WO2002020180A1

WO2002020180A1 - Method and machine for applying a thick layer of varnish to facing sheets in roll form

Info

Publication number: WO2002020180A1
Application number: PCT/EP2001/009958
Authority: WO
Inventors: Max Canti
Original assignee: Canti & Figli S.R.L.
Priority date: 2000-09-05
Filing date: 2001-08-29
Publication date: 2002-03-14

Abstract

A method and a machine for applying a thick layer of varnish to sheets used for facing in roll form, comprising the steps of: depositing a lamina of varnisch onto a sheet (2) which unwinds from a roll (1); and cross-linking the lamina to dry the lamina of varnish.

Description

METHOD AND MACHINE FOR APPLYING A THICK LAYER OF VARNISH TO FACING SHEETS IN ROLL FORM Technical field

The present invention relates to a method for applying to thin sheets used for the facing of panels a layer of varnishing or paint whose thickness allows subsequent sandpapering, in order to eliminate any imperfections and to achieve a higher degree of protection and a better finish. The invention also relates to a machine suitable to perform such method. Background art Current varnishing methods do not allow to apply to sheets of decorative paper, PVC, or other materials a layer of varnish whose thickness is such as to allow subsequent sandpapering of the manufactured article and its adequate protection. Varnish can in fact be applied by spray or curtain coating only to panels. For thin facing sheets, a Mayer bar or a flexographic system or roller spreading are used. The Mayer bar, constituted by a cylindrical element covered by a spiral, is capable of depositing only a thin layer of varnish, and if the spiral is not perfectly clean it can cause scoring on the treated surface.

The flexographic system also only allows to deposit a thin layer of varnish.

With roller spreading, the resulting surface has a rough appearance; moreover, the rollers, by wearing out in their active region, can score any wider surfaces treated at a later time. Disclosure of the Invention The aim of the present invention is to deposit, on the thin sheets of various widths that are commonly used for facing panels, a layer of varnish whose thickness is such as to allow its subsequent sandpapering, in order to eliminate any imperfections and achieve a higher degree of protection and a better finish. Another object is to allow the most appropriate choice of the grammage of the varnish applied and to keep it uniform and independent of the sheet advancement speed.

Further objects of the invention are to eliminate varnish reclaiming, consequently eliminating contamination and aging of the varnish and formation of air bubbles.

The above aim and objects, and further objects which will become better apparent hereinafter, are achieved by a method for applying a thick layer of varnish to sheets used for facing in roll form, comprising the steps of: depositing a lamina of varnish onto a sheet which unwinds from a roll; and cross-linking the lamina to dry the lamina of varnish. Brief description of the drawings

The invention is now described in detail with reference to the accompanying drawings, which illustrate only by way of example a preferred embodiment of the machine suitable to perform the method according to the invention, wherein:

Figure 1 is a schematic view of the main elements of the machine. Figure 2 is a cross sectional view of the extrusion head, which deposits a layer of varnish on the sheet; Figure 3 is a front view of a part of the modular extrusion head.

Ways to carrying out the invention

In the figures, the reference numeral 1 designates a roll from which a sheet of paper 2 to be varnished unwinds, and the reference numeral 3 designates a reel for taking up the coated sheet. The reference numerals 4, 5 and 6 designate sheet advancement and guiding rollers. The numeral 7 designates a modular extrusion head, from a lower slit of which a uniform lamina of varnish 8 flows out and is spread onto the advancing sheet 2 at adjustable contrast bars 9. The varnish to be applied is sent to the extrusion head through one or more ducts 10 by means of a variable-speed gear pump 11 applied to a tank 12. The resin contained in the tank is mixed continuously by means of an agitator 13 in order to prevent settling of the photoactivating agent. The tank 12, the duct 10 and the extrusion head 7 are preferably thermostat-controlled in order to control the viscosity of the resin.

In order to achieve different varnishing widths, the extrusion head is divided into multiple side-by-side modules, shown in Figures 3 and 4 which can be activated separately by means of cocks or solenoid-activated valves 14. Moreover, the extrusion head is applied to an adjustable head support, which allows to vary its distance and inclination with respect to the sheet. The mechanism for feeding the sheet to be varnished, contrasted by the brake of the unwinding unit, determines the correct tension of said sheet.

The deposited layer of varnish is then dried by exposure to ultraviolet light emitted by one or more lamps 16 and reflected by mirrors 17 contained within a unit 18. The radiating unit is cooled by means of a delivery duct 19 and a return duct 20. In order to achieve uniform irradiation of the sheet 2, there is a suction belt 15, which is designed to keep the sheet perfectly flat during the step of drying of the varnish.

Since the extruded varnish is deposited entirely onto the advancing sheet, its recycling and the consequent drawbacks mentioned above are eliminated. The speed of the gear pump, the rate of advancement of the sheet, the temperature of the tank, of the extrusion head and of the corresponding duct, the modules to be activated and any other parameters are controlled by means of a computer, so as to obtain a uniform layer of varnish having the chosen grammage. The described method and machine are used to initially distribute the primer or insulating agent onto the sheet in roll form and then to apply the varnish resin by means of the same machine or by means of multiple in-line machines.

From what has been described and illustrated, it is evident that the specified aim and objects have been achieved. The method and the machine according to the invention might also be used for cross-linking processes achieved by means of hot air, infrared rays, electronic bombardment, et cetera, instead of by means of ultraviolet light.

Obviously, the nonessential constructive details might be different from the ones illustrated only by way of non-limitative example without thereby abandoning the scope of the present invention.

The disclosures in Italian Patent Application No. PS2000A000013 from which this application claims priority are incorporated herein by reference.

Claims

1. A method for applying a thick layer of varnish to sheets used for facing in roll form, comprising the steps of: depositing a lamina of varnish onto a sheet (2) which unwinds from a roll (1); and cross-linking the lamina to dry the lamina of varnish.

2. The method according to claim 1, characterized in that said lamina is of photochemical type and is subjected to ultraviolet light.

3. The method according to claim 1, characterized in that said lamina is deposited by means of an extrusion head composed by side-by side modules which can be activated separately depending on the width of the sheet.

4. The method according to claim 3, characterized in that said extrusion head is fed by an adjustable pump.

5. The method according to claim 1, characterized in that it further comprises the step of adjusting the tension of the sheet, a suction belt being provided to ensure the flatness of said lamina deposited onto said sheet when cross-linking is to be performed.

6. A machine for applying a thick layer of varnish to sheets used for facing in roll form, characterized in that it comprises: an extrusion head fed by a pump; a tank adapted to contain said varnish; and an adjustable pump adapted to draw said varnish from the tank and deposit it onto the sheet.

7. The machine according to claim 6, characterized in that it comprises an agitator arranged inside said tank.

8; The machine according to claim 6, characterized in that said tank and said extrusion head are thermostat-controlled.

9. The machine according to claim 6, characterized in that said extrusion head is composed of side-by -side modules which can be activated separately depending on the width of the sheet.

10. The machine according to claim 6, characterized in that said extrusion head is applied to an adjustable head support, which allows to vary its distance and inclination with respect to said sheet.

11. The machine according to claim 6, characterized in that said extrusion > head acts at adjustable contrast bars.

12. The machine according to claim 6, characterized in that it comprises a control unit adapted to control all the parameters of the process.