Brazing composition and heat exchanger

Abstract

This brazing composition comprises a filler metal, a binder, a solvent, and an anti-settling agent. The filler metal comprises a nickel-based filler metal. The binder comprises an alkali-metal-free, water-soluble resin. The solvent comprises water. The anti-settling agent comprises cellulose nanofibers.

Description

Brazing composition and heat exchanger

[0001] The present invention relates to a brazing composition and a heat exchanger.

[0002] Brazing is a well-known method for joining metal members. In the brazing method, the metal members are brought into contact with a brazing composition and then heated under a vacuum or an inert gas atmosphere to melt the brazing composition and diffuse it into the metal members. The brazing composition is then cooled and solidified to join the metal members.

[0003] The brazing composition contains, for example, a brazing material, a solvent, and a binder. From the viewpoint of environmental friendliness, it is required to use water as the solvent and an aqueous binder as the binder.

[0004] The brazing material in the brazing composition is selected depending on the type of metal members to be joined. For example, when the metal members contain stainless steel, a nickel-based brazing material is selected as the brazing material.

[0005] More specifically, for example, the following brazing material suspension has been proposed as a brazing composition. The brazing material suspension contains a powder of nickel-based brazing material (BNi-5) and an aqueous binder solution. The aqueous binder solution contains pure water and a powdered cellulose-based aqueous binder (sodium carboxymethylcellulose). A stainless steel metal honeycomb is then immersed in the brazing material suspension and heat-treated in a vacuum heat treatment furnace, thereby achieving brazing (see, for example, Patent Document 1 (Example 1)).

[0006] Japanese Patent Application Publication No. 6-099082

[0007] On the other hand, known brazing methods include a method in which a metal member and a brazing composition are heat-treated in a vacuum atmosphere and a method in which a metal member and a brazing composition are heat-treated in an inert gas atmosphere.

[0008] However, when the brazing filler metal suspension is heat-treated under an inert gas atmosphere, the alkali metal (e.g., sodium) contained in the aqueous binder, sodium carboxymethyl cellulose, generates black foreign matter, which is a problem.

[0009] Therefore, the use of an aqueous binder that does not contain alkali metals (i.e., an alkali metal-free aqueous binder) instead of sodium carboxymethylcellulose has been considered. For example, Patent Document 1 above proposes hydroxyethylmethylcellulose. The use of hydroxyethylmethylcellulose (i.e., an alkali metal-free aqueous binder) suppresses the generation of foreign matter.

[0010] However, when an aqueous binder that does not contain alkali metals is used, sufficient dispersibility cannot be obtained, and the brazing material may settle.

[0011] Therefore, in the field of brazing, a new problem is required: a brazing composition that can suppress the generation of foreign matter when heat treated in an inert gas atmosphere and has excellent sedimentation resistance.

[0012] The present invention relates to a brazing composition that can suppress the generation of foreign matter and has excellent sedimentation resistance, and a heat exchanger obtained by using the brazing composition.

[0013] The present invention [1] includes a brazing composition containing a brazing filler metal, a binder, a solvent, and an anti-settling agent, wherein the brazing filler metal contains a nickel-based brazing filler metal, the binder contains an alkali metal-free water-soluble resin, the solvent contains water, and the anti-settling agent contains cellulose nanofibers.

[0014] The present invention [2] includes the brazing composition according to the above [1], which contains an alkali metal, and the content of the alkali metal is 2.00 μmol or more and 22.00 μmol or less per 1 g of the nickel-based brazing filler metal.

[0015] The present invention [3] includes the brazing composition according to the above [1] or [2], which contains an alkali metal-containing compound.

[0016] The present invention [4] includes the brazing composition according to the above [3], wherein the molecular weight of the portion excluding the alkali metal of the alkali metal-containing compound is 190 or more.

[0017] The present invention [5] includes the brazing composition according to any one of the above [1] to [4], wherein the content of the cellulose nanofibers is 0.01 mass% or more and 0.3 mass% or less with respect to the total amount of the brazing composition.

[0018] The present invention [6] includes the brazing composition according to any one of the above [1] to [5], wherein the cellulose nanofibers have an average fiber width of 200 nm or less.

[0019] The present invention [7] includes a heat exchanger comprising a metal member containing stainless steel and a brazing part obtained by brazing the metal member with the brazing composition according to any one of the above [1] to [6].

[0020] In the brazing composition and heat exchanger of the present invention, the binder contains an alkali-metal-free water-soluble resin, and therefore, the brazing composition of the present invention can suppress the generation of foreign matter when heat treated in an inert gas atmosphere, for example, compared to a case in which the binder is an alkali-metal-containing water-soluble resin.

[0021] On the other hand, if the binder contains an alkali metal-free water-soluble resin, the settling resistance (dispersibility) of the brazing filler metal may be reduced compared to when the binder is made of an alkali metal-containing water-soluble resin.

[0022] In contrast, the brazing composition contains an anti-settling agent, and the anti-settling agent contains cellulose nanofibers. Therefore, the brazing composition has superior resistance to settling (dispersibility) compared to, for example, a case in which the anti-settling agent does not contain cellulose nanofibers.

[0023] That is, the brazing composition and heat exchanger of the present invention can suppress the generation of foreign matter and also provide excellent sedimentation resistance (dispersibility).

[0024] FIG. 1 is a schematic diagram showing a bonded body sample in the example.

[0025] 1. Brazing Composition The brazing composition is used to braze metal members (described later) containing stainless steel, as will be described in detail later. In other words, the brazing composition is a brazing composition for stainless steel.

[0026] The brazing composition contains, as essential components, a brazing filler metal, a binder, a solvent, and an anti-settling agent. Furthermore, as will be described in detail later, the brazing composition may contain, as optional components, an alkali metal-containing compound and additives. Each of these will be described in detail below.

[0027] (1) Brazing Filler Metal The brazing filler metal contains a nickel-based brazing filler metal as an essential component, and is preferably made of a nickel-based brazing filler metal. The nickel-based brazing filler metal is, for example, in powder form. That is, the brazing filler metal is preferably a nickel-based brazing filler metal powder.

[0028] Nickel-based brazing filler metals have a melting point lower than that of metal members (described later). Examples of nickel-based brazing filler metals include powders of alloys containing nickel. More specifically, examples include Ni (nickel)-Cr (chromium)-Si (silicon)-P (phosphorus)-based alloy powders, Ni (nickel)-Cr (chromium)-Si (silicon)-based alloy powders, Ni (nickel)-Cr (chromium)-P (phosphorus)-based alloy powders, Ni (nickel)-Cr (chromium)-Si (silicon)-Fe (iron)-B (boron)-based alloy powders, Ni (nickel)-Cr (chromium)-Si (silicon)-B (boron)-based alloy powders, and Ni (nickel)-Cr (chromium)-B (boron)-based alloy powders. Examples of nickel-based brazing filler metals include nickel-based brazing filler metals commonly used in industry, such as those specified in JIS Z 3265 (1998). More specifically, such nickel-based brazing filler metals include BNi-1, BNi-1A, BNi-2, BNi-3, BNi-4, BNi-5, BNi-6, and BNi-7. These may be used alone or in combination of two or more. In the nickel-based brazing filler metal, the content ratio of each metal is not particularly limited and may be appropriately set depending on the purpose and application.

[0029] As the nickel-based brazing filler metal, preferably, an alloy powder containing nickel and silicon (i.e., a Ni-Si-based brazing filler metal) is used, more preferably, a Ni-Cr-Si-P-based alloy powder and a Ni-Cr-Si-based alloy powder are used, and even more preferably, a Ni-Cr-Si-P-based alloy powder is used.

[0030] The nickel-based brazing filler metal is produced by a known alloy production method. The average primary particle size of the nickel-based brazing filler metal is, for example, 10 μm or more and 100 μm or less.

[0031] The content of the brazing filler metal is, for example, 10 mass% or more, preferably 30 mass% or more, more preferably 50 mass% or more, and even more preferably 70 mass% or more, relative to the total amount of the brazing composition. The content of the brazing filler metal is, for example, 99 mass% or less, preferably 97 mass% or less, more preferably 95 mass% or less, and even more preferably 93 mass% or less, relative to the total amount of the brazing composition. That is, the content of the brazing filler metal is, for example, 10 mass% or more and 99 mass% or less, preferably 30 mass% or more and 97 mass% or less, more preferably 50 mass% or more and 95 mass% or less, and even more preferably 70 mass% or more and 93 mass% or less, relative to the total amount of the brazing composition.

[0032] (2) Binder The binder contains, as an essential component, an alkali metal-free water-soluble resin. The alkali metal-free water-soluble resin is a water-soluble resin that does not contain any alkali metals (described below) in one molecule.

[0033] The alkali metal-free water-soluble resin is not particularly limited as long as it is a water-soluble resin that does not contain an alkali metal (described later). More specifically, the alkali metal-free water-soluble resin may be, for example, a nonionic water-soluble resin.

[0034] The nonionic water-soluble resin may be, for example, a resin having a plurality of oxyethylene units (CH ２ CH ２Examples of oxyethylene-containing resins include resins containing 2-8 carbon atoms (hereinafter referred to as oxyethylene-containing resins). Examples of oxyethylene-containing resins include polyethylene glycol (PEG, also known as polyethylene oxide (PEO)), polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene alkylene alkyl ethers (alkylene having 2 to 8 carbon atoms, alkyl having 1 to 20 carbon atoms), and polyethylene glycol monostearate. In addition to the above-mentioned oxyethylene-containing resins, examples of nonionic water-soluble resins include polyvinyl alcohol (PVA), cellulose ethers, polyglycerin fatty acid esters, and polyvinylpyrrolidone (PVP). Examples of cellulose ethers include hydroxyethyl methylcellulose (HEMC). Examples of polyglycerin fatty acid esters include polyglyceryl oleate. These can be used alone or in combination of two or more types.

[0035] As the alkali metal-free water-soluble resin, preferably, an oxyethylene-containing resin is used, and more preferably, polyethylene glycol (also known as polyethylene oxide) is used.

[0036] The content of the oxyethylene units is not particularly limited and may be appropriately determined depending on the purpose and application.

[0037] The number average molecular weight (polyoxyethylene glycol equivalent molecular weight measured by GPC) of the alkali metal-free water-soluble resin is, for example, 100 or more and 10,000,000 or less.

[0038] From the viewpoint of suppressing the generation of foreign matter, the content of the alkali metal-free water-soluble resin relative to the total amount of the binder is, for example, 80 mass % or more, preferably 90 mass % or more, more preferably 100 mass %. That is, the binder is preferably composed of an alkali metal-free water-soluble resin.

[0039] The content of the alkali metal-free water-soluble resin is, for example, 0.05 mass% or more, preferably 0.1 mass% or more, more preferably 0.3 mass% or more, and even more preferably 0.5 mass% or more, relative to the total amount of the brazing composition. The content of the alkali metal-free water-soluble resin is, for example, 20 mass% or less, preferably 15 mass% or less, more preferably 5 mass% or less, and even more preferably 2 mass% or less, relative to the total amount of the brazing composition. That is, the content of the alkali metal-free water-soluble resin is, for example, 0.05 mass% or more and 20 mass% or less, preferably 0.1 mass% or more and 15 mass% or less, more preferably 0.3 mass% or more and 5 mass% or less, and even more preferably 0.5 mass% or more and 2 mass% or less, relative to the total amount of the brazing composition.

[0040] The content of the alkali metal-free water-soluble resin is, for example, 0.06 parts by mass or more, preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the brazing filler metal. The content of the alkali metal-free water-soluble resin is, for example, 20 parts by mass or less, preferably 15 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 2 parts by mass or less, relative to 100 parts by mass of the brazing filler metal. That is, the content of the alkali metal-free water-soluble resin is, for example, 0.06 parts by mass or more and 20 parts by mass or less, preferably 0.1 parts by mass or more and 15 parts by mass or less, more preferably 0.3 parts by mass or more and 5 parts by mass or less, and even more preferably 0.5 parts by mass or more and 2 parts by mass or less, relative to 100 parts by mass of the brazing filler metal.

[0041] The binder content is, for example, 0.05 mass% or more, preferably 0.1 mass% or more, more preferably 0.3 mass% or more, and even more preferably 0.5 mass% or more, relative to the total amount of the brazing composition. The binder content is, for example, 20 mass% or less, preferably 15 mass% or less, more preferably 5 mass% or less, and even more preferably 2 mass% or less, relative to the total amount of the brazing composition. That is, the binder content is, for example, 0.05 mass% or more and 20 mass% or less, preferably 0.1 mass% or more and 15 mass% or less, more preferably 0.3 mass% or more and 5 mass% or less, and even more preferably 0.5 mass% or more and 2 mass% or less, relative to the total amount of the brazing composition.

[0042] The binder content is, for example, 0.06 parts by mass or more, preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the brazing filler metal. The binder content is, for example, 20 parts by mass or less, preferably 15 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 2 parts by mass or less, relative to 100 parts by mass of the brazing filler metal. That is, the binder content is, for example, 0.06 parts by mass or more and 20 parts by mass or less, preferably 0.1 parts by mass or more and 15 parts by mass or less, more preferably 0.3 parts by mass or more and 5 parts by mass or less, and even more preferably 0.5 parts by mass or more and 2 parts by mass or less, relative to 100 parts by mass of the brazing filler metal.

[0043] (3) Solvent The solvent contains water as an essential component. The water is not particularly limited, and examples thereof include ion-exchanged water, distilled water, and ultrapure water. These may be used alone or in combination of two or more types.

[0044] From the viewpoint of coating workability, the water content is, for example, 1% by mass or more, preferably 10% by mass or more, more preferably 30% by mass or more, and even more preferably 50% by mass or more, relative to the total amount of solvent. Also, from the viewpoint of coating workability, the water content is, for example, 100% by mass or less, relative to the total amount of solvent. That is, the water content is, for example, 1% by mass or more and 100% by mass or less, preferably 10% by mass or more and 100% by mass or less, more preferably 30% by mass or more and 100% by mass or less, and even more preferably 50% by mass or more and 100% by mass or less, relative to the total amount of solvent. Particularly preferably, from the viewpoint of coating workability, the water content is 100% by mass, relative to the total amount of solvent. That is, preferably, the solvent consists of water.

[0045] From the viewpoint of application workability, the water content is, for example, 0.1 mass% or more, preferably 0.5 mass% or more, more preferably 1 mass% or more, and even more preferably 5 mass% or more, relative to the total amount of the brazing composition. From the viewpoint of application workability, the water content is, for example, 50 mass% or less, preferably 40 mass% or less, more preferably 30 mass% or less, and even more preferably 20 mass% or less, relative to the total amount of the brazing composition. In other words, from the viewpoint of application workability, the water content is, for example, 0.1 mass% or more and 50 mass% or less, preferably 0.5 mass% or more and 40 mass% or less, more preferably 1 mass% or more and 30 mass% or less, and even more preferably 5 mass% or more and 20 mass% or less, relative to the total amount of the brazing composition.

[0046] Furthermore, from the viewpoint of application workability, the water content is, for example, 0.1 parts by mass or more, preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 5 parts by mass or more, relative to 100 parts by mass of the brazing filler metal. Furthermore, from the viewpoint of application workability, the water content is, for example, 50 parts by mass or less, preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, relative to 100 parts by mass of the brazing filler metal. In other words, from the viewpoint of application workability, the water content is, for example, 0.1 parts by mass or more and 50 parts by mass or less, preferably 0.5 parts by mass or more and 40 parts by mass or less, more preferably 1 part by mass or more and 30 parts by mass or less, and even more preferably 5 parts by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the brazing filler metal.

[0047] The solvent may optionally contain an aqueous organic solvent.

[0048] Examples of aqueous organic solvents include monohydric alcohols and dihydric alcohols. Examples of monohydric alcohols include alkyl monools and monohydric ether alcohols. The alkyl alcohols have, for example, an alkyl group having 1 to 8 carbon atoms. Specific examples of alkyl alcohols include methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, s-butanol, t-butanol, and 2-ethylhexyl alcohol. Examples of monohydric ether alcohols include ethylene glycol monomethyl ether, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, and dipropylene glycol monomethyl ether. Examples of dihydric alcohols include alkanediols and dihydric ether alcohols. The alkanediols have, for example, an alkylene group having 1 to 8 carbon atoms. Examples of alkanediols include ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,2-butanediol, 1,5-pentanediol, and 1,6-hexanediol. Examples of dihydric ether alcohols include diethylene glycol and dipropylene glycol. These can be used alone or in combination of two or more.

[0049] The aqueous organic solvent is preferably a monohydric alcohol or a dihydric alcohol, more preferably an alkyl monool or an alkane diol. The alkyl monool is preferably ethanol. The alkane diol is preferably propylene glycol.

[0050] The content of the aqueous organic solvent is, for example, 0% by mass or more, relative to the total amount of the solvent. Furthermore, the content of the aqueous organic solvent is, for example, 99% by mass or less, preferably 90% by mass or less, more preferably 70% by mass or less, and even more preferably 50% by mass or less, relative to the total amount of the solvent. That is, the content of the aqueous organic solvent is, for example, 0% by mass or more and 99% by mass or less, preferably 0% by mass or more and 90% by mass or less, more preferably 0% by mass or more and 70% by mass or less, and even more preferably 0% by mass or more and 50% by mass or less, relative to the total amount of the solvent. Particularly preferably, from the viewpoint of coating workability, the content of the aqueous organic solvent is 0% by mass, relative to the total amount of the solvent. That is, preferably, the solvent does not contain an aqueous organic solvent.

[0051] The content of the aqueous organic solvent is, for example, 0 mass% or more, relative to the total amount of the brazing composition. The content of the aqueous organic solvent is, for example, 40 mass% or less, preferably 30 mass% or less, more preferably 20 mass% or less, and even more preferably 10 mass% or less, relative to the total amount of the brazing composition. That is, the content of the aqueous organic solvent is, for example, 0 mass% or more and 40 mass% or less, preferably 0 mass% or more and 30 mass% or less, more preferably 0 mass% or more and 20 mass% or less, and even more preferably 0 mass% or more and 10 mass% or less, relative to the total amount of the brazing composition.

[0052] The content of the aqueous organic solvent is, for example, 0 parts by mass or more relative to 100 parts by mass of the brazing filler metal. The content of the aqueous organic solvent is, for example, 40 parts by mass or less, preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less relative to 100 parts by mass of the brazing filler metal. That is, the content of the aqueous organic solvent is, for example, 0 parts by mass or more and 40 parts by mass or less, preferably 0 parts by mass or more and 30 parts by mass or less, more preferably 0 parts by mass or more and 20 parts by mass or less, and even more preferably 0 parts by mass or more and 10 parts by mass or less relative to 100 parts by mass of the brazing filler metal.

[0053] The content (total amount) of the solvent is, for example, 0.1 mass% or more, preferably 0.5 mass% or more, more preferably 1 mass% or more, and even more preferably 5 mass% or more, relative to the total amount of the brazing composition. The content (total amount) of the solvent is, for example, 50 mass% or less, preferably 40 mass% or less, more preferably 30 mass% or less, and even more preferably 20 mass% or less, relative to the total amount of the brazing composition. That is, the content (total amount) of the solvent is, for example, 0.1 mass% or more and 50 mass% or less, preferably 0.5 mass% or more and 40 mass% or less, more preferably 1 mass% or more and 30 mass% or less, and even more preferably 5 mass% or more and 20 mass% or less, relative to the total amount of the brazing composition.

[0054] The content (total amount) of the solvent is, for example, 0.1 parts by mass or more, preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 5 parts by mass or more, relative to 100 parts by mass of the brazing filler metal. The content (total amount) of the solvent is, for example, 50 parts by mass or less, preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, relative to 100 parts by mass of the brazing filler metal. In other words, the content (total amount) of the solvent is, for example, 0.1 parts by mass or more and 50 parts by mass or less, preferably 0.5 parts by mass or more and 40 parts by mass or less, more preferably 1 part by mass or more and 30 parts by mass or less, and even more preferably 5 parts by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the brazing filler metal.

[0055] (4) Anti-settling agent The anti-settling agent contains cellulose nanofibers as an essential component.

[0056] There are no particular limitations on the method for obtaining cellulose nanofibers. For example, cellulose nanofibers can be obtained by subjecting cellulose (raw material) to a defibration treatment.

[0057] The cellulose (raw material) may be cellulose isolated from plants, cellulose isolated from animals, or cellulose isolated from bacterial cellulose gel, preferably cellulose isolated from plants. Examples of plant cellulose include softwood pulp, hardwood pulp, cotton pulp, and non-wood pulp, preferably softwood pulp.

[0058] The method for defibrating cellulose (raw material) is not particularly limited, and known methods can be used. For example, there is a method in which cellulose (raw material) is oxidized and defibrated using an N-oxyl compound as a catalyst. Such a method can conform to the methods described in, for example, JP 2008-1728 A and WO 2009 / 069641 A.

[0059] Cellulose nanofibers are also available as commercially available products, such as "Nanocellulose Fiber" (manufactured by Chuetsu Pulp Co., Ltd.), "BiNFi-s" (manufactured by Sugino Machine Ltd.), "Leocrysta" (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.), "Cellfim" (manufactured by Mori Machinery Co., Ltd.), "Cellenpia" (manufactured by Nippon Paper Industries Co., Ltd.), and "AuroVisco" (manufactured by Oji Holdings Co., Ltd.).

[0060] The cellulose nanofibers preferably have a predetermined average fiber width. The average fiber width of the cellulose nanofibers is adjusted, for example, depending on the type of cellulose and the defibration conditions. The average fiber width of the cellulose nanofibers can also be adjusted, for example, by further defibrating the cellulose nanofibers.

[0061] From the viewpoint of obtaining excellent sedimentation resistance, the average fiber width of the cellulose nanofibers is, for example, 0.1 nm or more, preferably 1 nm or more, and more preferably 3 nm or more. Furthermore, from the viewpoint of obtaining excellent sedimentation resistance, the average fiber width of the cellulose nanofibers is, for example, 500 nm or less, preferably 300 nm or less, more preferably 200 nm or less, even more preferably 100 nm or less, even more preferably 50 nm or less, and particularly preferably 30 nm or less. That is, the average fiber width of the cellulose nanofibers is, for example, 0.1 nm or more and 500 nm or less, preferably 0.1 nm or less and 300 nm or less, more preferably 1 nm or less and 200 nm or less, even more preferably 1 nm or less and 100 nm or less, even more preferably 3 nm or less and 50 nm or less, and particularly preferably 3 nm or less and 30 nm or less.

[0062] The average fiber width of cellulose nanofibers can be measured using, for example, an atomic force microscope and / or a field emission scanning electron microscope. More specifically, for example, the fiber widths of 200 randomly selected cellulose nanofibers are measured, and the average (number average) of these values ​​can be calculated as the average fiber width. Details of the method for measuring the average fiber width follow those described in the Examples below.

[0063] The cellulose nanofibers preferably have a predetermined average fiber length. The average fiber length of the cellulose nanofibers is, for example, 1 nm or more, preferably 10 nm or more. The average fiber length of the cellulose nanofibers is, for example, 10 μm or less, preferably 1 μm or less. That is, the average fiber length of the cellulose nanofibers is, for example, 1 nm or more and 10 μm or less, preferably 10 nm or more and 1 μmm or less.

[0064] The average fiber length of cellulose nanofibers can be measured using, for example, an atomic force microscope and / or a field emission scanning electron microscope. More specifically, for example, the fiber lengths of 200 randomly selected cellulose nanofibers are measured, and the average of these can be calculated as the average fiber length.

[0065] The content of cellulose nanofibers relative to the total amount of the anti-settling agent is, for example, 80 mass% or more, preferably 90 mass% or more, and more preferably 100 mass%. That is, the anti-settling agent is preferably composed of cellulose nanofibers.

[0066] Furthermore, from the viewpoint of obtaining excellent sedimentation resistance, the content of the cellulose nanofibers is, for example, 0.01 mass% or more, preferably 0.03 mass% or more, and more preferably 0.05 mass% or more, relative to the total amount of the brazing composition. Furthermore, from the viewpoint of obtaining excellent brazing properties and application workability, the content of the cellulose nanofibers is, for example, 0.3 mass% or less, preferably 0.25 mass% or less, and more preferably 0.2 mass% or less, relative to the total amount of the brazing composition. In other words, from the viewpoint of obtaining excellent sedimentation resistance, brazing properties, and application workability, the content of the cellulose nanofibers is, for example, 0.01 mass% or more and 0.3 mass% or less, preferably 0.03 mass% or more and 0.25 mass% or less, and more preferably 0.05 mass% or more and 0.2 mass% or less, relative to the total amount of the brazing composition.

[0067] Furthermore, from the viewpoint of obtaining excellent sedimentation resistance, the content ratio of the cellulose nanofibers is, for example, 0.01 parts by mass or more, preferably 0.03 parts by mass or more, and more preferably 0.05 parts by mass or more, relative to 100 parts by mass of the brazing filler metal. Furthermore, from the viewpoint of obtaining excellent brazing properties and application workability, the content ratio of the cellulose nanofibers is, for example, 0.3 parts by mass or less, preferably 0.25 parts by mass or less, and more preferably 0.2 parts by mass or less, relative to 100 parts by mass of the brazing filler metal. In other words, from the viewpoint of obtaining excellent sedimentation resistance, brazing properties, and application workability, the content ratio of the cellulose nanofibers is, for example, 0.01 parts by mass or more and 0.3 parts by mass or less, preferably 0.03 parts by mass or more and 0.25 parts by mass or less, and more preferably 0.05 parts by mass or more and 0.2 parts by mass or less, relative to 100 parts by mass of the brazing filler metal.

[0068] The anti-settling agent may contain other anti-settling agents (i.e., anti-settling agents other than cellulose nanofibers) as optional components, provided that the excellent effects of the present invention are not impaired. Examples of other anti-settling agents include polyamides, acrylic resins, clays, natural gums, and hydrophilic fumed silica. These may be used alone or in combination of two or more types.

[0069] The content of the other anti-settling agents relative to the total amount of the anti-settling agents is, for example, 20% by mass or less, preferably 10% by mass or less, and more preferably 0% by mass. In other words, the anti-settling agent preferably does not contain other anti-settling agents (i.e., anti-settling agents other than cellulose nanofibers).

[0070] From the viewpoint of obtaining excellent sedimentation resistance, the content (total amount) of the anti-settling agent is, for example, 0.01 mass% or more, preferably 0.03 mass% or more, and more preferably 0.05 mass% or more, relative to the total amount of the brazing composition. From the viewpoint of obtaining excellent brazing performance and application workability, the content (total amount) of the anti-settling agent is, for example, 0.3 mass% or less, preferably 0.25 mass% or less, and more preferably 0.2 mass% or less, relative to the total amount of the brazing composition. In other words, from the viewpoint of obtaining excellent sedimentation resistance, brazing performance, and application workability, the content (total amount) of the anti-settling agent is, for example, 0.01 mass% or more and 0.3 mass% or less, preferably 0.03 mass% or more and 0.25 mass% or less, and more preferably 0.05 mass% or more and 0.2 mass% or less, relative to the total amount of the brazing composition.

[0071] Furthermore, from the viewpoint of obtaining excellent sedimentation resistance, the content (total amount) of the anti-settling agent is, for example, 0.01 parts by mass or more, preferably 0.03 parts by mass or more, and more preferably 0.05 parts by mass or more, relative to 100 parts by mass of the brazing filler metal. Furthermore, from the viewpoint of obtaining excellent brazing properties and application workability, the content (total amount) of the anti-settling agent is, for example, 0.3 parts by mass or less, preferably 0.25 parts by mass or less, and more preferably 0.2 parts by mass or less, relative to 100 parts by mass of the brazing filler metal. In other words, from the viewpoint of obtaining excellent sedimentation resistance, brazing properties, and application workability, the content (total amount) of the anti-settling agent is, for example, 0.01 parts by mass or more and 0.3 parts by mass or less, preferably 0.03 parts by mass or more and 0.25 parts by mass or less, and more preferably 0.05 parts by mass or more and 0.2 parts by mass or less, relative to 100 parts by mass of the brazing filler metal.

[0072] (5) Alkali Metal-Containing Compound The brazing composition can contain an alkali metal. The brazing composition preferably contains an alkali metal from the viewpoint of suppressing corrosion of metal members (described later). The form of the alkali metal is not particularly limited, and may be, for example, an alkali metal atom or an alkali metal ion. Preferably, the alkali metal refers to an alkali metal atom and / or an alkali metal ion (the same applies hereinafter).

[0073] The alkali metal is contained in the brazing composition, for example, as an alkali metal-containing compound. In other words, the brazing composition can contain an alkali metal-containing compound as an optional component. Preferably, the brazing composition contains an alkali metal-containing compound. The alkali metal-containing compound is a compound containing at least one alkali metal in one molecule.

[0074] Examples of alkali metals include lithium, sodium, potassium, rubidium, and cesium. These can be used alone or in combination of two or more. Preferred alkali metals are sodium and potassium.

[0075] Examples of the alkali metal-containing compound include an alkali metal-containing inorganic compound and an alkali metal-containing organic compound.

[0076] Examples of alkali metal-containing inorganic compounds include oxides, hydroxides, and hydrogen carbonates of alkali metals, and preferably hydroxides and hydrogen carbonates of alkali metals. More specific examples of alkali metal-containing inorganic compounds include sodium hydroxide, sodium hydrogen carbonate, potassium hydroxide, and potassium hydrogen carbonate.

[0077] The alkali metal-containing inorganic compound can be used alone or in combination of two or more kinds. Preferred alkali metal-containing inorganic compounds include sodium hydroxide, sodium hydrogen carbonate, and potassium hydroxide.

[0078] Examples of alkali metal-containing organic compounds include alkali metal salts of low-molecular-weight organic acids and alkali metal-containing water-soluble resins.

[0079] Examples of low-molecular-weight organic acids include organic acids having a relatively low molecular weight. A relatively low molecular weight refers to a molecular weight of less than 400. Specific examples of low-molecular-weight organic acids include monocarboxylic acids and dicarboxylic acids. Examples of monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, octanoic acid, lauric acid, stearic acid, behenic acid, (meth)acrylic acid, and benzoic acid. Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, adipic acid, sebacic acid, fumaric acid, phthalic acid, and toluic acid. These can be used alone or in combination of two or more. Preferred low-molecular-weight organic acids include formic acid, lauric acid, and stearic acid.

[0080] More specific examples of alkali metal salts of low-molecular-weight organic acids include sodium formate, sodium laurate, and sodium stearate. These can be used alone or in combination of two or more.

[0081] The molecular weight of the portion excluding the alkali metal of the alkali metal salt of a low-molecular-weight organic acid (molecular weight calculated from the chemical structural formula) is, for example, 30 or more and less than 400.

[0082] Examples of alkali metal-containing water-soluble resins include alkali metal salts of high molecular weight organic acids and ionic water-soluble resins containing alkali metals.

[0083] Examples of high molecular weight organic acids include organic acids having a relatively high molecular weight. Note that a relatively high molecular weight refers to a molecular weight (number average molecular weight in the case of a polymer) of 400 or more. More specific examples of high molecular weight organic acids include poly(meth)acrylic acid and alginic acid. These can be used alone or in combination of two or more. As the organic acid, poly(meth)acrylic acid is preferably used, and polyacrylic acid is more preferably used.

[0084] More specifically, examples of alkali metal salts of high molecular weight organic acids include sodium polyacrylate and sodium alginate. These can be used alone or in combination of two or more.

[0085] Examples of ionic water-soluble resins containing alkali metals include sodium carboxymethyl cellulose (CMC) (Na) and potassium carboxymethyl cellulose (CMC) (K). These can be used alone or in combination of two or more.

[0086] The number average molecular weight (polyoxyethylene glycol equivalent molecular weight by GPC) of the portion excluding the alkali metal of the alkali metal-containing water-soluble resin is, for example, 400 to 10,000,000.

[0087] The alkali metal-containing organic compound may be used alone or in combination of two or more kinds. As the alkali metal-containing organic compound, a preferred example is an alkali metal-containing water-soluble resin, and a more preferred example is carboxymethylcellulose sodium (CMC.Na).

[0088] The alkali metal-containing compound may be used alone or in combination of two or more kinds. As the alkali metal-containing compound, preferred examples include an alkali metal-containing inorganic compound used alone and an alkali metal-containing organic compound used alone.

[0089] From the viewpoint of sedimentation resistance, the molecular weight of the portion of the alkali metal-containing compound excluding the alkali metal is, for example, 10 or more, preferably 50 or more, more preferably 100 or more, even more preferably 190 or more, and particularly preferably 300 or more. Furthermore, from the viewpoint of sedimentation resistance, the molecular weight of the portion of the alkali metal-containing compound excluding the alkali metal is, for example, 10 million or less, preferably 5 million or less, more preferably 3 million or less, even more preferably 1 million or less, and particularly preferably 500,000 or less. In other words, from the viewpoint of sedimentation resistance, the molecular weight of the portion of the alkali metal-containing compound excluding the alkali metal is, for example, 10 to 10 million or less, preferably 50 to 5 million or less, more preferably 1 million to 3 million or less, even more preferably 190 to 1 million or less, and particularly preferably 300 to 500,000 or less. When the alkali metal-containing compound is a monomer, the molecular weight is calculated based on the chemical structural formula. When the alkali metal-containing compound is a polymer, the molecular weight is a number average molecular weight (a molecular weight calculated as polyoxyethylene glycol by GPC).

[0090] The alkali metal may be contained in the solvent as an inevitable impurity, for example, in an amount of 0.02 mass % or less relative to the total amount of the solvent.

[0091] The alkali metal may be contained as an inevitable impurity in the anti-settling agent, for example, in an amount of 3 mass % or less relative to the total amount of the anti-settling agent.

[0092] If the brazing composition contains an alkali metal, corrosion of metal members (described later) can be suppressed.

[0093] That is, if the brazing composition does not contain an alkali metal, the surface roughness of the metal member (described later) may become relatively high, making the metal member more susceptible to corrosion. In contrast, if the brazing composition contains an alkali metal, the surface roughness of the metal member (described later) can be made relatively low, thereby suppressing corrosion.

[0094] On the other hand, as mentioned above, when the brazing composition contains an alkali metal, black foreign matter may be generated.

[0095] Therefore, when the brazing composition contains an alkali metal, the content of the alkali metal is preferably set appropriately from the viewpoint of achieving both the suppression of corrosion and the suppression of the generation of black foreign matter.

[0096] More specifically, the content of the alkali metal is, from the viewpoint of the surface roughness of the metal member (described later), for example, 0.10 μmol or more, preferably 0.50 μmol or more, more preferably 1.00 μmol or more, even more preferably 2.00 μmol or more, and particularly preferably 5.00 μmol or more per gram of the nickel-based brazing filler metal. Also, from the viewpoint of suppressing the generation of foreign matter, the content of the alkali metal is, from the viewpoint of suppressing the generation of foreign matter, for example, 30.00 μmol or less, preferably 22.00 μmol or less, more preferably 15.00 μmol or less per gram of the nickel-based brazing filler metal. That is, from the viewpoint of the surface roughness of the metal member (described later) and the suppression of the generation of foreign matter, the content of the alkali metal per gram of the nickel-based brazing filler metal is, for example, 0.50 μmol to 30.00 μmol, preferably 0.50 μmol to 30.00 μmol, more preferably 1.00 μmol to 30.00 μmol, even more preferably 2.00 μmol to 22.00 μmol, and particularly preferably 5.00 μmol to 15.00 μmol.

[0097] The content of alkali metals per gram of nickel-based brazing filler metal is calculated from the content and alkali metal concentration of raw materials excluding the nickel-based brazing filler metal (binder, solvent, anti-settling agent, alkali metal-containing compound, and additives described below (the same applies hereinafter)) in accordance with the examples described later. The alkali metal concentration of the raw materials is measured by ICP atomic emission spectroscopy in accordance with the examples described later.

[0098] Furthermore, when the brazing composition contains an alkali metal-containing compound, it is industrially preferable to adjust the mass proportion of the alkali metal-containing compound.

[0099] For example, when the brazing composition contains an alkali metal-containing compound, the content of the alkali metal-containing compound is, for example, 0.02 mass% or more, preferably 0.1 mass% or more, more preferably 0.3 mass% or more, and even more preferably 0.5 mass% or more, relative to the total amount of the brazing composition. Furthermore, the content of the alkali metal-containing compound is, for example, 20 mass% or less, preferably 15 mass% or less, more preferably 5 mass% or less, and even more preferably 2 mass% or less, relative to the total amount of the brazing composition. That is, the content of the alkali metal-containing compound is, for example, 0.02 mass% or more and 20 mass% or less, preferably 0.1 mass% or more and 15 mass% or less, more preferably 0.3 mass% or more and 5 mass% or less, and even more preferably 0.5 mass% or more and 2 mass% or less, relative to the total amount of the brazing composition.

[0100] When the brazing composition contains an alkali metal-containing compound, the content of the alkali metal-containing compound is, for example, 0.01 parts by mass or more, preferably 0.1 parts by mass or more, and more preferably 0.5 parts by mass or more, relative to 100 parts by mass of the nickel-based brazing filler metal. When the brazing composition contains an alkali metal-containing compound, the content of the alkali metal-containing compound is, for example, 10 parts by mass or less, preferably 5 parts by mass or less, and more preferably 1 part by mass or less, relative to 100 parts by mass of the nickel-based brazing filler metal. That is, the content of the alkali metal-containing compound is, for example, 0.01 parts by mass or more and 10 parts by mass or less, preferably 0.1 parts by mass or more and 5 parts by mass or less, and more preferably 0.5 parts by mass or more and 1 part by mass or less, relative to 100 parts by mass of the nickel-based brazing filler metal.

[0101] Furthermore, when the brazing composition contains an alkali metal-containing compound, the content ratio of the alkali metal-containing compound is, for example, 1 part by mass or more, preferably 5 parts by mass or more, and more preferably 10 parts by mass or more, relative to 100 parts by mass of the binder. Furthermore, when the brazing composition contains an alkali metal-containing compound, the content ratio of the alkali metal-containing compound is, for example, 500 parts by mass or less, preferably 300 parts by mass or less, and more preferably 100 parts by mass or less, relative to 100 parts by mass of the binder. In other words, the content ratio of the alkali metal-containing compound is, for example, 1 part by mass or more and 500 parts by mass or less, preferably 5 parts by mass or more and 300 parts by mass or less, and more preferably 10 parts by mass or more and 100 parts by mass or less, relative to 100 parts by mass of the binder.

[0102] When the brazing composition contains an alkali metal-containing compound, the timing of adding the alkali metal-containing compound is appropriately set depending on the purpose and application.

[0103] (6) Additives The brazing composition may contain additives as needed. Examples of additives include alkaline earth metals (e.g., magnesium salts and calcium salts), antioxidants, corrosion inhibitors, antifoaming agents, viscosity modifiers, and colorants. These may be used alone or in combination of two or more. The amount and timing of addition of the additives are appropriately determined depending on the purpose and application. Note that alkaline earth metals may roughen the surface of metal members (described below). Therefore, the brazing composition preferably does not contain alkaline earth metals.

[0104] (7) Manufacturing Method and Properties of Brazing Composition The brazing composition is manufactured by, for example, mixing the above-described components by a known method. The brazing composition is, for example, a paste composition having a predetermined viscosity.

[0105] From the viewpoint of application workability, the viscosity (25°C) of the brazing composition is, for example, 1 Pa·s or more, preferably 3 Pa·s or more. The viscosity (25°C) of the brazing composition is, for example, 150 Pa·s or less, preferably 100 Pa·s or less.

[0106] The viscosity (25°C) of the brazing composition is measured, for example, using a spiral pump viscometer (measurement sample volume: 150 mL) at a stirring speed of 10 rpm.

[0107] The brazing composition is suitably used, for example, in brazing metal members containing stainless steel (described later), and is preferably used in brazing metal members containing stainless steel in an inert gas atmosphere (described later).

[0108] 2. Brazing Method The method for brazing stainless steel using the brazing composition described above will be described in detail below.

[0109] In this method, the brazing composition is first applied to a metal member (application step). The metal member may be, for example, a metal member containing stainless steel, and preferably a metal member made of stainless steel (hereinafter referred to as a stainless steel member).

[0110] The coating method is not particularly limited, and any known method may be used, such as dispensing, screen printing, brush coating, spray coating, roll coating, bar coating, and doctor blade coating.

[0111] The amount of the brazing composition to be applied and the shape of the applied area are not particularly limited and may be appropriately determined depending on the purpose and application.

[0112] Next, in this method, another stainless steel member is prepared, and the stainless steel member coated with the brazing composition is brought into contact with the other stainless steel member via the brazing composition, and these stainless steel members are assembled into any desired structure (contacting process).

[0113] In the abutting step, the brazing composition can be dried as needed before or after assembling the stainless steel members into a desired structure. The drying conditions are set according to the amount of brazing composition applied and the shape of the applied area.

[0114] Next, in this method, the brazing composition is heated to a predetermined brazing temperature in an inert gas atmosphere or a vacuum atmosphere (heating step).

[0115] In the heating step, the atmospheric conditions may be an inert gas atmosphere or a vacuum atmosphere. From the viewpoint that the brazing composition can suppress the generation of foreign matter in an inert gas atmosphere, the atmospheric conditions in the heating step are preferably an inert gas atmosphere.

[0116] Examples of the inert gas in the inert gas atmosphere include argon gas, helium gas, and nitrogen gas. When the brazing composition is heated in an inert gas atmosphere, the pressure conditions are not particularly limited and may be, for example, normal pressure (atmospheric pressure).

[0117] When the brazing composition is heated in a vacuum atmosphere, the degree of vacuum is, for example, 133×10 －３ Pa or less.

[0118] The brazing temperature (heating temperature) is, for example, equal to or higher than the melting point of the brazing material and lower than the melting point of the metal member (stainless steel member). More specifically, the brazing temperature is, for example, 900°C or higher and 1300°C or lower, preferably 950°C or higher and 1200°C or lower, and more preferably 1000°C or higher and 1150°C or lower.

[0119] In this step, the brazing temperature (heating temperature) is maintained for a predetermined time (heating time), for example, from 1 minute to 30 minutes, preferably from 5 minutes to 20 minutes.

[0120] As a result, the stainless steel members are brazed (joined) in an inert gas atmosphere or a vacuum atmosphere to form a brazed part, i.e., a joined body is formed that includes the metal members and the brazed part obtained using the brazing composition.

[0121] The joined body is not particularly limited as long as it is a joined body including stainless steel members. Specific examples of the joined body include stainless steel heat exchangers. The stainless steel heat exchanger includes, for example, the above-mentioned metal members including stainless steel and a brazed portion formed by brazing the metal members with the above-mentioned brazing composition. Examples of such heat exchangers include heat exchangers for vehicles, and specific examples include heat exchangers provided in exhaust gas recirculation (EGR) systems of automobiles.

[0122] 3. Effects and Effects The brazing composition and heat exchanger described above can suppress the generation of foreign matter and provide excellent resistance to sedimentation (dispersibility).

[0123] That is, in the brazing composition, the binder contains an alkali metal-free water-soluble resin, and therefore, the brazing composition can suppress the generation of foreign matter when heat treated in an inert gas atmosphere, for example, compared to a case where the binder is made of an alkali metal-containing water-soluble resin.

[0124] On the other hand, if the binder contains an alkali metal-free water-soluble resin, the settling resistance (dispersibility) of the brazing filler metal may be reduced compared to when the binder is made of an alkali metal-containing water-soluble resin.

[0125] In contrast, the brazing composition contains an anti-settling agent, and the anti-settling agent contains cellulose nanofibers. Therefore, the brazing composition has superior resistance to settling (dispersibility) compared to, for example, a case in which the anti-settling agent does not contain cellulose nanofibers.

[0126] That is, the brazing composition and the heat exchanger described above can suppress the generation of foreign matter and can provide excellent resistance to sedimentation (dispersibility).

[0127] Next, the present invention will be described based on examples and comparative examples, but the present invention is not limited to the following examples. Note that "parts" and "%" are by mass unless otherwise specified. Furthermore, specific numerical values ​​such as blending ratios (content ratios), physical property values, parameters, etc. used in the following description can be substituted with the corresponding upper limit values ​​(numeric values ​​defined as "equal to or less than") or lower limit values ​​(numeric values ​​defined as "equal to or more than" or "exceeding") of the blending ratios (content ratios), physical property values, parameters, etc. described in the above "Modes for Carrying Out the Invention."

[0128] 1. Measurement (1) Alkali metal content (μmol) per 1 g of nickel-based brazing filler metal The alkali metal concentration of each raw material (binder, solvent, anti-settling agent, alkali metal-containing compound, and additive) excluding the nickel-based brazing filler metal was measured using ICP atomic emission spectroscopy according to the following method. Then, the alkali metal content per 1 g of nickel-based brazing filler metal was calculated according to the following method.

[0129] That is, the "content (μmol) of alkali metal contained in the raw materials per 1 g of nickel-based brazing material" was calculated using the following formula based on the recipe of the brazing composition. Then, the sum of the "content (μmol) of alkali metal contained in each raw material per 1 g of nickel-based brazing material" calculated for each raw material was calculated. The obtained sum was defined as the "content (μmol) of alkali metal contained in 1 g of nickel-based brazing material."

[0130] [Content of alkali metal (μmol) contained in raw material per 1 g of nickel-based brazing material] = [{Amount of raw material (g) × Alkali metal concentration of raw material (% by mass) × 10 －２} / {atomic weight of alkali metal (g / mol) × nickel-based brazing filler metal (g)} × 10 ６

[0131] The measurement conditions for ICP emission spectrometry are as follows.

[0132] That is, the raw material was diluted with ultrapure water to an appropriate concentration to prepare a sample. The alkali metal concentration of the sample was then calculated by a calibration curve method using an ICP atomic emission spectrometer (model number Agilent 700 Series, manufactured by Agilent Technologies). In preparing the calibration curve, lithium hydroxide solution, sodium hydroxide solution, and potassium hydroxide solution were used as standard aqueous solutions. The measurement wavelength for lithium was 670.783 nm, the measurement wavelength for sodium was 589.592 nm, and the measurement wavelength for potassium was 766.491 nm.

[0133] 2. Raw Materials (1) Brazing Filler Metal Powder <Nickel-based Brazing Filler Metal> Ni-Cr-Si-P: Product Name FP-613, manufactured by Fukuda Metal Co., Ltd. Ni-Cr-Si: Product Name FP-605, manufactured by Fukuda Metal Co., Ltd.

[0134] (2) Binder <Alkali metal-free water-soluble resin (nonionic water-soluble resin)> Polyethylene oxide: trade name PEO-4, alkali metal concentration 0% by mass, manufactured by Sumitomo Seika Chemicals Co., Ltd. Polyvinylpyrrolidone: trade name Pitzcol K-90, alkali metal concentration 0% by mass, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd. Polyethylene glycol: trade name PEG#200, alkali metal concentration 0% by mass, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Hydroxyethyl methylcellulose: trade name Metrose SEB, alkali metal concentration 0% by mass, manufactured by Shin-Etsu Chemical Co., Ltd. Polyoxyethylene lauryl ether: trade name Emulgen 150, alkali metal concentration 0% by mass, manufactured by Kao Corporation Polyethylene glycol monostearate: trade name Emanone 3199VB, alkali metal concentration 0% by mass, manufactured by Kao Corporation Polyoxyethylene sorbitan monolaurate: trade name Rheodol TW-L120, alkali metal concentration 0% by mass, manufactured by Kao Corporation Polyoxyethylene alkylene alkyl ether: trade name Emulgen LS-110, alkali metal concentration 0% by mass, manufactured by Kao Corporation Polyglyceryl oleate: trade name MO-3S, alkali metal concentration 0% by mass, manufactured by Sakamoto Pharmaceutical Industry Co., Ltd. Polyoxyethylene oleyl ether: trade name Emulgen 420, alkali metal concentration 0% by mass, manufactured by Kao Corporation

[0135] (3) Solvents: Water, alkali metal concentration 0% by mass; Propylene glycol (aqueous organic solvent, alkali metal concentration 0% by mass, alkanediol); Ethanol (aqueous organic solvent, alkali metal concentration 0% by mass, alkylmonool);

[0136] (4) Anti-settling agent <Cellulose nanofibers> Cellulose nanofibers having an average fiber width of 3 nm: trade name Rheocrysta I-2SX, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd., alkali metal concentration 0.3 mass% Cellulose nanofibers having an average fiber width of 20 nm: trade name BiNFi-s, manufactured by Sugino Machine Ltd., alkali metal concentration 0.3 mass% Cellulose nanofibers having an average fiber width of 200 nm: trade name Cellfim C, manufactured by Mori Machinery Co., Ltd., alkali metal concentration 0.3 mass% Cellulose nanofibers having an average fiber width of 300 nm: trade name Cellfim L, manufactured by Mori Machinery Co., Ltd., alkali metal concentration 0.3 mass%

[0137] The average fiber width was measured using the following method and conditions. Specifically, pure water was added to each cellulose nanofiber and diluted until it was observable, yielding a cellulose nanofiber dispersion. The cellulose nanofiber dispersion was then freeze-dried and images were observed using an atomic force microscope (AFM). Specifically, a dozen or so cellulose fibers were randomly selected from a 1 μm square image. The fiber widths of three locations on each cellulose fiber were measured, and the arithmetic mean of these values ​​was calculated as the fiber width of that cellulose fiber. More specifically, for each cellulose fiber, the fiber width at a portion 25% of the length from the end, the fiber width at a portion 50% of the length from the end, and the fiber width at a portion 75% of the length from the end in the longitudinal direction were measured. The arithmetic mean of the fiber width measurements at these three locations was calculated as the fiber width of a single cellulose fiber. Furthermore, using multiple images taken from different positions, the fiber width of a single cellulose fiber was calculated as described above for a total of 200 cellulose fibers. Thereafter, the arithmetic mean value of the fiber widths of the 200 cellulose fibers was calculated as the average fiber width (nm) of the cellulose fibers.

[0138] <Other anti-settling agents> Hydrophilic fumed silica: trade name AEAROSIL 200, alkali metal concentration 0 mass%, manufactured by Nippon Aerosil Co., Ltd.

[0139] (5) Alkali metal-containing compounds Carboxymethyl cellulose (CMC) Na: trade name F05MC, manufactured by Nippon Paper Industries Co., Ltd., alkali metal concentration 6.7% by mass, molecular weight excluding alkali metals 70,000. Lithium formate: manufactured by Tokyo Chemical Industry Co., Ltd., alkali metal concentration 13.4% by mass, molecular weight excluding alkali metals 45. Sodium hydroxide: manufactured by Kishida Chemical Co., Ltd., alkali metal concentration 57.5% by mass, molecular weight excluding alkali metals 17. Sodium bicarbonate: manufactured by Kanto Chemical Co., Ltd., alkali metal concentration 27.4% by mass, molecular weight excluding alkali metals 61. Sodium formate: manufactured by Kanto Chemical Co., Ltd., alkali metal concentration 33.8% by mass, molecular weight excluding alkali metals 45. Sodium laurate: neutralization reaction product of lauric acid (manufactured by Miyoshi Oil & Fats) and sodium hydroxide (manufactured by Kishida Chemical Co., Ltd.), alkali metal concentration 10.3% by mass, molecular weight excluding alkali metals 199. Sodium stearate: neutralization reaction product of stearic acid (manufactured by Miyoshi Oil & Fats) and sodium hydroxide (manufactured by Kishida Chemical Co., Ltd.), alkali metal concentration 7.5% by mass, molecular weight excluding alkali metals 283 Sodium alginate: manufactured by Matsuba Pharmaceutical Co., Ltd., alkali metal concentration 17% by mass, molecular weight excluding alkali metals 200,000 Sodium polyacrylate: trade name AQUALIC IH-G, manufactured by Nippon Shokubai Co., Ltd., alkali metal concentration 17% by mass, molecular weight excluding alkali metals 4.5 million Potassium hydroxide: manufactured by Kanto Chemical Co., Ltd., alkali metal concentration 69.7% by mass, molecular weight excluding alkali metals 17 Potassium formate: manufactured by Kanto Chemical Co., Ltd., alkali metal concentration 46.5% by mass, molecular weight excluding alkali metals 45 Carboxymethylcellulose (CMC) K: neutralization product of carboxymethylcellulose ammonium (trade name CMC Daicel DN-800H, manufactured by Daicel Miraize Co., Ltd.) and potassium hydroxide (manufactured by Kanto Chemical Co., Ltd.), alkali metal concentration 2.3% by mass, molecular weight excluding alkali metals 200,000

[0140] <Other additives> Magnesium formate: alkali metal concentration 0% by mass, manufactured by Kishida Chemical Co., Ltd. Calcium formate: alkali metal concentration 0% by mass, manufactured by Alfa Aesar

[0141] 3. Brazing Compositions Examples 1 to 38 and Comparative Examples 1 to 4 Brazing compositions were obtained according to the formulations shown in Tables 1 to 11. More specifically, brazing materials, binders, anti-settling agents, and solvents were mixed according to the formulations shown in Tables 1 to 11 to obtain brazing compositions.

[0142] 4. Production of Joint Samples As shown in FIG. 1, a stainless steel plate (SUS304, 50×50×3 mm) and a stainless steel pipe (SUS304, φ34×1.7×18 mm) were prepared and assembled.

[0143] More specifically, 3 g of the brazing composition was applied to the inside of a stainless steel pipe, allowed to dry naturally at room temperature for 1 hour, and then heat-treated at 150° C. for 15 minutes to obtain a coating of the brazing composition.

[0144] Thereafter, the stainless steel plate and the stainless steel pipe were assembled via the coating film of the brazing composition and brazed together in an inert gas atmosphere. More specifically, the stainless steel plate and the stainless steel pipe were placed in a carbon muffle furnace (Oxynon furnace, manufactured by Kanto Yakin Kogyo Co., Ltd.) and heated at 1150°C for 15 minutes under atmospheric pressure and an argon atmosphere to braze the stainless steel plate and the stainless steel pipe.

[0145] 5. Evaluation (1) Brazeability The brazed portion between the stainless steel plate and the stainless steel pipe was visually observed to check the formation (appearance) of the fillet and the melting state of the brazing filler metal (presence or absence of residue). The brazeability was then evaluated according to the following criteria.

[0146] A: A fillet was formed, and no unmelted brazing material was observed. B: A fillet was formed, but unmelted brazing material was observed. C: A fillet was not formed, and unmelted brazing material was observed.

[0147] (2) Suppression of foreign matter The brazed portion between the stainless steel plate and the stainless steel pipe was observed under an optical microscope to check for the presence or absence of black foreign matter. Suppression of foreign matter was then evaluated according to the following criteria.

[0148] A: No black foreign matter was found. B: Black foreign matter was found. The diameter of the foreign matter was 50 μm or less. C: Black foreign matter was found. The diameter of the foreign matter was more than 50 μm and 100 μm or less. D: Black foreign matter was found. The diameter of the foreign matter was more than 100 μm.

[0149] (3) Sedimentation Resistance The brazing composition was placed in a container and stored for 10 days. After that, the state of the brazing composition was visually observed to check for the presence or absence of sedimentation. The sedimentation resistance was evaluated according to the following criteria.

[0150] A: No settling was observed. B: Settling was observed, but the brazing composition could be re-stirred manually. C: Settling was observed, but the brazing composition could not be re-stirred manually, but could be re-stirred with a stirrer. D: Settling was observed, but the brazing composition could not be re-stirred manually, but could not be re-stirred with a stirrer.

[0151] (4) Coating Workability The viscosity of the brazing composition at 25° C. was measured under the following conditions using a spiral pump viscometer (PCU-285 manufactured by Malcom Co., Ltd.).

[0152] Stirring speed: 10 rpm Measurement sample amount: 150 cc Sample container: High-resist container manufactured by Kinki Container Co., Ltd.

[0153] The application workability of the brazing composition (particularly the application workability in dispense application) was evaluated according to the following criteria.

[0154] A: Viscosity is 3 Pa·s ―１ Above, 100Pa・s ―１ B: Viscosity was 1 Pa·s or less. ―１ or more and less than 3 Pa·s-1, or 100 Pa·s ―１ Excess 150Pa・s ―１ C: Viscosity was 1 Pa·s or less. ―１ or less than 150 Pa·s ―１ It was excessive.

[0155] (5) Surface Roughness The surface roughness of the brazed portion between the stainless steel plate and the stainless steel pipe was measured using a white light interferometer. The surface roughness indicates the arithmetic mean roughness Sa specified in ISO 25178. The surface roughness was evaluated according to the following criteria.

[0156] A: The arithmetic mean roughness Sa was 1 μm or less. B: The arithmetic mean roughness Sa was more than 1 μm and not more than 3 μm. C: The arithmetic mean roughness Sa was more than 3 μm and not more than 10 μm. D: The arithmetic mean roughness Sa was more than 10 μm.

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[0168] The above invention is provided as an exemplary embodiment of the present invention, but it is merely an example and should not be interpreted as being limiting. Modifications of the present invention that are obvious to those skilled in the art are intended to be included in the scope of the following claims.

[0169] The brazing composition and heat exchanger of the present invention are suitable for use in heat exchangers for vehicles.

Claims

1. A brazing composition comprising a brazing filler metal, a binder, a solvent, and an anti-settling agent, wherein the brazing filler metal comprises a nickel-based brazing filler metal, the binder comprises an alkali metal-free water-soluble resin, the solvent comprises water, and the anti-settling agent comprises cellulose nanofibers.

2. The brazing composition according to claim 1, which contains an alkali metal, and the content of the alkali metal is 2.00 μmol or more and 22.00 μmol or less per 1 g of the nickel-based brazing filler metal.

3. The brazing composition of claim 1, further comprising an alkali metal-containing compound.

4. The brazing composition according to claim 3, wherein the molecular weight of the alkali metal-containing compound excluding the alkali metal is 190 or more.

5. The brazing composition according to claim 1, wherein the content of the cellulose nanofibers is 0.01 mass % or more and 0.3 mass % or less relative to the total amount of the brazing composition.

6. The brazing composition according to claim 1, wherein the cellulose nanofibers have an average fiber width of 200 nm or less.

7. A heat exchanger comprising: a metal member containing stainless steel; and a brazed portion formed by brazing said metal member with the brazing composition according to any one of claims 1 to 6.

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