Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D7/00—Processes, other than flocking, specially adapted for applying liquids or other fluent materials to particular surfaces or for applying particular liquids or other fluent materials
  • B05D7/50—Multilayers
  • B05D7/51—One specific pretreatment, e.g. phosphatation, chromatation, in combination with one specific coating
• • 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
  • C23C22/24—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 hexavalent chromium compounds
  • C23C22/30—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 hexavalent chromium compounds containing also trivalent chromium
• • 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
  • C23C22/24—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 hexavalent chromium compounds
  • C23C22/33—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 hexavalent chromium compounds containing also phosphates
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D—PROCESSES FOR APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
  • B05D2350/00—Pretreatment of the substrate
  • B05D2350/20—Chromatation
• • 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
  • C23C2222/00—Aspects relating to chemical surface treatment of metallic material by reaction of the surface with a reactive medium
  • C23C2222/10—Use of solutions containing trivalent chromium but free of hexavalent chromium

Definitions

• This invention relates to coated stainless steel strips and a process for preparing the same.
• Stainless steel characterized by high corrosion resistance has been widely used in a variety of fields including chemical industry.
• etched, polished, colored or otherwise surface treated stainless steel as interior materials of large buildings.
• etched or polished and colored stainless steel having decorative features now finds widespread use as entrance materials in hotels and apartments.
• the coating technique has several advantages over the chemical coloring method in that the coating method is easy to carry out and the coated stainless steel is resistant against fingerprint and easy in storage and maintenance when used as interior material. Therefore, attempts have been made in the coating technique in order to develop transparent color coatings capable of reflecting the surface of the underlying substrate, but none of them have succeeded in producing transparent color coated stainless steel meeting all the requirements of coating's durability, workability, and weather resistance.
• coated stainless steel is subject to a number of complex working steps. Since the paint coating can be stripped where substantial work is done, the use of coated stainless steel is limited in such applications requiring noticeable working.
• Stainless steel is well resistant against corrosion due to a passive film on its surface, but unsusceptible to surface treatment such as coating because of the same surface inertness.
• the passive film must be removed electrochemically before electroplating can be carried out.
• paint coating it is impossible in practice to carry out such complete pretreatment.
• a pretreatment for coating should be as easy as possible.
• One known pretreatment for coating is chromate treatment as disclosed in Japanese Patent Application Kokai No. 161069/1982.
• Transparent color coated stainless steel is generally required to have a faintly colored coating (having a reduced amount of coloring pigment) so that the finish of the underlying steel may be seen through the coating.
• Most chromate treatment results in a more or less colored steel surface. There is a need for chromate treatment capable of minimizing surface coloring.
• a coated stainless steel strip comprising a stainless steel strip having a chromate layer on a surface thereof with a total chromium content of 0.5 to 50 mg/m2.
• Trivalent chromium occupies at least 60% by weight of the total chromium content and amounts up to 40 mg/m2.
• a transparent resin coating is on the chromate layer.
• Such a coated stainless steel strip is produced by a process comprising the steps of chromating a stainless steel strip on a surface thereof to form a chromate layer as defined above and applying a transparent resin composition to the chromated strip.
• transparent used with the resin coating means that the texture of the underlying steel strip can be substantially seen through the coating.
• the subject stainless steel strip which is to be processed and coated according to the present invention is a group of cold rolled stainless steel plates, sheets, coils and similar products.
• Such starting strips are obtained by cold rolling hot rolled stainless steel slabs to a desired thickness, followed by annealing and pickling or bright annealing for relieving internal stresses introduced by the cold rolling and imparting appropriate mechanical properties, and optional shot blasting, dull skin pass, polishing or similar post-treatment for regulating the surface finish.
• the type of stainless steel is not critical. Any desired type of stainless steel may be used although high corrosion resistant stainless steel of a grade equal to or higher than SUS 304 is recommended for service as exterior materials.
• stainless steel strips are subject to chromate treatment prior to coating.
• the present invention employs chromate treatment for the purposes of imparting enhanced adhesion to subsequent overlying coatings and forming a light transmitting chromate film.
• a chromate layer capable of meeting both the requirements of coating adhesion and transparency can be formed by controlling such that the layer may have a total chromium content of 0.5 to 50 mg/m2, preferably 5 to 50 mg/m2, more preferably 5 to 30 mg/m2 and trivalent chromium occupy at least 60% by weight of the total chromium content and amount up to 40 mg/m2, preferably 5 to 30 mg/m2.
• a total chromium content of less than 0.5 mg/m2 fails to achieve any improvement in coating adhesion whereas chromate layers containing more than 50 mg/m2 of chromium become white or green and opaque even when the trivalent chromium content is at least 60% thereof. If the content of trivalent chromium is less than 60% by weight of the total chromium content, differently stated, if the proportion of hexavalent chromium increases, the chromate layer would lose transparency and exhibit brown colored spots. A trivalent chromium content in excess of 40 mg/m2 undesirably causes the entire chromate layer to turn green.
• the chromate layer may contain colloidal silica or a particulate organic resin such as acrylic resin.
• the chromate layer may be formed on a surface of a stainless steel strip by thoroughly degreasing and cleaning the strip surface, and applying a chromate treating solution thereto, followed by drying.
• the chromate solution used herein is an aqueous solution containing anhydrous chromic acid, phosphoric acid, silica, and optionally, acrylic resin, epoxy resin, silane coupling agent or the like.
• transparent coatings through which ultraviolet light can reach the chromate layer it is desirable, particularly in building exterior applications, to avoid the addition of resinous components to the chromate solution for the purpose of retaining weather resistance.
• a reducing agent for reducing hexavalent chromium of chromic acid into trivalent chromium the reducing agent including glycols (e.g., glycerin and ethylene glycol), hydrogen peroxide, saccharides (e.g., sucrose and starch), alcohols (e.g., methanol), and hydrazine.
• Phosphoric acid or phosphorous acid is added to the chromate solution for the purpose of adjusting pH and inhibiting precipitation of chromium ions.
• Silica is added for the purpose of retaining coating adhesion on bending and useful examples are colloidal silica and silica synthesized by gas phase method.
• the chromate solution may be applied to the strip surface to a predetermined build-up by means of a roll coater for transfer coating or by spray or shower coating followed by squeezing by means of a Ringer roll. Subsequent heating at a temperature of about 70 to 120°C yields a chromate layer.
• a specific total chromium content and specific trivalent chromium content and proportion of the chromate layer within the above-defined ranges may be achieved by regulating the coverage of the chromate solution and the proportion of trivalent chromium relative to the total chromium in the chromate solution which in turn, is regulated by controlling the degree of reduction.
• the thus pretreated stainless steel strip is adapted to receive a transparent resin coating thereon.
• the resin coating composition which can be coated herein include a resin component which may be selected from fluoro resins, acrylic resins, acrylic-silicone resins, epoxy resins, polyester resins, vinyl chloride resins, and urethane resins.
• the coating Since the coating is transparent enough to allow ultraviolet light to pass through the coating interior to the stainless steel surface where light reflects and reenters the coating, the coating undergoes severer deterioration than conventional opaque coatings.
• the use of fluoro resins characterized by weather resistance is recommended particularly for use as building exteriors.
• Pigments or dyes are added to the resin coating composition for coloring purpose insofar as the composition is maintained transparent.
• UV absorbers such as oxalic anilide are desirably blended for preventing pigments from being degraded by ultraviolet light.
• the pigment or dye include inorganic pigments such as red iron oxide, carbon black, and titanium oxide; and organic pigments or dyes such as Phthalocyanine Blue, Phthalocyanine Green, Quinacridone Red, and Indanthrene Orange.
• These coloring agents such as pigments and dyes are added in such amounts that their content in the dry coating is up to 3% by weight whereby a transparent color coating is obtained.
• any desired well-known coating techniques for example, brush coating, roll coating, flow coating, and spray coating may be used.
• Flow coating is desirable for coating a number of large flat plates.
• Roll coating is often used for steel coils.
• the resin coating composition is applied, it is cured into a transparent coating through an appropriate measure for a particular type of resin, for example, heating and UV exposure or simply by allowing to stand at room temperature.
• the resin coating is usually 5 to 30 ⁇ m thick.
• the coated stainless steel strips according to the present invention have the feature that the steel surface can be directly seen from the outside through the coating, thus offering products capable of taking advantage of the inherent surface texture of stainless steel.
• the present process to the stainless steel surface which has undergone a certain surface finish, for example, by hair line polishing, ordinary polishing, dull finishing, and various types of etching, there are obtained good looking coated steel strips which are particularly useful as building exteriors.
• the coated steel strips are worked by panel forming and roll forming into a variety of configured members which will find a variety of applications including interior and exterior wall members, roof covers, floor members, and ceiling members.
• the coated strips were visually observed for a change of the steel surface through the clear coating. Additionally, the coated strips were examined for coating adhesion by a cross cut tape test using a pressure sensitive adhesive Cellophane tape (Scribed peeling test) and a cross cut tape test using a pressure sensitive adhesive Cellophane tape following scribed Erichsen working (6 mm cupping) (Scribed Erichsen test) according to the standard coating adhesion test prescribed under JIS K5400, item 8.5.2.
• a sample was manufactured by the same procedure as above except that chromate treatment was omitted over a portion of the coil.
• the non-chromated and coated sample and the chromated and coated sample were compared by a visual observation. Both the samples had a bronze or gold colored coating which was enough transparent to see the underlying stainless steel therethrough.
• the chromated and coated sample exhibited no spots or color, with no recognizable difference from the non-chromated and coated sample.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Wood Science & Technology (AREA)
• Chemical Treatment Of Metals (AREA)
• Laminated Bodies (AREA)

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Citations (2)

• 1990
  • 1990-03-20 JP JP2071139A patent/JPH03271379A/ja active Pending
• 1991
  • 1991-09-18 EP EP91115852A patent/EP0532779A1/fr not_active Ceased

Patent Citations (2)

Non-Patent Citations (4)

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