METHOD OF HOT AIR SPRAYING THERMALLY MELTABLE POWDERED POLYMERIC COMPOSITIONS

Abstract: Method of applying and/or heat melting with optional contemporaneous or subsequent thermosetting thermally meltable powdered polymers by using hot air generators and convectors with variable velocity output and temperature. (Heats Guns for spray powder coatings or powder adhesives).

Description: "METHOD OF HOT AIR SPRAYING THERMALLY MELTABLE POWDERED POLYMERIC COMPOSITIONS" [Description] Powder paints are up to now used almost exclusively in industrial plants as they need cumbersome static equipment such as baking ovens and application booths. In order to remove these limitations flame guns were recently made available, allowing to apply thermoplastic powder paints in an open atmosphere through an annular flame which melts the projected powder paint. The molten paint deposits on a support, but the presence of the flame limits its use only to thermoplastic paints of high molecular weight. Moreover, to avoid combustion of the deposited molten paint it is necessary to move continuously and rapidly the point of projection of the flame. To apply hot melts heat guns are used, comprising glue sticks pressed against a heated nozzle that melts them, allowing only their spreading. Furthermore hot air dryers are available on the market, that are used for packaging articles with shrinkable films. Up to now, use of hot air generating apparatus to apply thermally meltable powdered compositions was not known. As it was realized that the flame, in view of the excessive heat delivered, charred already in the no.zzle the powdered paint, it was devised that by substituting a hot air flow for the flame, it was probably possible to melt and harden the paint. Therefore with a normal electrostatic gun a powder paint was deposited on some aluminum panels, then a conventional hot air dryer with variable temperature, used for thermally shrinkable packaging films, was used for projecting hot air on the surface coated with powder paint but said panels were not acceptable because air output was too strong and most paint was blown off. Thereafter the air output was reduced by partially covering air intake and it was surprisingly discovered that by regulating the air input it was not only possible to melt and harden the paint without blowing it out, but it was also possible to expand and spread it in the molten state, just as if it were done with a brush. Having proven that the principle of using hot air for the flame was a valuable idea, then a gun for projecting powder and a hot air dryer were designed in such a way that the outgoing hot air envelopped the gun no.zzle, thus the powder was deposited in a partially molten condition. Then temperature of the dryer was increased until the projected powder was deposited in a molten condition and thereafter discontinuing delivery of powder it was possible to crosslink it. Subsequently we tried to apply it in the molten condition on non conductive support and we found that it adhered perfectly on wood, plastics, paper, fabrics and the like just because it was deposited in the molten condition, and when applied in such a condition to metal supports it was no longer necessary that the gun was tribochargeable or electrostatic. In view of the foregoing the method of the present invention consists of the use of at least one equipment comprising at least one gun for spraying the powdered paint or glue and at least one dryer for delivering hot air with variable temperature and output, possibly with a single nozzle so that the gun and dryer may be used contemporaneously or alternately according to the need. The method allows the application of any meltable powdered composition or thermoplastic or thermosetting polymer on any kind of support or surface. Such an equipment has practically no limitations, as the powdered product to be applied may be projected in powder form from an adjustable close distance and can deposit on a surface in a molten or powdered condition. At the same time or subsequently the polymer can be melted and cross-linked by heat using the dryer part. Alternatively, the dryer can first be used to preheat the surface on which the powdered polymer is applied with the gun and then is melted during or after said application. As the equipment has a reduced size, it may be used as a single unit or a set of units, it may be movable or fixed, and it allows to paint either static or large surfaces, or small surfaces even for retouching purposes, by applying the paint melted at a temperature lower than the cross-linking. With the same technique it is also possible to paint thermally sensitive supports, or to apply a powdered photohardenable paint, melting it and subjecting the applied film to UV radiation when it is still hot or after cooling. It is also possible to paint with thermosetting powder paints which are caused to melt and expand, controlling that they are perfectly spread and faultless, and subsequently they can be thermoset at any desired time and with any heat source such as hot air, flame, IR ovens, EB and so forth. In order to better illustrate the present invention, some non limiting examples of embodiments thereof are given hereinafter. All parts are by weight unless where otherwise specified. Example 1 : By using at the same time the gun and the dryer with delivery of hot air at a speed of about 2,200 foot/min and at a temperature of 250°C a hybrid polyester-epoxy powder paint comprising: Alftalat AN 783 390 Epoxide resin (EEW 700-900) 180 Additol XL 496 30 Degassing agent 5 Blanc Fixe 105 TiO 2 290 was sprayed in a molten condition on a steel sheet having a size of 6 xl5 cm coating it uniformly with a layer about 60μ thick, then stopping spraying and at the same time raising the air temperature to about 500°C, only hot air is projected for 2 minutes to obtain cross-linking. The steel sheet is then subjected to analysis tests by comparing it with a sheet painted in the traditional way and hardened in an oven at 180°C for 20 minutes and it results in being equal to the standard sample. In order to highlight the good qualities of the method according to the present invention, namely that hot air can be used to melt and harden a thermosetting powdered paint, the same paint was applied with the gun only on a sheet and then the dryer was used with a hot air output lowered to 500 foot/min, reducing the air inlet opening to avoid that the deposited paint is removed and with the temperature adjusted to 200°C the deposited paint melted and expanded. After fusion, the output was raised to 2,000 foot/min, the temperature to 400°C and this condition was held for 3 minutes. Also this steel sheet resulted in hardening like that hardened in an oven at 180°C for 20 minutes. Example 2: Following the same procedure of Example 1 a polyester-polyurethane powder paint is deposited, consisting of: Alftalat AN 745 456 Additol XL 432 114 Additolo XL 496 30 Degassing agent 5 TiO 2 395 Example 3: Following the same procedure of Example 1 a transparent acrylic powder paint is prepared, consisting of: Synthacryl LH 897 721 Additol VXL 1381 216 Additol 03551 30 Degassing agent 3 UV Stabilizer 30 and it was sprayed in a molten condition on two steel sheets. Thereafter a sheet is undergoing the analysis tests by comparing it with a sheet painted in the traditional way and hardened in an oven at 180° C for 20 minutes and it resulted to be equal to the standard sample. Then from the second painted and hardened sheet a portion of the deposited paint was abraded with a steel brush and with the same procedure the paint was again applied on the abraded portion. After having discontinued the spraying operation, with hot air kept at the same temperature and increasing the output speed, the paint applied in the molten condition was expanded so that the retouched portion resulted to be uniform. Thereafter the output speed was reduced and air temperature increased to 500° C so as to crosslink the paint in 2 minutes. In this way, even the second, retouched sheet resulted to be equivalent to the standard sample. Example 4: A transparent UN hardenable powder paint consisting of: Alftalat VAN 1743 642 Additol 03546 275 Additol VXL 9824 50 UV Photoinitiator 30 Degassing agent 3 was projected in a molten condition on two small wooden boards, coating them with a layer about lOOμ thick, then one board was subjected with the still molten paint to UV radiation for 30 seconds, while the other board was cooled and after some days subjected with the applied cold paint to the same radiation but for one minute and surprisingly also the second board, when subjected to the acetone soaked cotten flock test, passed 100 back and forth rubs. Example 5: Thermoplastic powdered paint for traffic signs consisting of 600 parts of Mowilith 35-73 (vinylacetate - maleate - Hoechst AG), 300 parts of Blanc fixe and 100 parts of titanium dioxide, was applied in a molten condition on asphalt using a special equipment provided with spraying gun and dryed with no.zzle positioned at 5-10 cm from the soil and mounted on a mobile carriage provided with compressor and power generator. The output of hot air from the dryer is rased to 2200 foot/min and at a temperature of 700°C. This p∑tint was applied at a speed of 7-10 km/hour and five minutes after application and cooling it was subjected to tests of adhesion and abrasion resistance, largely passing the required specification, as it resulted perfectly adherent and wear resistant.

Claims: Claims 1) Method of contemporaneously or successively applying and /or thermally melting, with possible contemporaneous or successive thermosetting, powdered polymers or compositions which are thermally meltable by using apparatus comprising at least one gun to project and apply said powdered products and at least one hot air generators and convectors with variable temperature, speed and output and using the two elements of the apparatus jointly or severally in order to possibly preheat the surface to be coated and/or to apply and/or to melt and/or possibly to harden the applied product. 2) Method according to Claim 1, wherein the two elements of the apparatus may have a single nozzle to project both the powder product and the hot air or may be mounted separately or sequentially with the option that the element delivering the hot air, when sequentially mounted, may be arranged before the gun element so as to preheat the surface on which the paint has to be applied and/or after said gun element so as to melt and/or harden the applied product. 3) Method according to Claim 1, wherein the gun element to project the powdered product may be either electrostatic or triboelectric or simply spraying the powdered product. 4) Method according to Claim 1, wherein the element of the apparatus generating and conveying hot air consists of electric resistances or other sources generating heat at variable temperatures and of an adjustable air intake that is conveying said air with variable output and speed through said heat source onto the surface to be coated with a preheating and/or melting and/or thermosetting stage. 5) Method according to Claim 1 , wherein the thermally meltable powder polymers may be paints, glues, insulating and protecting layers and the like. 6) Method according to Claim 1, wherein the thermally meltable powdered polymers may be thermosetting or thermoplastics. 7) Method according to Claims 5-6, wherein the powdered thermosetting and thermally meltable polymers may be selected from the following groups: A) Epoxy or glycidil compound in combination with di-or polyamines, or dicyandiamide and/or substituted dicyandiamides, or saturated or unsaturated carboxylated polyesters, carboxylated acrilics or polyanhydride or polycarboxylic compounds; B) Hydroxylated compounds such as saturated and unsaturated polyesters, acrylics and the like, in combination with polyanhydrides, or block polyisocyanates or polyurethiodiones; C) Carboxylated compounds such as polyesters or acylics in combination with hydroxyalkylamides; D) Unsaturated polyesters and/or acrylated acrylics and the like in combination with photoinitiators and subsequent use of UV lamps or in combination with dialkyl or diacyl peroxides, or peroxyesters or peroxy chetals thermally activated at temperatures higher than the melting point; and E) Mixtures of groups A, B, C and D. 8) Method according to Claims 5-6, wherein the thermoplastic powdered polymers may be selected from the following groups; A) Poly (meth) acrylates such as polymethacrylate, polycyclohexyl (meth) acrylate, polyisobornyl (meth) acrylate, polytrifluoroisopropylmethacrylate and the like; B) Polyesters such as polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate and the like; C) Polyolefins and polyol olefins such as polyethylene, polypropylene, polytrifluorochloro ethylene, polyethylene acryl carboxylated copolymer and the like; D) Polystyrene, polystyrene oxide, A B S and polyhydroxyoxides; E) Vinyl and/or Vinylidene polymers such as polyvinyl alcohol, polyvinyl acetate, polyvinylacetal, polyvinyl chloride (PVC), polyvinyl formal, polyvinylcarbazole and the like; F) Polyamides such as Nylon and the like; G) Polycarbonates; H) Cellulose derivatives such as Acetobutyrate, Acetopropionate, triacetate and the like; I) Thermoplastic Hydrocarbon Resins; J) Indene, Cumarone, Cycloparaffinic Resins and the like.

Inventors: FARRONATO SILVESTRO, GAZZEA SERGIO, MARIKAR FARUQ, FARRONATO, SILVESTRO, GAZZEA, SERGIO, MARIKAR, FARUQ
Applicants: FARRONATO SILVESTRO, GAZZEA SERGIO, MARIKAR FARUQ, VIANOVA RESINS S P A, FARRONATO, SILVESTRO, GAZZEA, SERGIO, MARIKAR, FARUQ, VIANOVA RESINS S.P.A.
Application year: 1997
Main classification: B05D1
IPC codes: B05D1, B05D3