RU2778792C2 - Water-based primer - Google Patents

Abstract

FIELD: building materials.

SUBSTANCE: invention relates to primers for metal surfaces. Water-based primer is proposed, containing: (A) polysiloxane sol, (B) from 0.1 to 10% by wt. of water-soluble zinc salt with solubility in deionized water of at least 0.5 g/l at 25°C, and (C) at least one anti-corrosion pigment. In this case, the specified polysiloxane sol is sol obtained by a method including: (i) hydrolysis of at least one alkoxysilane with bis-amino-functional groups or alkoxysilane with an epoxide functional group; (ii) interaction of the resulting hydrolysis product with itself, with at least one optionally hydrolyzed alkylalkoxysilane or with at least one optionally hydrolyzed alkoxypolysiloxane with an amine functional group. A set for the production of primer, a method for protection of metal substrate from corrosion, using the specified primer, and metal substrate covered with cured primer are also proposed.

EFFECT: proposed primer quickly dries and imparts the surface improved corrosion resistance, is easy-to-use due to the balance of water resistance and stability during storage.

14 cl, 1 tbl, 4 ex

Description

WATER-BASED PRIMER

The present invention relates to a novel primer composition for application to substrates such as steel. In particular, the present invention relates to a primer composition comprising a polysiloxane sol, a water-soluble zinc salt, and an anti-corrosion pigment. The primer of the present invention is fast curing, abrasion resistant, low in volatile organic compounds (VOC) and, most importantly, has early water resistance. In addition, the primer preferably has good anti-corrosion properties, fast curing, low VOC content, and good abrasion resistance. Factory primers are preferred. The primer can also be coated with additional coats without significant pre-treatment and without loss of adhesion between coats.

BACKGROUND OF THE INVENTION

Solvent-based primer systems are known. However, with increasing attention to environmental issues, there is a strong desire to develop improved technology that would enable the use of water-based coating systems as primers and avoid solutions using organic solvents. In this direction, the leading water-based primer technology is based on alkali metal silicates.

Falberg (US5580371) provided an example of a zinc-containing primer providing a durable corrosion resistant coating combined with suitable weldability. The primer contains zinc, iron phosphide and an aqueous solution of potassium silicate.

More recently, US6468336 has proposed a silicate based shop primer containing zinc, mica iron oxide and silicate.

Therefore, water-based shop primers based on alkali metal silicate binders are well known in today's market, and usually have many of the features required for a primer, especially for shop primer, such as low volatile content, short drying time, weldability, and so on. . However, water-based factory primers containing alkali metal silicates suffer from one major problem. Water-based shop primers containing alkali metal silicates are based on sodium, potassium or lithium silicate binders, which in aqueous solution have a very high pH, typically in the pH range of 11 - 12. A high pH on the surface of the substrate will cause the next coat, usually an epoxy type paint, will lose adhesion and blister when the system is exposed to water. Any steel primed with an alkali metal silicate shop primer should either be completely stripped of the primer or rinsed thoroughly and repeatedly with fresh water prior to topcoating to avoid this problem.

In addition, alkali metal silicates require special manufacturing and application equipment in which all parts in contact with the wet paint must be made from non-metallic materials.

There is a significant need to develop new water-based primers not based on alkali metal silicates.

It is particularly desirable to provide a primer that meets these requirements while also drying quickly even under high humidity conditions. Under some conditions, it may be unavoidable that the primed article is exposed to high humidity.

The present inventors have provided a very low VOC, water-based primer that is diluted with water and dries quickly to provide water resistance. A further advantage of the present invention is a factory primer having excellent weldability with a minimum of pores, welding spatter and welding soot, excellent abrasion resistance, over which most paints can be applied directly. The primer also resists weathering, water, chemicals and solvents and is suitable for application with conventional equipment such as airless spray.

The primer is based on an aqueous polysiloxane binder combined with a water soluble zinc salt, and may also contain an anti-corrosion pigment. Surprisingly, it has been found that a certain combination of the components specified in claim 1 of the claims can give a composition that satisfies all the requirements for a primer, especially for a shop primer, in particular regarding drying time, water and chemical resistance, abrasion resistance and applicability. over the primer of new paint layers without the need to remove or rinse the primer multiple times.

The polysiloxane binder for use in a primer according to the present invention is not new and is described inter alia in US2011/0268899 and US2014/0106176. However, these documents are primarily concerned with the structure of the binder and not with specific primer compositions having advantageous characteristics. The authors of the present invention complement the ideas of these documents by defining specific primers that are extremely useful in the art, in particular as shop primers.

It is known that certain compounds, such as zinc oxide, have sometimes been added to primers as corrosion inhibitors. What is new is the understanding that the addition of certain water-soluble zinc salts results, among other things, in fast drying and topcoating benefits. Fast drying can be combined with the use of microspheres to improve hardness and reduce porosity and flame retardation.

The present invention relates in particular to shop primers. Shipping containers and other shipborne metal objects are usually assembled by welding a number of individual metal parts. In shipbuilding and industrial structures, it is generally desirable to pre-coat steel with a zinc-containing primer prior to the manufacture of parts, and many such coating compositions are known, referred to as shop primers or pre-primers. To prevent corrosion during welding, it is necessary to prepare the surface of the parts (for example, clean and roughen, for example, by shot blasting), and then apply shop primer compositions that provide temporary protection against corrosion. Such compositions provide the ability to weld primed parts through a layer of factory primer without the need to remove the primer near the weld.

After welding, an additional primer coat and optionally a top coat can be applied over the primer coat to provide additional corrosion protection and the desired aesthetic appearance.

Shop primers may be organic or inorganic and may be provided in a water or organic solvent base. Some shop primer compositions contain zinc powder in an organic resin such as epoxy, epoxy ester, polyurethane, polystyrene resin, or silicone resin. Coatings based on these organic binders are not very suitable for coating steel to be subsequently welded, since the binder tends to decompose at the welding temperature, leading to the formation of pores in the welds. The primers of the present invention may be particularly suitable as shop primers.

US2012/0204762 describes aqueous silane-based compositions containing metal salts that provide corrosion protection when coated on metal substrates. As an example of a coating, compositions based on silanes containing 0.5% wt. Cr(III) nitrate, Al(III) nitrate or Ce(III) nitrate used to coat galvanized steel panels. Panels coated with coating compositions containing a metal salt showed greater corrosion resistance after salt spray treatment than untreated panels, or than panels treated with a silane-based coating without metal salt. US2012/0204762 does not provide examples of silane compositions containing Zn(II) salts and does not describe the possibility of using silane-based compositions as shop primers.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the present invention, a water-based primer is provided, comprising:

(A) polysiloxane sol; and

(B) 0.1 to 30% wt. water-soluble zinc salt with a solubility in deionized water of at least 0.5 g/l at 25°C.

In some embodiments, the primer contains from 0 to 95% of the mass. at least one anti-corrosion pigment (C), preferably from 15 to 45% of the mass.

In another aspect of the present invention, a water based primer is provided comprising:

(A) polysiloxane sol;

(B) 0.1 to 30% wt. a water-soluble zinc salt with a solubility in deionized water of at least 0.5 g/l at 25°C;

(C) 15 to 90% wt. at least one anticorrosive pigment; and

(D) 0.5 to 20% wt. an accelerator selected from zinc oxide, zinc phosphate, calcium-strontium-zinc phosphosilicate, zirconium hydrogen phosphate, iron phosphide, calcium zirconate, barium zirconate, zirconium nitride, zinc titanate or iron(II) titanate, or mixtures of these compounds.

In another aspect of the present invention, a kit is provided comprising at least two parts; a first Component (I) containing component (A) as described above; and a second Component (II) containing component (B) and/or component (C) as described above. Parts of the kit are mixed shortly before application to the substrate. It should be noted that components (I) and (II) and, if present, (III) must be fed separately for mixing.

In another aspect of the present invention, a method is provided for protecting a substrate from corrosion, comprising applying a primer composition to said substrate as described above and allowing said primer to cure on said substrate.

In another aspect of the present invention, there is provided a substrate coated with a cured primer composition as described above.

In another aspect of the present invention, the use of a primer, as described above, is provided to temporarily protect the substrate from corrosion.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a primer composition suitable for application to a substrate to temporarily protect said substrate from corrosion. The primer of the present invention can be applied by spraying, is low in VOCs and can be diluted with water to achieve the ideal application viscosity. At the same time, the primers dry quickly and quickly acquire the ability to withstand mechanical abrasion and the effects of chemicals, water, and the like. The primers of the present invention may be shop primers and are weldable with minimal weld porosity, spatter, soot and flame backpropagation. Finally, along with corrosion resistance, primers can be overcoated with most types of paints without additional pre-treatment of the primer (other than cleaning to remove debris such as dust, salt and/or grease that has been deposited on the surface after priming and before applying the next coat) .

The primer according to the present invention contains at least one polysiloxane sol as component A.

Binder - Component (A)

The primer composition of the present invention contains a polysiloxane sol component (also referred to as a binder component) capable of curing after the coating composition is applied to a substrate, typically a steel substrate. The polysiloxane sol component is a component obtained by a condensation reaction of at least one silane to form a highly branched polysiloxane sol containing a plurality of free silanol functional groups. When this sol is combined with other components of the coating composition and applied to a substrate, a coating is formed and the free silanol groups contained in the sol form bonds with groups present on the surface of the substrate. The curing reaction proceeds spontaneously at room temperature to form a primer.

The polysiloxane sol is clearly a sol and not a gel. It can be considered as a solution, colloidal solution, emulsion or suspension. Therefore, the polysiloxane is in aqueous form prior to application. The polysiloxane gels during curing after mixing with the other primer components.

The polysiloxane sol of the present invention is ideally prepared from at least one alkoxysilane precursor which is hydrolyzed to form the corresponding silanol. It should be noted that many alkoxysilanes contain many alkoxy groups (usually up to three such groups), and therefore can form many hydrolysis products, depending on the hydrolysis technique. Products of complete hydrolysis and partial hydrolysis can be formed. This hydrolysis reaction leads to the formation of alcohol.

The hydrolyzed silanes/partially hydrolysed silanes can then condense together in a well known manner to form complex oligomers/polymers. Since various monomers are present after the hydrolysis reaction, a complex polysiloxane sol is formed, which is difficult to characterize by a general formula. For example, as a result of partial hydrolysis, two partially hydrolyzed molecules can join together in a condensation reaction to form a siloxane, and so on. This condensation process necessarily leads to the formation of alcohol and water as by-products.

Thus, condensation is associated with the formation of a 2- or 3-dimensional network structure of siloxane [Si-O-Si] bonds, accompanied by the formation of water and alcohol molecules.

The polysiloxane sol according to the present invention is usually present in aqueous form in component (A). In addition, it preferably does not contain VOCs (Volatile Organic Compounds). Therefore, it is easy to remove the generated alcohols by evaporation during the preparation of the sol. Importantly, since the ash contains free silanol groups, no additional alcohol is released during curing and the VOC content remains low.

The sol preferably cures at room temperature.

Preferably, the polysiloxane sol of the present invention is obtained by condensing at least one bis-amino-functional alkoxysilane which undergoes hydrolysis or an epoxy-functional alkoxysilane which undergoes hydrolysis. Surprisingly, it has been found that stable, substantially alcohol-free, organosilicon-based aqueous compositions can be prepared from bis-amino-functional alkoxysilanes or epoxy-functional alkoxysilane, optionally together with other organofunctional alkoxysilanes. In particular, sol-gel chemistry is based on bis-amino-functional alkoxysilanes or epoxy-functional alkoxysilanes, together with alkyl-functional alkoxysilanes. Ideally, the silane compounds are present in substantially fully hydrolysed form, but partially hydrolysed forms are also possible. These compositions are crosslinked at low temperatures.

Thus, the polysiloxane sol materials of the present invention are preferably based on condensation products of bis-amino-functional alkoxysilanes such as bis-(triethoxysilane)-amine or bis-(trimethoxysilane)-amine. These monomers can be hydrolysed to form fully or partially hydrolyzed analogues of bis-aminofunctional alkoxysilanes, such as bis-(triethoxysilane)-amine or bis-(trimethoxysilane)-amine. Epoxy-functional alkoxysilanes can also be hydrolyzed to give fully or partially hydrolyzed analogs. These silanes include 3-glycidyloxypropyltriethoxysilane (GLYEO), 3-glycidyloxypropyltrimethoxysilane (GLYMO).

These treated monomers can be used alone or in combination with other monomers to form a sol. Other preferred monomers include bis-(triethoxysilane)-amine, bis-(trimethoxysilane)-amine, n-propyltriethoxysilane, n-propyltrimethoxysilane (PTMO), 3-glycidyloxypropyltriethoxysilane (GLYEO), 3-glycidyloxypropyltrimethoxysilane (GLYMO), 3-aminopropyltriethoxysilane (AMEO ), 3-aminopropyltrimethoxysilane (AMMO), methacryloxypropyltriethoxysilane (MEEO), methacryloxypropyltrimethoxysilane (MEMO), N-(n-butyl)-3-aminopropyltriethoxysilane, vinyltrimethoxysilane (VTMO), N-(n-butyl)-3-aminopropyltrimethoxysilane (Dynasylan® 1189), 3-mercaptopropyltrimethoxysilane (MTMO), 3-mercaptopropyltriethoxysilane (MTEO), N-2-aminoethyl-3-aminopropyltrimethoxysilanes (DAMO), polyethylene glycol functional alkoxysilanes, tetraethoxysilane (Dynasylan A), tetramethoxysilane (Dynasylan M), methyltriethoxysilane ( MTES), methyltrimethoxysilane (MTMS), bis-(triethoxysilylpropyl)-tetrasulfan (Si 69), bis-(triethoxysilylpropyl)-disulfan (Si 266), bis-(trimethoxysilylpropyl)-disulfan, bis-(trimethoxysilylprop ил)-тетрасульфан, винилтриэтоксисилан (VTEO), 1-аминометилтриэтоксисилин, 1-аминометилтриметоксисилин, 1-метакрилоксиметилтриметоксисилан, 1-метакрилоксиметилтриэтоксисилан, 1-меркаптометилтриэтоксисилан, 1-меркаптометилтриметоксисилан, изобутилтриметоксисилан, изобутилтриэтоксисилан, октилтриэтоксисилан (Dynasylan®OTEO), октилтриметоксисилан, гексадецилтриэтоксисилан, гексадецилтриметоксисилан , phenyltrimethoxysilane, phenyltriethoxysilane, 2-aminoethyl-3-aminopropylmethyldimethoxysilanes, 2-aminoethyl-3-aminopropylmethyldiethoxysilanes, ureidopropyltrimethoxysilane, ureidopropyltriethoxysilane, tridecafluorooctyltriethoxysilane, tridecafluorooctyltrimethoxysilane, Dynasylan®1151 cocondensation of aminosilane and alkylsilane), Dynasylan® HS 2776 (aqueous, alcohol-free cocondensation of diaminosilane and alkylsilane), Dynasylan® HS 2909 (aqueous, alcohol-free cocondensation condensation of aminosilane and alkylsilane), Dynasylan® HS 2926 (aqueous, alcohol-free epoxysilane product), and Dynasylan® SIVO 110 (aqueous, alcohol-free epoxysilane product).

Any of these monomers may be hydrolyzed to form hydrolyzed or partially hydrolyzed monomers to react with bis-amino functional alkoxysilanes or epoxy functional alkoxysilanes, which may also be hydrolyzed or partially hydrolyzed. It is preferred to use hydrolysed bis-amino functional alkoxysilanes or epoxy functional alkoxysilanes together with a non-hydrolysed alkylalkoxysilane monomer. Another preferred option is epoxy-functional alkoxysilanes in combination with amino-functional alkoxysilanes.

The epoxy-functional alkoxysilanes used in the present invention are most preferably epoxyalkyl-functional alkoxysilanes.

The use of epoxy-functional alkoxysilanes is particularly preferred as sol starting materials. Any alkoxy group in the polysiloxane sol according to the present invention will preferably contain C1-6 carbon atoms, such as C1-4 carbon atoms, in particular C1-3 carbon atoms, for example methyl, ethyl, n-propyl, isopropyl or n- butyl.

In the most preferred embodiment, the sol is derived from the ω-glycidyloxyalkoxysilane cocondensate of formula I

X-Si(R) _x (OR ¹ ) _3-x (I),

where X represents a 2-(3,4-epoxycyclohexyl)-ethyl, 1-glycidyloxymethyl, 2-glycidyloxyethyl, 3-glycidyloxypropyl or 3-glycidyloxyisobutyl group,

R ¹ and R independently represent a linear or branched alkyl group containing from 1 to 4 C atoms; and

x is 0 or 1,

or

bis-(alkoxysilylalkyl)-amine of formula II

(OR ¹ ) ₃ Si-A-Si(OR ¹ ) ₃ (II),

where each R ¹ is independently a linear or branched alkyl group containing from 1 to 4 C atoms and A is a bis-amino functional group of formula IIa

-(CH ₂ ) _i -[NH(CH ₂ ) _f ] g-NH[(CH ₂ ) _f *-NH] _g *—(CH ₂ ) _i *- (IIa),

where i and i* are independently the integers 1, 2, 3, or 4, f and f* are independently the integers 1 or 2, and g and g* are independently the integers 0 or 1.

To prevent the content of VOCs in the product, all alcohols released during the formation of the sol are distilled off.

Hydrolysis of the starting alkoxysilanes can be carried out with formic acid or another mild hydrolysing agent, for example as shown in US2011/0268899. The condensation reaction is preferably carried out at a low pH, such as less than 7, such as 3 to 5. The reaction time is preferably controlled to ensure that a sol is obtained rather than a gel. The reaction time can be up to 3 hours. Too long a reaction time can cause the curing reaction to start. The synthesis of the required sol is described in US2011/0268899 or US2014/0106176.

In another aspect, the polysiloxane sol used in the present invention is produced by a process comprising:

(i) hydrolysis of at least one bis-amino functional alkoxysilane or epoxy functional alkoxysilanes;

(ii) reacting the resulting hydrolyzed product with at least one optionally hydrolyzed alkylalkoxysilane.

Any liberated alcohol can be removed so that the alcohol content of the ash does not exceed 3% by weight.

Alternatively, the polysiloxane sol used in the present invention is prepared by a method comprising hydrolyzing a bis-amino-functional alkoxysilane or an epoxy-functional alkoxysilane and allowing the resulting hydrolysis product to self-condensate to form a sol. Any liberated alcohol can be removed so that the alcohol content of the ash does not exceed 3% by weight.

It should be noted that more complex sols can be obtained by adding additional reagents to the mixture. While there must be at least one bis-amino functional alkoxysilane or epoxy functional alkoxysilane as defined above, other possible reagents include vinyl silanes, alkyl silanes, alkoxy silanes, and so on.

The ratio of bis-amino-functional alkoxysilanes or epoxy-functional alkoxysilanes to alkylalkoxysilanes may be from 10:1 to 1:10, such as from 5:1 to 1:5, by weight.

The resulting Sol should be dispersible in water at room temperature 23°C. By water dispersibility is meant that the sol can form an emulsion, suspension or colloidal solution in water.

It is important that the sol contains free silanol groups so that no additional alcohol is released during curing and VOC levels remain low.

Although the sols of the present invention are provided in water, polysiloxanes are often diluted with water prior to use to ensure ideal application viscosity. Note that the commercially available polysiloxanes used in the present invention are available as aqueous solutions.

The polysiloxane sol (i.e., including the weight of any water in the primer) can be from 10 to 80% by weight. primer, preferably from 25 to 80 wt. %, such as from 25 to 70 wt. %, preferably from 35 to 65 wt.

Preferably, the amount of water in the primer according to the present invention is from 10 to 65% by weight, such as from 20 to 65% by weight. water. Polysiloxane Sol as component A usually contains from 50 to 98 wt.%. water, such as from 65 to 95% of the mass. water. Often the solids content of the polysiloxane ash is from 2 to 35% by weight, preferably from 5 to 30% by weight. In particular, the content of solids in the ash is from 10 to 25 wt%. The sol, which may be purchased from a supplier, may still be diluted by the user as needed.

The water used for dilution is preferably deionized water. When calculating weight percent, all water for dilution in the present description is considered as part of the polysiloxane Sol. Although percentages of sol are given in the text, this refers to the total mass of sol and water in the primer.

The condensation products obtained from the reaction of, inter alia, bis-amino-functional alkoxysilanes or epoxy-functional alkoxysilanes and alkylalkoxysilanes may be oligo/polymeric. In the present description, both options are referred to as polysiloxane. They may have a particle size of 0.5 to 350 nm, preferably 0.5 to 130 nm. The weight average molecular weight may vary from 1,000 to 150,000 g/mol, preferably from 4,000 to 30,000 g/mol, more preferably from 1,000 to 50,000 g/mol, even more preferably from 1,000 to 5,000 g/mol. The viscosity of the polysiloxane (in water) can be between 5 and 20 mPa s at 20 °C.

The polysiloxane component is preferably free of VOCs (Volatile Organic Compounds). This means that it contains less than 3 wt. volatile organic compounds (according to ASTM D5201), such as 2% wt. or less, ideally, 1% of the mass. or less. Alternatively, it contains 100 g/l VOC or less, preferably 40 g/l VOC or less.

The polysiloxane sol must not release alcohol upon crosslinking. The curing of the sol must be possible at temperatures to which the coated substrate may be exposed, such as between 0 and 40 °C.

The polysiloxane sol preferably has a pH of 1.0 to 8.0, such as 3 to 5.5. The silane may have a pH in the range of 3.2-4.0.

Sol formation provides cross-linked structural elements such as chains, cyclic or three-dimensional structures, but these are difficult to determine using a general formula due to the large number of possible structures formed.

The polysiloxane used in the present invention is not new and can therefore be purchased from commercial sources. In particular, the polysiloxane of the present invention is available under the tradename Dynosylan Sivo 165. This material is available from Evonik. It is described as a nearly VOC-free aqueous organic-inorganic (hybrid) sol-gel system that cures at a relatively low temperature.

The volumetric median particle size is preferably 2 to 10 nm, such as 5.4 nm.

Determination of the content of polysiloxane sol in the primer according to the present invention is difficult because the amounts vary depending on the water content and the content of anti-corrosion material (which is heavy and therefore a disproportionate percentage of the weight of the primer). The solid binder (i.e. the weight of the polysiloxane solid excluding water) may comprise from 1 to 35 wt %, such as 2 to 30 wt %, in particular 2 to 20 wt % of the dry weight of the primer. More specifically, the dry matter content of the polysiloxane primer is 2 to 12 wt %, more specifically 4 to 10 wt %. The indicated percentages refer to the amount of polysiloxane calculated on the sum of all components of the mixture, but without taking into account the mass of water (dry mass).

Any "dry weight" percentage in the text/claims refers to weight percentages determined without regard to the contribution of water content. Unless "dry weight" is explicitly stated, percentages in the text/claims refer to the primer, including any water content, unless the context clearly dictates otherwise.

Component (A) is contained in component (I) of the kit, preferably only component (I) of the kit.

Water soluble zinc salt - Component B

The presence of a water soluble zinc salt is essential to provide a primer composition where fast drying time and water resistance is required. The water-soluble zinc salt is a salt having a solubility in deionized water of at least 0.5 g/l at 25° C., preferably at least 5.0 g/l, such as at least 10 g/l or at least measure 20 g/l. More preferably, the water solubility should be at least 50 g/L. For the avoidance of doubt, in the present description, solubility, for example, 10 g/l, means that the solubility is 10 g of salt in 1000 g of water at 25 °C.

Preferred zinc salts according to the present invention include organic zinc salts. Typically, the salt will have a relatively low molecular weight, such as up to 600 g/mol. Suitable salts include butyrate, acetate, gluconate, glycerate, glycolate, lactate, propionate, salicylate, citrate, oleate, benzoate, laurate, tartrate, stearate, valerate, formate, picolinate, ascorbate, biglycinate, lysinate, malate, mono-L-methionine sulfate , zinc pidolate and mixtures of these salts.

In some embodiments, the zinc salt may be a hydrate, such as zinc gluconate dihydrate or zinc citrate trihydrate.

It is also possible to use inorganic zinc salts such as zinc sulfate or zinc halides. A hygroscopic zinc salt may be used, but should not be present in the same kit component as the anti-corrosion pigment (C). Thus, when using a hygroscopic zinc salt, it is preferably either introduced into the sol as part of component (I) (and the anti-corrosion pigment (C) is present as a separate component), or preferably each of components (A), (B) and (C) are present as separate kit components (Components (I), (II) and (III)).

If zinc chloride is used as the zinc salt, then each of the sol, the zinc salt and, if present, the anticorrosive pigment should be provided as a separate kit component. However, it is preferred that the Zn halides are not present in the primer composition.

Preferably the zinc salt is organic. Preferably, the organic anion contains at least two carboxyl groups or contains at least one carboxyl group and at least one hydroxyl group.

In kits according to the present invention, the zinc salt may be included as part of Kit Component (I) and/or Kit Component (II), preferably in only one of the components. Most preferably, the zinc salt is in Component (II) of the kit, ie. separately from the sol (A).

If the zinc salt used is hydrated or hygroscopic, it is preferred that the zinc salt is not contained in the same kit component as the anti-corrosion pigment (C). Thus, if a zinc hydrate or hygroscopic zinc salt is used, it is preferably either added to the sol as part of component (I) (and anti-corrosion pigment (C) is present as a separate component), or each of components (A), (B) and (C ) is present as a separate kit component (Components (I), (II) and (III)).

If the zinc salt used is not hydrated and non-hygroscopic, the zinc salt may be contained in both Kit Component (I) and/or Kit Component (II). Most preferably, the zinc salt is contained in Component (II) of the kit, preferably only in Component (II) of the kit. If the zinc salt used is not hydrated and non-hygroscopic, the zinc salt may be contained in the same kit component as the anti-corrosion pigment (C) (i.e., component (II)). Alternatively, each of components (A), (B) and (C) may be present as separate kit components (Components (I), (II) and (III)).

Particularly preferred salts are zinc gluconate, zinc lactate and zinc citrate, and hydrates of the corresponding salts. Especially preferred are zinc gluconate and zinc citrate.

Mixtures of zinc salts can also be used.

In a preferred aspect, component (B) does not contain zinc nitrate or zinc acetate. This means that the composition contains less than 0.1% wt. each of zinc nitrate or zinc acetate, preferably less than 0.05% wt. each of zinc nitrate or zinc acetate preferably does not contain zinc nitrate or zinc acetate.

In a preferred aspect component (B) consists essentially of or consists of zinc gluconate, zinc citrate, zinc chloride, zinc acetate or mixtures of these salts. Preferably, component (B) consists essentially of or consists of zinc gluconate, zinc citrate, zinc chloride or mixtures of these salts. Even more preferably, component (B) consists essentially of or consists of zinc gluconate, zinc citrate or mixtures of these salts.

The zinc salt component (B) is from 0.1 to 30% by weight. relative to the entire primer, preferably from 0.1 to 10% by weight, preferably from 0.1 to 5% by weight, such as from 0.2 to 4% by weight, in particular from 0.5 to 2 % wt. concentration of 1% wt. ± 0.5% wt. especially preferred. In the case of a hydrate, this concentration does not include the water associated with the salt. If a mixture of zinc salts is used as Component (B), these concentrations refer to the combined concentrations of zinc salts.

The concentrations of Component (B) described above apply equally to the amount of zinc salt present in the kits according to the present invention. In the case of kits, the amounts are also calculated in relation to the combined amounts of components (I), (II) and, if present, (III) of the kit. For example, in the case of the Examples described below, a primer is obtained by combining approximately 44% of the mass. Component (I) of the set and 56% wt. Component (II) of the kit (containing a water-soluble zinc salt). The zinc salt is contained in an amount of 1% by weight of the primer (Component (I) + Component (II)), and 1.8% by weight of the Component (II) of the kit.

As described in the following sections, Components (II) or (III) of the kit may contain an anti-corrosion pigment component (C), such as zinc, and may further contain a water-insoluble zinc salt, such as zinc oxide. To avoid uncertainty, these substances are not taken into account when determining the concentration of Component (B).

Anticorrosion Pigment - Optional Component C

Depending on the end use of the primer composition, the primer composition of the present invention may also contain an anti-corrosion pigment. In case the primer is a shop primer, the inclusion of an anti-corrosion pigment is preferred.

If present, it is important that the anti-corrosion component is not contained in the sol component. That is, the anti-corrosion pigment is not contained in Component (I), but may be contained in Component (II) of the kit, for example, together with component (B). Alternatively, the anti-corrosion pigment may be included as a separate kit component (Component (III)). If present, component (C) is preferably contained in only one of Component (II) or (III), but not both.

Preferably, the anti-corrosion pigment is zinc based. The zinc used in the composition can be metallic zinc in powder or flake form, surface-embedded zinc hollow spheres, surface-embedded minerals, and surface-embedded zinc polymers. Alternatively, the zinc may be surface treated zinc metal that is chemically inert to the aqueous environment. Preferably the zinc has an average particle size in the range of 0.5-20 microns, such as 1-15 microns, preferably 2-5 microns or 6-9 microns. In particular, the zinc is in the form of zinc powder, preferably with the indicated particle sizes. The use of zinc dust as an anti-corrosion pigment is well known and its use is well known to those skilled in the art.

The content of the anti-corrosion pigment in the primer according to the present invention is from 0 to 90 wt %, such as from 15 to 45 wt %, such as from 20 to 40 wt %. In terms of dry weight, the anti-corrosion pigment may comprise from 0 to 95% by weight, from 10 to 90% by weight, such as from 20 to 85% by weight, in particular from 20 to 80% by weight of the primer (calculated by dry weight).

Accelerator - Optional Component D

Aqueous primers according to the present invention may also contain a mineral accelerator. When present, the accelerator is zinc oxide, zinc phosphate, calcium-strontium-zinc phosphosilicate, zirconium hydrogen phosphate, iron phosphide, calcium zirconate, barium zirconate, zirconium nitride, zinc titanate, and iron(II) titanate.

More specifically, the accelerator is zinc oxide, zirconium hydrogen phosphate or zinc phosphate.

Mixtures of accelerators can also be used. Other mineral compounds can be used in combination with these two accelerators.

The above accelerators can also be combined with other materials such as metal acetates, metaphosphates, metal titanates, hexafluorozirconates, zirconates and phosphates. The cation is usually Al, Zr, Ba, Ca or Zn.

If present, the amount of accelerator in the compositions according to the present invention may be from 0.5 to 20% wt., such as from 1 to 15% wt., in particular, from 2 to 15% wt.

On a dry weight basis, component (D) may comprise from 1.5 to 30% dry weight, such as 3 to 20% dry weight.

The preferred option is a combination of zirconium hydrogen phosphate and zinc phosphate. A combination of zirconium hydrogen phosphate and zinc oxide is also preferred as component (D). The most preferred option is to use zinc oxide as the sole accelerator.

Without wishing to be bound by theory, it has been found that these specific accelerators further enhance the excellent dry time and water resistance development rate achieved by the inclusion of a water soluble zinc salt component (B).

In another aspect of the present invention, a water based primer is provided comprising:

(A) polysiloxane sol;

(B) 0.1 to 10% wt. a water-soluble zinc salt with a solubility in deionized water of at least 0.5 g/l at 25°C;

(C) 15 to 45% wt. at least one anticorrosive pigment; and

(D) 0.5 to 20% wt. an accelerator selected from zinc oxide, zinc phosphate, calcium-strontium-zinc phosphosilicate, zirconium hydrogen phosphate, iron phosphide, calcium zirconate, barium zirconate, zirconium nitride, zinc titanate or iron(II) titanate, or mixtures of these compounds.

Microspheres

The primer may also contain microspheres to improve the hardness and weldability of the coating. The term microsphere refers to a substantially spherical particle having a D50 size of 100 nm to 500 microns. All kinds of microspheres can be used, satisfying at least one of the conditions given in the table below:

maybe More preferably Most preferred Hardness (Mohs scale) ≥5 ≥6 ≥7 Breaking strength
(90% passed) >5000psi >20,000psi >60,000 psi

The particle size can be determined, for example, using laser diffraction analysis (Malvern).

Preferably, the spheres have a specific surface area of ≤ 7000 cm ² /g, preferably ≤ 6000 cm ² /g, preferably ≤ 5000 cm ² /g (by Blaine, method EN196-6).

Preferred microspheres will satisfy all requirements in the "possible" column, in the "more preferred" column, or in the "most preferred" column. The microspheres are solid. In fact, the microspheres can be made from any suitable polymeric material, ceramic or glass. Preferably, the microspheres are made of ceramic or glass.

Examples of ceramics include aluminates, titanates, zirconates, silicates, doped (eg doped with lanthanides and actinides) variants of these ceramics, and mixtures of these ceramics.

Examples of commercially available ceramic microspheres include hollow ceramic microspheres available from, e.g., Sphere One, Inc., Chattanooga, TN, under the trade name "EXTENDOSPHERES" 14, SLG, SL-90, SL-150, and XOL-200); and solid ceramic microspheres supplied, for example, by 3M Company under the trade name "3M CERAMIC MICROSPHERES" (for example, grades G-200, G-400, G-600, W-210 and W-410, Osthoff Omega Group under the name Omega- SIL or Zeeospheres (e.g. G series (G200, G400, G600) or N series (N200, N400, N600)).

Examples of commercially available glass spheres include S38HS, S38XHS, K46, S60, S60HS, iM30K, iM16K from 3M, and hollow glass microspheres under the tradenames Q-Cel and Sphericel from Potters Industries. The particle size (D50) of the microparticles is preferably 1-100 microns, more preferably 2-50 microns, in particular 4-30 microns.

The action of the microspheres mainly adds hardness and abrasion resistance to the coating composition. Although there are alternative hardness improvers such as inorganic fillers, these ceramic microspheres offer an additional benefit over alternative hardness improvers because they have a large effect in relatively small amounts.

Preferably, the pH of the microspheres is in the range of 9 or less, preferably 8.5 or less (measured as a 10 wt % dispersion of the microspheres in deionized water). Preferably the pH is above 3. If the pH is >9, there is a reduction in the shelf life of the ink.

Microspheres can be from 0.5 to 10% of the mass. From the composition of the primer, such as from 1 to 7 wt. -%, in particular, from 2 to 7 wt. in some embodiments, the implementation of the content of microspheres can be from 0.5 to 5% of the mass.

On a dry weight basis, the microspheres may comprise from 0.5 to 15% dry weight, such as 2 to 10% by weight.

In a preferred embodiment, the microspheres are glass microspheres.

Other components

The primer layer composition may also contain various other components, for example, to improve anti-corrosion properties, and so on.

In particular, the primer layer composition may contain fillers such as other metal oxides, metal carbonates, feldspar, and so on, acting as anti-corrosion materials. In particular, the primer layer composition may contain fillers that act as weld improvers. Suitable weld improvers include titanium dioxide and fluorite. Surprisingly, these fillers have been found to improve the weldability of the coating. A primer containing these fillers suffers less from porosity, is less prone to flame backpropagation, and generates less soot and spatter.

If present, fillers are preferably contained in part (II) of the kit, preferably only in part (II) of the kit.

The composition of the primer as a whole may contain from 1 to 30% of the mass. filler additives, for example, titanium dioxide and fluorite, such as, for example, from 4 to 20% of the mass. in the dry weight, the fillers may comprise 3-50% dry weight, preferably 8-30% dry weight, most preferably 12-25% dry weight. It has been found that the use of titanium dioxide and fluorite as fillers demonstrates the particular benefit of these materials over talc, and provides a non-porous primer coating without flameback, soot and spatter. The shop primers of the present invention preferably contain titanium dioxide.

Color pigments may also be present, preferably inorganic pigments. Examples of color pigments include titanium white, iron oxides, chromium oxides and carbon black.

As stated previously, the primers of the present invention are designed to avoid the problems associated with some water-based silicate primers. Therefore, it is preferable that the primers according to the present invention do not contain alkali metal silicates such as lithium silicate, potassium silicate or sodium silicate.

It is also preferred that the primer does not contain organic solvents.

Incorporation of one or more thickeners/thixotropic agents in an amount of 0.01-10% by weight, such as 0.01-5% by weight, preferably 0.05-2% by weight, into the (wet) composition improves settling properties, film formation and primer spray properties. Examples of suitable thickeners are bentonite, silica fume/colloidal, natural thickeners (eg alginates), cellulosic thickeners, saccharides and polysaccharides. If present, thickeners are preferably contained in part (I) of the kit, preferably only in part (I) of the kit.

The primer of the present invention may also contain other conventional additives such as preservatives such as sodium benzoate and surface tension modifiers.

The water content in the primer, ready for application, can be from 5 to 20% of the mass.

Composition

In some embodiments of the present invention, a mixture of components (A), (B), and optionally (C) may have suitable storage stability and the primer may be supplied in a premixed form. This is especially true in the case where the anti-corrosion pigment component (C) is absent.

More often, however, the primer composition of the present invention is prepared by mixing the various components shortly before applying the primer to the substrate to avoid premature curing. Therefore, the primer is preferably supplied as a set of two or more components for mixing by the user.

Component (I) of such a kit contains the polysiloxane sol of component (A) and, optionally, a variety of conventional additives such as fillers, thickeners, preservatives, weld improvers and microspheres.

Component (II) contains a water-soluble zinc salt (component (B)) and/or an anti-corrosion pigment component (C) of the primer according to the present invention.

Preferably, the composition according to the present invention (ie mixed primer) has a VOC content of less than 100 g/l, preferably less than 50 g/l, most preferably less than 30, eg less than 15 g/l. In one embodiment, the primer of the present invention is provided in aqueous form. In another embodiment, the primer is provided with some water, but is intended to be further diluted prior to use.

The composition according to the present invention, when applied, preferably dries within 10 minutes at 23°C and 50% rel. vl., preferably within 2 minutes, according to the test protocols given in the test section of this description.

According to the test protocols below, it is also preferred that the composition dry to the full thickness and provide a surface resistant to mechanical abrasion within 20 ° C and 50% RH. vl., preferably within 5 minutes.

The finished primer according to the present invention is water resistant.

In this case, it is preferable that the primer has an early resistance to water, i.e. water resistance for 24 hours, preferably 12 hours curing at 23°C and 50% r.h. vl., preferably within 6 hours, according to the test reports given in the test section of this application (test for abrasion in water).

Primers according to the present invention also have good resistance to moisture. Primers according to the present invention are considered "resistant" if they show moisture resistance for at least 24 hours when tested according to the moisture resistance test (ISO 6270-2:2005). The primers according to the present invention preferably show durability for at least 36 hours, in particular at least 48 hours.

In one preferred embodiment, the primer of the present invention is a shop primer. It is important that the factory primer must be weldable. The main purpose of a factory primer is to provide temporary corrosion protection until all parts are welded together. Factory primers according to the present invention can be welded at a speed of at least 70 cm/min using MIG welding (Consumable Inert Gas Welding) or other similar welding technique, with the formation of less than 125 mm ^{2 of} pores per meter of welding. In addition, welding should produce a minimum of spatter, soot, and flame backpropagation.

A final and important purpose of the shop primer may be to allow the topcoat to be applied with additional pre-treatment of the shop primer coat. It should be noted that any surface to be painted must be cleaned before applying the next coat, for example, to remove dust, salt and/or grease that has adhered to the surface after applying the factory primer and before applying the next coat. This is not a pre-processing step. In particular, it is possible to apply an epoxy primer.

Pigment Volume Concentration (PVC) is an important parameter of the shop primer according to the present invention. The critical volume concentration is also important. PVC is the volume concentration of the pigment. CPVC represents the maximum volume concentration of the pigment at full resin coverage. PVC/CPVC>1 means that not all of the pigment is coated with resin. The paint will be porous. The ratio is a balance between barrier protection and cathodic protection. Too high a ratio leads to other problems such as cracking and loss of cohesion. Preferably PVC/CPVC is in the range 0.8-1.2, more preferably 0.9-1.1, most preferably 0.95-1.05.

Sets

Primers according to the present invention are preferably supplied as a set of at least two parts. Component (I) contains a binder (A) and component (II) contains a water-soluble zinc salt (B) and/or an anti-corrosion pigment (C).

The water-soluble zinc salt (B) can be provided in component (I) and/or component (II) of the binder, preferably in component (II), particularly preferably only in component (II).

If present, the anti-corrosion pigment (C) may be provided as a third component (component (III)), but is preferably included as part of component (II) together with the water-soluble zinc salt (B).

In a less preferred embodiment, the primers of the present invention are supplied as a kit of two components: a first component (I) containing a binder (A) and a water-soluble zinc salt (B) and a second component (II) containing an anti-corrosion pigment (C).

In a preferred embodiment, the primers according to the present invention are supplied as a set of two components: a first component (I) containing a binder (A) and a second component (II) containing a water-soluble zinc salt (B) and, if present, an anti-corrosion pigment ( C).

In another preferred embodiment, the primers according to the present invention are supplied as a set of three components: a first component (I) containing a binder (A), a second component (II) containing a water-soluble zinc salt (B), and a third component (III) containing an anti-corrosion pigment (C).

Components (I), (II), and if present, (III) are mixed to form the primer composition shortly before applying the primer to the substrate. In the case of a three-component set, the order of administration is not fundamentally important. For example, component (III) can be introduced into one of the components (I) and (II) before combining components (I) and (II); or you can enter simultaneously with the combination of components (I) and (II); or you can enter after combining components (I) and (II).

Application

The composition of the present invention can be applied using all types of application equipment such as brush or roller, conventional sprayer, airless sprayer and combination sprayer. Ideally, the paint is applied by airless spray to allow the primer to spontaneously cure after application to the substrate.

The substrate to be coated is preferably a metal substrate, ideally a steel substrate. The substrate may be one of the substrates used in marine equipment. So, typical substrates include ship parts, metal containers such as shipping containers, bridges, and so on.

After final mixing, the primer is usually applied to the steel surface, ideally with a final thickness of 5 - 150 microns, such as 50 - 150 microns (dry film thickness (DFT), measurement described in the test methods section). This coating will provide temporary protection to the steel surface. If component (C) is not present, DFT 50-150 microns is preferred. In the case of a factory primer, the final thickness is preferably 5-50 microns, such as 15-25 microns.

As already mentioned, the present invention also relates to a method for temporarily protecting a steel surface with an anti-corrosion coating, comprising coating the steel surface with a primer composition according to the present invention.

Steel surfaces coated in this way will typically have a shelf life of 2 to 40 weeks, such as up to 6 months, after which the steel surfaces can be used in the manufacture of steel structures, in which the steel surfaces are the surfaces of the steel parts that make up the body of the steel structure. The steel structure is assembled by welding and it is important that the steel body parts coated with the composition of the present invention can be easily welded to provide high quality connections between the steel body parts of the steel structures.

The present invention also relates to a method for manufacturing a steel structure, in which the steel structure is composed of a plurality of steel body parts, said method comprising the following steps:

a) coating at least one of the parts of the steel hull with a primer composition according to claim 1;

b) storage of coated steel hull part(s) for 2 to 40 weeks;

c) assembling at least part of the steel structure by welding at least two parts of the steel body, wherein at least one of said two parts of the steel body has been coated in step (a).

The rest of the steps and details of the fabrication of the steel structure will be apparent to a person skilled in the art.

Any type of paint can be applied over the primer without any pretreatment of the primer coat (other than cleaning to remove dust, grease, etc.).

Below, the present invention will be described with reference to the following non-limiting examples.

Test Methods

Moisture resistance

The panels were tested at 100% humidity and 40°C according to ISO 6270-2:2005. The panels were spray applied (25 µm DFT) with a conventional spray gun onto sandblasted SA2.5 steel panels. The panels were placed in a climate chamber (constant atmosphere) and checked every day for two weeks. The panel was intensively rubbed with a finger and the area of friction was visually inspected. After rubbing, no paint should be visible on the finger, and no damage should be visible on the paint film.

Friction test for resistance to water

The primer was thoroughly mixed and applied to sandblasted steel panels (7.5 x 15 x 3 mm) of SA2.5 cleanliness using a 30 µm gap applicator. After 24 hours, the steel panels were placed in a container of water at 23°C so that half of the panel was immersed. The panels were soaked in water for 5 minutes before performing a standard water resistance test: a clean cotton cloth was soaked in water and rubbed back and forth (double pass) with medium pressure (manual thumb pressure) 80 times. The coating and fabric were evaluated and a water resistance value was recorded from 0 to 5, with 4 being water resistant and 5 being fully water resistant or fully cured. At score 4, the friction area had a slightly glossy appearance, and a small amount of zinc was observed on the fabric.

Stability test

Component A was stored in a closed jar at 60°C with the addition of % wt. zinc salts to the binder, as in the examples below. The contents were checked at regular intervals (once a week). The paint was mixed by hand with a wooden stick and evaluated visually. The paint that has passed the test shall be free of clots, without significant change in color and uniformity.

Dry Film Thickness (DFT) Determination

The dry film thickness was measured with an electrometer on a smooth steel substrate.

Determination of dry matter content in compositions

The solids content of the compositions was calculated according to ASTM D5201.

Calculation of the content of volatile organic compounds (VOC) in coating compositions

The content of volatile organic compounds (VOC) in the compositions of the coating was calculated according to ASTM D5201.

Volume content of solids in compositions

The volume content of solids in the compositions was measured according to OCCA monograph No. 4.

EXAMPLES

Components

Bentone LT - Thixotropic Agent - Elementis Specialties

VPS SIVO 165 - binder polysiloxane sol - Evonik

Bayferrox black 318 M - iron oxide pigment

Table 1 . Test results.

% wt. indicated for the combined composition. The binder percentages for VPS SIVO 165 are based on the actual weight of the polysiloxane sol (+any dilution water).

Ingredient Comp. Etc. one Ex 2 Ex 3 Ex 4 Component I Bentone LT 0.23 0.23 0.23 0.23 0.23 VPS SIVO 165 36.45+6.91 36.09+6.84 36.09+6.84 36.09+6.84 36.08+6.84 Water for dilution 6.91 6.84 6.84 6.84 6.83 Component II zinc dust 28.62 28.34 28.34 28.34 28.34 Zinc Oxide RED SEAL 5.59 5.54 5.54 5.54 5.54 Bayferrox black 318 M 10.07 9.97 9.97 9.97 9.97 Zinc gluconate one zinc citrate one zinc chloride one zinc acetate one _TiO2 11.84 11.73 11.73 11.73 11.73 sodium benzoate 0.23 0.23 0.23 0.23 0.23 Oxalic acid dihydrate 0.07 0.07 0.07 0.07 0.07 Moisture resistance Dissolved in 6 hours stable stable stable Dissolved in 24 hours Friction test for resistance to water after 24 hours four four 5 5 5 Stability test Yes Yes Yes Turned to gel after 2 months Yes

The data showed that zinc gluconate, zinc citrate, zinc chloride and zinc acetate provided a composition with a better balance of moisture resistance and stability (water friction test) than the comparative example. Zinc gluconate, zinc citrate and zinc chloride provide particularly good moisture resistance. The zinc acetate provided better moisture performance than the comparative example without the zinc salt.

The coating from Example 3 was stable when zinc chloride was added as a separate component, i. when obtained from a 3-component kit.

Long-term storage of zinc chloride in Component A in Component (I) of the kit resulted in gelation, which meant that zinc chloride had to be included as a separate component. In addition, the combination of ZnCl ₂ + Zn also led to the formation of clots.

Comparative Example

Example 1 was repeated using aluminum nitrate from Sigma instead of Zn gluconate. Aluminum nitrate was found to be poorly soluble in Sivo 165 resulting in a formulation with unacceptable pot life.

Claims (28)

1. A water-based primer containing: (A) polysiloxane sol; (B) 0.1 to 10% wt. a water-soluble zinc salt with a solubility in deionized water of at least 0.5 g/l at 25°C and (C) at least one anticorrosive pigment; wherein said polysiloxane sol is a sol produced by a process comprising: (i) hydrolyzing at least one bis-amino-functional alkoxysilane or epoxy-functional alkoxysilane; (ii) reacting the resulting hydrolysis product with itself, with at least one optionally hydrolyzed alkyl alkoxysilane, or with at least one optionally hydrolyzed amine-functional alkoxypolysiloxane. 2. Water-based primer according to claim 1, additionally containing up to 95% of the mass. specified at least one anti-corrosion pigment (C), preferably from 15 to 45% of the mass. 3. The water-based primer according to claim 1 or 2, in which the polysiloxane Sol is contained in an amount of from 1.0 to 20% of the mass. (in terms of dry matter). 4. Water-based primer according to any one of paragraphs. 1-3, in which the polysiloxane Sol is contained in an amount of from 10 to 80 wt. -%, preferably from 25 to 70 wt.%. (i.e. total weight of polysiloxane and water). 5. Water-based primer according to any one of paragraphs. 1-4, wherein said water-soluble zinc salt is an organic zinc salt, preferably selected from zinc gluconate, zinc citrate, or mixtures of said salts. 6. Water-based primer according to any one of paragraphs. 1-5, not containing alkali metal silicates. 7. Water-based primer according to any one of paragraphs. 1-6, characterized in that said anti-corrosion pigment contains or consists of zinc. 8. Water-based primer according to any one of paragraphs. 1-7, containing an accelerator selected from zinc oxide, zinc phosphate, calcium-strontium-zinc phosphosilicate, zirconium hydrogen phosphate, iron phosphide, calcium zirconate, barium zirconate, zirconium nitride, zinc titanate, iron (II) titanate and mixtures of these compounds. 9. Water-based primer according to any one of paragraphs. 1-8 containing: (A) polysiloxane sol; (B) 0.1 to 10% wt. a water-soluble zinc salt with a solubility in deionized water of at least 0.5 g/l at 25°C; (C) from 15 to 90% of the mass. at least one anti-corrosion pigment and (D) 0.5 to 20% wt. an accelerator selected from zinc oxide, zinc phosphate, calcium-strontium-zinc phosphosilicate, zirconium hydrogen phosphate, iron phosphide, calcium zirconate, barium zirconate, zirconium nitride, zinc titanate or iron(II) titanate, or mixtures of these compounds. 10. Water-based primer according to any one of paragraphs. 1-9 containing zinc oxide and/or titanium dioxide and/or fluorite and/or microspheres. 11. Water-based primer according to any one of paragraphs. 1-10, which is a factory primer. 12. Kit for obtaining a primer, containing at least two parts: the first part (I) containing the component (A) according to any one of paragraphs. 1-11 and the second part (II) containing the component (C) according to any one of paragraphs. 1-11; and where the component (B) according to any one of paragraphs. 1-11 is contained in at least one of parts (I) or (II), preferably only one of parts (I) or (II); preferably, where component (B) is contained in part (II). 13. A method of protecting a metal substrate from corrosion, including applying a primer to said substrate according to any one of paragraphs. 1-11 and allowing said primer to cure on said substrate. 14. Metal substrate coated with a cured primer according to any one of paragraphs. 1-11.