CN111500191A

CN111500191A - Water-based primer

Info

Publication number: CN111500191A
Application number: CN201910091972.9A
Authority: CN
Inventors: 朱亚军; 刘冬平
Original assignee: Jotun GmbH
Current assignee: Jotun GmbH
Priority date: 2019-01-30
Filing date: 2019-01-30
Publication date: 2020-08-07
Also published as: CN113366065A; WO2020157150A1

Abstract

The invention provides a water-based primer. The present invention also provides a water-borne primer composition comprising: (A) a polysiloxane sol; (B) selected from BaSO₄Feldspar, talc, mica, CaSO₄Or a promoter for kaolin; (C) zn metal; and optionally (D) an organic Zn salt or zinc chloride.

Description

Water-based primer

Technical Field

The present invention relates to a novel aqueous primer composition for application to a substrate such as steel. In particular, the present invention relates to a primer composition comprising a polysiloxane sol (polysiloxane sol), a specific accelerator (accelerator), optionally a zinc metal, and optionally a water soluble organic zinc salt or zinc chloride. The primer of the present invention cures rapidly, resists abrasion, has low Volatile Organic Content (VOC), and, importantly, can be provided in a two component kit (two component kit) for ease of mixing prior to application. The kit of the present invention produces a smooth, uniform blend upon mixing without forming lumps or gels.

Shop primers (shop primers) are preferred. The primer may also be overcoated with further coatings without extensive pretreatment and without loss of interlayer adhesion.

Background

Primer coating systems based on organic solvents are known. However, with increasing environmental awareness, there is a strong need to develop improved techniques that will allow the use of water-based coating systems as primers and avoid organic solvent-based solutions. In this regard, one leading waterborne primer technology is based on alkali metal silicates. These systems produce a very high pH on the substrate surface, which results in the loss of adhesion and blistering of the next coating, usually an epoxy type coating, when the system is exposed to water. Any steel coated with an alkali silicate shop primer must be completely removed before overcoating or thoroughly cleaned with repeated use of clear water to overcome the problem.

In addition, alkali silicates (alkali silicates) require special production and application equipment, wherein all parts that come into contact with the wet coating must be made of non-metallic materials.

There is therefore a significant need to develop new primers which are aqueous but which do not rely on alkali metal silicates.

Some water-based shop primers are known. WO2017/129784 describes an aqueous shop primer comprising a polysilane sol, an accelerator, a corrosion inhibiting pigment and microspheres.

One problem that has been identified with prior art waterborne primers is incomplete mixing of the components of the multi-part kit (kit parts) in which the primer is provided. This results in lumps being formed in the composition and these can clog the spray equipment used to apply the primer composition to the substrate. Although this problem can be overcome using special mixing equipment, such devices are not generally available at the point of application of the composition to the substrate, where mixing of the components occurs.

It is also important that the components of the primer are stable. The Zn metal component of the primer composition must remain separate from the polysiloxane sol component until the composition is required to be applied to a substrate. One problem also encountered is the lack of storage stability of the compositions that make up the multi-part kit that are mixed to form the primer composition.

The inventors of the present invention have devised a water-borne primer (water-based primer) that has a very low VOC, is dilutable with water, and dries quickly to impart water resistance. The primer is also resistant to weathering, water, chemicals and solvents, and can be applied by conventional equipment such as by an airless spray machine (airless spray). Kits from which primers are made are storage stable and the components are readily mixed without complex equipment to produce a homogeneous blend.

The primer is based on an aqueous polysiloxane binder together with an accelerator and Zn metal. It has surprisingly been found that the specific combination of components described in the present invention results in a composition which meets all the requirements for a primer, in particular a shop primer, in particular in terms of mixing quality, storage stability, drying time, water and chemical resistance, abrasion resistance, and allows overcoating with a new paint layer without the need to remove the primer or to repeatedly wash the primer.

The polysiloxane sols used in the primers of the present invention are not new and are described in particular in US2011/0268899, WO2018202472 and US 2014/0106176. However, these documents primarily consider the structure of the binder rather than targeting specific primer compositions that perform favorably. The inventors of the present invention have supplemented the knowledge in these documents by identifying specific primers that are significantly useful in the art, particularly as shop primers.

The invention relates in particular to shop primers. Shipping containers and other marine metal objects are typically assembled by welding together a number of individual metal parts. In marine and industrial construction, it is often desirable to pre-coat steel with a zinc-containing primer prior to manufacture, and many such coating compositions are known, which are known as shop primers or pre-construction primers. To prevent corrosion during welding, the parts are surface prepared (e.g., cleaned and roughened by, for example, grit blasting) and then coated with a shop primer composition that provides temporary corrosion protection. Such compositions allow primed components to be welded through shop primer layers without the need to remove the primer coating near the weld.

After welding, the primer coating may be overcoated with an additional primer layer and an optional topcoat to provide extended corrosion protection and a desired aesthetic appearance.

The shop primer may be organic or inorganic and may be provided in water or in an organic solvent. Some shop primer compositions include zinc powder in an organic resin such as an epoxy, epoxy ester, polyurethane, polystyrene resin, or silicone resin. Coatings based on these organic binders are not well suited for coating steel that must ultimately be welded, as the binders tend to decompose due to the heat of welding, creating pores in the weld. The primer according to the invention can be particularly suitable as a shop primer.

Disclosure of Invention

Thus, viewed from one aspect, the invention provides an aqueous primer composition comprising:

(A) a polysiloxane sol;

(B) selected from BaSO₄Feldspar, talc, mica, CaSO₄Or kaolin (kaolin);

(C) zn metal (Zn metal); and optionally

(D) Organic Zn salts (organic Zn salt) or zinc chloride.

Viewed from another aspect, the present invention provides a Zn metal-free waterborne primer composition comprising:

(A) a polysiloxane sol;

(B) selected from BaSO₄(iii) an accelerator for wollastonite or feldspar; and optionally

(D) Organic Zn salts or zinc chloride.

Viewed from another aspect, the present invention provides an aqueous primer composition comprising:

(A) at least 5.0 wt%, such as 5 to 50 wt%, of a polysiloxane sol;

(B)0.1 to 50 wt% of a compound selected from BaSO₄For feldspar and slippery stoneStone, mica, CaSO₄Or a promoter for kaolin;

(C)10 to 90 wt% Zn metal; and optionally

(D)0.1 to 5.0 wt% of an organic Zn salt or zinc chloride.

(A) 0.5 to 35 wt% by dry weight of a polysiloxane sol;

(B)0.1 to 90 wt% by dry weight of a material selected from BaSO₄Feldspar, talc, mica, CaSO₄Or a promoter for kaolin;

(C)10 to 95 wt% Zn metal on a dry weight basis; and optionally

(D)0.1 to 5.0 wt% by dry weight of an organic Zn salt or zinc chloride.

(A)20 to 90 wt% of a polysiloxane sol;

(B) at least 10 wt% of a material selected from BaSO₄Wollastonite and feldspar; and optionally

(D)0.1 to 5.0 wt% of an organic Zn salt or zinc chloride.

It is preferred if any of the primer compositions of the present invention do not contain ZnO.

Viewed from another aspect the invention provides a kit of parts (kit of parts ) comprising:

(I) a first component comprising (a) a polysiloxane sol, (B) an accelerator as defined herein and optionally (D) an organic Zn salt or zinc chloride; and

(II) a second component comprising Zn metal.

The part(s) of the kit are mixed shortly before application to the substrate, such as within 1 or 2 hours of application. It is understood that components (I) and (II) will be provided separately for mixing.

Viewed from another aspect, the invention provides a kit of parts comprising:

(I) a first component comprising from 20 to 70 wt% of (a) a polysiloxane sol, from 20 to 75 wt% of (B) a promoter as defined herein and optionally from 0.5 to 10 wt% of an organic Zn salt or zinc chloride;

(II) a second component comprising at least 60 wt% Zn metal.

Viewed from another aspect, the invention provides a kit of parts comprising:

(I) a first component comprising 0.5 to 70 wt% by dry weight of (a) a polysiloxane sol, 20 to 95 wt% by dry weight of (B) an accelerator as defined herein and optionally 0.5 to 10 wt% by dry weight of an organic Zn salt or zinc chloride;

(II) a second component comprising at least 60 wt% Zn metal by dry weight.

Viewed from another aspect the invention provides a method for protecting a substrate from corrosion, the method comprising applying to the substrate a primer composition as hereinbefore defined or a blend of component (I) and component (II) as hereinbefore defined and allowing the primer composition or blend to cure on the substrate.

Viewed from a further aspect the invention provides a substrate coated with a cured primer composition or cured blend of component (I) and component (II) as hereinbefore defined.

Viewed from a further aspect the invention provides the use of a primer composition as hereinbefore defined or a blend of component (I) and component (II) as hereinbefore defined to provide temporary corrosion protection to a substrate.

Detailed Description

The present invention relates to a primer composition suitable for application to a substrate to provide corrosion protection, such as temporary corrosion protection, to the substrate. The primer of the present invention can be applied by spraying and has a low VOC and can be diluted with water to achieve the desired application viscosity. However, the primer is fast drying and quickly able to resist mechanical abrasion and treatment with chemicals, water, etc. They are easy to apply to the substrate and they resist sagging. The primer of the present invention may be shop primer and is weldable to minimize weld hole, weld spatter, weld fume and flash back (back burning). In addition to being corrosion resistant, the primer can be overcoated with most types of coatings without requiring any additional pretreatment of the primer coating (other than cleaning to remove debris such as dust, salt and/or grease that is obtained after the primer is applied and before the next coating is applied).

Last but not least, the components (I) and (II) constituting the primer composition are storage stable and easy to mix without requiring any complex equipment and produce a blend that does not clog spraying equipment.

Without wishing to be bound by theory, it is envisaged that ensuring that the presence of any base component such as any glass-based microspheres in component (II) of the kit will maximise blend homogeneity. While multiple mixing components may be used as an alternative, the use of a two component system is advantageous in terms of user compliance. The kit of the invention preferably comprises only component (I) and component (II).

Binder component (A)

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

Polysiloxane sols are specifically sols rather than gels. It can be considered as a solution, colloidal solution, emulsion or suspension. Thus, the polysiloxane is present in aqueous form prior to application. The polysiloxane gels during the curing process after mixing with the other components of the primer.

The polysiloxane sols of the present invention are desirably derived from at least one alkoxysilane precursor that has been subjected to hydrolysis to form the corresponding silanols. It is understood that there are multiple alkoxy groups (typically up to 3 such groups) in multiple alkoxysilanes and thus multiple hydrolysis products may be present depending on the hydrolysis step. Both fully hydrolysed and partially hydrolysed products may be formed. This hydrolysis reaction causes the formation of alcohol.

The hydrolyzed/partially hydrolyzed silanes can then be condensed together, as is well known, to form complex oligomers/polymers. Due to the presence of various monomers in carrying out the hydrolysis reaction, complex polysiloxane sols are formed which cannot be easily characterized by the general formula. For example, due to partial hydrolysis, two partially hydrolyzed molecules may be linked together in a condensation reaction to form a siloxane, or the like. This condensation process obviously results in the formation of alcohol and water by-products.

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

The polysiloxane sols of the present invention are typically provided in aqueous form in component (I). In addition, it is preferably substantially free of VOCs (volatile organic compounds). The alcohol formed is easily removed by evaporation during the sol formation process. Importantly, due to the presence of free silanol groups in the sol, no more alcohol is released upon curing, thereby maintaining a low VOC content.

The sol is preferably room temperature curable.

It is preferred if the polysiloxane sols according to the invention are based on the condensation of at least one bis-aminofunctional alkoxysilane (bis-aminofunctional alkoxysilane) which is subject to hydrolysis or an epoxyfunctional alkoxysilane (epoxyfunctional alkoxysilane) which is subject to hydrolysis. Surprisingly, it was found that stable aqueous, substantially alcohol-free compositions based on silicon compounds can be obtained from bisamino-or epoxy-functional alkoxysilanes, optionally together with organofunctional alkoxysilanes. In particular, sol gel chemistry relies on bis-amino-or epoxy-functional alkoxysilanes and alkyl-functional alkoxysilanes. The silane compound is desirably provided in a substantially fully hydrolyzed form, although partially hydrolyzed forms are also possible. These compositions crosslink at low temperatures.

Thus, the polysiloxane sol material of the present invention is preferably based on a condensation product of a bis-amino-functional alkoxysilane such as bis (triethoxysilane) amine or bis (trimethoxysilane) amine these monomers can be hydrolyzed to obtain fully or partially hydrolyzed analogs of bis-amino-functional alkoxysilanes such as bis (triethoxysilane) amine or bis (trimethoxysilane) amine epoxy-functional alkoxysilanes can also be hydrolyzed to obtain fully or partially hydrolyzed analogs such silanes include 3-glycidoxypropyltriethoxysilane (G L YEO), 3-glycidoxypropyltrimethoxysilane (G L YMO).

Other preferred monomers include bis (triethoxysilane) amine, bis (trimethoxysilane) amine, N-propyltriethoxysilane, N-Propyltrimethoxysilane (PTMO), 3-glycidoxypropyltriethoxysilane (G L YEO), 3-glycidoxypropyltrimethoxysilane (G L YMO), 3-Aminopropyltriethoxysilane (AMEO), 3-Aminopropyltrimethoxysilane (AMMO), Methacryloxypropyltriethoxysilane (MEEO), methacryloxypropyltrimethoxysilane (MEMO), N- (N-butyl) -3-aminopropyltriethoxysilane, Vinyltrimethoxysilane (VTMO), N- (N-butyl) -3-aminopropyltrimethoxysilane (Dynalalan) (R)1189), 3-mercaptopropyltrimethoxysilane (MTMO), 3-Mercaptopropyltriethoxysilane (MTEO), N-2-aminoethyl-3-aminopropyltrimethoxysilane (DAMO), polyethylene glycol-functional alkoxysilanes (TEOS), tetraethoxysilane (Dynasylsiloxane) and bis (triethoxy) silane (Dynaethyltrimethoxysilane (Dynaxosylsilane), triethoxy-triethoxy) and triethoxy-methyl-triethoxy) silanes (Dynaxosylsilanes), triethoxy-ethyl-3-aminopropyltrimethoxysilane (Dynaxysilane (Dynaxosylsilanes), triethoxy-2-aminopropyltrimethoxysilane (Dynaxysilane (Dysylsilanes), triethoxy) silanes (Dynaxosylsilanes), triethoxy-3-triethoxy-3-triethoxy (Dynaxysilanes (Dynaxosylsilanes), triethoxy) silanes (Dynasylsilanes), triethoxy-methoxy-triethoxy-ethyl-3-triethoxy-ethyl-3-triethoxy-silanes (Dynaoxy-triethoxy-silanes), triethoxy-N (Dy-triethoxy-N (Dy-N (Dy-N) silanes), triethoxy-N (Dy-N (ethyl-N.

Any of these monomers can also be hydrolyzed to produce hydrolyzed or partially hydrolyzed monomers for reaction with a bis-amino-functional alkoxysilane or epoxy-functional alkoxysilane that can also be hydrolyzed or partially hydrolyzed. It is preferred to use hydrolyzed diamino-or epoxy-functional alkoxysilanes with unhydrolyzed alkylalkoxysilane monomers. Other preferred options are epoxy-functional alkoxysilanes in combination with amino-functional alkoxysilanes.

The epoxy-functional alkoxysilane used in the present invention is most preferably an epoxyalkyl-functional alkoxysilane.

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

In a most preferred embodiment, the sol is formed from a co-condensate based on an omega-glycidyloxyalkylalkoxysilane of formula I

X—Si(R)_x(OR¹)_3-x(I)，

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

R¹and each R is independently a straight or branched alkyl group containing 1 to 4C atoms; and is

x is a number of 0 or 1,

or is

Bis (alkoxysilylalkyl) amines of formula II

(OR¹)₃Si-A-Si(OR¹)₃(II)，

Wherein each R¹Independently a straight or branched alkyl group containing 1 to 4C atoms, and A is a diamino functional group of formula IIa

-(CH₂)_i—[NH(CH₂)_f]g-NH[(CH₂)_f*-NH]_g*—(CH₂)_i*— (IIa)，

Wherein i and i are each independently an integer of 1, 2, 3 or 4, f and f are each independently an integer of 1 or 2, and g are each independently an integer of 0 or 1.

To prevent any VOC content, the alcohol released during sol-gel formation is distilled off.

The hydrolysis of the starting alkoxysilane may be performed using formic acid or other mild hydrolysis reagents, e.g., as shown in US 2011/0268899. The condensation reaction is preferably carried out at a low pH, e.g. a pH of less than 7, such as 3 to 5. The reaction time is preferably controlled to ensure that a sol is formed, rather than a gel. The reaction time may be up to 3 hours. Too long a reaction time may allow the curing reaction to start. The synthesis of the necessary sols is summarized in US2011/0268899, WO2018202472 or US 2014/0106176.

Thus, viewed from another aspect, the polysiloxane sol used in the present invention is a polysiloxane sol obtainable by a process comprising:

(i) hydrolyzing at least one bis-amino-or epoxy-functional alkoxysilane;

(ii) the resulting hydrolyzate is reacted with itself, with at least one optionally hydrolyzed alkylalkoxysilane or with at least one optionally hydrolyzed amino-functional alkoxypolysiloxane.

Any alcohol formed may be removed such that the alcohol content of the sol is less than 3 wt%.

Alternatively, the polysiloxane sol used in the present invention is a polysiloxane sol obtainable by a process comprising: the bis-amino-or epoxy-functional alkoxysilane is hydrolyzed and the resulting hydrolyzate is self-condensed to form a sol. Any alcohol formed may be removed such that the alcohol content of the sol is less than 3 wt%.

It will be appreciated that more complex sols can be prepared by adding further reactants to the mixture. Thus, while at least one bis-aminoalkoxysilane or epoxy-functionalized alkoxysilane reactant as defined hereinabove must be present, other possible reactants include vinylsilanes, alkylsilanes, alkoxysilanes, and the like.

The ratio of the bisamino-or epoxy-functional alkoxysilane to the alkylalkoxysilane can be 10:1 to 1:10, such as 5:1 to 1:5, by weight.

The sol formed should be dispersible in water at room temperature of 23 ℃. By water-dispersible is meant that the sol can form an emulsion, suspension or colloidal solution in water.

Alternatively, the polysiloxane sol used in the present invention is a polysiloxane sol obtainable by the reaction of at least the following components:

(i) glycidyloxypropylalkoxysilane of the general formula (I):

X-Si(OR)₃，

wherein X represents a 3-glycidyloxypropyl group and R represents a methyl or ethyl group,

(ii) an aqueous silica sol (aqueous silica sol, aqueous silicic acid sol) having an average particle size in the range from 5 to 150nm and a solids content of ≥ 45 to ≤ 55 wt.%,

(iii) at least one acid selected from the group consisting of nitric acid, sulfuric acid, hydrochloric acid, phosphoric acid, formic acid and acetic acid, and

(iv) bisaminosilane of the general formula (II)

(R¹O)₃Si(CH₂)₃(NH)(CH₂)₃Si(OR¹)₃(II)，

Wherein R is¹Is a methyl or ethyl group, and optionally

(v) At least one further alkoxysilane of the general formula (III)

Y_n-Si(OR₃)_4-n

Wherein Y represents a propyl-, butyl-, octyl-, 3-mercaptopropyl-, 3-ureidopropyl-, or 3-isocyanatopropyl (3-isocyanato propyl) group, R₃Represents a methyl or ethyl group and n is equal to 0 or 1.

It is important that the sol has free silanol groups so that no more alcohol is released upon curing to maintain low VOC levels.

Although the sols of the present invention are provided in water, the polysiloxanes are often diluted with water prior to use to achieve the desired application viscosity. In particular, commercially available polysiloxanes used in the present invention may be obtained as aqueous solutions.

Where wt% of polysiloxane sol is given herein, the wt% is derived from the water and polysiloxane content present, unless otherwise indicated. The polysiloxane sol (i.e., including the weight of any water in the primer composition) can form at least 5 weight percent, such as at least 10 weight percent, more preferably at least 30 weight percent of the primer composition. In some embodiments, the polysiloxane sol may form 5 to 50 wt%, preferably 10 to 45 wt%, such as 20 to 40 wt% of the primer composition. If the primer composition is diluted with water during its preparation, the water can be considered to become part of the polysiloxane sol. This makes determining a particular percentage challenging.

Preferably, the amount of water present in the primer composition of the invention is at least 5 wt%, such as at least 10 wt%. In some embodiments, the primer composition of the present invention comprises 5 to 50 wt%, such as 10 to 35 wt% water.

The polysiloxane sol component a typically contains 50 to 98 wt% water, such as 65 to 95 wt% water. Typically the solids content of the polysiloxane sol is from 2 to 50% by weight, preferably from 5 to 35% by weight. The solids content of the sol is in particular from 10 to 25% by weight. However, sols available from commercial suppliers can be diluted by the user as needed, which makes it difficult to specify the percentages. The skilled person will be able to design the appropriate level of polysiloxane sol in the composition.

The water used for dilution is preferably deionized water. Any water used for dilution herein is considered to be part of the polysiloxane sol in terms of weight percent. Whenever a sol percentage appears in the text, it refers to the total weight of sol and water in the primer.

The condensation products formed by the reaction of especially di-amino-functional alkoxysilanes or epoxy-functional alkoxysilanes with alkylalkoxysilanes can be oligomeric/polymeric. Both are referred to herein as polysiloxanes. They may have a particle size of between 0.5 and 350nm, or preferably between 0.5 and 130 nm. The weight average molecular weight may be in the range of 1000-150000g/mol, preferably between 4000-30000 g/mol, more preferably between 1000-50000 g/mol, even more preferably between 1000-5000 g/mol. The viscosity of the polysiloxane (in water) at 20 ℃ may be from 5 to 20 mPas.

The silicone component is preferably free of VOCs (volatile organic compounds) — meaning that it contains less than 3 wt% volatile organic compounds (per ASTM D5201), such as 2 wt% or less, desirably 1 wt% or less alternatively it contains 100 g/L VOC or less, preferably 40 g/L VOC or less.

The polysiloxane sol should not release additional alcohol upon crosslinking. Curing of the sol should be possible at temperatures that may be experienced at the coated substrate, such as 0 to 40 ℃.

The polysiloxane sol preferably has a pH of 1.0 to 8.0, such as 3.0 to 5.5. The silane may have a pH range of 3.2 to 4.0.

The formation of sols results in crosslinked structural elements, which are chain, cyclic or 3D, but due to the number of latent structures formed, it is difficult to define the structure by way of a generic formula.

The polysiloxanes used in the present invention are not new and these are commercially available.

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

It is difficult to define the content of polysiloxane sol in the primer of the invention, as the amount varies depending on the water content and the content of Zn metal (which is heavier and therefore a disproportionate percentage of the primer weight). The dry weight of the binder (i.e., the weight of the polysiloxane solids, neglecting water) may form 0.5 to 35 wt%, such as 1.0 to 20 wt%, particularly 2.0 to 10 dry weight% of the primer. More particularly, the dry weight of the polysiloxane in the primer is 2.0 to 12 wt%, especially 4.0 to 10 wt%. These percentages refer to the amount of polysiloxane (dry weight) calculated as the sum of all the mixed components but neglecting the weight of water.

If "dry weight" is not specified, then the weight percentages mentioned in the text/claims refer to the primer including any water content unless the context allows otherwise.

Component (a) is present only in kit component (I). Component (II) should be free of component (A).

Accelerator component B

The water-based primer of the invention contains an accelerator selected from BaSO₄Feldspar, talc, mica, CaSO₄Or kaolin, preferably selected from BaSO₄Feldspar, talc, mica, or kaolin. Preferably the accelerator is BaSO₄Or feldspars, especially BaSO₄。

The amount of accelerator in the primer composition of the invention may be 0.1 to 50 wt%, such as 1.0 to 40 wt%, preferably 3.0 to 30 wt%.

Component (B) may form 0.1 to 90 wt%, such as 1.0 to 75 wt%, more preferably 3.0 to 50 wt%, such as 5.0 to 30 wt%, especially 10 to 20 wt%, in terms of dry weight (in dry weight).

Accelerator (B) is present in component (I) of the kit of the present invention. It is preferred if accelerators are not present in component (II).

The primer composition of the present invention should not contain zinc oxide. The composition of the invention preferably does not contain ZnO. It is believed that ZnO causes component (I) of the kit of the present invention to gel and should not be used.

If the primer composition does not contain iron oxides such as Fe₃O₄It is also preferable. It is believed that iron oxide adversely affects the color of the composition and should not be used.

The optimum weight ratio of polysiloxane (dry weight) to accelerator is 1:5 to 1: 1.

Zn Metal component C

Preferred primer compositions of the invention contain Zn metal, preferably zinc powder. The Zn metal is not present in component (I) of the kit of the invention, but in component (II) of the kit.

The zinc used in the composition may be metallic zinc in the form of powder or flakes, hollow spheres having zinc embedded on the surface, minerals having zinc embedded on the surface, and polymers having zinc embedded on the surface. Alternatively, the zinc may be a surface treated metallic zinc that is chemically inert to aqueous environments.

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. Specifically, the zinc is in the form of zinc powder, specifically, having the stated particle size range. The use of zinc powder as a corrosion inhibiting pigment is well known and its use will be familiar to those skilled in the art.

The content of Zn metal in the primer of the invention may vary within wide limits depending on the corrosion resistance requirements of the composition in question. In some embodiments, the Zn content of the primer composition may be in the range of 10 to 90 wt%, such as 30 to 80 wt%, such as 50 to 80 wt%, such as 60 to 80 wt%. The Zn metal may constitute 10 to 95 wt%, preferably 20 to 90 wt%, such as 30 to 85 wt% (dry basis) in terms of dry weight.

In some embodiments of the invention, Zn metal is absent.

Water-soluble zinc salt component D

Preferably, a water soluble organic zinc salt or zinc chloride is present to provide the necessary fast drying time for the primer composition. The organic Zn salt or zinc chloride is part of component (I) of the kit of the invention.

The presence of organic zinc salts or zinc chloride accelerates the curing process. It works with the accelerator component to minimize cure time. However, an excess of this component may reduce the abrasion resistance of the primer composition.

A water soluble organic zinc salt is one that has a solubility in deionized water at 25 ℃ of at least 0.5 g/L, preferably at least 5.0 g/L, such as at least 10 g/L or at least 20 g/L.

Typically, organic zinc salts will have relatively low molecular weights, such as up to 600g/mol suitable salts include zinc butyrate, zinc acetate, zinc gluconate, zinc glycerate, zinc glycolate (zinc glycolate), zinc lactate, zinc propionate, zinc salicylate, zinc citrate, zinc oleate, zinc benzoate, zinc laurate, zinc tartrate, zinc stearate, zinc valerate, zinc formate, zinc picolinate, zinc ascorbate, zinc glycinate complexes (bisglycinate, zinc glycinate), zinc lysine, zinc malate, zinc mono-L-methionine sulfate (zinc mono-L-methionine sulfate), zinc pyrrolidone carboxylate, and mixtures thereof.

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

It is preferred if the organic anion comprises at least 2 carboxyl groups or contains at least 1 carboxyl group and at least 1 hydroxyl group.

In the kit according to the invention, the organic zinc salt or zinc chloride may be included as part of component (I) of the kit and thus together with the sol (a). Component (D) should not be present in component (II).

Particularly preferred salts are zinc gluconate, zinc lactate and zinc citrate, and their corresponding hydrates. Particularly preferred is zinc gluconate.

Barium sulfate as promoter and zinc gluconate as organic Zn salt are particularly preferred.

Mixtures of organic zinc salts may also be used.

In a preferred aspect, component (D) does not comprise zinc acetate. This means that the composition comprises less than 0.1 wt% of each zinc acetate, preferably less than 0.05 wt% of zinc acetate, preferably no zinc acetate.

In a preferred aspect, component (D) is zinc gluconate, zinc citrate, zinc chloride, zinc acetate, or a mixture thereof. Preferably, component (D) is zinc gluconate, zinc citrate, zinc chloride, or a mixture thereof. Further preferably, component (D) is zinc gluconate, zinc citrate, or a mixture thereof.

If present, the zinc salt component (D) preferably forms 0.1 to 5.0 wt%, preferably 0.25 to 5.0 wt%, preferably 0.5 to 5.0 wt%, such as 0.75 to 4.0 wt%, especially 1.0 to 3.0 wt% of the primer as a whole. A level of 2 wt% + -0.5 wt% is particularly preferred.

If present, the zinc salt component (D) preferably forms 0.1 to 5.0 wt% dry weight, preferably 0.25 to 5.0 wt% dry weight, preferably 0.5 to 5.0 wt% dry weight, such as 0.75 to 4.0 wt% dry weight, especially 1.0 to 3.0 wt% dry weight of the primer as a whole. A dry weight level of 2 wt% + -0.5 wt% is particularly preferred. In the case of hydrates, these levels do not include any water associated with the salt. In case a mixture of zinc salts is used as component (D), these levels refer to the levels of zinc salts combined.

The optimum level of Zn salt, such as zinc gluconate, is such that the weight ratio of polysiloxane sol to organic Zn salt is from 30:1 to 15: 1. If the ratio is below 15:1, too much organic Zn salt is present, and this reduces the wear resistance of the coating.

(A) a polysiloxane sol;

(B)BaSO₄；

(C) zn metal; and

(D) organic Zn salts such as zinc gluconate.

(A) at least 5.0 wt%, such as 5 to 50 wt% of a polysiloxane sol;

(B)0.1 to 50 wt% BaSO₄；

(C)10 to 90 wt% Zn metal; and

(D)0.1 to 5.0 wt% of an organic Zn salt.

(A) 0.5 to 35 wt% by dry weight of a polysiloxane sol;

(B)0.1 to 90 wt% BaSO by dry weight₄；

(C)10 to 95 wt% Zn metal on a dry weight basis; and optionally

(D)0.1 to 5.0 wt% by dry weight of an organic Zn salt, such as zinc gluconate.

Viewed from another aspect, the invention provides an aqueous primer composition comprising

(A) 0.5 to 20 wt% by dry weight of a polysiloxane sol;

(B) 5.0 to 30 wt% by dry weight of a material selected from BaSO₄Feldspar, talc, mica, CaSO₄Or a promoter for kaolin;

(C)10 to 90 wt% Zn metal on a dry weight basis; and

(D)0.1 to 5.0 wt% by dry weight of an organic Zn salt or zinc chloride.

(A) 0.5 to 20 wt% by dry weight of a polysiloxane sol;

(B) 5.0 to 30 wt% BaSO by dry weight₄；

(C)10 to 90 wt% Zn metal on a dry weight basis; and

(D)0.1 to 5.0 wt% by dry weight of an organic Zn salt, such as zinc gluconate.

In some embodiments of the invention, Zn metal is not present in the primer. In this embodiment, the promoter is BaSO₄Wollastonite and feldspar, preferably BaSO₄Or feldspar, most preferably BaSO₄. It is an option to provide a Zn-free composition as a kit, wherein the accelerator is part of component (II) of the kit.

In this embodiment, the present invention preferably provides a Zn metal-free water-based primer composition comprising:

(A)25 to 80 weight percent of a polysiloxane sol;

(B)15 to 70 wt% of a compound selected from BaSO₄Wollastonite and feldspar; and optionally (D)0.1 to 5.0 wt% of an organic Zn salt or zinc chloride.

Alternatively, the present invention preferably provides a Zn metal-free water-based primer composition comprising:

(A)5 to 50% by weight (dry weight) of a polysiloxane sol;

(B) from 30 to 90% by weight (dry weight)Self BaSO₄Wollastonite and feldspar; and optionally

(D)0.1 to 5.0 wt% by dry weight of an organic Zn salt or zinc chloride.

Other ingredients

The primer layer composition may also contain various other components, for example, to enhance its corrosion inhibiting properties, and the like.

The primer composition may contain a color pigment, such as an inorganic pigment. Examples of color pigments include titanium white, chromium oxide (chromium oxide), and carbon black.

The addition of one or more thickeners/thixotropic agents improves the anti-settling properties (anti-settling properties), film formation and spray properties of the primer. Examples of suitable thickeners are bentonite, pyrogenic/colloidal silica, natural thickeners (e.g. alginates), cellulosic thickeners, sugars, and polysaccharides. When present, the thickener is preferably present in part (I) of the kit, preferably only in part (I) of the kit. Particular preference is given to using pyrogenic silicon dioxide (fumed silica, pyrogenic silica, fumeidsilica). Silicon dioxide (silica) may also be used in component II together with Zn to improve the flow characteristics of the Zn powder.

As both a thixotropic agent and as a flow enhancer, it is used in a relatively small amount (additive level) of 0.01 to 2.0% by weight of the final composition, preferably 0.05 to 1.0% by weight of the final composition, preferably less than 0.5% by weight of the final composition, less than 0.2% by weight of the final composition.

Weld enhancers may also be used. Titanium dioxide acts both as a weld enhancer and as a color pigment.

The primer composition may also contain glass or ceramic particles or microspheres to improve the hardness and weldability of the coating. Examples of such particles/microspheres are mentioned in WO 2017/129784. Preferably glass and especially glass microspheres. The microspheres may form 1.0 to 20 wt%, such as 1.0 to 15 wt%, particularly 3.0 to 15 wt% of the primer composition. In terms of dry weight, the microspheres may form 1.0 to 20 dry weight percent, such as 2.0 to 15 wt% by dry weight.

If present, the microspheres will be part of component (II) of the kit of the invention. They are preferably not present in component (I).

In a preferred embodiment, a portion of the zinc dust is combined (merged) with a glass, such as a silicate glass, in component (II) of the kit of the invention. A suitable glass is borosilicate glass. The blend components may be 20-80 wt% such as about 50:50 blend of zinc powder and glass/microspheres.

When present, the colour and weld enhancer are preferably present in part (I) of the kit, preferably only in part (I) of the kit.

The primer composition as a whole preferably comprises 0.1 to 10 wt.%, preferably 1.0 to 5.0 wt.% of other additives (other than microspheres), such as titanium dioxide and thixotropic materials.

The primer composition may generally comprise 0.1 to 10 wt%, preferably 1.0 to 5.0 wt% (dry weight) of additives (other than microspheres), such as titanium dioxide and thixotropic materials.

As previously mentioned, the primers of the present invention are designed to avoid the problems associated with some waterborne silicate primers. Therefore, it is preferred if the primer of the invention does not contain an alkali metal silicate such as lithium silicate, potassium silicate or sodium silicate.

It is also preferred if the primer does not contain an organic solvent.

External member

The primer composition of the present invention is formed by mixing the various components shortly before applying the primer to the substrate to avoid premature curing. Thus, the primer is preferably provided as a two-component kit (two component kit) for mixing by the user.

Component (I) of such a kit contains a polysiloxane sol component (a), an accelerator (B), an organic Zn salt or zinc chloride (D) and the additives conventionally present, such as titanium dioxide and thixotropic materials.

Component (II) comprises the Zn metal component (C) of the primer of the invention and microspheres/glass if present. Desirably no other components are present in this component (II) of the kit, other than the optional silica flow enhancer.

Component (I) and component (II) may be mixed in a defined ratio depending on the content of each component. A mixing weight ratio of 1:1 to 1:3 of component (I) to component (II) is common, such as about 1: 2.

Component (I) preferably comprises from 20 to 70 wt% of (a) a polysiloxane sol, from 20 to 75 wt% of (B) an accelerator as defined herein and optionally from 0.5 to 10 wt% of an organic Zn salt or zinc chloride;

component (II) preferably comprises at least 60 wt%, such as at least 70 wt% Zn metal and 5 to 30 wt% microspheres/glass if present. It is preferred if no other components than the optional silica are present in component (II).

Component (I) preferably comprises 0.5 to 70 wt% such as 20 to 70 wt% by dry weight of (a) polysiloxane sol, 20 to 95 wt% by dry weight, preferably 20 to 75 wt% by dry weight of (B) accelerator as defined herein and optionally 0.5 to 10 wt% by dry weight of organic Zn salt or zinc chloride;

it is preferred if the composition of the invention (i.e. the hybrid primer) has a VOC of less than 100 g/L, preferably less than 50 g/L, most preferably less than 30 g/L, for example less than 15 g/L.

The composition of the invention is preferably dried within 10 minutes, preferably within 2 minutes at 23 ℃ 50% RH at the time of application according to the test protocol set out in the test section of application.

It is also preferred if the composition dries thoroughly and provides a mechanical wear resistant surface within 20 minutes, preferably within 5 minutes, at 23 ℃ 50% RH according to the test protocol set out below.

The final primer of the invention is water resistant (water repellent).

In this regard, it is preferred if the primer has an early water resistance, i.e. is water resistant within a curing time of 24 hours, preferably 12 hours, preferably within 6 hours at 23 ℃ 50% RH, according to the test procedure set out in the test section of application (stable water rub test).

The primers of the present invention also have good moisture resistance. Primers according to the invention are considered "stable" if they exhibit a moisture resistance of at least 24 hours when measured according to the moisture resistance test (ISO 6270-2: 2005). The primer of the invention preferably has a stability resistance (stability) of at least 36 hours, in particular at least 48 hours.

In a preferred embodiment, the primer of the present invention is a shop primer. It is important that shop primers can be welded. The primary purpose of shop primers is to provide temporary corrosion resistance when all parts of the welding takes place. The shop primer of the present invention may be welded (soldered) using MIG or similar welding techniques at a speed of at least 70 cm/min to produce less than 125mm per 1 meter of weld²The hole of (2). In addition, welding should produce minimal weld spatter, weld fumes, and flash back.

A final and important objective is that shop primer can be overcoated without any additional pre-treatment of the shop primer coating. It is understood that any surface to be painted is cleaned prior to overcoating, for example, to remove dust, salt and/or grease that has been obtained after shop primer application and prior to the application of the next coating. This is not a pre-treatment step. In particular, it is possible to apply an epoxy primer.

Pigment Volume Concentration (PVC) is an important parameter for the shop primer of the present invention. The critical volume concentration is also important. PVC is the pigment volume concentration. CPVC is the maximum volume concentration of pigment that is completely covered by resin. PVC/CPVC >1 means that not all of the pigment is covered by resin. The coating will be porous. The ratio is a balance between barrier protection (barrier protection) and cathodic protection. Too high a ratio results in other problems such as popping and loss of cohesion. Preferably, the PVC/CPVC is in the range of from 0.8 to 1.2, more preferably from 0.9 to 1.1, most preferably from 0.95 to 1.05.

At any time before, during or after the mixing process, water may be added to dilute the composition. Dilution of the composition can extend pot life, but slow drying times. It is possible to dilute 10 to 35 wt% of the total weight of the composition. It is clear that the amount of water required for dilution is determined in part by the amount of water present in the polysiloxane sol (a).

Application of

The compositions of the present invention can be applied by all types of application equipment, such as brushes and rollers, conventional spray guns, airless spray applicators, and air assisted airless spray applicators. Desirably, the coating is applied by an airless sprayer to produce a primer that cures spontaneously upon application to the substrate.

The substrate to be coated is preferably a metal substrate, ideally a steel substrate. The substrate may be a substrate for use in a marine environment. Typical substrates therefore include marine components, metal containers such as shipping containers, bridges, and the like.

After final mixing, the primer is typically applied to the steel surface, desirably to a final thickness of 5-200 microns, such as 50-150 microns (dry film thickness (DFT) as measured according to the test methods section). Such coatings provide temporary protection to the steel surface. In the case of shop primers, the final thickness is preferably 5-50 microns, such as 15-25 microns.

That is, the present invention also relates to a method for temporarily protecting a steel surface with an anti-corrosive coating, which method comprises coating the steel surface with a primer composition as defined herein.

The thus coated steel surface will typically be stored for 2-40 weeks, such as up to about 6 months, after which the steel surface may be used in the production of steel structures, wherein the coated steel surface is the surface of the steel body parts constituting the steel structure. The steel structures are assembled by welding and, importantly, steel body parts coated with the composition according to the invention can be easily welded to provide a high quality joint between the steel body parts of the steel structures.

The invention therefore also relates to a method for producing a steel structure, which is composed of a plurality of steel body parts, comprising the following steps:

a) coating at least one of the steel body parts with a primer composition according to the invention;

b) storing one or more thus coated steel body parts for a period of 2-40 weeks;

c) assembling at least a portion of the steel structure by welding at least two steel body parts together, at least one of the at least two steel body parts being coated as in step (a).

Other steps and details in producing the steel structure will be apparent to those skilled in the art.

The primer coating can be overcoated with any type of coating without any pretreatment of the primer coating except that it is cleaned to remove dust, grease, etc.

The invention will now be described with reference to the following non-limiting examples.

Test procedure

Storage stability test

Component (I) was stored in a closed jar at 50 ℃ for 1 month. The contents were checked at regular intervals (1 time per week). The paint was stirred by hand using a wooden stick and visually inspected.

1: by this, the coating is homogeneous, without lumps/gels or significant color changes.

0: otherwise, the coating is not uniform, contains lumps/gels or changes in color.

Determination of Dry Film Thickness (DFT)

The dry film thickness was measured on a smooth steel substrate using a film thickness gauge.

Calculation of Volatile Organic Compound (VOC) content, volume solids (volume solid), and solids content of coating compositions

The Volatile Organic Compound (VOC) content, volume solids and solids content of the coating compositions were calculated according to ASTM D5201-05.

Curing Friction test (curing rub test)

The plates were prepared by airless spray application (15-25 μm DFT) on SA2.5 grit blasted steel plates (blasted steel panel) (615 nozzle, 16MPa output pressure). After curing at 23 ℃ 50 RH% for a certain time (24 hours, 1 week or 1 month) in good ventilation, the plate is placed in a container with water at 23 ℃ so that half of the plate is immersed. The plate was immersed for 5 minutes; clean cotton cloth (clearwoven cotton cloth) soaked in water was rubbed back and forth (twice) 80 times with medium pressure. The coating and cotton were then evaluated by water resistance values from a rating of 0 to 5. A score of 0 refers to penetration to the substrate in 80 rubs or less. Score 1 means that the film was severely depressed (depression) after 80 rubs, but did not actually penetrate to the substrate. Score 2 refers to severe damage (scratching) and severe denting of the film after 80 rubs. Score 3 means that the film developed some damage and significant denting after 80 rubs. Score 4 means that the rubbed area had a buffed appearance (burnish wear) after 80 rubs and had a small amount of film on the cloth. Score 5 means that the film was fully cured, had no effect on the surface after 80 rubs and no film on the cloth.

Surface drying time

The panels were prepared by airless spray application (15-25 μm DFT) on SA2.5 grit blasted steel panels. The panel is placed in good air flow (air flow) or ventilation. The film was contacted after a specified time to check whether the film was transferred to a finger. If there is no film on the finger, the film has been surface dried according to GB 1728-79.

Film Forming Properties

Exposed areas (exposed areas) or unsealed areas (unsealed areas) on the film on Sa2.5 sandblasted panels were inspected by visual inspection.

Sag resistance (anti-bagging)

The shop primer was thoroughly mixed and diluted by 5% by weight. The (Sa 2.5 blasted) panels were placed close to vertical with a minimum angle of 80 degrees with 50% overlap. The distance from the nozzle to the plate to obtain a constant film thickness by airless spraying (615 nozzle, 16MPa output pressure) was 35-40 cm. Film thickness was measured using a comb (comb) immediately after application. 2-3 panels were sprayed at increasing film thickness and the maximum wet film thickness was determined to have good sag resistance.

Examples

TABLE 1 materials used

Example 1 stability of component (I) of the kit

The stability of component (I) of the kit was tested using various accelerators.

Accelerators are required in the coating to cure the coating.

TABLE 2 Accelerator for storage stability (all components in parts by weight)

These results demonstrate that the presence of ZnO with the binder causes gelation (gelation). The accelerator of the present invention does not gel.

Example 2

Component (I) and component (II) as defined in table 3 were combined (combined) in a weight ratio of 1: 2. All samples were diluted with 25% water by weight of components I + II. The curing characteristics are determined.

Table 3 shows all components in total parts by weight (i.e., after mixing)

These results demonstrate that for BaSO₄Optimum curing properties were observed.

Example 3 BaSO₄

To determine the optimum BaSO₄Content (preferred accelerator) the following experiment was performed. Component (I) and component (II) were mixed in a ratio of 1:2 and diluted with 25 wt% of water. By adjusting zinc powder and BaSO₄Was made the same volume solids (68%) in each example, which resulted in BaSO in the dry film₄The% are 15.1%, 31.7% and 45.3%. The corresponding Zn contents in the dry film were 68%, 50%, 35% by weight. The other components remained constant.

TABLE 4 BaSO₄Test dose of

Mixing ratio of (I) to (II) 1:2

(Sivo165 solid content 20 wt%)

With BaSO₄Increased amount of zinc metal and decreased amount of zinc metal, the surface drying time was longer, but curing and film formation were not affected and remained good in all 3 examples. For BaSO₄An optimum amount of providing a shop primer surface drying time<5 minutes).

Example 4

Ex.21 was prepared with fumed silica in component I at a mixing ratio of a: B of 100:166 and 4% to test the sag resistance characteristics.

Ex.22 was prepared at a mixing ratio a: B of 1:2 but using 1% fumed silica to test sag resistance. Both experiments were diluted with 5 wt% water.

Example 23 was prepared at a mixing ratio a: B ═ 1:2 and 1% silica but diluted with 10% water.

TABLE 5 sag resistance

Claims

1. An aqueous primer composition comprising:

(A) a polysiloxane sol;

(B) selected from BaSO₄Feldspar, talc, mica, CaSO₄Or a promoter for kaolin;

(C) zn metal; and optionally

(D) Organic Zn salts or zinc chloride.

2. A Zn metal-free waterborne primer composition comprising:

(A) a polysiloxane sol;

(B) selected from BaSO₄An accelerator for wollastonite, or feldspar; and optionally

(D) Organic Zn salts or zinc chloride.

3. An aqueous primer composition comprising:

(A) at least 5.0 wt% of a polysiloxane sol;

(B)0.1 to 50 wt% of a compound selected from BaSO₄Feldspar, talc, mica, CaSO₄Or a promoter for kaolin;

(C)10 to 90 wt% Zn metal; and optionally

(D)0.1 to 5.0 wt% of an organic Zn salt or zinc chloride.

4. An aqueous primer composition comprising:

(A) 0.5 to 35 wt% by dry weight of a polysiloxane sol;

(C)10 to 95 wt% Zn metal on a dry weight basis; and optionally

(D)0.1 to 5.0 wt% by dry weight of an organic Zn salt or zinc chloride.

5. A Zn metal-free waterborne primer composition comprising:

(A)20 to 90 wt% of a polysiloxane sol;

(B) at least 10 wt% of a material selected from BaSO₄Wollastonite and feldspar; and optionally (D)0.1 to 5.0 wt% of an organic Zn salt.

6. The aqueous primer composition according to any one of claims 1 to 5, wherein the polysiloxane sol is a polysiloxane sol obtained by a process comprising:

(i) hydrolyzing at least one bis-amino-or epoxy-functional alkoxysilane;

7. The waterborne primer composition of any one of the preceding claims, wherein the water soluble organic Zn salt is zinc gluconate.

8. The aqueous primer composition according to any one of claims 1 to 7, being free of alkali metal silicate.

9. The aqueous primer composition according to any one of the preceding claims, which is free of ZnO.

10. The waterborne primer composition of any one of the preceding claims, wherein the accelerator is barium sulfate.

11. The aqueous primer composition according to any one of the preceding claims, wherein the primer composition comprises titanium dioxide.

12. The aqueous primer composition according to any one of the preceding claims, wherein the primer composition comprises silica, such as fumed silica, preferably in an amount of 0.1 to 5.0 wt%.

13. The aqueous primer composition according to any one of the preceding claims, wherein the primer is a shop primer.

14. The aqueous primer composition according to any one of the preceding claims, wherein the primer composition comprises microspheres.

15. A kit of parts comprising:

(I) a first component comprising (A) a polysiloxane sol and (B) a compound selected from BaSO₄Feldspar, talc, mica, CaSO₄Or kaolin, and optionally (D) an organozn salt; and

(II) a second component comprising Zn metal.

16. A kit of parts comprising:

(I) a first component comprising from 20 to 70 wt% of (A) a polysiloxane sol, from 20 to 75 wt% of (B) a silicone selected from BaSO₄Feldspar, talc, mica, CaSO₄Or kaolin, and optionally from 0.5 to 10 wt% of (D) an organozn salt; and

(II) a second component comprising at least 60 wt% Zn metal.

17. The kit of claim 16, wherein the second component (II) comprises a blend of Zn metal and borosilicate glass.

18. The kit of claim 16, wherein the second component (II) comprises Zn metal and microspheres.

19. The kit of claim 16, wherein the first component (I) comprises zinc gluconate, titanium dioxide and silicon dioxide.

20. A method for protecting a substrate from corrosion comprising applying to the substrate the aqueous primer composition according to any one of claims 1 to 14 or the blend of the first component (I) and the second component (II) as defined in any one of claims 15 to 19, and curing the aqueous primer composition or the blend on the substrate.

21. A substrate coated with a cured aqueous primer composition according to any one of claims 1 to 14 or a cured blend of the first component (I) and the second component (II) as defined in any one of claims 15 to 19.