System and method for reducing draw resonance in plants for the production of plastic film

Abstract

A system and method for reducing draw resonance of plastic material in the molten state, so-called melt, leaving an extrusion group of a plant for the production of plastic film, includes at least one thermostatically-controlled cylinder, having an embracement angle, of the melt on the cylinder, adjustable on the basis of the process rate, i.e. the linear movement speed of the plastic film, and/or on the basis of the temperature measured in the proximity of or in correspondence with the clamping area of the melt in a thermoforming, calibration and cooling group included in the plant and positioned downstream of the system.

Claims

1. A system for reducing draw resonance of a melt of plastic material in molten state, leaving an extrusion group of a plant for production of plastic films, comprising: at least one thermostatically-controlled cylinder, having an embracement angle of the melt on the thermostatically-controlled cylinder, adjustable based on one or more of: process rate, the process rate comprising a linear movement speed of a plastic film, or temperature measured in proximity of or in correspondence with a clamping area of said melt in a thermoforming, calibration and cooling group included in said plant and positioned downstream of said system.

2. The system according to claim 1, wherein temperature regulation of said cylinder is performed through a heat-transfer fluid in liquid state conveyed by a rotating joint positioned coaxially inside said thermostatically-controlled cylinder.

3. The system according to claim 1, wherein temperature regulation of said thermostatically-controlled cylinder is performed through a heat-transfer fluid in gaseous state that flows from one or both bases of said cylinder and exits from holes provided on at least part of a mantle of thermostatically-controlled said cylinder.

4. The system according to claim 1, further comprising one or more of a regulation system of a horizontal movement or a regulation system of an angular movement of said thermostatically-controlled cylinder.

5. The system according to claim 1, wherein the embracement angle ranges from 0° to 180°.

6. The system according to claim 1, wherein the temperature of said cylinder ranges from 10 to 200° C.

7. The system according to claim 1, wherein said thermostatically-controlled cylinder is rotating or non-rotating.

8. A plant for production of a film made of a plastic material comprising: at least one extrusion group; at least one thermoforming, calibration and cooling group; and downstream of said at least one extrusion group, at least one system reducing draw resonance of a melt of the plastic material in molten state, leaving the extrusion group comprising: at least one thermostatically-controlled cylinder, having an embracement angle of the melt on the thermostatically-controlled cylinder, adjustable based on one or more of: process rate, the process rate comprising a linear movement speed of the film, or temperature measured in proximity of or in correspondence with a clamping area of said melt in a thermoforming, calibration and cooling group included in said plant and positioned downstream of said system.

9. The plant according to claim 8, wherein the plant is adapted to form flat-die film, causing the plant to be a cast film plant.

10. The plant according to claim 8, wherein, in correspondence with or in proximity of the clamping area, there is a detection sensor of the temperature of the melt.

11. A method of reducing draw resonance of a melt of a plastic material in molten state, leaving an extrusion group of a plant for production of a plastic film, comprising: between an extrusion step of the melt and a clamping step performed by at least one thermoforming, calibration and cooling group of the plant, causing a temperature regulation step of the melt performed through passage of said melt over at least one thermostatically-controlled cylinder, having an embracement angle, of the melt on said cylinder, adjustable based on: process rate, the process rate comprising one or more of a linear movement speed of the plastic film, or temperature measured in proximity of or in correspondence with the clamping area of said melt.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The structural and functional characteristics of the present invention and its advantages with respect to the known art will appear even more evident from the following description, referring to the enclosed schematic drawings, which show an embodiment example of the same invention:

[0037] In the drawings:

[0038] FIG. 1 is a transversal section of an extrusion plant of plastic film provided with a system according to the present invention;

[0039] FIG. 2 is a longitudinal section of a system according to the present invention;

[0040] FIG. 3 is a transversal section of an extrusion plant of plastic film provided with a system according to the present invention illustrating the two limit positions for the embracement angle of the thermostatically-controlled cylinder.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0041] With reference to the figures, FIG. 1 shows an extrusion plant for the production of film made of plastic material comprising at least one extrusion group 2 and, downstream of said extrusion group 2, at least one thermoforming, calibration and cooling group 3, for the formation of a mono-or multi-layer film.

[0042] According to the present invention, said plant is provided with a system 1 for the temperature regulation of the melt positioned upstream of said at least one thermoforming, calibration and cooling group 3.

[0043] Said apparatus can be provided in plants with a flat-die extrusion technology (cast film).

[0044] The system 1 object of the present invention, which allows a reduction in the draw resonance of the plastic material in the molten state, so-called melt 12, leaving an extrusion group 2 of a plant for the production of plastic film comprises at least one thermostatically-controlled cylinder 10, having an embracement angle A, of the melt 12, falling from the extrusion group 2 onto said cylinder 10, adjustable on the basis of the process rate, i.e. the linear movement speed of the plastic film and/or on the basis of the temperature measured in the proximity of or in correspondence with the clamping area 13 of said melt 12 in a thermoforming, calibration and cooling group 3 included in said plant and positioned downstream of said system 1.

[0045] Said cylinder 10 is preferably made of steel.

[0046] According to an embodiment, the temperature regulation of the cylinder 10 is effected through a heat-transfer fluid in the liquid state, such as water, oil or the like, conveyed by a rotating joint 11, positioned coaxially inside said cylinder 10.

[0047] Alternatively, the regulation of the surface temperature of the cylinder 10 can be effected by means of a heat-transfer fluid in the gaseous state.

[0048] The blowing of air or vapour inside the cylinder 10 can be provided, using any suitable means, such as a compressor or fan, creating a flow with an adjustable temperature and flow-rate, as said cylinder 10 is provided on at least part of the mantle with holes for the outflow of said air or vapour.

[0049] The blowing of air or vapour can be effected from one or both of the bases of said cylinder 10, to be discharged from the holes directly against the surface of the melt 12 falling from the extrusion group 2, thus causing a controlled cooling thereof and consequently eliminating the “draw resonance” phenomenon.

[0050] The flow of fluid, such as oil, water or the like, allows the surface temperature regulation of the cylinder 10 in an operating range that can vary from 10° C. to 200° C.

[0051] The system 1 comprises regulation means of the horizontal movement and/or regulation means of the angular movement of said cylinder 10.

[0052] Said embracement angle A can be varied:

[0053] by means of a horizontal movement within guides 14 secured by a pair of adjustment screws 15,

[0054] by means of an angular movement by rotation of the supporting levers 16 of the cylinder 10 around a fulcrum 17, by means of a second pair of adjustment screws 18.

[0055] The combination of the horizontal and angular movements allows the embracement angle A of the melt 12 on the cylinder 10 to be consistently varied.

[0056] As illustrated in FIG. 3, the embracement angle A can be preferably varied from 0° (no contact) up to about 180°.

[0057] The variation in the embracement angle A and the management of the surface temperature of said cylinder 10 therefore ensures, with great accuracy, the management of the temperature of the melt 12 at the moment of clamping 13, as it allows heat to be supplied or removed.

[0058] Said cylinder can be either rotating or non-rotating.

[0059] The motorization of the cylinder 10 is ensured by an external motorization 19 connected to the same cylinder 10, preferably but not exclusively, by means of a universal joint 20, which guarantees the management of the rate of the cylinder 10 independently of the other rotating elements, forming the extrusion and production line of plastic film.

[0060] This motorization can in any case also be adopted for other rotating elements of the extrusion and production line of plastic film, such as one or both cylinders forming the clamping 13, by means of transmission belts or any other known movement transmission system.

[0061] As an alternative to a rotating cylinder 10 and therefore motorized, a non-rotating cylinder 10, and therefore fixed, can be provided, but whose position can be equally adjusted analogously to what is described above.

[0062] According to an embodiment, a non-rotating cylinder can be provided, thermoregulated by means of an air flow: this embodiment avoids the use of both the motor 19 and the consequent universal joint 20, and also the hydraulic joint 11 for the passage of the carrier fluid, reducing the cylinder 10 to a kind of “tube” through which air passes, blown by a fan, a compressor or any other system suitable for creating a well-defined flow of air, whose flow-rate and temperature can be regulated.

[0063] An object of the present invention also relates to a plant for the production of film made of plastic material comprising:

[0064] at least one extrusion group 2;

[0065] at least one thermoforming, calibration and cooling group 3;

[0066] downstream of said at least one extrusion group 2, at least a system 1 for reducing the draw resonance of the plastic material in the molten state, so-called melt 12, leaving an extrusion group 2 produced as described above.

[0067] The plant is preferably a plant for the formation of flat-die film, a so-called cast film plant.

[0068] According to the present invention, a detection sensor of the temperature of the melt 12 is provided in correspondence with or in the proximity of the clamping area 13.

[0069] The temperature of the melt 12 is measured with great accuracy by means of a temperature sensor which exploits the known infrared technology, or using any other detection system; said temperature measurement is therefore used as reference for:

[0070] managing the embracement angle A of the cylinder 10 with the melt 12;

[0071] regulating the temperature of the cylinder 10 by adjustment of the temperature and/or flow-rate of the cooling fluid.

[0072] A further object of the present invention relates to a method for reducing the draw resonance of plastic material in the molten state, so-called melt 12, leaving an extrusion group 2 of a plant for the production of plastic film wherein, between the extrusion step of the melt 12 and the clamping step 13 effected by at least one thermoforming, calibration and cooling group 3 of the plant, there is a temperature regulation phase of the melt 12 effected through the passage of said melt 12 over at least one thermostatically-controlled cylinder 10, having an embracement angle A, of the melt 12 on said cylinder 10, adjustable on the basis of the process rate, i.e. the linear movement speed of the plastic film and/or on the basis of the temperature measured in the proximity of or in correspondence with the clamping area 13 of said melt 12.

[0073] The forms of the structure for implementing the system and method of the present invention, as also the materials and assembly modes, can naturally differ from those shown for purely illustrative and non-limiting purposes in the drawings.

[0074] The protection scope of the present invention is defined by the enclosed claims.