EP2411748A1

EP2411748A1 - Dehumidifying device for plastics materials

Info

Publication number: EP2411748A1
Application number: EP10716630A
Authority: EP
Inventors: Christian Schiavolin
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-03-23
Filing date: 2010-03-22
Publication date: 2012-02-01
Also published as: HK1165541A1; WO2010109403A1; ITPD20090055A1; TW201111137A; CN102362136A; IT1393394B1; CN102362136B

Abstract

A dehumidifying device (1; 1, 1') for plastics materials, comprising a container body (2; 2, 2') suitable for receiving a predefined amount of plastics material, processing means (20, 30) operatively associated with a processing region provided in said container body (2; 2, 2') for dehumidifying said plastics material in said container body (2; 2, 2'), and a conveying device (13, 13a, 13b, 13c, 18) provided in a conveying region of said container body (2; 2, 2') for conveying said plastics material to said processing means (20, 30) wherein said conveying device (13, 13a, 13b, 13c, 18) is configured in such a manner as to convey the plastics material in a conveying direction (F1) different from an advancing direction (F) of said plastics material in said container body (2; 2, 2').

Description

Dehumidifying device for plastics materials

DESCRIPTION

Technical field

The present invention relates to a dehumidifying device for plastics materials having the features set out in the preamble to the main claim.

The invention also relates to a system for dehumidifying plastics materials and to an installation for processing plastics materials, provided with a dehumidifier for plastics materials according to the invention.

Background art Various production processes including, for example, injection moulding and extrusion, can be used to produce plastics products or semi-finished products.

The plastics material to be processed which, for example, is in the form of granules, also known as "pellets", is stored in suitable containers and is then transformed into finished or semi-finished products in suitable transforming machines, for example, injection presses, extruders, blowers, etc...

However, plastics materials, particularly those that are classified as

"hygroscopic", absorb moisture, mainly from the atmosphere. As well as depending on the type of plastics material, the moisture absorbed also depends, amongst other things, on the exposure to air, and on the time for which the plastics material is stored prior to subsequent transformation and the storage conditions.

Moisture has adverse effects on the transformation process as well as detracting from the aesthetic and, above all, the mechanical characteristics (tensile strength, flexural strength and impact resistance) of the final product.

The plastics material must therefore be dehumidified before it is supplied to the transforming machines. For this purpose, in processes for transforming plastics materials, a dehumidification step is provided for upstream of the transformation step in order to remove the moisture that is present in the plastics material.

The dehumidification step is particularly important for hygroscopic polymers such as, for example, PA, ABS, PET, TPU, and PC which tend to absorb a substantial amount of water easily.

Various drying agents are known for removing the moisture from the plastics material, including, for example, infrared radiation, vacuum, and hot and dry air.

A problem with dehumidification systems which use infrared radiation is due to the low permeability of the plastics material to the radiation and hence to the shallow penetration of the drying radiation.

Because of this, only the plastics material that is close to the radiation device is reached by the infrared radiation sufficiently to trigger dehumidification. However, even a limited thickness of plastics material, for example, of the order of 4-5 cm, screens the infrared radiation, in fact preventing the heating and hence the dehumidification of the underlying plastics material.

The efficacy of the transformation process is therefore appreciably compromised. Dehumidifying devices for plastics materials which comprise a feed screw that conveys the plasties material in an advancing direction, and at least one radiation device, positioned along the advancing path of the plastics material, for heating and dehumidifying the plastics material, are known from US 6,035,546 and from US 4,430,057. However, since, as stated, plastics material has a low heat transfer coefficient, measures are provided for trying to increase the efficacy of the dehumidification.

For this purpose, in US 6,035,546, a screw with a pitch that increases in the advancing direction is provided; this reduces the thickness of the plastics material which develops on the edge of the screw during transportation in the advancing direction and, in particular, in the zone of action of the radiation device.

In US 4,430,057, fins mounted transversely along the edge of the screw are arranged to improve the mixing of the plastics material to be processed. However, known systems still have some disadvantages.

A shortcoming of known systems is that they do not enable a good level of dehumidification to be achieved.

In fact, only partial dehumidification of the plastics material is achieved due to its heating by irradiation with infrared radiation. Another shortcoming of known systems is that the heating, and hence partial dehumidification, process takes place during the transportation of the plastics material in the advancing direction when the plastics material passes through the zone of action of the radiation device/s.

A step that is dedicated to dehumidification is in fact not provided for in the process for treating the plastics material. To try to achieve adequate dehumidification, it is therefore necessary to provide a plurality of radiation devices positioned in cascade, or alternatively to lengthen the path of the plastics material. In known systems, in order to achieve good dehumidification levels, a dry and hot air dehumidification device commonly known as a "post-dryer" is therefore provided downstream of the screw conveyor. This leads to considerable plant costs and to the use of very extensive spaces for housing the apparatus used. For example, for PET, 50 ppm of moisture are normally required for processing in a transforming machine.

At the output from known infrared dehumidifying systems, PET having a moisture content of 200-300 ppm is obtained. The required value of 50 ppm of moisture is obtained only with the use of a hot and dry air post-dryer. Another shortcoming of known systems is that they are not flexible. In order to change the degree of heating/dehumidification, it is necessary to change the length of the feed screw and/or to change the number of radiation devices provided along the screw and/or to change the rate of revolution of the screw and suitably to coordinate and balance these factors in order to optimise the heating/dehumidification process. Another shortcoming of known systems is that, during processing, above all when the material to be processed is post-consumer, recovered material, dust is emitted, mixed with water vapour and possibly other substances that are present in the plastics material. These substances damage the infrared radiation devices of known systems and detract from their radiating power and hence heating/dehumidification efficiency.

Moreover, known processes are continuous and have to be coordinated with the processes upstream and downstream of the dehumidification process. Dehumidifying devices for plastics materials are also known which heat the plastics by conduction. These devices use hot and dry air and/or heating by contact with a resistor.

However, since plastics material is an insulator, it tends to resist this type of heating by conduction; these devices therefore have very long processing times, take up even more space, and have poor heating efficiency. In some of these devices a predetermined degree of vacuum is created whilst the plastics material is heated by conduction; these devices have even lower efficiency since vacuum is an insulator and slows down the heating of the plastics material by conduction. To try to reduce processing times and/or increase the degree of dehumidification, it is necessary to provide very extensive heating elements so as to increase the useful exchange surface used to heat the plastics material and to cause the plastics material to travel along long and intricate paths. The devices obtained are thus difficult to set up, expensive and very bulky. In any case, the efficiency of heating of the plastics material remains low. Devices for heating the plastics material by friction are also known; these devices heat the plastics material by rapid rubbing against metallic surfaces. However, in these devices, the granules or flakes of plastics material are damaged and broken up and large amounts of dust are thus created. Description of the invention An object of the invention is to provide a dehumidifying device which overcomes the shortcomings discussed above with reference to the prior art mentioned.

A further object is to provide a dehumidifying device which has low energy consumption in operation and which enables the plastics material to be processed effectively within considerably reduced periods of time.

A further object is to provide a dehumidifying system which is effective and energy efficient and has low energy consumption.

Finally, another object is to provide a dehumidifier which can also perform crystallization and regrading processes and processes to increase intrinsic viscosity and to "super-clean" amorphous or recycled PET.

A further object is to provide a dehumidifying system which can process recycled plastics material, in particular post-consumer, recycled PET, to produce regenerated PET having the same mechanical and, optionally, hygiene features as virgin PET.

These objects are achieved by the present invention by means of a dehumidifying device and a dehumidifying system for plastics materials implemented in accordance with the appended claims.

Brief description of the drawings The features and the advantages of the invention will become clearer from the detailed description of a preferred embodiment thereof which is described by way of non-limiting example with reference to the appended drawings, in which:

Figure 1 is a diagram of a process for the treatment of plastics materials; Figure 2 is a schematic view of a system for dehumidifying plastics materials according to the invention;

Figure 3 is an enlarged view of the dehumidifying device of the system of

Figure 2;

Figure 3a is a partial, schematic view of the dehumidifying device of Figure 3 showing the movement of the plastics material therein;

Figure 3b is a view of a detail of the dehumidifying device of Figure 3;

Figure 4a is a front view of the radiation devices of the dehumidifying device of Figure 3;

Figure 4b is a side view of the radiation devices of Figure 4a; Figure 4c is a side view of an alternative version of the radiation devices of

Figure 4a;

Figures 5a-5b are front views of another alternative version of the radiation devices according to the invention, in a first and a second operative position, respectively; Figure 6a is a front view of another alternative version of the radiation devices according to the invention;

Figures 6b-6c are side views of the radiation device of Figure 6a in a first and a second operative position, respectively;

Figure 7 is a schematic view of a variant of a dehumidifying system for plastics materials according to the invention; and

Figures 8a-8b are schematic views of the device of Figure 7 which show an alternative version of a loading device in a first and a second operative position thereof, respectively.

Preferred embodiment of the invention Figure 1 shows schematically a process 100 for the transformation of plastics material that can be implemented in a conventional plant for the transformation of plastics materials.

The plastics material may be, for example, in the form of granules, also known as pellets, flakes, regrind, that is material obtained by the grinding of production waste and/or post-consumer material, or even in powder form.

The plastics material is first of all formed, for example, into granules which are then stored in suitable storage containers 101 where they are left whilst waiting to be subjected to subsequent transformation processes in suitable transforming machines 102 by means of which the granules are transformed into finished or semi-finished products.

Although the following description refers in particular to plastics material in granular form, the invention may be applied to plastics material in any other form such as flakes or even powder. Before being sent to the transforming machines 102, the plastics material is sent to a dehumidifying system 103 to eliminate any moisture absorbed by the granules and to prevent the occurrence, in the transforming machines 102, of any problems such as, for example, air bubbles, blunting and scoring, hollows, degradation of the polymer, snags, low viscosity, or roughness, due to the presence of moisture.

Inside the dehumidifying system 103, the granules of plastics material coming from the storage container 101 are subjected to dehumidification by means of a drying agent. In the version shown, between the dehumidifying system 103 and the transforming machines 102, there is a storage device 104 in which the granules of dehumidified plastics material are stored before being sent to the transforming machines 102.

The storage device 104 acts as a buffer in the transformation process 100 to take up differences in the transformation rates in the various steps of the process.

For example, the storage device 104 avoids the interruption of the operation of the transforming machines 102 in the event of an interruption of the dehumidifying system 103, for example, for maintenance or, conversely, avoids the interruption of the operation of the dehumidifying system 103 in the event of an interruption of the transforming machines 102.

In some versions of a process 100 for treating plastics material, a storage device may not be provided between the dehumidifying system 103 and the transforming machines 102. With reference to Figure 2, this figure shows schematically a dehumidifying system 103 comprising a dehumidifying device 1, shown in greater detail in Figures 3 and 3a, into which the granules are fed in order to be subjected to dehumidification and from which they are subsequently supplied to the storage device 104 and then to the transforming machines 102. The dehumidifying device 1 comprises a container body 2 which is delimited by a wall 3 and is arranged to contain the plastics material coming from the storage container 101 for dehumidification.

The container body 2 comprises an inlet portion 2a in which an opening 9 is defined, through which the plastics material is introduced, and an outlet portion 2b in which an outlet hole 10 is defined, positioned at the end remote from the opening 9 and arranged to allow the plastics material to come out of the container body 2.

The dehumidifying device 1 also comprises a cover 19 formed so as to seal the opening 9 of the container body 2 hermetically and releasably. The cover 19 comprises an inner wall 19a and an outer wall 19b, shown in detail in Figures 4b and 4c, which are almost parallel to one another, are mutually connected by attachment means 19c, and are spaced apart by a space of about 3-5 cm.

The inner wall 19a is made of bright metal, for example, bright stainless steel, is intended to face the interior of the container body 2 and, during the operation of the dehumidifying device 1, limits the dissipation of heat towards the cover 19 to prevent energy wastage and overheating of the outer wall 19b, as explained further below.

The inner wall 19a may also be made of metal covered by a ceramic layer in order to reflect the infrared radiation and thus to limit the heat dissipation which would occur with a metallic material.

The outer wall 19b, on the other hand, faces outwardly relative to the container body 2 and is intended to be gripped in order to open/close the container body 2. The provision of two distinct walls 19a, 19b for the cover 19 and the separation of these walls by means of a space reduces heat dissipation via the cover 19 and also avoids overheating of the outer wall 19b of the cover

19 and hence danger to personnel.

The outlet portion 2b of the container body is provided with inclined walls which converge towards the outlet hole 10 so as to promote the transportation of the plastics material towards the outlet hole 10. The plastics material passes through the container body 2 in the direction indicated by the arrow F, that is, in the advancing direction of the plastics material in the process 100. The cover 19 and the outlet hole 10 are hermetically connected, respectively, to an inlet valve 11 and to an outlet valve 12 which are formed in such a manner as to allow the plastics material to flow into/out of the container body 2 when they are open and to close the container body hermetically when they are closed. The dehumidifying device 1 comprises a capacitive monitoring device for checking that the desired amount of plastics material to be subjected to dehumidification is introduced into the container body 2 so as to form a bed L of plastics material having a predetermined depth H. In the version shown, the capacitive monitoring device is a photocell 25 which is positioned at a predetermined level in the container body 2, that is, at a predetermined distance from the opening 9, and which is activated when the plastics material loaded into the container body 2 reaches the level corresponding to the position of the photocell 25. The signal of the photocell activates/de-activates the loading of the material into the container body 2 so as to regulate the amount of plastics material which is introduced and hence subjected to processing.

In a version not shown, a plurality of photocells may be provided, positioned at different levels in the container body 2, for use for different desired levels of filling of the dehumidifying device 1 and hence different amounts of plastics material to be processed. In another version, shown in Figures 7 and 8a-8b and described in detail below, the container body 2 may be mounted on top of load cells so as to weigh the amount of plastics material introduced into the container body 2. The dehumidifying device 1 also comprises radiation means 20 arranged for radiating infrared radiation inside the container body 2 in order to heat and dehumidify the plastics material.

The radiation means 20 are positioned in the container body 2 at a level higher than the maximum height H that can be reached by the bed L of plastics material in the container body 2 so that the plastics material does not come into direct contact with the radiation means 20.

This prevents localized overheating of the plastics material, degradation thereof, which would render it unusable, and the creation of agglomerations of molten plastics material which would obstruct the regular movement of the plastics material in the container body 2 and also damage to the radiation means 20.

A minimum distance is maintained between the radiation means 20 and the maximum level H and depends on the size of the container body 2 and on the type of plastics material being processed. This distance is at least 10 cm. The plastics material is thus heated in the container body 2 by radiation and not by contact.

In the version shown, two twin-tube infrared lamps 30 with tungsten or carbon filaments mounted inside quartz tubes are used as radiation means 20. The lamps 30 used preferably emit short and/or medium length infrared waves.

The dehumidifying device 1 may be provided with a number of lamps 30 depending on the type and quantity of plastics material being processed in the container 2, on the type and length of lamp used, and on the diametral dimension of the container body 2.

In the version shown, the two infrared lamps 30 are positioned in such a manner as to emit their infrared radiation in the inlet portion 2a of the container body 2, that is, in the region of the opening 9. In other versions, not shown, the radiation means 20 may be positioned in other suitable regions of the container body 2, for example, along the side walls of the container body 2, again avoiding even accidental contact with the plastics material.

The movement of the plastics material in the container body 2, which is described in detail below, thus advantageously takes place in such a manner as to keep the radiation means 20 separated from the plastics material. The radiation means 20 may in fact reach temperatures above 300°C, that is, above the melting point of the plastics material. Contact between the plastics material and the radiation means 20 would cause degradation of the plastics material and damage to the radiation means 20. As can best be seen from Figures 4a and 4b, the lamps 30 are associated with the inner wall 19a of the cover 19, a shielding device 29 being interposed between the lamps 30 and the inner wall of the cover 19a. As stated, the inner wall 19a is made of bright metal or metal covered with ceramics, preferably clear ceramics, and shields the infrared radiation which strikes it, limiting outward dispersal of the infrared rays. The shielding device 29 is formed so as partially to surround the lamps 30 in order to shield the radiation of the lamps 30 in some directions and hence to direct the infrared radiation of the lamps 30 towards the plastics material to be processed and to prevent dispersal of the radiation into undesired regions.

The shielding device 29 is made of metal. Optionally, to further increase shielding efficiency, the shielding device 29 may be made of metal covered with ceramics so as to maximize the reflection of the infrared rays and hence to limit dispersion in the metal. In the version of Figures 4a, 4b, the shielding device 29 is fixed to the inner wall 19a of the cover 19 by a horizontal wall 29a of the shielding device 29 and comprises at least one inclined wall 29b which is shaped so as to direct the infrared radiation of the lamps 30 in the direction indicated by the arrows F5, that is, towards the plastics material being processed, further increasing the efficacy of the dehumidification process.

The infrared radiation is oriented in a direction F5 which is as parallel as possible to the advancing direction F of the plastics material in the container body 2. This advancing direction F is defined between the inlet portion 2a and the outlet portion 2b of the container body 2. The particular configuration of the walls of the shielding device 29 depends on the number of lamps 30 provided and on their position in the dehumidifying device 1, relative to the plastics material to be processed. As well as directing the radiation onto the plastics material to be processed, the shielding device 29 also prevents the plastics material coming into contact with the lamps 30 and abrading them, as explained further below. In a variant shown in Figure 4c, the shielding device 29 with the lamps 30 may be interposed between the inner wall 19a and the outer wall 19b of the cover 19. In this solution, the distance between the inner wall 19a and the outer wall 19b is increased, this distance being 10-15 cm and depending on the type of lamps used.

This solution renders the insulation of the dehumidifying device 1 more efficient without increasing its overall size or, even less, the space occupied by the radiation means 20, by the shielding device 29 and by the cover 19 inside the container body 2. Space that is useful for processing the plastics material is thus not taken up and the capacity of the dehumidifying device 1 is not reduced. In this variant, the inner wall 19a acts as protection by preventing contact between the plastics material and the radiation means 20. As shown in detail in Figure 4a, the lamps 30 are supplied by supply wires 36 which are wired into an electric wiring box 34 and extend through a tube 28 interposed between the lamps 30 and the box 34.

The tube 28 is fixed to the horizontal wall 29a of the shielding device 29 and is connected, by means of a nozzle 35 provided on a wall 28a of the tube 28, to a cooling system 27 for the lamps which is arranged to cool the lamps 30 in order to increase their radiation efficiency and life.

The opening/closure of the nozzle 35 are controlled; a temperature sensor 56 provided in the dehumidifying device 1 detects the temperature of the lamps 30 and brings about opening/closure of the nozzle 35 on the basis of the temperature detected. The temperature sensor 56 is preferably positioned on the rear portion of the lamps 30 on the same side as the supply wire 36 since this is the region which must be cooled to preserve the life of the lamps 30.

When the nozzle 35 is opened, ambient air is conveyed through the tube 28 in order to cool the supply wires 36 of the lamps 30 and the lamps 30 themselves.

The cooling system 27 is configured in such a manner as to maintain the hermetic sealing of the tube 28 from the outside atmosphere. The flow of air inside the tube 28 is brought about by utilizing the reduced pressure inside the container body 2, as explained further below. However, air blowing devices may also be provided.

In applications in which the admission of oxygen to the container body 2 is to be avoided so that oxygen does not come into in contact with the plastics material to be processed, cooling nitrogen may be blown into the tube 28 by means of the cooling system 27 in order to cool the lamps 30. The dehumidifying device 1 also comprises a temperature detector 26 which is positioned in the vicinity of the radiation means 20 in order to control the operation thereof.

The temperature detector 26 is an infrared ray detector which reads the temperature of the plastics material inside the container body 2 and is connected to devices for operating the radiation means 20 in order to switch them on/off in order to reach the optimal temperature for the processing of the plastics material.

The radiation means 20 are operated discontinuously, that is, switched-on phases in which the radiation means 20 irradiate the plastics material, heating it, alternate with switched-off phases. The duration and alternation of the switched-on/off phases of the radiation means 20 depend on the temperature of the plasties material, on the temperature of the internal walls of the container body 2, on the type of radiation means used, and on the rate at which the plasties material is to be heated.

It has been found experimentally that the increase in temperature of the plasties material, and hence the degree of dehumidification that can be achieved, is not directly proportional to the amount of energy radiated during a predetermined period of time, that is, the heating of the plastics material and hence its dehumidification, do not increase proportionally with the amount of energy supplied over a continuous period of time. The alternation of heating/non-heating phases for a predetermined period of time achieves the same dehumidification of the plastics material as would be achieved by heating the plastics material continuously for the same period of time.

Discontinuous operation of the radiation means 20 thus leads to a considerable energy saving whilst maintaining a high degree of dehumidification efficiency. Moreover, discontinuous operation of the radiation means 20 prevents overheating of the plastics material and damage thereto.

The presence of the temperature detector 26 enables the desired amount of energy to be radiated to the plastics material being processed, avoiding wastage or risk of overheating and, at the same time, effectively dehumidifying the plastics material. Figures 5a-5b show another variant of the radiation devices 20' of the dehumidifying device 1 according to the invention in which the same parts are indicated by the same reference numerals.

In this configuration, the infrared lamp 30 is housed inside a shielding device 29' which is similar to that described with reference to Figures 4a-4c but is mounted on the inner wall 19a so that the inner wall 19a is interposed between the lamp 30 and the plastics material being processed.

The shielding device 29' is configured so as to enclose the lamp 30 on all sides, at the same time allowing the infrared rays emitted to reach and heat the plastics material. The lamp 30 is fixed to a wall 29'd of the shielding device 29' which is translatable relative to the shielding device 29' in the direction of the translation arrow T so that the lamp 30 can be introduced into/moved out of the shielding device 29'.

The assembly comprising the lamp 30 and the shielding device 29' is configured in such a way that, when the lamp 30 is moved into the shielding device 29', Figure 5a, and the dehumidifying device 1 is in operation, the assembly closes the container body 2 hermetically.

The variant of Figures 5a-5b has many advantages: the rear portion of the lamp 30, that is, the portion that is outside the shielding device 29' can be kept in ambient air, that is, not under vacuum, and can be cooled without varying the degree of vacuum inside the container body 2. Moreover, the useful space inside the container body 2 is increased and the mounting of the lamps 30 and any replacement thereof for maintenance are simplified.

Figures 6a-6c show a further variant of the radiation means 20" of the invention in which corresponding parts are indicated by the same reference numerals.

The shielding device 29" is configured as the shielding device 29' of Figures 5a-5b and is further provided with a curved wall 290 which preferably has a semi-circular shape and can be rotated by means of an actuator in a direction of rotation R between a first position Pl shown in Figure 6b and a second position P2 shown in Figure 6c.

The inner wall 19a of the cover 19 is formed so as to define seats for housing the curved wall 290 in the first position Pl. By moving the curved wall 290, it is possible to shield the lamps 30 in the upper portion, that is, towards the cover 19, position Pl, and also in the lower portion, in the radiation direction, position P2. In this variant, the container body 2 is again sealed hermetically so that the infrared rays can heat the material whilst the material is simultaneously kept under reduced pressure. The curved wall 290 constitutes a further protection for the lamps 30 from any contact with the plastics material and/or contaminants present therein. The curved wall 290 may be made of metal or metal covered by a layer of ceramics, preferably clear ceramics, in order to reflect the infrared radiation. A screw 13 is also provided inside the container body 2 and is driven by a motor 14, which is preferably positioned outside the container body 2 and is connected to the screw in such a manner as to ensure the hermetic closure of the container body 2 even when the screw 13 is in operation. The motor 14 is connected to an inverter, not shown, which regulates the speed of the screw 13 in dependence on the type and morphology of the material being processed: granular materials behave almost like fluids and require less mixing but flaked materials tend not to flow easily and require more vigorous mixing.

The screw 13 can mix the plastics material inside the container body 2 and convey it in the conveying direction indicated by the arrow Fl in order to move it towards the radiation means 20 so that the plastics material is subjected to dehumidification.

In the version shown, the screw 13 extends inside the container body 2 in a direction substantially parallel to or coinciding with the direction defined between the opening 9 and the outlet hole 10 and is configured in such a manner as to convey the plastics material from the region of the outlet hole

10 to the region of the opening 9, in the conveying direction Fl.

In this configuration, the conveying direction Fl is contrary to the advancing direction F of the plastics material. In general, the screw 13 may be positioned and operated in such a manner that the conveying direction Fl is different from and not the same as the advancing direction F.

In other versions, not shown, the conveying direction Fl and the advancing direction F may be arranged transversely relative to one another. The screw 13 comprises an inlet 13a by means of which the plastics material enters the screw 13, a body 13b along which the plastics is moved in the conveying direction Fl, and an outlet 13c from which the plastics material emerges from the screw 13.

The outlet 13c of the screw 13 is positioned in the vicinity of the radiation means 20 at a distance therefrom, or from the inner wall 19a (Figure 4c), such that the plasties material does not come into contact with the radiation means 20.

In a vertical configuration of the dehumidifying device 1 such as that shown in the drawings, in which the plasties material emerges from the body 2 by gravity 2, the inlet portion 2a and the outlet portion 2b are positioned in an upper portion and in a lower portion of the body 2, respectively, and the screw 13 is positioned so as to lift the plasties material from the outlet portion 2b to the inlet portion 2a.

In this version, the inlet 13a of the screw is positioned in the vicinity of the outlet hole 10 whereas the outlet 13c is positioned in the vicinity of the opening 9 but other configurations of the screw 13 in the container body 2 may be provided to permit movement of the plasties material in a conveying direction Fl other than the advancing direction F.

The body 13b of the screw 13 is externally provided with a sheathing 16 which extends almost parallel to the body 13b, partially covering it, and is arranged to guide the plasties material which is moved by the screw 13 to prevent undesired falling or movement thereof.

Successive portions having different outside diameters can be identified in the body 13b of the screw. In particular, a first portion 18 can be identified, which is positioned towards the outlet hole 10, that is, in the region of the inlet 13a, and has a smaller diameter than other portions of the screw 13.

The first portion 18 is at least partially free of the sheathing body 16. The first, smaller-diameter portion 18 enables the mixing of the plastics material in the vicinity of the inlet 13a of the screw 13 to be increased so as to promote the admission of the plastics material to the screw 13 and to prevent pockets of non-dehumidified plastics material forming in the container body 2.

The plastics material enters the screw 13 at the inlet 13a, is transported along the body 13b, as indicated by the conveying arrow Fl, and emerges from the outlet 13c forming a jet or spray which spreads out from the screw 13 owing to the centrifugal force, as indicated by the arrow F2 in Figure 3. The jet of plastics material moves into the zone of action of the lamps 30 so that the plastics material is subjected to irradiation and hence to heating and dehumidification.

The upper portion of the screw 13c is formed in such a manner that the jet of plastics material that has come out of the screw does not come into contact with the lamps 30, to prevent degradation, overheating or melting of the plastics material and damage to the lamps 30. Since the plastics material spreads out from the screw 13 to form a jet, extremely limited thicknesses of plastics material are created as it moves away from the screw 13 and into the zone of action of the lamps 30. The problem of the low permeability of the plastics material is thus eliminated and the plastics material which moves into the zone of action of the radiation means 20 is heated efficiently.

The jet of plastics material that has come out of the screw 13 is deposited on the bed L of plastics material in the container body 2 forming a layer Li which rests on the preceding layer Lj (which came out of the screw 13 previously). The bed L is thus formed by successive layers of plastics material that have come out of the screw 13. The upper layer Li of plastics material is also exposed to the action of the lamps 30 in the container body 2 and, as successive layers of plastics material form thereon, the heating effect of the lamps 30 on the layer Li decreases in dependence on the thermal permeability of the plastics material being processed.

By moving the plastics material, the screw 13 produces in the container body 2 a motion of the plastics material which is drawn back towards the inlet of the screw 13 and, as it emerges from the screw, forms successive new layers Lj, Li of the bed L. Variation of the rate of rotation of the screw 13 varies the rate at which the plastics material is moved inside the container body 2, its layering, and hence the temperature level that can be reached in each cycle, that is, upon each passage of the plastics material through the zone of action of the lamps 30, and the time for which each layer Li, Lj is subjected to the action of the lamps 30.

In some processing stages, the screw 13 may be stopped, as explained further below.

The presence of the shielding device 29 or the inner wall 19a protects the lamps 30, preventing particles of plastics material coming into contact with the lamps, thus preserving their operative capacity.

The jet of plastics material coming out of the screw 13 moves, as indicated by the arrow F2, with a falling arc the maximum height of which is below the level at which the lamps 30 are located. The jet of plastics material formed at the outlet from the screw 13 is also subject to the force of gravity which causes it to fall towards the inlet 13a of the screw 13, as indicated by the arrows F3.

The plasties material is thus carried back to the zone of action of the screw 13 and can be drawn in again and moved once more by the screw 13 in order to be brought to the zone of action of the radiation means 20 and to be subjected once more to the action of the infrared rays.

This enables the plasties material inside the container body 2 to be processed repeatedly by being brought repeatedly into the zone of action of the radiation means 20. A high degree of heating and dehumidification efficiency are thus achieved. This also enables the plastics material to be subjected to multiple heating/dehumidification operations with the use of the same radiation means 20.

It is not in fact necessary to provide separate, dedicated radiation means for each dehumidification operation to be carried out. By varying the time spent by the plastics material in the container body 2 and/or the rate of rotation of the screw 13, and hence the number of times the plastics material is brought into the zone of action of the radiation means 20, it is possible to vary the degree of heating and dehumidification of the plastics material output from the device 1 and to adapt the process effectively for processing input plastics material having any moisture content.

A flexible device which enables optimal performance to be maintained, even in the event of changes in input conditions and/or desired output conditions for the plastics material to be processed, is thus obtained. In versions not shown, for example, in dehumidifiers that are arranged horizontally, and/or with a screw that is not arranged vertically, movement means may be provided, which cooperate with the screw 13 and are arranged to bring the plastics material from the radiation means 20 towards the inlet portion 13a of the screw 13 so that the plastics material can be recirculated and repeatedly subjected to the action of the radiation means 20.

In the embodiment shown, this function is performed by gravity which returns the plastics material to the vicinity of the inlet 13a of the screw 13. Further radiation means may optionally be provided, positioned along the path of the plastics material from the outlet 13c to the inlet 13a, for example, on the side walls of the container body I₁ to further increase dehumidification efficiency, these further radiation means being separated from the plastics material so as not to come into contact therewith. As stated, this is to limit wear of the radiation means and degradation and/or melting of the plastics material.

Inside the container body 2, to facilitate the mixing of the plastics material, a deflector element 15, shown in Figure 3a may be provided on the path of the plastics material from the outlet 13c to the inlet 13a of the screw 13, to guide the plastics material towards the inlet 13a of the screw 13. The deflector 15 is fixed to the sheathing body 16 and comprises a surface Sl which faces towards the outlet portion 13c of the screw 13 and is arranged to receive the plastics material falling from the outlet 13c. The surface Sl is inclined towards the wall 3 of the container body 2 so as to cause the plastics material to flow towards the wall 3, as indicated by the arrows F3. The deflector element 15 is also of a size such that a passageway 17 is defined between the deflector element 15 and the wall 3 of the container body 2.

After coming out of the outlet 13c of the screw 13 and passing through the zone of action of the radiation means 20, the plastics material therefore falls onto the surface Sl, slides along it towards the wall 3, passes through the passageway 17, and flows towards the inlet 13a of the screw 13.

The overall movement of the plastics material in the container body 2 is indicated schematically by the arrows F1-F3 in Figure 3a. The inclined configuration of the outlet portion 2b of the container body 2 promotes the movement of the plastics material towards the inlet portion

13a of the screw 13.

This movement is also promoted by the provision of a reduced-pitch portion

18 of the screw 13 towards the inlet 13a. The dehumidifying device 1 may also comprise an injection device 37, shown in Figure 3b, which is arranged for injecting air or other fluid into the container body 2.

The injection device 37 is configured in such a manner as to permit a flow of air or other fluid into/from the container body 2 when open and to close the container body 2 hermetically when closed.

The injection device 37 is used in particular for the processing of sticky materials or materials which tend to form agglomerations known in slang as

"bridges" of plastics material.

These agglomerations weaken the mixing process of the screw 13 inside the container body 2 and may create obstructions or blockages and/or pockets of unprocessed and hence non-dehumidified plastics material. In particular, the injection device 37 is used in the processing of material in the form of flakes which have the tendency to agglomerate to form self- supporting structures which offer resistance to mixing. The injection device 37 breaks up the bridges of plastics material that have formed inside the container body 2, thus promoting the mixing and a good homogeneity of processing thereof.

The injection device 37 may also be used to regulate the degree of vacuum inside the container body 2 or, as explained further below, to introduce fluids or liquids into the container body 2, utilizing Fick's laws of diffusion. The injection device 37 comprises a metal duct 38 extending from outside the dehumidifying device 1 through the cover 19 and inside the container body 2 and terminating in a delivery portion 40 positioned in the vicinity of the inlet 13a of the screw 13. The delivery portion 40 is curved relative to the body of the duct 38 with a radius of curvature of between about 30° and about 45°.

An outlet opening 40a of the delivery portion 40 is thus oriented transversely relative to the duct 38 and preferably perpendicularly relative to the axis of the screw 13. The duct 38 is formed so as to close the container body 2 from the exterior in a leaktight manner.

The injection device 37 also comprises a fluid source, for example an air source, which is not shown in the drawings and is connected to the duct 38 by means of a valve 41 with controlled opening/closure, provided on an external portion 38a of the duct 38. The fluid source disposed outside the container body 2 is arranged for the injection of air or another fluid into the container body 2 in order to break up the agglomerations of plastics material. The airflow inside the duct 38 is produced by utilizing the reduced pressure inside the container body 2, as explained further below. However, air blowing devices, for example, a blower or a fan may also be provided for supplying the fluid into the container.

For particular applications, nitrogen or another gas may be injected to prevent oxidation or degradation of the plastics material being processed due, for example, to the presence of oxygen.

The fluid injected may optionally be preheated in order not to reduce the temperature of the plastics material in the container body 2. During the dehumidification process, it is also possible to inject fluids suitable for enhancing the dehumidification process or regulating the temperature of the plastics material and/or additives for improving the characteristics of the plastics material.

For example, water may be introduced in a quantity such as to bring about surface cooling to reduce the temperature of the plastics material or, in the event of an emergency due to overheating, complete cooling of the plastics material.

In one version of the dehumidifying device 1, a sheathing wall 4 is provided outside the wall 3 of the container body 2 and is positioned in such a manner as to define between the sheathing 4 and the wall 3 a space 5 which is connected by means of a duct, not shown, to a vacuum pump 7 for creating a desired reduced pressure inside the space 5. The vacuum pump 7 is operated so as to produce a relative pressure of between about -900 mbar and about -980 mbar in the space 5. The wall 3 and the sheathing wall 4 are formed in such a manner that the space 5 is hermetically sealed from the exterior. The wall 3 has holes the dimensions of which are selected on the basis of the dimensions of the granules to be dehumidified and which are spaced variously in the wall 3; the wall 3 may optionally be formed as a netting having a mesh size of between about 0.1 mm and about 3 mm. The interior of the container body 2 is thus in communication with the space 5 and almost the same degree of vacuum is thus produced therein as in the space 5.

The vacuum inside the container body 2 improves and increases the efficiency of the dehumidification process in the dehumidifying device 1 by facilitating the removal of the moisture. The presence of the space 5 and the vacuum inside it also thermally insulates the dehumidifying device 1 from the exterior. The conductivity values that can be achieved with a reduced pressure of between -900 mbar and -980 mbar are between about 0.013 and 0.00104 W/(m*K). In these conditions there is a quantity of air of between about 2% and 10% in the space 5. These conductivity values are considerably lower than the conductivity values obtained with a sheathing of insulating material.

This considerably increases the energy efficiency of a dehumidification process carried out with the dehumidifying device 1, drastically reducing heat losses to the exterior and considerably limiting dehumidification energy consumption.

Moreover, dehumidification times are considerably reduced and a more uniform temperature of the plastics material inside the container body 2 is achieved during dehumidification. The dehumidification is therefore performed with greater efficiency.

Moreover, by suitable operation of the vacuum pump 7, it is possible to regulate and maintain a desired level of reduced pressure in the space 5, thus regulating the thermal losses of the dehumidifying device 1 and hence the temperature of the plastics material inside the dehumidifying device 1. The vacuum reduces the boiling point of the water, promoting its evaporation and hence further facilitating dehumidification. Moreover, the "stripping" action performed by the vacuum also causes the discharge from the plastics material of any contaminants, which can be collected in a condenser, not shown, positioned, for example, upstream of the pump 7 and connected thereto.

In a version not shown, vacuum regulation means may be provided, for example, a valve operatively connected to the vacuum pump 7 and arranged to regulate the degree of vacuum in the space 5 between about - 200 and -1000 mbar, as explained further below. By reducing the degree of vacuum in the space 5, it is possible to increase the thermal losses of the dehumidifying device I₇ performing rapid cooling of the plastics inside the body 2, for example, in the event of overheating, bringing the plastics material to the desired temperature. It is useful to reduce the degree of vacuum in particular in some processes in which the material may have to be cooled and stored inside the dehumidifying device 1 after dehumidification or in an emergency in which it is necessary to reduce the temperature to prevent the triggering of dangerous processes.

Conversely, by increasing the degree of vacuum in the space 5 and hence in the container body 2, it is possible further to reduce thermal losses and hence to render the heating of the plastics material in the container body 2 more efficient.

Variation of the degree of vacuum enables the process to be adapted easily and quickly to the type of plastics being processed and/or to the final specifications required for the plastics material.

The degree of vacuum can be reduced by injecting a fluid, for example air, by means of the injection device 37 thus also facilitating the discharge of the water that was present in the plastics material from the container body 2 and increasing the dehumidification speed. By subjecting the plastics material to a predetermined degree of vacuum the discharge of the water molecules from the plastics material is promoted but, once the maximum degree of vacuum (for example -1000 mbar) has been reached, the discharged water molecules tend to remain immobile around the mass of plastics material or at most to move, but slowly, towards the coldest point in the container body 2.

By introducing the fluid into the container body 2 by means of the injection device 37 a change in the degree of vacuum is caused and the fluid entrains the water molecules discharged from the plastics material, carrying them out of the container body 2. The fluid thus acts as a transporting means for the rapid discharge of the moisture from the container body 2. The air introduced into the container body 2 with the injection device 37 is then drawn back by the vacuum pump 7.

In some applications, the vacuum pump 7 and the injection device 37 may be operated simultaneously in order to generate a continuous current of fluid passing through the container body 2 from the injection device 37 to the pump 7, entraining the moisture with it.

The vacuum pump 7 and the injection device 37 may be operated simultaneously so as to keep the degree of vacuum almost constant or progressively to increase/decrease the degree of vacuum, for example, from -1000 mbar to -200 mbar and then up to -1000 mbar, and so on, for a number of times that depends on the type and characteristics of the material being processed.

Alternatively, when the fluid is introduced by means of the injection device

37, the pump 7 is switched off so as to work in alternate phases. The level of vacuum in the container body 2 is discontinuous and the energy consumption of the device 1 is reduced whilst a high level of efficiency thereof is maintained.

Moreover, as well as increasing dehumidification efficiency, the presence of the vacuum inside the container body 2 also prevents the evaporation and deposition on the radiation means of the plastics material being processed, any dust, the water vapour, and/or any other substances dissolved in the plastics, which instead fall under the effect of gravity.

This further prevents wear of the lamps 30, keeping their radiation power almost unchanged over time. The vacuum also causes an increase of 30-40% in the performance of the infrared lamps, reducing energy consumption.

The injection of air into the container body 2 by means of the injection device 37 and/or the cooling system 27 leads to a loss of vacuum inside the container body 2 of about 100-200 mbar or even 800 mbar, which does not affect the quality of the dehumidification performed in the dehumidifying device 1, and which can be recovered extremely quickly by means of the vacuum pump 7.

It is thus possible to cool the lamps 30 and/or to break up agglomerations of plastics material and/or to regulate the level of vacuum with the use of the cooling system 27 and the injection device 37, respectively, without thereby detracting from dehumidification quality.

These operations can therefore be performed during the normal operation of the dehumidifying device 1. In a version not shown, the wall 3 may be formed so as also to seal the space 5 hermetically from the container body 2. Any desired pressure can thus be maintained inside the container body 2, irrespective of the degree of vacuum produced in the space 5.

A connecting valve is provided between the space 5 and the container body 2 and can put the space 5 and the container body 2 into flow communication when open and isolate them when closed. It is thus possible to produce the same vacuum or different degrees of vacuum in the space 5 and in the container body 2. In this case, the vacuum pump 7 is connected both to the space 5 and to the container body 2 or one pump may be provided for the space 5 and another for the container body 2. Optionally, the container body 2 may be connected directly to the vacuum pump 7 and the external insulation may be formed by a thickness of insulating material.

The dehumidifying device 1 is provided with at least one device for detecting the degree of vacuum, which is operatively connected to the vacuum pump 7 in order to regulate the degree of vacuum in the container body 2 and/or in the space 5.

Figure 7 shows a variant of the dehumidifying device according to the invention in which corresponding parts are indicated by the same reference numerals and are not described in detail. The dehumidifying device 1" of Figure 7 is mounted on load cells 40 for measuring the changes in weight of the dehumidifying device 1". In this variant, the amount of plastics material that can be processed in the container body 2 is established by preliminary calibration of the dehumidifying device 1", taking account of the apparent specific weight of the plastics material.

The container body 2 has a maximum load volume and the quantity of plastics material that can be loaded depends on the apparent specific gravity of the plastics material; by intersecting these two datums, it is also possible to vary the filling level of the container body 2, that is, the amount of plastics material by weight which can be introduced into the container body 2.

The use of the load cells 40 also enables the loading of two or more types of plastics material into the container body 2 to be metered accurately making the device 1" also a gravimetric dosing/mixing device. Moreover, by positioning the dehumidifying device 1" on the load cells 40, it is possible to monitor the efficacy of the dehumidification process by measuring the difference between the weight of the dehumidifying device 1" before and after the dehumidification process, this difference being almost equivalent to the moisture eliminated from the plasties material by the dehumidification process. Optionally, the moisture removed may also be condensed and its weight measured.

In the dehumidifying device 1" of Figure 7, the infrared temperature detector 26 is replaced by two contact temperature probes 41a, 41b which are positioned suitably in the container body 2 so as to detect the temperature of the plastics material being processed in distinct positions in the container body 2, a first probe 41a being positioned towards the opening 9 and a second probe 41b towards the outlet hole 10. In a version not shown, a different number of probes may be provided, suitably positioned in the container body 2. The dehumidifying device 1" is also provided with a temperature detector 42 which is positioned along the wall 3 and arranged to detect the temperature of the wall 3 in contact with the plastics material and consequently to regulate the action of the radiation means 20 so as to prevent overheating of the wall 3 which would lead to degradation of the plastics material in contact therewith.

In a version not shown, the dehumidifying device 1" may be provided with a temperature detector positioned on the sheathing body 16 so as to detect the temperature of the wall of the sheathing body 16 that is in contact with the plastics material and consequently to regulate the action of the radiation means 20 so as to prevent overheating of the plastics material. In this case again, the infrared lamps 30 are operated discontinuously, their operation depending on the temperature of the plastics material, of the walls with which it comes into contact, and of the lamps themselves. The dehumidifying device 1" is also provided with an additional mixer 45, positioned in the portion of the container body 2 in the vicinity of the outlet hole 10 and arranged to facilitate the movement of the plastics material towards the screw 13.

The additional mixer 45 comprises a paddle wheel 46 driven by a motor 47 which is preferably positioned outside the container body 2 and connected to the paddle wheel 46 in such a manner as to ensure hermetic closure of the container body 2, even during the operation of the paddle wheel 46. The rotation of the paddle wheel 46 moves the plastics material that is present in the vicinity of the outlet hole 10, promoting the homogenization of its temperature and its transportation towards the screw 13. The diameter of the outlet hole 10 of the container body 2 is larger than in the version of Figure 3 so as to facilitate the housing of the paddle wheel 46, the outlet valve 12 being positioned beside the paddle wheel 46. During the evacuation of the plastics material from the container 2, the additional mixer 45 may be positioned so as to facilitate the transportation of the plastics material towards the outlet valve 12.

The additional mixer 45, like the screw 13, may have discontinuous operation; its speed may be varied by means of an inverter associated with the motor 47 and it may be stopped after a desired temperature has been reached in the container body 2 and the temperature has been rendered homogeneous in the plastics material. Figures 8a-8b show a loading device 60 of the dehumidifying device 1" of Figure 7, comprising a telescopic tube 53 which is positioned outside the inlet valve 11 and concentrically relative thereto.

The telescopic tube 53 is slidable horizontally so as to ensure leaktightness with respect to the interior of the container body 2. The telescopic tube 53 is also slidable in both directions along the sliding axis indicated by the arrow M in order to be inserted in/removed from the container body 2. During the loading of the plastics material into the container body 2 through the inlet valve 11, the telescopic tube 53 is introduced into the container body 2, Figure 8a, until an end 53a is positioned almost at the same level as the level H¹ of plastic material in the container body 2. As new plastics material is gradually supplied and its level in the container body 2 therefore increases, the telescopic tube 53 is progressively raised, Figure 8b. The telescopic tube 53, and in particular its walls, act as a guide element for the plastics material introduced, guiding it as far as the bed L of plastics material. This prevents the plastics material admitted from spurting or bouncing back in uncontrolled manner inside the container body 2 and coming into contact with the lamps 30, owing to the input speed. The lamps 30 are protected from contact with the material and/or any contaminants, further increasing the life of the lamps 30.

The dehumidifying device 1 operates as follows: the inlet valve 11 is opened whilst the outlet valve 12 is kept closed and the telescopic tube, if provided, is inserted in the container body 2; a predetermined amount of plastics material is introduced into the container body 2, the lamps 30 optionally being operated to preheat the plastics material entering the container body 2, that is, as it passes in front of the lamps 30.

The container body 2 is filled with plasties material until the photocell 25 detects that the desired filling level has been reached. If load cells are provided, the filling of the container body 2 is stopped when the desired weight is reached. The telescopic tube 53, if provided, is progressively removed from the container body 2 according to the degree of filling thereof monitored by the photocell and/or by the load cells. During this stage, the radiation means 20 may be protected by the positioning of the curved wall 290 in the second position P2. The inlet valve 11 is then closed so as to close the container body 2 hermetically, the vacuum pump 7 is operated in order to generate a desired degree of vacuum inside the container body 2 and the space 5, and the screw 13 is operated and starts to move the plastics material in the container body 2, moving it towards the radiation means 20. If the additional mixer 45 is provided, it is also operated and facilitates the homogenization of the plastics material and its transportation towards the screw 13.

If the movable wall 290 is provided, it is positioned in the first position Pl so as to allow the infrared rays of the lamps 30 to pass towards the plastics material.

The plastics material discharged from the screw 13 is irradiated by the radiation means 20 and moved towards the screw 13 again, as explained above, in order to be transported towards the radiation means 20 once more by the screw 13. The radiation means 20 are positioned in such a manner that the plastics material is irradiated both whilst the plastics material discharged from the screw 13 is falling towards the bed L and whilst the jet is being deposited, creating the upper layer Li of the bed L of plastics material. The rate of rotation of the screw 13 may be varied in order to adapt the exposure of the plastics material to the infrared rays to the type of plastics material and/or to the process specifications, subjecting it to a suitable degree of heating.

The lamps 30 are operated in order to heat and dehumidify the plastics material at a temperature which depends on the temperature at which it is advisable to perform the dehumidification, on the type of plastics material being processed and on its form (granules, flakes,...), as well as on the temperature at which the granules are to be supplied to subsequent transforming machines 102. Usually, the granules are heated and dehumidified at a temperature of between about 40°C and about 200°C. The desired temperature is reached by discontinuous operation of the lamps 30 which are switched on/off in dependence on the temperatures detected by the temperature sensors/detectors 26, 56, 41, in particular in dependence on the temperatures detected on the wall 3, on the sheathing body 16, and on the lamps 30. Should the temperature of the lamps 30 be too high, they are cooled by the opening of the nozzle 35 which, by putting the outside atmosphere into communication with the container body 2 under vacuum, causes a jet of air or other fluid to pass through and strike the lamps 30 and, in particular, the rear portions thereof where the wires 36 are connected, cooling those portions. Optionally (Figures 5a-5b), the lamps 30 may be mounted in such a manner that the rear portions that are connected to the wires 36 are in ambient air and can be cooled by fans or other devices, not shown. The process is repeated for a desired period of time suitable for achieving the desired heating and dehumidification, the switching-on of the lamps 30 being adjusted in dependence on the temperature of the plastics material detected by the detection device 26 and/or by other detection devices suitably positioned in the container body 2. In particular, once the optimal temperature for the processing of the plastics material has been reached, the lamps 30 are switched off, the screw 13 and the additional mixer 45 are stopped, if necessary, and the dehumidification continues with the application of the desired degree of vacuum which is regulated by operation of the pump 7 and/or by the opening/closure of the nozzle 35 and/or of the valve 41 and/or by operation of the injection device 37, or of other means for regulating the vacuum, if they are provided.

Optionally, after the lamps 30 have been switched off, the plastics material may be mixed by means of the screw 13 and/or the additional mixer 45 to render its temperature homogeneous. To further facilitate dehumidification, a fluid may be injected by means of the injection device 37 in order to entrain out of the body 2 the moisture discharged by the plastics material.

During the injection, the vacuum pump 7 may be switched off so as to bring about an increase in pressure or the vacuum pump may be kept operating in order at least partially to balance the increase in pressure due to the admission of fluid, so as to prevent an increase in pressure or to cause a slower increase thereof.

In any case, a current of fluid is produced which entrains the moisture out of the container body. The fluid which is introduced in a controlled manner is drawn back by the vacuum pump 7, entraining the water molecules which have been detached from the plastics material. The vacuum may be varied from -1000 mbar to -200 mbar and then to -1000 mbar etc., facilitating the dehumidification process.

After the desired fluid has been injected for a predetermined period of time, the vacuum pump 7 may be operated again in order to increase the degree of vacuum in the container body 2 and/or the lamps 30 may be operated to heat the plastics material again.

The above-mentioned steps may be repeated a desired number of times until the desired degree of dehumidification is reached. The dehumidification takes place in regulated vacuum conditions to ensure its efficacy and efficiency. In particular, the heating by radiation takes place in vacuum conditions which, by eliminating the air medium between the radiation means and the plastics material, increases the efficiency of the radiation and, by minimizing volatilization, protects the radiation means from dust and vapours produced by the plastics material being processed.

Finally, the plastics material, which is kept in a reduced-pressure environment, is protected from the degradation which is typical of oxidation.

To summarize, therefore, the process is divided into two main steps: a first step in which radiation, mixing and vacuum combine to raise the temperature and dehumidify the plastics material; and a second step in which radiation and mixing are stopped and the vacuum continues to perform the dehumidification.

These two steps may be repeated cyclically a desired number of times, according to the type of plastics material being processed and the desired degree of dehumidification.

The vacuum which is applied to the container body 2 discontinuously throughout the process, protects and optionally cools the lamps 30, facilitating the passage of the infrared rays, thermally insulates the container body 2, maintaining its temperature, performs the moisture "stripping" action, and dehumidifies and optionally cleans the plastics material of contaminants or extraneous substances.

Optionally, as described above, it is possible to introduce into the container body 2, during the process, fluids to improve the dehumidification process or regulate the temperature, or even additives for the plastics material.

Upon completion of the dehumidification process, the outlet valve 12 is opened in order to discharge the plastics material from the container body 2 of the dehumidifying device 1 and to supply it to the storage device 104 where it is stored whilst waiting to be sent to subsequent transforming machines 102.

The duration and temperature of the dehumidification process are varied on the basis of the characteristics of the plastics material, the type and moisture content, the desired final conditions, etc.. The dehumidifying device of the invention is particularly efficient and flexible. Control elements, associated with the dehumidifying device and arranged to control the dehumidification process, may be provided in the dehumidification system 103.

Warning devices associated with the control elements may also be provided to generate a warning signal should the value of a quantity monitored by a control element depart from a desired value.

The storage device 104 comprises a further insulated container body 105 having dimensions larger than or the same as the container body 2 of the dehumidifying device 1. The insulation may be achieved by insulating material, for example, rock wool or by producing a desired degree of vacuum inside a further space 106 defined between two walls of the further container body 105. The further space 106 may be connected to the same vacuum pump 7 that is used in the dehumidifying device 1 or may be connected to a dedicated vacuum pump, not shown.

The storage device 104 is mounted on load cells 107 suitable for determining the variations in weight of the storage device 104 due to the amount of material supplied by the dehumidifying device 1 to the storage device 104, and by the storage device 104 to the transforming machines 102.

By means of the load cells 107, it is possible to determine the amount of plastics material used by the transforming machines 102 and hence also to regulate the quantity of material to be introduced into the dehumidifying device 1. The load cells 107 are operatively connected to the control elements of the dehumidifying system 103 in order to regulate the operation thereof. The detected value of the change in weight of the storage device 104 is thus sent as a signal to one of the control elements of the dehumidifying device 1 in order to regulate the starting of the dehumidifying device 1 and the amount of material to be processed in the subsequent working cycle. A central control unit which controls the correct operation of the transformation process 100, monitoring the various steps and indicating any warnings, is also provided. In an application, not shown, the amount of material supplied to the transforming machines 102 can be controlled by means of devices which monitor the level of material in the storage device 104, for example, laser, infrared or ultrasound devices.

The dehumidifying device 1 may be used for the processing of plastics materials of various types, in particular hygroscopic plastics materials such as, for example, ABS, PC, PET, PA, TPU, etc.

In a version which is not shown, the plastics material output from the dehumidifying device may be supplied directly to the transforming machines

102.

Figure 5 shows a variant 103' of the dehumidifying system according to the invention in which parts corresponding to the version described above are indicated by the same reference numerals.

In the dehumidifying system 103', downstream of the dehumidifying device 1, there is a second dehumidifying device 1' into which the plastics material output by the dehumidifying device 1 is fed to await delivery to subsequent transforming machines 102. The second dehumidifying device I¹ is structurally similar to the device 1 and is therefore not described in detail.

In the second dehumidifying device V₁ the plastics material is kept at a desired temperature or is even heated, if desired. Moreover, the dehumidification process may also be continued in the second dehumidifying device I¹.

The container body 2' of the second dehumidifying device 1' has a larger internal volume than the container body 2, preferably about twice that of the container body 2. The second dehumidifying device 1' thus acts as a buffer to allow for any accumulations of plastics material due to changes in process speed between the various zones of a transforming installation. This solution is particularly suitable in situations in which it is important to keep the temperature of the plastics material constant or to raise it before the subsequent transformation process in the transforming machines 102. In other versions, not shown, further drying agents, for example microwaves or vacuum, may be provided in addition or as an alternative to infrared radiation.

The dehumidifying device 1 according to the invention is also suitable for the crystallization of PET (polyethylene terephthalate). Recycled, post-consumer PET or processing waste can be regenerated by means of a so-called crystallization process which consists in restoring the molecular bonds of the material to the original form, changing it from the amorphous state to the crystalline state. This process, which is generally performed by exposing the material to hot air (about 140°C) for a period of about 60 minutes, can be performed with the dehumidifying device 1 with the use of the infrared rays which, in contrast, require from 5 to 15 minutes to complete the same process.

By keeping the plasties material being processed under a predetermined degree of vacuum, it is possible simultaneously to dehumidify the PET to optimal levels (less than 50 ppm of residual moisture in the plasties ).

Two processes can thus be combined in a single operation with considerable saving of time and energy consumption in comparison with conventional systems in which crystallization and dehumidification are two separate processes. The dehumidifying device 1 of the invention is also suitable for regrading PET. Regrading is performed at temperatures of up to 230°C and is directed particularly towards the recovery of recycled material (PET obtained by the recovery of bottles and containers, in order to re-establish the viscosity lost during extrusion operations) or towards improving the characteristics of the virgin material when the viscosity is to be increased in order to increase its mechanical strength. This process is generally performed by heating the material and then storing it in an environment under reduced pressure (an autoclave). The advantage of the present invention is that the PET can be heated very rapidly with the infrared rays whilst at the same time being kept under reduced pressure, and a constant temperature of the material that is being processed is also ensured. The efficiency of the process is thus improved, at the same time reducing energy consumption. The degree of vacuum can also be varied by injecting nitrogen which, if it is hot, cooperates with the infrared rays in the heating of the PET being processed in order to speed up the regrading. The dehumidifying device of the invention is also suitable for the mechanical "super-cleaning" of recycled, post-consumer PET (polyethylene terephthalate) or processing waste, that is, for the decontamination of recycled PET, which enables it to be re-used in products that are in contact with foodstuffs. The decontamination of PET is a process which is performed by keeping the material at a temperature of 200°C for several hours with the application of a vacuum; under these conditions, polar and non-polar, organic and inorganic substances such as toluene, chloroform, lindane, diazinon, benzophenone, etc., that is, agents that are toxic to the human body, are removed and reduced to permitted levels and the recovered material is once more usable to create products which can come into contact with foodstuffs. "Super-cleaning" also extracts from the PET other contaminants such as limonene which, although not harmful to the human body, may alter the flavour of some foodstuffs (for example, good-quality ham or carbonated beverages).

When applied to recycled PET (polyethylene terephthalate), the invention thus enables complete recycling to be performed in a single step, transforming post-consumer material into material that is ready for use and has the same mechanical and, optionally, hygiene characteristics as virgin PET.

The contaminants extracted from the plastics material can be collected in a condensation device, not shown, located, for example upstream of the vacuum pump 7 and connected thereto. The invention may also be extended to other fields of application in which is it necessary to dehumidify material, in particular hygroscopic materials and/or in situations in which moisture may have adverse effects during subsequent processes, for example, foods, building materials, etc. The simultaneous use of infrared radiation and vacuum in the dehumidifying device enables the overall efficiency of the dehumidifying system to be increased considerably. Moreover, the particular nature of these drying agents means that they can be used simultaneously in a synergic manner. In fact it is possible to heat the plastics material with the infrared radiation whilst at the same time keeping it under the desired degree of vacuum.

Claims

1. Dehumidifying device (1; 1, 1') for plastics materials, comprising a container body (2; 2, 2') suitable for receiving a predefined amount of plastics material, processing means (20, 30) operatively associated with a processing region provided in said container body (2; 2, 2') for dehumidifying said plastics material in said container body (2; 2, 2'), a conveying device (13, 13a, 13b, 13c, 18) provided in a conveying region of said container body (2; 2, 2') for conveying said plastics material to said processing means (20, 30), said conveying device (13, 13a, 13b, 13c, 18) being configured in such a manner as to convey said plastics material in a conveying direction (Fl) different from an advancing direction (F) of the plastics material in said container body (2; 2, 2'), said advancing direction (F) being defined between an inlet portion (2a) and an outlet portion (2b) of said container body (2; 2, 2'), wherein said processing means comprise radiation means (20, 30) which radiate infrared radiation for heating and dehumidifying said plastics material.

2. Device according to the preceding claim and also comprising vacuum- producing means (7) operatively associated with said container body (2) and arranged to create a predetermined degree of vacuum in said container body (2).

3. Device according to the preceding claim wherein said vacuum- producing means (7) are arranged to produce in the space (5; 5'; 5") a reduced pressure of between approximately -900 and -980 bar.

4. Device according to the preceding claim and also comprising vacuum- regulating means operatively associated with said container body (2) and arranged to vary the degree of vacuum in said container body (2).

5 Device according to any one of the preceding claims and also comprising an injection device (37) for injecting a fluid into said container body (2).

6. Device according to the preceding claim, when dependent on claim 3, wherein said injection device (37) and said vacuum-producing means (7) are formed in such a manner that the fluid injected by said injection device (37) is drawn back by said vacuum-producing means

(7) so as to generate a current of said fluid which passes through said container body (2) entraining with it the moisture that has come out of said plastics material.

7. Dehumidifying device according to the preceding claim and also comprising a shielding device (29) associated with said radiation means (20, 30) and arranged to direct the radiation towards said plastics material.

8. Dehumidifying device according to the preceding claim wherein said shielding device (29") comprises a movable wall (290) which is movable between a first operative position (Pl) and a second operative position (P2) in order to protect said processing means (20", 30) from contact with said plastics material.

9. Dehumidifying device according to any one of the preceding claims and also comprising a guide device (53) which is associated with a supply valve (11) of said container body (2), said guide device (53) is slidable in both directions along a sliding direction(M) in order to be inserted in/removed from said container body (2), and is arranged to guide said plastics material input into said container body (2) to prevent spurting thereof.

10. Dehumidifying device according to any one of the preceding claims, wherein said processing means (20, 30) are provided in the vicinity of said inlet portion (2a), and said conveying device (13, 13a, 13b, 13c, 18) conveys said plastics material said the outlet portion (2b) to said inlet portion (2a).

11. Dehumidifying device according to any one of the preceding claims, wherein said conveying device is a screw-type conveyor (13, 13a, 13b, 13c, 18).

12. Dehumidifying device according to any one of the preceding claims, and also comprising recirculating means for moving the plastics material from said processing region to said conveying region so that it can again be conveyed by said conveying device (13, 13a, 13b, 13c, 18) and processed by said processing means (20, 30).

13. Dehumidifying device according to any one of the preceding claims, wherein said conveying device (13, 13a, 13b, 13c, 18) is configured in such a manner as to generate a jet of plastics material at the outlet of the conveying device (13, 13a, 13b, 13c, 18), which jet disperses in said processing region for greater exposure to said processing means (20, 30).

14. Dehumidifying device according to any one of the preceding claims, wherein said container body (2; 2, 2') is delimited externally by a wall (3; 3, 3'), a sheathing wall (4) suitable for at least partially surrounding said wall (3; 3, 3') being positioned in such a manner that a space (5) is defined between said sheathing wall (4") and the wall (3; 3, 3'), wherein said space (5) is closed hermetically and is connected operatively to vacuum-producing means (7) suitable for creating a desired degree of vacuum inside said space (5; 5'; 5") in order to thermally insulate said container body (2; 2'; 2") from the outside.

15. Device according to the preceding claim, wherein said vacuum- producing means (7) are provided to produce a reduced pressure of approximately from -900 to -980 mbar in said space (5; 5'; 5").

16. Device according to any one of claims 14 to 15, wherein said wall (3; 3") is configured in such a manner as to isolate said container body (2; 2") in a sealed manner with respect to said space (5; 5").

17. Device according to any one of claims 14 to 16, wherein said wall (3') is provided with holes in order to connect said space (5') to said container body (2') in such a manner as to produce in said container body (2') almost the same degree of vacuum as in said space (5').

18. Device according to any one of the preceding claims wherein the plastics material is PET (amorphous or recycled).

19. Method of processing PET comprising processing the PET in a dehumidifying device according to any one of Claims 1 to 17 in such a manner as to obtain PET which is more workable by transforming machines.

20. Method of processing recycled PET comprising loading the recycled PET into a dehumidifying device according to any one of claims 1 to 16 and operating said device for a period of time sufficient to obtain so-called food-grade PET, that is PET that can be re-used to produce food containers.

21. Dehumidifying system (103) for dehumidifying plastics materials, comprising a dehumidifying device (1; 1'; 1") according to any one of the preceding claims.

22. Processing plant for processing plastics materials, comprising a device according to any one of claims 1 to 17.