JPS6238394B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to coating compositions, and more particularly to coating compositions containing aluminum flakes. The contamination problems caused by conventional paints that use organic solvents have made it difficult for manufacturing industries, such as the automotive and truck manufacturing industry, to use (1) dry powder coating compositions, (2) organic solvents in small amounts. (3) high solids coating compositions, ie, compositions containing very little, if any, liquid carrier. The use of aluminum flakes in conventional solvent-based coating compositions provides high quality finishes with an exceptionally glamorous appearance. The term "glamour" refers to a coating technique in which a metallic pigment is used which causes the intensity of the light reflected from the coated substrate to vary markedly depending on the angle from which it is viewed, and which also gives the coating the illusion of shimmer and depth. Used to refer to the properties of additive coatings. However, standard or untreated aluminum flakes provide a poor glamorous appearance in dry powder and high solids coating compositions, and are unstable in water-based coating compositions. When standard aluminum flakes are added to a dry powder coating composition, the appearance of the coating produced is usually poor and exhibits a marbling-like effect due to inefficient mixing. Additionally, all incompatible materials float to the surface in both dry powder and high solids coating compositions.
This reduces the glamor effect. In these coatings where the flakes are not properly aligned, the flakes also leak onto the surface of the coating. In water-based coating compositions, standard aluminum flakes react with the water in the composition to generate hydrogen gas, creating safety issues, especially at high temperatures, and also settle out in water-based coating compositions. Tends to form a hard cake. The improved coating compositions of the present invention solve these aforementioned problems in the art. In accordance with the present invention, an improvement is provided for coating compositions containing aluminum flakes, which comprises coating the aluminum flakes with a monoethylenically unsaturated silane prior to incorporating the flakes into the coating composition. and reacting the silane-coated flakes with a functionalized acrylic monomer to form a top coat of acrylic polymer on the flakes. The improved coating composition of the present invention utilizes treated aluminum flakes. This treatment of aluminum flakes (1) coats the flakes, (2) prevents undesirable reactions between the flakes or their impurities and the remaining components in the composition, and (3) removes coexistence from the surface of the flakes. removes sexual substances,
and (4) providing on the flakes an acrylic top coat having organic functional groups on the surface that are capable of reacting with the polymers used in the coating composition. This process solves all the problems mentioned above and produces a coating with excellent appearance. Aluminum flake-containing coating compositions are well known in the art as described in U.S. Pat. No. 3,998,768 and U.S. Pat.
No. 632195 (April 20, 1967) No. 302858 (1972
November 1, 1972) and No. 285590 (September 1, 1972)
) is well known as indicated in each specification. These coating compositions are applied to the substrate by conventional coating techniques such as spraying, brushing, flow coating, dip coating or electrocoating the coating composition onto the substrate. For example, the substrate can be primed or unprimed metal, glass, plastic or fiber-reinforced plastic. Plastics include, for example, polystyrene, styrene copolymers, polypropylene, and the like. These coating compositions are particularly suitable for use as exterior finishes on automobile or truck bodies. Aluminum flakes useful in the present invention can be as dry particles or as a paste of aluminum particles dispersed in an organic solvent. Aluminum flakes are usually made into a paste. The reason is that it is most readily available commercially in that form. The weight percent of aluminum flakes relative to the total weight of the paste is usually 30
~80%. The aluminum flakes themselves are generally flat in shape and have an average maximum dimension length of about 10 microns or more. Typically particles have a maximum dimension of about 20-50 microns, and some particles are as small as 1-5 microns in length. Although it is preferred to use raw flake particles having an average maximum dimension of 20-50μ, larger particles up to 100μ in length can be used. However, larger flake particles can cause problems with surface distortion of the coating. Generally, the amount of flake particles required to provide the desired appearance effect depends on the density of the flakes and their shape. An important structural factor is the length-to-thickness ratio (aspect ratio). An increase in aspect ratio generally results in a decrease in flake density to obtain the same appearance. Aluminum flakes are normally present in dry powder or high solids coating compositions at concentrations ranging from about 0.05 to 10% and preferably from about 0.1 to 2% by weight of the coating composition. For conventional and aqueous coating compositions, flake concentrations typically range from 0.1 to 4%. Monoethylenically unsaturated silanes used in the treatment of aluminum flakes have the formula RSiX ₃ , where R is a monoethylenically unsaturated group bonded to a silicon atom in a thermally and hydrolytically stable manner, and
is a hydrolyzable group). The R group may be separated from the silicon atom by an alkyl chain. The silane is applied to the aluminum flake surface in a dilute liquid solution, ie, a solution containing about 0.2 to 5.0 weight percent silane. Solubility and stability of the silane in solution are important considerations. This is because silanes represent a variety of different chemical molecules and the solubility is expected to be different as well. The following is a general description of silanes. (1) Among the factors that determine the hydrolysis rate of silane, solution pH is generally the strongest. For most silanes, the maximum hydrolysis rate is between PH 3 and 5.
is achieved. Some silanes themselves carry catalysts in the form of hydrolysis by-products. (2) Over time, all aqueous silane solutions reach homopolymer equilibrium levels (silane monomers react together due to silicon functional groups to form siloxane polymers). The following conditions influence this equilibrium: (a) PH (a range of 4-5 is generally preferred for maximum monomer content) and (b) silane concentration. Some of these homopolymers rapidly lose water solubility as their degree of polymerization increases. A weak polymeric gel may form which is insoluble. It is generally desirable to maintain the silane as a monomer or dimer in order to preserve its coupling functionality. Preferred silanes used to treat aluminum flakes are: (1) Vinyltrimethoxysilane CH ₂ = CHSi(OCH ₃ ) ₃ (2) Vinyltrichlorosilane CH ₂ = CHSi(CL) ₃ (3) Vinyltriethoxysilane CH ₂ = CHSi(OC ₂ H ₅ ) ₃ (4 ) Vinyltris(β-methoxyethoxy)silane CH ₂ =CHSi(OCH ₂ CH ₂ OCH ₃ ) ₂ (5) γ-methacryloxypropyl-trimethoxysilane A preferred silane is #5 above. It is believed that the present invention improves the appearance of coating compositions. This is because the coated aluminum flakes have amine, hydroxy or epoxy pendant functional groups on the acrylic coating surface. These pendant functional groups can react with the polymer of the coating composition. Monoethylenically unsaturated silanes, such as gamma-methacryloxypropyl-trimethoxysilane, form a siloxane coating with pendant ethylenically unsaturated groups on the surface of the aluminum flakes. A mixture of acrylic monomers, initiators, and chain transfer agents can be added to the silanized flakes to allow the monomers to react on the surface of the aluminum flakes to form an acrylic coating. The type of monomer can be varied to create the desired type of reactive group on the surface. Acrylic monomers that can be used with acrylic monomers providing amine, hydroxy or epoxy groups are alkyl acrylates and alkyl methacrylates containing 1 to 12 carbon atoms in the alkyl group. Typical alkyl acrylates and alkyl methacrylates are methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, pentyl methacrylate, hexyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, lauryl methacrylate, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl Acrylate, hexyl acrylate, octyl acrylate, nonyl acrylate, lauryl acrylate, and others. Typical acrylic monomers that provide hydroxyl groups are hydroxyalkyl acrylates and hydroxyalkyl methacrylates, such as hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, and others. Glycidyl acrylate and glycidyl methacrylate are acrylic monomers that provide epoxy groups. Typical monomers that provide the amine group are alkylaminoalkyl acrylates and methacrylates,
Examples include diethylaminoethyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, dimethylaminoethyl acrylate, dipropylaminoethyl methacrylate, methylethylaminoethyl methacrylate, butylaminoethyl methacrylate, tertiary butylaminoethyl methacrylate, and others. Polymerization initiators and chain transfer agents are generally used to form acrylic coatings on the flakes. Typical initiators are azobis-(α,γ-dimethylvaleronitrile), benzoyl peroxide, tertiary butyl peroxypivalate, azobisisobutyronitrile, and others. Molecular weight can be controlled using typical chain transfer agents such as dodecyl mercaptan and mercaptoethanol. Mercaptoethanol is preferred for producing acrylic polymers with terminal hydroxy groups. The reaction for coating silane on aluminum flakes is performed using at least 100% of the amount of silane required to form a monolayer over the surface area of the flakes.
%, preferably 200-1000%, more preferably 300
Use ~400%. The amount of silane required is determined by first measuring the surface area of the aluminum flakes using conventional techniques, then determining the minimum surface area coverage of the silane to be used using conventional techniques, and then determining the coating of the aluminum flakes using conventional techniques. Determined using the desired percentage of the minimum amount of silane required. The surface area of aluminum flakes is usually 1 to 10
It is in the range of m ² /g. The minimum surface area coverage of the silane typically ranges from about 200 to 500 square ^meters per gram of silane, depending on the chemical structure and molecular weight of the silane molecule. The reaction is carried out for a sufficient time and at a temperature sufficient to coat the aluminum flakes with silane. Preferably its temperature is about 50-100
℃ and the time is 1-5 hours. Longer times are required at lower temperatures.
Most preferably the temperature is about 60°C and the time is about 1 hour. An acrylic coating is produced on the flakes using normal polymerization times and temperatures. in general
Temperatures of 50-150°C are used with polymerization times of 0.5-4 hours. It has been discovered that other treatments of aluminum flakes improve the appearance of coating compositions containing treated aluminum flakes to varying degrees. Dispersing aluminum flakes in polar solvents such as butyl cellosolve, ethyl cellosolve, cellosolve acetate, etc. is effective in improving the appearance of both dry powder and high solids coating compositions. Treating aluminum flakes with ammonium phosphate provides an improved appearance of the dry powder coating compared to formulations using conventional aluminum paste. This treatment consists of replacing the long chain organic acids commonly used to treat aluminum flakes with phosphate ions. This treatment removes from the surface of the aluminum flakes materials that are incompatible with the vehicle system and therefore cause an inferior appearance. The following example illustrates the invention. Example: Aluminum flake paste (“Silverline” SS-3199) washed with “Cellosolve” acetate in a 3-volume round bottom resin kettle (equipped with Teflon stirrer, nitrogen inlet, thermometer, reflux condenser and addition funnel) Mix together 186.6 g (AR, Silverline Manufacturing Company product) and 1000 ml of methyl "Cellosolve" acetate. 5 under slow nitrogen flow at 300 rpm.
Stir the mixture until complete dispersion is obtained for ~10 min. Gradually add gamma-methacryloxypropyltrimethoxysilane (A-174 silane, a product of Union Carbide Corporation) to this mixture.
Add 15.92g and 0.002g hydroquinone. The resulting slurry was stirred (300 rpm) at room temperature for 20 minutes, then gradually heated to 60 °C and
Hold time. Dimethylvaleronitrile (VAZO
52, DuPont product) and 10 ml of methyl cellosolve acetate. Then over 30 minutes, methyl methacrylate
4.11g, ethylhexyl acrylate 1.39g, hydroxyethyl acrylate 0.36g,
A solution of 0.036 g of "VAZO52" and 25 ml of methyl cellosolve acetate is added dropwise. After the addition is complete, maintain the temperature at 60°C for 20 minutes.
Cool to room temperature and wash the flake paste several times with methyl cellosolve acetate. The % solids content of the silane coated aluminum flake paste is 67.5±0.2%. ESCA of coated flake paste
(Electron Spectroscopy Chemical Analysis)
The analysis gives the following results.

【table】

Table: The resulting coated flakes were used in water-based acrylic coating compositions, acrylic powder coating compositions and acrylic high solids coating compositions. Each of the above compositions was applied to a primed steel substrate and baked using conventional methods. Finishes with good appearance and excellent metallic glamor were obtained in each case.

Claims (1)

[Scope of Claims] 1. Vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxysilane) in an amount of at least 100% of the amount necessary to cause the aluminum flakes to form a monolayer on their surface area. and γ-methacryloxypropyltrimethoxysilane and reacted with a functional group-containing acrylic monomer to form an acrylic top coat on the flakes. A water-based coating composition or a high solids coating composition containing improved aluminum flakes, comprising using coated aluminum flakes that have been coated with aluminum flakes. 2. The composition according to item 1 above, wherein the silane is γ-methacryloxypropyltrimethoxysilane. 3 The aluminum flakes have a surface area of 1 to 10 m ² per gram of aluminum flakes, the silane has a minimum surface area coverage of 200 to 500 m ² per gram of silane, and the silane forms a monolayer on the aluminum flakes. The composition of claim 1, wherein the composition is present in a concentration of 200 to 1000% based on the minimum amount of silane required to form. 4 The acrylic monomer is glycidyl acrylate,
The composition according to item 1, which is an alkyl acrylate or alkyl methacrylate in combination with glycidyl methacrylate, hydroxyalkyl acrylate, hydroxyalkyl methacrylate, alkylaminoalkyl acrylate or alkylaminoalkyl methacrylate, or a mixture thereof. 5 The silane is γ-methacryloxypropyltrimethoxysilane, the aluminum flakes have a surface area of 1 to 10 m2 per gram of aluminum flakes, and the silane has a surface area of 200 to 500 ^m2 per gram of silane.
m ² and the silane is present in a concentration of 200-1000% based on the minimum amount of silane required to form a monolayer on the aluminum flake, and the acrylic monomer 2. The composition according to item 1, wherein the composition is methyl methacrylate, ethylhexyl acrylate and hydroxyethyl acrylate.