EP4691760A1 - Resin-coated metal sheet and resin-coated metal sheet production method - Google Patents

Resin-coated metal sheet and resin-coated metal sheet production method

Info

Publication number
EP4691760A1
EP4691760A1 EP24780690.4A EP24780690A EP4691760A1 EP 4691760 A1 EP4691760 A1 EP 4691760A1 EP 24780690 A EP24780690 A EP 24780690A EP 4691760 A1 EP4691760 A1 EP 4691760A1
Authority
EP
European Patent Office
Prior art keywords
resin
metal
resin layer
layer
coated metal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP24780690.4A
Other languages
German (de)
French (fr)
Inventor
Tomo OKUHIRA
Eiji Okamatsu
Koh Yoshioka
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Toyo Kohan Co Ltd
Original Assignee
Toyo Kohan Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Toyo Kohan Co Ltd filed Critical Toyo Kohan Co Ltd
Publication of EP4691760A1 publication Critical patent/EP4691760A1/en
Pending legal-status Critical Current

Links

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
    • B05D7/14—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 to metal, e.g. car bodies
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/04—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B15/08—Layered products comprising a layer of metal comprising metal as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • 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
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • 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
    • C23C28/00—Coating for obtaining at least two superposed coatings either by methods not provided for in a single one of groups C23C2/00 - C23C26/00 or by combinations of methods provided for in subclasses C23C and C25C or C25D
    • C23C28/30—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer
    • C23C28/32—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer
    • C23C28/322—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer only coatings of metal elements only
    • C23C28/3225—Coatings combining at least one metallic layer and at least one inorganic non-metallic layer including at least one pure metallic layer only coatings of metal elements only with at least one zinc-based layer
    • 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
    • B05D1/00—Processes for applying liquids or other fluent materials
    • B05D1/28—Processes for applying liquids or other fluent materials performed by transfer from the surfaces of elements carrying the liquid or other fluent material, e.g. brushes, pads, rollers
    • 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
    • B05D2202/00—Metallic substrate
    • B05D2202/10—Metallic substrate based on Fe
    • 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
    • B05D5/00—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures
    • B05D5/06—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain multicolour or other optical effects
    • B05D5/061—Special surface effect

Definitions

  • the present invention relates to a resin-coated metal sheet and a resin-coated metal sheet production method.
  • Patent Document 1 JP 2019-173544 A
  • the coated metal sheet disclosed in Patent Document 1 has a problem that air bubbles invade between a metal sheet and a coating layer, which may cause a bad appearance.
  • the coated metal sheet disclosed in Patent Document 1 includes a metal sheet subjected to chromate conversion coating and a coating layer disposed thereon.
  • chromate conversion coating a coating layer disposed thereon.
  • this technique has room for improvement in adhesion properties because peel-off of the coating layer from the metal sheet may occur.
  • An object of the present invention is to provide a resin-coated metal sheet having excellent adhesion properties to an adhesive resin used for bonding to a coating layer and providing a good appearance.
  • the present inventors who have conducted extensive research to achieve the above object, have found that the above object can be achieved by a resin-coated metal sheet comprising a metal base and a resin layer disposed on the metal base wherein the resin layer has a surface with a reduced peak height Rpk of 0.46 ⁇ m or more, and have completed the present invention.
  • the present invention provides a resin-coated metal sheet having excellent adhesion properties to an adhesive resin and providing a good appearance.
  • Fig. 1 is a cross-sectional view illustrating a configuration of a resin-coated metal sheet 1 according to the present embodiment.
  • the resin-coated metal sheet 1 according to the present embodiment includes a metal base 10, and a resin layer 20 disposed on the metal base 10.
  • the resin-coated metal sheet 1 according to the present embodiment is used in joint filling materials and automobile interior materials after a coating layer made from a resin material is formed on the resin layer 20 using an adhesive resin.
  • the metal base 10 is a plated sheet including a metal original sheet 11 and a metal plating layer 12 containing zinc formed on the metal original sheet 11.
  • metal original sheet can be used as the metal original sheet 11 without limitation, and examples thereof include metal original sheets based on iron or aluminum.
  • metal original sheets based on iron carbon steel sheets and stainless steel sheets can be used.
  • carbon steel sheets to be used include those formed from low carbon steels (carbon content: 0.01 to 0.15% by weight) such as low carbon aluminum-killed steel, extra-low carbon steels with a carbon content of less than 0.01% by weight, non-ageing carbon steels obtained by adding Ti or Nb to extra-low carbon steels, and the like.
  • a steel sheet When a steel sheet is used as the metal original sheet 11, preferred is use of steel sheets obtained by pickling hot-rolled sheets of these steels to remove scale (oxidized film) of their surfaces, and performing cold rolling, followed by electrolytic cleaning, annealing, and temper rolling.
  • the annealing method may be continuous annealing or batch annealing, and is not particularly limited.
  • the surface of the metal original sheet 11 on which the metal plating layer 12 is formed has an arithmetical mean height Sa 2 of preferably 0.5 ⁇ m or more, more preferably 0.75 ⁇ m or more.
  • a method of controlling the arithmetical mean height Sa 2 of the metal original sheet 11 within the above ranges include a method of rolling the above-mentioned steel into the metal original sheet 11 using a rolling roll having a predetermined surface roughness.
  • the arithmetic average roughness Ra of the rolling roll measured along the central axis of the rolling roll is preferably 0.8 ⁇ m or more, more preferably 2.5 ⁇ m or more, still more preferably 3.2 ⁇ m or more.
  • the upper limit of the arithmetic average roughness Ra of the rolling roll is not particularly limited.
  • the arithmetic average roughness Ra of the rolling roll is preferably 8.0 ⁇ m or less, more preferably 6.0 ⁇ m or less from the viewpoint of enhancing evenness stability of the metal plating layer 12 and the resin layer 20.
  • the upper limit of the arithmetical mean height Sa 2 of the metal original sheet 11 is preferably 2.0 ⁇ m or less.
  • the arithmetical mean height Sa 2 can be measured based on ISO 25178, and the arithmetic average roughness Ra can be measured based on JIS B 0671:2002.
  • the thickness of the metal original sheet 11 according to the present embodiment is preferably 0.04 to 2.0 mm, more preferably 0.04 to 1.5 mm, although not particularly limited.
  • the metal plating layer 12 is a layer containing zinc disposed on the metal original sheet 11.
  • metal plating forming the metal plating layer 12 include zinc-based platings such as zinc plating, zinc-cobalt-molybdenum alloy plating, zinc-nickel alloy plating, zinc-iron alloy plating, Galvannealed zinc plating, and zinc-aluminum-magnesium alloy plating.
  • zinc-based plating more preferred is zinc-cobalt-molybdenum alloy plating or pure zinc plating with a zinc weight proportion of 99.9% by weight or more (hereinafter, also referred to as pure zinc plating) from the viewpoint of improving the corrosion resistance of the resin-coated metal sheet 1.
  • the metal plating layer can be formed by electroplating the surfaces of the metal original sheet 11 using a plating bath having a predetermined composition.
  • the metal plating layer 12 when the metal plating layer 12 is formed by zinc-cobalt-molybdenum alloy plating, the metal plating layer 12 can be formed by electroplating using a plating bath having a composition comprising 150 to 300 g/L of zinc sulfate, 5 to 60 g/L of cobalt sulfate, 0.01 to 0.5 g/L of ammonium molybdate, 5 to 60 g/L of ammonium sulfate, and 50 g/L or less of sodium sulfate.
  • the pH is 2.5 to 4.0
  • the bath temperature is 30 to 60°C
  • the current density is 5 to 50 A/dm 2 .
  • the metal playing layer 12 can be formed by electroplating using a plating bath having a composition comprising 150 to 300 g/L of zinc sulfate and 10 to 100 g/L of sodium sulfate.
  • a plating bath having a composition comprising 150 to 300 g/L of zinc sulfate and 10 to 100 g/L of sodium sulfate.
  • the pH is 0.5 to 2.5
  • the bath temperature is 30 to 60°C
  • the current density is 5 to 80 A/dm 2 .
  • the proportions of zinc, cobalt, and molybdenum contained in the metal plating layer 12 are preferably 0.1 to 5% by weight for cobalt, 0.001 to 1% by weight for molybdenum, and the balance for zinc.
  • the proportions of the metals contained in the metal plating layer 12 can be adjusted by controlling the composition of the plating bath and the electroplating conditions within suitable ranges.
  • the thickness of the metal plating layer 12 is preferably 0.3 to 8.0 ⁇ m, although not particularly limited. As the metal plating layer 12 becomes thicker, the metal plating layer 12 is more likely to have a somewhat smoother surface, which may affect subsequent formation of the resin layer 20. In the case of zinc-based plating in particular, crystals are deposited in a platy form, and thus the metal plating layer 12 is likely to have a much smoother surface. For this reason, the thickness of the metal plating layer 12 is more preferably 0.3 to 5.0 ⁇ m from the viewpoint of controlling the surface roughness of the metal plating layer 12 and the reduced peak height of the resin layer 20. The thickness of the metal plating layer 12 is still more preferably 0.6 to 5.0 ⁇ m from the viewpoint of corrosion resistance. The thickness of the metal plating layer 12 is particularly preferably 0.7 ⁇ m to 4.5 ⁇ m from the viewpoint of satisfying the corrosion resistance and suppressing the decrease in the surface roughness caused by metal plating at the same time.
  • the embodiment of the metal base 10 is not particularly limited to this, and the metal plating layer 12 may be formed on only one surface of the metal original sheet 11.
  • the metal base 10 may include only the metal original sheet 11 without the metal plating layer 12.
  • the resin layer 20 is a layer formed on the metal plating layer 12.
  • the resin layer 20 is disposed to improve adhesion properties between the metal base 10 and an adhesive resin to be used with the resin-coated metal sheet 1 according to the present embodiment.
  • the resin layer 20 is formed on both surfaces of the metal base 10 in the present embodiment, any other configuration can be used, and the resin layer 20 may be formed on only one surface of the metal base 10.
  • Examples of the resin contained in the resin layer 20 include, but should not be limited to, olefin resins and urethane resins.
  • olefin resins include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic ester copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, and the like. More preferred are ethylene-acrylic acid copolymer and ethylene-methacrylic acid copolymer.
  • urethane resins include reaction products of a polyol such as polyacrylic polyol, polyester polyol, or polyether polyol with a polyisocyanate such as aliphatic diisocyanate, aromatic diisocyanate, or aromatic aliphatic diisocyanate, and the like. These olefin resins and urethane resins may be each used alone, or two of them may be used at the same time.
  • the resin layer 20 is formed by applying an aqueous dispersion containing a resin material as described later.
  • the resin layer 20 is substantially free of ingredients other than the resin material, excluding inevitable components derived from the additives contained in the aqueous dispersion.
  • the proportion of the resin contained in the resin layer 20 is preferably 90% by weight or more, more preferably 99% by weight or more.
  • the resin layer 20 is preferably formed substantially only from the above-mentioned resin.
  • the weight average molecular weight thereof is preferably 20,000 to 150,000, more preferably 30,000 to 100,000, still more preferably, 40,000 to 80,000.
  • the proportion of the polar component based on the surface free energies on the surface of the resin layer 20 is preferably 3% to 35%, more preferably 10% to 35%, still more preferably 20% to 35%.
  • the proportion of the polar component based on the surface free energies can be calculated from the surface free energies determined by applying the contact angles of deionized water, ethylene glycol, and diiodomethane measured using an automatic contact angle meter (DM-701, available from Kyowa Interface Science Co., Ltd.) to the equation of the Kitazaki-Hata theory.
  • the proportion of the polar component can be determined as follows: The surface free energy of the dispersive component, that of the dipole component, and that of the hydrogen bond component are determined, and then, the proportion of the sum of the surface free energy of the dipole component and that of the hydrogen bond component to the total of these surface free energies is determined as the proportion of the polar component.
  • a method of controlling the proportion of the polar component based on the surface free energies of the surface of the resin layer 20 to fall within the above ranges is not particularly limited, and examples of such a method include a method of selecting the resin material for forming the resin layer 20.
  • the proportion of the polar component based on the surface free energies of the surface of the resin layer 20 can be controlled by adjusting the content of the acrylic acid unit in the ethylene-acrylic acid copolymer.
  • the proportion of the polar component based on the surface free energies of the surface of the resin layer 20 can be controlled by adjusting the content of the methacrylic acid unit in the ethylene-methacrylic acid copolymer.
  • the thickness of the resin layer 20 is preferably 0.3 to 3.0 ⁇ m, although not particularly limited. To facilitate formation of a projected profile on the entire surface of the resin layer 20 for controlling the reduced peak height Rpk (described later) of the surface of the resin layer 20 within a specific range, the thickness of the resin layer 20 is preferably 0.5 ⁇ m or more, more preferably 0.6 ⁇ m or more. Although the upper limit of the thickness of the resin layer 20 is not particularly limited, it is preferably 2.0 ⁇ m or less because an excessively thick resin layer 20 may have weak adhesion strength to the adhesive resin.
  • the resin layer 20 in the resin-coated metal sheet 1 according to the present embodiment has a surface with a reduced peak height Rpk of 0.46 ⁇ m or more, preferably 0.60 ⁇ m or more, the reduced peak height Rpk being measured based on JIS B 0671:2002.
  • the upper limit of the reduced peak height Rpk is preferably 2.0 ⁇ m or less, more preferably 1.5 ⁇ m or less from the viewpoint of ease and stability of production, although not limited thereto.
  • the reduced peak height Rpk is one of parameters for evaluating the roughness profile specified by JIS B 0671-1, and represents the height of a peak projected in the roughness profile.
  • Rpk is the average height of projected peaks above the core when the surface profile is divided into three portions of peak, core, and valley based on the roughness profile.
  • a larger reduced peak height Rpk of the resin layer 20 indicates a larger average height of projections of the surface of the resin layer 20, and by controlling Rpk to be 0.46 ⁇ m or more, a projected profile corresponding to the projected peaks can be sufficiently formed. It is inferred that by controlling the reduced peak height Rpk within such a range, when the resin layer 20 is coated by a coating layer using an adhesive resin, the adhesive resin flows along the projections and spreads, thus improving adhesion properties. When the reduced peak height Rpk of the resin layer 20 falls within the above ranges, the resin-coated metal sheet 1 can have excellent adhesion properties to the adhesive resin.
  • the reduced peak height Rpk of the surface of the resin layer 20 can be measured at any point on the surface of the resin layer 20. To consider influences by projections formed in the resin layer 20 due to stripes (rolling marks) formed on the surface of the metal original sheet 11 by rolling the metal original sheet 11 in the surface profile of the resin layer 20 and evaluate further averaged roughness including rolling marks, it is more preferred that the reduced peak height Rpk on a line along the transverse direction of the resin-coated metal sheet 1 (direction perpendicular to the rolling direction of the metal original sheet 11 on the surface of the resin layer) be within the above ranges.
  • the adhesion properties can be further enhanced particularly when the reduced peak height Rpk of the resin layer 20 is 0.6 ⁇ m or more and the reduced peak height Spk is 0.6 ⁇ m or more.
  • the reason is not clarified, it is considered as follows: When the reduced peak height Rpk and the reduced peak height Spk fall within the above ranges, the adhesive resin can spread more uniformly and escape of air bubbles to the outside can be further facilitated; and as a result, unevenness of the thickness of the adhesive resin can be reduced and formation of air bubbles can be suppressed.
  • the arithmetical mean height Sa 1 of the surface of the resin layer 20 measured based on ISO 25178 is preferably 0.5 ⁇ m or more, more preferably 0.6 ⁇ m or more from the viewpoint of forming the projected profile for controlling the reduced peak height Rpk to fall within a specific range across the surface of the resin layer 20 to improve the adhesion properties to the adhesive resin.
  • the upper limit of the arithmetical mean height Sa 1 of the resin layer 20 is not particularly limited. Preferably, it is 2.0 ⁇ m or less because an excessively large value thereof may be likely to lead to an uneven thickness of the resin layer 20.
  • the resin-coated metal sheet 1 according to the present embodiment has excellent adhesion properties to the adhesive resin because the reduced peak height Rpk of the surface of the resin layer 20 is within the above ranges.
  • an adhesive resin include olefin resins such as polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic ester copolymer, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer, urethane resins, and the like.
  • the aqueous dispersion used in production of the resin-coated metal sheet 1 is an aqueous dispersion of the above-mentioned olefin resin and/or urethane resin dispersed in a medium such as water.
  • the solid concentration of the aqueous dispersion is 15% by weight or more. By selecting a solid concentration of 15% or more, when the aqueous dispersion brought into contact with the surface of the metal base 11 through a roll by direct roll coating is extruded together with the metal base 11 from the roll, the aqueous dispersion can be pulled by the roll and lifted from the metal base 10.
  • an original projected profile can be formed on the surface of the resin layer 20 in addition to the surface depressions and projections on the resin layer 20 derived from the surface of the metal base 10, and the Rpk and Spk of the resin layer 20 can be controlled within the above ranges.
  • the reduced peak heights Rpk and Spk of the surface of the resin layer 20 can be controlled within the above ranges by forming the resin layer 20 by direct roll coating using an aqueous dispersion containing a resin with a solid concentration of 15% by weight or more.
  • the solid concentration of the aqueous dispersion is preferably adjusted according to the arithmetical mean height Sa 2 of the surface of the metal original sheet 11 on which the metal plating layer 12 is formed.
  • the solid concentration of the aqueous dispersion is preferably 15% by weight or more, more preferably 20% by weight or more.
  • the upper limit of the solid concentration of the aqueous dispersion is not particularly limited, it is preferably 70% by weight, more preferably 65% by weight or less, still more preferably 55% by weight or less from the viewpoint of facilitating a suppression in degradation or solidification of the aqueous dispersion in continuous production to stably form the surface profile of the resin layer 20.
  • the solid concentration of the aqueous dispersion is 20% by weight or more and less than 70% by weight to facilitate formation of the original projected profile of the resin layer 20 or facilitate formation of a largely projected profile.
  • the lower limit of the solid concentration of the aqueous dispersion is more preferably 25% by weight or more, still more preferably 30% by weight or more.
  • the arithmetical mean height Sa 2 of the metal original sheet 11 be controlled within the above ranges, and the resin layer 20 be formed by direct roll coating using an aqueous dispersion with a solid concentration according to the arithmetical mean height Sa 2 .
  • Such a production method can control the Rpk and Spk of the surface of the resin layer 20, and can also control the arithmetical mean height Sa 1 of the surface of the resin layer 20 within a preferred range.
  • Examples of a method of producing such an aqueous dispersion include, but should not be limited to, a method of preparing an aqueous dispersion by producing the above-mentioned olefin resin and/or urethane resin by a known emulsion polymerization or solution polymerization method, and agitating the polymer solution.
  • the aqueous dispersion has a minimum film forming temperature (MFT) of preferably 0 to 200°C, more preferably 5 to 150°C.
  • MFT minimum film forming temperature
  • the minimum film forming temperature of the aqueous dispersion can be adjusted by selecting the type of the resin material contained in the aqueous dispersion.
  • the aqueous dispersion has a pH of preferably 3 to 11, more preferably 4 to 10.
  • the viscosity at 25°C of the aqueous dispersion used in formation of the resin layer 20 is not particularly limited as long as the solid concentration of the aqueous dispersion falls within the above ranges, the viscosity is preferably 10 to 150 mPa ⁇ s, more preferably 20 to 100 mPa ⁇ s. For many of aqueous dispersions, the viscosity changes significantly in response to an external force applied, and thus the viscosity of the aqueous dispersion is not always proportional to the solid concentration.
  • the aqueous dispersion used in formation of the resin layer 20 may contain a surfactant, an emulsifying aid, colloidal silica, and the like as needed, in addition to the above-mentioned resin.
  • a surfactant an emulsifying aid, colloidal silica, and the like as needed, in addition to the above-mentioned resin.
  • the aqueous dispersion contain no metal oxide and it is preferred that the resin layer 20 also contain no metal oxide.
  • the layer formed from the aqueous dispersion is preferably dried at a temperature of 50°C to 200°C for a drying time of 1 second to 60 seconds.
  • the resin-coated metal sheet 1 according to the present embodiment can be produced by a step of applying an aqueous dispersion onto the metal base 10 by direct roll coating, the aqueous dispersion containing a resin material in a solid concentration of 15% by weight or more; and a step of drying the layer formed from the aqueous dispersion to form the resin layer 20.
  • the aqueous dispersion to be used can be the one listed above.
  • Fig. 2(a) is a diagram for illustrating a method of applying an aqueous dispersion by direct roll coating according to the present embodiment
  • Fig. 2(b) is a cross-sectional view illustrating the surface profile of the resin layer 20 formed by applying an aqueous dispersion with a solid concentration of 15% by weight or more by direct roll coating
  • Fig. 3 is a referential diagram illustrating a resin layer formed by applying an aqueous dispersion with a solid concentration of less than 15% by weight by direct roll coating.
  • aqueous dispersion containing a resin material by direct roll coating As illustrated in Fig. 2(a) , in direct roll coating, the aqueous dispersion is applied while a roll is being rotated such that the rotational direction of the roll and the traveling direction of the metal base 10 are the same (such that the traveling direction of a contacting portion of the roll with the metal base 10 and the traveling direction of the metal base 10 are the same).
  • the solid concentration of the aqueous dispersion containing a resin material is 15% by weight or more, the aqueous dispersion extruded onto the metal base 10 is partially lifted from the metal base 10 toward the roll side with the rotation of the roll.
  • projections can be formed on the surface of the resin layer 20 formed from the aqueous dispersion, and thus, the reduced peak heights Rpk and Spk of the surface of the resin layer 20 can be controlled within predetermined ranges.
  • the aqueous dispersion is applied onto the metal base 10 by the roll, and projections are difficult to form.
  • the metal base 10 preferably used is a metal base including the metal original sheet 11 rolled with a rolling roll having an arithmetic average roughness Ra of 0.8 ⁇ m or more to have an arithmetical mean height Sa 2 of 0.5 m or more and the metal plating layer 12 formed on the metal original sheet 11 by performing zinc-based metal plating.
  • the resin layer 20 can have appropriately controlled reduced peak heights Rpk and Spk, can have excellent adhesion properties to the adhesive resin, and can provide good appearances of joint filling materials, automobile interior materials, and the like formed from a coated metal sheet produced using the resin-coated metal sheet 1.
  • the weight average molecular weight of the resin was measured by a high-temperature GPC-IR method.
  • the reduced peak height Rpk was determined in a cross-section along the transverse direction of the resin-coated metal sheet 1, that is, a direction (TD) perpendicular to the rolling direction (RD) of the metal original sheet 11 on the surface of the resin-coated metal sheet 1.
  • the arithmetical mean height Sa 2 of the metal original sheet 11 was measured in the same manner.
  • a T peel test (hereinafter, also referred to as peel test) in accordance with JIS K 6854-3 was performed for evaluation of adhesion properties to an adhesive resin to measure the peel strength of the resin layer-coated metal sheet 1.
  • peel test a T peel test
  • the resin-coated metal sheets 1 and the olefin adhesive resin were heat bonded for 2 minutes at a temperature of 150°C and a pressure of 0.5 MPa, giving a laminate.
  • the prepared laminate was subjected to a peel test at a peeling rate of 200 mm/min to measure the maximum peel strength [unit: N/25 mm] .
  • the prepared resin-coated metal sheet 1 was heated on a hot plate set at 130°C, and one spot of an olefin adhesive resin (trade name: Melthene, available from Tosoh Corporation) was placed on the resin layer 20 of the resin-coated metal sheet 1. Then, 9 cm 2 of a Teflon plate (Teflon is a registered trademark) having a weight of 3.5 g was placed on the olefin adhesive resin, a 150-g weight was placed over the Teflon plate, and these were held for 2 minutes. After 2 minutes had passed, the Teflon plate and the weight were removed, followed by cooling in the air. Thereafter, the presence/absence of air bubbles contained between the adhesive resin and the resin layer 20 was visually observed. The absence of air bubbles indicates that coated metal sheets produced using the resin-coated metal sheet 1 and joint filling materials and automobile interior materials formed from such coated metal sheets can have good appearances.
  • an olefin adhesive resin trade name: Melthene, available from Tosoh
  • the metal original sheet 11 a cold-rolled sheet (thickness: 0.16 mm) of a low carbon aluminum-killed steel was prepared.
  • the metal original sheet 11 was obtained by rolling a low carbon aluminum-killed steel sheet using a rolling roll having an arithmetic average roughness Ra of 2.5 to 5.5 ⁇ m, and the metal original sheet 11 had an arithmetical mean height Sa 2 of 0.95 ⁇ m.
  • the metal original sheet 11 was subjected to alkaline electrocleaning and pickling by immersion in sulfuric acid, and then, was plated at a bath temperature of 40°C and a current density of 15 A/dm 2 , thereby giving a metal base 10 including the metal original sheet 11 and a metal plating layer 12 formed on both surface thereof, the metal plating layer 12 having a thickness of 1.5 ⁇ m and being formed from zinc-cobalt-molybdenum alloy plating.
  • the compositional ratio in the metal plating layer was determined using X-ray fluorescence, which was 0.16% by weight of Co, 0.02% by weight of Mo, and the balance of Zn.
  • an aqueous dispersion (solid concentration: 20% by weight, viscosity: 70 mPa ⁇ s, pH: 9.3, MFT: 12°C) containing an olefin resin (ethylene-acrylic acid copolymer) was applied onto the metal plating layer 12 of the metal base 10 by direct roll coating. Thereby, a layer formed from the aqueous dispersion was formed. Subsequently, the layer was dried at a temperature of 150°C for 10 seconds, forming a resin layer 20 containing the olefin resin. The thickness of the resin layer 20 was 0.6 ⁇ m. The resin layer 20 was formed on both surfaces of the metal base 10.
  • a resin-coated metal sheet 1 including the resin layer 20 formed on both surfaces of the metal base 10 was obtained.
  • the above-mentioned reduced peak height and arithmetical mean height of the resin layer were measured, the proportion of the polar component based on the surface free energies of the resin layer surface was determined, and the peel strength to the adhesive resin, the appearance (presence/absence of air bubbles), and the spreading properties of the adhesive resin were evaluated.
  • the results are shown in Tables 1 to 3.
  • the weight average molecular weight of the ethylene-acrylic acid copolymer determined by high temperature GPC-IR was 49,900.
  • a resin-coated metal sheet 1 was obtained in the same manner as in Example 1 except that the aqueous dispersion containing the olefin resin (ethylene-acrylic acid copolymer) was replaced by an aqueous dispersion (solid concentration: 44.5% by weight, viscosity: 40 mPa ⁇ s, pH: 4.8, MFT: 100°C) containing an olefin resin (ethylene-methacrylic acid copolymer), and the reduced peak height and arithmetical mean height of the resin layer were measured, and the peel strength to the adhesive resin, the appearance (presence/absence of air bubbles), and the spreading properties of the adhesive resin were evaluated.
  • the results are shown in Tables 1 to 3.
  • the weight average molecular weight of the ethylene-acrylic acid copolymer determined by high temperature GPC-IR was 69,300.
  • the thickness of the resin layer 20 was 0.6 ⁇ m.
  • a resin-coated metal sheet 1 was obtained in the same manner as in Example 1 except that a metal original sheet 11 which was obtained by rolling using a rolling roll having an arithmetic average roughness Ra of 0.01 to 0.5 ⁇ m and had an arithmetical mean height Sa 2 of 0.3 ⁇ m was used, and the reduced peak height and arithmetical mean height of the resin layer were measured, and the appearance (presence/absence of air bubbles) was evaluated. The results are shown in Table 1. The thickness of the resin layer 20 was 0.6 ⁇ m.
  • a resin-coated metal sheet 1 was obtained in the same manner as in Example 1 except that a metal original sheet 11 which was obtained by rolling using a rolling roll having an arithmetic average roughness Ra of 0.8 to 2.3 ⁇ m and had an arithmetical mean height Sa 2 of 0.73 ⁇ m was used, and the reduced peak height and arithmetical mean height of the resin layer were measured, and the peel strength to the adhesive resin and the appearance (presence/absence of air bubbles) were evaluated.
  • the results are shown in Table 1.
  • the thickness of the resin layer 20 was 0.6 ⁇ m.
  • Table 1 shows that the resin-coated metal sheets 1 in Examples 1 and 2 had a reduced peak height Rpk of 0.46 ⁇ m or more, had high peel strength to the adhesive resin, and had excellent adhesion properties to the adhesive resin. In addition, air bubbles contained in the adhesive resin spread on the resin layer 20 were not observed, which indicates that joint filling materials having a good appearance can be provided.
  • the resin-coated metal sheets in Comparative Examples 1 and 2 had a reduced peak height Rpk of less than 0.46 ⁇ m, had low peel strength to adhesive resin, and had poor adhesion properties to the adhesive resin.
  • Rpk peak height
  • the resin-coated metal sheet in Comparative Example 1 air bubbles were contained in the adhesive resin spread on the resin layer, and joint filling materials including such a resin-coated metal sheet had a bad appearance.
  • the resin-coated metal sheet 1 in Example 2 had higher peel strength than that in Example 1. It is considered that this is because the circularity ratio is higher in Example 2 than in Example 1 as shown in Table 2, and the adhesive is more likely to uniformly spread.
  • a resin-coated metal sheet 1 was obtained by direct roll coating as in Example 1 except that a cold rolled sheet (thickness: 0.16 mm) obtained by cold rolling and annealing a low carbon aluminum-killed steel, followed by temper rolling with a roll having an arithmetic average roughness Ra of 2.5 to 5.5 ⁇ m was prepared as the metal original sheet 11, and was subjected to zinc plating at a bath temperature of 50°C and a current density of 30 A/dm 2 using a pure zinc plating bath to form a zinc plating layer of pure zinc as the metal plating layer 12.
  • the reduced peak height Rpk of the obtained resin-coated metal sheet 1 was measured as in Example 1.
  • a resin-coated metal sheet 1 was obtained in the same manner as in Referential Test Example 2 except that the aqueous dispersion containing an olefin resin (ethylene-acrylic acid copolymer) was replaced by an aqueous dispersion (solid concentration: 44.5% by weight, viscosity: 40 mPa ⁇ s, pH: 4.8, MFT: 100°C) containing an olefin resin (ethylene-methacrylic acid copolymer), and the reduced peak height Rpk was measured.
  • a resin-coated metal sheet was obtained as in Referential Test Example 1 except that the aqueous dispersion was applied by a bar coater instead of direct roll coating, and the reduced peak height Rpk was measured.
  • a bar coater a wireless bar coater (available from OSG System Products Co., Ltd., Select-Roller/A-Bar) was used, and a wireless bar model #0 (OSP-00) was used for a film thickness of 1 ⁇ m.
  • a resin-coated metal sheet was obtained as in Referential Test Example 2 except that the aqueous dispersion was applied by a bar coater instead by direct roll coating, and the reduced peak height Rpk was obtained.
  • the results of measurement of Rpk in Referential Test Examples 1 to 2 and Referential Comparative Examples 1 to 2 where Referential Comparative Example 1 is regarded as a reference are shown in Table 4.

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Abstract

Provided is a resin-coated metal sheet comprising a metal base, and a resin layer formed on the metal base, wherein the resin layer has a surface with a reduced peak height Rpk of 0.46 µm or more.

Description

    TECHNICAL FIELD
  • The present invention relates to a resin-coated metal sheet and a resin-coated metal sheet production method.
    • BACKGROUND ART
  • Coated metal sheets including a metal sheet and a coating layer formed from a resin are widely used in members for building exteriors and automobile members, and examples of such members including joint filling materials used in joints are known (for example, Patent Document 1).
    • RELATED ART DOCUMENTS PATENT DOCUMENTS
  • Patent Document 1: JP 2019-173544 A
    • SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION
  • The coated metal sheet disclosed in Patent Document 1 has a problem that air bubbles invade between a metal sheet and a coating layer, which may cause a bad appearance. The coated metal sheet disclosed in Patent Document 1 includes a metal sheet subjected to chromate conversion coating and a coating layer disposed thereon. On the other hand, in order to reduce environmental loads, there is a technique of disposing an adhesive layer between a metal sheet and a coating layer without performing chromate conversion coating. However, this technique has room for improvement in adhesion properties because peel-off of the coating layer from the metal sheet may occur.
  • An object of the present invention is to provide a resin-coated metal sheet having excellent adhesion properties to an adhesive resin used for bonding to a coating layer and providing a good appearance.
    • MEANS FOR SOLVING PROBLEMS
  • The present inventors, who have conducted extensive research to achieve the above object, have found that the above object can be achieved by a resin-coated metal sheet comprising a metal base and a resin layer disposed on the metal base wherein the resin layer has a surface with a reduced peak height Rpk of 0.46 µm or more, and have completed the present invention.
    1. [1] Specifically, aspect 1 according to the present invention provides a resin-coated metal sheet comprising a steel sheet, a metal base, and a resin layer disposed on the metal base, wherein the resin layer has a surface with a reduced peak height Rpk of 0.46 µm or more.
    2. [2] Aspect 2 according to the present invention provides a resin-coated metal sheet according to aspect 1, wherein the resin layer has a surface with a reduced peak height Spk of 0.6 µm or more.
    3. [3] Aspect 3 according to the present invention provides the resin-coated metal sheet according to aspect 1 or 2, wherein the resin layer is formed from a resin material containing an olefin-based and/or urethane-based resin.
    4. [4] Aspect 4 according to the present invention provides the resin-coated metal sheet according to any one of aspects 1 to 3, wherein the resin layer has an arithmetical mean height Sa1 of 0.5 µm or more.
    5. [5] Aspect 5 according to the present invention provides the resin-coated metal sheet according to any one of aspects 1 to 4, wherein the resin layer has a surface with a reduced peak height Rpk of 0.6 µm or more.
    6. [6] Aspect 6 according to the present invention provides the resin-coated metal sheet according to any one of aspects 1 to 5, wherein the metal base includes a metal original sheet and a metal plating layer containing zinc, and the resin layer is formed on the metal plating layer.
    7. [7] Aspect 7 according to the present invention provides the resin-coated metal sheet according to any one of aspects 1 to 6, wherein the surface of the metal original sheet on which the metal plating layer is formed has an arithmetical mean height Sa2 of 0.5 µm or more.
    8. [8] Aspect 8 according to the present invention provides a method of producing the resin-coated metal sheet according to any one of aspects 1 to 7, the method comprising a step of applying an aqueous dispersion onto the metal base by direct roll coating, the aqueous dispersion containing a resin material in a solid concentration of 15% by weight or more; and the step of drying the layer formed from the aqueous dispersion to form the resin layer.
    9. [9] Aspect 9 according to the present invention provides the method of producing the resin-coated metal sheet according to aspect 8, wherein the solid concentration in the aqueous dispersion is 15% by weight or more and less than 70% by weight, the metal base includes a metal original sheet and a metal plating layer containing zinc, and the surface of the metal original sheet on which the metal plating layer is formed has an arithmetical mean height Sa2 of 0.75 µm or more.
    10. [10] Aspect 10 according to the present invention provides the method of producing the resin-coated metal sheet according to aspect 8 or 9, wherein the resin material contains an olefin-based resin and/or a urethane-based resin.
    EFFECTS OF THE INVENTION
  • The present invention provides a resin-coated metal sheet having excellent adhesion properties to an adhesive resin and providing a good appearance.
    • BRIEF DESCRIPTION OF DRAWINGS
    • [Fig. 1] Fig. 1 is a cross-sectional view illustrating a configuration of a resin-coated metal sheet according to an embodiment of the present invention.
    • [Fig. 2] Fig. 2(a) is a diagram for illustrating a method of applying an aqueous dispersion by direct roll coating according to an embodiment of the present invention, and Fig. 2(b) is a cross-sectional view illustrating the surface profile of a resin layer 20 formed by applying an aqueous dispersion with a solid concentration of 15% by weight or more by direct roll coating.
    • [Fig. 3] Fig. 3 is a referential diagram illustrating a resin layer formed by applying an aqueous dispersion with a solid concentration of less than 15% by weight by direct roll coating.
    DESCRIPTION OF EMBODIMENTS
  • Hereinafter, embodiments according to the present invention will be described with reference to drawings.
  • Fig. 1 is a cross-sectional view illustrating a configuration of a resin-coated metal sheet 1 according to the present embodiment. The resin-coated metal sheet 1 according to the present embodiment includes a metal base 10, and a resin layer 20 disposed on the metal base 10. The resin-coated metal sheet 1 according to the present embodiment is used in joint filling materials and automobile interior materials after a coating layer made from a resin material is formed on the resin layer 20 using an adhesive resin.
    • <Metal base 10>
  • The metal base 10 according to the present embodiment is a plated sheet including a metal original sheet 11 and a metal plating layer 12 containing zinc formed on the metal original sheet 11.
  • Any metal original sheet can be used as the metal original sheet 11 without limitation, and examples thereof include metal original sheets based on iron or aluminum. As metal original sheets based on iron, carbon steel sheets and stainless steel sheets can be used. Examples of carbon steel sheets to be used include those formed from low carbon steels (carbon content: 0.01 to 0.15% by weight) such as low carbon aluminum-killed steel, extra-low carbon steels with a carbon content of less than 0.01% by weight, non-ageing carbon steels obtained by adding Ti or Nb to extra-low carbon steels, and the like. When a steel sheet is used as the metal original sheet 11, preferred is use of steel sheets obtained by pickling hot-rolled sheets of these steels to remove scale (oxidized film) of their surfaces, and performing cold rolling, followed by electrolytic cleaning, annealing, and temper rolling. The annealing method may be continuous annealing or batch annealing, and is not particularly limited.
  • From the viewpoint of controlling the reduced peak height of the resin layer 20 described later, the surface of the metal original sheet 11 on which the metal plating layer 12 is formed has an arithmetical mean height Sa2 of preferably 0.5 µm or more, more preferably 0.75 µm or more. Examples of a method of controlling the arithmetical mean height Sa2 of the metal original sheet 11 within the above ranges include a method of rolling the above-mentioned steel into the metal original sheet 11 using a rolling roll having a predetermined surface roughness. The arithmetic average roughness Ra of the rolling roll measured along the central axis of the rolling roll (direction perpendicular to the rolling direction of the metal original sheet 11) is preferably 0.8 µm or more, more preferably 2.5 µm or more, still more preferably 3.2 µm or more. The upper limit of the arithmetic average roughness Ra of the rolling roll is not particularly limited. However, because an excessively large arithmetical mean height Sa2 of the metal original sheet 11 may lead to an uneven thickness of the metal plating layer 12 or the resin layer 20 formed above the metal original sheet 11, the arithmetic average roughness Ra of the rolling roll is preferably 8.0 µm or less, more preferably 6.0 µm or less from the viewpoint of enhancing evenness stability of the metal plating layer 12 and the resin layer 20. From the same viewpoint as above, the upper limit of the arithmetical mean height Sa2 of the metal original sheet 11 is preferably 2.0 µm or less. The arithmetical mean height Sa2 can be measured based on ISO 25178, and the arithmetic average roughness Ra can be measured based on JIS B 0671:2002.
  • The thickness of the metal original sheet 11 according to the present embodiment is preferably 0.04 to 2.0 mm, more preferably 0.04 to 1.5 mm, although not particularly limited.
  • The metal plating layer 12 is a layer containing zinc disposed on the metal original sheet 11. Examples of metal plating forming the metal plating layer 12 include zinc-based platings such as zinc plating, zinc-cobalt-molybdenum alloy plating, zinc-nickel alloy plating, zinc-iron alloy plating, Galvannealed zinc plating, and zinc-aluminum-magnesium alloy plating. Among these zinc-based plating, more preferred is zinc-cobalt-molybdenum alloy plating or pure zinc plating with a zinc weight proportion of 99.9% by weight or more (hereinafter, also referred to as pure zinc plating) from the viewpoint of improving the corrosion resistance of the resin-coated metal sheet 1. The metal plating layer can be formed by electroplating the surfaces of the metal original sheet 11 using a plating bath having a predetermined composition.
  • For example, when the metal plating layer 12 is formed by zinc-cobalt-molybdenum alloy plating, the metal plating layer 12 can be formed by electroplating using a plating bath having a composition comprising 150 to 300 g/L of zinc sulfate, 5 to 60 g/L of cobalt sulfate, 0.01 to 0.5 g/L of ammonium molybdate, 5 to 60 g/L of ammonium sulfate, and 50 g/L or less of sodium sulfate. As preferred electroplating conditions, the pH is 2.5 to 4.0, the bath temperature is 30 to 60°C, and the current density is 5 to 50 A/dm2. When the metal plating layer 12 is formed by pure zinc plating, the metal playing layer 12 can be formed by electroplating using a plating bath having a composition comprising 150 to 300 g/L of zinc sulfate and 10 to 100 g/L of sodium sulfate. As preferred electroplating conditions, the pH is 0.5 to 2.5, the bath temperature is 30 to 60°C, and the current density is 5 to 80 A/dm2.
  • When the metal plating layer 12 is formed by zinc-cobalt-molybdenum alloy plating, the proportions of zinc, cobalt, and molybdenum contained in the metal plating layer 12 are preferably 0.1 to 5% by weight for cobalt, 0.001 to 1% by weight for molybdenum, and the balance for zinc. The proportions of the metals contained in the metal plating layer 12 can be adjusted by controlling the composition of the plating bath and the electroplating conditions within suitable ranges.
  • The thickness of the metal plating layer 12 is preferably 0.3 to 8.0 µm, although not particularly limited. As the metal plating layer 12 becomes thicker, the metal plating layer 12 is more likely to have a somewhat smoother surface, which may affect subsequent formation of the resin layer 20. In the case of zinc-based plating in particular, crystals are deposited in a platy form, and thus the metal plating layer 12 is likely to have a much smoother surface. For this reason, the thickness of the metal plating layer 12 is more preferably 0.3 to 5.0 µm from the viewpoint of controlling the surface roughness of the metal plating layer 12 and the reduced peak height of the resin layer 20. The thickness of the metal plating layer 12 is still more preferably 0.6 to 5.0 µm from the viewpoint of corrosion resistance. The thickness of the metal plating layer 12 is particularly preferably 0.7 µm to 4.5 µm from the viewpoint of satisfying the corrosion resistance and suppressing the decrease in the surface roughness caused by metal plating at the same time.
  • Although the metal plating layer 12 is formed on both surfaces of the metal original sheet 11 in the metal base 10 according to the present embodiment, the embodiment of the metal base 10 is not particularly limited to this, and the metal plating layer 12 may be formed on only one surface of the metal original sheet 11. Alternatively, the metal base 10 may include only the metal original sheet 11 without the metal plating layer 12.
    • <Resin layer 20>
  • The resin layer 20 is a layer formed on the metal plating layer 12. The resin layer 20 is disposed to improve adhesion properties between the metal base 10 and an adhesive resin to be used with the resin-coated metal sheet 1 according to the present embodiment. Although the resin layer 20 is formed on both surfaces of the metal base 10 in the present embodiment, any other configuration can be used, and the resin layer 20 may be formed on only one surface of the metal base 10.
  • Examples of the resin contained in the resin layer 20 include, but should not be limited to, olefin resins and urethane resins. Examples of olefin resins include polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic ester copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, and the like. More preferred are ethylene-acrylic acid copolymer and ethylene-methacrylic acid copolymer. Examples of urethane resins include reaction products of a polyol such as polyacrylic polyol, polyester polyol, or polyether polyol with a polyisocyanate such as aliphatic diisocyanate, aromatic diisocyanate, or aromatic aliphatic diisocyanate, and the like. These olefin resins and urethane resins may be each used alone, or two of them may be used at the same time. The resin layer 20 is formed by applying an aqueous dispersion containing a resin material as described later. Preferably, the resin layer 20 is substantially free of ingredients other than the resin material, excluding inevitable components derived from the additives contained in the aqueous dispersion. The proportion of the resin contained in the resin layer 20 is preferably 90% by weight or more, more preferably 99% by weight or more. Specifically, the resin layer 20 is preferably formed substantially only from the above-mentioned resin.
  • When an ethylene-acrylic acid copolymer or an ethylene-methacrylic acid copolymer is used as the resin contained in the resin layer 20, the weight average molecular weight thereof is preferably 20,000 to 150,000, more preferably 30,000 to 100,000, still more preferably, 40,000 to 80,000.
  • In the resin layer 20, the proportion of the polar component based on the surface free energies on the surface of the resin layer 20 is preferably 3% to 35%, more preferably 10% to 35%, still more preferably 20% to 35%. The proportion of the polar component based on the surface free energies can be calculated from the surface free energies determined by applying the contact angles of deionized water, ethylene glycol, and diiodomethane measured using an automatic contact angle meter (DM-701, available from Kyowa Interface Science Co., Ltd.) to the equation of the Kitazaki-Hata theory. Specifically, the proportion of the polar component can be determined as follows: The surface free energy of the dispersive component, that of the dipole component, and that of the hydrogen bond component are determined, and then, the proportion of the sum of the surface free energy of the dipole component and that of the hydrogen bond component to the total of these surface free energies is determined as the proportion of the polar component. A method of controlling the proportion of the polar component based on the surface free energies of the surface of the resin layer 20 to fall within the above ranges is not particularly limited, and examples of such a method include a method of selecting the resin material for forming the resin layer 20. For example, when an ethylene-acrylic acid copolymer is used as the resin for forming the resin layer 20, the proportion of the polar component based on the surface free energies of the surface of the resin layer 20 can be controlled by adjusting the content of the acrylic acid unit in the ethylene-acrylic acid copolymer. When an ethylene-methacrylic acid copolymer is used as the resin for forming the resin layer 20, the proportion of the polar component based on the surface free energies of the surface of the resin layer 20 can be controlled by adjusting the content of the methacrylic acid unit in the ethylene-methacrylic acid copolymer.
  • The thickness of the resin layer 20 is preferably 0.3 to 3.0 µm, although not particularly limited. To facilitate formation of a projected profile on the entire surface of the resin layer 20 for controlling the reduced peak height Rpk (described later) of the surface of the resin layer 20 within a specific range, the thickness of the resin layer 20 is preferably 0.5 µm or more, more preferably 0.6 µm or more. Although the upper limit of the thickness of the resin layer 20 is not particularly limited, it is preferably 2.0 µm or less because an excessively thick resin layer 20 may have weak adhesion strength to the adhesive resin.
  • The resin layer 20 in the resin-coated metal sheet 1 according to the present embodiment has a surface with a reduced peak height Rpk of 0.46 µm or more, preferably 0.60 µm or more, the reduced peak height Rpk being measured based on JIS B 0671:2002. The upper limit of the reduced peak height Rpk is preferably 2.0 µm or less, more preferably 1.5 µm or less from the viewpoint of ease and stability of production, although not limited thereto. The reduced peak height Rpk is one of parameters for evaluating the roughness profile specified by JIS B 0671-1, and represents the height of a peak projected in the roughness profile. More specifically, Rpk is the average height of projected peaks above the core when the surface profile is divided into three portions of peak, core, and valley based on the roughness profile. A larger reduced peak height Rpk of the resin layer 20 indicates a larger average height of projections of the surface of the resin layer 20, and by controlling Rpk to be 0.46 µm or more, a projected profile corresponding to the projected peaks can be sufficiently formed. It is inferred that by controlling the reduced peak height Rpk within such a range, when the resin layer 20 is coated by a coating layer using an adhesive resin, the adhesive resin flows along the projections and spreads, thus improving adhesion properties. When the reduced peak height Rpk of the resin layer 20 falls within the above ranges, the resin-coated metal sheet 1 can have excellent adhesion properties to the adhesive resin.
  • Conventionally, when a metal base including a metal original sheet and a metal plating layer containing zinc formed thereon is used and the metal base is chromium-free for environmental reasons, it may be difficult in some cases to improve the adhesion properties to the adhesive resin even if a resin layer is formed on the metal base. In the resin-coated metal sheet 1 according to the present embodiment, by controlling the reduced peak height Rpk of the surface of the resin layer 20, the adhesion properties of the resin layer 20 to the adhesive resin can be improved even if the metal base 10 including the metal plating layer 12 containing zinc is used.
  • The reduced peak height Rpk of the surface of the resin layer 20 can be measured at any point on the surface of the resin layer 20. To consider influences by projections formed in the resin layer 20 due to stripes (rolling marks) formed on the surface of the metal original sheet 11 by rolling the metal original sheet 11 in the surface profile of the resin layer 20 and evaluate further averaged roughness including rolling marks, it is more preferred that the reduced peak height Rpk on a line along the transverse direction of the resin-coated metal sheet 1 (direction perpendicular to the rolling direction of the metal original sheet 11 on the surface of the resin layer) be within the above ranges.
  • The resin layer 20 of the resin-coated metal sheet 1 according to the present embodiment has a surface with a reduced peak height Spk of preferably 0.60 µm or more, more preferably 0.70 µm or more, still more preferably 0.80 µm or more, the reduced peak height Spk being measured based on ISO 25178. While the reduced peak height Rpk is the value calculated from the bearing curve of line roughness, the reduced peak height Spk is the value calculated from the bearing curve of surface roughness and represents the average height of projected peaks in a more comprehensive view of the surface of the resin layer. A larger reduced peak height Spk indicates that higher projections are present across the resin layer 20. When the reduced peak height Spk is within the above ranges, during coating of the resin layer 20 by a coating resin using an adhesive resin, air bubbles generated between the resin layer 20 and the adhesive resin can escape from gaps between projections to the outside. More specifically, when the adhesive resin and the coating layer are simultaneously and continuously flown onto the resin layer 20, air bubbles can escape along gaps between the projections present across the surface to the outside. This can provide a coated metal sheet having a good appearance produced using the resin-coated metal sheet 1.
  • In the resin-coated metal sheet 1 according to the present embodiment, the adhesion properties can be further enhanced particularly when the reduced peak height Rpk of the resin layer 20 is 0.6 µm or more and the reduced peak height Spk is 0.6 µm or more. Although the reason is not clarified, it is considered as follows: When the reduced peak height Rpk and the reduced peak height Spk fall within the above ranges, the adhesive resin can spread more uniformly and escape of air bubbles to the outside can be further facilitated; and as a result, unevenness of the thickness of the adhesive resin can be reduced and formation of air bubbles can be suppressed.
  • The arithmetical mean height Sa1 of the surface of the resin layer 20 measured based on ISO 25178 is preferably 0.5 µm or more, more preferably 0.6 µm or more from the viewpoint of forming the projected profile for controlling the reduced peak height Rpk to fall within a specific range across the surface of the resin layer 20 to improve the adhesion properties to the adhesive resin. The upper limit of the arithmetical mean height Sa1 of the resin layer 20 is not particularly limited. Preferably, it is 2.0 µm or less because an excessively large value thereof may be likely to lead to an uneven thickness of the resin layer 20.
  • As a general relationship between surface roughness and adhesion strength, it is known that as the arithmetical mean height of the surface of a material is larger, resin adhesion strength to the material is likely to be higher. On the other hand, in extensive research on improvement of adhesion strength between the metal base coated by the resin layer and the adhesive resin, the present inventors have noticed that the degree of adhesion strength of the adhesive resin to the resin layer is not dependent on the arithmetical mean height of the resin layer, and have found that the adhesion strength can be improved by controlling the surface profile of the resin layer 20 and controlling the reduced peak height Rpk within the specific range.
  • As described above, the resin-coated metal sheet 1 according to the present embodiment has excellent adhesion properties to the adhesive resin because the reduced peak height Rpk of the surface of the resin layer 20 is within the above ranges. Examples of such an adhesive resin include olefin resins such as polyethylene, polypropylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic ester copolymer, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer, urethane resins, and the like.
  • The resin-coated metal sheet 1 according to the present embodiment can be produced by the following method. Specifically, the resin-coated metal sheet 1 can be produced by a step of applying an aqueous dispersion onto the metal base 10 by direct roll coating, the aqueous dispersion containing a resin material in a solid concentration of 15% by weight or more; and a step of drying the layer formed from the aqueous dispersion to form the resin layer 20.
  • The aqueous dispersion used in production of the resin-coated metal sheet 1 is an aqueous dispersion of the above-mentioned olefin resin and/or urethane resin dispersed in a medium such as water. The solid concentration of the aqueous dispersion is 15% by weight or more. By selecting a solid concentration of 15% or more, when the aqueous dispersion brought into contact with the surface of the metal base 11 through a roll by direct roll coating is extruded together with the metal base 11 from the roll, the aqueous dispersion can be pulled by the roll and lifted from the metal base 10. As a result, an original projected profile can be formed on the surface of the resin layer 20 in addition to the surface depressions and projections on the resin layer 20 derived from the surface of the metal base 10, and the Rpk and Spk of the resin layer 20 can be controlled within the above ranges. In the present invention, the reduced peak heights Rpk and Spk of the surface of the resin layer 20 can be controlled within the above ranges by forming the resin layer 20 by direct roll coating using an aqueous dispersion containing a resin with a solid concentration of 15% by weight or more.
  • The solid concentration of the aqueous dispersion is preferably adjusted according to the arithmetical mean height Sa2 of the surface of the metal original sheet 11 on which the metal plating layer 12 is formed. For example, when the metal original sheet 11 has an arithmetical mean height Sa2 of 0.75 to 2.0 µm, from the viewpoint of facilitating formation of the original projected profile of the resin layer 20 or facilitating formation of a largely projected profile, the solid concentration of the aqueous dispersion is preferably 15% by weight or more, more preferably 20% by weight or more. In this case, although the upper limit of the solid concentration of the aqueous dispersion is not particularly limited, it is preferably 70% by weight, more preferably 65% by weight or less, still more preferably 55% by weight or less from the viewpoint of facilitating a suppression in degradation or solidification of the aqueous dispersion in continuous production to stably form the surface profile of the resin layer 20. When the arithmetical mean height Sa2 of the metal original sheet 11 is 0.65 µm or more and less than 0.75 µm, or the arithmetical mean height Sa2 of the metal original sheet 11 is relatively small, preferably, the solid concentration of the aqueous dispersion is 20% by weight or more and less than 70% by weight to facilitate formation of the original projected profile of the resin layer 20 or facilitate formation of a largely projected profile. When the arithmetical mean height Sa2 of the metal original sheet 11 is 0.65 µm or more and less than 0.75 µm, the lower limit of the solid concentration of the aqueous dispersion is more preferably 25% by weight or more, still more preferably 30% by weight or more. As described above, from the viewpoint of improving the adhesion strength, it is preferred that the arithmetical mean height Sa2 of the metal original sheet 11 be controlled within the above ranges, and the resin layer 20 be formed by direct roll coating using an aqueous dispersion with a solid concentration according to the arithmetical mean height Sa2. Such a production method can control the Rpk and Spk of the surface of the resin layer 20, and can also control the arithmetical mean height Sa1 of the surface of the resin layer 20 within a preferred range.
  • Examples of a method of producing such an aqueous dispersion include, but should not be limited to, a method of preparing an aqueous dispersion by producing the above-mentioned olefin resin and/or urethane resin by a known emulsion polymerization or solution polymerization method, and agitating the polymer solution.
  • The aqueous dispersion has a minimum film forming temperature (MFT) of preferably 0 to 200°C, more preferably 5 to 150°C. The minimum film forming temperature of the aqueous dispersion can be adjusted by selecting the type of the resin material contained in the aqueous dispersion.
  • The aqueous dispersion has a pH of preferably 3 to 11, more preferably 4 to 10.
  • Although the viscosity at 25°C of the aqueous dispersion used in formation of the resin layer 20 is not particularly limited as long as the solid concentration of the aqueous dispersion falls within the above ranges, the viscosity is preferably 10 to 150 mPa·s, more preferably 20 to 100 mPa·s. For many of aqueous dispersions, the viscosity changes significantly in response to an external force applied, and thus the viscosity of the aqueous dispersion is not always proportional to the solid concentration.
  • The aqueous dispersion used in formation of the resin layer 20 may contain a surfactant, an emulsifying aid, colloidal silica, and the like as needed, in addition to the above-mentioned resin. On the other hand, to form projected peaks of the resin on the surface thereof by lifting the resin by a roll, it is preferred that the aqueous dispersion contain no metal oxide and it is preferred that the resin layer 20 also contain no metal oxide.
  • The layer formed from the aqueous dispersion is preferably dried at a temperature of 50°C to 200°C for a drying time of 1 second to 60 seconds.
    • <Method of producing resin-coated metal sheet 1>
  • The resin-coated metal sheet 1 according to the present embodiment can be produced by a step of applying an aqueous dispersion onto the metal base 10 by direct roll coating, the aqueous dispersion containing a resin material in a solid concentration of 15% by weight or more; and a step of drying the layer formed from the aqueous dispersion to form the resin layer 20. The aqueous dispersion to be used can be the one listed above.
  • Fig. 2(a) is a diagram for illustrating a method of applying an aqueous dispersion by direct roll coating according to the present embodiment, and Fig. 2(b) is a cross-sectional view illustrating the surface profile of the resin layer 20 formed by applying an aqueous dispersion with a solid concentration of 15% by weight or more by direct roll coating. Fig. 3 is a referential diagram illustrating a resin layer formed by applying an aqueous dispersion with a solid concentration of less than 15% by weight by direct roll coating.
  • The step of applying an aqueous dispersion containing a resin material by direct roll coating will be described. As illustrated in Fig. 2(a), in direct roll coating, the aqueous dispersion is applied while a roll is being rotated such that the rotational direction of the roll and the traveling direction of the metal base 10 are the same (such that the traveling direction of a contacting portion of the roll with the metal base 10 and the traveling direction of the metal base 10 are the same). In the present embodiment, when the solid concentration of the aqueous dispersion containing a resin material is 15% by weight or more, the aqueous dispersion extruded onto the metal base 10 is partially lifted from the metal base 10 toward the roll side with the rotation of the roll. Thereby, as illustrated in Fig. 2(b), projections can be formed on the surface of the resin layer 20 formed from the aqueous dispersion, and thus, the reduced peak heights Rpk and Spk of the surface of the resin layer 20 can be controlled within predetermined ranges. In contrast, in reverse roll coating in which the rotational direction of the roll is opposite to the traveling direction of the metal base 10, the aqueous dispersion is applied onto the metal base 10 by the roll, and projections are difficult to form.
  • On the other hand, when the solid concentration of the aqueous dispersion is less than 15% by weight, the aqueous dispersion is not lifted by the roll even if direct roll coating is used. Thus, as illustrated in Fig. 3, a resin layer having a smooth surface profile is formed.
  • As described above, the metal base 10 preferably used is a metal base including the metal original sheet 11 rolled with a rolling roll having an arithmetic average roughness Ra of 0.8 µm or more to have an arithmetical mean height Sa2 of 0.5 m or more and the metal plating layer 12 formed on the metal original sheet 11 by performing zinc-based metal plating.
  • In the resin-coated metal sheet 1 thus obtained, the resin layer 20 can have appropriately controlled reduced peak heights Rpk and Spk, can have excellent adhesion properties to the adhesive resin, and can provide good appearances of joint filling materials, automobile interior materials, and the like formed from a coated metal sheet produced using the resin-coated metal sheet 1.
    • EXAMPLES
  • Hereinafter, the present invention will be more specifically described by way of Examples and Comparative Examples, but the present invention will not be limited only to these Examples.
    • <Weight average molecular weight of resin>
  • For the aqueous dispersions containing a resin material which were used in Examples, the weight average molecular weight of the resin was measured by a high-temperature GPC-IR method.
    • <Reduced peak height and arithmetical mean height of resin layer, and arithmetical mean height of metal original sheet>
  • Using a laser microscope (available from Olympus Corporation, 3D Measuring Laser Microscope LEXT OLS5000) with a 20x object lens (name of lens: MPLAPON20xLEXT), an image for analysis was obtained with a field of 645 µm × 645 µm. In the next step, using analysis application, the obtained image for analysis was subjected to denoising and tilt correction as automatic correction processing. Subsequently, analysis was performed by clicking icons for line roughness measurement and surface roughness measurement, and the reduced peak heights Rpk and Spk and arithmetical mean height Sa1 of the resin layer 20 in the resin-coated metal sheet 1 were determined. The reduced peak height Rpk was determined in a cross-section along the transverse direction of the resin-coated metal sheet 1, that is, a direction (TD) perpendicular to the rolling direction (RD) of the metal original sheet 11 on the surface of the resin-coated metal sheet 1. The arithmetical mean height Sa2 of the metal original sheet 11 was measured in the same manner.
    • <Proportion of polar component based on surface free energies on surface of resin layer>
  • Using an automatic contact angle meter (DM-701 available from Kyowa Interface Science Co., Ltd.), contact angles of deionized water, ethylene glycol, and diiodomethane to the surface of the resin layer 20 in the resin layer-coated metal sheet 1 were measured. By applying the measured values of the contact angles to the equation of the Kitazaki-Hata theory, the surface free energy of the dispersive component, that of the dipole component, and that of the hydrogen bond component were determined. The proportion of the sum of the surface free energy of the dipole component and that of the hydrogen bond component to the total value of these was determined as the proportion of the polar component.
    • <Peel strength to adhesive resin>
  • A T peel test (hereinafter, also referred to as peel test) in accordance with JIS K 6854-3 was performed for evaluation of adhesion properties to an adhesive resin to measure the peel strength of the resin layer-coated metal sheet 1. Specifically, two resin-coated metal sheets 1 having a width of 25 mm and a length of 80 mm were disposed to face each other, and nine spots of an olefin adhesive resin (trade name: Melthene, available from Tosoh Corporation) were sandwiched between the two resin-coated metal sheets 1. The resin-coated metal sheets 1 and the olefin adhesive resin were heat bonded for 2 minutes at a temperature of 150°C and a pressure of 0.5 MPa, giving a laminate. Using a tensile tester (product name "AGX-V", available from SHIMADZU Corporation), the prepared laminate was subjected to a peel test at a peeling rate of 200 mm/min to measure the maximum peel strength [unit: N/25 mm] .
    • <Appearance (presence/absence of air bubbles), spreading properties of adhesive resin>
  • The prepared resin-coated metal sheet 1 was heated on a hot plate set at 130°C, and one spot of an olefin adhesive resin (trade name: Melthene, available from Tosoh Corporation) was placed on the resin layer 20 of the resin-coated metal sheet 1. Then, 9 cm2 of a Teflon plate (Teflon is a registered trademark) having a weight of 3.5 g was placed on the olefin adhesive resin, a 150-g weight was placed over the Teflon plate, and these were held for 2 minutes. After 2 minutes had passed, the Teflon plate and the weight were removed, followed by cooling in the air. Thereafter, the presence/absence of air bubbles contained between the adhesive resin and the resin layer 20 was visually observed. The absence of air bubbles indicates that coated metal sheets produced using the resin-coated metal sheet 1 and joint filling materials and automobile interior materials formed from such coated metal sheets can have good appearances.
  • The differences of spreading properties were verified as follows: A test was performed by the same procedure as above except that the temperature of the hot plate was changed to 100°C and 110°C. After cooling in the air, a circularity ratio c (c = b/a) of a major axis length a and a minor axis length b of the adhesive resin spread on the resin layer was determined. A higher circularity ratio c indicates that the adhesive resin more uniformly spreads.
    • <Example 1>
  • As the metal original sheet 11, a cold-rolled sheet (thickness: 0.16 mm) of a low carbon aluminum-killed steel was prepared. The metal original sheet 11 was obtained by rolling a low carbon aluminum-killed steel sheet using a rolling roll having an arithmetic average roughness Ra of 2.5 to 5.5 µm, and the metal original sheet 11 had an arithmetical mean height Sa2 of 0.95 µm. In the next step, the metal original sheet 11 was subjected to alkaline electrocleaning and pickling by immersion in sulfuric acid, and then, was plated at a bath temperature of 40°C and a current density of 15 A/dm2, thereby giving a metal base 10 including the metal original sheet 11 and a metal plating layer 12 formed on both surface thereof, the metal plating layer 12 having a thickness of 1.5 µm and being formed from zinc-cobalt-molybdenum alloy plating. The compositional ratio in the metal plating layer was determined using X-ray fluorescence, which was 0.16% by weight of Co, 0.02% by weight of Mo, and the balance of Zn.
  • In the next step, an aqueous dispersion (solid concentration: 20% by weight, viscosity: 70 mPa·s, pH: 9.3, MFT: 12°C) containing an olefin resin (ethylene-acrylic acid copolymer) was applied onto the metal plating layer 12 of the metal base 10 by direct roll coating. Thereby, a layer formed from the aqueous dispersion was formed. Subsequently, the layer was dried at a temperature of 150°C for 10 seconds, forming a resin layer 20 containing the olefin resin. The thickness of the resin layer 20 was 0.6 µm. The resin layer 20 was formed on both surfaces of the metal base 10. Thus, a resin-coated metal sheet 1 including the resin layer 20 formed on both surfaces of the metal base 10 was obtained. For the obtained resin-coated metal sheet 1, the above-mentioned reduced peak height and arithmetical mean height of the resin layer were measured, the proportion of the polar component based on the surface free energies of the resin layer surface was determined, and the peel strength to the adhesive resin, the appearance (presence/absence of air bubbles), and the spreading properties of the adhesive resin were evaluated. The results are shown in Tables 1 to 3. The weight average molecular weight of the ethylene-acrylic acid copolymer determined by high temperature GPC-IR was 49,900.
    • <Example 2>
  • A resin-coated metal sheet 1 was obtained in the same manner as in Example 1 except that the aqueous dispersion containing the olefin resin (ethylene-acrylic acid copolymer) was replaced by an aqueous dispersion (solid concentration: 44.5% by weight, viscosity: 40 mPa·s, pH: 4.8, MFT: 100°C) containing an olefin resin (ethylene-methacrylic acid copolymer), and the reduced peak height and arithmetical mean height of the resin layer were measured, and the peel strength to the adhesive resin, the appearance (presence/absence of air bubbles), and the spreading properties of the adhesive resin were evaluated. The results are shown in Tables 1 to 3. The weight average molecular weight of the ethylene-acrylic acid copolymer determined by high temperature GPC-IR was 69,300. The thickness of the resin layer 20 was 0.6 µm.
    • <Comparative Example 1>
  • A resin-coated metal sheet 1 was obtained in the same manner as in Example 1 except that a metal original sheet 11 which was obtained by rolling using a rolling roll having an arithmetic average roughness Ra of 0.01 to 0.5 µm and had an arithmetical mean height Sa2 of 0.3 µm was used, and the reduced peak height and arithmetical mean height of the resin layer were measured, and the appearance (presence/absence of air bubbles) was evaluated. The results are shown in Table 1. The thickness of the resin layer 20 was 0.6 µm.
    • <Comparative Example 2>
  • A resin-coated metal sheet 1 was obtained in the same manner as in Example 1 except that a metal original sheet 11 which was obtained by rolling using a rolling roll having an arithmetic average roughness Ra of 0.8 to 2.3 µm and had an arithmetical mean height Sa2 of 0.73 µm was used, and the reduced peak height and arithmetical mean height of the resin layer were measured, and the peel strength to the adhesive resin and the appearance (presence/absence of air bubbles) were evaluated. The results are shown in Table 1. The thickness of the resin layer 20 was 0.6 µm.
    • [Table 1]
  • Table 1
    Metal base Aqueous dispersion Resin layer Evaluation concerning adhesive resin
    Arithmetical mean height Sa2 [µm] of metal base sheet Solid concentration [wt%] Type of resin Reduced peak height Arithmetical mean height Peel strength [N/25mm] Presence/ absence of air bubbles
    Rpk [µm] Spk [µm] Sa1 [µm]
    Ex. 1 0.95 20 Ethylene-acrylic acid copolymer 0.49 0.89 0.82 11.6 Absent
    Ex. 2 0.95 44.5 Ethylene-methacrylic acid copolymer 0.76 1.26 0.94 19.4 Absent
    Comp. Ex. 1 0.30 20 Ethylene-acrylic acid copolymer 0.40 0.50 0.41 Present
    Comp. Ex. 2 0.73 20 Ethylene-acrylic acid copolymer 0.40 0.61 0.87 10.8 Absent
    • [Table 2]
  • Table 2
    Evaluation concerning adhesive resin
    Peel strength [N/25mm] Circularity ratio c [-]
    Heating temperature [°C]
    100 110
    Example 1 11.6 0.73 0.88
    Example 2 19.4 0.95 0.99
    • [Table 3]
  • Table 3
    Type of resin Surface free energy
    Dispersive component [mJ/m2] Dipole component [mJ/m2] Hydrogen bond component [mJ/m2] Total [mJ/m2] Proportion of polar component [-]
    Example 1 Ethylene-acrylic acid copolymer 32.6 2.3 0.1 35 0.07
    Example 2 Ethylene-methacrylic acid copolymer 26.4 10.6 0.9 37.9 0.30
  • Table 1 shows that the resin-coated metal sheets 1 in Examples 1 and 2 had a reduced peak height Rpk of 0.46 µm or more, had high peel strength to the adhesive resin, and had excellent adhesion properties to the adhesive resin. In addition, air bubbles contained in the adhesive resin spread on the resin layer 20 were not observed, which indicates that joint filling materials having a good appearance can be provided.
  • In contrast, the resin-coated metal sheets in Comparative Examples 1 and 2 had a reduced peak height Rpk of less than 0.46 µm, had low peel strength to adhesive resin, and had poor adhesion properties to the adhesive resin. In the resin-coated metal sheet in Comparative Example 1, air bubbles were contained in the adhesive resin spread on the resin layer, and joint filling materials including such a resin-coated metal sheet had a bad appearance.
  • Comparison of Examples 1 and 2 to Comparative Examples 1 and 2 reveals that there was no correlation between the arithmetical mean height Sa1 of the resin layer 20 and the peel strength. This indicates that the adhesion properties to the adhesive resin cannot be enhanced only by increasing the arithmetical mean height of the resin layer 20, and the adhesion properties to the adhesive resin are successfully enhanced by controlling the reduced peak height Rpk of the resin layer 20 to be 0.46 µm or more.
  • The resin-coated metal sheet 1 in Example 2 had higher peel strength than that in Example 1. It is considered that this is because the circularity ratio is higher in Example 2 than in Example 1 as shown in Table 2, and the adhesive is more likely to uniformly spread.
    • <Referential Test Example 1>
  • A resin-coated metal sheet 1 was obtained by direct roll coating as in Example 1 except that a cold rolled sheet (thickness: 0.16 mm) obtained by cold rolling and annealing a low carbon aluminum-killed steel, followed by temper rolling with a roll having an arithmetic average roughness Ra of 2.5 to 5.5 µm was prepared as the metal original sheet 11, and was subjected to zinc plating at a bath temperature of 50°C and a current density of 30 A/dm2 using a pure zinc plating bath to form a zinc plating layer of pure zinc as the metal plating layer 12. The reduced peak height Rpk of the obtained resin-coated metal sheet 1 was measured as in Example 1.
    • <Referential Test Example 2>
  • A resin-coated metal sheet 1 was obtained in the same manner as in Referential Test Example 2 except that the aqueous dispersion containing an olefin resin (ethylene-acrylic acid copolymer) was replaced by an aqueous dispersion (solid concentration: 44.5% by weight, viscosity: 40 mPa·s, pH: 4.8, MFT: 100°C) containing an olefin resin (ethylene-methacrylic acid copolymer), and the reduced peak height Rpk was measured.
    • <Referential Comparative Example 1>
  • A resin-coated metal sheet was obtained as in Referential Test Example 1 except that the aqueous dispersion was applied by a bar coater instead of direct roll coating, and the reduced peak height Rpk was measured. In the application by a bar coater, a wireless bar coater (available from OSG System Products Co., Ltd., Select-Roller/A-Bar) was used, and a wireless bar model #0 (OSP-00) was used for a film thickness of 1 µm.
    • <Referential Comparative Example 2>
  • A resin-coated metal sheet was obtained as in Referential Test Example 2 except that the aqueous dispersion was applied by a bar coater instead by direct roll coating, and the reduced peak height Rpk was obtained. The results of measurement of Rpk in Referential Test Examples 1 to 2 and Referential Comparative Examples 1 to 2 where Referential Comparative Example 1 is regarded as a reference are shown in Table 4.
    • [Table 4]
  • Table 4
    Type of resin Coating method Rpk ratio
    Referential Test Example 1 Ethylene-acrylic acid copolymer Direct roll coating 1.65
    Referential Test Example 2 Ethylene-methacrylic acid copolymer Direct roll coating 1.81
    Referential Comparative Example 1 Ethylene-acrylic acid copolymer Bar coater 1 (reference)
    Referential Comparative Example 2 Ethylene-methacrylic acid copolymer Bar coater 0.61
  • It can be verified that the Rpk is significantly higher in Referential Test Examples 1 to 2 where the aqueous dispersion was applied by direct roll coating than in Referential Comparative Examples 1 to 2 where the aqueous dispersion was applied by a bar coater. It is considered that a high reduced peak height Rpk was obtained because of direct roll coating in which the aqueous dispersion is lifted as shown in Fig. 2(a) when the metal base 11 is sent from the roll, compared to the application by a bar coater without lifting the solution when applied.
    • REFERENCE SIGNS LIST
    • 1
    resin-coated metal sheet
    10
    metal base
    11
    metal original sheet
    12
    metal plating layer
    20
    resin layer

Claims (10)

  1. A resin-coated metal sheet comprising a metal base, and a resin layer disposed on the metal base,
    wherein the resin layer has a surface with a reduced peak height Rpk of 0.46 µm or more.
  2. The resin-coated metal sheet according to claim 1,
    wherein the resin layer has a surface with a reduced peak height Spk of 0.6 µm or more.
  3. The resin-coated metal sheet according to claim 1 or 2,
    wherein the resin layer is formed from a resin material containing an olefin-based resin and/or a urethane-based resin.
  4. The resin-coated metal sheet according to any one of claims 1 to 3,
    wherein the resin layer has an arithmetical mean height Sa1 of 0.5 µm or more.
  5. The resin-coated metal sheet according to any one of claims 1 to 4,
    wherein the resin layer has a surface with a reduced peak height Rpk of 0.6 µm or more.
  6. The resin-coated metal sheet according to any one of claims 1 to 5,
    wherein the metal base includes a metal original sheet and a metal plating layer containing zinc, and
    the resin layer is formed on the metal plating layer.
  7. The resin-coated metal sheet according to claim 6,
    wherein the surface of the metal original sheet on which the metal plating layer is formed has an arithmetical mean height Sa2 of 0.5 µm or more.
  8. A method of producing the resin-coated metal sheet according to any one of claims 1 to 7, the method comprising:
    a step of applying an aqueous dispersion onto the metal base by direct roll coating, the aqueous dispersion containing a resin material in a solid concentration of 15% by weight or more; and a step of drying the layer formed from the aqueous dispersion to form the resin layer.
  9. The method of producing the resin-coated metal sheet according to claim 8,
    wherein the solid concentration in the aqueous dispersion is 15% by weight or more and less than 70% by weight,
    the metal base includes a metal original sheet and a metal plating layer containing zinc, and
    the surface of the metal original sheet on which the metal plating layer is formed has an arithmetical mean height Sa2 of 0.75 µm or more.
  10. The method of producing the resin-coated metal sheet according to claim 8 or 9,
    wherein the resin material contains an olefin-based resin and/or a urethane-based resin.
EP24780690.4A 2023-03-31 2024-03-28 Resin-coated metal sheet and resin-coated metal sheet production method Pending EP4691760A1 (en)

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