JPH0515749B2 - - Google Patents

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is capable of forming a silicone-based coating film with excellent heat resistance, scratch resistance, chemical resistance, etc. on the surface of metals and ceramics, and The present invention relates to a method for producing a coating composition with excellent long-term storage stability.

(Prior art) The surfaces of various molded objects such as metals and ceramics are coated with silicone-based polymer compositions to give them smoothness, or to improve scratch resistance, chemical resistance, corrosion resistance,
Efforts are being made to improve weather resistance, water resistance, etc. For example, a silicone varnish in which organopolysiloxane (an initial polymer with a relatively low degree of polymerization) is dissolved in a solvent is widely used as a heat-resistant paint. The skeleton structure of organopolysiloxane includes a trifunctional component (R ₁ SiO _3/2 ) and a bifunctional component (R ₂ SiO _2/2 ) as polymerization components. When a varnish containing this organopolysiloxane is applied to, for example, a metal surface, the solvent is removed, and then heated, the organopolysiloxane is further polymerized and the entire silicone varnish is cured. At this time, in the trifunctional component portion, branching from the polymer main chain and crosslinking between polymer chains occur, further promoting curing.
The use of silicone varnish has the advantage that, compared to other resins, it loses less weight due to heating; and the resulting coating film is less likely to discolor. However, to cure silicone varnish, it is usually necessary to
It requires long-term heating (baking) of more than 1 minute. This is thought to be due to the high content of bifunctional components in the organopolysiloxane.

In order to cure in a short time, the above silicone varnish is coated with alkyd, epoxy, acrylic,
Modified silicone varnishes containing thermosetting resins such as urethane-based, polyester-based, phenol-based, and melamine-based resins are used. By adding the thermosetting resin, the sol coating paint is cured in a short time and becomes dry. However, since the proportion of silicone resin in the entire modified silicone varnish is low, heat resistance is reduced. Further, even if the modified silicone varnish is cured, the organopolysiloxane in the varnish remains dispersed in the resin matrix in an uncured state. This uncured resin is cured over time or by heating again. Therefore, the physical properties of the coating film immediately after curing are significantly different from the physical properties of the coating film after reheating or aging.
Therefore, for example, if the coating is used in equipment or plants where the temperature differs in some areas, the adhesion of the coating may decrease, causing peeling or rust.

When using the above-mentioned unmodified silicone varnish alone, its main component, organopolysiloxane, has many organic groups in its molecular skeleton, so if it is exposed to temperatures of 300°C or higher during or after curing, Decomposition occurs, causing distortion and cracks in the paint film. Gas generation also occurs due to decomposition.
In particular, when the organopolysiloxane contains a large amount of bifunctional components, such drawbacks are exacerbated.

In contrast, a coating composition for coating using an organopolysiloxane having a trifunctional or higher functional component has been proposed. For example, JP-A-53-88099 discloses methylpolysilsesquioxane (what is silsesquioxane) obtained by hydrolyzing and polymerizing methyltrichlorosilane in a ketone-ether solvent in the presence of an amine? , referring to a siloxane in which the ratio of the number of oxygen atoms to silicon atoms is 1.5). This methylpolysilsesquioxane has a molecular weight of about 9,000 to 100,000 and is soluble in organic solvents. When a coating film containing this methylpolysilsesquioxane is used to form a coating film, the film has heat resistance of 400°C or higher. but,
It is not practical because it requires a long time of 2 hours or more at 200°C for curing. Furthermore, since volume shrinkage occurs due to the dehydration reaction during curing, there is a drawback that cracks occur when the film is made thicker.

Japanese Patent Publication No. 53-5042 discloses a coating composition containing a reaction condensate obtained by adding methyltrimethoxysilane to aqueous colloidal silica and adjusting the pH with an organic acid, and a pigment (extender pigment). .
According to this reaction, hydrolysis and partial condensation of methyltrimethoxysilane proceed, and at the same time, active silanol on the surface of the silica particles of colloidal silica also participates in the condensation reaction. In this way, since the active silanol on the surface of the silica particles participates in the reaction and increases the molecular weight, aggregation and gelation of the silica particles are likely to occur. Therefore, it is necessary to set the reaction conditions to extremely mild conditions. Moreover, the resulting paint has poor stability and must be used within 24 hours after preparation. Furthermore, since the degree of condensation of the methyltrimethoxysilane condensate, which is a film-forming component when forming a coating film, is low, cracks occur when the film thickness is 3 μm or more. The surface smoothness of the coating film is poor, and the gloss is also poor.

JP-A-62-105987 discloses a coating composition comprising a reaction mixture obtained by adding an aqueous acid solution to a mixture of a tetraalkyl silicate and an organosilica gel. This paint is used to coat the surface of a ceramic substrate to provide smoothness. When preparing this composition, it is possible to control the amount and rate of addition of water, which has the advantage of controlling the molecular weight of the resulting polymer. Furthermore, since tetraalkyl silicate is used, which is tetrafunctional,
The coating film obtained using the above composition has extremely excellent heat resistance. However, the silica particles of the organosilica sol react with the silanol groups generated by the reaction between the tetraalkyl silicate and water.
The disadvantage of agglomeration and gelation of the silica particles is the same as in the case of Japanese Patent Publication No. 5042/1983, which uses methyltrimethoxysilane and aqueous colloidal silica. Furthermore, when preparing this composition, the amount of water added is adjusted to control the hydrolysis of the tetraalkyl silicate, leaving behind alkoxy groups to stabilize the resulting reaction mixture. As described above, since alkoxy groups remain in the polymer, in order to form a coating film using this paint, it is necessary to eliminate the alkoxy groups during curing of the paint film. Therefore, a post-process of firing at a high temperature of 500°C or higher is required during curing.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned conventional problems, and its purpose is to provide a silicone coating composition for coating the surfaces of metals, ceramic molded bodies, etc. The object of the present invention is to provide a method for producing a coating composition having the following properties: A coating composition that has excellent storage stability and can be stored for a long time without gelling; Preparation of a coating film. A coating composition that does not require long-term curing treatment at high temperatures and does not cause cracks even when forming a relatively thick coating; and has heat resistance, corrosion resistance, scratch resistance, and water resistance. A coating composition that can form an excellent coating film on, etc.

(Means and effects for solving the problems) The method for producing the coating composition of the present invention is based on the formula
The organosilicon compound represented by RSi(OR') ₃ (where R is a hydrocarbon group having 1 to 8 carbon atoms, and R' is a hydrocarbon group having 1 to 4 carbon atoms) is Hydrolyzed in the presence of an acid catalyst with 1.5 to about 10 moles of water per mole to achieve a molecular weight of about 1000 to about
The method includes the steps of obtaining a reaction mixture containing a condensate of 10,000 and adding an organosilica sol to the reaction mixture for reaction, thereby achieving the above object.

As mentioned above, the organosilicon compound used in the method of the present invention is a compound represented by the formula RSi(OR') ₃ , where R is a hydrocarbon group having 1 to 8 carbon atoms, and R' is a hydrocarbon group having 1 to 4 carbon atoms. is a hydrocarbon group. R and
If the number of carbon atoms in R' is too large, the rate of hydrolysis by an acid catalyst, which will be described later, will be extremely slow, and in some cases, hydrolysis will hardly proceed.

The above R is methyl, ethyl, propyl,
Examples include alkyl groups such as hexyl and octyl; aryl groups such as phenyl, tolyl, and xylyl; and cycloalkyl groups such as cyclohexyl, cyclobutyl, and cyclopentyl. Examples of R' include methyl, ethyl, propyl, and butyl groups. Examples of such organosilicon compounds include methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltributoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltripropoxysilane, and Examples include enyltributoxysilane.

In the present invention, the amount of water used for hydrolyzing the organosilicon compound is from 1.5 to about 10 mol, preferably from 1.5 to 5 mol, per 1 mol of the organosilicon compound. This amount includes when an acid aqueous solution is used as the acid described below.Theoretically, the amount of water required for hydrolysis of the organosilicon compound is calculated as shown in the formula below. , 1.5 mol. If the amount of water is too small, hydrolysis and condensation will not proceed sufficiently. Therefore, when a coating film is formed using the obtained coating material, the film-forming ability is poor, and the coating film is inferior in hardness, heat resistance, and water resistance.
The upper limit of the amount of water varies depending on the organosilicon compound used, the type of acid catalyst described below, reaction temperature, reaction time, etc., but is usually about 10 mol. If the amount of water is excessive, even if a sufficient amount of organic solvent is added to dilute the reaction mixture after the reaction is completed, a gel is likely to be formed and the storage stability will be extremely poor.

The organosilica sol used in the present invention is a liquid material in which silica particles are colloidally dispersed in an organic solvent. Examples of organic solvents include alcohols such as methanol, ethanol, isopropanol, and butanol; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; esters such as methyl acetate, ethyl acetate, and butyl acetate; and hexane and heptane. Aliphatic hydrocarbons; aromatic hydrocarbons such as benzene, toluene and xylene; ethers such as diisopropyl ether and glycol ether; mixtures thereof; and the like. The particle diameter of the silica particles of the organosilica sol is 5 to 200 mμ. When the particle size is less than 5 mμ, cracks are likely to occur when forming a cured film using the obtained paint.
On the other hand, if it exceeds 200 mμ, film forming properties are poor and the resulting coating film is poor in hardness and smoothness. These organosilica sols usually contain silica particles (as SiO ₂ ) in a proportion of 5 to 50% by weight.
Organosilica sols are prepared by known methods. As a method, for example, the particle size is 5 to 200.
Examples include a method of distilling and replacing water with an organic solvent while adding an organic solvent to mμ stable aqueous colloidal silica.

Organosilica sol is an organic silicon compound RSi
Assuming that (OR′) ₃ has changed to RSiO _3/2 , we can write this as
10-200 parts by weight as 100 parts by weight (as _SiO2 )
used at a rate of If the amount is less than 10 parts by weight, cracks will occur during curing if the coating film is thick when forming a coating film using the obtained coating material. On the other hand, if it exceeds 200 parts by weight, the adhesion of the cured film to the substrate to be coated will be poor, and the film will have poor hardness and smoothness, as well as poor gloss.

The acid catalyst has the function of promoting the polymerization reaction of the organosilicon compound, and the polymerization reaction is controlled by appropriately setting the type and amount of this acid. As the acid, any of mineral acids such as hydrochloric acid, sulfuric acid, and phosphoric acid; and organic acids such as formic acid and acetic acid may be used. When using mineral acids, organosilicon compounds
5×10 ^-5 to 1×10 ^-2 parts by weight per 100 parts by weight,
Preferably, it is used in a proportion of 1×10 ⁻⁴ to 5×10 ⁻³ parts by weight. If it exceeds 1 x 10 ^-2 parts by weight, the condensation rate will increase, making it difficult to control the reaction. The resulting paint is more likely to form a gel during storage. When using an organic acid, 0.07 to 4 parts by weight per 100 parts by weight of the organosilicon compound;
It is preferably used in a proportion of 0.2 to 2 parts by weight.
If the organosilicon compound used contains an acid as an impurity or contains a compound that can be decomposed to produce an acid, the type and amount of the acid to be used must be determined taking these into consideration. be. When an organic acid is used as the acid, a more stable coating material is obtained.

Two or more types of the above organosilicon compound, organosilica sol, and acid may be used as a mixture.

To prepare coating paints by the method of the invention,
For example, first, the above organosilicon compound is prepared, and a water-soluble organic solvent is added thereto as necessary. Examples of water-soluble organic solvents include alcohol solvents, cellosolve solvents, cellosolve acetate solvents, and glyme solvents. The predetermined amounts of water and acid described above are added to this, and the mixture is heated for about 30 minutes to about 20 hours at a temperature of about 20° C. or higher up to the reflux temperature to perform hydrolysis.

Here, the hydrolysis and condensation of the organosilicon compound is shown by the following formula. From this equation, it can be seen that the theoretical amount of water required for hydrolysis is 1.5 times the mole of the organosilicon compound.

nRSi(OR′) ₃ +3nH ₂ OnRSi(OH) ₃ +3nR′OH nRSi(OH) ₃ (RSiO _1.5 ) _o +1.5nH ₂ O Putting this equation together, we get the following equation.

nRSi(OR′) ₃ +1.5nH ₂ O(RSiO _1.5 ) _o +3nR′OH
The molecular weight of the condensation product is about 1,000 to about 10,000, preferably about 1,000 to about 5,000. Molecular weight is approximately 1000
When it is below , the resulting paint has a high silanol content. Therefore, if a thick coating film is formed using this paint, cracks are likely to occur. Furthermore, since the activity of silanol is high, the polymerization reaction proceeds excessively in the reaction with the organosilica sol described below, which tends to cause gelation. On the other hand, if the molecular weight exceeds about 10,000, the silanol content is low, so it takes a long time to form a coating, which is not practical.

Next, the organosilica sol is added to the reaction mixture containing the condensation product, and the reaction is carried out at a temperature below the reflux temperature, preferably below 50°C. The reaction time at this time varies depending on the reaction temperature, the type of organosilicon compound and acid used in the condensation reaction, the degree of condensation, etc., but is usually about 30 minutes to about 10 days. If the reaction at this time is insufficient (typically, when the organosilica sol is simply added), when the resulting paint is applied and baked to harden,
Since the condensate derived from the organosilicon compound and the organosilica sol are cured independently, whitening and cracks occur in the coating film. Conversely, if the reaction proceeds excessively, gelation will occur. Even if gelation does not occur during the reaction, it often occurs during storage.

Although it is not possible to specify the reaction that occurs when organosilica gel is added, it is assumed that a reaction occurs in which the silanol groups of the silane condensate react with the silanol groups on the surface of the silica particles of the organosilica sol, resulting in a condensation reaction that forms new siloxane bonds. Conceivable. By combining the organosilica sol with the silane condensate, shrinkage of the silane condensate during curing is suppressed. As a result, a coating film with excellent hardness, heat resistance, chemical resistance, etc. can be obtained by thermosetting.

The coating paint thus obtained is diluted or concentrated as appropriate to adjust the solid content, and then stored or used. This paint is obtained through a predetermined process of controlling the amount of water used during its preparation and preparing an intermediate condensate of a specific molecular weight from an organosilicon compound. Therefore, the crosslinking density of the polymer in the paint is appropriately adjusted. As a result, gelation is less likely to occur and storage stability is excellent. Since the solid content in the resulting paint has sufficient performance as an inorganic binder for the paint, a relatively thick coating layer of 5 to 20 μm is formed even when the paint is directly applied to the surface to be painted and cured. The paint can be cured under relatively mild conditions of about 120 to 200°C for 10 to 60 minutes, and it is possible to form a relatively thick coating without cracking or peeling during curing. . The coating film obtained from the paint is transparent, and unlike conventional paints, the coating film does not turn white due to aggregation of silica particles. It is also possible to add extender pigments and coloring pigments to this paint as appropriate to use it as an enamel colored in a desired color. It is also possible to add a large amount of pigment to form a coating film with a thickness of 30 μm or more without causing cracks or peeling.

The cured coating film obtained in this way has heat resistance,
Excellent corrosion resistance, chemical resistance and weather resistance. For example, it is stable up to about 1000℃ and does not discolor or change its physical properties, so it can be used to coat areas that require heat resistance (for example, coating the surface of metal plates used in stoves, car (coating for light reflectors). Furthermore, it is also suitable for applications such as coating for corrosion resistance of iron or rare earth magnet molded bodies (bond magnets, sintered magnets, etc.) used as electronic components; coating for chemical resistance of plant piping. It will be done.

(Example) The present invention will be explained below using examples.

Example 1 136 g of methyltrimethoxysilane and 1 g of formic acid were added to a reaction vessel and heated to 80°C while stirring.
And so. 54 g of water was added to this, heated at reflux temperature, and reacted over about 2 hours until the molecular weight reached about 2000. The molecular weight was measured by gel permeation chromatography using a standard styrene conversion method. The same applies to Examples 2 and 3 below. This reaction mixture was then charged with SiO ₂
220 g of methanol silica gel having a particle size of 10 to 20 mμ at a concentration of 30% by weight was added and reacted at 50°C for 10 hours. The reaction mixture thus obtained had a viscosity of 5.5 centipoise. When this product was stored at 30°C for 2 months, its viscosity was 6.5 centipoise, indicating excellent storage stability.

Next, the above reaction product was coated on a molten aluminized steel plate to a film thickness of 10 μm, and the temperature was 150°C.
I let it harden for 30 minutes. No abnormalities such as cracks were observed in the formed coating film. After heating this at 400°C for 16 hours, a salt spray resistance test (JIS Z 2371) was conducted, and no spot rust was observed even after 10 days.

Example 2 178 g of methyltrimethoxysilane was added to a reaction vessel and heated to 80° C. while stirring. 42 g of water containing 10 ppm of hydrochloric acid was added thereto, heated at reflux temperature, and reacted over 10 hours until the molecular weight reached approximately 3000. Next, 220 g of isopropanol silica gel with a SiO ₂ concentration of 30% by weight and a particle size of 20 to 30 mμ was added to this reaction mixture, and the mixture was reacted at 30° C. for 30 hours. The solvent was evaporated until the solids content of the reaction mixture was approximately 50% by weight, and then diluted with methyl cellosolve to a solids concentration of 40% by weight. The reaction mixture thus obtained had a viscosity of 11.0 centipoise. When this was stored at 30°C for 2 months, its viscosity was 12.5 centipoise, indicating excellent storage stability.

Next, add 100PHR of titanium oxide to the above reaction mixture.
The mixture was dispersed at a ratio of 1,000 ml, and coated on a polished mild steel plate to a film thickness of 30 μm, and cured at a temperature of 180° C. for 20 minutes. No abnormalities such as cracks were observed in the formed coating film, and it passed the salt spray resistance test (JIS
Z 2371) No spot rust was observed even after 10 days. Similar results were obtained when a salt spray resistance test was performed after heating at 400°C for 16 hours.

Example 3 160g of methyltrimethoxysilane in a reaction vessel,
20g phenyltrimethoxysilane and 4g formic acid
was added and heated to 80°C while stirring. 54 g of water was added to this, heated to reflux temperature, and reacted until the molecular weight reached about 3000. Next, 200 g of isopropanol silica sol having a particle size of 20 to 30 mμ with a SiO ₂ concentration of 30% by weight was added to this reaction mixture, and the mixture was reacted at reflux temperature for 2 hours. The resulting reaction mixture had a viscosity of 7.0 centipoise. This at 30℃
When stored for two months, its viscosity was 8.2 centipoise, indicating excellent storage stability.

Next, apply the above reaction mixture to an aluminum alloy plate until the film thickness is
It was coated to a thickness of 10 μm and cured at a temperature of 180°C for 20 minutes. A glossy coating film with good adhesion was obtained. When this was heated at 400°C for 16 hours, no cracks were observed and the gloss did not change. When an accelerated weathering test (JIS B 7752) was conducted, no change was observed in the coating film even after 2000 hours.

Comparative example 1 SiO ₂ concentration 20% by weight in reaction vessel, particle size 20-30
300g of mμ aqueous colloidal silica (PH: 3.1),
and 2 g of acetic acid were added, and 136 g of methyltrimethoxysilane was gradually added in an ice bath. This was stirred at 10°C for about 1 hour. When the reaction mixture thus obtained was allowed to stand at 30°C, it gelled on the third day.

Separately, the above new reaction mixture was coated on an aluminum alloy plate to a film thickness of 5 μm, and the temperature was 150℃ for 30 minutes.
When cured over a period of time, a coating film with no gloss was formed. Separately, when the curing temperature was set to 400°C and heating was performed for 30 minutes, cracks appeared on the entire surface of the coating film.

Comparative Example 2 136g of methyltrimethoxysilane in the reaction vessel;
220 g of isopropanol silica gel with a SiO ₂ concentration of 30% by weight and a particle size of 20 to 30 mμ; and 2 g of acetic acid were added, and the mixture was heated to 80° C. with stirring. 54 g of water was added to this, and the mixture was reacted at reflux temperature for 2 hours. The reaction mixture thus obtained was left at 30°C for 3 days. This was applied to a molten aluminized steel plate to a film thickness of 3 μm, and the coating was applied at a temperature of 180℃ for 20 minutes.
After curing for several minutes, the coating became white. When similar experiments were conducted with different film thicknesses, cracks occurred in all films with a film thickness of 5 μm or more when heated to 400° C. or more.

(Effects of the Invention) According to the present invention, a silicone-based coating coating composition that can easily form a coating film with excellent properties on the surface of a metal or ceramic substrate and has excellent storage stability is provided. A method of manufacturing is provided. The coating film obtained using the coating paint obtained by this method has extremely excellent heat resistance, water resistance, chemical resistance, weather resistance, etc. In particular, it has excellent properties not found in conventional silicone coating paints, such as not discoloring or deteriorating even when left under high temperatures. can be advantageously used as a paint. It is also suitable as a paint for coating the surfaces of electronic components such as small magnets and plant piping materials for the purpose of corrosion resistance and chemical resistance.

Claims (1)

[Scope of Claims] 1 Organosilicon represented by the formula RSi(OR') ₃ (where R is a hydrocarbon group having 1 to 8 carbon atoms, and R' is a hydrocarbon group having 1 to 4 carbon atoms) The compound is hydrolyzed with 1.5 to about 10 moles of water per mole of the organosilicon compound in the presence of an acid catalyst to obtain a molecular weight of about
1. A method for producing a coating composition, comprising the steps of: obtaining a reaction mixture containing 1,000 to about 10,000 condensates; and adding organosilica sol to the reaction mixture for reaction.