PROCEDIMENTO E DISPOSITIVO PER IL TRATTAMENTO DI RIVESTIMENTI DI CONTENITORI IN RESINA TERMOPLASTICA.

Description

NOTARBARTOLO & CERCASI SpA V DESCRIPTION ,. ., £ fj 9 2 A ° in support of a patent application for an industrial invention entitled: “Process and device for the treatment of thermoplastic resin container coatings” Anomedi SIPAS.pA Based in VITTORIO VENETO (TV) Inventors: Matteo ZOPPAS, Alberto ARM ELLIN, Andrea SARAN, Ottorino VENDRAMELLI. Deposited with the number * ** *** ** * Field of invention The present invention relates to a process and the related implementation device for treating thermoplastic resin container coatings and, more specifically, it relates to a process, and the related implementation device, for drying protective paints deposited on thermoplastic resin containers, in particular bottles. State of the art In the field of containers, particularly for food, and more specifically for liquid containers, the use of thermoplastic materials such as PET (polyethylene terephthalate) has long been established. Although these containers can be of various types, they will be referred to here generically as bottles, which are in fact the most commonly used containers. Bottles made using these thermoplastic materials are undoubtedly convenient in terms of lightness, impact resistance, cost and the like, but they also have some drawbacks. For example, a A certain microporosity of the material, combined with the limited wall thickness, makes the bottle permeable to gases. This allows both oxygen to penetrate the bottle, causing changes in the contents, for example through oxidation, and the carbon dioxide present in many beverages to escape, making the drinks less fizzy and less palatable. Many solutions have been proposed to address these problems. One suggestion is to increase the bottle wall thickness, which naturally increases production costs and can cause manufacturing problems. Using multilayer bottles has also been proposed, but this also increases production costs and complexity. Yet another proposed solution is to deposit a thin barrier layer on the inside wall of the bottles; this solution, too, is complex and expensive. The problem of obtaining a gas barrier layer appears to have a simple and effective solution with the painting of the outside of the bottles, especially by dipping. For example, U.S. Patent 5,658,619 describes a process for coating bottles in which the bottles are fed to a coating section, where they are each gripped and dipped into a container that is part of a plurality of containers into which the coating solution, consisting of resin dispersed in a solvent, is placed, with only one bottle at a time being present in each of the containers; after being extracted from the coating solution, the bottles are released and then fed to an evaporation section, during which time the bottles are NOTARBARTOLO & GSpVASI SpA pours the solvent from the coating solution into the bottle. Once evaporation is complete, the bottles are sent to a cross-linking section, where the resin forming the coating is cross-linked. Such a system appears complex and presents several critical points, particularly the possibility of paint dripping during the dripping phase, when transferring from the coating to the evaporation stage. Furthermore, eliminating the paint solvent through simple evaporation is a lengthy and poorly controlled process. In some cases, the paints used use water as a solvent, to save costs and reduce pollution. However, the paint dries slowly, requiring either excessive drying times or heating the bottles to a temperature that facilitates rapid solvent removal. If you want to work as quickly as possible, this temperature is dangerously close to, if not higher than, the softening temperature of the thermoplastic material used to make the bottles. It is therefore very important to design a paint drying system that allows for operation without any risk of damaging the bottles and, at the same time, guarantees treatment methods and limited drying times after painting, such as to avoid possible irregularities in the paint thickness. A simple way to dry such water-based paints is to heat them, for example by exposure to infrared (IR) radiation. An infrared heating system is described, for example, in patent application PCT / EP00 / 10540, in the name of the same applicant, which, however, refers to a system for conditioning preforms to be sent for final forming, i.e., for bringing said preforms to a temperature suitable for final forming. In this document, the preforms are passed past a series of IR lamps, while a controlled flow of air at room temperature is passed first around the preforms and then over the IR lamps to cool them. This solution, although interesting, concerns unpainted preforms, which simply need to be heated to a specific temperature, with different treatment methods and short heating times. Summary of the invention The present invention relates to a process for perfectly drying a protective layer placed on containers, in particular bottles, made of thermoplastic material to reduce the permeability of the bottle itself to gases which, by penetrating or exiting the bottle, could cause qualitative alterations to the contents. Another object of the present invention is a process for drying a protective layer deposited on containers, in particular bottles, made of thermoplastic material without causing overheating of the thermoplastic material, and therefore distortion of the bottles and waste of energy. Another object of the present invention is a system for carrying out the above-mentioned process. These and other objects of the present invention will be made clear by the following detailed description, relating to currently preferred embodiments, but which absolutely do not exclude possible further variations and improvements. Description of the invention The present invention relates to a process in which thermoplastic bottles, gripped at the mouth by special, uniformly spaced grips, are immersed in a solution of resin in a solvent to form a protective layer on their external surface, said solvent having subsequently evaporated, characterised by the following steps: (i) passing the covered bottles, from whose surface the excess resin solution has been removed, in a manner per se known, through a first zone of a treatment oven, located beneath heating elements spaced apart from each other; (ii) passing a flow of air, taken from outside the treatment oven, inside said first zone of the oven, from the bottom upwards first around the bottles and then over said heating elements;(iii) sending said bottles, after they have passed under the heating elements, into a second zone of the oven, above said heating elements; (iv) passing the flow of air, which has previously passed over said heating elements, around the bottles in said second zone; (v) mixing at least part of the flow of hot air exiting said second zone with the air taken from outside before it is sent to said first zone of the oven.; Inside the drying oven, in both the first and second zones, the bottles are kept in a horizontal position. This process is further characterized by the fact that the radiation emitted upward by the heating elements is reflected back towards the bottles by means of a reflective element, which also allows the flow of air that has passed the heating elements to pass towards the second zone. This reflective element is suitably uniformly perforated over 10-30% of its surface, preferably 15-25%. The elongated heating elements consist of a plurality of infrared (IR) lamps, preferably arranged in multiple distinct groups. These heating elements are arranged with their major axes horizontal. The air flow that passes over the bottles, passing under the heating elements, has a temperature between 50 and 70 °C and a speed, around the bottles, between 1.5 and 2.5 m / s, these parameters being controlled and regulated so that the temperature of the bottles under the heating elements never exceeds 65 °C. Subsequently, the air flow, which has reached a higher temperature of approximately 60 to 80 °C as it passes through the heating elements, again encounters the bottles already treated in the oven in the second zone of the oven above the heating elements, at a speed of 1.5-2.5 m / s, so that the temperature of the latter here too does not exceed 65 °C. The power emitted by the lamps, the air flow, the residence time of the bottles and the % of air recirculation in the oven are balanced among themselves so that, in the first area of ​​the oven, with infrared heating, 75 to 95% of the solvent is removed from the coating, preferably 85 to 92%, the remainder being removed in the second zone of the oven, with hot air. In this way, that is, by removing only part of the solvent from the coating in the first zone of the oven, it is possible to very well control the temperature reached by the bottles under the heating elements, so as not to cause distortion of their walls or crystallization of the resin. The hot air from the first oven zone is, as previously seen, used again to remove residual solvent from the coating in the second oven zone, avoiding energy waste. Furthermore, the air exiting the second oven zone is, at least partially, directed back into the first oven zone, allowing not only further energy savings but also easier maintenance of the desired temperature in the first and second oven zones, resulting in excellent process consistency regardless of ambient temperature. Furthermore, it is expected that part of the cold air conveyed from outside the oven is diverted, before entering the first zone of the oven, to keep the necks of the bottles at a temperature not exceeding 55 °C. The bottles are kept in a horizontal position throughout the drying treatment and, at least in the infrared oven, are kept rotating at a speed between 100 and 300 rpm. The infrared lamps are of the “medium wave” type and the time spent in front of the lamps is between 15 and 30 seconds, preferably of 25 sec. The device which is the object of the present invention will now be described, in an absolutely exemplary and non-limiting manner of the scope and breadth of the invention itself, in relation to a preferred embodiment thereof, shown in the attached drawing tables in which: Figure 1 is a vertical cross-section of a first realization of the plant; Figure 2 is a vertical cross-section of a second embodiment of the plant; Figure 1 represents the basic cell of the system according to the present invention. It is made up of a chamber 1, delimited by walls 8, 15, 17 and 18, characterised by comprising (i) a first lower zone 2 for treating bottles 4 and a second upper zone 5 for treating bottles, (ii) an oven 2' placed inside the zone 2, equipped with means 3 suitable for emitting thermal radiation, for example infrared lamps, and delimited by a wall 14, by part of the external wall 17, by an upper wall 10 and by a lower wall 11, both suitable for reflecting the thermal radiation and for allowing the passage of a gaseous flow, (iii) means, known in themselves and not shown in the figures, suitable for producing a flow 6 of ambient air and for regulating its flow rate, (iv) a chamber 12 suitable for receiving said flow 6, delimited by the walls 8, 15 and by a door 7, communicating with a vertical duct 19, delimited by the wall 8 and by the element 9, in turn communicating with said lower zone 2, (v) a chain .which has a plurality of pads 13 suitable for gripping and holding. hold the bottles, said plates, when in proximity of the oven 2', passing outside the oven itself, parallel to the wall 14, equipped with an opening suitable for allowing the passage of the neck of the bottles, said wall 14 also allowing the neck of the bottles to be kept out of the oven 2' and acting as a divider of the air flow 6. In operation, the bottles 4 enter the oven 2' at position 4", i.e., near the lamps, pass through the entire oven in this position, then exit the oven, rise upwards, and are brought to position 4". Meanwhile, a flow of air 6, generated and regulated by means not shown, passes from chamber 12 to the lower area 2 through duct 19; upon reaching said area, the air flow is divided by wall 14 into two parts, a first part passing through wall 11 to enter the oven 2', control the temperature of the bottles, and thus cool the means 3 for emitting thermal radiation, or heating, and a second part passing upwards outside the oven 2', touching wall 14 to keep the necks of the bottles 4 cool, held by the plates 13. The first part of the air flow, once the heating means 3 have cooled, passes through the wall 10 and rises towards the upper area of ​​the chamber 1, where it grazes the bottles in position 4'”, completing the drying of the paint, and then passes into the exhaust chamber 16. In this chamber, the flow of hot air is at least partially sent back into the chamber 12 by means of the door 7, to recover heat and keep the temperature of the oven 2' constant. In case you don't have enough space, in length, to manage a At a given production level, it is possible to place two sections of the system side by side, instead of having them in line, as shown in Figure 2, where all the parts are numbered exactly as in Figure 1. In this case, the bottles follow the following path, considered according to the surface of the drawing sheet: starting from the right, they enter chamber 1 at position 4”, pass through oven 2' towards the observer, then bend to the left, enter oven 2' a on the left side of the system, following it so as to move away from the observer; at this point they rise to position 4”'a, pass through the upper zone 5a on the left side of the system coming back towards the observer, bend to the right and finally enter at position 4'” in section 5 which they travel along completely, moving away from the observer, towards the exit from the drying system. NOTARBARTOLO & GER\|ASI SpA

Claims

claims 2 0 0 2 R 000452 1. Process for the treatment of thermoplastic bottle coatings, coming from a plant in which each of said bottles has its neck arranged within uniformly spaced plates connected to a drive chain, and is immersed in a solution of resin in a solvent to form on its external surface a gas barrier and protective coating, the excess paint being appropriately removed and said solvent being subsequently evaporated, characterised by the following steps: (i) passing the bottles through a first zone (2') of a treatment oven, located below spaced heating elements; (ii) passing a flow of air, taken from outside the treatment oven, inside said first zone (2') of the oven, from the bottom upwards first around the bottles and then over said heating elements;(iii) sending said bottles, after they have passed under the heating elements, into a second zone of the oven, above said heating elements; (iv) passing the flow of air, which has previously passed over said heating elements, around the bottles in said second zone; (v) mixing at least part of the flow of hot air exiting from said second zone with the air taken from outside before it is sent to said first zone of the oven.; 2. Process according to claim 1, wherein said heating elements consist of a plurality of infrared (IR) lamps of the “medium wave” type.

3. Process according to claim 2, wherein said lamps in the infrared they are arranged in a plurality of distinct groups.

4. Process according to claim 1, wherein said air flow in said first zone (2') has a temperature between 50 and 70 °C, and a speed around the bottles between 1.5 and 2.5 m / min.

5. Method according to claim 4, wherein said parameters are regulated by appropriately modifying the flow rate of air admitted from outside the system and the quantity of hot air coming from said second zone and mixed with said air flow.

6. Process according to claim 1, wherein said flow of air which, in passing through the heating elements, has reached a temperature of between 60°C and 80°C, still encounters, at a speed of between 1.5 and 2.5 m / s, in the second zone of the oven, above the heating elements, the previously treated bottles and maintains them at a temperature below 65°C.

7. Process according to claim 1, wherein the power emitted by the heating elements, air flow rate, % air recirculation and residence time of the bottles in the oven are balanced so that, in the first zone of the oven, 75 to 95% of the solvent is removed from the coating, the remainder being removed in the second zone of the oven.

8. The process of claim 7, wherein the amount of solvent removed from the coating is between 85 and 92%.

9. Process according to claim 2, wherein the flow of hot air exiting from said second zone after having completely dried the coating is recycled into the oven, in a quantity between 0 and 90%.

10. Process according to claim 5, wherein the period of time during which the bottles remain in front of the lamps is between 15 and 30 seconds.

11. Process according to claim 5, wherein the period of residence of the bottles in front of the lamps is 25 seconds.

12. Device for the treatment of bottle coatings made of thermoplastic material according to the process described in claim 1, comprising a chamber (1), delimited by walls (8, 15, 17 and 18), characterised by comprising (i) a first lower zone (2) for treating bottles (4) and a second upper zone (5) for treating bottles, (ii) an oven (2') placed inside the zone (2), equipped with means (3) suitable for emitting thermal radiation and delimited by a wall (14), by part of the external wall (17), and by an upper wall (10) and a lower wall (11), both suitable for reflecting the thermal radiation and for allowing the passage of a gaseous flow, (iii) means, suitable for producing a flow (6) of ambient air and for regulating its flow, (iv) a chamber (12) suitable for receiving said flow (6), delimited by the walls (8, 15) and by a door (7), communicating with a vertical duct (19), (v) a chamber (12) suitable for receiving said flow (6), delimited by the walls (8, 15) and by a door (7), communicating with a vertical duct (19),delimited by the wall (8) and by the element (9), in turn communicating with said lower area (2), for the passage of the air flow from the chamber (12) to the area (2); (v) - a chain on which are fixed a plurality of plates (13) suitable for gripping and supporting the bottles, said plates, when in proximity of the oven (2'), passing outside the oven itself, parallel to the wall (14), equipped with an opening suitable for allowing the passage of the neck of the bottles, said wall (14) also allowing the neck of the bottles to be kept outside the oven (2') and acting as a divider, 13.

14. of the air flow (6). Device according to claim 12, wherein the door (7) divides the air inlet chamber (12) from an exhaust chamber (16) from which the air, after having passed from the lower zone (2) to the upper zone (5), having been heated by the heating elements (3) in the passage, is discharged to the outside, said door (7) being able to be operated to re-admit part of the hot air exiting from the chamber 16 into the chamber (12). Device according to claim 12, wherein said wall 14 also serves to deflect part of the air flow coming from the duct 19, inside the zone 2 to send it to the plates 13 and cool the necks of the bottles. / GM-BCQ Rome, September 9, 2002 For SIPA SpA The Never Dr. Giulio Mariani NOTARBARTOLO & GERVASI SPA