KR100939008B1 - Coating composition for metal substrates - Google Patents

Abstract

The present invention relates to a composition for coating a metal substrate for manufacturing and overcoating,

The binder comprises an aqueous silica sol having a molar ratio of SiO ₂ / M ₂ O, where M represents the entire alkali metal and ammonium ion, at least 6: 1, and the ratio of the pigment volume concentration to the critical pigment volume concentration of the composition. Is less than one.

Description

Coating composition for metal substrates {COATING COMPOSITION FOR METAL SUBSTRATES}             

The present invention relates to coating compositions that can be used for coating metal substrates such as steel substrates. In particular, the present invention relates to coating compositions for semi-finished steel products that are manufactured by a heat-intensive method and are overcoated. The semi-finished steel products are used in other large structures such as shipbuilding industry and petroleum production platforms and include various steel parts used for steel plates, bars, girders and aggregates with a thickness of 6 to 75 mm. The most important heat-intensive method is the welding method; Virtually all of the semi-finished steel products are welded. Other important heat-intensive methods include cutting methods such as oxygen-fuel cutting, plasma cutting or laser cutting, and thermal shaping in which the steel bends into shaped bodies during heating. The steel products are often exposed to the climate during construction and during storage during construction, which are commonly referred to as "shop primers" to avoid corrosion of the steel that occurs before steel coatings, such as ships, before full coating of anticorrosive paint. It is coated by a coating called "or" pre-construction coating ", which solves the problem of overcoating or removing steel corrosion products. In most large shipyards, shop primer as one of several treatments performed on a manufacturing line that is preheated, shot-blasted or grit-blasted, shop primed, and passed through a drying booth to remove millscale and corrosion products. Is applied. In addition, shop primer may be applied by a trade coater or steel feeder before the steel is transported to the shipyard or other structural location.

Although the main purpose of shop primers is to provide temporary corrosion protection in the structure, it is preferred by ship manufacturers that shop primers can remain on steel during and after manufacture without having to be removed. Thus, the steel coated by the shop primer needs to be weldable without removing the shop primer, and with the protective coating commonly used on ships and other steel structures, with good adhesion between the primer and the coating to be subsequently applied. It needs to be overcoated by kind. The shop primed steel should be weldable without a significant detrimental effect on weld quality or weld throughput, and the shop primer should be sufficiently sufficient to retain the corrosion resistance in the area heated during welding or fairing the opposite side of the steel. It must be heat resistant.

Commercially successful shop primers today are solvent borne coatings based on prehydrolyzed tetraethyl orthosilicate binder and zinc powder. The coating contains large amounts of about 650 g of volatile organic solvent per liter to stabilize the paint binder and allow it to be applied to the product as a thin film about 20 microns thick. Emissions of volatile organic solvents can be harmful to the environment and are regulated by legislation in many countries. There is a need for shop primers that emit no or volatile organic solvents at all. Examples of such coatings are described in US Pat. No. 4,888,056 and JP-A-7-70476.             

JP-A-6-200188 is associated with shop primer coatings and mentions the possibility of using binders of the aqueous alkali silicate salt type. Coatings comprising aqueous alkali metal silicates and zinc powders are presented in GB-A-1226360, GB-A-1007481, GB-A-997094, US-A-4,230,496 and JP-A-55-106271. Alkali silicate binders for anticorrosive coatings are also mentioned in US-A-3,522,066, US-A-3,620,784, US-A-4,162,169 and US-A-4,479,824. EP-A-295 834 mentions a coating material containing a mixture of alkali metal silicates with small amounts of colloidal silica, Al ₂ O ₃ powder as filler, and metal powder as toughening agent. The inventors have found that primer coatings based on aqueous alkali silicate binders containing zinc powder can provide adequate corrosion protection and cause the steel surfaces they coat to be welded, but cause problems when overcoated. Aqueous silicates contain large amounts of alkali metal cations required to maintain the silicate in aqueous solution, and the ions are still present in the coating after drying. The inventors have found that blistering (local peeling of the coating) occurs when the primer coating having such a large amount of alkali metal ions is overcoated with a conventional organic coating and then impregnated in water. The inventors conducted a test showing that the problem could be reduced by exposing the coating to the weather outside for some time after applying the shop primer, or cleaning the coating before overcoating. However, these methods are not suitable for use in today's high-productivity shipyards.

Aqueous silica sols with very low alkali metal ion contents are commercially available, but most conventionally based sol coatings usually exhibit very poor (initial) film strength in terms of adhesion, cohesion, hardness and wear resistance and water resistance. Have Bad physical properties of the coating make it prone to damage during handling or further processing. Because of this, repairing the coating would be potentially costly. US-A-3,320,082 adds water-immiscible organic amines, GB-A-1541022 adds water-soluble acrylamide polymers, and GB-A-1485169 adds quaternary ammonium, suggesting improvements to silica sol coatings. Or alkali metal silicates are added, and in JP-A-55-100921 clay materials and / or metal oxides such as Al ₂ O ₃ , and aluminum biphosphate and / or ethyl silicate are added. However, the coating did not yield similar physical properties as the coating based on alkali metal silicates. Coatings based on silica sol exhibit low levels of blistering when overcoated / impregnated. Even with low water soluble salt content and osmotic pressure, blistering can still occur because of its poor physical properties because the coating exhibits low resistance to initiation / growth of blistering.

There is a need for a low alkali metal ion content aqueous shop primer with improved adhesion to substrates and improved film strength in view of the above properties for inhibiting blistering initiation and growth. In addition, there is a need for an aqueous shop primer without blistering that indicates the rapid development of physical coating properties after application, in order to be able to handle and further process the substrate without risk of damaging the coating.

It has been found that the ratio of pigment volume concentration (PVC) to critical pigment volume concentration (CPVC) has a significant effect on film properties. In addition, the rate of property development of the film can be adjusted by changing the PVC / CPVC ratio.

Pigment volume concentration (PVC) is the volume percentage of pigment in anhydrous paint film. Critical Pigment Volume Concentration (CPVC) is commonly defined as the pigment volume concentration of the binder sufficient to provide a fully absorbed binder layer on the pigment surface and fill all gaps between particles in the hermetically filled system. Critical pigment volume concentrations can be measured by wetting the dry pigment with linseed oil sufficient to form a tacky material. The method yields a value known as "oil absorption" from which a critical pigment volume concentration can be calculated. Methods for measuring oil absorption are described in British Standard 3483 (BS3483).

US-A-3,721,574 discloses a coating containing a mixture of a small amount of colloidal silica and alkali metal silicate, preferably the colloidal silica being modified Al ₂ O ₃ . Also mentioned are coatings containing small amounts of colloidal silica and alkali metal silicates and zinc dust. In zinc-modified coatings, mixtures of alkali metal silicates and small amounts of non-modified colloidal silica are preferably used. In the examples, zinc powder is used in extremely high proportions. This results in a film containing about 95% by weight of zinc in the dried coating. However, this high level of zinc content has a detrimental effect on the weldability of the coating. Thus, the coating is not suitable for use as a shop primer for semi-finished steel products that are later shaped or welded and overcoated. US-A-3,721,574 does not refer to the PVC / CPVC ratio of coatings that are neither zinc-free coatings nor zinc-containing coatings. The document does not disclose that the PVC / CPVC ratio has a significant effect on the film development rate and film properties.

WO 00/55260 discloses coating compositions comprising silica or silicate binders and zinc powders and / or zinc alloys. The binder has a SiO ₂ / M ₂ O molar ratio, where M represents the total of at least 6: 1 alkali metal and ammonium ions. The document discloses that the pigment volume concentration of the coating should be at least equal to the critical pigment volume concentration. The inventors have found that the film properties of the coating composition and the rate of occurrence of the properties of the film can be improved by using the coating composition according to the invention when the binder comprises silica or silicate particles having an average size of greater than 10 nm.

Compositions according to the invention which can be used to coat metal substrates for production and overcoating have a PVC / CPVC ratio of less than one. The coating comprises an aqueous silica sol as an essential component and a silica binder comprising a small amount of alkali metal silicate as an optional component, wherein the silica and / or silicate particles in the composition have an average size of greater than 10 nm. The binder has a SiO ₂ / M ₂ O molar ratio of at least 6: 1, wherein M represents the entirety of the alkali metal and ammonium ions. In the use of the present invention, a small amount of alkali metal silicate means that the weight ratio of alkali metal silicate to silica sol in the composition is 0.5 or less, preferably 0.25 or less, more preferably 0.1 or less.

It has been found that improved initial coating properties can be obtained using coating materials having PVC of 35% to 65%, more preferably 40% to 55%. In coatings having less than 35% PVC and comprising only zinc as the pigment, zinc is not sufficient to provide effective corrosion protection during outdoor exposure if more than 6 months of protection is required. When using a coating with a low zinc level of 10 to 40%, one or more secondary corrosion inhibitors are added, or when a conductivity enhancer such as di-iron phosphide is added, the acceptable corrosion protection is Can be obtained.

The primer coating preferably contains zinc powder having a volume average particle size of 2 to 12 microns, most preferably the zinc powder is a commercially obtainable product as zinc powder having an average particle size of 2 to 8 microns. The zinc powder protects the steel by a galvanic mechanism and forms a protective layer of zinc corrosion product, improving the corrosion protection provided by the coating.

All or part of the zinc powder may be replaced with a zinc alloy. The amount of zinc powder and / or alloy in the coating is usually at least 10% and may account for 90% by volume of the coating, based on the dry film. The zinc powder and / or alloy may be substantially the entire coloring of the coating, or may comprise up to 70% by volume of the coating, for example 25 to 55% by volume, based on the dry film, the coating also comprising US- Auxiliary corrosion inhibitors such as molybdate, phosphate, tungstate or vanadate as described in A-5246488, ultrafine titanium dioxide and / or zinc oxide and / or fillers such as silica, as described in KR 8101300, It may also contain calcined clay, alumina silicate, talc, barite or mica. The amount of zinc powder and / or alloy in the coating is 35 to 60%, more preferably 40 to 50%.

Other pigments may be used in combination with the zinc based pigments. Examples of such non-zinc pigments include conductivity enhancers such as di-iron phosphide (Ferrophos ™), mica iron oxide, and the like. The use of such conductive non-zinc pigments can reduce zinc levels while maintaining effective corrosion protection. In order to obtain optimum coating properties, it is desirable that the enhancer be sufficiently dispersed in the coating composition. The type and size of enhancer used can be adjusted to obtain a suitable dispersion. For example, an average particle size of 3 μm or less, preferably 2 μm or less may be used when the enhancer pigment Satintone (trade name) (manufactured by Lawrence Industries) is selected.

Most preferably the binder is based on an aqueous silica sol. The sol may use the Akzo Nobel trademark "Bindzil" or the DuPont trademark "Ludox", but their related literature emphasizes that prior grade colloidal silica is not a good film former. Doing. Various grades of sols having various colloidal silica particle sizes and containing various stabilizers are available. The particle size of the colloidal silica may be in the range of 10 to 100 nm; Preference is given to particles in the lower range of this range, such as from 10 to 22 nm. In the composition according to the invention, it is more preferred that the binder has colloidal silica particles having an average particle size of 10 nm to 20 nm, more preferably 10 nm to 16 nm.

Silica sol is 10: 1 or more, more preferably 25: 1 or more, more preferably 50 more than 1 or more SiO ₂ / M ₂ O molar ratio has, to 200: 1 can have more than SiO ₂ / M ₂ O mole ratio have. It is also possible to use mixtures of two or more silica sols having different SiO ₂ / M ₂ O molar ratios, with a SiO ₂ / M ₂ O molar ratio of at least 25: 1. The sol can be stabilized by alkali, for example sodium, potassium or lithium hydroxide or quaternary ammonium hydroxide, or by water-soluble organic amines such as alkanolamines.

The silica sol may be kneaded with small amounts of alkali metal silicates, for example lithium silicate, sodium-lithium silicate or potassium silicate, or may be kneaded with ammonium silicate or quaternary ammonium silicate. Other examples of suitable sol-silicate blends or mixtures can be found in US Pat. No. 4,902,442. The addition of alkali metal or ammonium silicate may improve the initial film-forming properties of the silica sol, but the amount of alkali metal silicate is at least 6: 1, preferably at least 8: 1 and most preferably at least 15: 1. It must be low enough to have a molar ratio of SiO ₂ / M ₂ O. For the purposes of the present invention, small amounts of alkali metal silicate means that the weight ratio of alkali metal silicate to silica sol in the composition is 0.5 or less, preferably 0.25 or less, more preferably 0.1 or less.

Silica sol has a low agglomeration level. This can be measured by assuming the S-value of the sol. S-values are calculated from Iler & Dalton in J. Phys. Chem. Vol. 60 (1956), pp. Can be measured and calculated as described in 955-975. Silica content, volume of dispersion phase, density and viscosity of the silica sol influence the S-value. Low S-values may be considered to indicate high particle agglomeration or internal-particle attraction. The silica sol used in the coating composition according to the invention may have an S-value of 20-100%, preferably 30-90%, even more preferably 50-85%.

Silica sols with low levels of aggregation have been found to provide very good results in the systems and methods described in WO 00/55260, WO 00/55261, WO 02/22745, WO 02/22746. In such systems and methods, the silica sol may have an S-value of 20-100%, preferably 30-90%, even more preferably 50-85%.

The silica sol may optionally or additionally contain dissolved or dispersed organic resin. The organic resin is preferably a latex such as styrene butadiene copolymer latex, styrene acrylic copolymer latex, vinyl acetate ethylene copolymer latex, polyvinyl butyral dispersion, silicon / siloxane dispersion, or acrylic latex dispersion. Examples of suitable latex dispersions that can be used include XZ 94770 and XZ 94755 (both manufactured by Dow Chemicals), Airflex® 500, Airflex EP3333 DEV, Airflex CEF 52 and Flexcryl® SAF34 ( All made by Air Products), Primal (Primal®) E-330DF and Primeal MV23 LO (both Rohm and Haas) and Siles (trade name) MP42E, Siles M50E and SLM 43164 (all Wacker Chemicals) There is). Water soluble polymers such as acrylamide polymers can be used but are less preferred. The organic resin is used at 30 wt% or less, more preferably 10-20 wt%, based on the solid binder. A large amount of organic resin can then cause weld porosity during welding. The addition of the organic resin was found to improve the adhesion / cohesion measured in the cross hatch test.

Alternatively, the silica sol may contain an organic component containing a functional group such as an amino group, an epoxide group or an isocyanate group and a silane coupling agent containing an alkoxysilane group. The silane coupling agent is preferably an aminosilane, such as γ-aminopropyl triethoxy silane or γ-aminopropyl trimethoxy silane, or a partial hydrolyzate thereof, but preferably with γ-glycidoxypropyl trimethoxy silane. The same epoxy silane may be used. The silane coupling agent is present up to 30 wt%, for example 1-20 wt%, based on the solid binder.

The binder of the primer coating may further comprise an aqueous solution of an alkali metal or ammonium silicate stabilized by a silonate substituted by one or more anionic groups having a pKa lower than silicic acid, such as carboxylate groups or sulfonate groups. The binder is preferably a solution having a SiO ₂ / M ₂ O molar ratio of 8: 1 to 30: 1 and a pH of 7 to 11.5, prepared by lowering the pH of the solution of silicate and silicate by cation exchange. Thus, the siliconates may be added at a relatively low level, for example, 1: 2 to 1:20, relative to conventional 3.9: 1 SiO ₂ / K ₂ O alkali silicates. Thereafter, the solids are reduced to improve the ease of treatment and further improve the stability. In this step, the solution has a pH of 12-12.5. The solution is ion-exchanged using standard ion-exchange resins. K ⁺ ions are replaced by H ⁺ ions, reducing both the alkali content and the pH of the binder. Without the presence of siliconates, the silicates are gels when the pH is reduced. A clear stable solution with a pH of 8 or less was obtained. The binder obtained has a SiO ₂ / K ₂ O molar ratio in the range of 8-20: 1 and can be concentrated to increase the solid if desired. The binder is a clear and stable solution and stable in the presence of zinc, but coatings based on the ion-exchanged binders have a relatively poor film strength compared to coatings based on alkali silicate binders.

Preferably a binder having a pH of 9 to 11.5, more preferably of 9.5 to 11 is used. Without being bound by any theory describing the pH effect on film properties, it has been found that increasing the pH increases the amount of silica ions and / or silicate ions in solution. This appears to be potential for performing in situ gel strengthening after applying the coating composition. In addition, pH adjustment can have a minor pot life-extension effect. When a commercially available silica sol is used, a high pH sol may be selected and / or the pH of the sol may be adjusted. The pH can be adjusted by adding a pH-affecting pot life extender or dilute sulfuric acid, such as dimethyl amino ethanol (DMAE), or by adding sodium hydroxide. For example, the pH of commercially available 22 nm silica sol is usually about 8.5-9. Increasing the pH of the sol to 10-11 significantly improves the rate of coating character development.

The solids content of the primer coating is usually at least 15% by volume and preferably 20 to 35% by volume. The volume solids content is a theoretical value calculated based on all components present in the coating composition. The coating is easily applied by a spray applicator, in particular a conventional coating applicator such as a vacuum spray or high volume low pressure (HVLP) spray applicator to have a dry film thickness of less than 40 microns, preferably 12 to 25-30 microns. It has a viscosity so that it can be provided.

Optionally, the coating composition may be further additives well known to those skilled in the art, for example thixotropes and / or rheology modifiers (organic clays, xanthan gum, cellulose thickeners, polyether urea polyurethanes, (pyrogenic) silicas). , Acrylics, etc.), antifoams (especially where latex denaturants are present), and optionally secondary pot life extenders such as chromate (eg sodium dichromate) or tertiary amines (eg triethylamine or dimethyl Aminoethanol). Preferred thixotropes and / or rheology modifiers are Benton® EW (manufactured by Elementis), which is sodium magnesium silicate (organic clay), Benolite® (manufactured by WH), a hydrous aluminum silicate, hydrated Laponite (trade name) RD (manufactured by Rockwood), a sodium magnesium lithium silicate, HDK (trade name) -N20 (manufactured by Wacker Chemie), a pyrogenic silica, and Rheolate (trade name) 425, a proprietary acrylic dispersion. (Made by Elementis) is included. Preferred antifoaming agents include Foamaster® NDW (manufactured by Cognis), Tego Foamex® 88 (manufactured by Tego Chemie) and Dapro® 1760 (manufactured by Elementis). . It has been found that other compounds that may be present in the coating composition for other reasons may also act as secondary pot life extenders. For example, the addition of molybdenum-based pigments or styrene butadiene latexes may result in minor pot life extension. Preferred secondary pot life extenders are tertiary amines that impart chromate-free selectivity for pot life extension.

The longer the pot life, the more the system was found to contain alumina. In the present application, the concentration of alumina in the coating composition is given as weight percent of Al ₂ O ₃ based on the silica sol or silicate particles present in the composition. In order to obtain optimal properties, it is preferable to use an alumina-stabilized silica sol, such as an alumina-modified silica sol. In an alumina-modified sol, the surface of the particles is modified by sodium aluminate that is bound to the particles. Preferably, the silica sol is modified with 0.05 to 2.5% by weight of alumina, more preferably 0.05 to 2.0% by weight of alumina.

Usually, the coating system is provided as a two (or more) component system in which the components are mixed as a whole before applying the coating. It is also possible to prepare a coating composition prior to applying the coating by adding all the components of the coating composition just before applying and mixing throughout. The method may also mean on-line mixing of the components in the coating composition. The method is particularly suitable for coating compositions with limited pot life.

The generation of properties can be accelerated by a post-treatment method in which the substrate can be treated with a solution that increases the film strength of the primer coating. Preferably, the metal substrate is primer coated by the coating according to the invention, which is then treated with a film strengthening solution after the primer coating has been dried to the extent of the touch drying. The solution which increases the film strength of the primer coating can usually be an aqueous solution of an inorganic salt or a solution of a material having reactive silicon-containing groups.

The development of properties can be accelerated by optionally impregnating the post-treated coating substrate in water or by conditioning the selectively post-treated coating substrate in an atmosphere having a relative humidity of at least 50%, preferably at least 80%. Can be. Preferably, the metal substrate is primer coated with the coating according to the invention, and after the primer coating has been dried to the degree of dry touch, it is impregnated in water or has an atmosphere with a relative humidity of at least 50%, more preferably at least 80%. Is optionally maintained within. More preferably the metal substrate is primer coated by the coating according to the invention, after which the primer coating is dried to the extent of the dry touch, which is first treated with a film strengthening solution and then impregnated in water or at least 50%, more Preferably it is optionally maintained in the atmosphere with a relative humidity of at least 80%.

If rapid drying is not an issue, the post-treated coating may be dried at low relative humidity, such as 25-50% relative humidity. The generation of coating properties will proceed less quickly, but eventually good coating properties are obtained.

In a preferred embodiment, the coating composition according to the invention is an aqueous shop primer for the coating of steel substrates which are produced and overcoated, said composition having a solids content of 20-40% by volume and pigment volume relative to critical pigment volume concentrations. The ratio of concentrations is less than 1 and the composition comprises the following components:

An aqueous silica sol binder having a SiO ₂ / M ₂ O molar ratio of at least 6: 1 and a pH of 9.5 to 11, wherein M represents the total of the alkali metal and ammonium ions, and optionally the average size of the alumina modified silica particles Greater than 10 nm and less than or equal to 16 nm),

Zinc powders, zinc alloys, or zinc powders and zinc alloys with an average particle size of from 2 μm to 12 μm, accounting for 10% to 55% by volume of the coating, based on the dry film,

0-35% by weight of organic resins, based on solid binders,

0-30% by weight of silane coupling agent based on the solid binder,

Optionally non-zinc pigment (s), and

-Optional pot life extender.

The invention will be explained with reference to the following examples. They are intended to detail the invention and are not to be considered as limiting the scope of the invention in any way.             

The compounds used as starting materials in this example have the following raw materials:

Ludox SM concentration 30 wt%, average particle size 7 nm, SiO ₂ / Na ₂ O molar ratio 50: 1, DuPont, silica sol with pH 10.3

Ludox HS-40 concentration 40 wt%, particle size 12 nm, silica sol with SiO ₂ / Na ₂ O molar ratio 95: 1, DuPont, pH 9.8

Ludox TM-40 concentration 40 wt%, average particle size 22 nm, SiO ₂ / Na ₂ O molar ratio 225: 1, DuPont, pH 8.8 silica sol

Bindzil 40/170 concentration 40% by weight, average particle size 20nm, SiO ₂ / Na ₂ O molar ratio 160: 1, silica sol made by Akzo Nobel (Eka Chemicals), pH 9.4

Nyacol concentration 40% by weight, average particle size 16 nm, SiO ₂ / Na ₂ O molar ratio 105: 1, silica sol from Akzo Nobel (Eka Chemicals), pH 9.8

Niacol Alumina-Modified Al Niacol, pH 9.9

XZ 94770 50% by volume solids styrene / butadiene organic latex from Dow Chemicals

Minex 20 sodium potassium aluminum silicate extender pigment with average particle size of 2.95 μm, manufactured by North Cape Minerals

Zinc Powder 7㎛ Average Particle Size Metal Powder, Made by Trident Alloys

Molywhite 212 calcium zinc molybdate, anticorrosive pigment with a particle size of 4.1 μm, manufactured by Sherwin Williams

Benton EW sodium magnesium silicate thixotropes, made by Elementis

In this experimental example, silica sol having the same pH as above was used unless otherwise specified. When the pH is different from the above, pH adjustment was performed as follows:

(Iii) pH 9 was obtained by adding dilute sulfuric acid having a pH of 1.5 to the stirred sol.

(Ii) pH 10 was obtained by adding sodium hydroxide having a pH of 14 to the stirred sol.

(Iii) pH 11 was added to the stirred sol to give pH 11.

Example 1

Several compositions were prepared having a solids concentration of about 28% by volume to determine the effect of varying PVC in a coating comprising 12nm silica sol and having 40% by volume zinc in the dry film.

The composition used in Example 1c was prepared from the following ingredients.

For Examples 1a, 1b, 1d, and 1e, the PVC was changed by adding Mollywhite 212 and Minex 20 to the composition of Example 1c, or by removing Mollywhite 212 and Minex 20 from the composition of Example 1c. Were prepared.

The primer coating obtained above was applied to a 15 cm × 10 cm steel panel with a dry film thickness of 15-20 μm at 35 ° C. and 30% relative humidity. The primers were dried at 23 ° C., 60% RH and tested for their physical properties 1 hour and 1 day after application. The test results are shown in Table 1.

Example 2

To measure the effect of latex XZ 94770 in a coating comprising 12 nm silica sol and 40% zinc in a dry film, several compositions were prepared having a solids concentration of about 28% by volume. Shop primer compositions similar to Examples 1a-1f were prepared. The latex level in all compositions prepared for Example 2 was 20% by volume based on the silica sol.

The composition used in Example 2c was prepared from the following ingredients.

The primer coating obtained above was applied to a 15 cm × 10 cm steel panel with a dry film thickness of 15-20 μm at 35 ° C. and 30% relative humidity. The primers were dried at 23 ° C., 60% RH and tested for their physical properties 1 hour and 1 day after application. The test results are shown in Table 2.

The results in Table 2 compared to the results in Table 1 show that film properties can be improved by adding latex to the composition. Coating properties occurred fastest in PVC 50-55%.

Example 3

In order to determine the effect of raising the latex level in the coating with 12 nm silica sol and having 40% zinc in the dry film, several compositions with a solids concentration of 28% by volume were prepared. The primer coating had a pigment volume concentration of 50%, which is 0.72 times the critical pigment volume concentration.

The composition used in Example 3a was prepared from the following ingredients.

For Examples 3b-3d, the composition was prepared by reducing the amount of silica sol and adding increasing amounts of latex XZ 94770.

Application and curing conditions were the same as used in the above examples. The physical properties of the primers were tested 1 hour and 1 day after application. The test results are shown in Table 3. The amount of silica sol and latex XZ 94770 refers to the volume percentage in the dry film.

Example 4-7

Several compositions were prepared having a sol size of at least 12 nm and a pigment volume concentration of 50% (Λ = 0.72). All compositions contained 40% zinc, 5% Molliwhite 212, 5% Minex 20, and 20 volume% latex XZ 94770 based on silica sol. In addition, Example 4 ^{1 which} is a comparative example was implemented with 70% PVC ((lambda = 1.06).

Application and curing conditions were the same as used in the above examples. The test results are shown in Table 4.             

This example shows that for 16 nm sol the coating properties can be generated quickly at 50-55% of PVC. In addition, the present examples show that the coating properties deteriorate as the sol size increases.

Examples 8 and 9

Using the sol kneader, two primer coatings were prepared having a solids concentration of 28% by volume. Both primer coatings have a pigment volume concentration of 50%, which is 0.72 times the critical pigment volume concentration.

The primer coating used in Example 8 was prepared with the following components, and a coating having an average sol size of 10 nm was obtained.

The primer coating used in Example 9 was prepared with the following components, and a coating having an average sol size of 10 nm was obtained.

The resulting primer coating was applied to a 15 cm x 10 cm steel panel with a dry film thickness of 15-20 μm and dried at 35 ° C., 30% RH. Within 1 hour, prime substrates were stored in 60% RH. The physical properties of the coatings were then tested for 1 hour and 1 day after application. The test results are shown in Table 5.

The results in Table 5 show that good film properties can be obtained using the sol blend.

Example 10-13

Several compositions were prepared with varying pH and having a pigment volume concentration of 50% (Λ = 0.72). All compositions contained 40% zinc, 5% Molliwhite 212, 8% Minex 20, and 20% by volume latex based on the silica sol.

The application and curing conditions used were the same as those used in Example 1. Test results are shown in Tables 6, 7, 8 and 9.             

In Table 6-9, it was evident that reducing the pH of the sol having an average particle size of 12-20 nm adversely affects the development of coating properties. On the other hand, increasing the pH of the 22 nm sol improves the coating properties (rate of occurrence).

Claims (16)

A composition for coating a metal substrate to be manufactured and overcoated, The composition comprises a silica binder; The ratio of pigment volume concentration to critical pigment volume concentration of said composition is less than 1; The binder comprises an aqueous silica sol, with or without an alkali metal silicate, and wherein the average size of the silica, silicate particles, or silica and silicate particles is greater than 10 nm; And Coating composition, characterized in that the molar ratio of SiO ₂ / M ₂ O (where M represents the entire alkali metal and ammonium ion) of 6: 1 or more. The method of claim 1, The coating composition, characterized in that the pigment volume concentration is 40% to 55%. The method according to claim 1 or 2, The binder is a coating composition, characterized in that the silica sol having a SiO ₂ / M ₂ O molar ratio of at least 25: 1. The method according to claim 1 or 2, The binder comprises colloidal silica particles having an average particle size greater than 10 nm and no more than 22 nm. The method of claim 4, wherein And the binder comprises colloidal silica particles having an average particle size greater than 10 nm and no greater than 16 nm. The method of claim 5, wherein Coating composition, characterized in that the pH of the aqueous silica sol is in the range of 9.5 to 11. The method according to claim 1 or 2, The coating composition further comprises 0% to 30% by weight of an organic resin based on the solid binder. The method of claim 7, wherein The coating composition further comprises 10% to 20% by weight of organic resin based on the solid binder. The method according to claim 1 or 2, The binder comprises an alumina surface-modified aqueous silica sol. The method of claim 9, The binder comprises 0.05% to 2.5% by weight of alumina (calculated as the weight percentage of Al ₂ O ₃ ) based on the silica sol particles in the composition. The method according to claim 1 or 2, Coating composition, characterized in that the water-based shop primer (water based shop primer). The method according to claim 1 or 2, The coating composition further comprises zinc powder, zinc alloy, or zinc powder and zinc alloy. An aqueous shop primer for coating a steel substrate to be manufactured and overcoated, The composition constituting the aqueous shop primer has a solids content of 20% by volume to 40% by volume, and the ratio of the pigment volume concentration to the critical pigment volume concentration is less than 1, the following components a), b), c) and d ) Or comprising the following components a), b), c), d) and e) or comprising the following components a), b), c), d) and f), or Aqueous shop primers comprising b), c), d), e) and f): a) an aqueous silica sol binder having a SiO ₂ / M ₂ O molar ratio of at least 6: 1 and a pH of 9.5 to 11, wherein M represents the total of the alkali metal and ammonium ions, and the average of the alumina modified or unmodified silica particles The size is greater than 10 nm and no greater than 16 nm); b) zinc powder, zinc alloy, or zinc powder and zinc alloy with an average particle size of 2 μm to 12 μm, accounting for 10% to 55% by volume of the coating, based on the dry film; c) 0% to 35% by weight of organic resin based on the solid binder; d) 0% to 30% by weight of the silane coupling agent based on the solid binder; e) non-zinc pigment (s); And f) pot life extenders; As a primer coating method of a steel substrate, A method for coating a primer on a steel base, characterized in that the metal is primer coated with the coating composition according to claim 1 prepared using a silica sol having a pH adjusted from 9.5 to 11. As a primer coating method of a steel substrate, The metal is primer coated with the coating composition according to claim 1; And The primer coating method of drying a steel substrate, characterized in that after drying to the touch dry (touch dry) can be treated with a film reinforcement solution. As a primer coating method of a steel substrate, Primer coating the metal with the coating composition according to claim 1; And And drying the primer coating to a dry extent to the touch and then impregnating the coated substrate in water, or alternatively, maintaining the primer coating in an atmosphere having a relative humidity of at least 50%.