JPH04323281A - Coating composition, heat radiating insulation film and metallic base substrate - Google Patents

Abstract

PURPOSE:To obtain a coating composition providing insulating layers having high radiating properties and high electrical insulating properties, comprising a silica dispersed oligomer solution of a specific organosilane, a polyorganosiloxane, a catalyst, aluminum nitride powder as essential components. CONSTITUTION:A coating composition comprising (A) a silica dispersed oligomer solution of an organosilane obtained by hydrolyzing a hydrolyzable organosilane shown by formula I [R<1> is 1-18C monofunctional hydrocarbon; n is 0-3; X is hydrolyzable group] in colloidal silica dispersed in an organic solvent or water, (B) a polyorganosiloxane shown by formula II (R<2> is 1-8C monofunctional hydrocarbon; 0.2<=a<=2, 0.0001<=b<=3 and a+b<4) containing a silanol group in the molecule, (C) a catalyst such as alkyl titanate and (D) aluminum nitride powder as essential components.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a coating composition and a heat dissipating insulating film used as an insulating layer of a metal base substrate, and more particularly to a metal base having an insulating layer with excellent heat dissipation and water resistance. Regarding the board.

0002

2. Description of the Related Art In the field of electronics, including substrates for electronic circuits, insulating layers with high heat dissipation properties are strongly desired. Conventionally, aluminum nitride (hereinafter sometimes referred to as "AlN") has been used as an insulating layer with high heat dissipation.
and alumina ceramics are used. these are,
Both require high-temperature heat treatment to manufacture, and are usually obtained as ceramic sintered bodies, making it difficult to manufacture them over a large area at low cost. Also, methods of forming these ceramics into films are being considered, and CVD (C
(chemical vapor deposition)
Act, PVD (Physical Vapor Depot)
The sol-gel method and the sol-gel method have been proposed.

On the other hand, resin is used as an insulating layer in metal base substrates, but the heat dissipation properties are poor. For this reason, heat dissipation has been improved by dispersing ceramic powder in resin. As such ceramic powder, aluminum nitride, which has excellent heat dissipation properties, is expected to be used.

0004

[Problem to be solved by the invention] The CVD method has five
A high temperature of 00° C. or higher is usually required, and problems remain in increasing the area. In the PVD method and the sol-gel method, it is difficult to obtain a sufficient film thickness, so there are problems with the withstand voltage of the insulating layer. When using an insulating layer made of resin, resin inherently does not have sufficient water resistance, so long-term reliability remains unsatisfactory. Even if an attempt is made to use aluminum nitride powder as the dispersed ceramic powder, since aluminum nitride itself has poor water resistance, the water permeability level of the resin layer deteriorates significantly and cannot be used.

[0005] The first object of the present invention is to provide a coating composition that allows the production of a large-area insulating layer having high heat dissipation and high electrical insulation at low cost. A second object of the present invention is to provide a heat dissipating insulating film that serves as an insulating layer having high heat dissipation properties and high electrical insulation properties. Furthermore, a third object of the present invention is to provide a metal base substrate having such an insulating layer.

[0006]

[Means for Solving the Problems] As a result of studying improvements in the above points, the inventors have completed this invention, which enables the production of an insulating layer with high heat dissipation and high electrical insulation over a large area at low cost. did. That is, in order to solve the first problem, the present invention provides (A) general formula (I) R1nSiX4-n
...(I) (wherein R1 represents the same or different substituted or unsubstituted monovalent hydrocarbon group having 1 to 8 carbon atoms,
n is an integer of 0 to 3, and X represents a hydrolyzable group. ) A silica-dispersed oligomer solution of organosilane obtained by partially hydrolyzing a hydrolyzable organosilane represented by (B) in an organic solvent or colloidal silica dispersed in water, (B) Average composition formula (II) R2aSi(OH) bO(4-a-b)/2...(
II) (wherein R2 represents the same or different substituted or unsubstituted monovalent hydrocarbon group having 1 to 8 carbon atoms, and a and b are respectively 0.2≦a≦2, 0.0001≦b≦ 3
, a+b<4. ) A coating composition containing as essential components a polyorganosiloxane containing a silanol group in the molecule, (C) a catalyst, and (D) aluminum nitride powder is provided.

[0007] In order to solve the second problem, the present invention provides a heat dissipating insulating film made from such a coating composition. This invention further provides the third aspect of the invention.
In order to solve this problem, a metal base substrate having such a heat dissipating insulating film as an insulating layer is provided. General formula (
The group R1 in the hydrolyzable organosilane represented by I)
represents a substituted or unsubstituted monovalent hydrocarbon group having 1 to 8 carbon atoms, such as an alkyl group such as a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, etc. ; Cycloalkyl groups such as cyclopentyl group and cyclohexyl group; Aralkyl groups such as 2-phenylethyl group, 2-phenylpropyl group and 3-phenylpropyl group; Aryl groups such as phenyl group and tolyl group; Vinyl group and allyl group alkenyl groups such as; halogen-substituted hydrocarbon groups such as chloromethyl group, γ-chloropropyl group, 3,3,3-trifluoropropyl group, and γ-methacryloxypropyl group, γ-glycidoxypropyl group; Examples include substituted hydrocarbon groups such as 3,4-epoxycyclohexylethyl group and γ-mercaptopropyl group. Among these, alkyl groups having 1 to 4 carbon atoms and phenyl groups are preferred from the viewpoint of ease of synthesis or availability.

The hydrolyzable group X is an alkoxy group,
Examples include an acetoxy group, an oxime group (see formula 1 below), an enoxy group (see formula 2 below), an amino group, an aminoxy group (see formula 3 below), an amide group (see formula 4 below), and the like. An alkoxy group is preferred because it is easily available and it is easy to prepare a silica-dispersed oligomer solution.

[0009]

[Chemical formula 1]

0010

[Case 2]

[0011]

[Chemical formula 3]

0012

[C4]

[0013] Such hydrolyzable organosilanes include mono-silanes in which n in the general formula (I) is an integer of 0 to 3;
, di-, tri-, and tetra-functional alkoxysilanes, acetoxysilanes, oximesilanes, enoxysilanes, aminosilanes, aminoxysilanes, amidosilanes, and the like. Alkoxysilanes are preferred because of their ease of availability and ease of preparing a silica-dispersed organosilane oligomer solution.

In particular, examples of the tetraalkoxysilane with n=0 include tetramethoxysilane and tetraethoxysilane, and examples of the organotrialkoxysilane with n=1 include methyltrimethoxysilane, methyltriethoxysilane, and methyltriisosilane. propoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane,
Examples include 3,3,3-trifluoropropyltrimethoxysilane. Further, as the diorganodialkoxysilane where n=2, dimethyldimethoxysilane, dimethyldiethoxysilane, diphenyldimethoxysilane,
Examples include diphenyldiethoxysilane and methylphenyldimethoxysilane. Examples of the triorganoalkoxysilane where n=3 include trimethylmethoxysilane, trimethylethoxysilane, trimethylisopropoxysilane, and dimethylisobutylmethoxysilane. Furthermore, organosilane compounds generally called silane coupling agents are also included in alkoxysilanes.

Furthermore, when water-dispersible colloidal silica is used, water present as a component other than the solid content can be used to hydrolyze the organosilicon compound of component (A). These are usually made from water glass, and such colloidal silica is readily available commercially. Furthermore, organic solvent-dispersed colloidal silica can be easily prepared by replacing the water in the water-dispersible colloidal silica with an organic solvent. Such organic solvent-dispersed colloidal silica can also be easily obtained as a commercial product like water-dispersed colloidal silica. The types of organic solvents in which colloidal silica is dispersed include, for example, lower aliphatic alcohols such as methanol, ethanol, isopropanol (also called IPA), n-butanol, and isobutanol; ethylene glycol, ethylene glycol monobutyl ether, and ethylene acetate. Examples include ethylene glycol derivatives such as glycol monoethyl ether; diethylene glycol derivatives such as diethylene glycol, diethylene glycol monobutyl ether, and diacetone alcohol; one or more selected from the group consisting of these may be used. be able to. Toluene, xylene, ethyl acetate, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, methyl ethyl ketoxime, etc. can also be used in combination with these hydrophilic organic solvents.

The amount of water used is preferably 0.001 to 0.5 mol per 1 mol of the hydrolyzable group (X). If the proportion is less than 0.001 mol, a sufficient partial hydrolyzate cannot be obtained, and if it exceeds 0.5 mol, the stability of the partial hydrolyzate may deteriorate. The method of partial hydrolysis is not particularly limited. For example, a hydrolyzable organosilane and colloidal silica may be mixed and a necessary amount of water may be added and blended, and the partial hydrolysis reaction proceeds at room temperature. You may heat to 60-100 degreeC in order to promote a partial hydrolysis reaction. Furthermore, for the purpose of promoting the partial hydrolysis reaction, hydrochloric acid, acetic acid, halogenated silane, chloroacetic acid,
Organic and inorganic acids such as citric acid, benzoic acid, dimethylmalonic acid, formic acid, propionic acid, glutaric acid, glycolic acid, maleic acid, malonic acid, toluenesulfonic acid, oxalic acid, etc. may be used as catalysts.

It is preferable that 50 mol % or more of these hydrolyzable organosilanes represented by the general formula (I) be trifunctional compounds represented by n=1, more preferably 60 mol %. or more, and most preferably 70 mol% or more. If it is less than 50 mol%, sufficient coating film hardness may not be obtained and dry curability may tend to be poor.

Colloidal silica in component (A) is essential for increasing the hardness of the cured film of the coating composition used in the present invention. As such colloidal silica, water-dispersible colloidal silica or colloidal silica dispersible in non-aqueous organic solvents such as alcohol can be used. Generally, such colloidal silica contains 20 to 50% by weight of silica as a solid content, and the amount of silica to be blended can be determined from this value. In addition, when using water-dispersible colloidal silica, water present as a component other than the solid content (
It can be used to hydrolyze the organosilicon compound of component A). These are usually made from water glass, and such colloidal silica is readily available commercially.

In component (A), colloidal silica is preferably contained in an amount of 5 to 95% by weight as silica. More preferably the range is 10 to 90% by weight, most preferably 20 to 85% by weight. Content is 5% by weight
If it is less than 95% by weight, it will be difficult to uniformly disperse the silica, and component (A) may cause problems such as gelation.

Furthermore, when forming a coating layer with the components of the above formulas (I) and (II), the component (II), that is, the component (B), a silanol group-containing polyorganosiloxane, has the characteristics of the present invention. It is an important ingredient in eggplant. Such component (B) has an average compositional formula R2aSi(OH)bO(4-a-b)/2...(
II) (wherein R2 represents the same or different substituted or unsubstituted monovalent hydrocarbon group having 1 to 8 carbon atoms, and a and b are respectively 0.2≦a≦2, 0.0001≦b≦ 3
, a+b<4. ) can be expressed as In the formula, R2 is exemplified by the same group as R1 in (I) above, but is preferably an alkyl group having 1 to 4 carbon atoms, a phenyl group, a vinyl group, a γ-glycidoxypropyl group, or a γ-methacrylate group. Substituted hydrocarbon groups such as roxypropyl group, γ-aminopropyl group, and 3,3,3-trifluoropropyl group, more preferably methyl group and phenyl group. In addition, a and b in the formula are numbers that satisfy the above relationship, and if a is less than 0.2 or b exceeds 3, there will be problems such as cracking in the cured film, and if a exceeds 2, When b is less than 4 or when b is less than 0.0001, curing does not proceed well.

Such silanol group-containing polyorganosiloxanes include, for example, methyltrichlorosilane, dimethyldichlorosilane, phenyltrichlorosilane, diphenyldichlorosilane, or one or a mixture of two or more corresponding alkoxysilanes. It can be obtained by hydrolysis using a large amount of water using the method described in the following. When hydrolyzing an alkoxysilane by a known method to obtain a silanol group-containing polyorganosiloxane, a trace amount of unhydrolyzed alkoxy groups may remain. In other words, a polyorganosiloxane in which a silanol group and a trace amount of alkoxy group coexist may be obtained in some cases, but such a polyorganosiloxane may be used in the present invention.

The curing catalyst which is component (C) of the present invention promotes the condensation reaction between component (A) and component (B),
It hardens the coating. Such catalysts include alkyl titanates, metal salts of carboxylic acids such as tin octylate and dibutyltin dilaurate, dioctyltin dimaleate; amine salts such as dibutylamine-2-hexoate, dimethylamine acetate, ethanolamine acetate; Quaternary ammonium carboxylic acid salts such as tetramethylammonium acetate; Amines such as tetraethylpentamine; N-β-aminoethyl-γ-aminopropyltrimethoxysilane, N-β-aminoethyl-γ
-Amine-based silane coupling agents such as aminopropylmethyldimethoxysilane; Acids such as p-toluenesulfonic acid, phthalic acid, and hydrochloric acid; Aluminum compounds such as aluminum alkoxide and aluminum chelate; Alkali catalysts such as potassium hydroxide; Tetraisopropyl titanate , titanium compounds such as tetrabutyl titanate and titanium tetraacetylacetonate, and halogenated silanes such as methyltrichlorosilane, dimethyldichlorosilane and trimethylmonochlorosilane, but in addition to the above catalysts, components (A) and (B) There is no particular restriction as long as it is effective in the condensation reaction with.

The blending ratio of component (A) and component (B) is 99 to 99 parts by weight of component (B) to 1 to 99 parts by weight of component (A).
Preferably 1 part by weight, more preferably 5 to 9 parts by weight of component (A)
95 to 5 parts by weight of component (B) to 5 parts by weight, most preferably 90 to 10 parts by weight of component (B) to 10 to 90 parts by weight of component (A) (however, component (A) (B)
The total amount of ingredients is 100 parts by weight). If component (A) is less than 1 part by weight, room temperature curability will be poor and sufficient film hardness will not be obtained; on the other hand, if it exceeds 99 parts by weight, curability will be unstable and a good coating film will not be obtained. Sometimes there isn't.

The amount of component (C) added is 0.0001 parts by weight per 100 parts by weight of components (A) and (B).
It is preferable that it is 10 parts by weight. More preferably 0
．． 0005 to 8 parts by weight, most preferably 0.00
07 to 5 parts by weight. If it is less than 0.0001 parts by weight, it may not harden at room temperature, and if it exceeds 10 parts by weight, heat resistance and weather resistance may deteriorate.

Component (D) is a dispersed ceramic powder for imparting sufficient heat dissipation to the insulating layer, for example,
Contains at least AlN powder (wholly or partially AlN
powder) is an inorganic powder. The particle size of this inorganic powder is not particularly limited, but is preferably 0.2 to 40 μm, more preferably 0.4 to 30 μm. The amount of ceramic powder added is, for example, 40 wt% with respect to the insulating layer.
to 88 wt%. If it is less than 40wt%, heat dissipation will be insufficient, and if it exceeds 88wt%,
The smoothness of the insulating layer may be significantly reduced. Also, A
The amount of IN powder added is preferably 30 parts by weight or more per 100 parts by weight of the ceramic powder. If the amount is less than 30 parts by weight, it may become difficult to obtain sufficient heat dissipation performance.

[0026] As a method for preserving the coating composition of the present invention, either (A) or (B) (D
) and then add component (C) at the time of use 3
It is generally packaged, but it contains (A) and (D).
Disperse the ingredients and then separate the mixed ingredients (C) and (B) into two packages and mix them together when using, or mix all the ingredients and package them in one container. It is also possible to make it into a single package that is stored in a container.

[0027] The coating composition of the present invention can be coated by a conventional coating method, for example, various coating methods such as brush coating, spraying, dipping, flow, roll, curtain, and knife coating can be selected. Further, there is no particular restriction on the dilution ratio with the organic solvent, and the dilution ratio may be determined as necessary. In addition, the coating composition of the present invention may optionally contain a leveling agent, a thickening agent,
Pigments, dyes, aluminum paste, glass frit, metal powder, antioxidants, etc. can be added within the range that does not affect the present invention.

[0028] The ceramic powder may be dispersed by a conventional method. Further, at that time, it is possible to use a dispersant, a dispersion aid, a thickener, a coupling agent, etc. Furthermore, leveling agents, dyes, metal powders, glass powders, antioxidants, etc. can be added. The coating composition of the present invention can be used after being diluted with various organic solvents for ease of handling. The type of organic solvent is component (A) or component (B).
) can be selected depending on the type of monovalent hydrocarbon group or molecular weight of the component. Examples of such organic solvents include those shown as dispersion solvents for colloidal silica, and one or more solvents selected from the group consisting of these can be used. These hydrophilic organic solvents can be used in combination with solvents such as toluene, xylene, ethyl acetate, butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, and methyl ethyl ketoxime.

The insulating film (including the case where it is a film) of the present invention formed using this coating composition has high heat dissipation properties. The processing temperature for forming a film of the coating composition may be appropriately set, for example, between room temperature and heating temperature. This treatment produces an insulating film made of an organosilicon compound having siloxane bonds. All or part of the powder dispersed in this insulating film is
It is IN powder.

Further, the thickness of the coating is not particularly limited, and may be 0.
The thickness may be 1 to 150 μm, but it is more preferably 1 to 100 μm in order for the coating film to be stably adhered and maintained over a long period of time and to prevent cracking or peeling. The metal base substrate of the present invention has such an insulating film as an insulating layer. That is, a metal layer is coated with the coating composition of the present invention to form a film. Examples of metal layers include those used for normal metal-based substrates (
For example, a metal plate or metal foil made of Cu, Al, etc.) is used.

In the present invention, for example, as shown in FIG. 1, a metal base substrate 4 in which an organosilicon compound insulating layer 3 containing aluminum nitride powder 2 is formed on one side of a metal plate 1 made of Cu, Al, etc. As shown in FIG. The metal base substrate 7 on which the organosilicon compound insulating layer 3 containing the powder 2 is formed may be used, and there is no particular limitation.

[0032]

[Operation] The insulating film formed from the coating composition containing the above-mentioned components (A) to (D) as essential components has AlN powder dispersed therein, has high heat dissipation properties, and has good water resistance.

[0033]

[Examples] Specific examples and comparative examples of the present invention are shown below, but the present invention is not limited to the following embodiments. In addition, in the following, all "parts" represent "parts by weight", and all "%" represent "weight %". First, an example of a method for preparing component (A) will be explained. (Preparation Example A-1) IPA-ST (
Isopropanol dispersed colloidal silica sol: particle size 1
0 to 20 mμ, solid content 30%, H2O 0.5%, manufactured by Nissan Chemical Industries, Ltd.) 100 parts, methyltrimethoxysilane 68
18 parts of dimethyldimethoxysilane, 2.7 parts of water, and 0.1 part of acetic anhydride, a partial hydrolysis reaction was carried out at a temperature of 80°C for about 3 hours with stirring, and the mixture was cooled.
A) Component was obtained. This product had a solid content of 36% when left at room temperature for 48 hours. The component (A) obtained here is referred to as A-1. The preparation conditions for A-1 were as follows.・Number of moles of water per mole of hydrolyzable group: 1 x 10-
1. Silica content of component (A): 40.2%, n=1
Mol% of hydrolyzable organosilane: 77 mol% (Preparation Example A-2) In a flask equipped with a stirrer, a heating jacket, a condenser, and a thermometer, IPA-ST (isopropanol-dispersed colloidal silica sol: particle size 10~ 20mμ,
Solid content 30%, H2O 0.5% (manufactured by Nissan Chemical Industries, Ltd.) 1
00 parts, 68 parts of methyltrimethoxysilane, 49.5 parts of phenyltrimethoxysilane, and 7.7 parts of water, a partial hydrolysis reaction was carried out at a temperature of 65°C for about 5 hours with stirring, and the mixture was cooled. Component (A) was obtained. This product had a solid content of 36% when left at room temperature for 48 hours. The component (A) obtained here is referred to as A-2. The preparation conditions for A-2 were as follows.・Number of moles of water per mole of hydrolyzable group: 2 x 10-
1. Silica content of component (A): 31.3%, n=1
Mol% of hydrolyzable organosilane: 100% by mole Next, an example of a method for preparing component (B) will be explained. (Preparation Example B-1) Weigh out a mixed solution of 220 parts (1 mole) of methyltriisopropoxysilane and 150 parts of toluene into a flask equipped with a stirrer, a heating jacket, a condenser, a dropping funnel, and a thermometer. Hydrochloric acid aqueous solution 1
08 parts were added dropwise to the above mixture over 20 minutes to hydrolyze methyltripropoxysilane. After 40 minutes of dropping, the stirring was stopped, and the mixture of water and isopropyl alcohol in the lower layer containing a small amount of hydrochloric acid was separated into two layers, and then the remaining hydrochloric acid in the toluene resin solution was removed by water washing, and then After removing toluene under reduced pressure, the mixture was diluted with isopropyl alcohol to obtain a 40% isopropyl alcohol solution of a silanol group-containing organopolysiloxane having an average molecular weight of about 2,000. This is called B-1. In addition, the molecular weight was determined by GPC (gel permeation chromatography) using a measurement model HLC-802UR (manufactured by Tosoh Corporation).
A calibration curve was created and measured using standard polystyrene. Subsequent molecular weights were also measured in the same manner. (Preparation Example B-2) A flask equipped with a stirrer, a heating jacket, a condenser, a dropping funnel, and a thermometer was filled with 1 liter of water.
000 parts and 50 parts of acetone, and 44.8 parts (0.3 mol) of methyltrichlorosilane were added to the mixed solution.
, 38.7 parts (0.3 mol) of dimethyldichlorosilane,
A solution of 84.6 parts (0.4 mol) of phenyltrichlorosilane in 200 parts of toluene was hydrolyzed while being added dropwise with stirring. After 40 minutes of dropping, stirring was stopped, and the reaction solution was transferred to a separating funnel and allowed to stand. The lower layer of hydrochloric acid water separated into two layers was separated and removed, and then added to the toluene solution of organopolysiloxane in the upper layer. The remaining water and hydrochloric acid were distilled off along with excess toluene by vacuum stripping to obtain a 60% toluene solution of a silanol group-containing organopolysiloxane having an average molecular weight of about 3,000. This is called B-2.

-Examples 1 to 3- AlN powder (particle size 15 μm) was added to each component A shown in Table 1.
After adding it to the coating material at a concentration of 70% (total of 100% of components A to C), it was dispersed in a Glen Mill (manufactured by Asada Tekko Co., Ltd.) for a residence time of 15 minutes. Al
A coating liquid consisting of a coating composition was obtained by mixing components B and C to liquid A in which N powder was dispersed so as to have the formulations shown in Table 1.

[0035]

[Table 1]

-Examples 4 to 6- Each of the coating solutions of Examples 1 to 3 was air-sprayed onto a chemical conversion treated aluminum plate having a thickness of 1 mm to a thickness of 70 μm, and setting was performed for 10 minutes. After that, after crimping with a 35 μm copper foil using a press,
The treatment was carried out at 0° C. for 30 minutes to obtain a metal base substrate on which an organosilicon compound insulating film was integrally formed on the copper foil. The metal base substrates manufactured in this manner are respectively referred to as (1), (2), and (2).

- Comparative Example - A metal base substrate was produced in the same manner as in Example 1, except that the insulating layer was formed of an epoxy resin containing 70% alumina powder with an average size of 5 μm. The thermal resistance and withstand voltage of the metal base substrates ① to ② of the examples and the metal base substrate of the comparative example were investigated, and the results are shown in Table 2.

[0038]

[Table 2]

As shown in Table 2, the metal base substrate of the example is superior in thermal resistance and withstand voltage compared to that of the comparative example.

[0040]

[Effects of the Invention] According to the present invention, the heat dissipation layer has unprecedented high performance (for example, excellent heat dissipation properties and excellent water resistance) as an insulating layer of various electronic components including an insulating layer of a metal base substrate. It is possible to realize a transparent insulating layer.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view schematically showing one embodiment of a metal base substrate of the present invention.

FIG. 2 is a cross-sectional view schematically showing another embodiment of the metal base substrate of the present invention.

[Explanation of symbols]

1 Metal plate 2 Aluminum nitride powder 3 Organosilicon compound insulation layer 4 Metal base substrate 5 Metal plate 6 Metal foil 7 Metal base board

Claims (3)

[Claims] Claim 1: (A) General formula (I) R1nSiX4-n
...(I) (wherein R1 represents the same or different substituted or unsubstituted monovalent hydrocarbon group having 1 to 8 carbon atoms,
n is an integer of 0 to 3, and X represents a hydrolyzable group. ) A silica-dispersed oligomer solution of organosilane obtained by partially hydrolyzing a hydrolyzable organosilane represented by (B) in an organic solvent or colloidal silica dispersed in water, (B) Average composition formula (II) R2aSi(OH) bO(4-a-b)/2...(
II) (wherein R2 represents the same or different substituted or unsubstituted monovalent hydrocarbon group having 1 to 8 carbon atoms, and a and b are respectively 0.2≦a≦2, 0.0001≦b≦ 3
, a+b<4. ) A coating composition containing as essential components a polyorganosiloxane containing a silanol group in the molecule, (C) a catalyst, and (D) aluminum nitride powder. 2. A heat dissipating insulating film comprising the coating composition according to claim 1. 3. A metal base substrate comprising the heat dissipating insulating film according to claim 2 as an insulating layer.