Coating for Aluminum Packaging
Thanks to the availability of equipment and technically qualified personnel, in 2005 the decision was made to start the development and production of enamels and paints for the outer and inner protection of aluminium packaging. As customary in Reinol, we are investing all our energy to become a landmark in this sector in the shortest possible time.
These exist in 4 main types
They are manufactured starting from aluminum tablets (Al grade 99,8) which, after lubrication with wax-like or stearic products (e.g. vegetable fat-based salts), are extruded until obtaining cylinders with the same diameter of the initial tablets. Before going on to the painting phase each cylinder is degreased from lubricants with hot NaOH solutions, washed, rinsed (with demineralized water) and dried. Cylinders cleaned from all extrusion residues are first painted inside with spray guns using as a rule epoxy- phenol paints, either pigmented or transparent gold color. The thickness of the wet paint layer varies from 8-10 to 15-20 micron depending on the area painted (bottom, central part or top). After painting, the cylinder is put into an oven to bake the paint at temperatures from 240 to 280 deg. C and for a time from 3 to 6 min. Baking time and temperature depend both on the thickness of metal and effectiveness of ovens. The following step is the enameling of the outer side of cylinders, which is carried out horizontally with rollers.
Base coats are oil-free, polyester-based, and can be white (80% of consumption), in pigmented pastel colors or transparent (either colorless or colored). After application of the base coat (20 to 30 g/cm2) the can goes into the baking oven for 5 to 7 min at 140-160 deg. C. At this stage the can, protected by inner paint and outer enamel, is printed (horizontally with rollers) with offset inks and clichés with writings, logos, etc. The inks are baked in second oven (150/150 deg. C for 3 to 5 min). When coming out of second oven, cans already have a finished outer look. The last protection layer is then applied: an overprint paint is applied horizontally with a roller to protect the printed layer of the can from scratching and abrasion. At this stage paints used are glossy and transparent, solvent-based (yet more and more frequently water-borne as well), oil-free, polyester-based. This paint is also baked (third oven) at 170-180 deg. C for 4 to 6 min. On coming out of third oven the can protection is complete. The can is then cooled and brought to the cone-shaping machinery. After about 18 passages through this machinery cans are completely finished, they are packed and forwarded to manufacturers of food, pharmaceutical, cosmetic products for to be filled into cans.
(pilferproof caps used for bottles of alcoholics and other liquid products)
Caps are manufactured from aluminum foil preliminarily painted on one side (this will be the inner side of cap) and with thickness abt 220 microns. Caps have lengths varying from 2 cm (for pharmaceuticals) to 5-6 cm (for bottles of alcoholics).
Caps are protected by applying an outer coating for two reasons: after molding aluminum looks opaque and has a loose grain, moreover it is necessary to print on caps every kind of information such as logos, writings, trademarks, identification of the content, etc. The coating is carried out by a system and with equipment similar to those used for flexible tubes.
First a ground coating is applied (white, colorless or differently colored enamel), then the caps are put into a continuous oven in order to dry and partially bake the coating. Baking temperatures are 130 to 150 deg. C for 4 to 6 min.
After this passage in oven, caps are offset-printed with the various color of writings, logos, etc.
After inking, caps are again fed into oven for drying and complete polymerization of the ground coating and the printing inks. Caps are then sent to screw threading to allow their screwing on top of bottles. After this operation cap production is complete and caps are put into cardboard boxes for shipment to end
Flexible containers are manufactured starting from aluminum tablets of the same diameter of the tubes to be manufactured. Tablets (Al grade 99,5) are lubricated with waxes or vegetable stearic products, then extruded until they become tubes. During extrusion with punch presses aluminum undergoes hardening and must therefore be softened in high-temperature ovens (annealing ovens). The temperature in these ovens varies from 350 to 400 deg. C according to the degree of softness/flexibility to be attained in tubes (the higher the annealing temperature, the softer the tube). During this operation the metal changes its crystalline structure and from hard/rigid becomes soft/annealed. The high-temperature annealing treatment also eliminates all lubricant residues left after extrusion. After leaving the annealing oven, tubes are fed into the painting unit (tubes are still lukewarm, with a temperature of about 30-40 deg. C). Paint guns with extra-small nozzles are used to apply a protection layer of (usually) epoxy- phenol paints onto the inner surface of tubes. The paint is then baked at 260-280 deg. C for 3 to 4 min. The inner tube surface is thus covered with a gold color layer resisting the many different products to be filled in tubes:
Foodstuff: tomato sauce, mustard, mayonnaise sauce, olive and tuna fish pate, etc. Cosmetic products: creams, hair dyes, etc.
Pharmaceuticals: balms, ointments and creams
Technical products: glues, silicones, lubricating fats, adhesives, etc.
After inner painting, the tube outer base coat (white or transparent) protection layer is applied with rollers. Enameled tubes are then moved on conveyor belts to the enamel baking oven (first oven) (120-140 deg. C for 4 to 6 min). After this treatment the outer coating (base coat, either transparent or white enamel) is not yet fully baked, as tubes must go through inking (5-6 color inking machines) necessary to print writings, logos, symbols, etc. After printing, tubes go into second oven (160-170 deg. C for 4 to 6 min), in which the baking of enamels is completed and printing inks are also baked. The inner bottom part of tubes is then puttied for a length of about 1 cm. This will ensure sealing and insulation of tubes after their filling. Tubes are then forwarded to manufacturers of the products to be filled into tubes.
The substrate is normally either steel or aluminium, although other metals can be coil-coated too. In the case of steel, it is usually cold-reduced and generally with a zinc or zinc alloy metallic coating to provide galvanic corrosion protection. About 95% of the organic coatings are paints with 5% being plastic films, laminated to the surface.
The output of the coil coating industry is a coated metal strip. This has numerous applications in various industries, including: in the construction industry for both indoor and outdoor applications; the automotive and transport industries; in the production of white goods including washing machines; cabinets for electronic goods; office furniture; lighting envelopes; bakeware.
The coated surface can have a wide range of colours, gloss levels and surface textures. What dictates the choice of coating is the end use of the finished product. The user may require non-stick properties, great flexibility or high chemical resistance. Modern developments have provided many new coating types to meet the increasing demands of users.
Coated coil can be slit for narrow widths, cut to required lengths, bent, profiled or deep drawn, without damaging the organic coating. It can be processed into any number of shapes, depending on the end use.