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
  • B05D7/16—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 using synthetic lacquers or varnishes
• • 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
  • B05D5/08—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain an anti-friction or anti-adhesive surface
  • B05D5/083—Processes for applying liquids or other fluent materials to surfaces to obtain special surface effects, finishes or structures to obtain an anti-friction or anti-adhesive surface involving the use of fluoropolymers

Definitions

• the present invention relates to a process for the application of no-stick and heat-resistant coatings to aluminium sheets.
• the invention relates to a process consisting of the lapping of the aluminium surface, which is then coated with a no-stick paint layer on one side and with a heat-resistant paint layer on the other side, both paint layers being applied by roll units.
• the claimed process is particularly useful for the production of aluminium cookware provided with no-stick lining and heat-resistant coating.
• doctorware is used herein to mean pots and relevant lids, pans, baking pans, oven trays, toaster or oven racks, kitchen utensils, spatulas, mixing spoons, and all other utensils usually employed for food preparation and cooking.
• no-stick cookware has extraordinarily increased during the last 30 years. Consequently, studies have been and are still being conducted to develop no-stick paint formulations and relevant methods of application to the pot and pan surface coming into contact with food.
• a water paint without PTFE, containing a surfactant, finely divided silica particles, a polyethersulphone (PES) or polyamidoimide (PAI) for application to a degreased metal substrate and acting as a bridge with the successive PTFE-based paint layer is disclosed in US patents Nos. 5,049,437 and 5,079,073.
• This treatment consists of aluminium sheet annealing at a temperature of 450°C approx.
• the system removes any residual trace of oil from the rolling mill process, but is ineffective towards the salts and oxides, if any, occurring on the surface. It involves high power costs and the sheet cooling phase is a hindrance to plant productivity.
• the surface is treated at 30°C to 60°C with an anionic or non-ionic surfactant added with sodium hydroxide and sequestering agents. A considerable surface cleaning is obtained; however, traces of sodium hydroxide are left on the surface even after repeated washings with water. It raises the problem of liquid effluents disposal.
• the surface is treated at 30°C to 60°C with an anionic or non-ionic surfactant added with mineral acids and sequestering agents.
• the surface cleaning obtained is fairly good; however, salt residues are left on the surface even after repeated washings with water. It raises the problem of liquid effluents disposal.
• the surface is treated with chlorinated organic solvents.
• the system is ineffective towards mineral salts and raises problems of solvents treatment and recycle.
• the paint layer must be so flexible as not to allow the formation of scalings and checkings during shaping and, at the same time, must be firmly fixed to the metal surface.
• the outer and inner sides have different functions, the former being meant for coming into contact with the source of heat, necessary for food cooking, while the latter is meant for coming into contact with food. Therefore, the two sides of the aluminium disk to be shaped into cookware are painted with layers of paints of different chemical characteristics, but with analogous mechanical properties making them capable of withstanding, without any damage, the deformations caused by disk drawing, which is performed when both sides have been painted. Furthermore, the two coatings must get through all standard tests reproducing the pot duty conditions (dishwashing machine, hot-scratching, repeated use vs. colour maintenance).
• the process for applying two different coatings - one heat-resistant and the other no-stick - to an aluminiun sheet comprises the following main steps:
• Texture is measured by profilometers.
• the measurements of the surface texture referred to herein were performed by a profilometer, Mod. RT 60, available from ALPA SM, Milan.
• the texture index number (Ra) is given by the ratio of the integral of the surface microcavities to the sheet portion length explored in a cross direction in respect of the direction of rolling.
• Typical water paints useful for the formation of the first no-stick paint layer are as disclosed in the European patent application No. 94119007.6 filed on Dec. 2, 1994 by the Applicant, and consist of aqueous dispersions of PTFE, PPS and PAI mixtures, with a PAI content of 5% to 10% by wt. and a carbon black content of 10% to 15% by wt.
• the paint layer in contact with the aluminium surface is overlaid with another layer of paint based on PTFE, without mixing PTFE with PPS and PAI.
• the investigations conducted provide evidence that the paint film in contact with the aluminium surface secures not only a coating with the adhesiveness and flexibility required by drawing, but also a perfect adhesion both to the aluminium surface and to the paint superficial layer, even if this contains PTFE only.
• a first layer of paint containing PTFE and PPS in a ratio ranging between 35:65 and 55:45 w/w is applied, dried, and overlaid with a second layer of paint containing PTFE and PPS in a ratio ranging between 55:45 and 80:20 w/w so as to obtain a layer of intermediate characteristics (and therefore acting as a bridge) between those of the layer in contact with the aluminium disk and of the outer layer.
• the paint After application of each layer, the paint is air dried slowly to evaporate the water and solvents, if any, present therein.
• the paint may be applied on a single application or with more coats, repeating steps b) and c) as many times as desired.
• One or more water paint layers may also be applied as primers and then one or more layers as finish. Once all layers have been applied, the layer is baked.
• the paints are applied to the aluminium sheet to be drawn in such amounts as to form coatings which, when dry, are 10 to 25 ⁇ m thick, each time providing a paint layer of 5 ⁇ m max.
• Drying is carried out at a disk temperature of 30°C to 50°C, with an air stream at 120°C max., to no aftertack to the touch.
• the paints that may be used for the formation of the second heat-resistant paint layer are as disclosed in the Italian patent No. 1,230,623 and Italian patent application MI91 A 001983 (open to public inspection), filed both by the Applicant; said paints are based on silicone polyesters, associated, if necessary, with immiscible silicone oils, to obtain a polychrome and particularly attractive surface finish.
• the paint After application, the paint is air dried slowly to evaporate the water and solvents, if any, present therein.
• the paint may be applied on a single application or with more coats.
• the dried layer is baked.
• the paints are applied to the aluminium sheet to be drawn in such amounts as to form coatings which, when dry, are 10 to 25 ⁇ m thick, each time providing a paint layer of 5 ⁇ m max.
• drying is carried out at a disk temperature of 30°C to 50°C, with an air stream at 120°C max., to no aftertack to the touch.
• the cookware obtained by drawing aluminium sheets after painting as per the process of this invention exhibits a coating as high in quality as that of analogous cookware painted by spraying, after moulding and sandblasting of the aluminium disk.
• compositions (%) of water paints A to F which were subjected to the application tests described hereinafter, are reported in Table 1 below.
• Table 1 Compositions (%) of water paints A to F Component A B C D E F Algoflon D60® 15.2 19.6 15.2 15.2 15.1 23.9
• Fortron X0205/60 R 13.1 11.4 13.1 13.1 13.1 9.7 Rhodeftal 200® 5.5 5.5 5.5 5.5 11.2 5.5 DMEA 0.7 0.7 0.7 0.6 1.3 0.7 Printex 85® 3.5 3.5 3.0 1.2 3.5 3.5
• PSS before being used in paint formulation, was milled in the presence of water in a steatite ball mill for a period of 72 hours to obtain a homogeneous dispersion including solid particles sized 8 ⁇ m max.
• water paints A to F were prepared by mixing the various components in the aforesaid amounts (in addition to the components pretreated as described above) in a steatite ball mill for a period of 72 to 96 hours. A perfect homogenization of the mixture and a lowering in the solid particle size below 8 ⁇ m were thus secured.
• the apparatus used for continuous application of water paints to aluminium disks to be shaped into cookware consisted of a lapping machine followed by two consecutive painting lines, each consisting of four roll units, each of the first three units being followed by a hot-air tunnel for painted disk drying and the fourth by a small heater for disks final drying and baking. Aluminium disks were caused to pass under the lapping machine twice, i.e. for the lapping of both sides, and were then placed on a conveyor belt and continuously transferred from one painting line to the other.
• the first painting line applied the no-stick coating (inside the pot) while the second line applied the heat-resistant coating (outside the pot).
• the conveyor belt speed was set to secure no aftertack to the touch of the painted disks after drying.
• the disks painted with the aforesaid apparatus were made of aluminium sheet, type 1050 (99.5% aluminium), which had been lapped to a surface texture (Ra) of 1 ⁇ m.
• the first and the second roll units were set to secure a paint layer to be 5 ⁇ m thick (after drying).
• the air temperature in the first three tunnels was set to 70°C and the residence time of the painted disks in each tunnel was of 5 minutes.
• the temperature of the last heater was set to obtain a 5 minutes' disks baking at 420°C.
• the third roll unit was set to secure a paint layer 5 ⁇ m thick (after drying).
• Examples 1 to 5 were obtained as follows: the first roll unit was fed with paints A to E, the second roll unit was fed in all cases with paint F, and the third roll unit was fed in all cases with paint A, but without PPS and PAI.
• the operating parameters of the second painting line were the same as those of the first line, except that the last heater was set to obtain an 8 minutes' disks baking at 290°C. All roll units of the second painting line were fed with a silicone polyester paint having the following composition:
• the sheet is repeatedly bent by 180°.
• the successive bendings are indicated by an increasing T-bend number: the first bending is given No. 0, the second No. 1, and so on.
• the lower the number of T-bends the severer the stress withstood by the coating.
• the presence or the absence of microcheckings in the coating is observed at the external point of maximum bending.

Landscapes

• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Wood Science & Technology (AREA)
• Application Of Or Painting With Fluid Materials (AREA)
• Laminated Bodies (AREA)
• Paints Or Removers (AREA)
• Treatments For Attaching Organic Compounds To Fibrous Goods (AREA)
• Cookers (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (2)

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Family Applications (1)

Country Status (9)

Cited By (5)

Families Citing this family (1)

Citations (3)

• 1994
  • 1994-07-14 IT ITMI941480A patent/IT1270622B/it active IP Right Grant
• 1995
  • 1995-05-12 AT AT95107199T patent/ATE187363T1/de not_active IP Right Cessation
  • 1995-05-12 DK DK95107199T patent/DK0692316T3/da active
  • 1995-05-12 EP EP95107199A patent/EP0692316B1/de not_active Expired - Lifetime
  • 1995-05-12 DE DE69513739T patent/DE69513739T2/de not_active Expired - Fee Related
  • 1995-05-12 SI SI9530380T patent/SI0692316T1/xx unknown
  • 1995-05-12 PT PT95107199T patent/PT692316E/pt unknown
  • 1995-05-12 ES ES95107199T patent/ES2142422T3/es not_active Expired - Lifetime
• 2000
  • 2000-03-06 GR GR20000400565T patent/GR3032873T3/el not_active IP Right Cessation

Patent Citations (3)

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