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
  • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
  • B05D3/02—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by baking
  • B05D3/0254—After-treatment
  • B05D3/0272—After-treatment with ovens
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B3/00—Drying solid materials or objects by processes involving the application of heat
  • F26B3/32—Drying solid materials or objects by processes involving the application of heat by development of heat within the materials or objects to be dried, e.g. by fermentation or other microbiological action
  • F26B3/34—Drying solid materials or objects by processes involving the application of heat by development of heat within the materials or objects to be dried, e.g. by fermentation or other microbiological action by using electrical effects
  • F26B3/343—Drying solid materials or objects by processes involving the application of heat by development of heat within the materials or objects to be dried, e.g. by fermentation or other microbiological action by using electrical effects in combination with convection
• • 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
  • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
  • B05D3/02—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by baking
  • B05D3/0209—Multistage baking
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F26—DRYING
  • F26B—DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM
  • F26B13/00—Machines and apparatus for drying fabrics, fibres, yarns, or other materials in long lengths, with progressive movement
  • F26B13/10—Arrangements for feeding, heating or supporting materials; Controlling movement, tension or position of materials
• • 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
  • B05D2401/00—Form of the coating product, e.g. solution, water dispersion, powders or the like
  • B05D2401/20—Aqueous dispersion or solution
• • 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
  • B05D3/00—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials
  • B05D3/02—Pretreatment of surfaces to which liquids or other fluent materials are to be applied; After-treatment of applied coatings, e.g. intermediate treating of an applied coating preparatory to subsequent applications of liquids or other fluent materials by baking
  • B05D3/0254—After-treatment

Definitions

• the present invention relates to forming a coating of a water-borne paint on a substrate.
• the invention relates particularly, although by no means exclusively, to a method of forming a thin ornamental and/or protective coating of a water-borne paint on a substrate that is in the form of a metal strip,
• w water-borne paint is understood herein to mean a paint that includes (i) water that acts as a dispersant or carrier liquid (ii) polymeric material (thermosetting and thermoplastic) , such as polymeric film forming material, dispersed and/or dissolved in the water, (iii) a pigment or pigments dispersed in the water and/or the polymeric material; and (iv) optionally additives, eg wetting, dispersion and antimicrobial agents.
• polymeric material thermosetting and thermoplastic
• a pigment or pigments dispersed in the water and/or the polymeric material
• optionally additives eg wetting, dispersion and antimicrobial agents.
• coating thickness is understood to mean a coating thickness of up to 60 micron.
• the invention is applicable to the production of painted metallic (including steel, aluminium and other non-ferrous metals and alloys) strip, particularly painted metal coated steel strip, that is suitable to be used as the starting material in the production of building cladding sheets and other steel metal products for the building industry, appliance cabinets, vehicle bodies and many other sheet metal products.
• painted metallic including steel, aluminium and other non-ferrous metals and alloys
• painted metal coated steel strip that is suitable to be used as the starting material in the production of building cladding sheets and other steel metal products for the building industry, appliance cabinets, vehicle bodies and many other sheet metal products.
• Ornamental and protective paint coatings are conventionally applied to metal coated steel strip, such as galvanised or ZINCALUME (Registered Trade Mark) coated coiled stock, by coating the strip with solvent-based and water-based paint compositions by means of a liquid paint applicator such as a roll coater or a curtain ⁇ oater.
• a liquid paint applicator such as a roll coater or a curtain ⁇ oater.
• the paint includes polymeric film-forming materials, pigments and inert fillers dispersed and/or dissolved in a solvent or water.
• the coated strip is transferred from the liquid paint applicator station to an oven, such as a hot air convection oven, an induction oven or an infra-red oven, and the strip is heated to cure the paint.
• the oven heats the coated strip to a curing temperature and holds the coated strip at that temperature for a predetermined period of time.
• ovens be capable of heating coated strip quickly so that the curing step does not limit production rate on paint lines.
• An object of the present invention is to provide a method of curing water-borne paint that enables water- borne paints to be cured quickly.
• a method of curing a water-borne paint that has been applied as a liquid onto a substrate and forms a paint coating on the substrate including the steps of:
• step (b) heating the substrate in a subsequent curing step to a higher temperature than the evaporation temperature of step (a) and curing the paint.
• the above-described 2-stage curing method can produce a substrate, such as a metal coated steel strip, that has a paint coating with minimal solvent boil in a very short time period and that the method is a viable option for use on existing paint lines known to the applicant without adversely affecting production rates and at a reasonable capital cost.
• the 2-stage curing method is also a viable option as part of a paint line retrofit to metal coating lines that do not include paint lines, and this is a very important application of the present invention.
• the 2-stage curing method does not require substantial space for equipment, and this is an important consideration in relation to retrofitting to es ⁇ isting paint lines and metal coating lines.
• cure as used herein is understood to mean cross-linking of thermosetting polymeric material in paint and drying thermoplastic polymeric material.
• boiling point of water in the paint is understood herein to mean the lowest boiling point liquid in the paint. Due to boiling point depression by slight amounts of solvent in paint, the "boiling point” is likely to be that of a solvent/water azeotrope, not of pure water.
• the method of the present invention can achieve very fast cures of water-borne coatings without significant solvent boil by heating the coating rapidly, for example with induction or infra-red heating, in 2 stages and preferably with a temperature hold zone between the 2 stage .
• the purpose of the temperature hold sone which should be maintained a little below the boiling point of water (ie mostly ⁇ 100°C at 1 atmosphere pressure) , is to facilitate separation of the processes of evaporation and boiling.
• the release of the majority of the water is fast but controlled by the process of evaporation only in this hold section. With most of the water released in this way, by the end of the hold zone the coating can then be ramped quickly through the boiling point of water to the desired peak cure temperature .
• step (a) includes evaporating a substantial amount of the water in the paint.
• substantially amount of the water is understood herein to mean at least 50% by weight of the water in the paint.
• step (a) evaporates at least 60% by weight of the water in the paint.
• step (a) includes holding the temperature at the evaporation temperature for less than 5 seconds .
• ste (a) includes holding the temperature at the evaporation temperature for 1-5 seconds .
• the evaporation temperature is as close to the boiling point of water in the paint (as defined herein) as possible.
• the evaporation temperature is selected to be at least 5°C lower than the boiling point of water in the paint - for line operation reasons to avoid boiling the water in the paint.
• the evaporation temperature is between 5 and 10°C lower than the boiling point of water in the paint.
• step (a) includes heating the coated substrate to the evaporation temperature from a lower starting temperature.
• step (a) includes ramping the temperature up to the evaporation temperature from the starting temperature in less than 2 seconds.
• step (a) includes ramping the temperature up to the evaporation temperature from the starting temperature in 0.5-1.5 seconds.
• step (a) includes supplying moving hot air to facilitate evaporation of water in the paint.
• step (b) includes heating the substrate to the higher temperature in less than 6 seconds . More preferably step (b) includes heating the substrate to the higher temperature in less than 4 seconds .
• step (b) includes heating the substrate to the higher temperature in less than 2 seconds.
• step (b) includes heating the substrate from the evaporation temperature to a peak metal temperature of 180-260°C.
• step (b) includes heating the substrate from the evaporation temperature to a peak metal temperature of 190-260°C.
• step (b) includes heating the substrate from the evaporation temperature to a peak metal temperature of 210-260°C.
• the paint should include as high a solids loading as possible.
• the paint typically includes 25-50% solids by volume (polymeric material and pigment) and the balance liquid, predominantly water.
• the method includes heating the substrate in evaporation stage (a) and cure stage (b) for less than 10 seconds.
• the method includes heating the substrate in stages (a) and (b) for less than 8 seconds.
• the method includes heating the substrate in stages (a) and (b) for less than 6 seconds.
• the method includes passing the coated substrate continuously through an evaporation oven and carrying out evaporation stage (a) in the evaporation oven and thereafter passing the coated substrate through a separate curing oven and curing the paint in the curing oven.
• the method includes heating the coated substrate to the evaporation temperature in the evaporation oven and allowing evaporation to continue during the period of time that the coated substrate travels from the evaporation oven to the curing oven.
• the spacing between the ovens and the rate of movement of the substrate between the ovens is selected so that there is sufficient time at the evaporation temperature to achieve the required amount of evaporation.
• the substrate is a steel strip that has a coating of zinc or zinc/aluminium alloy on the strip.
• a method of forming a coating of a paint on a substrate that includes the steps of:
• the dry paint coating thickness is less than 25 microns.
• the dry paint coating thickness is less than 20 microns.
• the dry paint coating thickness is less than 15 microns .
• the dry paint coating thickness be less than 12 microns.
• a metallic (including steel, aluminium and other non-ferrous metals and alloys) strip that is suitable for use as a starting material in the production of building cladding sheets and other steel metal products for the building industry having a paint coating of a water borne paint cured by the above-described method.
• a paint line for forming a paint coating of a predetermined dry paint coating thickness on metal coated strip, the paint line including: (a) a means for applying a water-borne paint as a liquid onto a substrate and forming a paint coating on metal coated strip; and
• Figure 1 is a flow chart illustrating a production line for forming a metal coating and thereafter a water borne-paint coating on steel strip;
• Figure 2 is a temperature/time plot for a preferred embodiment of a 2-stage method of curing painted metal coated steel strip in accordance with the present invention.
• steel strip is uncoiled from a coiler 3 and fed continuously through a metal coating section 5, a paint applicator section 7, and a curing section 9 to produce painted metal coated steel strip.
• the metal coating section 5 may be of any suitable configuration to form a coating of zinc or aluminium/zinc alloy on the exposed surfaces of the steel strip.
• the steel strip may be coated by a hot dip coating method that involves passing strip through one or more heat treatment furnaces and thereafter into and through a bath of molten coating metal held in a coating pot. Within the bath the strip passes around one or more sink rolls and is taken upwardly out of the bath. After leaving the coating bath the strip passes through a coating thickness station, such as a gas knife or gas wiping station at which its coated surfaces are subjected to jets of wiping gas to control the thickness of the coating.
• a hot dip coating method that involves passing strip through one or more heat treatment furnaces and thereafter into and through a bath of molten coating metal held in a coating pot. Within the bath the strip passes around one or more sink rolls and is taken upwardly out of the bath. After leaving the coating bath the strip passes through a coating thickness station, such as a gas knife or gas wiping station at which its coated surfaces are subjected to jets of wiping gas to control the thickness of the coating.
• the paint applicator section 7 may be of any suitable configuration for applying a water-borne paint in a liquid form onto at least one of the surfaces of the steel strip.
• the paint applicator 7 may include one or more liquid paint applicators, such as roll coaters or curtain coaters that can form a uniform, preselected thickness, wet coating of paint on the strip.
• liquid paint applicators such as roll coaters or curtain coaters that can form a uniform, preselected thickness, wet coating of paint on the strip.
• the curing section 9 includes two spaced apart induction ovens 11, 13 that are capable of heating the painted metal coated steel strip from the paint applicator 7 in accordance with the temperature/time profile shown in Figure 2 to produce a dry paint coating having a preselected thickness.
• the Figure 2 profile is a profile that is applicable for dry paint coating thicknesses up to and including 12 microns .
• the as-painted metal coated strip is heated in the upstream oven 11 for a period of time of 0.60 seconds from a starting temperature Ti to an evaporation temperature T 2 that is at least 5°C lower than the boiling point of water in the paint.
• the strip exiting the evaporation oven 11 travels to the downstream oven 13 in a period of 3.23 seconds and during this period remains substantially at the evaporation temperature T 2 .
• the strip is heated to a peak metal temperature T 3 of 210°C in the downstream curing oven and is held at that temperature to allow curing of the thermosetting polymeric material in the paint.
• the residence time of the strip in the curing oven is 2.13 second.
• the above-described temperature/time profile enables the production of high quality painted metal coated steel strip in a surprisingly short overall heating time period.
• .Paint D Grey colour with volume solids of 41 %, mainly used in the table of results, and marked (D) .
• Paint E Light Blue colour with volume solids of 43%, and marked (E) in table .
• Paint F Light Blue colour with volume solids of 50%, and marked (F) in table

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Microbiology (AREA)
• Textile Engineering (AREA)
• Health & Medical Sciences (AREA)
• Biomedical Technology (AREA)
• Biotechnology (AREA)
• Molecular Biology (AREA)
• Application Of Or Painting With Fluid Materials (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

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Citations (13)

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• 2003
  • 2003-02-04 AU AU2003900491A patent/AU2003900491A0/en not_active Abandoned
• 2004
  • 2004-02-03 KR KR1020057014400A patent/KR20050095892A/ko not_active Ceased
  • 2004-02-03 CN CNA2004800077205A patent/CN1761533A/zh active Pending
  • 2004-02-03 NZ NZ541838A patent/NZ541838A/en unknown
  • 2004-02-03 JP JP2006501346A patent/JP2006516472A/ja active Pending
  • 2004-02-03 WO PCT/AU2004/000122 patent/WO2004069428A1/en not_active Ceased
  • 2004-02-04 MY MYPI20040316A patent/MY136993A/en unknown

Patent Citations (13)

Non-Patent Citations (1)

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