Patent Publication Number: US-2016237542-A1

Title: Metal thermal spray method

Description:
TECHNICAL FIELD 
     The present invention relates to apply a metal thermal spray to a surface of a base material consisting of a metal such as bridges, towers, pipes, guardrails, ship, and various types of steel. 
     BACKGROUND ART 
     In order to impart an anchor effect to a thermally sprayed film, a conventional metal thermal spray method employs a method of obtaining the anchor effect in such a manner that a base material surface is subjected to blasting in advance to roughen and is formed into an uneven shape or that, as described in Patent Literature 1 below, a base material surface is previously coated with a coating film composition containing an epoxy resin to form a coating film having an uneven shape and a metal thermal spray is applied to the surface having such an uneven shape. 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: JP 3106480 B1 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the method of roughening the base material surface by the blasting and forming the uneven shape, however, there are problems that not only working efficiency becomes poor depending on the degree of skill of a worker but also costs become increase. 
     In addition, according to the method of the Patent Literature 1 described above, the blasting becomes unnecessary and thus working efficiency is improved, but a coating film formed on the entire base material surface contains an epoxy resin having high insulation, thereby becoming an insulator, so that the flow of current to the thermally sprayed film from the base material will be blocked. 
     For this reason, the thermally sprayed film having a larger ionization tendency than the base material cannot be sacrificially dissolved, and there is a concern of not being capable of achieving an original purpose of the metal thermal spray, that is, a purpose that the thermally sprayed film is sacrificed instead of the base material and thus the base material is prevented from becoming rusty. 
     Solution to Problem 
     In the present invention, the process of imparting the uneven shape to the surface of the base material in advance as in the related art described above is eliminated, a metal is directly thermally-sprayed onto the base material surface, and thus an innovative metal thermal spray method is provided in which an adhesion strength between the thermally sprayed film and the surface of the base material is reinforced after the thermally sprayed film formed. 
     In summary, according to the present invention, a metal thermal spray method of thermally spraying a metal onto a surface of a base material made of a metal, the metal having an ionization tendency larger than that of the metal of the base material, includes: thermally spraying the metal onto the surface of the base material; and impregnating a thermally sprayed film formed by the thermal spraying with a coating material that contains silane and polyisocyanate and has viscosity of 50 to 500 mPa·s at 25° C. and curing the coating material, whereby a pore sealing treatment in the thermally sprayed film and adhesion strength of the thermally sprayed film onto the surface of the base material can be reinforced. Therefore, the base material can be appropriately protected. 
     Preferably, the coating material contains alkylalkoxysilane as the silane, and the alkylalkoxysilane and the polyisocyanate contained in the coating material has a weight ratio of 10 to 90:90 to 10 to effectively promote a curing reaction of both them. 
     Advantageous Effects of Invention 
     According to the metal thermal spray method of the present invention, it is possible to reinforce the adhesion strength of the thermally sprayed film in such a manner that the metal can be thermally sprayed onto the flat base material surface without impartment of the uneven shape to the base material surface and that the thermally sprayed film is impregnated with the coating material having low viscosity before curing and high bonding strength after curing, whereby the coating material enters into fins pores present in the thermally sprayed film and is then cured to appropriately seal the fine pores, and the coating material is filled and cured in the fine cavities formed between the back surface of the thermally sprayed film and the surface of the base material. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view schematically illustrating a state where a thermally sprayed film is formed on a surface of a base material which is thermally sprayed by a metal. 
         FIG. 2  is a cross-sectional view schematically illustrating a state where the thermally sprayed film is impregnated with a coating material and the coating material is cured. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of a metal thermal spray method according to the present invention will be described with reference to  FIGS. 1 and 2 . 
     As illustrated in  FIG. 1 , in the metal thermal spray method according to the present invention, a surface  1   a  of abase material  1  is subjected to a scraping treatment using a known disk sander, if necessary, to remove contaminations or oils, a degraded coating film, floating rust, and the like, and a metal is thermally sprayed onto the surface  1   a  of the base material  1  using a known thermal spraying machine to form a thermally sprayed film  2 . 
     The thermally sprayed film  2  is formed to have a thickness of 50 to 500 μm. The most preferred thickness is 50 to 150 μm. 
     As the metal to be thermally sprayed, a metal is used that has an ionization tendency larger than that of a metal constituting the base material  1 . For example, when the base material  1  is constituted by iron (steel), zinc, aluminum, or the like is thermally sprayed. Further, a thermal spray method is not particularly limited in the present invention. 
     In the state of  FIG. 1 , a back surface  2   b  of the thermally sprayed film  2  includes a portion coming in close contact with the surface  1   a  of the base material and a portion apart from the surface  1   a  of the base material to be formed with fine cavities  4  in a region to line surface  1   a  of the base material therefrom, and adhesion strength of the thermally sprayed film  2  is in a weak state with respect to the surface  1   a  of the base material toy the presence of the fine cavities  4 . In addition, fine pores  3  are formed in the thermally sprayed film  2 . 
     In the present invention, from the state of  FIG. 1 , the front surface  2   a  of the thermally sprayed film  2  is coated with a coating material  5  consisting of a liquid containing silane and polyisocyanate as a main material, using a known coating means such as a brush, a roller, or a spray, and the thermally sprayed film  2  is impregnated with the coating material  5 . 
     Preferably, alkylalkoxysilane is used as the silane. The alkylalkoxysilane reacts with moisture in the air to generate silanol and ethyl alcohol, and the other polyisocyanate reacts with moisture in the air to generate polyurea and carbon dioxide. 
     As described above, the silanol to be generated by alteration of the alkylalkoxysilane and the polyurea to be generated by alteration of the polyisocyanate cause a curing reaction, and exhibit high bonding strength after the curing. The ethyl alcohol generated from the alkylalkoxysilane is volatized at the time of coating of the coating material, and the carbon dioxide generated from the polyisocyanate is dispersed at the time of coating of the coating material. 
     Furthermore, a weight ratio between the alkylalkoxysilane and the polyisocyanate contained in the coating material  5  is set to be 10 to 90:90 to 10 to effectively promote the curing reaction of both them. Mixing examples of the coating material  5  are as follows, and the coating material  5  does not require a solvent. 
     MIXING EXAMPLE 1 
     Amount to be mixed per 1 kg of the coating material 5 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Polyisocyanate (liquid) 
                 800 g 
               
               
                   
                 Alkylalkoxysilane (liquid) 
                 200 g 
               
               
                   
                   
               
            
           
         
       
     
     MIXING EXAMPLE 2 
     Amount to be mixed per 1 kg of the coating material 5 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 Polyisocyanate (liquid) 
                 500 g 
               
               
                   
                 Alkylalkoxysilane (liquid) 
                 500 g 
               
               
                   
                   
               
            
           
         
       
     
     In addition, the coating material  5  is adjusted to be a liquid having low viscosity of 50 to 500 mPa·s and preferably 200 mPa·s or less at a temperature of 25° C. by adjustment of the amount of alkylalkoxysilane. 
     As described above, the coating material  5  having the low viscosity easily enters into the fine pores  3  formed in the thermally sprayed film  2  and easily reaches the fine cavities  4  formed between the back surface  2   b  of the thermally sprayed film and the surface  1   a  of the base material through the fine pores  3  at the same time as illustrated in  FIG. 2 , thereby being filled and cured in the fine cavities  4 . 
     Then, the coating material  5  is cured without a gap in the fine pores  3  and is also cured without a gap in the fine cavities  4 , and exhibits high bonding strength after being cured. The coating material  5  cured in the fine cavities  4  firmly bonds to the surface  1   a  of the base material and also imparts an anchor effect to the thermally sprayed film  2 . In addition, a non-impregnated part of the coating material  5  forms a strong coating film  5 ′ on the front surface  2   a  of the thermally sprayed film  2 . 
     That is, the coating material  5  enters into the fine pores  3  and is then cured to appropriately seal the fine pores  3 , and, at the same time, is filled and cured in the fine cavities  4  formed between the back surface  2   b  of the thermally sprayed film and the surface  1   a  of the base material, whereby the thermally sprayed film  2  and the base material  1  can be firmly combined with each other to increase adhesion strength. Furthermore, the costing film  5 ′ is formed on the front surface  2   a  of the thermally sprayed film  2  to appropriately protect the thermally sprayed film  2 . 
     In the metal thermal spray method according to the present invention, furthermore, as illustrated in  FIGS. 1 and 2 , a portion of the back surface  2   b  of the thermally sprayed film  2  comes in close contact with the surface  1   a  of the base material  1 , whereby the flow of current to the thermally sprayed film  2  from the base material  1  is not inhibited; and the thermally sprayed film  2  made of a metal having a larger ionization tendency than the metal of the base material  1  is sacrificially dissolved, whereby the base material  1  is protected by being prevented from becoming rusty as appropriate. 
     As a result in which the inventors made use of the coating material  5  according to each of the mixing examples and carried out a tensile test of the thermally sprayed film using the thermal spray method according to the present invention, it was confirmed that the bonding strength of 1.5 N/mm 2  or more was exhibited even when the coating material  5  according to any of the mixing examples was used. Specifically, zinc and aluminum were thermally sprayed onto the surface of an iron plate which was a base material to form a thermally sprayed film having a thickness of 200 ηm, the coating material  5  according to each of the mixing examples was coated on the surface of the thermally sprayed film to impregnate the thermally sprayed film with the coating material  5 , the coating material  5  was provided with square incisions of which one side had a length of 4 cm after being cured, the incision reaching the base material, an attachment was attached to the thermally sprayed film divided into the square shape, to be pulled using a bonding force tester, whereby the bonding strength was measured. 
     As described above, the metal thermal spray method according to the present invention does not require a pre-treatment used in the conventional method, the pre-treatment imparting an uneven shape to the surface of the base material to obtain an anchor effect. 
     Then, the metal is directly thermally-sprayed onto the surface of the base material not having the uneven shape, and after the thermally sprayed film is formed, the thermally sprayed film is impregnated with the coating material, which exhibits the low viscosity before the curing and the high bonding strength after the curing, through the fine pores. In this way, the metal thermal spray method according to the present invention is an incommensurable thermal spray method capable of sealing the fine pores and reinforcing the adhesion strength of the thermally sprayed film. 
     Furthermore, since the metal thermal spray method according to the present invention is a simple method in which the metal is thermally sprayed onto the surface of the base material in a known manner and the thermally sprayed film formed by the thermal spray is coated and impregnated with the coating material, the metal cap fee effectively thermally-sprayed onto metal structures such as existing bridges in the field, especially. 
     In this description, the numerical range between the lower limit value and the upper limit value indicated by “to” represents all numerical values (integer value and fractional value) between the lower limit value and the upper limit value. In appended Claims, the same is also applied. 
     REFERENCE SIGNS LIST 
       1  Base material 
       1   a : Surface of base material 
       2 : Thermally sprayed film 
       2   a : Front surface of thermally sprayed film 
       2   b : Back surface of thermally sprayed film 
       3 : Fine pore 
       4 : Fine cavity 
       5 : Coating material 
       5 ′: Coating film