WO2019234209A1

WO2019234209A1 - Concentrate comprising brazing flux

Info

Publication number: WO2019234209A1
Application number: PCT/EP2019/064917
Authority: WO
Inventors: Stefanie VOLMER; Hynek PAWERA
Original assignee: Solvay Sa
Priority date: 2018-06-08
Filing date: 2019-06-07
Publication date: 2019-12-12

Abstract

The present invention concerns a concentrate comprising at least one brazing flux, at least one binder and water in a specific ratio; a process for the manufacture of a brazing flux paint composition which comprises the steps of a) providing the concentrate and b) mixing the concentrate with at least one liquid carrier; and a process for brazing of parts of aluminum, aluminum alloy, in particular aluminum alloy comprising magnesium, steel, copper and titanium with parts of aluminum or aluminum alloy, which comprises the process for the manufacture of a brazing flux paint composition.

Description

Concentrate comprising brazing flux

This application claims priority to European application No. 18176813.6 filed on June 8^th 2018 the whole content of which is being incorporated herein by reference for all purposes.

Brazing fluxes are used to remove oxide layers on aluminum or aluminum alloy part surfaces which are to be joined by brazing or welding. The brazing fluxes are often applied to the aluminum or aluminum alloy part surfaces in various ways, for example by dry application, plasma application, electrostatic application, in aqueous suspensions and suspensions comprising organic suspension agents. The application of the brazing fluxes is often performed by way of a brazing flux paint composition, which comprises the brazing flux, a binder and water. Such paint compositions are applied to surfaces which are to be joined by brazing or welding, for example, by brush application, tampon application, roll application or spray application. Brazing flux paint compositions often should not exceed certain viscosity levels, should be stable and re- suspendable after settling of particulate components. Mixing the components just before application (on site mixing) often is not favourable due to dust handling of the particulate components, which requires technology, processes and safety measures not readily available at all brazing manufacturing sites. Commercial brazing flux paint compositions often cannot exceed certain contents of flux as the growing viscosity, particle settling and certain binder/flux interactions often have proven to be detrimental to stability and re-suspension properties. This usually results in commercial, ready-to-use paint fluxes with a high content of liquid carrier, in particular water, having to be transported, which results in higher transportation cost and a less favourable carbon dioxide footprint.

It was now found that the concentrates according to the present invention circumvent the above problems. The concentrates are stable, re-dispersible brazing flux compositions with a high content in flux. In the present invention, designations in singular are in intended to include the plural;“a binder” is intended to denote also“more than one binder” or“a plurality of binders”.

In the context of the present invention, the term“comprising” is intended to include the meaning of“consisting of’. All aspects and embodiments of the present invention are combinable.

The invention concerns, in a first aspect, a concentrate comprising a brazing flux, at least one binder and water, wherein the content of brazing flux is equal to or more than 48 wt% and equal to or less than 70 wt%, the content of binder is equal to or more than 1 wt% and equal to or less than 25 wt% and the content of water is equal to or more than 20 wt% and equal to or less than 50 wt%, wherein the combined content of brazing flux, binder and water is set to 100 wt%. While the combined content of brazing flux, binder and water is set to 100 wt% to define the relative content of the three components, it is to be understood that the concentrate can comprise further components, as will be explained below. The term“a brazing flux” intends to denote the presence of one brazing flux, or of a mixture of brazing fluxes, also to be read as“at least one brazing flux”. The term“a binder” intends to denote the presence of one binder, or of a mixture of binders, also to be read as“at least one binder”.

Brazing fluxes are known to the person skilled in the art, in particular non- corrosive brazing fluxes. Preferably, brazing fluxes according to the invention comprise at least one compound of the group consisting of potassium

fluoroaluminates, such as KAlF₄, K₂AlF₅, K₂AlF₅-H₂0, cesium

fluoroaluminates, such as CsAlF₄, Cs₂AlF₅, CS3AIF6, and cesium potassium fluoroaluminates such as KCs₂Al3Fi₂. The brazing flux can be present in one or more crystalline phases, in an amorphous phase, or any mixtures of crystalline and amorphous phases. Generally, brazing fluxes and their manufacture is known; for example, potassium fluoroaluminates can be manufactured from HAlF₄ obtained from HF and Al(OH)3 or Al₂C>3, and KOH. This is described for example in US4,428,920, US4,579,605 and US5, 968, 288. US 3,951,328, US6,22l,l29 or US3,97l,50l describe a flux based on KAlF₄ and K₃AlF₆.

US4,689,092 describes a flux based on potassium fluoroaluminate and cesium fluoroaluminate. In one aspect, preferred fluxes comprise KAlF₄ and at least one of K₂AlF5 and K₂AlFs-H₂0, and the weight ratio between KAlF₄ (including any hydrate if present) and K₂AlF₅ (including any hydrate K₂AlFs-H₂0 if present) is from 1 : 99 to 99: 1. Often, it is in the range of 1 : 10 to 10: 1. In another preferred aspect, the flux essentially consists of KAlF₄ and at least one of K2AIF5 and K2AIF5 H2O. The term“essentially” intends to denote that further components that are present, for example unavoidable impurities, are components not materially affecting the essential characteristics of the flux or the flux composition. In this aspect,“essentially” preferably denotes that the sum of KAIF4 and at least one of K2AIF5 and K₂AIF₅ FLO constitutes equal to or more than 95 % by weight, more preferably, equal to or more than 98 % by weight of the flux. A flux comprising 10 to 40 % by weight of K₂A1F₅, K₂AlF₅ Fl₂0 or any mixtures thereof, the balance to 100 % by weight being essentially KAlF₄ is very suitable. Generally, the content in K3AIF6 in a flux comprising potassium fluoroaluminate is low, preferably equal to or less than 5% by weight, more preferably equal to or less than 3% by weight, even more preferably equal to or less than 1% by weight. Most preferably, K3AIF6 is absent in the flux comprising potassium fluoroaluminate, which is equal to 0 weight % of K3AIF6 in the flux comprising potassium fluoroaluminate. In another aspect, the flux comprises or consists of cesium fluoroaluminate or potassium cesium fluoroaluminate, for example in the form of CsAlF₄, Cs₂AlF₅, Cs₃AlF₆, KCS2AI3F12, their hydrates and any mixture of two, three or more thereof. CSAIF4 and Cs₂AlFs, or their hydrates, and mixtures thereof are preferred. CSAIF4 is most preferred. Often, the flux comprising cesium fluoroaluminate, preferably CSAIF4, further comprises K₂AlF₅ and optionally KAIF4. Fluxes containing potassium fluoroaluminate and cesium cations, e.g. in the form of cesium fluoroaluminate, as described in US4670067 and US4689062 are also very suitable. Those cesium-containing basic fluxes are especially suitable to solder, weld or, in particular, braze aluminum-magnesium alloys. The weight ratio of KAlF₄ and K₂AlF₅ and/or its hydrate is preferably as described above. The Cs content is, calculated as content in CsF, between 2 and 74 mol-%. The sum of KAlF₄, K₂AlF₅ and the cesium fluoroaluminate compound or compounds, including any hydrate, is preferably equal to or greater than 95 % by weight, more preferably equal to or more than 98 % by weight. The content of K₃AlF₆ is preferably equal to or less than 2 % by weight, and most preferably equal to or less than 1 % by weight including 0 % by weight. Commercial brazing fluxes are, for example, a flux consisting of KAIF4 and K2AIF5, preferably in a weight ratio of about 4:1, which is known as NOCOLOK®; KZnF3 known as NOCOLOK® Zn Flux; potassium hexafluorosilicate such as NOCOLOK® CB Flux; KAIF4 and K2AIF5 and Li additive also known as NOCOLOK® Li Flux. Further suitable flux materials which are commercially available include NOCOLOK® Flux Drystatic and NOCOLOK® Flux.

Binders improve the adhesion of the flux after their application on the parts to be joined, in particular brazed. Suitable binders according to the present invention are preferably organic polymers. Such polymers are physically drying (i.e., they form a solid coating after the liquid is removed), or they are chemically drying (they may form a solid coating e.g. under the influence of chemicals, or under the influence of oxygen or light which causes a cross linking of the molecules), or both. Preferably, the binder is selected from the group consisting of polyurethanes, vinyl resins, polysaccharide based binders, polyacrylates, polyvinyl butyral, epoxy resins and polyvinyl alcohols. Suitable polysaccharide based binders are, for example, xanthan, nitrocellulose, carboxymethyl cellulose and polysaccharide acetates, such as acetylated starch or cellulose. Suitable polyacrylates includes polymethacrylate, polyethylmethacrylate and polybutyl acrylate. Particularly preferred are polyurethane binders, such as aliphatic polyester polyurethane binders.

Any binders, additives, solvents or other components comprised in the concentrate, must be selected such as not to interfere with the brazing conditions. Usually, the components, in particular binders, are removed / pyrolyzed / combusted in an amount of equal to or more than 90%, preferably equal to or more than 95%, and even more preferably equal to or more than 98% when a dry film of the component, in particular binder, or dried flux composition is heated to a temperature of 450°C.

According to the present invention, the concentrate can comprise at least one additive from the group consisting of surfactants, thixotropic agents, defoaming agents (e.g. silicon oil or glycerine), corrosion inhibitors (e.g.

benzotriazol), antioxidants (e.g. butylated hydroxytoluene BHT), thickeners (for example waxes, hardened oil, e.g. hardened castor oil, fatty acid amides and polyamides, as described in US-A 8,075,706, and ethers, e.g. methyl butyl ether) and suspension stabilizers (e.g. sodium carboxy methylcellulose). Surfactants are a preferred group of additives, in particular surfactants that have a wetting and/or dispersing action. Most preferred in this group are surfactants which combine a wetting and a dispersing action. Wetting and dispersing additives result in a fine and homogeneous distribution of solid particles in liquid media and ensure the long-term stability of such systems. The wetting activity improves interaction between liquid and solids by lowering the surface tension of the liquid. Dispersing agents prevent particles flocculating by assuring repulsion between the particles. Preferred surfactants are, for example, block polymeric agents consisting of polyether and polystyrene blocks. Preferred surfactants are, for example, surfactants of the Disperbyk 19c series (190-199) obtainable from Byk, and Antarox BL 225, a mixture of linear C8 to C10 ethoxylated and

propoxylated alcohols. Thixotropic agents can be selected, for example, from gelatine, pectines and polyurethanes.

According to the present invention, the amount of brazing flux comprised in the concentrate often is equal to or more than 50 wt% and equal to or less than 68 wt%, preferably equal to or more than 52 wt% and equal to or less than 66 wt%. Particularly suitable amounts are equal to or more than 55 wt% and equal to or less than 61 wt%.

The amount of water in the concentrate is equal to or more than 20 wt% and equal to or less than 50 wt%, and preferably is equal to or more than 25 wt% and equal to or less than 40 wt%.

The content of binder in the concentrate is equal to or more than 1 wt% and equal to or less than 25 wt%. Often, the content of binder in the concentrate can be equal to or more than 1 wt% and equal to or less than 22 wt%, preferably equal to or more than 1 wt% and equal to or less than 15 wt%. Particularly suitable amounts are equal to or more than 1.5 wt% and equal to or less than 10 wt%.

The concentrate often has a viscosity, of equal to or more than 2000 mPas, preferably equal to or more than 2500 mPas, and more preferably of equal to or more than 3000 cp. The concentrate often has a viscosity of equal to or less than 17000 mPas, preferably equal to or less than 16000 mPas, and more preferably of equal to or less than 15000 mPas, wherein a viscosity of equal to or less than 14000 mPas is most preferred. In another aspect, the viscosity of the concentrate after 6 months at +5°C to +30°C generally is equal to or more than 60% of the value measured after preparation (measured at most 24 hours after preparation), preferably equal to or more than 80% of the value measured after preparation, and more preferably equal to or more than 100% of the value measured after preparation. The viscosity of the concentrate after 6 months at +5°C to +30°C generally is equal to or less than 140% of the value measured after preparation (measured at most eight hours after preparation), preferably equal to or less than 120% of the value measured after preparation, and more preferably equal to or less than 115% of the value measured after preparation. The viscosity is determined according to methods known to the person skilled in the art, for example with a HAAKE™ Viscotester™ 550 Rotational Viscometer at 20°C, sensor FL100.

Generally, in the concentrate according to the present invention, the at least one brazing flux is not particularly limited with respect to particle size. Brazing fluxes with particle sizes generally suitable for brazing fluxes can be used.

In one preferred aspect of the present invention, the at least one brazing flux has a particle size distribution wherein the X₅₀ value is 3.5 < X₅₀ £ 25 pm, and the X₉₉ value is < 70 pm. Preferably, the at least one brazing flux has a particle size distribution wherein the X₁₀ value is 1.2 < X_|0 < 1.8 pm, the X₅₀ value is 5 < X₅₀ £ 8 pm, and the X₉₀ value is 2l< X₉₀ < 35 pm. More preferably, the at least one brazing flux has a particle size distribution wherein the X₁₀ value is 1.4 < X_|0 < 1.6 pm, the X₅₀ value is 6 < X₅₀ < 7.8 pm, and the X₉₀ value is 23 < X₉₀ < 30 pm. According to this aspect, it is advantageous when the flux is a mixture of approximately 80% by weight KAlF₄ and 20% by weight K₂AIF₅ and/or its hydrate, or wherein the flux comprises cesium fluoroaluminate, in the form of CsAlF₄, Cs₂AlF₅, CS₃AIF₆, or potassium cesium fluoroaluminate KCS₂AI₃F₁₂, their hydrates and any mixture of two, three or more thereof, wherein CsAlF₄ is preferred. Very preferred is a flux which comprises K₂AlF₅ (and/or its hydrate) and/or KAlF₄ in addition to cesium fluoroaluminate, in particular CSAIF₄. The respective X values are determined by laser scattering. They can be measured, for example, in a Sympatec Helos particle size analyzer, e.g. model Helos H2068. The analysis refers to secondary particles.

In another preferred aspect of the present invention, the at least one brazing flux has a particle size distribution wherein the X₅₀ value is 2 < X₅₀ < 6 pm.

Preferably, the at least one brazing flux has a particle size distribution wherein the X₁₀ value is 0.7 < X₁₀ < 1.28 pm, the X₅₀ value is 1.5 < X₅₀ < 4.5 pm, and the X₉₀ value is 7 < X₉₀ < 21 pm. More preferably, the at least one brazing flux has a particle size distribution wherein the X₁₀ value is 0.8 < X₁₀ < 1.0 pm, the

X₅₀ value is 2.5 < X₅₀ < 3.5 pm, and the X₉₀ value is 9 < X₉₀ < 18 pm.

The invention further concerns a process for the manufacture of a brazing flux paint composition which comprises the steps of a) providing a concentrate according to the present invention and b) mixing the concentrate with at least one liquid carrier. Liquid carriers according to the present invention are preferably selected from the group consisting of water, mono-, di-or tribasic aliphatic alcohols, ethylene glycol and glycol alkyl ethers, wherein water is preferred. Mono-, di-or tribasic aliphatic alcohols comprise especially those with 1 to 4 carbon atoms, e.g. methanol, ethanol, isopropanol, or ethylene glycol, or glycol alkyl ethers, wherein alkyl preferably denotes linear aliphatic C 1 to C4 alkyl or C3 to C4 branched alkyl. Non-limiting examples are glycol monoalkyl ethers, e.g. 2-methoxyethanol, propylene glycol or diethylene glycol, or glycol dialky lethers, for example, dimethyl glycol (dimethoxy ethane), N-Methyl-2- pyrrolidon, 3 -Methoxy-3 -methyl- 1 -butanol and l-Methoxy-2-propyl acetate. Mixtures comprising two or more of the liquid carriers are also suited very well. Isopropanol or mixtures containing isopropanol are especially suitable. The most preferred liquid carrier is water, especially de-ionized water. The term“liquid carrier” also denotes mixtures of two or more liquid carriers. While fluxes for use of manufacturing flux compositions according to the present invention generally are essentially insoluble in the liquid carrier, this does not exclude that a part of the flux composition can be dissolved in the liquid carrier; this may be the case especially when water or aqueous organic liquids are contained in the flux composition. Often, there is a time lag between step a) and step b), for example a time lag of one day, one week, or even one or more months.

Generally, the time lag is less than 12 months, preferably 6 months. Often, there is a step of transporting the concentrate from one manufacturing site to another manufacturing site between step a) and step b). The step of transporting the concentrate covers often more than 100 meters, and preferably more than 1000 meters.

In one aspect of the present invention, the at least one liquid carrier is added in step b) in an amount as to effect a wt% of the brazing flux in the brazing flux paint composition of equal to or more than 20 wt% and equal to or less than 40 wt%, preferably equal to or more than 25 wt% and equal to or less than 35 wt%. A flux content of 30 wt% is particularly suitable.

In the process for the manufacture of a brazing flux paint composition which comprises steps a) and b), the concentrate preferably is mixed with at least one liquid carrier by adding the liquid carrier to the concentrate. Inverse addition can also be performed. Preferably, the mixture is stirred during addition of the liquid carrier or the concentrate by means of a propeller mixer, turbine mixer, impeller mixer, a rotor-stator stirrer or pitched blade turbine mixer. Other stirrer types can also be applied. The temperature preferably does not exceed 70°C, more preferably does not exceed 50°C, and most preferably does not exceed 30°C in step b). Low temperatures can be used, for example 0°C, 5°C or l0°C, when the temperature is not detrimental to the physical characteristics of the composition, such as viscosity. While the product of step b) generally is ready to use, where desirable, after step b), the product of step b) can also be subject to a sieving procedure.

Another object of the present invention is a process for brazing of parts of aluminum, aluminum alloy, in particular aluminum alloy comprising

magnesium, steel, copper and titanium with parts of aluminum or aluminum alloy which comprises the process for the manufacture of a brazing flux paint composition which comprises the steps of a) and b) as described above, and which further comprises a step wherein at least one of the parts to be joined is coated at least partially with the brazing flux paint composition, a step wherein the parts to be joined are assembled, and a step wherein the assembled parts are heated to a temperature of equal to or higher than 570°C. Particularly suitable is the Controlled Atmosphere Brazing procedure, as described, for example in H. Zhao et al, chapter 10 in“Advances in Brazing: Science, Technology and Applications”, Ed. D.P. Sekulic, Woodhead Publishing Limited, 2013.

The invention further concerns aluminium or aluminium alloy parts which are at least partially coated with the brazing flux paint composition.

The concentrates according to the present invention make it possible to reduce transportation cost by reducing the content of liquid carriers in a composition which can be diluted to a paint flux composition. Surprisingly, the concentrate according to the present invention has good shelf life, good re- suspensability, good brazing results and good application properties, in particular once the concentrate is diluted to a paint flux compositions. The concentrate and the process for the manufacture of a brazing flux paint composition can be favourable against a process wherein liquid and solid components, which often represent a dust, safety and contamination problem, are mixed immediately prior to application as paint flux composition.

Should the disclosure of any of the patents, patent applications, and publications that are incorporated herein by reference conflict with the present description to the extent that it might render a term unclear, the present description shall take precedence.

The following examples will describe the invention in further detail without the intention to limit it. Examples

Weight percentages given in wt% based on all components in the concentrate; in parentheses, wt% of component based on the sum of binder, water and flux set to 100%.

Flux A is a potassium fluoroluminate flux which has a particle size distribution wherein the Xio value is > 0.7 and < 1.28 pm, the X50 value is ³ 1.5 and < 4.5 pm, and the X90 value is > 7 and <21 pm.

Flux B is a potassium fluoroaluminate flux which has a particle size distribution wherein the Xio value is > 1.2 and < 1.8 pm, the X50 value is > 5 and < 8 pm, and the X90 value is > 21 and < 35 pm. This flux, as is seen in table 1, gives a particularly advantageous low viscosity which changes least over time. The wt% numbers given in brackets relate to the wt% if the binder, water and flux together are 100%.

1 binder: polyurethane based binder available as NOCOFOK® Precoating

² acrylic binder

³ surfactant based on poly ether and polystyrene block polymer

⁴ available from Fankwitzer as ZS WZ- 1460/1 acrylic binder

All batches were mixed with water after 6 months to obtain a paint flux of0 wt% content. All concentrates gave well suspendable paint flux compositions.

Claims

1. Concentrate comprising a brazing flux, a binder and water, wherein the content of brazing flux is equal to or more than 48 wt% and equal to or less than 70 wt%, the content of binder is equal to or more than 1 wt% and equal to or less than 25 wt% and the content of water is equal to or more than 20 wt% and equal to or less than 50 wt%, wherein the combined content of brazing flux, binder and water is set to 100 wt%.

2. Concentrate according to claim 1, wherein the at least brazing flux comprises at least one compound of the group consisting of potassium

fluoroaluminates, such as KAlF₄, K₂AlF₅, K₂AlF₅-H₂0, cesium

fluoroaluminates, such as CsAlF₄, Cs₂AlF₅, CS₃AIF₆, cesium potassium fluoroaluminates such as KCs₂Al₃Fi₂, potassium fluorozincate, cesium

fluorozincate, potassium fluorostannate, and cesium fluorostannate.

3. Concentrate according to claim 1 or 2, wherein the at least one binder is selected from the group consisting of polyurethanes, vinyl resins, polysaccharide based binders, polyacrylates, polyvinyl butyral, epoxy resins and polyvinyl alcohols.

4. Concentrate according to anyone of claims 1 to 3, wherein the content of brazing flux is equal to or more than 50 wt% and equal to or less than 68 wt%, preferably equal to or more than 52 wt% and equal to or less than 66 wt%.

5. Concentrate according to anyone of claims 1 to 4, wherein the content of binder is equal to or more than 1 wt% and equal to or less than 22 wt%, preferably equal to or more than 1 wt% and equal to or less than 15 wt%.

6. Concentrate according to anyone of claims 1 to 5, wherein the concentrates comprises at least one additive from the group consisting of surfactants, thixotropic agents, defoaming agents, corrosion inhibitors, antioxidants, thickeners and suspension stabilizers.

7. Concentrate according to anyone of claims 1 to 6, wherein the at least one brazing flux has a particle size distribution wherein the X50 value is 3.5 < X50 < 25 pm, and the X99 value is < 70 pm.

8. Concentrate according to anyone of claims 1 to 6, wherein the at least one brazing flux has a particle size distribution wherein the Xio value is 0.7 <

Xio < 1.28 pm, the X50 value is 1.5 < X50 £ 4.5 pm, and the X90 value is 7 < X90 < 21 pm.

9. Concentrate according to anyone of claims 1 to 8, wherein the concentrate has a viscosity of equal to or more than 2000 mPas and equal to or less than 17000 mPas.

10. Process for the manufacture of a brazing flux paint composition which comprises the steps of comprises the steps of a) providing concentrate according to anyone of claims 1 to 9 and b) mixing the concentrate with at least one liquid carrier.

11. Process according to claim 10, wherein the at least one liquid carrier is selected from the group consisting of water, mono-, di-or tribasic aliphatic alcohols, ethylene glycol and glycol alkyl ethers, wherein water is preferred.

12. Process according to claim 10 or 11, wherein the at least one liquid carrier is added in an amount as to effect a wt% of the brazing flux in the brazing flux paint composition of equal to or more than 20 wt% and equal to or less than 40 wt%, preferably equal to or more than 25 wt% and equal to or less than 35 wt%.

13. A process for brazing of parts of aluminum, aluminum alloy, in particular aluminum alloy comprising magnesium, steel, copper and titanium with parts of aluminum or aluminum alloy which comprises the process according to anyone of claims 10 to 12, and which further comprises a step wherein at least one of the parts to be joined is coated at least partially with the brazing flux paint composition, a step wherein the parts to be joined are assembled, and a step wherein the assembled parts are heated to a temperature of equal to or higher than 570°C.