

  As a manufacturing method of (A) component, what is necessary is just to use a well-known method, For example, after combining the compound used as each unit source in the ratio mentioned above, the method of cohydrolyzing in presence of an acid etc. are mentioned.

  The component (A) is semi-solid or liquid at 25 ° C., and has a viscosity of 1,000,000 mPa · s or less, particularly 5000 to 500,000 mPa · s in adjusting the viscosity of the obtained composition and the hardness after curing. It is preferable. As the component (A), it is preferable to use a single siloxane having a resin structure represented by the above average unit formula.

[Component (B)]
(B) A component is a crosslinking agent of this composition. It contains R ³ ₂ HSiO _1/2 units and has hydrogen atoms (SiH groups) bonded to two or more silicon atoms in one molecule. The SiH group may be bonded to the silicon atom at the end of the molecular chain, and may be bonded to both silicon atoms in the middle of the molecular chain. The molecular structure may be any of linear, branched, cyclic, and three-dimensional network.

As the component (B), for example, an average unit formula:
(SiO _4/2 ) _d (R ³ ₂ HSiO _1/2 ) _e (R ³ ₃ SiO _1/2 ) _f
The three-dimensional network-like polyorganohydrogensiloxane represented by these is mentioned.
In the above formula, R ³ represents the same or different substituted or unsubstituted monovalent hydrocarbon group excluding an aliphatic unsaturated bond. The R ^3, can be exemplified the same ones as exemplified as R ² in component (A). A methyl group is particularly preferable.
d and e are positive numbers, f is a number of 0 or more, d / (d + e + f) is a number of 0.2 to 0.6, and e / (d + e + f) is a number of 0.1 to 0.8. .

That is, the SiO _4/2 unit preferably has a ratio of 0.2 to 0.6, particularly 0.2 to 0.4 in the component (B). By setting it as such a range, the outstanding fluidity | liquidity can be provided to the obtained composition.
The R ³ ₂ HSiO _1/2 unit preferably has a ratio of 0.1 to 0.8, particularly 0.2 to 0.7 in the component (B). If it is less than 0.1, it will become difficult to give moderate hardness to hardened | cured material, and it will become difficult to synthesize | combine the crosslinking agent which has SiH group with a sufficient yield. On the other hand, when it exceeds 0.8, the hardness after curing becomes too high, and a rubber-like elastic body cannot be obtained.

で表される直鎖状のポリオルガノハイドロジェンシロキサンであってもよく、網目状、分岐状、直鎖状のものを併用してもよい。 Examples of the component (B) include the following general formula:

A linear polyorganohydrogensiloxane represented by the following formula may be used, and network, branched or linear ones may be used in combination.

In the above formula, R ³ is as defined above.
p is a positive number, q is a number of 0 or more, and satisfies 0.2 ≦ p / (p + q) ≦ 1, particularly 0.4 ≦ p / (p + q) ≦ 0.7. p + q is not limited, but is preferably 100 or less, particularly preferably in the range of 10-50. If it exceeds 100, not only will the viscosity of the obtained composition increase and workability will decrease, but the cured product will easily develop tackiness.
Further, s is a number greater than or equal to 0, t is a positive number, and 0 ≦ s / (s + t) ≦ 0.8, in particular 0.3 ≦ s / (s + t) ≦ 0.7. . s + t is not limited, but is preferably 100 or less, particularly preferably in the range of 10-50. When it exceeds 100, the viscosity of the obtained composition becomes high and workability is likely to be lowered, and further, tackiness is easily exhibited in the cured product.

  The component (B) is liquid at 25 ° C., and its viscosity is preferably 100 mPa · s or less, particularly 10 to 20 mPa · s.

  The amount of the component (B) is preferably such that the SiH group is 0.3 to 3 mol, particularly 0.5 to 2 mol, with respect to 1 mol of the silicon atom-bonded alkenyl group of the component (A). When the amount is less than 0.3 mol, the obtained composition is hardly cured. On the other hand, when it exceeds 3 mol, unreacted SiH groups remain, and the rubber physical properties after curing tend to be unstable.

[Component (C)]
(C) component is a component which accelerates | stimulates hardening of this composition.
As the component (C), a known catalyst can be used as a catalyst used in the hydrosilylation reaction. For example, platinum black, secondary platinum chloride, chloroplatinic acid, a reaction product of chloroplatinic acid and a monohydric alcohol, a complex of chloroplatinic acid and olefins or vinyl siloxane, platinum-based catalysts such as platinum bisacetoacetate, palladium-based Examples thereof include platinum group metal catalysts such as catalysts and rhodium catalysts.

  The blending amount of the component (C) may be an amount necessary for curing, and can be appropriately adjusted according to a desired curing rate. Usually, it is preferable to set it as 0.01-100 ppm in conversion of a platinum element with respect to the total weight of the composition obtained, especially 1-50 ppm at the point of sclerosis | hardenability, transparency of hardened | cured material, and cost.

In the curable composition of the present invention, the above components (A) to (C) may be used as basic components, and if necessary, a silane coupling agent may be blended as other optional components.
A silane coupling agent is a component which provides the adhesiveness with respect to various electrical / electronic components, and can use a well-known thing. Examples include epoxy group-containing alkoxysilanes, SiH group-containing alkoxysilanes, vinyl group-containing alkoxysilanes, and reaction products thereof.

  It is preferable that the compounding quantity of a silane coupling agent is 0.1-5 weight part with respect to 100 weight part of total weight of (A)-(C) component. If it is less than 0.1 parts by weight, it is difficult to obtain good adhesion to various electric / electronic components. On the other hand, if it exceeds 5 parts by weight, the cured product becomes brittle, which is disadvantageous in cost.

Moreover, you may mix | blend various fillers as other arbitrary components according to a reinforcement improvement and other characteristics.
The average particle diameter of the filler is preferably 100 nm or less, particularly preferably 50 nm or less, considering the transparency of the cured product. Examples of the filler include fumed silica and wet silica having a specific surface area of 150 m ² / g or more by the BET method. The filler may be used as it is, but may be used that which has been surface-treated with a known treatment agent such as hexamethyldisilazane, which has been reacted in-process with the treatment agent. Also good.

  The blending amount of the filler is preferably 0.5 to 100 parts by weight with respect to 100 parts by weight of the component (A). When the amount exceeds 100 parts by weight, the fluidity of the obtained composition is lowered, and the workability is easily deteriorated. On the other hand, if it is less than 0.5 part by weight, the properties imparted to the cured product will not be sufficient.

  Furthermore, reaction inhibitors for adjusting the curing speed as other optional components, dyes, pigments, flame retardants, heat resistance improvers, oxidation degradation agents, in a range that does not affect the transparency of the cured product, You may add a wavelength adjusting agent etc. in the range which does not impair the objective of this invention.

  As a manufacturing method of the curable composition of this invention, the method etc. which mix the basic component of (A)-(C) and the arbitrary component mentioned above uniformly with a mixing stirrer etc. are mentioned. The obtained composition preferably has a viscosity at 25 ° C. of not more than 100,000 mPa · s, particularly 500 to 10,000 mPa · s.

  The method for curing the composition is not particularly limited. For example, the composition is injected into a suitable mold and cured, and the composition is coated on a suitable substrate and then cured. Methods and the like. Curing proceeds at room temperature or by heating, but it is preferable to heat at 50 to 200 ° C. for rapid curing. The obtained cured product is preferably a rubber-like, particularly a soft rubber-like elastic body. When the composition is used, for example, for sealing an optical element, the adhesiveness with a supporting base material can be improved and good followability to the base material shape can be obtained.

  The present invention can coat various electric / electronic parts using the curable composition described above. In this case, examples of the electric / electronic parts coated with the cured product of the present composition include light emitting elements (LED) elements, transistors, thyristors, laser elements, solid-state imaging elements and the like that require high transparency. And can be suitably used as a sealing agent for these potting agents, protective agents, coating agents, foundations or exteriors. Moreover, you may laminate | stack and use for lenses and a gel-like hardened | cured material.

  The present invention will be described in detail with reference to examples, but the present invention is not limited to the examples. In the examples and comparative examples, the viscosity is a value measured at 25 ° C. Further, the curable compositions obtained in Examples and Comparative Examples were evaluated as follows, and the results are shown in Table 1. The characteristics shown in Table 1 are values measured at 25 ° C.

[Hardness]
The obtained curable composition was heat-cured at 150 ° C. for 1 hour to produce a cured product. Using this cured product, it was measured with a durometer A hardness meter specified in JIS K 6253.

[Surface tackiness]
The obtained curable composition was heat-cured at 150 ° C. for 1 hour to produce a cured product. After rubbing silica powder on the surface of the cured product, 2.5 kgf / cm ² of air was blown to visually check the silica powder remaining on the surface of the cured product.

[Example 1]
(A-1) Viscosity 20000 mPa · s, formula:
(SiO _4/2 ) ₄ [(CH ₃ ) ₃ SiO _1/2 ] ₅ [CH ₂ = CH (CH ₃ ) ₂ SiO _1/2 ]
100 parts by weight of the polyorganosiloxane represented by the formula (B-1): a viscosity of 20 mPa · s, and the formula:
(SiO _4/2 ) ₄ [(CH ₃ ) ₂ HSiO _1/2 ] ₈
10 parts by weight of polyorganohydrogensiloxane represented by the formula: (C) 5 ppm of platinum-based catalyst as platinum atom, CH ₂ ═C (CH ₃ ) COO (CH ₂ ) ₃ Si (OCH ₃ ) ₃ as silane coupling agent And the formula:
1.5 parts by weight of a reaction product with a siloxane represented by [(CH ₃ ) HSiO] ₃ (CH ₃ ) ₂ SiO, a formula as a reaction inhibitor:
0.02 part by weight of siloxane represented by [(CH ₂ ═CH) (CH ₃ ) SiO] ₄ was added to a universal kneader and mixed uniformly to obtain a curable composition.
The properties of this composition were measured and the results are shown in Table 1.

[Example 2]
(A-1) Viscosity 20000 mPa · s, formula:
(SiO _4/2 ) ₄ [(CH ₃ ) ₃ SiO _1/2 ] ₅ [CH ₂ = CH (CH ₃ ) ₂ SiO _1/2 ]
100 parts by weight of the polyorganosiloxane represented by the formula (B-1): a viscosity of 20 mPa · s, and the formula:
(SiO _4/2 ) ₄ [(CH ₃ ) ₂ HSiO _1/2 ] ₈
19 parts by weight of polyorganohydrogensiloxane represented by the formula: (C) 5 ppm of platinum-based catalyst as platinum atom, CH ₂ ═C (CH ₃ ) COO (CH ₂ ) ₃ Si (OCH ₃ ) ₃ as silane coupling agent And the formula:
1.5 parts by weight of a reaction product with a siloxane represented by [(CH ₃ ) HSiO] ₃ (CH ₃ ) ₂ SiO, a formula as a reaction inhibitor:
0.02 part by weight of siloxane represented by [(CH ₂ ═CH) (CH ₃ ) SiO] ₄ was added to a universal kneader and mixed uniformly to obtain a curable composition.
The properties of this composition were measured and the results are shown in Table 1.

[Example 3]
(A-1) Viscosity 20000 mPa · s, formula:
(SiO _4/2 ) ₄ [(CH ₃ ) ₃ SiO _1/2 ] ₅ [CH ₂ = CH (CH ₃ ) ₂ SiO _1/2 ]
100 parts by weight of the polyorganosiloxane represented by the formula (B-1): a viscosity of 20 mPa · s, and the formula:
(SiO _4/2 ) ₄ [(CH ₃ ) ₂ HSiO _1/2 ] ₈
7 parts by weight of polyorganohydrogensiloxane represented by the formula: (C) 5 ppm of platinum-based catalyst as platinum atom, CH ₂ ═C (CH ₃ ) COO (CH ₂ ) ₃ Si (OCH ₃ ) ₃ as silane coupling agent And the formula:
1.5 parts by weight of a reaction product with a siloxane represented by [(CH ₃ ) HSiO] ₃ (CH ₃ ) ₂ SiO, a formula as a reaction inhibitor:
0.02 part by weight of siloxane represented by [(CH ₂ ═CH) (CH ₃ ) SiO] ₄ was added to a universal kneader and mixed uniformly to obtain a curable composition.
The properties of this composition were measured and the results are shown in Table 1.

[Example 4]
(A-1) Viscosity 20000 mPa · s, formula:
(SiO _4/2 ) ₄ [(CH ₃ ) ₃ SiO _1/2 ] ₅ [CH ₂ = CH (CH ₃ ) ₂ SiO _1/2 ]
100 parts by weight of polyorganosiloxane represented by the formula: (B-2) viscosity is 15 mPa · s, and the formula:
[(CH ₃ ) ₂ HSiO _1/2 ] [(CH ₃ ) ₂ SiO] ₁₁ [(CH ₃ ) HSiO] ₉ [(CH ₃ ) ₂ HSiO _1/2 ]
13 parts by weight of polyorganohydrogensiloxane represented by the formula: (C) 5 ppm of platinum-based catalyst as platinum atoms, CH ₂ ═C (CH ₃ ) COO (CH ₂ ) ₃ Si (OCH ₃ ) ₃ as silane coupling agent And the formula:
1.5 parts by weight of a reaction product with a siloxane represented by [(CH ₃ ) HSiO] ₃ (CH ₃ ) ₂ SiO, a formula as a reaction inhibitor:
0.02 part by weight of siloxane represented by [(CH ₂ ═CH) (CH ₃ ) SiO] ₄ was added to a universal kneader and mixed uniformly to obtain a curable composition.
The properties of this composition were measured and the results are shown in Table 1.

[Comparative Example 1]
(A-2) Solid at 25 ° C., formula:
(SiO _4/2 ) ₈ [(CH ₃ ) ₃ SiO _1/2 ] ₅ [CH ₂ = CH (CH ₃ ) ₂ SiO _1/2 ]
25 parts by weight of a polyorganosiloxane represented by the formula (A-3): viscosity 3000 mPa · s, formula:
75 parts by weight of polyorganosiloxane represented by [CH ₂ = CH (CH ₃ ) ₂ SiO _1/2 ] [(CH ₃ ) ₂ SiO] ₃₄₀ [CH ₂ = CH (CH ₃ ) ₂ SiO _1/2 ] (B-3) Viscosity 25 mPa · s, formula:
[(CH ₃ ) ₃ SiO _1/2 ] [(CH ₃ ) ₂ SiO] ₁₅ [(CH ₃ ) HSiO] ₂₀ [(CH ₃ ) ₃ SiO _1/2 ]
6 parts by weight of a polyorganohydrogensiloxane represented by the formula: (C) 5 ppm of a platinum-based catalyst as a platinum atom, and CH ₂ ═C (CH ₃ ) COO (CH ₂ ) ₃ Si (OCH ₃ ) ₃ as a silane coupling agent And the formula:
1.5 parts by weight of a reaction product with a siloxane represented by [(CH ₃ ) HSiO] ₃ (CH ₃ ) ₂ SiO, a formula as a reaction inhibitor:
0.02 part by weight of siloxane represented by [(CH ₂ ═CH) (CH ₃ ) SiO] ₄ was added to a universal kneader and mixed uniformly to obtain a curable composition.
The properties of this composition were measured and the results are shown in Table 1.

[Comparative Example 2]
(A-2) Solid at 25 ° C., formula:
(SiO _4/2 ) ₈ [(CH ₃ ) ₃ SiO _1/2 ] ₅ [CH ₂ = CH (CH ₃ ) ₂ SiO _1/2 ]
60 parts by weight of a polyorganosiloxane represented by the formula (A-3) with a viscosity of 3000 mPa · s, the formula:
[CH ₂ = CH (CH ₃ ) ₂ SiO _1/2 ] [(CH ₃ ) ₂ SiO] ₃₄₀ 40 parts by weight of polyorganosiloxane represented by [CH ₂ = CH (CH ₃ ) ₂ SiO _1/2 ] (B-3) Viscosity 25 mPa · s, formula:
[(CH ₃ ) ₃ SiO _1/2 ] [(CH ₃ ) ₂ SiO] ₁₅ [(CH ₃ ) HSiO] ₂₀ [(CH ₃ ) ₃ SiO _1/2 ]
15 parts by weight of polyorganohydrogensiloxane represented by the formula: (C) 5 ppm of platinum-based catalyst as platinum atom, CH ₂ ═C (CH ₃ ) COO (CH ₂ ) ₃ Si (OCH ₃ ) ₃ as silane coupling agent And the formula:
1.5 parts by weight of a reaction product with a siloxane represented by [(CH ₃ ) HSiO] ₃ (CH ₃ ) ₂ SiO, a formula as a reaction inhibitor:
0.02 part by weight of siloxane represented by [(CH ₂ ═CH) (CH ₃ ) SiO] ₄ was added to a universal kneader and mixed uniformly to obtain a curable composition.
The properties of this composition were measured and the results are shown in Table 1.

As can be seen from Table 1, each example using a crosslinking agent having a SiH group at the terminal and a base polymer containing SiO _4/2 units alone has a significantly reduced surface tack after curing. Yes. In particular, Example 3 shows a hardness of 10 after curing, but exhibits excellent non-adhesiveness. Therefore, even if the hardness is low, adhesion of dust and the like to the surface of the cured product can be suppressed and appearance defects can be avoided.

  Therefore, since it has the above characteristics, the curable composition of the present invention is a sealing agent for potting agents, protective agents, coating agents, bases or exteriors for electric and electronic parts, particularly optical elements such as LED elements. Suitable for agents, lenses and the like.

Claims (4)

(A) Average unit formula:
(SiO _4/2 ) _a (R ¹ R ² ₂ SiO _1/2 ) _b (R ² ₃ SiO _1/2 ) _c
Wherein R ¹ is an alkenyl group, R ² is the same or different substituted or unsubstituted monovalent hydrocarbon group excluding an aliphatic unsaturated bond, a, b and c are each a positive number, and a / (A + b + c) is a number of 0.2 to 0.6, and b / (a + b + c) is a number of 0.001 to 0.2), and is a liquid or semi-solid polyorganosiloxane at 25 ° C.,
(B) including R ³ ₂ HSiO _1/2 units (R ³ is the same or different substituted or unsubstituted monovalent hydrocarbon group excluding aliphatic unsaturated bonds), and 2 units in one molecule The amount of SiH group to be 0.3 to 3.0 mol with respect to 1 mol of silicon atom-bonded alkenyl group of the above-mentioned polyorganohydrogensiloxane (A) component having SiH group,
And (C) a platinum-based catalyst. A curable composition for coating electrical and electronic parts having low tack, characterized by containing a catalytic amount. The component (B) is an average unit formula:
(SiO _4/2 ) _d (R ³ ₂ HSiO _1/2 ) _e (R ³ ₃ SiO _1/2 ) _f
(Wherein R ³ is as defined above, d and e are positive numbers, f is a number of 0 or more, and d / (d + e + f) is a number of 0.2 to 0.6, e / (d + e + f) The curable composition for coating electric and electronic parts having low tack property according to claim 1, wherein the curable composition is a liquid at 25 ° C. . The component (B) or a part thereof has the following general formula:

(In the above formula, as defined above, R ³ is a positive number, q is a number of 0 or more, and a number satisfying 0.2 ≦ p / (p + q) ≦ 1). The curable composition for coating electric / electronic parts according to claim 1, which has low tackiness.   The curable composition for covering electric / electronic parts according to any one of claims 1 to 3, further comprising a silane coupling agent.