Coating processes – Direct application of electrical – magnetic – wave – or... – Pretreatment of substrate or post-treatment of coated substrate
Patent
1998-09-24
2000-07-18
Pianalto, Bernard
Coating processes
Direct application of electrical, magnetic, wave, or...
Pretreatment of substrate or post-treatment of coated substrate
427105, 427106, 427180, 427230, 427508, B05D 122
Patent
active
060904542
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for providing a hollow object formed of a low electrically conductive material with a coating of a thermoplastic polymer, and in a preferred embodiment, providing a glass or ceramic container with a coating of an ionomeric polymer.
BACKGROUND OF THE INVENTION
Polymer coatings are provided on objects having low electrical conductivity such as ceramics and glass for a variety of reasons such as for weight savings, shatter protection, aesthetics and touch. In particular, providing shatter protection to glass bottles containing carbonated beverages is of particular importance where the glass bottles are defective or mishandled.
Polymeric coatings can be applied by various means. The objects to be coated can be dipped into a polymeric melt or can be dipped into a fluidised bed of polymer powder particles. It is also known to coat objects using an electrostatic powder spraying process; c.f. DE 2424220, DE 2750370 C2 and DE 2750372 C2.
DE 2750370 C2 and DE 2750372 C2 disclose electrostatic spray coating processes in which the substrate (a glass bottle) is maintained at a temperature below the melting point of the polymer, and the powder is applied by way of silent discharge. Afterwards, the bottle is heated to melt the powder to form a coating, which is subsequently cured. These processes, however, require high investment costs, can lead to corrosion of the equipment as they require continuous discharge, have limitations to the speed at which they can be carried out, require the use of very fine polymer powder which is expensive to produce, often produce non-uniform coatings due to local discharges at the bottle surface, and can be dangerous to carry out due to shattering of the bottles during heating and quenching steps.
These disadvantages are overcome by the current invention.
DETAILED DESCRIPTION OF THE CURRENT INVENTION
The present invention provides a process for forming a coating of a thermoplastic polymer to a hollow object formed of a low electrically conductive material, characterised in that the thermoplastic polymer has its maximum IR absorption between 1300 and 1900 nm and/or 2800 and 3000 nm, is applied electrostatically as a powder to the object while the object is held at a temperature below the melting point of the thermoplastic polymer, and thereafter the object is heated by IR radiation to form the coating.
Advantages of the process include annealing ovens of the glass bottle plants, thereby avoiding the need for large, expensive to preheat the objects prior to coating; needed; size polymer.
As mentioned, suitable thermoplastic polymers to be used in the process according to the invention will have their maximum IR absorption between 1300 and 1900 nm and/or 2800 and 3000 nm. Preferred such polymers are ethylene/acid copolymers and ethylene/acid/acrylate terpolymers and their corresponding ionomers.
Ethylene/acid copolymers and their corresponding ionomers are well known in the art to be copolymers of ethylene with an olefinically unsaturated organic acid such as acrylic or methacrylic acid, the acid comprising about 1 to 50 mole percent of the total polymeric material. The ethylene/acid copolymers and their methods of preparation are well known in the art and are disclosed in, for example U.S. Pat. Nos. 3,264,272, 3,404,134, 3,355,319 and 4,321,337. The copolymers are termed ionomers when the acid is neutralized in whole or in part, preferably up to 80% to produce a salt. The cation for said salts may be a metal ion chosen from the first, second or third group of the periodic table of elements, and is preferably an alkali metal such as sodium, potassium or zinc.
Ethylene/acid/acrylate terpolymers and corresponding ionomers are well known in the art to be terpolymers of the aforementioned ethylene and olefinically unsaturated organic acids, together with an alkyl acrylate or methacrylate (e.g. ethylacrylate, n-butyl acrylate, isobutylacrylate or methacrylate). The terpolymers will typically contain between 1 and 40 weight % of alkyl acrylate or me
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PCT International Search Report for International Application No. PCT/US97/04706 (No Date Avail.).
Hausmann Karlheinz
Vanlancker Thierry
E.I. Du Pont de Nemours and Company
Evans Craig H.
Pianalto Bernard
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