FR2567446A1 - PROCESS FOR PRODUCING POLYSTYRENE PELLETS AND EXPANDABLE POLYSTYRENE PELLETS - Google Patents

Abstract

A PROCESS FOR PREPARING POLYSTYRENE GRANULES, IN PARTICULAR EXPANDABLE POLYSTYRENE, BY FORMING A MOLTEN STYRENE POLYMER, BY EXTRUDING IT THROUGH A DIE TO FORM A CONTINUOUS WIRE. ON EXIT FROM THE DIE, BUT BEFORE THE PROPER COOLING, THE PELLETS ARE CUT, THROUGH THE SCREEN TO SEPARATE THOSE OF NON-CONFORMING DIMENSIONS. THE ADEQUATE PELLETS ARE PUT INTO A HEATED REACTOR AND INJECTED WITH A BLOWING AGENT. THE EXPANDABLE POLYSTYRENE BALLS SO PRODUCED ARE PRACTICALLY SPHERICAL.

Description

The present invention relates to a method of manufacturing

expandable polystyrene.

  When making expandable polystyrene granules, it is

  It is desirable that these granules meet three characteristics.

  First of all the granules must have a practically spherical shape.

  Then, the distribution of the dimensions of the spherical granules must remain narrow, that is to say that the granules must have dimensions as uniform as possible. In addition, the granules must be small because the molding or thermoforming is even better than their size is small. In addition, the process must also make it possible to recycle

  waste and rejected products.

  Generally, expandable polystyrene is prepared by suspension polymerization in one or two stages. According to the process in two

  steps, the styrene monomer is placed in a large poly-

  suspended suspension filled with water and containing a suspending agent. The monomer is stirred inside the reactor to form droplets which, when heated, polymerize to form individual beads of polymer. This suspension polymerization method is used in one or two stages. In the two-step process, when the polymer beads are formed, they are removed from the reactor, dried, and those of irregular size are separated. The balls of normal or desired dimensions are then reintroduced into another reactor filled with water,

  in which they are impregnated with a gaseous hydrocarbon such as pentane.

  After the impregnation, the balls are removed from the reactor again, dried and prepared for expansion. Expansion includes everything - first, a pre-expansion which consists in subjecting the balls to steam

  in an unconfined space to form partially expanded beads.

  These pre-expanded beads are then placed in the desired mold and subjected to steam at high temperature to expand them indoors.

  from the mold until reaching the final shape.

  According to the one-stage suspension polymerization process,

  the polymer beads formed in the polymer reactor are impregnated

  with a hydrocarbon blowing agent before carrying out the

  separation of the balls having an irregular shape. By impregnating

  in this way, it eliminates the cost and the duration of the first ball drying as well as that and the separation of normal beads

  those with irregular dimensions.

  In addition, the one-step process makes it possible to reduce the number of reactors required since the beads are formed and impregnated in the same reactor. But this process has the disadvantage that

  the balls of irregular dimensions are impregnated with an agent gon-

flammable flanger.

  It would be desirable to have a method that avoids the need to form beads in a first reactor.

  suspension, to remove them to separate the balls of irregular dimensions.

  to put the balls of good dimensions back into a second reaction.

  in suspension, but which makes it possible to separate the balls from

  dimensions before impregnation with a blowing agent.

  In addition, by using a suspension polymerization process whether in one or two steps, this leads to restrictions on the possibility of recycling the wrong sized balls that are rejected as well as waste. A suspension type process is very

  sensitive to the ingredients that are introduced.

  Suspension formulations are very delicate since they are developed to give a range of specific dimensions for

beads or granules.

  The introduction of waste or recycling materials would change the delicate balance of formulation and give at least one interval

wider dimensions of balls.

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  Therefore, it would be advantageous to have a process for producing practically spherical expandable polystyrene beads,

  that allows the use of waste or recycling materials.

  Thus US Pat. No. 3,664,366 to Jablonski describes a method in which expandable styrene polymers are prepared by incorporating into the particles an alkali metal salt. One method for making these particles is to extrude the resinous material containing the alkali metal salt through a multi-hole die having a diameter of about 1.7 mm. The extruded wires are cooled and cut in a

  granulator for making granules having a length of about 2.5 mm.

  These granules are then transported in a pressurized reactor, suspended in water in the presence of a blowing agent, and heated for a time sufficient to allow the blowing agent to react.

  the granules. Generally, spherical particles are obtained.

  US Pat. No. 3,449,268 describes a process according to which isotactic polystyrene can be obtained under amorphous conditions, by introducing crystalline polystyrene into an extruder, in which it is pressed, heated to a temperature above its melting point, and preferably extruded. in the form of a wire or several wires, then cooled rapidly, by contacting, generally by i =, the conversion of the son in cold water, and finally sent to a granulator where it forms

granules.

  The above process has certain disadvantages such as

  cold page of the granules which results in (1) the creation of granules of

  my irregular and (2) the creation of small particles unusable for threads of small diameters. This leads to a large amount of waste when a certain size range is desired. In addition, it is practically impossible to obtain balls having a length and / or a width which is not greater than 2 mm. Cutting cold wires is a major problem and creates a significant amount

of materials to reject.

  The present invention relates to a method for producing expandable polystyrene granules having substantially

  uniform, while reducing the amount of material to be rejected.

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  The present invention also relates to a process for

  expandable polystyrene, which reduces the amount of energy required and the time required to form the granules

expandable polystyrene.

  The present invention also relates to a process for

  expandable polystyrene to separate particles of irregular size prior to the impregnation step of the granules

  of required dimensions with a blowing agent.

  The present invention also relates to a process for

  expandable polystyrene to reduce the number of reactions

  required to increase production by using all suspension reactors to impregnate

of polystyrene.

  Another subject of the present invention is a process for

  expandable polystyrene using polystyrene from a continuous bulk polymerization unit, or granules

  of polystyrene whose dimensions are not in conformity.

  The process of the present invention for producing polystyrene particles, and in particular expandable polystyrene particles, is characterized in that it comprises: - forming a molten styrene polymer, - extruding this molten styrene polymer into a die to form a continuous wire, and - cut this wire into pellets at the exit of the die, but before

subject them to cooling.

  In the case where it is desired to produce particles of expanded polystyrene

  The method also comprises the steps of: - suspending the granules in a reactor and introducing a blowing agent under conditions of sufficient temperatures and pressures to impregnate the granules with the blowing agent; and removing the reactor granules as substantially spherical beads.

  According to one embodiment of the invention, the granules

  in a heated reactor containing water, and then introducing a blowing agent. The granules rotate in the reactor to form spherical beads. The balls are then removed from the reactor and heated to a high temperature so as to promote the expansion of the balls which have

absorbed the blowing agent.

  According to another embodiment of the invention, the

  granules having the desired size of the other granules before introducing them

in the heated reactor.

  According to yet another embodiment of the present invention, the styrene polymer is formed by a continuous bulk polymerization process. The molten polystyrene obtained by this continuous process is sent to a die to form continuous yarns, which are cut to form granules. These granules are then introduced into the reactor

  heated to impregnate with a blowing agent.

  According to another embodiment, the molten polystyrene is prepared by introducing polystyrene into an extruder and extruding it to

through a sector.

  The cooling of the polymer strands can occur during

  whether pellets are cut or cut. The wires can

  may be cooled during granulation by either water, air or vapor dispersion; when we cool after granulation, we

  uses the cutting system to discharge the pellets into the water.

  It can also perform a partial cooling before cutting

granulated threads.

  The present invention is also described with the aid of drawings in which: Figure I shows a diagram of an embodiment of the method of the invention; FIG. 2 represents a diagram of another embodiment of the method

of the invention.

  The method of the present invention makes it possible to prepare

  polystyrene, impregnate them with a swelling agent to form

  sea expansible polystyrene granules which are practically spherical -6 - and which have dimensions that are within a narrower range

  that it was possible to obtain before.

  According to the present invention, a polymer of

  styrene melted. This step can be carried out according to a method of poly-

  Continuous massing, or simply by melting polystyrene.

  The polystyrene is extruded through a die to form

  tinus. These son may be extruded optionally in a coolant medium such as water. The yarns are cut into pellets before the actual cooling. The term "before proper cooling" means that the pellets formed retain sufficient

  heat to allow the granules to be deformed from the cylindrical shape

  when cut, to a spherical shape. So the pellets

  formed are usually ovoid, pear or spherical

  early than a cylindrical form. In addition, by cutting the pellets when

  they are still hot, this considerably reduces the quantities

  particulate matter out of specification.

  When the yarns are extruded into the water, or if the pellets are discharged into a coolant medium, the outer surface of the yarns or balls can be cooled so that the balls

  do not stick to each other, and so as to prevent their agglomeration.

  The granules formed can also be inspected for further

  to narrow the size range, and then recycle the reject granules

in the molten polymer.

  The desired granules are suspended in a heated reactor, and a blowing agent, such as pentane, is introduced under conditions of sufficient temperature and pressure to impregnate the granules with this blowing agent. This extra step completes the transformation

  granules of a cylindrical shape into a spherical form.

  The process described above is particularly suitable when

  that small beads of expandable polystyrene are desired, as

  example those having less than 0.25 cm.

  Referring to Figure 1, a continuous wire 12 of

  molten styrene polymer leaving a die 14.

  In the vicinity of the die 14, a cutting device 16 is placed.

  which cuts the threads into individual granules.

  The cutting device may be a rotary blade system which

  are placed immediately after the exit of the die 14 for

  kill a cutting of the hot wires coming out of this die.

  We can obviously have other devices than rotating blades,

  however, any device which can give granules of small dimensions

  which has sufficient flow and is economical may be perfectly suitable. The granules have an approximate diameter of 0.099 cm and a length of preferably 0.25 cm, although a length of 10096 cm is preferable. These length and diameter criteria are obviously based on current market data, which can therefore be subject to fluctuations. A rotating blade device can be used at high speed to obtain small granules. We can

  also impregnate granules of larger dimensions, which

  in the suspension, but customer deandes are focused on

  granules of smaller sizes.

  The cutting device 16 can be placed immediately at the end of the die 14 for better results, so that the wires 12 coming out of the die are cut into pellets while they still have a high temperature and therefore have less of

blade resistance.

  According to one embodiment, the polymer son coming from the die 14 exit into a tray filled with water (not shown on

  the figure), in which the cutting device has been introduced.

  It has been found that cutting the wires 12 under water-provides more accurate cutting of the ball because of the cooling effect of the water on the outer surface of the thermoplastic wire. Moreover, the cutting

  underwater allows to obtain a more spherical shape.

  According to another embodiment, the cutting device 16 is placed at the outlet of the die 14. A tray filled with

  water, or a continuous stream of water, near the disconnecting device.

  page 16 so that as soon as they are cut, the pellets fall

  directly in the water, simply by the mechanical action of cutting.

  Immediately below the cutting device 16, a sieve-type separator 18 is placed to separate and remove the pellets.

  specifications. The granules of good dimensions of the sepa-

  18 to a reactor 20 equipped with a stirring device, filled

  water and maintained at a temperature of approximately 104 C.

  whose sizes are those who pass the specifications

  for subsequent uses, based in particular on commercial criteria. It will be appreciated that the reactor 20 may be a slurry reactor of any known type. The blowing agent is introduced into the

  reactor 20 to impregnate the styrenic polymer contained therein.

  After a sufficient impregnation time, the impregnated granules are removed.

  20 and then in a dryer 24. After the dryer 24, the granules are stored in a silo 26 filled with an inert gas such as nitrogen, and in which the

  granules are preserved before packing and transport.

  The thermoplastic materials used in the process of the present invention may be styrenic polymers capable of being impregnated with a suitable blowing agent, and which may be foamed

  by heating the blowing agent to produce expanded polystyrene.

  Examples of such materials include polymers of styrene, 2-methylstyrene, p-methylstyrene, m-methylstyrene and alpha-methylstyrene; it is also possible to use copolymers of

  styrene / p-methylstyrene, styrene / alpha-methylstyrene and other analogs.

  The blowing agent used in the process of the invention is chosen from butane, pentane, hexane and their structural isomers such as npentane, isopentane, neopentane, n-butane and isobutane.

  n-hexane and isohexane. However, pentane is preferred.

  The separator 18 may comprise several layers of vibrating screens which allow the granules of desired dimensions to fall down.

  in the background by simple gravity while retaining the others on the cou-

  to remove and recycle or sell them.

  Impregnation of the granules of required dimensions with the blowing agent is carried out as in the previous methods. Normally, we

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  utilizes a slurry reactor, filled with water and maintained at a temperature of about 104 C. Pressurized blowing agent is introduced into the reactor 20. Generally, the pressure inside the reactor will be between 0 and 6.3 kg / cm2. The pentane injection is carried out over a period of about 7 hours at about 104 ° C. and during a further 3 hours cycle at 168 ° C..

  high, it can reduce the duration of the impregnation.

  According to the method of the invention, it is also possible to add

  nucleating agents, chemical blowing agents or flame retardants

  The additives may also be introduced into the slurry reactor, if they are heat sensitive, or if they react chemically.

at higher temperature.

  The styrene polymer can be prepared by any method known in the state of the art. In fact, in the process of the invention it is possible to use general purpose polystyrene, either of higher quality or out of specification and prepared by other polymerization processes than that mentioned above. This polystyrene is then passed through an extruder to have it melt and transported to a wire die. General purpose polystyrene can be prepared by any known method such as suspension polymerization,

  continuous mass polymerization, as described in "Practical Poly-

  merization for Polystyrene "by Bishop.

  However, according to a preferred embodiment, the

  polystyrene by a continuous mass polymerization process.

  Continuous mass processes include those using a single multi-zone temperature reactor, a single back-mixed reactor

  at constant temperature, a reactor with two configurations or with a configuration

multiple ration.

  It should be noted that the process according to which the poly-

  styrene has no direct action on the granulation or impregnation step. Polystyrene can be prepared and suspended

  at one point and be expanded at another time.

  According to a preferred embodiment, the polymerization process

  continuous mass is directly related to granulation as well as

  gnation with the blowing agent. An example of a direct link is given in FIG. 2, in which the continuous mass unit 30 comprises a stirred vertical reactor 32 and three horizontal reactors 34, 36 and 38.

  containing a heating coil 39 to act as a heat exchanger

  to control the temperature inside the reactor. The pump 33 supplies the styrene reactor 32, stored in the tank 40. A polymerization initiator is added to the pipe 17, before entering the reactor 32. The presence of an initiator is advantageous for having

  better control over the final molecular weight of the polymer formed.

  As initiators can be used those of the family of peroxides and

  peresters such as benzoyl peroxide and tert-butyl peroctoate.

  The reactors 34, 36 and 38 are successively maintained at higher temperatures by means of a serpentine heat exchanger 39 which can be removed or refitted at will. The use of a zone of incremental increase in temperature allows the controlled addition or removal of the heat of polymerization, and allows the maintenance

  the desired temperature in each reactor. The polymer unit 30

  Continuous mass conversion uses a multiple reactor and is well known

  in the state of the art and will not be further described here.

  After reactor 38, the polymer is sent to devolatilizer 46 to remove residual volatiles and monomers. The polymer then passes into a second devolatilizer 47 to remove the residual monomers. After the devolatilizer 47, the polymer is pumped by the gear pump 48 to send it to the wire die. The cutting device 16 is located at the end of the thread die 14 and allows the cutting of the son into granules. The rest of the process described in Figure 2

  is similar to Figure 1.

  The operating conditions in the polymerization line in

  30 depend on the viscosity of the styrene, the desired flow rate, the

  of exchangers and their length. The conditions for the polymerization

  continuously using a multiple reactor, are normally those

  used in the state of the art.

  According to other methods for making expandable polystyrene, the continuous polymerization process is not used, but a slurry process in which the monomer is introduced into a slurry reactor, filled with water and containing an agent. suspension and a catalyst. The monomer and the agent are stirred in suspension with a

  agitation device and the polymerization is carried out. When the poly-

  Merification is complete, the beads formed in the reactor are removed, dried and separated; the balls of the required dimensions are reintroduced into a second suspension reactor, to be resuspended in water for impregnated impregnated with penteaneo Other methods recommend reducing the duration of operations in

  introducing the pentane into the first reactor just after the polymer.

  because the cost of removing the balls from the suspension, their

  drying, separation from the balls of good dimensions and the kidney

  troduction of the latter in the second suspension reactor

  is very high. It should be noted that a plant with a fixed number of reactors

  The suspending agents will be able to produce double expandable polystyrene using the process of the invention, since half of the suspending reactors, normally used for suspending during the initial polymerization, will be free for use in impregnation with the swelling agent Formerly, it was believed that the formation of polymer beads by a slurry process was necessary to produce round beads. Surprisingly, it has been found that the granules produced by rotary cutting of the son of thermoplastic materials obtained by continuous bulk polymerization, will have a better spherical shape when they are suspended for pentanization. It is not known for the moment whether the presence of a blowing agent leads to this round shape or if it is simply to the suspension in water, heat or a combination of the three; however, rounding

  the balls during the suspension makes it possible to produce the balls

  from the cutting of the wires. In addition, it is believed that impregnation of the blowing agent into the granules would not occur because of the granule density and the small amount of suspending medium.

  in relation to the large size of the granule.

  Surprisingly, a complete impregnation is obtained sufficiently

  quickly according to the conditions of the invention.

  Another advantage of the invention lies in the fact that one

  impregnates that the balls having the required dimensions.

  In the one-stage suspension process, all the beads were impregnated with pentane. These marbles are not only a hazard when handled, but they can not be regrinded or even sold for other purposes,

additional costs.

  The following examples are given to better illustrate

  the present invention but without limiting its scope.

Example 1

  A 253 liter reactor was filled with water and heated to 710C. When at this temperature, tricalcium phosphate was added and stirred for 5 minutes. Polystyrene

  produced in the multiple reactor continuous mass unit described above.

  above, was cut into pellets approximately 0.125 cm long and 0.2 cm wide by means of a hot-water and hot-cut granulator manufactured by Farrel Co. The granules were then introduced into the reactor and stirred for 5 minutes; a suspending agent was also added. After heating the reactor to 104 C, it was

  injected 12.46 kg of n-pentane over a period of 7 hours. After the injection

  of pentane, the reactor was heated to 112 ° C and maintained at this temperature for 3 hours. After these 3 hours, the impregnated granules were in the form of spherical beads. We cooled

  the beads, dried and removed for testing.

  The impregnated beads were subjected to steam at a temperature of

  115.5 C and at a pressure of 0.5 kg / cm 2 for 280 seconds

  to form pre-expansive beads.

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  These beads are aged for 11 hours and placed in a mold and subjected to steam injection at a temperature of 146 ° C and a pressure of 0.84 kg / cm 2 for 21 seconds. The molded article was allowed to cool, removed from the mold and subjected to the melt test whereby the molded article was torn into pieces to obtain a comparison of the percentage of beads left torn in relation to the number of molds. balls which were detached at their periphery. The molded article produced under the above conditions has a melting degree of 85%, i.e. 85% of the beads exposed on the release layer

were torn.

Example 2

  The procedure described in Example 1 was repeated except that steam was injected into the mold at a temperature of 146 ° C for 19 seconds, the pressure reached being 1.05 kg / cm 2. found

in fusion test was 75%.

Example 3

  The procedure described in Example I was repeated except that steam was injected into the mold at a temperature of 146 ° C for seconds, the pressure reached being 11.9 kg / cm 2. Find value

the fusion test was 45%.

  The above data show that the expanded polystyrene beads produced by the process of the invention have acceptable melting characteristics, i.e. a degree of fusion which is directly controllable over a wide range using the temperatures and

adequate pressures in the mold.

  Although the present invention has been described by means of a description

  of various modes of execution, it is not limited to these.

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Claims (12)

  1) Process for preparing polystyrene granules characterized in that it comprises the steps of: - forming a molten styrene polymer - extruding the molten styrene polymer in a die to form continuous yarns; and - cut these granulated yarns after leaving the die but before   their cooling proper.   2) Method according to claim I characterized in that one extrudes son less than 0.25 cm in diameter and that is cut pellets   same diameter and length less than 0.5cm.   3) Process according to any one of claims I and 2 characterized   in that the granules are discharged in a cooling medium during the cutting step.   4) Process according to any one of claims I to 3 characterized in   what we extrude the wires in a cooling medium and in especially in water.   A process for preparing expandable polystyrene characterized in that it comprises the steps of: - forming a molten styrene polymer - extruding the molten styrene polymer through a die to form continuous yarns; - cut the granulated threads after leaving the die but before -_, 5_-. 2567446 their cooling.   suspending the granules in a reactor and introducing a blowing agent under conditions of sufficient temperature and pressure to impregnate the granules with the blowing agent; and - withdrawing the granules from the reactor in the form of substantially spherical beads. 6) A method according to claim 5 characterized in that one extrudes son diameter less than 0.25 cm and cut pellets of the same diameter and length less than 0.5 cmo   7) Method according to any one of claims 5 and 6 characterized   in that the granules are discharged in cooling medium   8) Method according to any one of claims 5 to 7 characterized   in that the yarns are extruded in a cooling medium and especially in water.   9) Process for preparing polystyrene granules characterized in that it comprises the steps of: - forming a molten styrene polymer - extruding the molten styrene polymer through a die to form a continuous wire which is extruded into a medium cooling; and - cut the granulated wire at the exit of the die but before a   substantial cooling, in which the granules are at room temperature   sufficiently high to allow granules to be processed in a spherical form.   ) The method of claim 9 characterized in that it further comprises the steps of: - suspending the granules in a heated reactor, introducing a blowing agent into the reactor under sufficient conditions of temperature and pressure to ensure impregnating the granules with the blowing agent; and removing the pellets from the reactor in the form of beads substantially   spherical expandable polystyrene.   11) Method according to claim 9 characterized in that the medium of cooling is water.   12) Method according to any one of claims 9 to 11 characterized   in that wire of a diameter smaller than 0.25 cm is extruded   and that pellets less than 0.25 cm in length are cut.   13) Method according to any one of claims 5 to 12 characterized   in that the molten styrene polymer is prepared by a process   continuous bulk polymerization.   14) Method according to claim 9 characterized in that one separates the   granules of undesired size and removed.   ) Method according to claim 14 characterized in that one recycles   granules having undesired dimensions.   16) Method according to any one of claims 5 to 15 characterized   in that a blowing agent selected from butanes is used,   pentanes, hexanes and their mixtures.