Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/78—Pretreatment of the material to be coated
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C22/00—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C22/05—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
  • C23C22/06—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
  • C23C22/07—Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 containing phosphates

Definitions

• the present invention relates to an aqueous surface conditioner for use in a phosphate coating treatment performed on the surface of a metal material such as a sheet of iron, steel, zinc -plated steel, or aluminum in order to promote the chemical conversion reaction and shorten the duration thereof and to achieve greater fineness of the crystals that make up the phosphate coating.
• the invention also relates to a method for the surface conditioning of a metal material.
• a surface conditioning step is carried out prior to a phosphate coating chemical conversion step for the purpose of activating the metal surface so that fine and closely-spaced phosphate coating crystals will be obtained and creating nuclei for the deposition of phosphate coating crystals.
• the following is a typical example of a phosphate coating chemical conversion process performed in order to obtain fine and closely-spaced phosphate coating crystals.
• Surface conditioning is performed in order to make phosphate coating crystals finer and more closely-spaced.
• Compositions with this aim have been discussed in U.S. Patents 2,874,081, 2,322,349, and 2,310,239, for example, and examples of the main constituent components of the surface conditioner include titanium, pyrophosphoric acid ions, orthophosphoric acid ions, and sodium ions.
• the above-mentioned surface conditioning compositions are called "Jernstedt salts," and titanium ions and titanium colloids are included in aqueous solutions thereof.
• a metal that has been degreased and rinsed with water is immersed in an aqueous solution of one of the above-mentioned surface conditioning compositions, or a phosphating treatment surface conditioner is sprayed onto the metal, causing the titanium colloid to be adsorbed to the metal surface.
• the adsorbed titanium colloid forms the nuclei for phosphate coating crystal precipitation in the subsequent phosphate coating chemical conversion step, which promotes the chemical conversion reaction and makes the phosphate coating crystals finer and more closely-spaced.
• All of the surface conditioning compositions in industrial use today make use of Jernstedt salts.
• Various problems have been encountered, however, when a titanium colloid obtained from a Jernstedt salt is used in a surface conditioning process.
• the first of these problems is that the phosphating treatment surface conditioner deteriorates over time.
• this composition is extremely effective in terms of making the phosphate coating crystals finer more closely-spaced immediately after an aqueous solution is produced.
• the titanium colloid agglomerates a few days after the aqueous solution is prepared.
• the phosphating treatment surface conditioner loses its effect within this time regardless of whether it has been used or not, and the phosphate coating crystals that are obtained end up being coarse.
• Japanese Laid-Open Patent Application S63-76883 proposes a method for measuring the average particle diameter of the titanium colloid in a phosphating treatment surface conditioner, continuously discarding the phosphating treatment surface conditioner so that the average particle diameter will be less than a specified value, and supplying fresh surface conditioning composition in an amount coixesponding to the discarded amount, thereby maintaining the surface conditioning effect at a constant level.
• this method does allow the effect of the phosphating treatment surface conditioner to be maintained quantitatively, the phosphating treatment surface conditioner has to be discarded for the effect to be maintained.
• a large quantity of phosphating treatment surface conditioner must be discarded with this method in order to keep the effect of the phosphating treatment surface conditioner at the same level as when the aqueous solution was first produced.
• the wastewater treatment capacity of the plant where this method is used also comes into question, so the effect is maintained through a combination of continuous discarding and complete replacement of the phosphating treatment surface conditioner.
• the second problem is that the effect and service life of a phosphating treatment surface conditioner are greatly affected by the hardness of the water used during replenishment.
• Industrial water is usually used for replenishing a phosphating treatment surface conditioner.
• industrial water contains calcium, magnesium, and other such cationic components that are the source of the total hardness, although the amounts contained can vary greatly depending on the source of the industrial water.
• the titanium colloid that is the main component of a conventional phosphating treatment surface conditioner takes on an anionic charge in an aqueous solution, and the electrical repulsion thereof disperses the colloid and keeps it from settling. Therefore, if cationic components such as calcium or magnesium are present in large quantity in industrial water, the titanium colloid will be electrically neutralized by the cationic components, the repulsive force will be lost, agglomeration and settling will occur, and the effect of the colloid will be lost.
• a condensed phosphate such as a pyrophosphate is added to a phosphating treatment surface conditioner for the purpose of sequestering the cationic components and maintaining the stability of the titanium colloid.
• a condensed phosphate such as a pyrophosphate
• the condensed phosphoric acid reacts with the surface of a steel sheet and forms an inert film, which results in poor chemical conversion in the subsequent phosphate coating chemical conversion process.
• purified water must be used for supplying and replenishing the phosphating treatment surface conditioner, which is a major drawback in terms of cost.
• the third problem is that the temperature and pH are limited in their range. Specifically, if the temperature is over 35°C and the pH is outside a range of 8.0 to
• the titanium colloid will agglomerate and lose its surface conditioning effect. Therefore, the predetermined temperature and pH range must be used with a conventional surface conditioning composition, and the surface conditioning composition cannot be added to a degreasing agent or the like so that the effect of cleaning and activating a metal surface will be obtained with a single liquid over an extended period of time.
• the fourth problem is that there is a limit to how fine phosphate coating crystals can be made through the effect of a phosphating treatment surface conditioner.
• the surface conditioning effect is obtained by causing the titanium colloid to adsorb to a metal surface and form the nuclei during phosphate coating crystal precipitation. Therefore, the more titanium colloid particles are adsorbed to the metal surface in the surface conditioning step, the finer and more closely-spaced the resulting phosphate coating crystals will be. The most obvious way to achieve this would be increase the number of titanium colloid particles in the phosphating treatment surface conditioner, that is, raise the titanium colloid concentration.
• the concentration of titanium colloids currently being used is 100 ppm or less (as titanium in the phosphating treatment surface conditioner), and it has been impossible to make phosphate coating crystals finer by increasing the titanium colloid concentration over this level.
• Japanese Laid-Open Patent Applications S56-156778 and S57-23066 disclose a surface conditioning method in which a suspension containing an insoluble phosphate of a divalent or trivalent metal is sprayed under pressure onto the surface of a steel strip as a surface conditioner other than a Jernstedt salt.
• this surface conditioning method however, the effect is only realized when the suspension is sprayed under pressure onto the target material, so this method cannot be used for surface conditioning in a phosphate coating chemical conversion treatment performed by ordinary dipping or spraying.
• Japanese Patent Publication S40-1095 discloses a surface conditioning method in which a zinc plated steel sheet is dipped in a high-concentration suspension of an insoluble phosphate of a divalent or trivalent metal.
• the examples given for this method are limited to a zinc plated steel sheet, and obtaining a surface conditioning effect requires the use of a high-concentration insoluble phosphate suspension of no less than 30 g/L.
• the inventors examined means for solving the above problems, and closely studied the mechanism by which surface conditioners function. This led to the discovery that in the course of producing a phosphate coating, the coating components reach a state of supersaturation as the metal dissolves.
• the most important effect of a surface conditioner is that the crystals it produces function as nuclei for phosphate coating crystals.
• the performance of a surface conditioner is determined by how effectively it can act as crystal nuclei. In other words, the inventors found that crystals with a lattice constant close to that of phosphate coating crystals function as pseudo-crystal nuclei, resulting in a surface conditioning effect. Further research in this area led to the perfection of the present invention.
• the present invention relates to an aqueous surface conditioner for use in a phosphating treatment, which contains crystals having an average diameter of 5 ⁇ m or less in an amount of at least 0.1 g/L, said crystals having a two- dimensional epitaxy that matches within 3% of misfit with the crystal lattice of one phosphate coating selected from among (1) hopeite (Zn 3 (PO 4 ) 2 • 4H 2 O) and/or phosphophyllite (Zn 2 Fe(PO 4 ) 2 • 4H 2 O), (2) scholzite (CaZn 2 (PO 4 ) 2 • 2H 2 O), and (3) hureaulite (Mn 5 (PO 4 ) 2 [PO 3 (OH)] 2 • 4H 2 O).
• hopeite Zn 3 (PO 4 ) 2 • 4H 2 O
• phosphophyllite Zn 2 Fe(PO 4 ) 2 • 4H 2 O
• scholzite CaZn 2 (PO 4 ) 2 • 2H 2 O
• Fig. 1 is a concept diagram in which a LaMer diagram is applied to a surface conditioner (crystal growth steps);
• Fig. 2 shows the unit crystal lattices for hopeite (zinc phosphate) and magnesium hydrogenphosphate
• Fig. 3 is a diagram in which unit crystal lattices of hopeite have been arranged, with the grid-shaped solid line portion being a view of these crystal lattices viewed perpendicular to the (020) plane, and the dashed line portion being the unit crystal lattices of magnesium hydrogenphosphate arranged over these.
• phosphate coating crystals can be described by a LaMer diagram that shows the process in which crystals precipitate from a solution as a result of increased concentration.
• solute concentration rises, crystal precipitation will not occur as soon as the saturation concentration is exceeded, and crystal production occurs only when the crystal nucleus production concentration C * m ⁇ n is reached, after which the crystals grow, so the solute concentration decreases.
• Phosphate coating crystals are believed to precipitate through the same process, and this corresponds to when no surface conditioner is used (corresponds to the solid line portion in Fig. 1). In this case, crystal nuclei are produced only in the shaded area in Fig. 1. Because there are few crystal nuclei, the crystal coating is often coarse, and it takes a long time for the coating production reaction to conclude.
• the titanium colloid particles or the like that constitute this component function as pseudo-nuclei for the phosphate coating crystals
• crystal growth already begins at a concentration C*x that is lower than the crystal nucleus production concentration C * min .
• the number of crystal nuclei is determined by the number of titanium colloid particles or the like contained in the surface conditioner, so closely-spaced coating crystals can be produced by increasing the number of these particles.
• the coating crystals are produced in a short time, so the phosphate chemical conversion treatment does not take as long.
• the closer the concentration C * x at which crystal growth commences on the pseudo-crystal nuclei is to the saturation concentration C s , the less time it will take to produce the coating, so efficiency is higher.
• the term "mainly” as used above means that the hopeite and/or phosphophyllite; scholzite; or hureaulite accounts for at least 50 mass%, and preferably at least 70 mass%, of the phosphate coating.
• These surface conditioning substances can be used singly or in combinations of two or more types according to the corresponding phosphate coating.
• the inventors turned their attention to the lattice constant of the crystals of these surface conditioning substances, and found it to be close to the lattice constant of the phosphate coating crystals. If the crystal structures are similar, this means that these substances will be effective as pseudo-crystal nuclei; this is known as epitaxy.
• Manmade rain is often given as an example of epitaxy.
• a micropowder of silver bromide When a micropowder of silver bromide is scattered in water vapor that is supersaturated and supercooled, the silver bromide becomes the nuclei for the growth of ice crystals, resulting in rain.
• This phenomenon occurs because the lattice constant of the silver bromide crystals is extremely close to the lattice constant of ice, and the growth on one type of crystal of a different type of crystal with a similar lattice constant is known in the semiconductor field as epitaxial growth.
• a substance that has a surface conditioning effect on a phosphate coating is a substance whose epitaxy closely matches that of the phosphate coating crystals.
• Fig. 2 shows the unit lattice of hopeite (Zn 3 (PO 4 ) 2 • 4H 2 O).
• the grid-shaped solid line portion in Fig. 3 is a view of these crystal lattices arranged and viewed perpendicular to the (020) plane.
• the dashed line portion in Fig. 3 illustrates the unit lattices of magnesium hydrogenphosphate (MgHPO 4 ⁇ 3H 2 O) arranged over these, and the lattices match up well.
• magnesium hydrogenphosphate MgHPO 4 ⁇ 3H 2 O
• zinc phosphate is deposited over magnesium hydrogenphosphate, and as long as there is a good match between the lattices as above, the crystals will seat well and grow readily.
• misfit there is a certain amount of lattice misalignment in this example as well, and this is called misfit.
• Table 1 is an example of calculating the misfit for the above-mentioned surface conditioning substances used when a zinc phosphate coating is hopeite and/or phosphophyllite (Zn 2 Fe(PO 4 ) 2 • 4H 2 O).
• the two-dimensional misfit was within 3% in every case, and a surface conditioning effect was observed.
• a zinc phosphate coating contains not only hopeite but also a large amount of phosphophyllite.
• Phosphophyllite has a crystal structure that is extremely similar to that of hopeite, and the crystal lattices are also very close, so the two precipitate as mixed crystals.
• the above description of epitaxy was for when a zinc phosphate coating is produced, but the same applies to when the coating produced is scholzite or hureaulite.
• the misfit should be calculated by taking into account all possible arrangement combinations of the crystal lattice of scholzite or hureaulite instead of the crystal lattice of the zinc phosphate shown in Fig. 2.
• Table 2 is an example of calculating the misfit for the above-mentioned surface conditioning substances used when a zinc phosphate coating is scholzite.
• the two-dimensional misfit was within 3% in every case, and a surface conditioning effect was observed when a scholzite coating was produced.
• Table 3 is an example of calculating the misfit for the above-mentioned surface conditioning substances used when a zinc phosphate coating is hureaulite.
• the two-dimensional misfit was within 3% in every case, and a surface conditioning effect was observed when hureaulite was produced. It is preferable for the two-dimensional misfit to be within 2.5%, whether with (1) hopeite and/or phosphophyllite, (2) scholzite, or (3) hureaulite.
• the average diameter of the crystals of these surface conditioning substances must be no more than 5 ⁇ m, and 1 ⁇ m or less is preferable.
• the surface conditioning effect will be weak if the average diameter is over 5 ⁇ m.
• concentration of these crystals in the surface conditioner of the present invention there are no particular restrictions on the concentration of these crystals in the surface conditioner of the present invention, but the crystals must be contained in an amount of at least 0.1 g/L, with 0.1 to 50 g/L being preferable, and 1 to 5 g/L being even better.
• the surface conditioning effect will be inadequate if the amount is less than 0.1 g/L, but no further effect will be obtained by exceeding 50 g/L, so this would merely be a waste of money.
• Another essential component of the surface conditioner of the present invention is water.
• This water may be purified water, tap water, or industrial water.
• the above-mentioned surface conditioning substances are usually suspended in water. If needed, a dispersant may be used to suspend the substances.
• a monosaccharide, oligosaccharide, polysaccharide, etherified monosaccharide, etherified oligosaccharide, etherified polysaccharide, water-soluble macromolecular compound, or the like can be used as a dispersant.
• Examples of monosaccharides include glucose, fructose, mannose, galactose, and ribose; examples of oligosaccharides include sucrose, maltose, lactose, trehalose, and maltotriose; examples of polysaccharides include starch, dextrin, dextran, and glycogen; examples of etherified monosaccharides, oligosaccharides, and polysaccharides include compounds obtained by etherifying the hydroxyl groups of the constituent monosaccharides with substituents such as -NO 2 , -CH 3 , -C 2 H 4 OH, -CH 2 CH(OH)CH 3 , and -CH 2 COOH; and examples of water-soluble macromolecular compounds include poly vinyl acetate, partially hydrolyzed polyvinyl acetate, polyvinyl alcohol, polyvinyl alcohol derivatives (such as cyanoethylated acrylonitrile, acetalated formaldehyde,
• the concentration of the dispersant is any metal material that will undergo a phosphate chemical conversion treatment, examples of which include steel, zinc and zinc plated materials, materials plated with zinc alloys, aluminum and aluminum plated materials, and magnesium.
• the surface conditioner of the present invention is usually applied after the metal material has been degreased and rinsed with water, but this is not necessarily the case.
• the surface conditioning performed with the surface conditioner of the present invention is performed by bringing this conditioner into contact with the surface of a metal material for at least 1 second. More specifically and preferably, the metal material is either immersed in the conditioner for about 10 seconds to 2 minutes, or the conditioner is sprayed onto the metal material for about 10 seconds to 2 minutes.
• This treatment is ordinarily carried out with the surface conditioner at normal ambient temperature (i.e., about 15°C to about 30°C), but can be carried out at anywhere between normal temperature and about 80°C.
• any of a great number of substances can be selected with the present invention as dictated by the intended application, so it is also possible to disperse these crystals in a degreasing agent, and perform the degreasing and surface conditioning at the same time.
• the treatment is usually performed by immersion or spraying for about 1 to 3 minutes at 50 to 80°C.
• Al aluminum sheet, JIS 5052
• FALNCLEANA L4460 (registered trademark of Nihon Parkerizing Co., Ltd.) was diluted to 2% with tap water and used in both the examples and the comparative examples.
• PALBOND L3020 (registered trademark of Nihon Parkerizing Co., Ltd.) was diluted with tap water, adjusted to a component concentration of 4.8%, 23 point total acidity, 0.9 point free acidity, and 3 point accelerator, and used in both the examples and the comparative examples (these concentrations are commonly used today in automotive zinc phosphate treatments).
• Treatment steps (1) alkali degreasing, 42°C, spraying for 120 seconds
• a magnesium hydrogenphosphate (MgHPO 4 • 3H 2 O) reagent was pulverized for 60 minutes in a ball mill using zirconia beads, and this product was used as a crystal powder whose epitaxy matched within 3%. This powder was suspended in purified water and then filtered through a 5 ⁇ m paper filter. The magnesium hydrogenphosphate concentration was adjusted to 5 g/L, and this product was used as a surface conditioner.
• MgHPO 4 • 3H 2 O magnesium hydrogenphosphate
• a zinc oxalate dihydrate (Zn(COO) 2 • 2H 2 O) reagent was baked for 1 hour at 200°C and then analyzed with an X-ray analyzer, which confirmed it to be zinc oxalate (Zn(COO) 2 ).
• This was pulverized for 60 minutes in a ball mill using zirconia beads, and this product was used as a crystal powder whose epitaxy matched within 3%.
• This powder was suspended in purified water and then filtered through a 5 ⁇ m paper filter.
• the zinc oxalate concentration was adjusted to 5 g/L, and this product was used as a surface conditioner.
• a cobalt oxalate dihydrate (Co(COO) 2 • 2H 2 O) reagent was baked for 1 hour at 200°C and then analyzed with an X-ray analyzer, which confirmed it to be cobalt oxalate (Co(COO) 2 ).
• This was pulverized for 60 minutes in a ball mill using zirconia beads, and this product was used as a crystal powder whose epitaxy matched within 3%. This powder was suspended in purified water and then filtered through a 5 ⁇ m paper filter. The cobalt oxalate concentration was adjusted to 5 g/L, and this product was used as a surface conditioner.
• Comparative Example 1 A silicon dioxide (SiO 2 ) reagent was pulverized for 60 minutes in a ball mill using zirconia beads, and this product was used as a crystal powder. This powder was suspended in purified water and then filtered through a 5 ⁇ m paper filter. The silicon dioxide concentration was adjusted to 5 g/L, and this product was used as a surface conditioner. Comparative Example 2 A magnesium oxide (MgO) reagent was pulverized for 60 minutes in a ball mill using zirconia beads, and this product was used as a crystal powder. This powder was suspended in purified water and then filtered through a 5 ⁇ m paper filter. The magnesium oxide concentration was adjusted to 5 g/L, and this product was used as a surface conditioner.
• SiO 2 silicon dioxide
• MgO magnesium oxide
• each test sheet that had undergone the above-mentioned zinc phosphate treatment steps (1) to (6) was painted with a cationic electrodeposition paint (ELECRON 2000, made by Kansai Paint) in a film thickness of 20 ⁇ m. This was baked for 25 minutes at 180°C, after which an intermediate coat (automotive-use intermediate coat made by Kansai Paint) was applied such that the intermediate coat thickness would be 40 ⁇ m, and this was baked for 30 minutes at 140°C. Each test sheet that had been given an intermediate coat was then given a top coat (automotive-use top coat made by Kansai Paint) in a top coat thickness of 40 ⁇ m, which was then baked for 30 minutes at 140°C. The triple-coated sheet with a total film thickness of 100 ⁇ m thus obtained was subjected to a saltwater spray test.
• a cationic electrodeposition paint (ELECRON 2000, made by Kansai Paint)
• Wl (g) The mass of the treated sheet after the chemical conversion was measured (referred to as Wl (g)), then the chemical conversion treated sheet was subjected to a coating removal treatment with the stripper and stripping conditions given below, the mass of this product was measured (referred to as W2 (g)), and the coating weight was calculated using Formula I.
• the paint film was evaluated by the method given below in both the examples and the comparative examples.
• Saltwater spray test JIS Z 2371 An electropainted sheet in which cross-cuts had been made was sprayed for
• Table 4 shows the characteristics of a chemical conversion coating obtained in a zinc phosphate treatment using the various phosphating treatment-use aqueous surface conditioners of the examples and comparative examples, and shows the results of a performance evaluation conducted after painting.
• a dash (-) in Table 4 means that the coating mass was not measured because the coating was not deposited properly. It was confirmed from the results in Table 4 that the phosphating treatment aqueous surface conditioners whose epitaxy was within 3%, which were the products of the present invention, had a surface conditioning effect. On the other hand, calculation of the epitaxy for SiO 2 and hopeite
• MgO is a cubic crystal, so only the a axis was used.

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• 2001
  • 2001-01-09 JP JP2001001885A patent/JP2002206176A/ja active Pending
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