APPARATUS AND PROCESS FOR THE MANUFACTURING OF SHEETS OF SAFETY GLASS WITH A SUPERFICIAL COATING OF PLASTIC MATERIAL

Abstract: An apparatus for the manufacture on a commercial scale of safety glass sheets for motor cars and/or build­ ings, having a superficial coating of plastic material, comprises and automatical activated and self-propelling carriage (5) for carrying out the operations of spraying, centrifugation and irirradiation of the plastic coating on the glass. The carriage follows a closed ring path to be able to effect the operations a number of times such as to be sufficient for obtaining a desired thickness of coating.

Description: Background of the Invention 1. Field of the Invention The present invention relates to an apparatus and process for the manufacturing of a sheet of safety glass, for use in motor cars or buildings, provided with a coating of plastic material for improving its behaviour on breaking. 2. Desription of the Prior Art Sheets of safety glass are known in the prior art typically comprising a glass substrate and a coating of plastic material applied on one of the two surfaces of the sheet. In the case of use of such safety glass as a motor car windscreen, the plastic coating serves to avoid injuries to the passengers caused by sharp fragments in the case of breaking. Moreover the plastic coating should also have particular mechanical and optical properties, such as properties of non-tearing, self-healing, resistance to abrasion and to ageing, in order to meet the tests required by the International Standards, such as DIN, ECE, ASA standards and the like. Compositions and methods are known in the prior art for producing a coating of plastic material to be applied on a glass substrate. Typically, Italian published application n. 19459A/86 (corresponding to EP-A-0 233 519, priority: 19.02.86; date of publication of application: 26.08.87) describes a composition based upon polycaprolactones, acryl monomers, aliphatic polyisocyanates, flowing agents, reaction catalysts and the like selected and mixed one to the other, in such a way as to be particularly able to form a plastic coating with the desired optical and mechanical features and able to provide the glass substrate with the required safety characteristics. A composition of this type is sprayed in a liquid state with a viscosity from 40 to 200 mPa·s (centipoise) on a glass substrate which, in the case of use in motor cars, has been previously cut and curved to the desired configuration. Immediately after spraying, the glass substrate is caused to rotate horizontally at a speed from 10 to 50 rpm, so as to ensure a levelling of the liquid film and maintaining of a uniform thickness on the whole surface of the substrate. The polimerization of the sprayed liquid takes place directly on the substrate to which the coating intimately adheres and successive treatments by infrared and ultraviolet irradiation help to complete it. As in a single spraying operation it is advisable to lay a thickness from 80 to 150 µm, further spraying and polimerization operations can be carried out to reach a coating thickness sufficient to provide the glass with the desired safety characteristics. For the manufacture on a commercial scale of safety sheets of glass provided with a plastic coating of high optical and mechanical quality, typically obtained by a composition and a process as previously described, the problem arises of ensuring a sufficient centrifugal force to the liquid layer during the treatment by infrared and ultraviolet irradiation and moreover it is necessary to have the possibility of repeating the coating and polimerization process a number of times until the desired thickness is obtained without affecting the production times. Summary of the Invention An object of the present invention is an apparatus for the application of a coating of plastic material including a plurality of machines for effecting spraying and irradiation operations in series for the manifacture of a sheet of safety glass of the type having said coating applied on one of its two opposed surfaces by said spraying and irradiation operations, said apparatus comprising: a closed ring track along which a sheet loading station, a spraying station, infrared and ultraviolet irradiation stations and a sheet unloading station are positioned in successive relationship; a self-propelling carriage running along said track; a power supply borne on said carriage; a control processor unit for programming and controlling said operations, borne on said carriage and powered by said power supply; an electric motor for driving said carriage, borne on said carriage, powered by said power supply and controlled by said processor unit; a rotary shaft vertically mounted on said carriage in driving connection with said electric motor; a frame fixed horizontally on top of said shaft for receiving at said loading station said sheet of glass to be subjected to said operations; suction cups fixed to said frame for retaining said sheet; said processor unit being programmed to provide control instructions for cyclically subjecting said sheet of glass to said spraying and irradiation operations a number of times sufficient to obtain a desired thickness of coating on said sheet and simultaneously rotating said sheet for a centrifugation of said coating after said spraying operation and during said irradiation operations. A further object of the present invention is a process for the application of a coating of plastic material including spraying and irradiation operations in series for the manufacture of a sheet of safety glass of the type having said coating applied on one of its two opposed surfaces by said spraying and irradiation operations, said process comprising: positioning said sheet of glass on a self-propelling carriage provided with an electric motor and a control processor unit for controlling and programming said operations; carrying said sheet of glass along a closed ring path for subjecting it successively to operations of spraying, infrared irradiation and ultraviolet irradiation and rotating said sheet horizontally for centrifugating said coating during the irradiation operations; and cyclically repeating said steps a number of times sufficient to obtain a coating of a desired thickness on said sheet. The advantages obtained with the present invention consist in that it is possible to realize a carousel of carriages, each carriage being able to centrifugate the sheet of glass during its travel, capable of obtaining different depths of coating for each sheet depending on the individual requirements, thus making the plant fit to respond to the requirements of furnishing different types of final product without effecting the production times. It has to be understood, however, that while the apparatus and process according to the present invention are particularly referred to a coating obtained with the compositions described in the Italian published patent application number 19459A/86, the same apparatus can be advantageously used for the manufacturing on a commercial scale of sheets of safety glass with plastic coating formed by other types of compositions. Moreover the glass substrate can be a sheet of laminated safety glass, tempered or half-tempered safety glass, or curved or flat monolithic glass. Brief description of the Drawings The present invention will be better understood with reference to the accompanying drawings in which, for an illustrative and not limitative purpose, the manufacture of a curved safety glass for motor cars is illustrated. Figure 1 shows a general and schematic view of the apparatus for the manufacture of safety glass sheets according to the present invention; figure 2 shows a side view of the automatic and self-propelled carriage, object of the present invention; and figure 3 shows a plan view of the carriage of figure 2. Description of the preferred embodiment Referring to figures 1 to 3, a plant for the manufacture of sheets of safety glass according to the invention comprises a horizontal conveyor 1, a machine 2 for washing and drying the sheets of glass, horizontal conveyor belts 3, a machine 4 for loading the sheets of glass and a carriage 5, receiving said glass. Additionally the plant comprises a spraying station or device 12, a tunnel oven 13 for infrared irradiation, a tunnel oven 14 for ultraviolet irradiation, a machine 15 for unloading the coated sheets of glass from the carriage, a tunnel oven 16 for infrared irradiation and a successive hot air tunnel oven 17 for completing the polimerization reaction. A sheet of glass previously cut and curved, is loaded on the conveyor table 1 and introduced into a room A, which is carefully insulated from the outside and dust-free. The sheet is washed and dried by the machine 2 and then transferred by means of the conveyors 3 and the machine 4 to the carriage 5. The carriage 5 is powered by means of a bank of batteries mounted directly on board, so as to be completely independent from the rest of the manufacturing line. An electric motor also mounted on board the carriage, enables the travelling to be effected by operating metal wheels 6 rolling on a closed ring metal track secured to the floor, the path of which is indicated in 7. In order to control the operation sequence, on the carriage 5 a control processor unit is mounted provided with a programmable unit for the control of the production cycle. The carriage 5 is capable of carrying out the following operations in a self-sufficient manner: travelling along the track 7, centrifugation of the sheet of glass, production of vacuum to enable the sheet to be fixed, speed regulation and control in relation to the operation being carried out. The carriage 5 is provided with a mechanical system for the centrifugation of the sheet of glass. In fact the sheet is positioned on a frame 9 (fig. 2, 3) provided with suction cups 10 and horizontally rotated by a rotating shaft 8 having a vertical axis. The angular speed of the shaft can be controlled in a continuous manner at about 200 rpm. On the same rotating shaft 8, a frame 11 is fixed having the same configuration as the sheet to be coated and on which the sheet is positioned. The frame 11, by means of its outer rim, serves the purpose of preventing the liquid laid on the concave curved area of the sheet from dropping beyond the edge of the sheet, and wetting the underlying surface. Once centered on the carriage 5, the sheet of glass is fixed to the frame 11 by means of the suction cups 10. The carriage 5 starts its travel and following the path of the track 7 moves to the spraying station 12 where it stops and an amount of liquid is sprayed to obtain a coating depth from 80 to 150 µm. As soon as the spraying is completed, the shaft 8 starts to rotate with an angular speed from 10 to 50 rpm. At the same time the carriage 5 moves again and passes through the tunnel oven 13 where it is subjected to an infrared irradiation for a time from 5 to 10 minutes. Successively the carriage 5 passes through the tunnel oven 14 where it is subjected to an ultra-violet irradiation for a time of from 2 to 10 seconds. Upon completion of the ultraviolet irradiation, the movement of the shaft 8 is stopped. The carriage 5 runs the remaining portion of the track 7 reaching an unloading station where a machine 15 takes the sheet from the carriage 5 and delivers it to a first tunnel oven 16 for a final infrared irradiation and to a second tunnel 17 for a final hot air drying. Whenever it is desired to increase the thickness of the polymerized solid coating, the carriage 5 repeats the spraying operation and the infrared and ultraviolet irradiation operations for a number of times necessary to obtain the desired thickness.

Claims: Apparatus for the application of a coating of plastic material including a plurality of machines for effecting spraying and irradiation operations in series for the manifacture of a sheet of safety glass of the type having said coating applied on one of its two opposed surfaces by said spraying and irradiation operations, said apparatus comprising: a closed ring track (7) along which a sheet loading station (4), a spraying station (12), infrared (13) and ultraviolet (14) irradiation stations and a sheet unloading station (15) are positioned in successive relationship; a self-propelling carriage (5) running along said track (7); a power supply borne on said carriage; a control processor unit for programming and controlling said operations, borne on said carriage and powered by said power supply; an electric motor for driving said carriage, borne on said carriage, powered by said power supply and controlled by said processor unit; a rotary shaft (8) vertically mounted on said carriage in driving connection with said electric motor; a frame (9; 11) fixed horizontally on top of said shaft (8) for receiving at said loading station (4) said sheet of glass to be subjected to said operations; suction cups (10) fixed to said frame for retaining said sheet; said processor unit being programmed to provide control instructions for cyclically subjecting said sheet of glass to said spraying and irradiation operations a number of times sufficient to obtain a desired thickness of coating on said sheet and simultaneously rotating said sheet for a centrifugation of said coating after said spraying operation and during said irradiation operations. Process for the application of a coating of plastic material including spraying and irradiation operations in series for the manufacture of a sheet of safety glass of the type having said coating applied on one of its two opposed surfaces by said spraying and irradiation operations, said process comprising: positioning said sheet of glass on a self-propelling carriage (5) provided with an electric motor and a control processor unit for controlling and programming said operations; carrying said sheet of glass along a closed ring path (7) for subjecting it successively to operations of spraying, infrared irradiation and ultraviolet irradiation and rotating said sheet horizontally for centrifugating said coating during the irradiation operations; and cyclically repeating said steps a number of times sufficient to obtain a coating of a desired thickness on said sheet. A process according to claim 2, wherein said sheet is of laminated safety glass. A process according to claim 2, wherein said sheet is of a tempered or a half-tempered safety glass. A process according to claim 2, wherein said sheet is of a previously curved monolithic glass. A process according to claim 2, wherein said sheet is of a flat monolithic glass.

Inventors: CAPRIOTTI, LUIGI, PUCCINELLI, MASSIMO
Applicants: SOCIETA ITALIANA VETRO - SIV S.P.A.
Application year: 1988
Main classification: B32B17
IPC codes: B05D3, B32B17, C03C17, C03C27, B32B37