GB1560768A - Prefoaming process for expansible materials - Google Patents

Description

(54) A PREFOAMING PROCESS FOR EXPANSIBLE MATERIALS (71) We, GERARD LEZIER, of 1 Boulevard Mariette, 62200 Esoulogne sur Mer, France, and BERNARD VASSEUR, of Beaudricourt, 62810 Avesnes le Comte, France, both of French nationality, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to a process and to an apparatus for the prefoaming of expansible plastics materials, and in particular, for the prefoaming of styrene copolymers.

Nominally, the moulding of plastics materials comprises three operations, the premoulding or pre-expansion of the starting materials, the intermediate storage of these materials, and the actual moulding.

Premoulding is performed by heating the starting material in the form of beads, in which is incorporated a foaming agent, to between 90 and 105 C by means of steam, which has the effect of expanding the beads.

Unlike other gases, steam has the advantage of on the one hand giving off a large quantity of heat at the time of its condensation without causing a temperature drop and on the other hand of rapdily diffusing within the beads which increases the action of the foaming agent.

For performing the process, a cylindrical apparatus is used in which the material is mechanically stirred and heated with steam.

In a single operation of this type, the density of the beads is reduced from 600kg/m3 to 20kg/m'! and by means of a subsequent operation, the beads can be made even lighter.

The beads obtained in this way cannot be used for immediate moulding. The reason is that during heating the beads absorb steam, and during cooling the condensation of the steam causes a certain vacuum within said beads which is filled up by a gas and in particular by air. This reabsorption of gas, which is called maturing, takes place during the intermediate storage.

According to another process, the expansible material in the form for example of beads is stirred and heated in an enclosure having heated walls. As soon as the beads have reached a certain temperature, a vacuum is produced within the enclosure which aids the expansion of the beads. Expansion is stopped by spraying water, whereby the beads are cooled to below their softening temperature. This process has the advantage of decreasing the maturing time, but requires the use of relatively complicated expanders and the operations take a relatively long time.

Moreover, the beads contain water and the foaming agent, for example pentane, is present in smaller quantities than in the previous process.

The present invention provides a prefoaming process for expansible material and in particular styrene copolymers, which comprises preheating the material in the form of beads, stirring and heating the preheated beads by subjecting the beads to the action of a rotary ascending hot gas whose flow rate and temperature are regulated in such a way as to raise the beads, stir them and heat them to their softening temperature, whereby the thus obtained pre-expanded beads are suitable for immediate moulding, the gas being selected from CO2, air, nitrogen, and fluorinated hydrocarbons.

Suitable fluorinated hydrocarbons are known under the registered Trade Mark "Freon", in particular "Freon 114".

This invention also provides an apparatus for preforming this process, which apparatus comprises means for preheating beads of expansible material, a tank means for supplying the tank with preheated expansible material beads, a source of hot gas, means for directing the hot gas in an ascending turbulent rotary flow in the tank, means for regulating the intake and discharge flow rate of the beads, the gas flow rate, and the temperaure of the gas and tank, and means for discharging the preexpanded beads at the top of the tank.

The new or blank beads are preheated to about 50 C prior to introduction into the expander. Steam has a much higher calorific capacity per kg of fluid than a gas such as nitrogen, C02 or air. It is for this reason that preheating is necessary in order to decrease the quantity of calories necessary in the actual expander for the expansion of the beads, thus making it possible to maintain within the expander a gas temperature which it is much easier to keep homogeneous and which varies very little.

The most suitable gas is CO2, which is a harmless inert gas and which, after steam, is one of the gases which penetrates most easily into the expanding beads. Within the expander, the gas flow rate is approximately 10kglhlkg of expanded polystyrene.

Expansion takes place in gas maintained at between 95 and 100etc in the case of polystyrene, and its temperature, flow rate and the residence time of the beads in the expander determines the density of the discharged products.

It should be noted that in this apparatus the beads are kept in suspension and are agitated by the gas, which ensures a constant temperature at all points in the tank. The beads which have not yet expanded are heaviest and tend to remain on the bottom of the tank and rise as they become hotter and as their density decreases.

The originality of the present apparatus is mainly due to the fact that a preheating chamber is used for the beads before they are introduced into the tank, and in addition particularly effective means are used for directing the fluid in an ascending turbulent rotary flow.

To obtain this turbulent rotary flow, the following means are used: a) A hot gas supply nozzle with holes disposed along a helical line, the nozzle axis being vertical and the nozzle issuing above the apex of a conical member on the base of the tank.

b) A conical member placed on the bottom of the tank, a movable plate around and at the base of the conical member, a horizontal wire placed just above the plate, a hot gas inlet at the bottom of the tank, and a plurality of slots provided in the tank walls for the entry of hot gas.

c) A double hot gas supply which enters both via the bottom of the tank and holes made in the tank wall, and by a hot gas supply pipe which issues into a pipe supplying the preheated beads to the tank.

Other features and advantages of the invention can be gathered from the following description of three embodiments of the apparatus given in non-limitative manner with reference to Figs 1, 2 and 3 respectively of the accompanying drawings.

In a first embodiment, shown in Fig. 1, the apparatus comprises a funnel-shaped tank 1 above which is centred and fixed a hot gas source 2, and a hot air blower 3 positioned laterally on the top of the tank.

The upper part of the tank is permanently supplied with beads of expansible material which are preheated in a chamber 4 to about 50 C. The wall 5 of the tank is externally heated by a jacket 4 traversed by a hot fluid. Its temperature is regulated to a constant value so selected that the beads can reach their softening temperature.

The gas source 2 is equipped with a nozzle 7 whose periphery is provided with openings 8 arranged along a helical path and whose outlet 9 is just above the base 10 of the tank facing a conical member 11 which ensures an equal distribution of the gas in the tank.

The hot air blower 3, which has a variable flow rate, supplies air pulsed by means of a member 12 which faces the top of the wall of tank 1 in such a way that it prevents certain beads from agglomerating on the wall under the action of the reduced pressure at this point. The treated beads are discharged at the top of the tank by pipe 13.

In this apparatus, the beads which are continuously introduced by means of an automatic metering device, enter the tank where they are subject to the action of a rotating flow of an ascending hot gas, for example hot air, which is particularly turbulent because it comes from the bottom of the tank from all sides of conical member 11 and also from openings 8 which are disposed along a helical line on the nozzle.

Only those beads which have acquired a certain lightness are discharged at the top of the tank by pipe 13, the remaining beads dropping back again and being additionally heated by the gas until in turn they have also become sufficiently light to enable them to be discharged.

In a second embodiment, shown in Fig. 2, the apparatus comprises a cylindroconical enclosure 20 at the base of which issue a pipe 21 for supplying preheated new or blank beads, and a hot air supply nozzle 22.

To the base 27 of the enclosure is fixed a conical member 23 which aids the rotary movement of the hot air jet from the time it enters the enclosure. At the top of the enclosure is provided a system 24 for discharing the pre-expanded beads and the hot air.

Before being introduced in the pre-expander enclosure 20, the new beads are pre-heated in a chamber 25 which is linked with a metering device 2O which ensures that the enclosure 20 is provided with an appropriate supply of new beads.

The conical member 23 is surrounded by a movable plate 28 able to rotate on ball bearings (not shown) under the action of the hot air jet issuing through nozzle 22. As a variant, it is possible to use a conical member and a plate which are fixed to one another and are consequently both rotatable. Above plate 28, a wire 29, for example made from metal and having a diameter of approximately 0.5 mm, is stretched horizontally between conical member 23 and the intake of nozzle 22 so as to remove beads which could remain on the plate.

Hot air is supplied not only via nozzle 22 but also via a funnel-shaped pipe 30 which opens into a chamber 31 adjacent to enclosure 20 and provided with slots such as 32 in the wall of the enclosure 20. The flow rate of the air which is reheated in chamber 33 is controlled by a detector 34 which controls the opening or closing of flaps 35 and 36 and the operation of variable speed motor 37 which drives a blower 38 which extracts and recirculates the air contained in enclosure 20. To make good air leaks, air is periodically supplied at 39 to a pipe 40 linking blower 38 and a screen 41 located at the top and preferably in the centre of the enclosure for sucking up the air, separated from the pre-expanded beads, which are sucked up by a discharge pipe whose opening 42 of rectangular cross-section is regulated by moving together to a greater or lesser extent the two members 43 and 44, shown by dotted lines, of a slide gate.

The operation of the expander can be gathered from the descripton provided hereinbefore and will only be indicated briefly hereinafter.

As soon as the preheated new beads enter enclosure 20, they are rotated on the plate 28, which itself is rotated by the hot air jet from nozzle 22. Wire 29 aids the detachement of the beads which are driven by the hot air jet firstly around conical member 23 and then in a rotary ascending movement towards the top of the enclosure.

The entry of hot air through slots 32 increases the action of the hot air jet. The most expanded beads are displaced towards the top of the tank, whilst the heavier beads tend to drop and are again subjected to the action of the ascending hot air jet until they are completely pre-expanded. The preexpanded beads are sucked through opening 42 into a discharge pipe.

Polystyrene beads are heated at between 95 and 1000C, corresponding to their softening point. At this temperature, the foaming agent, for example pentane, expands and causes the expansion of the beads. In a single operation, expanded beads are obtained with a density of 16kg/ml.

In order to regulate the density of the expanded beads, three parameters are varied, namely the flow rate of the supply of beads, the hot gas flow rate and the time spent by the beads in the hot gas.

In this way, a regular expansion of the balls is obtained and the beads having an equal density, are brighter and mechanically stronger than beads expanded by steam.

It is pointed out that even if expansion in a gas lasts slightly longer than in the case of steam expansion, the beads have the great advantage of being directly usable for moulding. Thus, it is possible to incorporate the pre-expander in the moulding machine system, thus obviating any loss of material due to material transfers, which can represent 2% by weight of the material.

According to a third embodiment shown in Fig. 3, the apparatus comprises a truncated cone-shaped tank 50 having double walls 51, 52 surmounted by a hot air ventilation system comprising a blower 53, circular air heating resistors 54 positioned at the top of and between the two walls 51 and 52, discharge slots 55 for the expanded beads, the height of said slots being regulatable, and an air filter 56 which prevents the passage of the beads.

The air is heated to about 100air by resistors 54 and is circulated by the rotation of the blades 57 of blower 53 which gives a rotary movement to the air passing between walls 51, 52. This air enters the interior of the tank through openings (not shown) in inner wall 51 which are open tangentially to the walls in such a way that they initiate a rotary ascending movement of the hot air introduced.

There are more than 20.000 of these openings which are located in the straight bottom part 58 of the tank where the holes are largest (approx. 3mm), over the entire frusto-conical surface, 10 cm up into the reference region 59 (approx 1.5mm), and at the top of the tank above slots 55, in order to detach any beads which may have stuck to the screen 56.

The air temperature is strictly controlled by an electronic system which controls a voltage regulator (not shown).

The base of the tank is constituted by a plate 60 which is fixed to the tank body, for example by means of U-bolts 61 which permit rapid disassembly of the bottom of the tank during emptying.

Plate 60 is surmounted by a conical arch 62 dotted with small holes 63. Part of the air contained in the double wall penetrates beneath said arch through holes 64 and 65, and issues from the holes 63.

A second special blower 66, for a low flow rate at high pressure, sucks in the ambient air which it passes by way of a pipe 67 into a heater 68 in a chamber 69. A reservoir 70 with two perforated walls 71, 72 is incorporated into chamber 69 and between said walls descend the beads arriving through pipe 73 during the operation of the apparatus.

Thus, the reservoir 70 is traversed radially by hot air from the heater 68, which dries the beads and escapes through the central passage formed by wall 71. chamber 69 is provided at its lower end with an electrode 74 connected to a detector 75 which regulates the temperature of the air leaving the heater 68, as well as with a valve 76 for regulating the air flow reservoir 70.

The preheated beads coming from reservoir 70 descend through a pipe 77 which is bent towards the base of the tank so as to form horizontal pipe 78 which issues radially into the tank.

A hot air inlet pipe 79 fitted with a regulating valve 80 and connected to heater 68 is extended by a rectilinear nozzle 81 which can be made to slide to a greater or lesser extent into horizontal pipe 78 by operation of the handwheel 82 of a screw 83.

The regulating valve 80 and screw 83 make it possible to regulate the quantity of starting material introduced into the expander.

The closing of a gate valve permits a total stoppage of incoming material.

The operation of the apparatus can be gathered from the description given herein before and only certain additional comments will be made.

The beads are generally introduced continuously through pipe 73 and after being heated in chamber 69 enter the base of the tank at a more or less high speed, which can be regulated by operating handwheel 82.

The beads are then subject to the action of several air currents, from openings 63, from nozzle 81, and from the holes in the inner wall 51 of the tank. The air rises in a whirling movement, being sucked in by blades 57 which return it to between the double walls. Therefore, the beads are suspended as an ascending fluidized bed, without touching the expander walls.

It should be noted that the double wall is also perforated at the top of the tank above slots 55 and the air which enters through -the holes detaches the beads which would tend to become attached to the screen 56.

As the beads cannot pass through screen 56, they are discharged through slots 55 prior to being used for moulding.

The density of the beads can be regulated by varying three parameters, namely the height of slots 55, the flow rate of the air injected through valve 80, and the forward or rearward movement of nozzle 81 through the rotation of handwheel 82.

The use of this apparatus makes it possible to obtain beads of excellent quality due to the fact that they can have a density of approximately 8 to 25 kg/m3 and neither stick to one another nor to the components of the apparatus. Moreover, their production flow rate can reach 12 to 50kg per hour with a precision of the order of 1%.

WHAT WE CLAIM IS: 1. A prefoaming process for expansible material and in particular styrene copolymers, which comprise preheating the material in the form of beads, stirring and heating the preheated beads by subjecting the beads to the action of a rotary ascending hot gas whose flow rate and temperature are regulated in such a way as to raise the beads, stir them and heat them to their softening temperature, whereby the thus obtained pre-expanded beads are suitable for immediate moulding the gas being selected from C02, air, nitrogen, and fluorinated hydrocarbons.

2. A process according to claim 1, wherein the balls are preheated in an enclosure heated to a temperature of apgroximately 500C.

process according to claim 1 or 2, wherein the beads are of polystyrene and are heated by the hot gas to between 95 and 1000C.

4. An apparatus for performing the prefoaming process according to claim 1, which apparatus comprises means for preheating beads of expansible material, a tank, means for supplying the tank with preheated expansible material beads, a source of hot gas, means for directing the hot gas in an ascending turbulent rotary flow in the tank, means for regulating the intake and discharge flow rate of the beads, the gas flow rate, and the temperature of the gas and tank, and means for discharging the pre-expanded beads at the top of the tank.

5. An apparatus according to claim 4, wherein the means for directing the gas in a turbulent ascending rotary flow comprise a hot gas supply nozzle provided with holes arranged along a helical line, the nozzle axis bein & disposed vertically and the nozzle issuing above the apex of a conical member located on the base of the tank.

6. An apparatus according to claim 4, wherein the means for directing the gas in a turbulent rotary flow comprise a conical member placed on the bottom of the tank, a plate which moves around and at the base of the conical member, a horizontal wire placed just above the plate, a hot gas inlet at the base of the tank and a plurality of slots made in the wall of the tank for the introduction of hot gas.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (1)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   rate at high pressure, sucks in the ambient air which it passes by way of a pipe 67 into a heater 68 in a chamber 69. A reservoir 70 with two perforated walls 71, 72 is incorporated into chamber 69 and between said walls descend the beads arriving through pipe 73 during the operation of the apparatus.

   Thus, the reservoir 70 is traversed radially by hot air from the heater 68, which dries the beads and escapes through the central passage formed by wall 71. chamber 69 is provided at its lower end with an electrode

   74 connected to a detector 75 which regulates the temperature of the air leaving the heater 68, as well as with a valve 76 for regulating the air flow reservoir 70.

   The preheated beads coming from reservoir 70 descend through a pipe 77 which is bent towards the base of the tank so as to form horizontal pipe 78 which issues radially into the tank.

   A hot air inlet pipe 79 fitted with a regulating valve 80 and connected to heater

   68 is extended by a rectilinear nozzle 81 which can be made to slide to a greater or lesser extent into horizontal pipe 78 by operation of the handwheel 82 of a screw 83.

   The regulating valve 80 and screw 83 make it possible to regulate the quantity of starting material introduced into the expander.

   The closing of a gate valve permits a total stoppage of incoming material.

   The operation of the apparatus can be gathered from the description given herein before and only certain additional comments will be made.

   The beads are generally introduced continuously through pipe 73 and after being heated in chamber 69 enter the base of the tank at a more or less high speed, which can be regulated by operating handwheel 82.

   The beads are then subject to the action of several air currents, from openings 63, from nozzle 81, and from the holes in the inner wall 51 of the tank. The air rises in a whirling movement, being sucked in by blades 57 which return it to between the double walls. Therefore, the beads are suspended as an ascending fluidized bed, without touching the expander walls.

   It should be noted that the double wall is also perforated at the top of the tank above slots 55 and the air which enters through -the holes detaches the beads which would tend to become attached to the screen 56.

   As the beads cannot pass through screen 56, they are discharged through slots 55 prior to being used for moulding.

   The density of the beads can be regulated by varying three parameters, namely the height of slots 55, the flow rate of the air injected through valve 80, and the forward or rearward movement of nozzle 81 through the rotation of handwheel 82.

   The use of this apparatus makes it possible to obtain beads of excellent quality due to the fact that they can have a density of approximately 8 to 25 kg/m3 and neither stick to one another nor to the components of the apparatus. Moreover, their production flow rate can reach 12 to 50kg per hour with a precision of the order of 1%.

   WHAT WE CLAIM IS: 1. A prefoaming process for expansible material and in particular styrene copolymers, which comprise preheating the material in the form of beads, stirring and heating the preheated beads by subjecting the beads to the action of a rotary ascending hot gas whose flow rate and temperature are regulated in such a way as to raise the beads, stir them and heat them to their softening temperature, whereby the thus obtained pre-expanded beads are suitable for immediate moulding the gas being selected from C02, air, nitrogen, and fluorinated hydrocarbons.

   2. A process according to claim 1, wherein the balls are preheated in an enclosure heated to a temperature of apgroximately 500C.

   process according to claim 1 or 2, wherein the beads are of polystyrene and are heated by the hot gas to between 95 and 1000C.

   4. An apparatus for performing the prefoaming process according to claim 1, which apparatus comprises means for preheating beads of expansible material, a tank, means for supplying the tank with preheated expansible material beads, a source of hot gas, means for directing the hot gas in an ascending turbulent rotary flow in the tank, means for regulating the intake and discharge flow rate of the beads, the gas flow rate, and the temperature of the gas and tank, and means for discharging the pre-expanded beads at the top of the tank.

   5. An apparatus according to claim 4, wherein the means for directing the gas in a turbulent ascending rotary flow comprise a hot gas supply nozzle provided with holes arranged along a helical line, the nozzle axis bein & disposed vertically and the nozzle issuing above the apex of a conical member located on the base of the tank.

   6. An apparatus according to claim 4, wherein the means for directing the gas in a turbulent rotary flow comprise a conical member placed on the bottom of the tank, a plate which moves around and at the base of the conical member, a horizontal wire placed just above the plate, a hot gas inlet at the base of the tank and a plurality of slots made in the wall of the tank for the introduction of hot gas.

   7. An apparatus according to claim 4,

   wherein the means for directing the gas in a turbulent rotary flow comprises a double hot gas supply which enters both through the bottom of the tank and openings in its wall and by a hot gas supply pipe which issues into a pipe for supplying the preheated beads.

   8. A prefoaming apparatus according to claim 7, wherein the hot gas supply pipe is able to slide within the supply pipe for the preheated beads and is thus able to modify the speed at which the beads are supplied.

   9. A prefoaming apparatus accordmg to claim 7 or 8, wherein a blower is used for sucking the hot gas towards the top of the tank and passing it between double walls of the tank and to the bottom of the tank, and a second blower is used for passing ambient air through a heater and thereafter via the hot gas supply pipe to the bottom of the tank.

   10. A prefoaming apparatus according to claim 9, wherein a portion of the inner wall of the tank is frusto-conical and the inner wall is preforated over at least part of its frusto-conical portion.

   11. A prefoaming apparatus according to claim 9 or 10, wherein the inner wall of the tank is perforated in its upper area above the discharge openings for the beads, in order to aid the detachment of the beads which tend to become attached and clog a screen provided at the hot gas outlet.

   12. Apparatus for prefoaming expansible material, substantially as herein described with reference to Fig. 1, Fig. 2 or Fig. 3 of the accompanying drawings.