JP2011020157A - Sheet material for brazing, sheet constituting body for brazing, composition for brazing, brazing method and heat exchanger made of stainless steel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet material for brazing, a brazing method using the sheet material for brazing, and the like by which a required amount of brazing filler metal can be correctly fed to a portion to be subjected to brazing when the brazing is performed by using a brazing filler metal containing nickel based alloy powder, and also the fed brazing filler metal is detained at the portion to suppress displacement or the like. <P>SOLUTION: In the sheet material 1 for brazing comprising nickel based alloy powder of 50 to 90 mass% and a binder resin of 10 to 50 mass%, the binder resin is obtained by cross-linking an acrylic resin with a hydroxyl group having a glass transition temperature of ≤0°C and a weight average molecular weight of ≥100,000 with a crosslinking agent. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to, for example, a brazing sheet material used for brazing a plurality of metal members, a brazing method using the brazing sheet material, and the like.

  An exhaust gas recirculation device (EGR) is known as a device for purifying exhaust gas such as diesel automobiles. EGR is a device that reduces the emission temperature of nitrogen oxides by lowering the combustion temperature and the combustion speed by introducing a part of exhaust gas in a diesel vehicle to the intake side to lower the oxygen concentration of the intake air. In this EGR, an exhaust heat exchanger for cooling high-temperature exhaust gas discharged from the engine with cooling water is provided.

  The exhaust heat exchanger provided in the EGR is required to have high heat resistance that can withstand high-temperature exhaust gas. Therefore, it is preferable to use a stainless steel heat exchanger having excellent heat resistance. High heat resistance is naturally required for the brazing material used for brazing when producing a heat exchanger made of stainless steel. Nickel brazing is preferably used as a brazing material having high heat resistance.

  Specific examples of general nickel brazing include, for example, boron (B), silicon (which is a component that imparts fluidity to a nickel (Ni) or nickel-chromium (Ni-Cr) alloy by lowering the melting point). An alloy to which Si), phosphorus (P) and the like are further added may be mentioned. Such alloys are extremely poor in workability because they become hard and brittle by containing B, Si, P and the like. Therefore, usually, such nickel brazing is difficult to be processed into a plate shape or a line shape, and is therefore used as a powder brazing material, a metal foil brazing material, or a paste brazing material.

  Examples of the powder brazing material include a brazing material made only of a nickel-based alloy powder, and a non-adhesive hot-melt resin powder such as a nickel-based alloy powder and butyral resin as described in Patent Document 1 below. Known are powder compositions obtained by mixing with a body. According to the disclosure of Patent Document 1, the prepared powder composition is heated after being electrostatically coated on the surface of the joining member. By such heating, the hot-melt resin is heated and melted to form a film containing the brazing material on the surface of the joining member. Then, only the brazing material made of nickel-based alloy powder is left on the surface of the member by firing the formed film and thermally decomposing only the hot-melt resin. And it is described that brazing is performed by this brazing material.

  As another form, a foil-like brazing material in which a nickel-based alloy is formed in a metal foil shape as described in Patent Document 2 below is also known.

  As another form, for example, a paste-like wax prepared by mixing a binder resin, a diluting solvent, and a nickel-based alloy powder as disclosed in the following Patent Document 3 and Patent Document 4 below. The material is also known. In such brazing, a paste-like brazing material is applied to the brazed portion and dried, and then the binder resin is thermally decomposed by heating, and the members are joined by melting the nickel-based alloy powder.

JP 2003-19592 A JP 2002-137054 A Japanese Patent Application Laid-Open No. 2004-293989 JP 2007-203352 A

  As described above, various types of nickel-based brazing materials have been proposed, but each had problems to be solved.

  When a powdery brazing material made of nickel-based alloy powder is used, it is difficult to accurately dispose the brazing material at the joint. Moreover, even if the brazing material is accurately arranged at the joint, the powder may flow and move after the arrangement. As described above, when a powdery brazing material is used, it is not easy to accurately retain the powdery brazing material at the joint. Moreover, the method of mixing a heat-meltable resin powder with a nickel-based alloy powder as described in Patent Document 1 and disposing it on the surface of a member by electrostatic coating is a process that requires an electrostatic coating process. There was a problem that became complicated.

  In addition, the foil-like brazing material obtained by forming a nickel-based alloy into a metal foil rapidly cools the molten nickel-based alloy material during the manufacturing process of the nickel-based alloy in order to maintain the strength of the foil. It was necessary to make the crystal structure amorphous. Such an amorphization process has a problem that it is costly due to low mass productivity.

  In addition, when a paste-like brazing material is used, there is a problem that the operation of applying the paste is complicated. Further, even if the paste is accurately applied to the joint, there is a problem that the paste is softened or fluidized and spreads from the applied portion during the brazing temperature rising process, or the joint is misaligned. In such a case, there arises a problem that the joint strength of the joint portion is reduced.

  According to the present invention, when brazing using a brazing material containing nickel-based alloy powder, it is possible to accurately supply a required amount of brazing material only to a portion to be brazed, and the supplied brazing material is An object of the present invention is to provide a brazing sheet material, a brazing method using the brazing sheet material, and the like, which can suppress misalignment and the like by being retained in a part.

  One aspect of the present invention is a brazing sheet material containing 50 to 90% by mass of nickel-based alloy powder and 10 to 50% by mass of a binder resin, and the binder resin has a glass transition temperature of 0 ° C. or less. The resin is obtained by crosslinking a hydroxyl group-containing acrylic resin having a weight average molecular weight of 100,000 or more with a crosslinking agent. Since such a brazing sheet material has adhesiveness on the surface, it can be easily attached to the joint to be brazed. Further, since the acrylic resin is cross-linked, the binder resin does not fluidize even when the temperature is raised, and therefore the nickel alloy powder does not flow. In addition, by using an acrylic resin having a hydroxyl group, it is possible to suppress the formation of an oxide film on the surface of the nickel-based alloy powder. As a result, an increase in melting point due to the formation of nickel oxide can be suppressed, and good bondability can be maintained.

  The thickness of the brazing sheet material is preferably in the range of 50 to 1000 μm. In the case of such a thickness, a sufficient amount of nickel-based alloy powder can be supplied to the joint. Therefore, since the fillet formed by the brazing material protruding from the gap of the joint portion can be sufficiently formed, high joint strength can be maintained.

  Further, another aspect of the present invention is characterized in that brazing is characterized in that a support base material and a protective sheet having different peeling forces are adhered to both surfaces of any one of the above brazing sheet materials. It is a sheet | seat structure. According to such a brazing sheet structure, it is easy to stick the brazing sheet material to the joint.

  Further, a structure in which the brazing sheet material is formed in a label seal shape and adhered to the surface of the supporting base material is also a preferable form. According to such a structure, for example, in the case where a plurality of joints are joined at the same time, the brazing sheet material is molded and supported so as to have a pattern reflecting the spacing and positional relationship between the joints. By being able to adhere and support the substrate surface, it becomes easy to adhere the brazing sheet material to a plurality of joints.

  Another aspect of the present invention is a brazing composition for producing a brazing sheet material. As a nonvolatile component, an acrylic resin 10 having a nickel-based alloy powder of 50 to 90% by mass and a hydroxyl group is used. The composition for brazing containing ˜50 mass% and a crosslinking agent, wherein the acrylic resin has a glass transition temperature of 0 ° C. or less and a weight average molecular weight of 100,000 or more. According to such a composition, the above-described brazing sheet material can be easily produced.

  Another aspect of the present invention is a bonding step of bonding the brazing sheet material according to any of the above to a brazing site of the first metal member, and the bonded brazing sheet material A combination step of forming a combined body by arranging a brazed portion of the second metal member on the surface, and melting the nickel-based alloy powder by heating the combined body to a temperature equal to or higher than the melting point of the nickel-based alloy powder. And a brazing process for brazing. According to such a method, brazing can be performed easily and accurately.

  Another aspect of the present invention is a stainless steel heat exchanger having a plurality of stainless steel members brazed to each other, wherein the brazed portion is obtained by brazing by the above method. It is a stainless steel heat exchanger.

  Since the sheet material for brazing of the present invention has an adhesive property on the surface, the brazing material can be accurately arranged at the joint portion to be brazed. Further, since a crosslinkable binder resin is used, the brazing material is prevented from flowing and being displaced even at the time of temperature rise during brazing. Moreover, it can suppress that an oxide film is formed in the surface of nickel-type alloy powder by using acrylic resin which has a hydroxyl group for binder resin. Thereby, since the raise of melting | fusing point by the production | generation of nickel oxide can also be suppressed, favorable joining property can also be maintained.

It is a cross-sectional schematic diagram for demonstrating an example of the sheet | seat structure for brazing in this embodiment. It is a cross-sectional schematic diagram for demonstrating an example of the sheet | seat structure for brazing formed in the shape of a winding tape in this embodiment. It is a schematic diagram for demonstrating an example of the sheet | seat structure body for brazing formed in the label form in this embodiment. It is a schematic cross section for demonstrating the process of manufacturing the inner fin structure obtained by the brazing method in this embodiment. It is a schematic diagram for demonstrating the inner fin structure in this embodiment. It is a schematic diagram for demonstrating the inner fin structure accommodated in the box which is a unit of the stainless steel heat exchanger in this embodiment. It is a schematic diagram for demonstrating the structure of the stainless steel heat exchanger in this embodiment. It is a schematic diagram for demonstrating bondability evaluation in an Example.

  Hereinafter, preferred embodiments of the present invention will be described in detail.

  The brazing sheet material of the present embodiment contains 50 to 90% by mass of nickel-based alloy powder and 10 to 90% by mass of a binder resin, and the binder resin has a glass transition temperature of 0 ° C. or less and a weight average. It is a resin obtained by crosslinking a hydroxyl group-containing acrylic resin having a molecular weight of 100,000 or more with a crosslinking agent.

  First, the nickel-based alloy powder in the present embodiment will be described.

  The nickel-based alloy powder can be used without particular limitation as long as it is a powdered nickel-based alloy powder conventionally used as a brazing material and has a melting point lower than the melting point of the metal member to be joined. . Specific examples thereof include, for example, Ni-Cr-Si-based BNi-5 (Ni-19Cr-10P) and Ni-Cr-P-based BNi-7 (JIS standard nickel brazing (JIS Z 3265)). Ni-13Cr-10P), Ni-Cr-Si-P type nickel brazing (Ni-27Cr-4Si-6P) and the like as disclosed in Japanese Patent No. 3168158 which is not JIS standard.

  The average particle diameter of the nickel-based alloy powder is appropriately selected from the range of 1 to 600 μm depending on the thickness of the target brazing sheet material. From the viewpoint of film formability, it is preferable that the average particle diameter is smaller than the target thickness of the sheet material. Specifically, it is preferable that the average particle diameter is in the range of 0.01 to 1 time, and further 0.1 to 0.8 times with respect to the sheet thickness from the viewpoint that the sheet thickness can be controlled to be constant. . In addition, the said average particle diameter is the value measured by the particle size distribution analyzer Microtrac MT3000 type (made by Nikkiso Co., Ltd.).

  Next, the binder resin in this embodiment will be described.

  The binder resin is a resin obtained by crosslinking a hydroxyl group-containing acrylic resin having a glass transition temperature of 0 ° C. or less and a weight average molecular weight of 100,000 or more with a crosslinking agent. Such a binder resin imparts adhesiveness (tackiness) to the surface of the obtained brazing sheet material. Moreover, form retainability can be provided to the obtained brazing sheet material by crosslinking of the acrylic resin. In addition, functional groups having active hydrogen such as a carboxyl group, a sulfonic acid group, an amino group, and an amide group are generally used for crosslinking of the acrylic resin in addition to the hydroxyl group. When a crosslinked acrylic resin is used as the binder resin, an oxide film may be formed on the surface of the nickel-based alloy powder. Such an oxide film increases the melting point of the nickel-based alloy powder, and thus causes a decrease in bonding strength. As a result of various studies, the present inventors have found that when an acrylic resin having a hydroxyl group is used, the formation of such an oxide film can be suppressed.

  The monomer composition used for the polymerization of the acrylic resin includes a monomer capable of forming a polymer having at least a radical reactive monomer having a hydroxyl group capable of forming a crosslink and having a glass transition temperature of 0 ° C. or lower. Any composition can be used without particular limitation.

  Specific examples of the radical-reactive monomer having a hydroxyl group include hydroxyalkyl (meth) acrylates such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and the like. Esters; hydroxyalkyl vinyl ethers such as 4-hydroxybutyl vinyl ether and cyclohexanedimethanol monovinyl ether; hydroxyalkyl allyl ethers such as hydroxyethyl allyl ether and cyclohexanedimethanol monoallyl ether; polyalkylenes such as polyethylene glycol, polypropylene glycol, and tetramethylene glycol Polyol mono (meth) acrylate, which is an ester of a polyol and (meth) acrylic acid. Among these, 2-hydroxyethyl acrylate is preferable from the viewpoint of cost while the target hydroxyl value can be obtained with low addition because the molecular weight of the monomer is low.

  Specific examples of the radical polymerizable monomer other than the radical reactive monomer having a hydroxyl group include, for example, n-butyl (meth) acrylate, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, and cyclohexyl. Examples thereof include alkyl (meth) acrylates such as (meth) acrylate, benzyl (meth) acrylate, and dicyclopentadienyl (meth) acrylate; glycidyl (meth) acrylate and the like. Among these, n-butyl acrylate is preferable because an acrylic resin having a glass transition temperature of 0 ° C. or lower can be easily prepared because of its low glass transition temperature.

  These monomers may be used alone or in combination of two or more.

  As a content rate of the radical reactive monomer which has a hydroxyl group in the monomer composition used for superposition | polymerization of acrylic resin, it is preferable that it is 0.5-3 mol%, Furthermore, it is preferable that it is 0.75-2 mol%. When the ratio of the radical-reactive monomer having a hydroxyl group is too small, the film formability tends to be lowered, and when it is too high, the amount of the crosslinking agent is increased to increase the cost.

  Moreover, as long as the effect of this invention is not impaired, you may mix | blend the monomer containing active hydrogen other than a hydroxyl group like a carboxyl group and an amino group in a monomer composition. However, when such a monomer is copolymerized, an oxide film is easily formed. Such an oxide film may lower the bonding property by increasing the melting point of the nickel-based alloy powder. Therefore, the blending amount is limited, and preferably it is not blended.

  The glass transition temperature of the acrylic resin used in this embodiment is 0 ° C. or lower, and preferably in the range of −80 to −30 ° C. By using such an acrylic resin having a glass transition temperature, it is possible to sufficiently impart adhesiveness (tackiness) to the surface of the obtained brazing sheet material so that it can be attached to a metal member.

The weight average molecular weight (M _w ) of the acrylic resin used in the present embodiment is 100,000 or more, preferably 300,000 to 1,000,000, more preferably 400,000 to 600,000. It is preferable that it is the range of these. When the said weight average molecular weight is less than 100,000, the intensity | strength of the sheet | seat for brazing obtained will fall. Further, when the weight average molecular weight is too high, the dispersibility of the nickel-based alloy powder is lowered, and thus the brazing sheet tends to be aggregated or a good sheet cannot be obtained.

  The acrylic resin having a hydroxyl group can be obtained by polymerizing the monomer mixture prepared in the above-described monomer composition. Specific examples of the polymerization method include solution polymerization, suspension polymerization, emulsion polymerization and the like. Among these, it is preferable to use solution polymerization in which a monomer mixed solution is dissolved in a solvent and polymerized in the presence of a polymerization initiator as necessary.

  Specific examples of the polymerization initiator include organic peroxides such as benzoyl peroxide, lauroyl peroxide, caproyl peroxide, t-hexyl peroxyneodecanate, and t-butyl peroxybivalate. -Azo compounds such as azobis-iso-butyronitrile, 2,2-azobis-2,4-dimethylvaleronitrile, 2,2-azobis-4-methoxy-2,4-dimethylvaleronitrile. The polymerization initiators may be used alone or in combination of two or more. The blending ratio of the polymerization initiator is preferably 0.1 to 5 parts by mass, and more preferably 0.2 to 3 parts by mass with respect to 100 parts by mass of the radical polymerizable monomer.

  Examples of the solvent used in the solution polymerization include ketone organic solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, ester organic solvents such as methyl acetate, ethyl acetate, and butyl acetate, dimethylformamide, dimethyl sulfoxide, and N-methyl-2- Polar solvents such as pyrrolidone, alcoholic organic solvents such as methyl alcohol, ethyl alcohol, and isopropyl alcohol, aromatic hydrocarbon organic solvents such as toluene, xylene, “Sorvesso 100” (manufactured by Exxon Chemical), n-hexane, cyclohexane Aliphatic hydrocarbon / alicyclic hydrocarbon organic solvents such as methylcyclohexane, “Loose”, “Mineral Spirit EC” (both manufactured by Shell), cellosolve organic solvents such as methyl cellosolve, ethyl cellosolve, butyl cellosolve, Te Examples thereof include ether organic solvents such as trahydrofuran and dioxane, and carbitol organic solvents such as n-butyl carbitol and iso-amyl carbitol. These may be used alone or in combination of two or more.

  The acrylic resin is blended in a liquid form such as an acrylic resin solution, an acrylic resin emulsion, and an acrylic resin suspension. The solid content concentration of the acrylic resin in the solution, emulsion, or suspension is 10 to 80% by mass, more preferably 20 to 60% by mass in terms of stability and workability during the production of the acrylic resin. To preferred.

  Next, the crosslinking agent which is a component for crosslinking the acrylic resin having a hydroxyl group will be described.

  The crosslinking agent is not particularly limited as long as it is a compound having at least two functional groups having reactivity with hydroxyl groups. Specific examples thereof include an isocyanate crosslinking agent, a melamine crosslinking agent, an epoxy crosslinking agent, a carbodiimide crosslinking agent, and an oxazoline crosslinking agent. In these, an isocyanate type crosslinking agent is preferable from the point which is excellent in reactivity. Specific examples of the isocyanate crosslinking agent include hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, or derivatives thereof.

  Next, a method for producing a brazing sheet material will be described.

  In the production of the brazing sheet material, first, a brazing composition is prepared.

  The brazing composition is obtained by stirring and mixing a nickel-based alloy powder and a crosslinking agent in a predetermined ratio to a solution of an acrylic resin having a hydroxyl group. In addition, it is preferable that a crosslinking agent is mixed just before application | coating.

  The content ratio of the nickel-based alloy powder in the solid content of the brazing composition is 50 to 90% by mass, preferably 55 to 85% by mass, and more preferably 60 to 70% by mass. When the content ratio of the nickel-based alloy powder is less than 50% by mass, the ratio of the brazing material in the sheet is lowered. Therefore, in order to secure the amount of brazing material necessary for brazing, the thickness of the sheet is set. It is necessary to increase it, and it becomes disadvantageous in cost. On the other hand, when the content ratio of the nickel-based alloy powder exceeds 90% by mass, the content ratio of the acrylic resin having a hydroxyl group is relatively decreased, and it becomes difficult to maintain the sheet shape. Also, the tackiness of the surface is lowered.

  On the other hand, the content ratio of the acrylic resin having a hydroxyl group in the solid content of the brazing composition is 10 to 50% by mass, preferably 20 to 45% by mass, more preferably 30 to 40% by mass. It is. When the content ratio of the acrylic resin is less than 10% by mass, it becomes difficult to maintain the sheet shape, and the adhesiveness of the surface also decreases. On the other hand, when the content ratio of the acrylic resin exceeds 50% by mass, the ratio of the nickel-based alloy powder is relatively decreased, so that the ratio of the brazing material in the sheet is decreased. In order to secure the amount of brazing material necessary for the sheet, it is necessary to increase the thickness of the sheet, which is disadvantageous in terms of cost.

  In addition to the above components, known thickeners, antifoaming agents, thixocontrol agents, surfactants, dispersants and the like may be appropriately added to the brazing composition as necessary.

  The stirring and mixing means is not particularly limited, and a stirring means or the like using a normal disper can be used without any particular limitation. In addition, since the brazing composition is subsequently applied to the support substrate, it is preferable to adjust the viscosity to be suitable for application by adding a solvent. The solvent is not particularly limited, but ethyl acetate or the like is preferably used from the viewpoint of excellent volatility. The viscosity is preferably about 100 to 50,000 mPa · s.

  And the composition for brazing is obtained by mix | blending and mixing a crosslinking agent just before apply | coating to a support base material.

  The mixing ratio of the crosslinking agent is appropriately selected depending on the hydroxyl group content ratio of the acrylic resin having a hydroxyl group. Specifically, for example, the blending ratio is preferably such that the isocyanate group of the polyisocyanate is 0.2 to 3 equivalents relative to 1 equivalent of the hydroxyl group of the acrylic resin having a hydroxyl group.

  A brazing sheet material is obtained by applying the brazing composition thus prepared to the surface of the supporting substrate and then drying.

  A support base material is a base material which supports the sheet material for brazing, and is a base material which peels, after sticking the sheet | seat for brazing to the junction part of a metal member.

  As a specific example of such a supporting substrate, for example, a material such as a PET film or the like on which a film such as a silicone compound having excellent releasability is formed is used. The thickness of the support substrate is not particularly limited.

  The brazing composition is applied to the surface of the support substrate by a coating means such as a roll coater, a blade coater, or a lip coater. At this time, the clearance of the coater is adjusted so that the thickness of the obtained brazing sheet material becomes a desired thickness. And after apply | coating, the sheet | seat material for brazing is obtained by volatilizing the solvent in a composition by drying and hardening an acrylic resin.

  Although the thickness of the brazing sheet material is not particularly limited, for example, a thickness of 1 to 1000 μm, and further 100 to 1000 μm is preferably used. If the thickness of the brazing sheet material is too thin, the supply amount of the nickel-based alloy powder is insufficient, and thus there is a tendency that sufficient bonding strength cannot be obtained. When melted, the clearance between the joining members increases, which tends to cause joint failure.

  From the viewpoint of handling properties, as shown in FIG. 1, it is preferable to protect the surface of the brazing sheet material 1 formed on the surface of the support base 2 by attaching a protective sheet 3. Thus, the brazing sheet structure 4 in which the brazing sheet material 1 is interposed between the support base 2 and the protective sheet 3 is obtained. In addition, it is preferable that the peeling force of the protective sheet 3 is smaller than the peeling force of the support substrate 2. Thus, only the protective sheet 3 is first peeled off and the brazing sheet is adhered to the joint, and then the support base material 2 is peeled off from the brazing sheet, thereby brazing the sheet material 2 to the joint. Can only leave.

  Moreover, with reference to FIG. 2, another form of the sheet | seat structure for brazing is demonstrated. The brazing sheet structure 5 shown in FIG. 2 is a winding tape in which a brazing sheet material 1 is laminated on the surface of a support base 2 ′ having a releasable film on both sides. It is a form of shape. In this case, sticking is particularly facilitated by making a difference in the peelability (that is, surface free energy) between the front surface and the back surface of the support substrate 2 ′.

  Furthermore, the brazing sheet structure 6 which is another form of the brazing sheet structure is demonstrated using FIG. FIG. 3A is a top view of a brazing sheet structure 6 in which the brazing sheet material 1 is formed in the form of a label seal on the surface of the support base 2, and FIG. It is AA 'sectional drawing of a).

  As shown in FIGS. 3A and 3B, the brazing sheet structure 6 has a brazing sheet material 1 in a label seal shape in a pattern shape corresponding to the arrangement of a plurality of joints in the metal member. It is arranged. According to such a configuration, when joining a plurality of joints in the metal member at the same time, the brazing sheet material 1 is arranged and supported in advance so as to have a pattern reflecting the positional relationship between the plurality of joints. By sticking and supporting on the surface of the base material 2, it becomes easy to stick the brazing sheet material 1 to a precise position with respect to a plurality of joint portions. In the brazing sheet material 1 formed in such a label seal shape, for example, a brazing composition is applied only to a portion on the support base 2 where the brazing sheet material 1 is to be disposed using a dispenser. It can be formed by masking a portion other than the portion where the brazing sheet material is to be formed and applying the brazing composition.

  Next, a method for assembling a heat exchanger using the brazing sheet structure 6 will be described with reference to FIGS.

  FIG. 4 is a schematic process diagram for explaining a process of laminating corrugated stainless steel inner fins as an example of a brazing method. Note that the space formed by the brazed inner fin after being laminated becomes a fluid flow path of the exhaust gas in the heat exchanger of the exhaust gas recirculation device.

  In the step of laminating the inner fins made of stainless steel, first, as shown in FIG. 4A, the brazing sheet structure 6 is used to braze the brazed portion 11 of the stainless steel inner fin 10. The sheet material 1 is stuck (sticking process). Adhesion is arranged so that the position of the brazing sheet material 1 of the brazing sheet structure 6 and each brazing part 11 of the inner fin 10 face each other, and the brazing sheet material 1 is the brazing of the inner fin 10. Press so as to stick to the surface of the attachment part 11.

  After the pressing, the support base material 2 of the brazing sheet structure 6 is peeled off, so that the brazing sheet material 1 remains only in each brazing portion 11 of the inner fin 10 as shown in FIG. It is. On the other hand, in the same manner as described above, another inner fin 10 on which another set of brazing sheet material 1 is bonded is prepared.

  And as shown in FIG.4 (c), each brazing site | part 11 of the inner fin 10 with which the sheet material 1 for brazing was stuck to two sets of brazing site | parts 11 prepared separately opposingly arrange | positions. Then, the combination body 15 is formed (combination process).

  Next, the brazing sheet material 1 was adhered in the same manner to the brazing part 11 on the surface of the combined body 15, and the brazing sheet material 1 was further adhered to another brazing part 11. The operation of overlapping the inner fins 10 is repeated. Thereby, the inner fin structure 20 in which the inner fins 10 are laminated in a predetermined number of stages as shown in FIG. 5 is obtained. A brazing sheet material 1 for brazing to a stainless steel box 25 described later is bonded to the brazing region 11 of the outermost layer of the inner fin structure 20.

  And the obtained inner fin structure 20 is accommodated in the stainless steel box 25 as shown in FIG. A brazing margin 26 is provided in a convex shape on the outer periphery of the upper surface of the box body 25, and a notch 27 serving as a refrigerant flow path is provided in a part of the brazing margin 26. A plurality of brazing margins 28 having the same height as the brazing margins 26 are provided on the inner side of the upper surface of the box 25 in a convex shape.

  And the box 25 in which the inner fin structure 20 was accommodated is laminated | stacked by the predetermined | prescribed number of steps, as shown in FIG. In this case, the brazing sheet material 1 is bonded to the brazing margin 26 and the brazing margin 28 in advance. The boxes 25 stacked in a predetermined number of stages are put into a brazing furnace, and the temperature is equal to or higher than the melting point of the nickel-based alloy powder contained in the brazing sheet material 1, and the stainless steel constituting each member The nickel-based alloy powder is melted and heated to a temperature not higher than the melting point of (a brazing step).

  By such a process, each brazing part is brazed in a multipoint manner, and a stainless steel heat exchanger 40 as shown in FIG. 7 is assembled.

  The stainless steel heat exchanger 40 thus obtained is preferably used as an exhaust heat exchanger such as an EGR cooler because it has better heat resistance and corrosion resistance than an aluminum heat exchanger or the like. In the stainless steel heat exchanger 40, high-temperature exhaust gas from the engine is introduced into the space formed from the honeycomb-like stainless steel structure formed from the inner fin structure 20. On the other hand, a coolant such as cooling water is introduced into the coolant channel 41 formed by the notch 27 from the direction of the arrow in FIG. The exhaust gas is cooled by exchanging heat between the inner fin structure 20 and the refrigerant to be passed. The cooled exhaust gas is reintroduced to the intake side of the engine.

  The present invention will be described more specifically with reference to examples. In addition, this invention is not limited at all by the following examples.

  First, a method for producing an acrylic resin solution used in this example will be described.

(Production Example 1)
A reactor equipped with a stirrer, a cooling tube, a dropping funnel and a nitrogen introduction tube was charged with 300 parts by mass of ethyl acetate and 80 parts by mass of toluene as a reaction solvent, and the system temperature was raised to 80 ° C. under a nitrogen stream. Warm up. Next, a solution in which 396 parts by mass of n-butyl acrylate, 4 parts by mass of 4-hydroxybutyl acrylate, and 2 parts by mass of a peroxide polymerization initiator (Perbutyl O: manufactured by NOF Corporation) were mixed for 3 hours. Then, the reaction system was added dropwise while maintaining at 80 ° C. Even after completion of the dropping, the inside of the reactor system was kept at 80 ° C. for 10 hours to complete the polymerization reaction. Thereafter, a certain amount of toluene was added to adjust the nonvolatile content concentration to 50%, thereby obtaining an acrylic resin A solution.

(Production Example 2)
A reactor equipped with a stirrer, a cooling tube, a dropping funnel and a nitrogen introduction tube was charged with 300 parts by mass of ethyl acetate and 80 parts by mass of toluene as a reaction solvent, and the system temperature was raised to 80 ° C. under a nitrogen stream. Warm up. Next, a solution in which 396 parts by mass of n-butyl methacrylate, 4 parts by mass of 4-hydroxybutyl acrylate, and 2 parts by mass of a peroxide polymerization initiator (Perbutyl O: manufactured by NOF Corporation) were mixed for 3 hours. Then, the reaction system was added dropwise while maintaining at 80 ° C. Even after completion of the dropping, the inside of the reactor system was kept at 80 ° C. for 10 hours to complete the polymerization reaction. Then, the solution of the acrylic resin B was obtained by adding a fixed amount of toluene and adjusting so that a non volatile matter density | concentration might be 50%.

(Production Example 3)
A reactor equipped with a stirrer, a cooling tube, a dropping funnel and a nitrogen introduction tube was charged with 300 parts by mass of ethyl acetate and 80 parts by mass of toluene as a reaction solvent, and the system temperature was raised to 80 ° C. under a nitrogen stream. Warm up. Next, a reactor system in which a solution prepared by previously mixing 396 parts by mass of n-butyl acrylate, 4 parts by mass of acrylic acid and 2 parts by mass of a peroxide-based polymerization initiator (Perbutyl O: manufactured by NOF Corporation) over 3 hours was used. It was dropped while keeping the inside at 80 ° C. Even after completion of the dropping, the inside of the reactor system was kept at 80 ° C. for 10 hours to complete the polymerization reaction. Then, the solution of the acrylic resin C was obtained by adding a fixed amount of toluene and adjusting so that a non-volatile content density | concentration might be 50%.

(Production Example 4)
A reactor equipped with a stirrer, a cooling tube, a dropping funnel and a nitrogen introducing tube was charged with 300 parts by mass of ethyl acetate and 80 parts by mass of toluene as a reaction solvent, and the system temperature was raised to 80 ° C. under a nitrogen stream. Warm up. Next, a solution in which 396 parts by mass of n-butyl acrylate, 4 parts by mass of 4-hydroxybutyl acrylate, and 10 parts by mass of a peroxide polymerization initiator (Perbutyl O: manufactured by NOF Corporation) were mixed for 3 hours. The reaction system was then added dropwise while maintaining at 80 ° C. Even after the completion of the dropping, the inside of the reactor system was maintained at 80 ° C. for 10 hours to complete the polymerization reaction. Then, the solution of the acrylic resin D was obtained by adding a fixed amount of toluene and adjusting so that a non-volatile content density | concentration might be 50%.

The constituent monomer composition, glass transition temperature (T _g ), nonvolatile content, and weight average molecular weight (M _w ) of the acrylic resins A to D obtained in Production Examples 1 to 4 are collectively shown in Table 1 below. The glass transition temperature in Table 1 is a value measured by a differential scanning calorimeter (DSC) method, the non-volatile content is a value measured at 130 ° C. with a ket non-volatile content measuring apparatus, and the weight average molecular weight is a THF solution. Is measured by gel permeation chromatography (GPC) and calculated by polystyrene conversion.

Example 1
According to the blending composition in Table 2, the nickel-based alloy powder and the crosslinking agent were blended into the acrylic resin A solution obtained in Production Example 1. In addition, the ratio of the acrylic resin in Table 2 is a value converted by the resin content. And it stir-mixed for about 30 minutes-1 hour using the Hibismix type | mold stirring apparatus by a Primix company, and also mix | blended the crosslinking agent, and obtained the composition for brazing. In addition, as a nickel-based alloy powder, an alloy composition (mass%) obtained by using the gas atomization method is Ni / Cr / Si / P = 61.2 / 29.5 / 4.0 / 5.3, and a true spherical shape having an average particle diameter of 550 μm. Nickel-based alloy powder E was used. Moreover, as a crosslinking agent, the isocyanate type crosslinking agent (Brand name Coronate L-45E: Nippon Polyurethane company make) was used.

  And the obtained composition for brazing was apply | coated to the release surface of the support base material using the bar coater. In addition, the support base material provided the mold release surface which has the film which consists of a silicone resin in the single side | surface of a 50-micrometer-thick PET film. Then, the coating film was dried at 100 ° C. for 1 minute to form a brazing sheet material having a thickness of 50 μm. And the protective sheet which has surface free energy lower than the surface free energy of a support base material was bonded together on the surface of the formed sheet | seat for brazing. And the sheet | seat structure for brazing was obtained by aging for 3 days in a 40 degreeC environment.

  And the obtained sheet | seat material for brazing was evaluated with the following method.

[Adhesiveness]
A brazing sheet material cut to 2 mm × 100 mm was attached to the central portion of stainless steel (SUS-304 compliant with JIS standards) having a thickness of 30 mm × 100 mm and a thickness of 2 mm. And the sticking property with respect to the stainless steel of the sheet | seat material for brazing was determined by the following references | standards.

◯: There was a feeling of tack and the adhesiveness to stainless steel was good.
X: There was no tackiness and there was no sticking property to stainless steel.

[Film formability]
The state when the surface of the brazing sheet material was lightly rubbed with a finger after the protective sheet was peeled off from the brazing sheet structure was determined according to the following criteria.

○: Even when rubbed, the film formation state did not collapse and the appearance did not change.
X: The film formation state collapsed or was worn when rubbed.

[Discoloration of nickel-based alloy powder]
A total of 200 g of the acrylic resin solution and the nickel-based alloy powder were put into a 200 cc glass container so as to have the blending ratio shown in Table 2, and mixed by stirring to prepare a composition for evaluation. And the discoloration state after hold | maintaining the composition for evaluation for 3 days with a 40 degreeC thermostat in the state which sealed the glass container was visually observed.

○: No discoloration was observed.
X: Discolored to light green.

[Jointability]
As shown in FIGS. 8 (a) and 8 (b), 30 mm × 100 mm and 2 mm thick stainless steel 50 (SUS-304 compliant with JIS standard) was cut into a central portion of 2 mm × 100 mm in the longitudinal direction. A sheet material 1 for brazing was pasted. Then, as shown in FIG. 8 (c), another 30 mm × 100 mm stainless steel 51 having a thickness of 2 mm was vertically held on the surface of the brazing sheet material 1 to which the stainless steel 51 was attached. While maintaining this state, it was put into a brazing furnace in a nitrogen atmosphere set at 1000 ° C. and held for 30 minutes. And the brazing state when it took out from the brazing furnace was determined according to the following criteria.

(Double-circle): It was joined correctly according to the hold | maintained position, and the fillet which is the part which the brazing protruded from the clearance gap of the junction part was fully formed.
○: Although it was joined exactly according to the held position, the fillet was small.
(Triangle | delta): Position shift occurred and it was not joined correctly according to the held position.
X: Not fully joined.

  The results are shown in Table 2.

(Examples 2 to 4 and Comparative Examples 1 to 4)
A brazing sheet material was prepared and evaluated in the same manner as in Example 1 except that the composition in Table 2 was followed. In Example 2, although the composition was the same as the true spherical nickel-based alloy powder E having an average particle diameter of 50 μm, an alloy powder F having an average particle diameter of 550 μm was used. The results are shown in Table 2.

  From the result of Table 2, in Examples 1-4 which concern on this invention, all were excellent in sticking property and film-forming property, and there was also no discoloration of a nickel-type brazing material. Also, the bonding strength was sufficient. In particular, Examples 1 and 2 having sheet thicknesses of 200 μm and 700 μm were particularly excellent in bonding strength. On the other hand, the brazing sheet material in Comparative Example 1 using an acrylic resin having a high glass transition temperature did not have sticking properties. Therefore, a positional shift occurred in the joint portion, and exactly according to the held position. Not joined. Further, in the brazing sheet material in Comparative Example 2 using the acrylic resin having a carboxyl group, oxidation of the surface of the nickel brazing material was observed. For this reason, the melting point of the nickel-based brazing material has become high, resulting in insufficient bonding. Further, the brazing sheet material in Comparative Example 3 using the acrylic resin having a low weight average molecular weight has low strength of the obtained sheet, and the sheet collapsed when the surface was rubbed with a finger to give a shearing force. . Further, Comparative Example 3 and Comparative Example 4 could not maintain the shape as a sheet, and could not be brazed because a test piece as shown in FIG. 8 could not be prepared.

DESCRIPTION OF SYMBOLS 1 Brazing sheet material 2 Support base material 3 Protection sheet 4, 5, 6 Brazing sheet structure 10 Inner fin 11 Brazing part 15 Combined body 20 Inner fin structure 25 Box body 26, 28 Brazing margin 27 Refrigerant Notch to be used as flow path of 40 Stainless steel heat exchanger 41 Refrigerant flow path 50, 51 Stainless steel

Claims (8)

A brazing sheet material containing 50 to 90% by weight of a nickel-based alloy powder and 10 to 50% by weight of a binder resin,
The binder resin is a resin obtained by crosslinking an acrylic resin having a hydroxyl group with a crosslinking agent, having a glass transition temperature of 0 ° C. or less and a weight average molecular weight of 100,000 or more. Brazing sheet material.   The brazing sheet material according to claim 1, wherein the nickel-based alloy powder is a Ni-Cr-Si-based alloy.   The brazing sheet material according to claim 1 or 2, wherein the thickness is in the range of 100 to 1000 µm.   A brazing sheet obtained by adhering a support base and a protective sheet having different peeling forces to both surfaces of the brazing sheet material according to any one of claims 1 to 3. Construct.   The brazing sheet structure according to any one of claims 1 to 3, wherein the brazing sheet material according to any one of claims 1 to 3 formed in a label seal shape is attached to a surface of a supporting substrate. A brazing composition for producing the brazing sheet material according to any one of claims 1 to 3,
As a non-volatile content, nickel-based alloy powder 50 to 90% by mass, acrylic resin 10 to 50% by mass having a hydroxyl group, and a crosslinking agent,
The brazing composition, wherein the acrylic resin has a glass transition temperature of 0 ° C. or lower and a weight average molecular weight of 100,000 or higher.   A bonding step of bonding the brazing sheet material according to any one of claims 1 to 3 to a brazing site of the first metal member; A combination step of arranging a brazing portion of the metal member to form a combined body, and heating the combined body to a temperature equal to or higher than a melting point of the nickel-based alloy powder to melt and braze the nickel-based alloy powder. And a brazing process.   A stainless steel heat exchanger assembled by brazing a plurality of stainless steel members to each other, wherein the brazed portion is obtained by brazing according to the method of claim 7. Exchanger.

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